Emerging Trends in Photoredox Synthetic Transformation 9789819782048

Citation preview

Emerging Trends in Photoredox Synthetic Transformation

Mousumi Sen · Devalina Ray Editors

Emerging Trends in Photoredox Synthetic Transformation

Editors Mousumi Sen Department of Chemistry Amity Institute of Applied Sciences Amity University Noida, Uttar Pradesh, India

Devalina Ray Amity Institute of Biotechnology Amity University Noida, Uttar Pradesh, India Amity Institute of Click Chemistry Research and Studies Amity University Noida, Uttar Pradesh, India

ISBN 978-981-97-8204-8 ISBN 978-981-97-8205-5 (eBook) https://doi.org/10.1007/978-981-97-8205-5 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore If disposing of this product, please recycle the paper.

Preface

This book entitled Emerging Trends in Photoredox Synthetic Transformation offers a concise overview on the application of photo-redox processes in various essential and important aspects of science and technology through subdividing it into 15 significant chapters. Photo-redox processes are emerging as the means to empower the existing protocols with green, sustainable, and environmentally benign version which holds enormous potential in industry and academia. In this context, the applications of photo-redox reactions proposed in this book range from waste management, photo remediation, photo deposition, photocatalysis, sustainable therapeutic approaches, natural product synthesis, and derivatization to photocatalytic degradation and beyond. Photocatalytic conditions mostly deal with the utilization of light-driven chemical reactions to ease up the processes in terms of ambient and greener reaction environment. The photo-redox transformations of inorganic and organic substrates lead to various useful products under mild conditions that are otherwise hard to access. Moreover, the application of photocatalytic reactions in organic synthesis has taken a hype in the last few years where the light-mediated access to bioactive and medicinal compounds along with natural products has drawn the focus of the scientific world. The application in drug derivatization and degradation has explicitly boosted up the potency of photocatalytic processes. The concept of nanophotocatalyst for drug-free therapeutics has added a new essence to the existing processes. This is the first book of its own kind to endorse a thorough venture into green chemistry and engineering which paved a pathway to develop chemical processes that do not implement hazardous conditions decreasing the dependence on such elements (Chap. 1). In continuation, due to the widespread availability of plant extracts, and biologically active molecules, the biosynthesis of nanoparticles has proven to be a more reliable pathway when compared to its contemporaries. In the pursuit of developing sustainable and environmentally conscious chemical synthesis, the introduction of photo-redox catalysis has emerged as a promising strategy to improve the transformative potential of synthetic methodologies. In this context, the principles and applications of photo-redox catalysis to drive challenging chemical transformations with high efficiency and selectivity across a range of synthetic contexts, including organic synthesis, medicinal chemistry, and material v

vi

Preface

science, have been highlighted. The modern advancement of visible-light photocatalysis has addressed various challenging arenas such as Csp3 -Csp2 cross-coupling reactions including C-C, C-N, or C-O bond formations (Chaps. 2–4). The promising capability of the photocatalytic platform has been channelized in drug discovery indicating a prototype transferal through single electron transfer pathway. Focusing on drug synthesis and derivatization, the photocatalysis technique has acknowledged diverse late-stage functionalization and protein bioconjugation. This is essentially due to the greener aspect of visible-light irradiation and their tolerance towards the biologically related solvents (Chaps. 5 and 6). By utilizing diverse catalytic systems such as photocatalysts, oxidative degradation catalysts, and non-photochemical catalysts, substantial progress can be achieved in sustainably eliminating drug residues from ecosystems. In essence, catalytic drug degradation holds significant potential as an advanced technique in the realm of drug utilization, with far-reaching implications for improving drug safety and optimizing therapeutic results (Chap. 7). On the other hand, the photochemical synthesis and derivatization of naturally occurring compounds have escalated the utility of photo-redox catalysis enormously (Chap. 8). Photoremediation is one of the promising dye degradation techniques which involves the use of light and a catalyst for the decontamination of waste through oxidation and hydrolysis. Several nanoparticles based on TiO2 and ZnO2 are extensively studied for their photocatalytic properties and the subsequent degradation of a wide array of dyes. The studies show promising catalytic performance for the dye degradation application which can be the future of dye wastewater treatment (Chap. 9). Advanced oxidation processes (AOPs) offer versatility in wastewater purification and generate radical species, such as HO2 , OH, O2 − , and SO4 − , which are responsible for the mineralization of the organic contaminants. Among AOPs, photocatalysis has enormous potential for treating industrial discharge, which is reflected by the numerous investigations. Photocatalytic treatment of wastewater is considered as a “zero” waste technology and has been integrated with a variety of techniques to accelerate the degradation of pollutants (Chap. 10). The application of nanophotocatalysis in waste management, especially in wastewater treatment, has exhibited breakthroughs in technology development and enhancement of water quality and lowering pollution (Chap. 11). On the other hand, the light-induced conversion of waste biomass to energy production is a promising approach to create valuable chemicals and renewable energy more sustainably. However, emphasis on strategies and mechanistic considerations is necessary for the practical implementation of sustainable photocatalytic reactions and has been demonstrated in this book (Chap. 12). The oxidative and reductive transformation of biomass-feedstocks can be performed with the effect of metal nanoparticles due to their ability of activating molecular oxygen and hydrogen. In this aspect, designing the catalysts that control efficient mass transportation of the reactant and reagents to the active site of the

Preface

vii

catalyst is considered enormously important and has been considered to get insight into the physical restrictions in the catalytic process (Chap. 13). A very promising technique for effectively creating cocatalytic nanoparticles on semiconductor materials is photodeposition. In this regard, the employment of sacrificial agents, pH ranges, the presence of air or inert atmospheres, metal precursor kinds and concentrations, temperature, and more were analyzed along with other crucial process parameters (Chap. 14). The photoremediation process from renewable feedstock enforces the sustainability of developed protocols. Additionally, the analysis directs to the underlying mechanisms of photocatalytic processes to assesses the feasibility of large-scale implementation (Chap. 15). The core audiences of this book include material scientists, nanoscientists, nanotechnologists, chemical and biological Engineers, biochemists, green technologists and green scientists, biotechnologists, and scientists working in the field of waste minimization, green and sustainable science, and technology. Additionally, this book offers an excellent resource for Ph.D. and master students, R&D experts, researchers in academia and industry working in chemical synthesis, and process engineers in industries who will find this book extremely valuable and will benefit. Noida, India

Dr. Devalina Ray Dr. Mousumi Sen

Contents

1

Photo-Redox Reactions: Definition and Classification . . . . . . . . . . . . . Mousumi Sen

2

Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mookan Rajeswari, Mookan Sarath Babu, and Mookan Natarajan

3

4

Photoredox Strategies in Green and Sustainable Organic Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gitumoni Kalita, Yafia Kousin Mirza, Milan Bera, and Paresh Nath Chatterjee The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed C−H Bond Functionalization . . . . . . . . . . . . . . . . . . . Subhash Chandra Ghosh, Dharmik M. Patel, and Sachinkumar D. Patel

1

17

55

81

5

Photocatalysis: Application in Drugs and Analogues Synthesis . . . . . 147 Shikha Sharma

6

Photocatalysis: Application in Drug Derivatization . . . . . . . . . . . . . . . 163 Priyanka Chaudhary and Sureshbabu Popuri

7

Catalytic Degradation of Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Vinod Kumar Yadav, Siddharth Baranwal, and Jeyakumar Kandasamy

8

Synthesis and Functionalization of Natural Products with Light-Driven Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Suman Majee, Km. Anjali, Sonu Yadav, and Devalina Ray

9

Photoremediation—An Emerging Approach for Dye Degradation in Wastewater Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 249 Ramuel John I. Tamargo and Juniper V. Magallanes-Nava

ix

x

Contents

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Pratibha Sharma and Amit Kumar 11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Abhishek Tiwari, Varsha Tiwari, and Bimal Krishna Banik 12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341 Swati Dhamija, Rafia Siddiqui, Kumar Shivam, and Ranjan Patra 13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic Applications to Important Chemicals . . . . . . . . . . . . . . 373 Arindam Modak 14 Photodeposition for Highly Effective Photocatalytic Materials . . . . . 403 Akshita, Sunil Kumar, Deepshikha Gupta, Ravi Kant Choubey, and Tejendra K. Gupta 15 Photocatalysts Derived from Renewable Feedstock for Environmental Application/Remediation . . . . . . . . . . . . . . . . . . . . . 451 M. Amin Mir

About the Editors

Mousumi Sen has a doctorate degree from the Indian Institute of Technology, Delhi, India. She is currently an Assistant Professor in the Department of Chemistry at Amity University. Her research focuses on the prediction of pollutants dispersion from industrial areas, development of effective and sustainable methods for the removal of inorganic and organic pollutants from polluted water, food chemistry, heavy metals detoxification, composites/nanocomposites, water research, bio-inorganic chemistry and nanochemistry. She has published numerous peer-reviewed research articles in journals of high repute as well as edited book chapters, authored books, edited books and conference proceedings papers in her credit. Devalina Ray is Ph.D. from the Indian Institute of Technology, Kharagpur, India. Currently, she is an Associate Professor in the Department of Biotechnology at Amity University, Noida. Her research area comprises of synthetic organic chemistry, medicinal and natural product chemistry, green and sustainable chemistry, peptide synthesis, transition metal-catalyzed and metal-free C-H functionalization, etc. She has published patents and copyrights along with numerous international publications in reputed journals. She has published book chapters and is currently editing another book. She is an executive guest editor and editorial board member of various journals and a co-chief editor as well as founder of two new journals with Asian Publishing House.

xi

Chapter 1

Photo-Redox Reactions: Definition and Classification Mousumi Sen

1.1 Introduction Creating greener and more sustainable methods for chemical synthesis has received greater attention in recent years. The investigation of novel catalytic techniques that offer increased efficiency and selectivity has been prompted by the desire to reduce environmental impact, decrease waste output, and conserve energy. Among these cutting-edge tactics, photo-redox catalysis has emerged as a possible route for more environmentally friendly synthesis methods. Photocatalysis is a photoactivated chemical process that occurs when free radical mechanisms are triggered when a substance comes into contact with photons with high adequate energy levels. These chemical reactions involve a catalyst, known as a photocatalyst, to lower the reaction’s activation energy and allow photons from the sun to drive the reaction. Photocatalysis with visible light has emerged as a strong method in organic synthesis, employing photons as traceless, long-lasting reagents. The idea of employing photochemical processes to synthesize valuable organic molecules was first proposed in an article published in Science in 1912 by Giacomo Ciamician. UV light was once used to stimulate substrates or reagents in photochemical processes. The great energy of these light sources necessitates the employment of specialized equipment, and they frequently result in non-selective reactions that can be very tough to think of and manage. It has evolved along this invention of the photocatalysts which may become triggered through the minimal energy photon, forming its foundation for feasible synthesis reactions carried out via the eco-friendly visible light (Teoh et al. 2012a). Visible light photo-redox catalysis, in particular, has become well-known as a useful technique in organic synthesis. A catalyst that has been excited donates as a choice

M. Sen (B) Department of Chemistry, Amity Institute of Applied Sciences, Amity University, Noida, Uttar Pradesh 201313, India e-mail: [email protected] 1

2

M. Sen

or receives a one/single electron after being irradiated, allowing oxidative or reductive cycles to occur depending on the substrates and agents involved in the reaction. Photocatalysis now has perfect affordable and energy-efficient light sources thanks to technological advancements and widespread commercialized obtainability of lightemitting diodes (LEDs) that can generate visible light that produces a great level of intensity in a limited area of wavelength for each and every color. Many photo-redox processes involving visible light involve radical or radical ions intermediates. This ability to generate such reacting intermediates using visible radiation has reignited curiosity in such radicals’ reactions in synthesis in organic chemistry (Teoh et al. 2012a). Photocatalysts or stimulators of this type can be found in a variety of forms, either soluble or insoluble in reaction media, resulting in reaction mixes that are homogenous or heterogeneous. Photocatalysts in heterogeneous systems are solid phase photoactive semiconductors, whereas photosensitive compounds that may become dissolved in the reactions’ fluids, just like the photoactive dyes, are used in homogeneous systems (Basyach et al. 2022). Organic chemicals are required for the production of a wide range of items as well as other chemicals, such as medications, insecticides, and food additives, all of which are commonplace in modern society. Organic synthesis pathways and manufacturing techniques in the chemical industry are well-established and haven’t been modified much over time. Environmental policies have become increasingly stringent as understanding about the ecological effects of various agents, catalytic, produced side-products, and the wasted solutions has grown. Simultaneously, there is already a situation for addressing energy expenses in order to stay in competition, as well as significant safety concerns involved with the handling of hazardous and reactive chemicals. Apart from these “eco-friendly” synthesis ways and “green” mechanisms procedures have been considered by chemical makers at each step of their operations. As a result, developing photocatalytic synthesis pathways that use light as a source of energy to drive chemical processes under considerably mild process conditions is extremely desirable (Basyach et al. 2022).

1.2 Photocatalytic Processes/Underlying Ideas in Photocatalysis Photocatalysis is a flexible and promising technique that uses light energy to start chemical reactions on the surfaces of semiconducting materials (Herrmann 2010). The basic processes that take place when light interacts with photocatalytic materials, producing charge carriers and subsequently transforming chemical species, are known as photocatalytic mechanisms in heterogeneous photocatalysis. These procedures play a crucial role in initiating photocatalytic reactions and are beneficial for chemical compound synthesis, energy conversion, and environmental restoration (Zhang and Nosaka 2014). A deep comprehension of the intricate workings of these systems is necessary for designing efficient photocatalysts and optimizing their

1 Photo-Redox Reactions: Definition and Classification

3

performance. The key steps involved in the photocatalytic mechanism are the underlying principles of this procedure, which also offer a thorough comprehension of the major ideas and methods involved, including charge carrier creation, bandgap engineering, and separation, all of which are essential for comprehending and improving photocatalytic processes.

1.3 Generation and Separation of Charge Carrier A crucial part of the photocatalytic process is the creation of electron–hole pairs or charge carriers. As photons are taken up by the photocatalyst material, the photocatalytic process begins. These photons carry energy associated with a certain wavelength of light. When a photon with energy over the bandgap of the photocatalyst hits its surface, one of the electrons absorbs it and moves from the valence band to the conduction band. As a result, a photo-generated electron–hole pair (e-/h+) is produced by this process. The photocatalyst’s bandgap energy is determined by the difference in energy levels between the valence and conduction bands, which in turn determines the wavelength of light that it can effectively absorb (Zhang and Nosaka 2014; Kamat 2012a). Although the effective synthesis of charge carriers is the first step, it is as important to separate them and take steps to avoid recombination afterward. Lower photocatalytic efficiency results from the waste of light absorption energy caused by the rapid recombination of electrons and holes (Gillespie and Martsinovich 2017). The problem of charge carrier separation has been addressed in a number of ways to enhance it. One tactic is to create heterojunctions, or interfaces, between different semiconducting materials which play role as surfaces function as charge sinks by effectively separating the electrons and holes, which lowers the chance of recombination (Zhang et al. 2018).

1.4 Bandgap Engineering The energy range of semiconductors employed as photocatalysts is referred to as their bandgap. The energy difference between electrons in their lowest energy state (the valence band), and the highest energy state (the conduction band) indicates the region where electrons are in their maximum energy state. There is a barrier between these two states created by this bandgap. Electrons move from the valence band to the conduction band when photons with energy equal to or greater than the bandgap’s value are absorbed by the photocatalyst. Electron–hole pairs are created as a result of this transition, and the material’s photocatalytic performance is significantly influenced by the bandgap’s width. Materials with broader bandgaps generally absorb UV light, while those with narrower bandgaps generally absorb visible light. By adjusting the bandgap, researchers can maximize the photocatalysts’ capacity to absorb light and so increase the efficacy of charge carrier formation (Mahdi and Hanandeh 2022).

4

M. Sen

1.5 On the Surface of the Photocatalyst, Charge Carrier Separation and Redox Reactions Occur Within the photocatalyst, electron–hole pairs (e-/h+) are created when light is absorbed. The efficacy of photocatalysis is largely dependent on how well these charge carriers are separated and kept stable. Following their effective separation, the photo-induced electrons and holes participate in redox reactions occurring on the surface of the photocatalyst. Strong oxidizing characteristics of the photo-induced holes (H+) allow them to interact with water or hydroxyl groups (OH_ ) on the surface of the photocatalyst, producing hydroxyl radicals (OH•). Strong oxidative properties are exhibited by these radicals, which are essential for the breakdown of contaminants and the creation of organic molecules (Kamat 2012a; Kamat and Bisquert 2013).

1.6 Generation of Reactive Oxygen Species (ROS) The formation of reactive oxygen species (ROS) is a crucial requirement for the photocatalytic mechanism discussed earlier. Superoxide radicals (O2 •_ ) and hydroxyl radicals (OH•) are the two most important ROS in photocatalysis. In water and air treatment applications, these ROS can be extremely important in eliminating bacteria and other microbes in addition to aiding in the oxidation and breakdown of contaminants. The adsorption of reactants onto the photocatalyst surface is a critical stage in many photocatalytic reactions. This process is key to the Langmuir–Hinshelwood (L–H) mechanism. Reactants are absorbed on active sites in the L–H mechanism, which is followed by other reaction steps that result in the creation of products. To achieve effective photocatalytic performance, catalysts that are well-designed and have a sufficient number of active sites as well as appropriate reaction intermediates are essential. Gaining an understanding of these mechanisms is crucial to customizing materials and maximizing their performance for particular applications, increasing the field’s potential to address global energy and environmental concerns (Zhang and Nosaka 2014; Wang et al. 2015a).

1.7 Photocatalytic Materials’ Function A photocatalytic procedure’s overall efficacy and specificity are greatly influenced by the choice of photocatalytic material. One of the most well-studied and commonly used photocatalysts is titanium dioxide (TiO2 ). Because of its exceptional stability, lack of toxicity, and simple synthesis, it is favored (Ibhadon and Fitzpatrick 2013). However, TiO2 ’s photocatalytic properties are limited to the UV spectrum due to its broad bandgap, which limits its usefulness in visible light applications (Tachikawa

1 Photo-Redox Reactions: Definition and Classification

5

et al. 2007). This restriction has led to the investigation of alternative semiconducting materials with different properties and bandgap engineering choices. Tungsten trioxide (WO3 ) and tantalum pentoxide (Ta2 O5 ) provide viable options for visiblelight-active metal (ZnO). Furthermore, non-oxide semiconductors for visible-lightactive photocatalysis, like bismuth vanadate (BiVO4 ), cadmium telluride (CdTe), and cadmium sulfide (CdS), have drawn interest as prospective photocatalysts for visible light because they have adjustable bandgaps and distinct electrical characteristics (Fujishima et al. 2000). The creation of hybrid and composite photocatalytic materials has been made easier by recent advancements that combine multiple semiconducting materials or integrate photocatalysts with other advantageous components like plasmonic nanoparticles or carbon-based materials. The complex process of photocatalysis controls a number of variables that affect the efficiency and effectiveness of the photocatalytic reaction. Understanding these underlying characteristics is critical to achieving peak performance in photocatalytic systems and to designing highly efficient photocatalysts. The semiconductor properties of a material mostly determine how efficient it is as a photocatalyst. In particular, a semiconductor’s bandgap energy (Eg) is a critical factor in determining the range of light wavelengths that it can absorb and hence promote the formation of electron–hole pairs. Visible light can be absorbed by the material when the bandgap is quite narrow, which significantly increases its photocatalytic activity (Wei et al. 2012). When the bandgap is not sufficiently broad, electron–hole pairs recombine quickly, which can reduce the photocatalytic efficiency. Wide bandgaps, however, may limit the material’s ability to absorb visible light, rendering it useless for solar-powered applications. The photocatalysts’ surface area and morphology have a major impact on their photocatalytic activity. A larger surface area provides more active sites for reactants to adsorb on, increasing the possibility that molecules may interact with the photocatalyst surface and accelerating the pace of reaction. Furthermore, the efficiency of light absorption and the availability of reactive sites might be impacted by the photocatalyst’s arrangement. Optimizing light absorption and enhancing charge carrier separation by the controlled synthesis of well-defined morphologies can result in increased photocatalytic efficiency. One widely used technique for changing a photocatalyst’s band structure, promoting better charge separation, and increasing its ability to absorb a wider range of light is doping. For instance, adding sulfur or nitrogen to titanium dioxide (TiO2 ) can successfully lower the bandgap, allowing visible light to be absorbed and increasing the material’s total photocatalytic efficiency. The concentration and choice of dopants must be carefully considered; however, overdoping might result in undesired energy levels or recombination centers that reduce photocatalytic efficiency. The degree of ionization of the reactants and the surface charge properties of the photocatalyst, which in turn affect photocatalytic efficacy, are both greatly influenced by the pH level of the reaction medium. Changes in pH can have an impact on the rate of reactant adsorption, surface reaction, and photocatalyst stability. Setting the ideal pH for particular photocatalytic reactions is crucial to getting the required results. Temperature is another crucial element in photocatalysis because it affects both the kinetics of the charge transfer processes and the pace of the surface reactions. It is important to carefully manage the temperature during

6

M. Sen

photocatalytic tests since extreme temperatures might cause thermal deterioration or lower stability of the photocatalyst. Through the optimization of semiconductor characteristics, surface area, doping, co-catalysts, pH, and temperature, researchers can customize photocatalysts for particular uses and promote environmentally friendly and sustainable energy solutions (Ibhadon et al. 2008; Yu et al. 2002).

1.8 Heterogeneous Photocatalysts Recently, significant progress has been made in heterogeneous photocatalysis, leading to the emergence of innovative and highly effective photocatalytic materials. These developments are driven by the demand for effective and sustainable responses to a range of environmental and energy-related problems. They include a variety of substances and methods, each with special qualities and advantages for certain uses, which have significantly expanded the scope and practicality of photocatalysis as a sustainable technology. Researchers continue to unlock the potential of photocatalysts by customizing materials, improving their structures, and investigating cutting-edge ideas (Ibhadon and Fitzpatrick 2013; Singh et al. 2023) This will lead to a greener and more sustainable future. Heterogeneous photocatalysis has emerged as a versatile and prospective technology offering a wide array of potential applications spanning from energy generation and environmental cleanup to healthcare and materials science, including antibacterial applications, self-cleaning coatings, air purification, photocatalytic sensors, environmental remediation, and energy storage. With the advancement of this field’s study, the range of applications is expected to expand further, paving the way for a more sustainable and environmentally friendly future (Pirkanniemi and Sillanpää 2002; Teoh et al. 2012b). The combination of photocatalysis with advanced materials and innovative designs continues to drive the exploration of new applications and optimize existing ones. The primary areas of interest in this section will encompass significant applications, such as water splitting, CO2 reduction, the degradation of pollutants, and chemical synthesis.

1.9 Photo-Redox Catalysis Even though photochemistry has enabled countless changes over the past century, light-mediated mechanisms have not yet been widely used in all scientific disciplines. Achieving low activation energy would greatly affect the reaction route and allow for the desired product’s energy profile. The photocatalyst, a molecule or substance capable of absorbing light and undergoing photochemical reaction, is at the heart of photo-redox catalysis. Chemical bonds that are ordinarily inert can be activated by the photocatalyst in its excited state through the initiation of energy and electron transfer activities. Due to the unusual reactivity, transformations that were previously difficult or impossible can now be carried out quickly and selectively to create complex

1 Photo-Redox Reactions: Definition and Classification

7

compounds. The HOMO is normally filled with metal electrons in transition metal catalysts, whereas the LUMO is left vacant, i.e., that metal has the capacity to either donate electrons to the substrate or accept them from it. Surprisingly, dual-synergistic catalysts rather than transitional metal catalysts may have been able to lower the energy between HOMO–LUMO. In a dual catalysis system, where the photocatalytic cycle is connected to a second catalytic cycle, photo-redox catalysis can therefore also be used. By using either catalyst separately, it may not be able to undergo certain organic conversions. One technique for the catalytic activation of organic molecules that has recently attracted a lot of interest is visible light photo-redox catalysis. It’s been used to study almost anything in organic reactions from simple reduction and oxidation to the creation of bonds between differently hybridized carbon atoms, as well as cycloadditions and formation of bonds of carbon atoms with several heteroatoms like sulfur, oxygen, phosphorus, nitrogen, etc. (Oyetade et al. 2022). In more environmentally friendly synthetic methods, photographic redox catalysts have attracted a lot of attention recently by using reaction pathways that are more precisely controlled and under gentler reaction circumstances. The environmental advantages of photo-redox catalysis are extensive. Energy conservation and the reduction of the production of dangerous byproducts are both facilitated by the capacity to carry out reactions at lower temperatures and with less energy. Additionally, the wide substrate range of photo-redox catalysts enables the development of numerous chemical frameworks. This adaptability has been used in numerous synthetic processes, such as cross-coupling reactions, C-H functionalization, and the creation of carbon–carbon and heteroatom bonds. With such synthetic capabilities, it is possible to develop greener synthetic routes with fewer stages, less waste, and less usage of hazardous chemicals. The importance of photo-redox catalysis comes from its capacity to create a variety of reactive intermediaries using mono electron transfer, rather than by their potential to strengthen a single sort of link creation. Radical species of trifluoromethyl, electrophilic carbonyls, arene cations, enone anions, iminium ions, etc. are among these species. Combining photo-redox catalysts with metals or organic catalysts is very beneficial; so as a result, double catalysis frees up a chance of stereoselective conversions under extremely mild conditions, often at ambient temperature with visible-light irradiation (Kamat 2012b). In essence, photo-redox catalysis uses an additional light-absorbing component to initiate or regulate the redox reaction. It is then retrieved before, during, or after the phase of end-product synthesis. As a result, the catalyst can be used as a PET (Photoelectron Transfer) catalytic compound in the majority of its applications (Oyetade et al. 2022). Catalysis triangle would effectively depict the system for the PET procedure launched by light for synthesis objectives, wherein the constituent that is catalytically active is passed across three stages that are: (a) excitation by photon absorption (photoexcitation: direct or through sensitization), (b) transfer of electron, and finally (c) restoration of the ground state. The quenching process in the excited state can be either reductive or oxidative since electronically excited states are superior reductants and oxidants (Yadav et al. 2023; Mohd et al. 2022). Hardness of photo-redox catalysis when compared to conventional thermal approaches, the ability of light to promote chemical change offers distinct advantages. Photo-redox catalysis provides a more environmentally friendly

8

M. Sen

alternative to UV or high-energy photons, which are frequently linked to environmental concerns, by using the visible spectrum as an energy source. Because visible light is a renewable and abundant energy source, the potential to use it in environmental applications opens up new possibilities for sustainable chemistry. This chapter explores the fascinating area of photo-redox catalysis, which is a major force behind more environmentally friendly synthetic methods. In this chapter, we examine the basic idea behind photo-redox catalysis, emphasizing how it can strengthen visible light and speed up energy and electron transfer procedures. There has also been a discussion of the synthetic uses of photo-redox catalysis, demonstrating its value in the production of complex compounds, medicines, and fine chemicals. Overall, the incorporation of photo-redox catalysis in more environmentally friendly synthetic methods shows significant promise for achieving chemical changes that are sustainable. We may adopt eco-friendly techniques, reduce waste, and work toward a more sustainable future in the field of synthetic chemistry by utilizing the power of light. Due to its prominent role in contemporary chemistry and capacity to start a variety of photochemical processes and due to their distinctive characteristics, contemporary chemistry greatly benefits from them.

1.10 Role of Photo-Redox Catalysts Photo-redox catalysts play a critical and varied function in photochemical processes. Notify some important roles that photochemical transformations using photo-redox catalysts play. A few other elements, such as light absorption, may also influence the reaction. Electron transfer, creation of excited states, single-electron transfer, sensitization, catalytic cycles, selectivity regulation, and redox mediators are some of the processes involved. Typically, organic and inorganic compounds that can absorb light as energy in the visible or ultraviolet ranges of the electromagnetic spectrum are used as photo-redox catalysts. They may take in photons and go through photoexcitation because of particular electrical structures in their bodies. The photo-redox catalyst can therefore conduct an electron transfer process after being photoexcited, either from the catalysts to the substrate (oxidation) or from the substrate to the catalyst (reduction). This phase of the electron transfer process is crucial in starting the desired photochemical reaction. Excited states, which have greater energies than the ground state, are created when light energy is absorbed by the photo-redox catalysts. These excited states have a distinctive reactivity and can interact with other molecules to undergo subsequent reactions that result in the desired changes. It is noteworthy that the photo-redox catalysts can participate in SET reactions. A single electron can be transferred from one molecule to another in these processes, resulting in the production of radicals or radical ions. These reactive intermediates have the potential to take part in a variety of following events, such as bond formation, rearrangements, and fragmentations. As sensitizers, they effectively transfer the energy of their excited states to molecules that aren’t directly triggered by light. The range of transformations is increased by this sensitization process, which makes it possible

1 Photo-Redox Reactions: Definition and Classification

9

to use substrates that would typically be inert in photochemical processes. To create the catalytic cycle, which allows for repeated rounds of excitation, electron transfer, and regeneration, this catalytic behavior increases the catalyst’s overall efficiency and enables its effective application in a variety of processes. It may present chances for the targeted activation of particular bonds or functional groups inside a molecule. High selectivity in the photochemical transformation can be attained by adjusting the catalyst’s electronic and steric characteristics as well as the reaction conditions. When a redox mediator is present or active and allows the movement of electrons between reactants without causing a significant change in their oxidation state, they move electrons between various species, allowing transformations that would not otherwise be advantageous from a thermodynamic standpoint. In general, photoredox catalysts allow for the mild activation of normally unreactive molecules and give access to a variety of reactive intermediates. They have substantially broadened the range of photochemical reactions and their applications in numerous areas of chemistry to their exceptional capacity to harness light energy and enhance electron transfer processes.

1.11 A Few Reactions via Photo-Redox Catalysis (i) Photo-redox catalysts can have a significant influence on the photoluminescent properties of materials, especially, in the context of photoactive and light-emitting materials. The photoluminescent principle refers to the process by which a material absorbs photons and subsequently emits light. This phenomenon occurs when certain materials, called photoluminescent materials or phosphors, absorb energy in the form of photons and then re-emit that energy as light of a different wavelength. Photoluminescent materials can be broadly categorized into two types: fluorescence and phosphorescence. Fluorescent materials are commonly used in various applications, such as fluorescent lamps, bioimaging, and fluorescent dyes and phosphorescent materials suitable for applications like glow-in-the-dark products, security inks, and certain types of sensors. (ii) Water Splitting One of the crucial applications of photocatalysis is water splitting, which aims to harness solar energy to make clean, sustainable hydrogen fuel. Heterogeneous photocatalysts have a crucial function in the process of water splitting, facilitating the efficient separation of photo-generated charge carriers, namely holes and electrons. This separation is essential for driving the redox reactions required for the process (Kudo and Miseki 2009) The water splitting process itself encompasses two half-reactions: the reduction of protons (H+ ) to yield hydrogen gas (H2 ) and the oxidation of water, resulting in the formation of oxygen (O2 ) as its product. The reaction occurring in water splitting can be expressed as follows: (a) Hydrogen Evolution Reaction (HER): 4H+ + 4 e− → 2H2

10

M. Sen

(b) Oxygen Evolution Reaction (OER): 2H2 O + hν → O2 + 4H+ + 4 e− The overall reaction is 2H2 O + hν → 2H2 + O2 . In this process, the photocatalyst captures photons, leading to the formation of electron–hole pairs (e− /h+ ). The electrons generated by this process (e− ) play a crucial role in reducing protons (H+ ) to form H2 gas, while the photo-generated holes (h+ ) are actively engaged in the oxidation of water, resulting in the production of protons and O2 gas. Efficient charge separation and the prevention of electron–hole recombination are critical factors in achieving high water splitting efficiency (Kudo 2011). Titanium dioxide (TiO2 ), metal oxides, and certain perovskite materials have shown promising ability for water splitting. The latest developments in water splitting photocatalysts have focused on improving efficiency and stability. Researchers used co-catalysts and catalytic metal sites to accelerate the hydrogen evolution reaction while reducing electron–hole recombination. Furthermore, novel tandem photocatalytic devices that combine several semiconductors with complementary bandgap energies have demonstrated enhanced solar-to-hydrogen conversion efficiency (Ryu and Choi 2008). (iii) Pollutant Degradation These days, toxic pollutants are a major problem worldwide. Contaminants like petroleum oil, heavy metals, organic dyes, xenobiotics, hydrocarbons, pharmaceuticals, and other emerging pollutants are discharged into the environment and biota as a result of human actions. The increased awareness of environmental contamination has prompted scientists and researchers to devise and implement a variety of approaches that utilize the use of cutting-edge technology to identify and address this worldwide issue. Photocatalysis has demonstrated impressive effectiveness in the breakdown of various emerging pollutants, pharmaceuticals, and organic substances found in both water and air (Rajeshwar et al. 2008). Within the process of photocatalytic degradation, illumination activates the photocatalyst, resulting in the creation of reactive oxygen species (ROS) and electron–hole pairs. These ROS, which encompass hydroxyl radicals (OH•), superoxide radicals (O2 _ •), and hydrogen peroxide (H2 O2 ), play a vital role in the transformation of organic contaminants into less harmful byproducts (Zhang et al. 2015a). Simultaneously, the freed electrons and holes actively engage in redox reactions that facilitate the decomposition of organic compounds. Titanium dioxide (TiO2 ) stands out as a widely recognized photocatalyst due to its robust oxidative properties, which make it highly effective for breaking down pollutants. Conventional TiO2 photocatalysis, on the other hand, is limited to UV light absorption, restricting its application in natural sunlight (Coleman et al. 2005). Researchers have placed their emphasis on modifying the attributes of the photocatalyst with the aim of broadening its light absorption capabilities into the visible spectrum. This endeavor has been undertaken to address and overcome this particular limitation effectively. Doping, co-catalyst integration, and surface functionalization have all been investigated as ways to optimize light consumption and photocatalytic activity (Xu et al. 1999; Arabatzis et al. 2002). (iv) Organic Synthesis

1 Photo-Redox Reactions: Definition and Classification

11

With the ability to directly activate and functionalize bonds using visible light, Photocatalysis has arisen as an eco-friendly and sustainable approach to chemical synthesis. This approach offers advantages over traditional chemical synthesis methods that rely on high temperatures and hazardous reagents (Nguyen et al. 2015). It is an environmentally friendly method for performing chemical reactions using light energy. It involves the use of photocatalysts to initiate photochemical transformations of organic molecules, resulting in the formation of complex molecular structures and new chemical bonds (Gautam et al. 2022). In photocatalytic organic synthesis, the photocatalyst absorbs visible light, initiating photochemical reactions that activate organic molecules. The photocatalyst’s excited state can participate in single-electron transfer reactions, generating radicals and initiating a cascade of chemical transformations. These photo-generated charge carriers can be involved in a variety of reactions, including single-electron transfer, energy transfer, and radical reactions. The excited state of the photocatalyst can transfer energy to nearby reactant molecules, leading to the activation of chemical bonds and subsequent transformations (Gong et al. 2016). Photocatalysis has been widely applied to C–C bond formation reactions, enabling the construction of complex molecular frameworks. Cross-coupling of aryl halides with alkyl nucleophiles is facilitated by visible light. Researchers have used photocatalysts like iridium complexes to encourage the establishment of C–C bonds between distinct functional groups, providing an efficient and selective route to valuable organic compounds. Photocatalytic C-H functionalization reactions enable direct alteration of C-H bonds in organic compounds, eliminating the need for pre-functionalized starting materials (Denny et al. 2007; Teoh et al. 2007). Oxygenation and Oxidation by Photo-redox catalysts: Oxygenation is the process of transferring molecular oxygen to a substrate molecule. Stabilized state tripletoxygen molecule is not reacting with mostly close-shelled organic substances due to spin limitations. Single-electron oxidizing of the substance or single-electron reducing of oxygen to superoxide can activate these reactions. For these reactions, a variety of photocatalysts have been used, ranging from neutralized organic or positive charged substances (pyridinium, thiopyrydium, and acridinium salt) toward transition metal complexes with basis on Ru and Ir (Reckenthäler and Griesbeck 2013).

1.12 Conclusion Without a doubt, photocatalysis has given organic chemists access to a far wider range of tools and opened up opportunities for sustainable synthesis in both academic and commercial settings. A recent trend is the creation of multifunctional photocatalytic systems, which attempt to accomplish several chemical transformations or uses at once. This involves integrating photocatalysis with other technologies, including catalytic ozonation, or creating photocatalysts that can split water and degrade pollutants simultaneously (Zhang et al. 2015b; Wang et al. 2015b). Through

12

M. Sen

the usage of several processes, multifunctional systems have the potential to improve overall performance and optimize resource utilization. Present efforts to successfully use the entire visible light spectrum for photocatalysis may eventually become a modest strategy in the chemicals industries, which were initially envisioned more than a century ago (Maeda and Domen 2010). In order to make photocatalysis processes faster and more energy-efficient, quantum efficiency needs to be significantly increased. The energetics of many photocatalytic conversions have not been investigated, and scientists are just now beginning to create endothermic organic synthesis reactions that are made possible by the additional light energy. Technological developments like lasers and flow chemistries are very beneficial to photochemistry, and multidisciplinary review initiatives combining chemistry experts and engineers should be essential to the commercial application of photocatalytic reactions (Maeda and Domen 2010). The customized design of photocatalysts with particular features optimized for target applications is likely to be the main focus of future heterogeneous photocatalysis research. Customizing the material composition, charge separation, structure, light absorption, and surface characteristics is necessary to increase catalytic activity. Using logical design techniques, backed by powerful characterization tools and computational modeling, will be essential to achieving this. More sophisticated and effective photocatalytic processes may be possible with the integration of several photocatalysts or catalytic functions into a single system (Loddo et al. 2018). Research in this area is likely to primarily focus on optimizing charge carrier dynamics and energy transmission between different components. Creating sustainable and abundant materials is a viable avenue for heterogeneous photocatalysis. Noble metals and rare elements constitute the foundation of many effective photocatalysts; however, there is increasing focus on finding and creating environmentally acceptable substitute materials. This involves investigating non-metallic materials to open the door to scalable and affordable photocatalytic technologies, such as carbon-based nanomaterials, metal-free semiconductors, and readily available metal oxides (Tahir et al. 2020; Thakur et al. 2022). In the realm of heterogeneous photocatalysis, catalyst stability is still a serious concern, especially for long-duration reactions or under challenging reaction conditions. Catalyst degradation can eventually result from surface poisoning, aggregation, and photo-corrosion. (80). Developing stable photocatalyst designs, protective coatings, and surface reaction mitigation techniques will be necessary to address these problems. It is still difficult to maximize the quantum efficiency of photocatalytic reactions because efficient charge carrier dynamics are necessary for high photocatalytic efficiency, and a significant percentage of photo-generated charge carriers frequently recombine before taking part in desired processes. Charge carrier recombination can limit performance, especially in systems with limited carrier lifetimes. To improve charge separation and extend charge carrier lifetimes, researchers will need to look into cutting-edge strategies like co-catalyst engineering, defect control, and advanced heterostructures. It is crucial to comprehend reaction mechanisms and regulate reaction pathways in order to create desired products selectively (SchmittKopplin et al. 1998). Subsequent investigations will encompass clarifying reaction processes via sophisticated spectroscopic and computational techniques, as well as

1 Photo-Redox Reactions: Definition and Classification

13

creating catalysts that prioritize particular pathways. Large-scale practical application of photocatalytic technology is a difficulty that necessitates taking into account elements including reactor design, catalyst immobilization, and synthesis technique scaling. Researchers need to create scalable and affordable production processes to close the gap between lab-scale experiments and practical applications. The potential for ecologically beneficial processes provided by photocatalysis must be carefully considered, as must the toxicity and environmental impact of the photocatalytic materials. It is highly likely that heterogeneous photocatalysis will change chemical synthesis, energy synthesis, and environmental cleanup (Mills et al. 1993). The issues of catalyst stability, charge carrier dynamics, selectivity, scalability, and environmental impact need to be resolved in order to fully realize the potential of photocatalysis. With further interdisciplinary research and collaboration, heterogeneous photocatalysis is poised to be an important part of clean and sustainable technologies for a future that is more environmentally and energy-conscious.

References Arabatzis IM, Antonaraki S, Stergiopoulos T, Hiskia A, Papaconstantinou E, Bernard MC et al (2002) Preparation, characterization and photocatalytic activity of nanocrystalline thin film TiO2 catalysts towards 3,5-dichlorophenol degradation. J Photochem Photobiol, A 149(1–3):237–245. https://doi.org/10.1016/S1010-6030(01)00645-1 Basyach P, Sonowal K, Chetia P, Kalita L, Borthakur S, Saikia L (2022) Photocatalytic conversion of CO2 into value added and renewable fuels over heterogeneous nanocatalysts: a green and environmental benign approach. Heterog Nano Catal Energy Environ Sustain 2–2:221–274. https://doi.org/10.1002/9781119772057.CH23 Coleman HM, Chiang K, Amal R (2005) Effects of Ag and Pt on photocatalytic degradation of endocrine disrupting chemicals in water. Chem Eng J 113(1):65–72. https://doi.org/10.1016/J. CEJ.2005.07.014 Denny F, Scott J, Chiang K, Teoh WY, Amal R (2007) Insight towards the role of platinum in the photocatalytic mineralisation of organic compounds. J Mol Catal a: Chem 263(1–2):93–102. https://doi.org/10.1016/J.MOLCATA.2006.08.031 Fujishima A, Rao TN, Tryk DA (2000) Titanium dioxide photocatalysis. J Photochem Photobiol, C 1(1):1–21. https://doi.org/10.1016/S1389-5567(00)00002-2 Gautam A, Sk S, Pal U (2022) Recent advances in solution assisted synthesis of transition metal chalcogenides for photo-electrocatalytic hydrogen evolution. Phys Chem Chem Phys 24(35):20638–20673. https://doi.org/10.1039/D2CP02089K Gillespie PNO, Martsinovich N (2017) Electronic structure and charge transfer in the TiO2 rutile (110)/graphene composite using hybrid DFT calculations. J Phys Chem C 121(8):4158–4171. https://doi.org/10.1021/ACS.JPCC.6B12506 Gong T, Liu R, Zuo Z, Che Y, Yu H, Song C et al (2016) Metabolic engineering of pseudomonas putida KT2440 for complete mineralization of methyl parathion and γ-hexachlorocyclohexane. ACS Synth Biol 5(5):434–442. https://doi.org/10.1021/ACSSYNBIO.6B00025 Herrmann JM (2010) Fundamentals and misconceptions in photocatalysis. J Photochem Photobiol, A 216(2–3):85–93. https://doi.org/10.1016/J.JPHOTOCHEM.2010.05.015 Ibhadon AO, Greenway GM, Yue Y (2008) Photocatalytic activity of surface modified TiO2/RuO2/ SiO2 nanoparticles for azo-dye degradation. Catal Commun 9(1):153–157. https://doi.org/10. 1016/J.CATCOM.2007.05.038

14

M. Sen

Ibhadon AO, Fitzpatrick P (2013) Heterogeneous photocatalysis: recent advances and applications. Catal 3:189–218. https://doi.org/10.3390/CATAL3010189 Kamat PV (2012a) Manipulation of charge transfer across semiconductor interface. A criterion that cannot be ignored in photocatalyst design. J Phys Chem Lett 3(5):663–672. https://doi.org/10. 1021/JZ201629P Kamat PV (2012b) TiO2 nanostructures: recent physical chemistry advances. J Phys Chem C 116(22):11849–11851. https://doi.org/10.1021/JP305026H Kamat PV, Bisquert J (2013) Solar fuels. Photocatalytic hydrogen generation. J Phys Chem C 117(29):14873–14875. https://doi.org/10.1021/JP406523W Kudo A (2011) Z-scheme photocatalyst systems for water splitting under visible light irradiation. MRS Bull 36(1):32–38. https://doi.org/10.1557/MRS.2010.3 Kudo A, Miseki Y (2009) Heterogeneous photocatalyst materials for water splitting. Chem Soc Rev 38(1):253–278. https://doi.org/10.1039/B800489G Loddo V, Bellardita M, Camera-Roda G, Parrino F, Palmisano L (2018) Heterogeneous photocatalysis. In: Current trends and future developments on (bio-) membranes: photocatalytic membranes and photocatalytic membrane reactors. Elsevier, pp 1–43. https://doi.org/10.1016/B978-0-12813549-5.00001-3 Maeda K, Domen K (2010) Photocatalytic water splitting: recent progress and future challenges. J Phys Chem Lett 1(18):2655–2661. https://doi.org/10.1021/JZ1007966 Mahdi Z, El Hanandeh A (2022) Insight into copper and nickel adsorption from aqueous solutions onto carbon-coated-sand: Isotherms, kinetics, mechanisms, and cost analysis. Clean Chem Eng 3:100045. https://doi.org/10.1016/j.clce.2022.100045 Mills A, Davies RH, Worsley D (1993) Water purification by semiconductor photocatalysis. Chem Soc Rev 22(6):417–425. https://doi.org/10.1039/CS9932200417 Mohd S, Wani AA, Khan AM (2022) ZnO/POA functionalized metal-organic framework ZIF8 nanomaterial for dye removal. Clean Chem Eng 3:100047. https://doi.org/10.1016/J.CLCE. 2022.100047 Nguyen MA, Bedford NM, Ren Y, Zahran EM, Goodin RC, Chagani FF et al (2015) Direct synthetic control over the size, composition, and photocatalytic activity of octahedral copper oxide materials: correlation between surface structure and catalytic functionality. ACS Appl Mater Interfaces 7(24):13238–13250. https://doi.org/10.1021/ACSAMI.5B04282 Oyetade JA, Machunda RL, Hilonga A (2022) Photocatalytic degradation of azo dyes in textile wastewater by polyaniline composite catalyst-a review. Sci Afr 17. https://doi.org/10.1016/J. SCIAF.2022.E01305 Pirkanniemi K, Sillanpää M (2002) Heterogeneous water phase catalysis as an environmental application: a review. Chemosphere 48(10):1047–1060. https://doi.org/10.1016/S0045-6535(02)001 68-6 Rajeshwar K, Osugi ME, Chanmanee W, Chenthamarakshan CR, Zanoni MVB, Kajitvichyanukul P et al (2008) Heterogeneous photocatalytic treatment of organic dyes in air and aqueous media. J Photochem Photobiol, C 9(4):171–192. https://doi.org/10.1016/J.JPHOTOCHEMREV.2008. 09.001 Reckenthäler M, Griesbeck AG (2013) Photoredox catalysis for organic syntheses. Adv Synth Catal 355(14–15):2727–2744. Wiley-VCH Verlag. https://doi.org/10.1002/adsc.201300751 Ryu J, Choi W (2008) Substrate-specific photocatalytic activities of TiO2 and multiactivity test for water treatment application. Environ Sci Technol 42(1):294–300. https://doi.org/10.1021/ES0 71470X Schmitt-Kopplin P, Hertkorn N, Schulten HR, Kettrup A (1998) Structural changes in a dissolved soil humic acid during photochemical degradation processes under O2 and N2 atmosphere. Environ Sci Technol 32(17):2531–2541. https://doi.org/10.1021/ES970636Z Singh SK, Mishra PK, Upadhyay SN (2023) Recent developments in photocatalytic degradation of insecticides and pesticides. Rev Chem Eng 39(2):225–270. https://doi.org/10.1515/REVCE2020-0074

1 Photo-Redox Reactions: Definition and Classification

15

Tachikawa T, Fujitsuka M, Majima T (2007) Mechanistic insight into the TiO2 photocatalytic reactions: design of new photocatalysts. J Phys Chem C 111(14):5259–5275. https://doi.org/10. 1021/JP069005U Tahir MB, Iqbal T, Rafique M, Rafique MS, Nawaz T, Sagir M (2020) Nanomaterials for photocatalysis. In: Nanotechnology and photocatalysis for environmental applications. Elsevier, pp 65–76. https://doi.org/10.1016/b978-0-12-821192-2.00005-x Teoh WY, Mädler L, Amal R (2007) Inter-relationship between Pt oxidation states on TiO2 and the photocatalytic mineralisation of organic matters. J Catal 251(2):271–280. https://doi.org/10. 1016/J.JCAT.2007.08.008 Teoh WY, Scott JA, Amal R (2012a) Progress in heterogeneous photocatalysis: from classical radical chemistry to engineering nanomaterials and solar reactors. J Phys Chem Lett 3(5):629–639 Teoh WY, Scott JA, Amal R (2012b) Progress in heterogeneous photocatalysis: from classical radical chemistry to engineering nanomaterials and solar reactors. J Phys Chem Lett 3(5):629–639. https://doi.org/10.1021/JZ3000646 Thakur N, Singh SB, Anshuman (2022) Use of photocatalyst in self-cleaning constructions material: a review 117–132. https://doi.org/10.1007/978-981-16-9744-9_8 Wang F, Jiang Y, Lawes DJ, Ball GE, Zhou C, Liu Z et al (2015a) Analysis of the promoted activity and molecular mechanism of hydrogen production over fine Au-Pt alloyed TiO2 photocatalysts. ACS Catal 5(7):3924–3931. https://doi.org/10.1021/ACSCATAL.5B00623 Wang F, Ho JH, Jiang Y, Amal R (2015b) Tuning Phase composition of TiO2 by Sn4+ doping for efficient photocatalytic hydrogen generation. ACS Appl Mater Interfaces 7(43):23941–23948. https://doi.org/10.1021/ACSAMI.5B06287 Wei Y, Han S, Walker DA, Warren SC, Grzybowski BA (2012) Enhanced photocatalytic activity of hybrid Fe2O3-Pd nanoparticulate catalysts. Chem Sci 3(4):1090–1094. https://doi.org/10.1039/ C2SC00673A Xu N, Shi Z, Fan Y, Dong J, Shi J, Hu MZC (1999) Effects of particle size of TiO2 on photocatalytic degradation of methylene blue in aqueous suspensions. Ind Eng Chem Res 38(2):373–379. https://doi.org/10.1021/IE980378U Yadav S, Shakya K, Gupta A, Singh D, Chandran AR, VarayilAanappalli A et al (2023) A review on degradation of organic dyes by using metal oxide semiconductors. Environ Sci Pollut Res 30(28):71912–71932. https://doi.org/10.1007/S11356-022-20818-6 Yu JC, Yu J, Ho W, Jiang Z, Zhang L (2002) Effects of F- doping on the photocatalytic activity and microstructures of nanocrystalline TiO2 powders. Chem Mater 14(9):3808–3816. https:// doi.org/10.1021/CM020027C Zhang J, Nosaka Y (2014) Mechanism of the OH radical generation in photocatalysis with TiO2 of different crystalline types. J Phys Chem C 118(20):10824–10832. https://doi.org/10.1021/JP5 01214M Zhang H, Guo LH, Zhao L, Wan B, Yang Y (2015a) Switching oxygen reduction pathway by exfoliating graphitic carbon nitride for enhanced photocatalytic phenol degradation. J Phys Chem Lett 6(6):958–963. https://doi.org/10.1021/ACS.JPCLETT.5B00149 Zhang H, Guo LH, Wang D, Zhao L, Wan B (2015b) Light-induced efficient molecular oxygen activation on a Cu(II)-grafted TiO2/graphene photocatalyst for phenol degradation. ACS Appl Mater Interfaces 7(3):1816–1823. https://doi.org/10.1021/AM507483Q Zhang H, Wang W, Zhao H, Zhao L, Gan LY, Guo LH (2018) Facet-dependent interfacial charge transfer in Fe(III)-grafted TiO2 nanostructures activated by visible light. ACS Catal 8(10):9399– 9407. https://doi.org/10.1021/ACSCATAL.8B02075

Chapter 2

Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds Mookan Rajeswari, Mookan Sarath Babu , and Mookan Natarajan

2.1 Introduction In recent years, there has been a growing emphasis on developing greener and more sustainable approaches to chemical synthesis (Kharissova et al. 2019). The need to minimize environmental impact, reduce waste generation, and conserve energy has led to the exploration of novel catalytic methodologies that offer improved efficiency and selectivity. Among these innovative strategies, photo-redox catalysis has emerged as a promising avenue for greener synthetic approaches (Tucker and Stephenson 2012; Dou and Zeng 2023; Wang et al. 2020; Shaw et al. 2016; Samuel et al. 2022). Transition metal catalysis plays a significant role as a reliable and modular method to construct a complex that will promote the reaction rate and serve as a starting material. Since the beginning of twentieth century, development in the areas of stereoselectivity, metathesis, and cross-coupling processes has received a Nobel prize (Chan et al. 2022). Chemists have therefore been able to create small-molecule fragments and activate them under an in situ reaction pathway allowing a metal-mediated bond breaking and bond forming (Li et al. 2020). Even though photochemistry has enabled countless changes over the past century, light-mediated mechanisms have not yet been widely used in all scientific disciplines. Achieving low activation energy to afford the desired product’s energy profile would M. Natarajan (B) Department of Chemical Sciences, and Centre for Advanced Functional Materials, Indian Institute of Science Education and Research (IISER), Kolkata, Mohanpur 741246, India e-mail: [email protected] M. Rajeswari Department of Chemistry, Government Arts College, The Nilgiris-643002, UdhagamandalamTamil Nadu, India M. S. Babu Department of Chemistry, Gargi College, University of Delhi, New Delhi-110049, India e-mail: [email protected] 17

18

M. Rajeswari et al.

significantly influence the reaction pathway (Scheme 2.1). In transition metal catalysts, the HOMO is typically filled with electrons from metal, while the LUMO is empty, i.e., that metal can donate electrons to the substrate or accept electrons from the substrate. Remarkably, the presence of dual-synergistic catalysts could reduce the energy between HOMO–LUMO even further than the transitional metal catalysts (Fig. 2.1). Photo-redox catalysis can therefore be used in a dual catalysis system, where the photocatalytic cycle is connected to a second catalytic cycle. Organic reactions that would have been infeasible are made feasible using these catalysts. By harnessing the power of light to drive chemical transformations, photo-redox catalysis offers a unique advantage over traditional thermal methods. Photo-redox catalysis uses visible spectrum of electromagnetic radiation as an energy source and offers a greener alternative to UV or high-energy photons which are often associated with environmental concerns. The ability to exploit visible light open to the environment is a new possibility for sustainable chemistry, as it represents a renewable and abundant energy source. The most integral part of photo-redox catalysis is the photocatalyst, a molecule or material capable of absorbing photons and undergoing photochemical reactions. The excited state of the photocatalyst can initiate energy and electron transfer processes, enabling the activation of typically inert chemical bonds. This unique reactivity of photocatalysts under milder reaction conditions and with increased control over the reaction pathways enables the synthesis of complex molecules through efficient and selective transformations that were once challenging or inaccessible. From an environmental perspective, photo-redox catalysis offers numerous benefits. The ability to perform reactions at lower temperatures and with reduced energy requirements contributes to energy conservation and mitigates the generation of hazardous by-products. Furthermore, photo-redox catalysts exhibit a broad substrate scope, allowing for the construction of diverse chemical frameworks. This versatility has found application in various synthetic transformations, including cross-coupling reactions, C-H functionalization, and carbon–carbon/ heteroatom bond formations. Such synthetic capabilities provide opportunities for designing greener synthetic routes with reduced steps, waste or by-products, and the use of environmentally harmful reagents. This chapter delves into the exciting field of photo-redox catalysis as a key driver for greener synthetic approaches. We explore the fundamental principle behind photo-redox catalysis, highlighting its ability to harness visible light and facilitate energy and electron transfer processes. Moreover, we discuss the synthetic applications of photo-redox catalysis, showcasing its utility in the synthesis of complex molecules, pharmaceuticals, and fine chemicals. Overall, the integration of photo-redox catalysis in greener synthetic approaches holds great promise for achieving sustainable chemical transformations. By leveraging the power of light, we can embrace environmentally friendly practices, minimize waste, and contribute to a more sustainable future in the field of synthetic chemistry. Photochemical transformations have a wide range of applications in modern chemistry, which makes them very advantageous. This chapter includes diverse applications of photo-redox catalysts and how they influence various sections. Moreover,

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

19

Ni Ha PC

Br +

R

light

R R

EWG/ Aryl

S

EWG/ Aryl

Br

Triple catalysis Regioirregular a-C-H functionalization a-Arylated alkenes 1,3-enynes and 1,3-dienes

R

SO2Ar' EWG

EWG A Ar'SO2 Ar-Br hv PC

PCn

n

Ni0

ArNiIIBr

B

Photoredox catalysis cycle

SET

Ni catalysis cycle

C-C

SET NiI

Pnn-1

Sufinate catalysis cycle

Ar'SO2

Ar ArO2S D

EWG

Ar E EWG

Scheme 2.1 Design and mechanistic proposal with three interwoven catalysis cycles (Liu et al. 2022)

this field continues to emerge rapidly and new applications are being discovered, highlighting the versatility and utility of photo-redox catalysis in various aspects of chemical synthesis that are beneficial in greener synthetic approaches under sustainable chemistry.

20

M. Rajeswari et al.

a)

A

Catalyst 1

LUMO

A'

A

LUMO

A

A'

A'

C DE B

DE

Catalyst 2

B'

activated intermediate

B HOMO

B B traditional catalysis

not catalyzed

HOMO

B

dual synergistic catalysis

not catalyzed

b) 1. bifunctional catalysis catalyst

E

Nu

3. double activation catalysis

cat. A

cat. B E

Nu

2. casecade catalysis cat. A

cat. B

E

E'

Nu

4. dual synergistic catalysis

cat. A

cat. B

E

Nu

Fig. 2.1 a Schematic representation of dual-synergistic catalysis b Classification of a catalytic system involving two catalysts (Allen and MacMillan 2012)

2.2 Synthesis of an Organic Molecule Using a Greener Approach In photo-redox catalysis, the catalysts are excited by the visible region where the excited state induces the single-electron transfer (SET) processes in the substrate and facilitates reactions that might otherwise not occur. Photocatalytic approaches involving the activation of a substrate through hydrogen atom transfer (HAT) offer unique opportunities promoted through a direct and indirect photocatalytic approach in organic synthesis (Fig. 2.2) (Capaldo and Ravelli 2017). Further, photocatalysts relax back to the ground state, ready for a new light-induced catalytic cycle. In contrast, the carbonyl moiety plays a crucial role in many synthetic transformation and fragment coupling processes in coupling reaction and organic transformation. This made the direct alkylation of carbonyl utilizing cheap and plentiful aldehyde a persistent problem in chemical synthesis. MacMillan group created an excellent approach for the asymmetric intermolecular α-alkylation of aldehyde by

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds R-H a

R

21

Direct Hydrogen Atom Transfer -W+ / Wb''

PC*

Y

Y-W

Y-W

R-H

b

Y-W

b'

h Y-W c

R-H

R

-W' Y-W*

R-H Y

c'

Single Electron Transfer

b'''

Energy Transfer R

BPC

Y-H B-H d PC R-H Y-W(H) B-H / B-

+

R-H Y

R

Proton-Coupled Electron Transfer

= Photocatalyst = Substrate = Additive/ Co-catalyst = Conjugate acid/ base couple

Fig. 2.2 Substrate activation through a HAT step promoted through a direct and indirect photocatalytic approach (Capaldo and Ravelli 2017) (Reproduced with permission from Ref 10 © Wiley Materials 2018)

combining dual photo-redox/ organocatalytic approaches in 2008 to address this difficulty. Remarkably, merging photo-redox catalysis with organocatalysis solved problems in asymmetric chemical synthesis (Nicewicz and MacMillan 2008; Beeson et al. 2007). Thereafter, previous elusive sort-out regarding various transformations, for example, Aldol, Friedel–crafts, vinylation (Kim and MacMillan 2008), allylations (Jang et al. 2007), enolation (Jang et al. 2007), enol reduction (Sibi and Hasegawa 2007) and Diels–alder reaction which are broadly applicable in H2 , O2 , CH4 production and energy storage materials in the presence of one-electron photo-redox metal catalysts (Kalyanasundaram 1982; Juris et al. 1988; Giese 1986). The efficiency and role of dual catalysis aldehyde alkylation have been described in the next section.

2.2.1 Cross-Coupling Reactions In the realm of modern chemistry, the quest for more efficient, selective, and sustainable synthetic methodologies has driven the development of innovative approaches. Among them, the conventional coupling reactions with the principles of photo-redox catalysis have emerged as a revolutionary strategy that promises to redefine the landscape of chemical synthesis. This dynamic and rapidly evolving field leverages the

22

M. Rajeswari et al.

power of light to initiate and control chemical transformation, with plenty of opportunities to streamline and enhance the synthesis of diverse compounds, from pharmaceuticals and agrochemicals to advanced materials. Historically, coupling reactions have played a pivotal role in organic chemistry, enabling the creation of intricate molecular structures by forging covalent bonds between two or more reactants. These reactions, often catalyzed by transition metals, have been fundamentally used in the synthesis of a variety of chemical transformations including complex natural products and functional polymers. However, they often come with limitations, such as the costly, hazardous, harsh reaction conditions, and limited substrate compatibility. Moreover, we try to delve into the diverse applications of photo-redox catalysis in coupling reactions, ranging from the formation of C–C, and C-X (X = N, P, O, S, Cl) bonds to make bioactive molecules. By highlighting specific examples and case studies, we will try to showcase the remarkable scope and potential of this innovative approach across various sub-disciplines of chemistry. This chapter/section aims to provide an insightful exploration of the principles, applications, and potential of this dynamic field, offering a glimpse into the future of sustainable and efficient chemical synthesis. The Suzuki, Mizoroki–heck reaction between alkene and aryl halides represents one of the most important methods of bond formation in synthetic chemistry. Due to their electronics, the nature of steric, alkenes are commonly arylated with high regioselectivity (Liu et al. 2022).

2.2.2 Dual Catalysis A two-fold catalysis system that couples the photocatalytic cycle to the secondary catalytic cycle can also include photo-redox catalysis. When each catalyst is used separately, organic changes that would not be feasible are made possibly mentioned in the previous section.

2.2.2.1

Enamine Catalysis

Enamine catalysis has been extensively researched since MacMillan and coworkers’ article in 2008, expanding the application of the two-fold catalysis system. The use of carbonyl compounds (aldehydes and ketones) as a range of electrophiles is heavily influenced by α- and β-alkylation. α-Alkylation A chiral secondary amine catalyst and a Ru or Ir-photocatalyst can be used to bond carbonyl compounds with alkyl halide. The general outcome of this approach is products that have good enantioselectivity. The catalytic cycle requires reducing the alkyl halide to make radical species which is then added to the enamine intermediate

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds Photoredox

O + Br

H

CN

+

H

Br

EWG

R

R R R b-cyanoaldehyde Enantioneriched motifs

TfOH

N

O

tBu N Me H 20 mol%

+

H

X

F

Me R2

R

+

Br

tBu N H 20 mol%

Ar

R

R2

+ R

Br

Me

Organocatalytic cycle

Me N

O

tBu

N

Me

EWG

Me N tBu

N

O

H

Ar

*

R

Ru(bppy)3

68-91% yield , 82-93% ee

TfOH

1 mol% Ru(bppy)3Cl2 2,6-lutidine,DMSO visible light

R

SET

Ru(bppy)32+

EWG

Photoredox cycle

Me N

EWG

R

TfOH

N

tBu N Me H 20 mol% CN

R

R

Br

H

tBu

N Me

O

61-89% yield , 90-99% ee

Me N

EWG

Me

O

O

tBu

F

H

0.5 mol% Ir cat. 2,6-lutidine,DMSO visible light

O

N NH

Me

R

O F

Bn N Me H 20 mol%

O H

Me

H

0.5 mol% Ir cat. 2,6-lutidine, DMF visible light

O

O EWG

66-94% yield , 89-99% ee

TFA

N

O

EWG R

Me O F

R

H

H

0.5 mol% Ru(bppy)3Cl2 2,6-lutidine,DMF visible light

O

N

O

O

Me O

O H

CN

H

R aldehyde alkyl halide

O

O

organocatalysis

23

O

SET

H

CN R

69-95% yield , 91-98% ee

+ Br

EWG

visible light

Ru(bppy)32+

Scheme 2.2 Merging photo-redox catalysis with organocatalysis (left) and proposed mechanism (right) (Nicewicz and MacMillan 2008)

made by the amine catalyst and aldehyde. (Scheme 2.2). After the α-amino radical is oxidized to an iminium ion, it is hydrolyzed to produce an alkylated product and regenerate the amine catalyst (Nicewicz and MacMillan 2008; Du and Yoon 2009; Condie et al. 2010; Welin et al. 2015). β-Functionalization Using dual catalysis, it is possible to perform a difficult transition of βfunctionalization of saturated carbonyl compounds. All these kinds of reactions follow the same catalytic cycle. Undoubtedly, in the case of substituted aryl nitrile (benzonitrile), reduction occurs first under an activated photo-redox catalyst. The photocatalyst will then oxidize an enamine intermediate to produce an enaminyl radical cation, which will then deprotonated to produce a radical with β atom at the center. The arylated product is produced by combining the radical intermediate and

24

M. Rajeswari et al. Ir(ppy)3

(1 mol%)

CN

+

R1 R2

(20 mol%)

NH EWG

N

R

R1

O

EWG

R

H

R

O

CN

O

R1

R2

EWG

DABCO, DMPU, RT blue LEDs

R

43-81%

EWG

R

N

R2 EWG

-CNO

R1

Ir photocat. (1 mol%) 20% Cy2NH

R2

+

H

EWG

DABCO,TFA, H2O, DMPU, RT blue LEDs

[DABCO-H]

R2

R

EWG

50-83% Ir(ppy)3 O

R2

H

DABCO

PMP

+

R2

H

DABCO,TFA, DMPU, RT visible light

R

R2

H

H

SET

Ar IV

III

[Ir (ppy)3]

[Ir (ppy)3]

O R1

Ar

N

R2

H

NH

+

R2

R

R

O R1

CN

(20 mol%)

N

N

OH

DABCO,AcOH, DMPU, H2O visible light

43-61%

O

R

R2

R1

Ir photocat. (1 mol%)

R1

R

O

NH Ar

N H

Organocatalytic cycle

(1 mol%)

(20 mol%)

O

+

R1

R

R2

O R1

H

NHPMP

EWG

Photoredox cycle

SET

R2 Ar 57-90%

CN

* III

[Ir (ppy)3]

visible light

EWG

Scheme 2.3 Photo-redox C-H β-arylation (left): Proposed mechanistic pathway (right)

then eliminating the cyanide (Pirnot et al. 2013; Terrett et al. 2014; Petronijević et al. 2013; Jeffrey et al. 2015a) (Scheme 2.3).

2.2.2.2

Hydrogen Atom Transfer (HAT) Catalysis

By using a hydrogen atom transfer (HAT) catalyst, the range of radical species that can be produced under photo-redox catalysis can be increased (Referred Fig. 2.2). The photocatalyst oxidizes the HAT catalyst, which is frequently a thiol or an amine, and the ensuing radical intermediate takes an atom of H2 from the starting materials to form the desired product. Under specific conditions, methanol can be used to methylate a few heteroarenes. For example, the synthesis of lactones from alcohols and methyl acrylate can be accomplished using a similar catalytic method. Both of these reactions are carried out via the production of -oxo radical species (Jeffrey et al. 2015b; Jin and MacMillan 2015) (Scheme 2.4). The coupling of aromatic alcohol with aromatic nitrile or imines, as well as direct C-H arylation with aromatic nitrile species, are other examples of HAT/ photo-redox catalysis (Jeffrey et al. 2015b; Jin and MacMillan 2015).

2.2.2.3

NHC-Catalysis

Remarkably, organic synthesis has long struggled to create C–C bonds in an effective and selective manner. Historically, preactivated starting materials have been the mainstay of C–C bond formation (Armin de Meijere 2004). While stoichiometric

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

Scheme 2.4 Direct alkylation of heteroaromatic C-H bonds: proposed process

25

26

M. Rajeswari et al.

amounts of metal salts are frequently produced as a by-product of these reactions, the prevention of each substrate typically needs at least one chemical manipulation to prepare. Because of this, transition metal-catalyzed C-H activation has become one of the most rapidly developing areas of organic chemistry (Crabtree 2010; Davies et al. 2011) C-H activation has had an impact on chemical synthesis, but these processes still significantly rely on the partial functionalization on one partner to produce the C–C bond. One of the most common ways to create C–C bonds is through cross-coupling reactions, although this process has significant limitations. Tetrahydroquinolines and aldehydes can be oxidatively coupled using a mix of photo-redox and NHC catalysis. A photogenerated iminium ion can be attacked by the highly nucleophilic Breslow intermediate (Pareek et al. 2021) to continue the process, producing acylated compounds with moderated to poor enantioselectivity (DiRocco and Rovis 2012a). As no pre-activation of the substrate is necessary and the reaction conditions are mild, using visible light photo-redox catalysis to produce these reactive species may allow for compatibility between various catalytic pathways. By creating acyl anion or homoenolate equivalents from aldehydes an aldehyde is converted to a nucleophilic species in N-heterocyclic carbene catalysis under relatively mild conditions. These compounds have proven to be capable nucleophiles in a variety of reactions (Scheme 2.5) (Moore and Rovis 2009; Vora and Rovis 2011). It was suggested by Daniel A. DiRocco and Tomislav Rovis that chiral NHC catalysis of aldehydes and visible light photo-redox catalysis of tertiary amines would result in direct asymmetric-acylation of tertiary amines (DiRocco and Rovis 2012b; Murry et al. 2001; Mennen et al. 2005; Li et al. 2007; Enders et al. 2009; He and Bode 2005; Mattson and Scheidt 2004) The projected coupling mechanism, which would rely on two chemically distinct activation routes and yield H2 (in the form of H2 O in the presence of a weak oxidant), would result in the formation of a stereoselective C–C bond. This is a desired transition due to the biological importance of these products and the synthetic value of the generated 1,2-amino alcohols.

2.3 Photo-Redox Reaction Under Metal Catalysts One of the areas of organic synthesis that is expanding the fastest is visible light-mediated photo-redox catalysis (Such as [Ru(bpy)3 Cl2 ], [Ru(phen)3 Cl2 ], [Ru(bpz)3 (BArF)2 ], IrIII (ppy)3 , and Ir(ppy)2 (dtbby)PF6 ). In addition to these general advantages, Ru and Ir complexes also have a number of specific properties that make them well-suited for particular photocatalytic applications. For instance, [Ru(bpy)3 Cl2 ] is a strong reduct, while [Ir(ppy)3 (Cl)3 ] is a strong oxidant. These supremacy properties allow them to be used to catalyze a wide range of radical reactions. A photoactive catalyst often participates in single-electron transfer reactions with organic substrates and absorbs visible light. To promote radical-based organic transformation and successfully remove obstacles in novel reaction routes, these catalysts’ reactions continue under benign conditions and through cost-effective

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

27

Scheme 2.5 The direct transformation of C-H bonds into C–C bonds in the presence of dual catalysis (insert: Single-Crystal structure of NHC catalysis)

and environmentally friendly approaches. Few metal catalysts, such as those made of ruthenium and iridium, have been explored as photo-redox catalysts. Examples in general include tris[2-phenylpyridinato-C2, N]iridium(III) and tris(2,2’bipyridine)ruthenium(II). Since the ligand-cantered orbital has lower energy than the metal-cantered eg orbital, these complexes have demonstrated unusual behaviors when exposed to radiation (Bawden etal. 2022; Prier et al. 2013). An electron is transported from the t2g orbital to the * orbital (ligand) under visible radiation (400–800 nm). This might take place after an intersystem crossing, resulting in an excited triplet state (Fig. 2.2). One single-electron transfer process between the photocatalyst and organic molecules is possible because of the triplet state’s extended duration (1100 ns). The substrate can control whether the excited photocatalysts serve as oxidants or reducing agents during the reaction (See Fig. 2.2b). A

28

M. Rajeswari et al. Ru(bpy)3(I) eg* *

a) triple state

b) A

reduction

D

A D

t2g eg* *

Ru(bpy)3(II) Ru(bpy)3(I)

Reductive Quenching Cycle

V isible light

*Ru(bpy)

light

Oxidative Quenching Ru(bpy)3(III) Cycle

3(II)

eg* t2g Ru(bpy)3(II)

*

D

A D

A

*Ru(bpy)3(II) oxidation t2g Ru(bpy)3(III)

Fig. 2.3 a Schematic representation of electron-transition under photo reductive condition of metal catalysts; b The proposed reaction pathway for metal catalysts (Kalyanasundaram 1982; Prier et al. 2013)

second single-electron oxidation/reduction will be performed on the resulting metal species to put the catalysts back in their oxidized state. The substrates of the photocatalyzed reaction can then participate in any redox stage of the catalytic cycle and frequently do so simultaneously. Such as the way that other substances and metal species can modify the reduction potential in chemical reactions (Fig. 2.3). Since the twentieth century, researchers have examined how light absorption might cause chemical reactions. It has also been extensively researched how photocatalysts can be used to gather light energy in industries like the creation of chemical fuels and synthetic photosynthesis. On the other hand, until recently, visible light-based photocatalysis for organic synthesis was a very uncommon process. Below are a few significant examples that helped set the way for a current explosion in the industry. The reduction of an electron-deficient alkene with the help of BNAH as a stoichiometric reducing agent and Ru(bpy)3 Cl2 as a catalyst was the first notable instance of visible light photo-redox catalysis (Pac et al. 1981). An early example of reductive dehalogenation of α-Bromo carbonyl compounds employing Ru(bpy)3 Cl2 as a photocatalyst was presented by Fukuzumi et al. (Fukuzumi et al. 1990). In 1984, Cano-Yelo and Deronzier et al. reported one of the earliest instances of photocatalytic oxidation. The oxidation of benzyl alcohol to aldehyde could be accomplished using a ruthenium photocatalyst and stoichiometric aryldiazonium salt (Cano-Yelo and Deronzier 1984). According to Hiroaki Kotani et al. in 2004, the cycloaddition of dioxygen with anthracene derivatives was the first reaction that made use of photocatalysts using Ru catalysts. Later, a variety of additional transformations were used for these catalysts (Kotani et al. 2004). The notion of visible light-mediated photoredox catalysis had some early examples that were specifically documented in the 1980s and 1990s; however, the substantial rise of interest in this area is frequently credited to three important articles published between 2008 and 2009.

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

29

In 2008, Macmillan et al. showed that SOMO organocatalysis and photo-redox catalysis could co-exist. Alkyl halide was added as an electrophile in the enamine catalysis process agreed to the dual catalysis system (Zuo et al. 2014). The intramolecular [2 + 2] cycloaddition of dienones can be aided by photo-redox catalysis, Tehshik P Yoon and coworkers reported in 2008 (Ischay et al. 2008). For the reductive cleavage of aliphatic halides, Stephenson et al. used photo-redox catalysis in 2009. This transformation investigated an alternative to the usage of toxic reagents and was tolerated in a variety of functional groups that are routinely utilized in a wide range of different reactions (Narayanam et al. 2009). Importantly, the ability of the substrate to undergo a net oxidative, reductive, or redox-neutral transformation allows for the classification of photo-redox-catalyzed processes. A stoichiometric oxidant or reducing agent is necessary for the net oxidative or net reductive reaction; however, in redox-neutral processes, the substrate will go through both single-electron reduction and oxidation. The mechanism of the process includes oxidation. The size of the cation and the acidity of the metal cations that affect the reaction in photo-redox catalysts must not be disregarded. Organic Photo-redox catalysts are more reactive in oxidation reactions when Lewis acids are introduced in some circumstances to boost the catalyst’s capacity to oxidize (Fukuzumi et al. 2017). Metal ions that resemble Lewis’s acid, like Sc3+ , can attach to flavins and increase their one-electron reduction potentials and photocatalytic stability. The Sc3+ ion can form bonds with acridine and pyrene to boost their photo-redox catalytic activity in the oxidation of substrates by dioxygen. The binding of Lewis acids to radical anions enhances the system’s overall photocatalytic activity by preventing a back electron transfer from the radical anions of the substrates to oxidized photocatalysts (Fig. 2.4).

2.3.1 Net Oxidative Reactions 2.3.1.1

Formation of Iminium Ions Through Photo-Redox Catalysis

The oxidation of amines is a key application of oxidative photo-redox catalysis. Numerous procedures have been developed that rely on an amine’s two-electron oxidation to produce its corresponding iminium ion. For instance, a tertiary amine substrate can be two-electron oxidized to provide iminium ions. Tertiary amine functions well as an electron donor and can quickly undergo single-electron oxidation to create aminium radical cations. An iminium ion can be foamed by a reducing agent by abstracting an H2 atom from an aminium radical cation’s protons due to their low C-H bond dissociation energy. The foamy α-amino radical produced by the deprotonation of the aminium radical cation can then undergo a second single-electron oxidation to yield the iminium ion (Scheme 2.6) (Dinnocenzo and Banach 1989). The reaction could be accessible only on a substrate containing an adjacent hydrogen atom acceptor that can extract a hydrogen atom from one of these sites.

30

M. Rajeswari et al. 

Mn+

PH2

D

0. 81

r : ionic radius

h DH2

M

P

P Ca2+

Mg2+

AH2

O2

h

Mn+

Mn+

Ba3+

 ....

n+

+ DH2

Zn2+

La3+

Yb3+

Sc3+

1. 14 1. 16

A Sc3+

A

1. 00 e V 0. 8 3+ La 3e A V 0. . 0 89 82 Zn2+ A e 1. V 0. 12 70 Mg2+ r : A e 1. V 0. 48 65 Ca2+ A e V 0. 58 Ba3+ e V 0. 48 e V

Mn+

0. 90

A

Yb3+

Fig. 2.4 a Photocatalytic cycle for the oxidation of substrate DH2 by A with photocatalyst P binding to Lewis’s acid metal ions Mn+ . P-Mn+ exhibits photocatalytic reactivity, whereas P without the binding of Mn+ has no photocatalytic reactivity; b. A quantitative measure of the Lewis acidity (E) and ionic radius of redox-inactive metal ions (Fukuzumi et al. 2017)

R1

N R2

R3

e

R1

H

N

R1

R3

R2

N

R3

R2 e H

R1

N

R3

R2 Scheme 2.6 Pathways of amine oxidation to iminium ions

The experiment’s photocatalyst is the iridium complex Ir(ppy)2 (dtbbpy)PF6, which may oxidize N-phenyltetrahydroisoquinoline (Scheme 2.7a) to its radical cation when photoexcited. It is suggested that the intermediate Ir(III) species reduce dioxygen to finish the photo-redox cycle. After that, superoxide may remove a hydrogen atom from the amine’s position to produce the crucial iminium intermediate (Scheme 2.7a). The nitromethane anion is added to produce the aza-henry adduct (Narayanam 2009). Thus, minimum ions created by photo-redox catalysis can interact with nucleophiles to create new C–C bonds. The aza-henry reaction, which uses an iminium ion intermediate to catalyze the photo-redox reaction, is a prime example. For this net oxidative reaction, another oxygen serves as the terminal oxidant (Condie et al. 2010; Cai et al. 2012) The C–C bonds in straightforward vicinal diamine precursors

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

31

Scheme 2.7 a Photo-redox aza-Henry Reaction via Iminium Intermediate; (Cai et al. 2012) b Photo-redox Generation of the Vilsmeier-Haack Reagent (Narayanam 2009)

could be broken down by visible light-promoted photo-redox cleavage under relatively moderate reaction conditions, yielding structurally flexible and synthetically reliable iminium ions and amino radical species (Scheme 2.7b).

2.3.1.2

Oxidative Cyclization

Additionally, the oxidative cyclization of benzothiazoles and indoles using oxygen as the terminal oxidant has been accomplished via photo-redox catalysis (Cheng et al. 2012; Maity and Zheng 2012). Under oxidative photo-redox conditions, thiabenzanilides can also be converted to benzothiazole, as shown by Li and coworkers. A hypothetical mechanism

32

R1

M. Rajeswari et al.

R2

H N

1.0 mol%, 1 eq. DBU 5 % O2 ; DMF Ru(bpy)3(PF6)2 visible light

S

R1

R2 N S

Scheme 2.8 Oxidative Conversion of Thiobenzanilides to benzothiazoles (Cheng et al. 2012)

(Scheme 2.8) suggests that oxygen might act as an oxidative quencher of *Ru(bpy)3 2+ by absorbing an electron from the photocatalysts to create superoxide and the highly oxidizing Ru(bpy)3 3+ . Thiobenzanilide is inert in the absence of a base, but when 1,8diazabicycloundec-7-ene (DBU) is added, the thiobenzanilide anion deprotonates to form the more readily oxidized imidothialate anion (Cheng et al. 2012).

2.3.2 Net Reductive Reactions Photo-redox catalysis is utilized to decrease the substrate in the presence of a stoichiometric reducing agent.

2.3.2.1

Alkene Reduction

The reduction of electron-deficient unsaturated alkenes required the utilization of photo-redox catalysis, with 1-benzyl-1,4-dihydronicotinamide (BNAH) serving as the stoichiometric reductant. The excited ruthenium catalyst is reduced by the BNAH, and the resulting Ru(I) complex being subsequently reduced to an akene with an inadequate electron supply (Pac et al. 1981) (Scheme 2.9). BNAH is shown to quench *Ru(bpy)3 2+ while dimethyl maleate does not, which follows the catalytic cycle that has been postulated and is strongly supported by Stern–Volmer experiments. This discovery offers convincing proof that the reaction proceeds by reductive quenching of electron-deficient olefins *Ru(bpy)3 2+ to produce a Ru(bpy)3 2+ intermediate as opposed to via oxidative quenching to produce a Ru(bpy)3 3+ intermediate. Different electron-withdrawing groups, like ketoarens and nitriles, helped the process (Pac et al. 1984; Ishitani et al. 1985, 1983, 1987).

2.3.2.2

Ring Opening/Allylation

For the concurrent, epoxide opening and allylation of ketoepoxide, an iridium photocatalyst and stoichiometric Hantsch ester have been utilized (Larraufie et al. 2011) (Scheme 2.10).

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

33

O CO2Me

NH2

+ CO2Me

Ru(bpy)3Cl2 , (2 mol%) pyridine, MeOH

N

MeO2C

visible light

Bn

CO2Me 96 %

BNAH 2 equiv.

MeO2C

CO2Me

CO2Me

MeO2C

Ru(bpy)32+

e

light

H

*Ru(bpy) 2+

Ru(bpy)3+

3

H

MeO2C

O

O

O NH2

NH2

MeO2C

CO2Me

O NH2

H

CO2Me

e

NH2

N

N

N

N

Bn

Bn

Bn

Bn

Scheme 2.9 A reduction of electron-deficient olefins by photo-redox

OO Ph

+ TsO Ph

Ir(ppy)2(dtbpy)PF6(5 mol%) OH 4-Mo-Hantzch ester (2.1 eq) DMSO Ph visible light COOEt EtO2C 67%, >20:1 d.r

O Ph

Scheme 2.10 Photocatalytic reductive ring opening of epoxide and subsequent C–C bond formation (Larraufie et al. 2011)

2.3.2.3

Reductive Dehalogenation

Photo-redox catalysis can be used under mild conditions for reductive dehalogenation. This reaction can occur with DIPEA. The reagent DIPEA acts as a reducing agent in the reductive quenching cycle and it is one of the hydrogen sources for radical intermediate during reaction (Scheme 2.11). Joseph W. Tucker and coworkers report the use of a commercial bulb and the photo-redox catalyst, wherein they used tris(2,2’-bipyridyl) ruthenium dichloride to perform radical cyclization on indoles and pyrroles at room temperature. Ru(I), a single-electron reductant produced in a photocatalytic cycle triggered by visible light, reduces an activated C–Br bond to produce a reactive free radical intermediate. With this system, the use of photo-redox catalysis in common free radical reactions is expanded.

34

M. Rajeswari et al.

X R1

H

[Ru(bpy)3]Cl2 (2.5 mol%) HCOOH, iPr2NEt, DMF R2

R1

visible light

R2

R = arly or acyl -

i Pr2NEt + HCOOH

Visible light

Ru(II)

reductive quenching cycle Ru(I)

H

HCOOH N

*

Ru(II) H

N

X R1

H R2

R1

R2

R1

R2

Scheme 2.11 Phenacyl/Phenaryl halide reductive dehalogenation

The radical intermediate is formed under the construction of C–C bond formation by reductive dehalogenation. For instance, functionalization of indoles, pyrroles, and furan with alkyl halides (Tucker et al. 2010) (Scheme 2.12). The fact that ruthenium-catalyzed reduction dehalogenation only works in activated halides (adjacent to an aryl group) is a significant drawback. It is possible to

Visible light

Ru(III)*

Br

COOMe COOMe

N N Ru(I)

Ru(II)

N

e

N

N Ru

2Cl

N N

SET

H

N

Radical C-C Bond Formation

CO2Me CO2Me H

+ X

COOEt

Ru(bppy)3Cl2 (1 mo%) 4-OMe-C 6H4NPh2

COOEt

blue LEDs

Br

COOEt X

COOEt

97-91 %

Scheme 2.12 Cascade Radical Cyclization (insert: Single-Crystal XRD structure for diastereoisomer)

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds OBn

OBn I OBn I

NC

35

I

Ir(ppy)3 (1-2.5 mol%) Hantzsch ester (2 eq.) or HCO2H (5-10 eq.) nBu3N, MeCN

H2N

H OBn H

visible light

NC

H

H2N

Scheme 2.13 Reductive Dehalogenation in aliphatic and aromatic halides

use an iridium photocatalyst to broaden the scope of this reaction. As a result of iridium complexes’ higher reduction potential, inactive alkyl, vinyl, and aryl halide can be reduced (Nguyen et al. 2012) (Scheme 2.13).

2.3.3 Redox Neutral Reaction When a reaction is redox-neutral, the substrates participate in both the oxidative and reductive phases of the photocatalytic cycle without affecting the degree to which the starting materials or products are oxidized overall. The reaction pathways that would not be conceivable otherwise may be made possible by the ability to have both oxidation and reduction processes taking place concurrently for one overall reaction.

2.3.3.1

[2 + 2] Cycloaddition

This reaction of radical cations with enamine demonstrates that photo-redox catalysis can be utilized to access stable radical cations and radical anions that do not fragment to form neutral radicals. These radical ions frequently have intrinsic reactivity that is different from what would be expected in their natural oxidation state, and these species can be employed to access novel reactions. Yoon and coworkers’ inventions of cycloaddition chemistry serve as a prime illustration of this reaction type promoted by information suggesting that certain bis(enone) substrates can undergo single-electron reductions that start [2 + 2] cycloaddition process (Yang et al. 2004a, 2004b; Baik et al. 2001; Wang et al. 2002; Roh et al. 2002; Felton and Bauld 2004). Photo-redox catalysis can be used to proceed with certain reactions which are thermally forbidden such as [2 + 2] cycloaddition to foam cyclobutene derivative from dienones. Especially, such cycloaddition is possible and proceeds with good diastereoselectivity and strictly prohibits non-dimeric products under conditions that starting materials could be aryl enone. By employing Eu(OTf)3 as a Lewis acid and a chiral ligand derived from amino acid, this reaction can be designed to be carried out in an enantioselective manner (Du and Yoon 2009; Tyson et al. 2012; Du et al. 2014) (Scheme 2.14).

36

M. Rajeswari et al. a)

O

Ph

O

O

O Ru(bppy)3Cl2 (5 mol %) i-prNEt(2 eq.), LiBF4 (2 eq)

Ph

H

visible light

H

89%, >10:1 d.r.

O

O i-Pr2NEt

+ Ru(bpy)3

O

Ph

Ph H

Ph

H

Ph i-Pr2NEt

-e *Ru(bpy)

2+ 3

Li

Ru(bpy)32+

Li O

Ph

Ph

Ph

light

[2+2]

O

b) O

O Ph

O

O

+ Me

O

visible light

O Me

64%, >10:1 d.r.

H

Me

84%, >10:1 d.r.

O

i-Pr

H

Me

2.5 eq.

Ph

Ph

O

Ru(bppy)3Cl2 (5 mol %) i-pr2NEt (2 eq.), LiBF4 (4 eq.) Ph

Me

O

O

Ph

O OMe

Me 65%, > 5:1 d.r.

Me

O

Ph

SEt

Me 57%, > 5:1 d.r.

Scheme 2.14 a Photo-redox Reductive cyclization of Bis(enones); b Crossed Intermolecular [2 + 2] Cycloadditions

2.3.3.2

[4 + 2] Cycloaddition-Diels–Alder Reaction

Along with this radical anion hetero-Diels–Alder reaction, it has been discovered that radical cations produced using photo-redox catalysis can also interact with dienes to form Diels–Alder adducts. In particular, it was discovered that after trans product, which is oxidized, radical cation reacts with isoprene in a [4 + 2] cycloaddition to produce cyclohexane Diels–Alder adduct (Lin et al. 2011). In general, in thermal circumstances, numerous Diels–Alder reactions are typically not feasible between an electron-rich diene and a dienophile. However, it is possible to use photo-redox catalysis to encourage the [4 + 2] cycloaddition between diene and dienophile in cases where both became electron-rich (Lin et al. 2011) (Scheme 2.15).

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

37

MeO MeO

Ru(bpz) 3(BArF)2 (0.5 mol%) Me

+

DCM, air, RT Me

visible light

Me

Me

MeO

*

Me

MeO

Me

Ru(bpz)32+

light

Me +e MeO MeO

Ru(bpz)32+

[4+2]

+

+

Ru(bpz)3

O2

Me

Me

Me

Me

O2 MeO

o

PMP Me

o Me

Me

Me

Me TBSO

Me

H 98%

92%

80%

Scheme 2.15 Radical cation Diels–Alder reaction (Lin et al. 2011)

2.3.3.3

C-H Arylation of Amine

An Ir-photocatalyst can catalyze the direct C-H arylation of amines with cyanocontaining aromatic derivatives (Terrett 2014). In this reaction it was discovered that an α-amino C-H arylation has been successfully carried out under the strategy of accelerated serendipity. Surprisingly, a crucial structural motif seen in pharmacological molecules cannot easily be reached by a straightforward substrate. It was discovered that this reaction may be used to functionalize N-aryl amine substrates. Additionally, heterocyclic amines like N-phenyl morpoline and N-phenyl pyrrolidine may be employed. According to the arene scope analysis, benzonitriles with a second electronwithdrawing group are required to make sure that the arene is sufficiently electrondeficient to undergo single-electron reduction. As a result, it was discovered that benzonitrile with esters and amides in the para position made good substrates (Scheme 2.16). It is also possible to use heteroaromatics, which are by nature electrondeficient compounds like 4-cyanaopyridine. A chloride substituent can act as the leaving group for specific five-membered heterocycles, making it possible to install

38

M. Rajeswari et al. a)

CN

Ar

Ir(ppy)3 (1 mol %)

N

+

EWG

NaOAc, DMA, RT N

visible light

Ar

EWG

N CN N

COOEt N

PMP

N N

Ph

88 % PMP, para-methoxyphenyl

80 %

N

N Ph

Ph

72%

BOC

92%

b) N Ph

Ph

NaOAc

CN

IrIV(ppy)3 N

*

Ph

IrIII(ppy)3

Ph

IrIII(ppy)3 N Ph

light

Scheme 2.16 a Scope of the photo-redox Amine α-Arylation Reaction; b Proposed Mechanism

benzoxazole, N-Boc benzimidazole, and caffeine at the amine’s position with good yield (McNally et al. 2011; Schnermann and Overman 2012).

2.3.3.4

Late-Stage Methylation and Cyclopropanation of Bioactive Heterocycles

Modern drug development now heavily relies on the late-stage functionalization (LSF) of sophisticated synthetic intermediates and therapeutic candidates (Godula and Sames 2006). Among the approaches that medicinal chemists find most appealing are those that permit direct manipulation of structural diversity without the requirement for synthetic handles that have already been pre-functionalized. The direct C-H functionalization of heterocycles has become a remarkably valuable tool in modern drug discovery. Recently, DiRocco and a coworker have applied

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

39

O OtBu

H

Het

H

O

+

Ir cat.(2 mol%) TFA/MeCN, RT +

Or O

visible light

X

+

Het

Het

X

X

O O

23% (bis)

H

57%

N

H N

N

O N

N

N

Me

HO

N

N

37%

N O

N

N

H

3 CN

H

N O

21% (bis)

N

O

29%

Me

H

HN

OMe

Cl

Cl

N

Eszopiclone (methylation)

Voriconazole (methylation)

Bosutinib (cyclopr opanation)

Cl

Scheme 2.17 Late-stage compounds are efficiently under visible light irradiation in the presence of photocatalysts (Methylation and Cyclopropylation of complex medicinal and agrochemical agents)

photo-redox catalysis for late-stage C-H methylation and ring constrain aliphatic system of medicinal compounds. Moderate reaction conditions offer an ideal way to change complicated compounds when a variety of derivatives are present (DiRocco et al. 2014) (Scheme 2.17).

2.3.3.5

Trifluoromethylation

According to Scheme 2.18, David A. Nagib and David W.C. MacMillan discovered that using just TfCl and a regular light bulb enables the direct integration of CF3 into a variety of arene and heteroarene rings. Their photo-redox techniques are effective at room temperature, whereas atom transfer pathways for trifluoromethylation require a high temperature (120 °C), enabling efficient generation of trifluoromethyl radicals. Similarly, trifluoromethyl chloride can also be used in photo-redox catalysis to do C-H trimethylation of aromatic and heteroaromatic compounds. This can be utilized to functionalize complicated compounds at a late stage (Nagib and MacMillan 2011). Trifluoroacetic anhydride has been investigated as a more accessible and manageable CF3 source than trifluoromethylation. Trifluoroacetic anhydride has a much more oxidation potential than the TFA-ester adduct that is produced in this reaction welcoming the role of pyridine N-oxide as a redox auxiliary (Beatty et al. 2015).

2.3.3.6

Decarboxylative Coupling

It is appealing to use radical decarboxylation to create organic compounds. Interesting features include the availability and low cost of carboxylic acids, the versatility of the radical intermediate created, and the evolution of CO2 as an almost undetectable

40

M. Rajeswari et al. H

Y

Y

H X

Ru(phen)3Cl2(1-2 mole%) CF3SO2Cl, K2HPO4

Y

CF3

CF3 X

Trimethylfluoronation of Lipitor 4-CF3 (27%)

O

Y

visible light

Z

H

X

X

CF3

Ru(bpy)3Cl2 (0.1-1 mol%) TFAA (1.1-2.1 equiv.) MeCN, 8-15h, 25-35 °C

O N

+ Z

F

CF3

Y

Blue LEDs

X

Ir(Fppy)3 (1 mol%) CF3SO2Cl (2 eq.) K2HPO4, MeCN visible light 74% total yield (1:1:1)

2-CF3 (25%) 4 '-CF3 (22%)

Y

O OH

N

NH Z

OH OH

Me Me

Z

X

1-2-equiv CF3

O

CF3 OMe

O CF3

OMe

N

45%

25%

Boc

N

N CO2Me

Me

54%

Boc

CF3

O

54% (4.0 g)

Me N

HN

CF3 N H

N

58%(3.9 g)

Scheme 2.18 Radical trifluoromethylation of 5- and 6-membered heteroarenes and C-H arenes via photo-redox catalysis

by-product. Although there are numerous techniques for radical decarboxylation, most of them allow for specific circumstances as hashing, functionalizing the acid, or using more UV radiation. This catalysis also provides a gentle substitute for producing radical intermediate from carboxylic acid (Zuo and MacMillan 2014). The radical decarboxylation of α-amino and α-oxo acids is conceivable under photo-redox catalysis. This cyano-substituted aromatic derivative can be linked to the radical intermediates (Zuo and MacMillan 2014) (Scheme 2.19). Notify that this mediated decarboxylation has been approved for the conjugated addition of an array of carboxylic acids to Michael acceptors, offering a practical alternative to the production of organometallic nucleophiles. These techniques have also been developed for the creation of C-F bonds through radical decarboxylation. There were aryloxy acetic acid examples accessible at the time. Later, however, techniques were created to enable the decarboxylative fluorination of a wide range of carboxylic acids (Rueda-Becerril et al. 2014; Noble and MacMillan 2014; Ventre et al. 2015) (Scheme 2.20). The second-generation complete synthesis of apliviolene is more effective and requires five less isolated intermediates than our original synthesis. (Schemes 2.21, 2.22) (Schnermann and Overman 2011). The key step in this synthesis is the addition of the tertiary radical formed by the photo-redox-mediated fragmentation of N(acyoxy)phthalimide to α-chlorocyclopentenone. This reaction combines two highly complex fragments and produces stereospecific adjacent quaternary and tertiary carbon centers, and this transformation demonstrates the usefulness of tertiary carbon radical addition reactions in the production of quaternary carbon stereocenters and in the stereoselective synthesis of challenging σ-bonds that connect two rings, which is

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

41

Scheme 2.19 Proposed catalytic cycle for decarboxylative arylation

R1 R2

E1 COOH

+ R3

R3

Ir [dF(CF3)ppy)2(dtbbpy)PF6 (1 mol%) R1 K2HPO4 , DMF, RT E2

E1 E2

R2

26 W CFL

68-97% Selectfluor Ru(bpy)3Cl2(1 mole%) O

COOH 500W lmp

R

O R X

Selectfluor

X

Ru(bpz)3PF6 (1 mole%)

F

52-92%

Ir [dF(CF 3)ppy)2(dtbbpy)PF6 (1 mol%)

R

R

COOH blue LED

F

70-99%

Scheme 2.20 Decarboxylative Arylation: Acid Scope

yet completely untapped. Additionally, this study’s finding and those in the communication that goes along will demonstrate that complimentary stereo-selection can occur when trialkyl tertiary carbon radicals, (Schnermann and Overman 2011; Schnermann et al. 2012a, 2012b) associated organometallic intermediates, and carbon electrophiles are combined to form quaternary carbon stereocenters (Scheme 2.21). As a result, the essential step in the synthesis of apliviolene was influenced by photo-redox catalysis, encouraging fragmentation of an acyloxy phthalimide and radical conjugated addition. With an excellent high stereoselectivity produced by this reaction is an all-carbon quaternary one (Schnermann and Overman 2012).

42

M. Rajeswari et al.

R

MLn

Me

Me R m

m Me

X

n

n

tertiary organometallic opposite stereochemical outcome

m n

Me

Me

R

R m

m n tertiary radical

n R = carbon electrophile

Scheme 2.21 Proposed mechanism for deriving the quaternary carbon stereocenter

O Me O O H O N O H

CO2Me TBSO

O

H Cl

[Ru(bpy)3](PF6)2 (1 mol%) TBSO Hantzsch ester (1.5 eq) Me DIPEA, DCM H blue LEDs 61%

CO2Me

H

O H Cl

O Me H

H

AcO O

H

Scheme 2.22 Structurally complex rearranged spongian diterpenes (apliviolene) (Keyzers et al. 2006)

2.4 Role in Photochemical Reactions The role of photo-redox catalysts in photochemical reactions is crucial and multifaceted. Notify, some key roles which are influential in photochemical transformation under photo-redox catalysts. Additionally, a few factors could be used to determine the reaction. For instance, light absorption, electron transfer, generation of excited states, single-electron transfer, Sensitization, catalytic cycles, selectivity control, and redox mediators. The Photo-redox catalysts are typically organic and inorganic compounds that can absorb light as energy in the visible or UV regions of the electromagnetic spectrum. They have specific electronic structures that enable them to absorb photons and undergo photoexcitation. Thus, after being photoexcited, the photo-redox catalyst can conduct an electron transfer process that involves either the catalysts transferring electrons to the substrate (oxidation) or the substrate transferring electrons to the catalyst (reduction). This electron transfer step is a key event that initiates the desired photochemical reaction. Absorption of light energy by

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

43

the photo-redox catalysts leads to the formation of excited states, which are higher energy states than the ground state. These excited states can possess unique reactivity and undergo subsequent reactions with other molecules, leading to the desired transformations. Noteworthy, the photo-redox catalysts can engage in single-electron transfer (SET) reactions. In these processes, the catalysts facilitate the transfer of a single electron from one molecule to another, resulting in the formation of radical or radical ions. These reactive intermediates can participate in a wide range of subsequent reactions, for example, bond formation, rearrangements, and fragmentations. While acting as sensitizers, they efficiently transfer their excited state energy to other molecules that are not directly activated by light. This sensitization process enables the use of otherwise non-reactive substrates in photochemical reactions, expanding the scope of transformations. To derive the catalytic cycle where they can undergo multiple cycles of excitation, electron transfer, and regeneration, this catalytic behavior permits the efficient use of the catalyst in multiple reactions and enhances its overall effectiveness. It can offer opportunities for the selective activation of specific bonds or functional groups within a molecule. By tuning the catalyst’s electronic and steric properties as well as reaction conditions, it is possible to achieve high selectivity in the photochemical transformation. While acting as a redox mediator they can facilitate the transfer of electrons between reactants without undergoing a net change in their oxidation state. They shuttle electrons between different species, enabling transformation that would not be thermodynamically favorable otherwise. In general, photo-redox catalysts allow for the mild activation of normally unreactive molecules and give access to a variety of reactive intermediates. Their unique ability to harness light energy and facilitate electron transfer processes has substantially broadened the scope of photochemical reactions and their applications in various fields of chemistry.

2.4.1 Synthesis of Photo-Luminescent Materials (Example: MOF, M-COF, and Hybrid Materials) Photo-redox catalysts can have a significant influence on the photo-luminescent properties of materials, especially, in the context of photoactive and light-emitting materials. Here are a few ways in which photo-redox catalysts can impact photoluminescent materials. Indeed, the sensitization acts as a sensitizer in photoluminescent materials. It can absorb light energy and emit it efficiently to luminescent molecules or chromophores present in the materials. Furthermore, this sensitization process enhances the luminescence efficiently and prolongs the brightness of the materials. The properties of electron transfer facilitated energy transfer processes within photo-luminescent materials. Upon excitation, catalysts can transfer their excited state energy to nearby luminescent species, promoting their transition to higher energy states and resulting in luminescence emission. The special feature of

44

M. Rajeswari et al.

molecular activation in photo-redox catalysts enormously can activate certain molecular species within photo-luminescence materials through photochemical transformation. This activation can lead to changes in the electronic structure, energy level, and chemical environment of the luminescent chromophore thereby influencing their photo-luminescence properties. Additionally, the redox processes play a vital role in modulating the oxidation states and charge distribution of luminescent species, thereby affecting their luminescence properties, such as emission wavelength or intensity by reversible oxidation undergoing reaction. The lifespan and stability also impact issues such as photochemical degradation or quenching of luminescent species by facilitating efficient energy transfer or redox processes, promoting longer-lasting and more stable photo-luminescence. Those properties can enable the emission properties which can be tuning of the emission properties of photoluminescent materials. By choosing appropriate catalysts and reaction conditions, it is possible to control the emission wavelength, intensity, and lifetime of the material, allowing for the establishment of their properties. Thereby, photo-redox catalysis can also be employed in the synthesis of photo-luminescent materials. By using photo-redox catalysts as key components in the synthetic routes, it is possible to achieve precise control over the structure, composition, and photo-luminescent properties of the resulting materials. The precise influence of photo-redox catalysts on photo-luminescent materials will depend on factors such as the specific catalysts used, the composition of the materials, and the desired photo-luminescent properties. Through the strategic application of photo-redox catalysis, it is available to enhance the luminescence efficiency, control emission properties, and develop new classes of photoactive materials with tailored luminescent properties. The nature of properties and their application can be utilized widely, despite the various available methods and a few factors that significantly influence the synthesis. Temperature is one of the most important elements in the synthesis of MOFs, and temperature ranges, solvothermal and non-solvothermal, are commonly distinct (Fig. 2.5).

2.4.2 Application of Photo-Luminescent Materials The photo-luminescent principle refers to the process by which a material absorbs photons and subsequently emits light. This phenomenon occurs when certain materials, called photo-luminescent materials or phosphors, absorb energy in the form of photons and then re-emit that energy as light of a different wavelength. Photoluminescent materials can be broadly categorized into two types: fluorescence and phosphorescence. Fluorescence: In fluorescence, the absorption of photons elevates an electron to an excited state, and when the electron returns to its ground state, it emits light almost instantaneously. The emitted light ceases shortly after the excitation source is removed. Fluorescent materials are commonly used in various applications, such as fluorescent lamps, bioimaging, and fluorescent dyes.

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

45

Fig. 2.5 A description of the synthesis procedures, potential reaction temperatures, and reaction outcomes for MOFs (Stock and Biswas 2012)

Phosphorescence: Phosphorescent materials exhibit a similar absorption and emission process to fluorescence. However, in phosphorescence, the excited state of the material persists for a longer duration before the electron returns to the ground state and emits light. This delayed emission makes phosphorescent materials suitable for applications like glow-in-the-dark products, security inks, and certain types of sensors. Now, when we talk about the applications of photo-luminescent materials under photocatalysis, we are referring to their usage as photocatalysts. Photocatalysts are substances that use light energy to catalyze a chemical reaction. Photo-luminescent materials can be incorporated into photocatalysts to enhance their efficiency and functionality. Here are a few applications of photo-luminescent materials under photocatalysis: Photocatalytic water splitting: Photo-luminescent materials can be used as cocatalysts in photocatalytic systems for water splitting. These materials can help dissociate water molecules into hydrogen and oxygen by absorbing light energy and

46

M. Rajeswari et al.

producing excited states, enabling the creation of clean and sustainable hydrogen fuel. Photocatalytic pollutant degradation: Photo-luminescent materials can be utilized as sensitizers or co-catalysts in photocatalytic systems for the degradation of organic pollutants in air or water. By absorbing light and creating reactive species (such as hydroxyl radicals), these materials can enhance degradation efficiency and accelerate the removal of harmful pollutants. Photocatalytic synthesis: Photo-luminescent materials can be employed as photocatalysts in various synthetic reactions. They can absorb light and generate highly reactive species, allowing to produce valuable chemicals or materials under milder reaction conditions and with improved selectivity. Photovoltaics: Some photo-luminescent materials can be used in photovoltaic devices, such as dye-sensitized solar cells (DSSCs) and perovskite solar cells. These materials help capture a broader range of light wavelengths and improve the efficiency of light-to-electricity conversion. These are just a few examples of how photo-luminescent materials can be utilized in photocatalysis. The specific applications and mechanisms can vary depending on the material properties, desired reactions, and targeted functionalities. Photo-luminescent materials find a wide range of applications across various fields due to their ability to emit light when excited by photons. Here are some notable applications of photo-luminescent materials with emphasis on concerning properties. The main significant feature of lighting and displays is that they can be incorporated into fluorescent lamps, LEDs, and OLEDs to achieve efficient light emission for general illumination, signage, and electronic displays. In addition, these materials are employed for security and anti-counterfeiting fields for domestic purposes. It can also be used in banknotes, passports, identification cards, and product labels to incorporate luminescent features that are difficult to replicate, providing a means for authentication and protection against forgery. In addition, photo-luminescent materials are commonly used in glow-in-the-dark products such as toys, novelty items, and safety equipment. These materials absorb light energy and slowly release it over time, resulting in a prolonged afterglow effect. They are used in applications like emergency signage, watch dials, and exit signs. Photo-luminescent materials can be employed in environmental monitoring systems to detect and measure various parameters. For instance, luminescent sensors can be designed to respond to specific analytes such as pH, temperature, oxygen levels, or pollutant concentrations enabling real-time monitoring in fields like environmental science and healthcare. Additionally, it can be widely applicable to be utilized in the fabrication of optoelectronic devices, including solar cells and photodetectors. This can be used as active layers or sensitizers to convert light into electrical energy, enabling efficient energy harvesting and detection. These materials are largely applied to various surfaces such as walls, roads, and safety equipment to enhance visibility in low-light conditions during emergencies from the light-emitting coating and paint industries. Especially a few of the

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

47

techniques that promote renewable energy technologies, like making energy storage and conversion devices, and photonics and lasers.

2.4.2.1

Sensing

The application of photo-luminescent materials in sensing is a broad topic, but here are some specific examples: • Gas sensors: The materials can be used to detect gases by measuring the changes in their luminescence properties when exposed to different gases. For example, metal–organic frameworks (MOFs) have been used to detect gases such as ammonia, nitrogen dioxide, and hydrogen sulfide. • Biosensors: They can be used to detect biomolecules such as DNA, proteins, and bacteria. For example, quantum dots have been used to detect DNA and proteins, and carbon nanotubes have been used to detect bacteria. • Chemical sensors: The materials can be used to detect chemicals such as pollutants and toxins. For example, lanthanide-doped materials have been used to detect pollutants such as mercury and lead. • Temperature sensors: Photo-luminescent materials can be used to measure temperature by measuring the changes in their luminescence properties with temperature. For example, europium-doped materials have been used to measure temperature. • Pressure sensors: Photo-luminescent materials can be used to measure pressure by measuring the changes in their luminescence properties with pressure. For example, cerium-doped materials have been used to measure pressure. These are just a few examples of the many applications of photo-luminescent materials in sensing. As research in this area continues, we will likely see even more innovative and practical applications of these materials in the future. In addition to the specific examples mentioned above, here are some other general topics that you could write about for the application of photo-luminescent materials in sense: • The principles of photo-luminescence. • The different types of photo-luminescent materials. • The factors that affect the luminescence properties of photo-luminescent materials. • The methods for using photo-luminescent materials in sensing. • The advantages and disadvantages of using photo-luminescent materials in sensing. • The future trends in the application of photo-luminescent materials in sensing. 2.4.2.2

Catalysis

The application of photo-luminescent materials in catalysis is a relatively new field of research, but it has the potential to revolutionize the way we design and use catalysts.

48

M. Rajeswari et al.

Photo-luminescent materials can be used to monitor the activity of catalysts, visualize the reaction mechanism, and improve the selectivity of the reaction. Here are some specific examples of the application of photo-luminescent materials in catalysis: • Monitoring the activity of catalysts: Photo-luminescent materials can be used to monitor the activity of catalysts by measuring the changes in their luminescence properties over time. This can be used to track the progress of a reaction and to optimize the reaction conditions. For example, quantum dots have been used to monitor the activity of catalysts for the degradation of pollutants. • Visualizing the reaction mechanism: Photo-luminescent materials can be used to visualize the reaction mechanism by tracking the movement of electrons and atoms during the reaction. This can be used to understand how the catalyst works and to improve its efficiency. For example, lanthanide-doped materials have been used to visualize the reaction mechanism for the water splitting reaction. • Improving the selectivity of the reaction: Photo-luminescent materials can be used to improve the selectivity of the reaction by targeting specific reaction pathways. This can be done by designing photo-luminescent materials that have a high affinity for the desired reaction products. For example, carbon nanotubes have been used to improve the selectivity of the hydrogenation reaction. These are just a few examples of the many potential applications of photo-luminescent materials in catalysis. As research in this area continues, we will likely see even more innovative and practical applications of these materials in the future. In addition to the specific examples mentioned above, here are some other general topics that you could write about for the application of photo-luminescent materials in catalysis: • The principles of photocatalysis. • The different types of photo-luminescent materials. • The factors that affect the luminescence properties of photo-luminescent materials. • The methods for using photo-luminescent materials in catalysis. • The advantages and disadvantages of using photo-luminescent materials in catalysis. • The future trends in the application of photo-luminescent materials in catalysis. 2.4.2.3

Energy Storage Material

Photo-luminescent materials have been explored for a variety of energy storage applications, including the following: • Solar cells: The materials can be used to convert sunlight into electricity. This is done by absorbing the sunlight and then emitting electrons, which can then be used to generate electricity. For example, quantum dots have been used to make solar cells that are more efficient than traditional solar cells.

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

49

• Lithium-ion batteries: Photo-luminescent materials can be used to improve the performance of lithium-ion batteries. This is done by storing energy in the photoluminescent material and then releasing it when required. For example, lanthanidedoped materials have been used to make lithium-ion batteries that have a longer lifespan. • Supercapacitors: They can be used to make supercapacitors that have a higher energy density. This is done by storing energy in the photo-luminescent material and then releasing it when needed. For example, carbon nanotubes have been used to make supercapacitors that have a higher energy density than traditional supercapacitors. • Thermoelectric generators: Photo-luminescent materials can be used to make thermoelectric generators that convert heat into electricity. This is done by absorbing the heat and then emitting electrons, which can then be used to generate electricity. For example, metal–organic frameworks (MOFs) have been used to make thermoelectric generators that are more efficient than traditional thermoelectric generators. These are just a few examples of the many potential applications of photo-luminescent materials in energy storage. As research in this area continues, we will likely see even more innovative and practical applications of these materials in the future. In addition to the specific examples mentioned above, here are some other general topics that you could write about for the application of photo-luminescent materials in energy storage: • The principles of photo-luminescent energy storage. • The different types of photo-luminescent energy storage materials. • The factors that affect the energy storage properties of photo-luminescent materials. • The methods for using photo-luminescent materials in energy storage. • The advantages and disadvantages of using photo-luminescent materials in energy storage. • The future trends in the application of photo-luminescent materials in energy storage.

2.5 Future Prospectus and Outlook The outlook for greener synthetic approaches with photo-redox catalysts is promising, as these catalysts offer several advantages for sustainable and environmentally friendly chemical synthesis. Here are some of the potential future prospectus and trends in this field listed below. Atom Economical Reaction: This approach reduces the reducing consumption of resources and mitigates the environmental impacts. Mild reaction conditions: These catalysts often operate under mild conditions such as ambient temperature and atmospheric pressure. This characteristic reduces energy

50

M. Rajeswari et al.

requirements and the need for harsh reaction conditions, leading to more sustainable and energy-efficient synthetic conditions. Green oxidation and reduction reactions: Photo-redox catalysts can drive selective oxidation and reduction reactions, which are essential transformations in large-scale organic synthesis. By using light energy and avoiding stoichiometric reagents, these catalysts offer greener alternatives to traditional oxidations and reaction methods. Sustainable Energy Conversion: It can play a crucial role in sustainable energy conversion technologies. They can make the process of converting solar energy into chemical energy easier. Such as the production of fossil fuel through photocatalytic water splitting into renewable energy as molecular hydrogen (H2 ) and CO2 reduction reaction into a lower number of carbon-based molecules. These approaches offer environmentally friendly ways to store and utilize renewable energy. Photocatalytic Organic Transformations: It can highly enable various organic transformations including C–C and C-N bond formation, functional group manipulation, and complex molecule synthesis. Thereby, using photocatalysts it is possible to perform this reaction under mild conditions with high selectivity, efficiency reducing side product, and energy consumption. Waste Reduction and Step Economy: Photocatalysts can improve step economy by enabling multi-step transformations to occur in single-step reactions. This reduces the number of synthetic steps, purification requirements, and overall waste generation leading to more sustainable and efficient synthetic routes. Renewable Feedstocks: These can utilize renewable feedstocks such as biomassderived compounds as starting materials for chemical synthesis. This approach reduces reliance on fossil fuels and offers opportunities for the development of sustainable and renewable production methods. Continuous Flow Processes: The combination of photo-redox catalysis with continuous flow technology holds promise for greener synthetic approaches. A continuous flow system can enhance reaction efficiency, and reduce solvent usage, enabling controlled polymerizations and the use of renewable monomers; these catalysts contribute to the development of environmentally friendly polymer materials. As the field of photo-redox catalysis continues to advance, it is expected that further innovations, discoveries, and applications will emerge leading to more sustainable and greener synthetic approaches. The integration of photo-redox catalysis with other green chemistry principles and techniques will play a crucial role in achieving the goal of sustainable and environmentally friendly chemical synthesis.

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

51

2.6 Summary and Conclusion In concluding this chapter, photo-redox catalysts in greener synthetic approaches hold immense potential for advancing sustainable and environmentally friendly chemical synthesis. These catalysts offer numerous advantages, including atom economy and mild reactions. By harnessing light energy, photo-redox catalyst enables the transformation of renewable feedstocks, promotes step economy, and minimizes the side product generations. Moreover, they play a pivotal role in sustainable energy conversion, photocatalytic organic transformation, and the development of green polymers. The integration of photo-redox catalysis with continuous flow systems further enhances the efficiency and sustainability of synthetic processes. As research and development in this field progress, it is expected that discoveries and applications will continue to derive the adoption of greener synthetic approaches paving the way for a more sustainable and environmentally conscious and steady future in chemical synthesis. Acknowledgements This work has been supported by IISER Kolkata, University of Delhi, and Government Arts and Science College, Udhagamandalam, The Nilgiris. All authors would like to thank to above-mentioned Institution, University, and College for their valuable support. Conflicts of Interest There are no conflicts to declare.

References Allen AE, MacMillan DWC (2012) Chem Sci 3:633–658 Armin de Meijere FDE (Editor) (2004). https://www.wiley.com/en-us/9783527305186, 938 Baik T-G, Luis AL, Wang L-C, Krische MJ (2001) J Am Chem Soc 123:6716–6717 Bawden JC, Francis PS, DiLuzio S, Hayne DJ, Doeven EH, Truong J, Alexander R, Henderson LC, Gómez DE, Massi M, Armstrong BI, Draper FA, Bernhard S, Connell TU (2022) J Am Chem Soc 144:11189–11202 Beatty JW, Douglas JJ, Cole KP, Stephenson CR (2015) Nat Commun 6:7919 Beeson TD, Mastracchio A, Hong JB, Ashton K, Macmillan DW (2007) Science 316:582–585 Cai S, Zhao X, Wang X, Liu Q, Li Z, Wang DZ (2012) Angew Chem Int Ed 51:8050–8053 Cano-Yelo H, Deronzier A (1984) Tetrahedron Lett 25:5517–5520 Capaldo L, Ravelli D (2017) Eur J Org Chem 2017:2056–2071 Chan AY, Perry IB, Bissonnette NB, Buksh BF, Edwards GA, Frye LI, Garry OL, Lavagnino MN, Li BX, Liang Y, Mao E, Millet A, Oakley JV, Reed NL, Sakai HA, Seath CP, MacMillan DWC (2022) Chem Rev 122:1485–1542 Cheng Y, Yang J, Qu Y, Li P (2012) Org Lett 14:98–101 Condie AG, González-Gómez JC, Stephenson CR (2010) J Am Chem Soc 132:1464–1465 Crabtree RH (2010) Journal 110:575–575 Davies HM, Du Bois J, Yu J-Q (2011) Chem Soc Rev 40:1855–1856 Dinnocenzo J, Banach T (1989) J Am Chem Soc 111:8646–8653 DiRocco DA, Rovis T (2012a) J Am Chem Soc 134:8094–8097 DiRocco DA, Dykstra K, Krska S, Vachal P, Conway DV, Tudge M (2014) Angew Chem Int Ed 53:4802–4806 DiRocco DA, Rovis T (2012) Angewandte Chemie (International ed. in English), 51, 5904

52

M. Rajeswari et al.

Dou Q, Zeng H (2023) Curr Opin Green Sustain Chem 40:100766 Du J, Yoon TP (2009) J Am Chem Soc 131:14604–14605 Du J, Skubi KL, Schultz DM, Yoon TP (2014) Sci 344:392–396 Enders D, Henseler A, Lowins S (2009) Synthesis, 4125–4128 Felton GA, Bauld NL (2004) Tetrahedron Lett 45:8465–8469 Fukuzumi S, Mochizuki S, Tanaka T (1990) J Phys Chem 94:722–726 Fukuzumi S, Jung J, Lee YM, Nam W (2017) Asian J Org Chem 6:397–409 Giese B (1986) Radicals in organic synthesis: formation of carbon-carbon bonds, CRC Press Reprints Godula K, Sames D (2006) Science 312:67–72 He M, Bode JW (2005) Org Lett 7:3131–3134 Ischay MA, Anzovino ME, Du J, Yoon TP (2008) J Am Chem Soc 130:12886–12887 Ishitani O, Pac C, Sakurai H (1983) J Org Chem 48:2941–2942 Ishitani O, Ihama M, Miyauchi Y, Pac C (1985) Journal of the chemical society. Perkin Trans 1:1527–1531 Ishitani O, Yanagida S, Takamuku S, Pac C (1987) J Org Chem 52:2790–2796 Jang H-Y, Hong J-B, MacMillan DWC (2007) J Am Chem Soc 129:7004–7005 Jeffrey JL, Petronijević FR, MacMillan DWC (2015a) J Am Chem Soc 137:8404–8407 Jeffrey JL, Terrett JA, MacMillan DWC (2015b) Sci 349:1532–1536 Jin J, MacMillan DWC (2015) Nature 525:87–90 Juris A, Balzani V, Barigelletti F, Campagna S, Belser P, von Zelewsky A (1988) Coord Chem Rev 84:85–277 Kalyanasundaram K (1982) Coord Chem Rev 46:159–244 Keyzers RA, Northcote PT, Davies-Coleman MT (2006) Nat Prod Rep 23:321–334 Kharissova OV, Kharisov B.I, Oliva González C.M, Méndez YP, López I (2019) Royal Society open science, 6, 191378 Kim H, MacMillan DWC (2008) J Am Chem Soc 130:398–399 Kotani H, Ohkubo K, Fukuzumi S (2004) J Am Chem Soc 126:15999–16006 Larraufie MH, Pellet R, Fensterbank L, Goddard JP, Lacôte E, Malacria M, Ollivier C (2011) Angew Chem Int Ed 50:4463–4466 Li P, Terrett JA, Zbieg JR (2020) ACS Med Chem Lett 11:2120–2130 Li G-Q, Dai L-X, You S-L (2007) Chem Commun, 2007, 852–854 Lin S, Ischay MA, Fry CG, Yoon TP (2011) J Am Chem Soc 133:19350–19353 Liu K, Leifert D, Studer A (2022) Nature Synthesis 1:565–575 Maity S, Zheng N (2012) Angew Chem Int Ed 51:9562–9566 Mattson AE, Scheidt KA (2004) Org Lett 6:4363–4366 McNally A, Prier CK, MacMillan DWC (2011) Science 334:1114–1117 Mennen SM, Gipson JD, Kim YR, Miller SJ (2005) J Am Chem Soc 127:1654–1655 Moore JL, Rovis T (2009) Asymmetric Organocatalysis, 118–144 Murry JA, Frantz DE, Soheili A, Tillyer R, Grabowski EJ, Reider PJ (2001) J Am Chem Soc 123:9696–9697 Nagib DA, MacMillan DW (2011) Nature 480:224–228 Narayanam JM, Tucker JW, Stephenson CR (2009) J Am Chem Soc 131:8756–8757 J. D. Nguyen, E. M. D’amato, J. M. Narayanam and C. R. Stephenson, nature chemistry, 2012, 4, 854–859. Nicewicz DA, MacMillan DWC (2008) Sci 322:77–80 Noble A, MacMillan DW (2014) J Am Chem Soc 136:11602–11605 Pac C, Ihama M, Yasuda M, Miyauchi Y, Sakurai H (1981) J Am Chem Soc 103:6495–6497 Pac C, Miyauchi Y, Ishitani O, Ihama M, Yasuda M, Sakurai H (1984) J Org Chem 49:26–34 Pareek M, Reddi Y, Sunoj RB (2021) Chem Sci 12:7973–7992 Petronijević FR, Nappi M, MacMillan DWC (2013) J Am Chem Soc 135:18323–18326 Pirnot MT, Rankic DA, Martin DBC, MacMillan DWC (2013) Sci 339:1593–1596 Prier CK, Rankic DA, MacMillan DW (2013) Chem Rev 113:5322–5363

2 Photo-Redox Catalyst-Mediated Green Synthesis of Various Compounds

53

Roh Y, Jang H-Y, Lynch V, Bauld NL, Krische MJ (2002) Org Lett 4:611–613 Rueda-Becerril M, Mahe O, Drouin M, Majewski MB, West JG, Wolf MO, Sammis GM, Paquin J-F (2014) J Am Chem Soc 136:2637–2641 Samuel MS, Ravikumar M, John A, Selvarajan JE, Patel H, Chander PS, Soundarya J, Vuppala S, Balaji R, Chandrasekar N, (2022) Catalysts, 12, 459 Schnermann MJ, Overman LE (2011) J Am Chem Soc 133:16425–16427 Schnermann MJ, Overman LE (2012) Angew Chem Int Ed 51:9576–9580 Schnermann MJ, Untiedt NL, Jiménez-Osés G, Houk KN, Overman LE (2012a) Angew Chem Int Ed Engl 51:9581–9586 Schnermann MJ, Untiedt NL, Jiménez-Osés G, Houk KN, Overman LE (2012b) Angew Chem Int Ed 51:9581–9586 Shaw MH, Twilton J, MacMillan DWC (2016) J Org Chem 81:6898–6926 Sibi MP, Hasegawa M (2007) J Am Chem Soc 129:4124–4125 Stock N, Biswas S (2012) Chem Rev 112:933–969 Terrett JA, Clift MD, MacMillan DWC (2014) J Am Chem Soc 136:6858–6861 Tucker JW, Stephenson CRJ (2012) J Org Chem 77:1617–1622 Tucker JW, Narayanam JM, Krabbe SW, Stephenson CR (2010) Org Lett 12:368–371 Tyson EL, Farney EP, Yoon TP (2012) Org Lett 14:1110–1113 Ventre S, Petronijevic FR, MacMillan DW (2015) J Am Chem Soc 137:5654–5657 Vora HU, Rovis T (2011) Aldrichimica Acta 44:3 Wang L-C, Jang H-Y, Roh Y, Lynch V, Schultz AJ, Wang X, Krische MJ (2002) J Am Chem Soc 124:9448–9453 Wang P, Zhao Q, Xiao W, Chen J (2020) Green Synthesis and Catalysis 1:42–51 Welin ER, Warkentin AA, Conrad JC, MacMillan DWC (2015) Angew Chem Int Ed 54:9668–9672 Yang J, Felton GA, Bauld NL, Krische MJ (2004a) J Am Chem Soc 126:1634–1635 Yang J, Cauble DF, Berro AJ, Bauld NL, Krische MJ (2004b) J Org Chem 69:7979–7984 Zuo Z, MacMillan DW (2014) J Am Chem Soc 136:5257–5260 Zuo Z, Ahneman DT, Chu L, Terrett JA, Doyle AG, MacMillan DW (2014) Sci 345:437–440

Chapter 3

Photoredox Strategies in Green and Sustainable Organic Synthesis Gitumoni Kalita , Yafia Kousin Mirza , Milan Bera , and Paresh Nath Chatterjee

3.1 Introduction When navigating reaction coordinates, synthetic chemists typically use pregenerated high energy species, heat activation, or catalytic activation to allow the functionalization of compounds in organic syntheses. To provide new pathways for retrosynthetic assessment, there has been a sharp increase in interest in adopting unconventional chemical activation techniques, such as photochemical and electrochemical methods, in recent years. The ensuing novel changes have completely changed contemporary synthetic tactics. Advancements in photochemical methods have made some of the most reactive intermediates, such as radicals, radical ions, and charge transfer complexes, more readily accessible. The discovery of reactions and new bond disconnection tactics that are challenging or unattainable with other methods is made possible by photoredox process (Liu et al. 2020). The last decade has viewed a revival in synthetic photochemistry, with a focus on developing sustainable approaches. The light-absorbing chromophores are generally used for a wide spectrum of organic reactions of traditionally non-photoreactive organic molecules. Photocatalysis involving chromophores mainly proceeds via the electron transfer (ET) or EnT route. The ET route, recognized photoredox catalysis, G. Kalita · P. N. Chatterjee (B) Department of Chemistry, National Institute of Technology Meghalaya, Bijni Complex, Laitumkhrah, Shillong, Meghalaya 793003, India e-mail: [email protected]; [email protected] Y. K. Mirza · M. Bera (B) Photocatalysis and Synthetic Methodology Lab (PSML), Amity Institute of Click Chemistry Research and Studies (AICCRS), Amity University, Noida 201303, India e-mail: [email protected] P. N. Chatterjee Department of Chemistry, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur, West Bengal 713209, India 55

56

G. Kalita et al.

performs via single-electron transfer (SET) depending on the redox characteristics of the excited photocatalyst (PC) and the reactant. To complete the catalytic cycle, photoredox processes often rely on sacrificial electron donors or acceptors. In addition, appropriate tuning of the PC and organic substrate redox potentials is vital for successful photoredox catalysis (Fig. 3.1) (Bera et al. 2021). In general, both transition metal complexes (inorganic photoredox catalysts) and organic dyes (organic photoredox catalysts) are mostly used for photoredox-initiated reactions (Fig. 3.2). The metal polypyridyl complexes, like Ru(II)-based polypyridine complexes or cyclometalated Ir(III)-based complexes, are often utilized in transition metal-based photoredox processes. On the other hand, organic dyes such as acridiniums, eosin, 9-fluorenone, methylene blue, rhodamine, xanthone, and rose Bengal, capable of absorbing visible light or near-visible light, have been utilized for developments of metal-free conditions (Wang et al. 2018). The photoredox catalysts (PC) can exploit visible light as a cheap, nonpolluting, and easily available renewable resource of clean energy. When exposed to visible light, the PC produces long-lasting photoexcited states (PC*), which can be easily involved in a bimolecular electron-transfer reaction to donate or accept one electron R

PC

PC*

PC

SET

.+

PC Frequently needs sacrificial electron donor and acceptors.

+ R + R

Dependent upon redox potential.

Fig. 3.1 Photoredox process a) 2 N N

N Ru N

2

N

N

N

N

or

+

+

+

N Ru N

N N

Ir

N

N

N N

F3C F

N

Ir

N

N

Ru(phen)3Cl2 Ru(phen)3(PF6)2

fac -[Ir(ppy)3]

O

OH Br

OH

O

NHEt

N

I

S

HO

Br

R = Br Eosin Y R = NO2 Eosin B

Rhodamine 6G (RA 6G)

tBu

10 -Phenyl phenothiazine

Fig. 3.2 Representative examples of photocatalyst

Ir

tBu CF3

Cl Cl

O O I

N

[Ir{dF(CF3)ppy}2(dtbpy)] (PF6)

O

CO2Et HCl EtN

N

Cl

Cl

R

N

F

[Ir(ppy)2(dpbpy)(PF6)]

b) HO2C R

F

N tBu

or

Ru(bpy)3Cl2 Ru(bpy)3(PF6)2

+

F

tBu

tBu +

I OH

tBu

NH BF 4

I

Rose Bengal (RB)

+ Mes - Acr - Ph

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

b) Oxidative Quenching Cycles

a) Reductive Quenching Cycles Sub or [Red]

PC*

E1/2b

Sub or [Red]

Sub or [Ox]

Sub or [Ox]

E1/2a

PC

Sub or [Ox]

57

PC

E1/2c

E1/2d

PC Sub or [Ox]

Sub or [Red]

Sub or [Red]

Fig. 3.3 The photoredox quenching cycles

to or from molecules. During reductive quenching cycles, PC* accepts an electron from the substrate (Sub) or reductant (Red) and produces the radical anion [PC]•− , which is then oxidized. Alternatively, in an oxidative quenching process, PC* donates an electron to a substrate (Sub) or an oxidant (Ox) in the reaction mixture, producing the radical cation of the photocatalyst [PC]•+ , which is subsequently reduced. Such single-electron transfer (SET) occurrences have directed radical generation and grant a new life to radical conversion in organic synthesis (Fig. 3.3) (Wang et al. 2018; Crisenza and Melchiorre 2020). In 1912, Giacomo Ciamician, a pioneer figure in the field of organic photochemistry, delivered a wonderful speech at the 8th International Congress of Applied Chemistry, entitled “The Photochemistry of the Future,” that clean, economical photochemical transformations could take the place of high-energy synthetic processes in a new, environmentally conscious chemical industry (Yoon et al. 2010). The green method uses a set of guidelines to reduce or eliminate the use of dangerous toxic compounds and their synthesis during the creation, production, and use of chemicals. The ultimate form of sustainable chemical reactivity and the goal of green chemistry is photosynthesis. Perhaps recent developments in photochemical techniques, particularly photoredox catalysis, have moved us closer to this goal. Alike aspirating leaves, these tactics produce reactive radicals by utilizing colored catalysts (organic dyes or transition metal complexes) to absorb light and activate low-energy, stable organic molecules via single-electron processes (oxidation or reduction). The use of water or alcohol as the reaction solvent and visible light as the only energy source is the future goal for developing various organic transformations that may be deemed cutting-edge sustainable chemistry. This chapter focus on

58

G. Kalita et al.

recent advances on sustainable approaches of organic transformation by photoredox catalysis, describing the merits and limitations associated with photoredox catalysts.

3.2 Water as a Hydride Source in Visible-Light Photocatalytic Reactions A combination of proflavine (PF) as a photocatalyst, [Cp*Rh(III)(bpy)H]Cl as the mediator, and triethanolamine (TEOA) as a sacrificial electron donor leads to the chemoselective photocatalytic reduction of aldehydes over ketones (Scheme 3.1) (Ghosh et al. 2015). A thorough mechanistic investigation shows that the major reaction pathway is represented by the reduction of the proflavine triplet photochemically and the subsequent reduction of the Rh catalyst, which produces Rh(III)–H in situ. Water plays a pivotal role in this reaction by supplying protons to produce Rh(III)–H in the reaction. Fillol’s group introduced dual cobalt-copper photoredox catalyst which is capable of reducing aldehydes and aromatic ketones in the presence of water and an electron donor (i Pr2 EtN/Et3 N) as a hydride source of using 447 nm of light (Scheme 3.2) (Call et al. 2017). Mechanistic investigations showed that the organic substrates get reduced due to the production of a [Co–H] intermediate. However, Wan and his group reported that water plays an important role in promoting an intramolecular reaction of 2-(hydroxymethyl)anthraquinone under the irradiation of UV light source (300–350 nm) (Scheme 3.3) (Hou and Wan 2008; Hou et al. 2009). An intramolecular redox product was formed in the reaction which readily oxidized anthraquinone derivative when exposed to air or oxygen.

H

O H O Me

PF (10 mol%), Rh (III) (10 mol%) TEOA (2 equiv.), DMF:H2O (1:1), 20 °C N2, 455 nm

H2N H OH

N

NH2

Proflavine (PF)

H Me OH

N

H2 O RhIII

N 12 examples 3-97% yield

Rh (III) catalyst

Scheme 3.1 Photocatalytic generation of alcohols using Rh(III)–H species

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

PSCu (1.5 mol%) 1 (1 mol%)

O R1

OH

R2

H

Cu N

R2

Ph

H 92%

OH

HO

Me Me 82%

94%

P

Ts

Ph

OH

Me

N

N

HO

H Me

S 93%

N OTf

1

OH Me H

H

H

Co

PSCu

selected examples Me

N

O

Ph

R1 = H, 3 examples, 93-94% R1 = CH 3, 22 examples, 3-99% aliphatic aldehydes = 3 examples, 64-93%

OH

N

P

N

R1

H2O:MeCN:Et3N (6:4:0.2 ml) 30 °C, 447 nm

Ph

Ph

Ph

59

H H

OH

50%

89%

Scheme 3.2 Dual catalysis for the photoreduction of aldehydes and aromatic ketones OH

O CH2OH

O CHO

300-350 nm

CHO

O2

H2O-MeCN O

pH 7

OH

O

Scheme 3.3 Intramolecular photoredox reaction in aqueous solution

3.3 Water-Mediated Rate Acceleration in the Photocatalytic Synthesis of Isoxazolidines The oxidative [3+2] cycloaddition reaction of N-alkyl-substituted hydroxylamines with alkenes was described using 1 mol% [Ir(ppy)2 (bpy)]PF6 photoredox catalyst under 11 W light source in ethyl acetate medium (Scheme 3.4) (Hou et al. 2014). Notably, they found that the addition of 2.5 equiv. H2 O in the reaction mixture increased the rate of the reaction and produced the desired isoxazolidine products in good yields. This observation proves that the reaction is largely dependent on water. To support the mechanistic route of this rate enhancement, the author proposed a hypothesis of water splitting by photoredox catalyst generating active species HO• , HO− , H2 O2 which may be implicated in the reaction (Goez et al. 2002, 2004). In spite of this, the theory that substances like H3 O+ and H2 O in the reaction mixture may catalyze the cycloaddition process was rejected (Xu et al. 2010).

3.4 Deboronative Cyanation by Photoredox Catalysis Most of the photocatalytic methods employing water either as a cosolvent or additive did not study its mechanistic influence in the reaction. It is to be noted that the radical precursor such as trifluoroborate salts, diazonium salts, and alkyl and aryl bromides are stable in aqueous condition (Lennox and Lloyd-Jones 2012). Xu and

60

G. Kalita et al. R2

OH Ph

R1 +

N

R2

R1

Ir(ppy)2(bpy)PF6 (1 mol%)

R3 N O 27 examples 42-97% yield

EtOAc, H2O (2.5 equiv.), 11 W CFL Ph

R3

O Alkene

R1

N

Ph

Reactive Intermediate

selected examples O

O Ph N O

OEt

94%, (dr, 85:15)

Ph

O

O

EtO

EtO

N Me N

O

O

EtO O

N

O

Me

83%, (dr > 99:1)

N

OEt

O

Me

EtO O

N Me N

OEt

Cl

64%, (dr, 85:15)

O

EtO O

O

Me 72%, (dr, 80:20)

84%, (dr > 99:1)

Scheme 3.4 [3+2] cycloaddition reaction catalyzed by visible-light photoredox catalyst

R

BF3K +

TsCN

1°, 2° and 3°

selected examples CN

[Ru(bpy)3](PF6)2 (2 mol%) BI-OAc (3 equiv.), TFA (2 equiv.) CH2Cl2/H2O, RT, blue LEDs

O

R

CN

28 examples 41-87% yield

CN

CN

BI-OAc O CN

CN

N O 71%

OAc I O

53%

78%

N Ts 52%

59%

Scheme 3.5 Deboronative cyanation reaction of alkyltrifluoroborates

co-workers achieved alkyl nitrile from the direct photocatalytic cyanation reaction of alkyltrifluoroborates with the combination of [Ru(bpy)3 ](PF6 )2 photocatalyst, hypervalent iodine as an oxidant, and TFA as an additive (Scheme 3.5) (Dai et al. 2016). The reaction tolerated several functionalities with a wide range of substrate scope. The involvement of an alkyl radical intermediate in the reaction was established by trapping the free radical using a radical scavenger, TEMPO.

3.5 LUMO Lowering Effect by Water A LUMO lowering effect of carbonyl was observed in the photocatalytic crosscoupling reaction of α-acetoxy acetophenones and styrene derivatives followed by Markovnikov functionalization to 1,4-substituted product (Scheme 3.6) (Speckmeier et al. 2018). The coupling process was obtained by the quenching of photocatalyst facIr(ppy)3 oxidatively in combination with the carbonyl group activation in the presence of water and Nd(OTf)3 as a Lewis acid catalyst. The use of aqueous medium with

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

61

fac-Ir(ppy) (0.5 mol%) 3 Nd(OTf)3 (10 mol%) K2CO3 (2.0 equiv)

O + R 1

R2

OAc

O

R1

OH 20 examples 39-93% yield

MeCN/H2O (4:1), blue LEDs

R2

[Nd] O

O

O OAc

Ered = -1.72 V in MeCN vs SCE

OAc Ered = -1.54 V in MeCN/H2O vs SCE

OAc Ered = -1.27 V in MeCN/H2O vs SCE

Scheme 3.6 Photocatalytic C–C cross-coupling reaction

a water-compatible Lewis acid enhances the LUMO-lowering effect of carbonyls by increasing the Ered of α-acetoxy acetophenones from −1.72 to −1.27 V versus SCE contributes to more exergonic electron transfer process, which is further confirmed by performing cyclic voltammetry and Stern–Volmer experiments. However, without the Lewis acid catalyst, they did not yield the 1,4-difunctionalized product.

3.6 Water Influences Chemoselectivity Water might be used not only as a solubilizer for polar substrates, but also for its nonsolvent qualities toward lipophilic hydrophobic additives. Jui et al. provided a spectacular example of such abilities using the radical method to heteroaryl radical conjugate addition. 1 mol% (Ir[dF(CF3 )ppy]2 (dtbbpy))PF6 was employed as a photocatalyst competent for the formation of reductive 2-pyridyl radical under irradiation of blue LED. In this work, Hantzsch ester was used to maintain redox neutrality by donating H-atom and an electron. The author demonstrated the reactant solubility by introduction of water cosolvent where Hantzsch ester increased the selectivity of the formation of radical conjugate addition product over the reduction of nitrogen heterocycles (Scheme 3.7) (Aycock et al. 2017). However, Qing recently demonstrated a remarkable solvent effect for chemoselective addition to alkene. Changing the reaction solvent from THF to a DMF/H2 O combination allowed for the chemoselective synthesis of dibromofluoromethylated products via the radical addition of CHBr2 F to alkenes under photoredox catalysis. It was found that 1:4 DMF/ H2 O gave superior result of the desired product than the other solvents (Scheme 3.8) (Chen et al. 2021).

62

G. Kalita et al. CO2Me + X

N

+

[Ir{dF(CF3)ppy}2(dtbbpy)] (1 mol%)

CO2Me

CO2Me

Hantzsch ester, blue LED, 23 °C

Me

N Me

X = Br, I % H2O in DMSO

ratio (2:3)

0% 9% 20% 25% 33%

3:1 10:1 18:1 19:1 20:1

+ N

CO2Me 2

3

36 examples 39-89% yield EtO2C

CO2Et

N Me H Hantzsch ester

Me

Scheme 3.7 Heteroaryl radical conjugate addition

Br R

+ H

Br 22 examples 48-87% yield

Hydro-bromofluoromethylation (with base: KHCO3) O F O

F

O

Br 62%

F

Br

N

57%

Br O OHC

R

DMF/H2O, blue LED, RT with or without KHCO3

F

selected examples

H/Br F

[Ir[dF(CF3)ppy]2(dtbbpy)]PF6 (1 mol%)

Br

O

Br 75%

Bromo-bromofluoromethylation (with out base: KHCO3) F

Cl Br

O

Br

Br

O

68%

OMe

F

76%

Cl

Scheme 3.8 Chemoselective addition of dibromofluoromethane to alkenes

3.7 C–H Functionalization of Heteroarenes in Water by Photoredox Catalyst The direct C–H arylation method of electron-deficient N-heteroarenes has been established using aryldiazonium salts as coupling partner under photocatalytic medium. [Ru(bpy)3 ]Cl2 ·6H2 O was selected as the photocatalyst under the exposure of visible light (45 W LED bulb) producing a series of aryl-heteroaryl motifs (Scheme 3.9). Water was chosen as a greener medium, since the solubility and stability of both substrates and catalyst are excellent in aqueous solution (Xue et al. 2014).

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

. HCl + R

R1

N2BF4 [Ru(bpy)3] Cl2.6H2O (2.5 mol%)

63

o

45 W bulb, H2O, 25 C, Ar, 80 h

N

R

R1 N

22 examples 50-93% yield

selected examples Me

CN

CF3

CF3

N

N

N

N

OMe 65%

CO2Et

OMe 54%

Cl

51%

54%

Scheme 3.9 Synthesis of aryl-heteroaryl motifs under photocatalytic medium

The mechanism was investigated by adding radical quencher TEMPO to the optimized conditions of the reaction. The TEMPO experiments did not yield the desired product and confirm the radical species in the reaction medium. Based on these observations, the mechanism was proposed with three crucial steps: (1) The excited [Ru(bpy)3 ]II * species is generated by irradiation of light to [Ru(bpy)3 ]II catalyst. (2) Formation of phenyl radical via single-electron transfer (SET) from [Ru(bpy)3 ]II * to aryldiazonium salt and the catalyst is oxidized to [Ru(bpy)3 ]III . (3) Combination of the phenyl radical with pyridine hydrochloride gave another radical intermediate and transformed into carbocation via two possible routes. The deprotonation of the intermediate furnished the coupling product (Scheme 3.10) (Xue et al. 2014). Lei et al. developed a comparable approach to arylate isoquinolines using [Ru(bpy)3 ]Cl2 ·6H2 O as a photosensitizer (Scheme 3.11). Unlike the earlier report, which used pyridinium salts as the starting substrates, Lei et al. utilized TFA for in situ protonation of the N-heterocycles in the reaction medium (Zhang et al. 2014).

3.8 Remote C–H Bromination The exploration of visible-light photocatalysis that provides homogenous conditions in water is an intriguing area of research. Based on these objectives, researchers have synthesized several photocatalysts that operate in the aqueous environment. A catalytic system has been developed by merging FeCl3 with Alizarin Red S, an organo-photocatalyst which is soluble in water, for the C5–H halogenation reaction of 8-aminoquinoline. The reaction afforded highly regioselective formation of C5 halogenated 8-aminoquinoline amides at room temperature with the presence of K2 S2 O8 as an oxidant and KBr as an additive under the irradiation of domestic light in air atmosphere (Scheme 3.12) (Qiao et al. 2017).

64

G. Kalita et al.

N H

Ar

N2BF4 2+

[Ru(bpy)3]

N H

R

Ar

a

2+*

b

N H

3+

[Ru(bpy)3]

[Ru(bpy)3]

N2BF4

N N BF4

Ar N2 + BF4

R

R

-

Ar

Ar

N H

-

Scheme 3.10 Plausible mechanistic pathway for arylation of heteroarenes

+

Het

N

[Ru(bpy)3]Cl2.6H2O (2.5 mol%) TFA (1 equiv) Ar

N2BF4

Het

MeOH (0.1 M), 25 °C lightbulb (40 W) N

N

N N

N

N

N OMe

42%

Ar

49%

OMe

51%

OMe 21%

Scheme 3.11 Arylation of isoquinolines

The probable reaction pathway proposed by Wu and his group is presented in Scheme 3.13. The excited state Alizarin S* producing a bromine radical (Br• ) and alizarin red S radical anion by reduction with bromide ion. In the presence of K2 S2 O8 , alizarin red S radical anion can undergo oxidation, completing the photocatalytic cycle and causing the ground state alizarin red S to regenerate.

3 Photoredox Strategies in Green and Sustainable Organic Synthesis alizarin red S (5 mol%) FeCl3 (15 mol%), K2S2O8 (2.0 equiv)

O R1

65

N H

R1

KBr/KI (2.0 equiv), H2O, household light, RT

N

Br/I

O

R2

N H

N

28 examples up to 99% yield

R2

selected examples Br

O

Br

O F3C

N H

N

96%

N H

N Cl

97% Br

O N H

S

Cl

N H

Br

O N H

N

N

71% Br

O N H

N

86%

Br

O

84%

N

90%

Scheme 3.12 Regioselective synthesis of halogenated 8-aminoquinoline amides

R

O

Br

O N H

R

N H

Cl

HCl

-

SO42-

S2O82-

SO4

O R

Br H

O R

N

FeCl3

N

N

Cl Fe

N alizarin red S

Cl

N N

Cl Fe Cl

alizarin red S h

Br Br

SO42SO4

H

O R

Br

N

Cl Fe

alizarin red S*

N

Cl

Scheme 3.13 Probable reaction mechanism

Majority of the Ir- and Ru-polypyridyl complexes which are used as photoredox catalysts have limited solubility in water (from < 1 to 1000 ppm) based on the substituent and the counter anion, and hence they require organic solvent to solubilize both catalyst and substrates (Jespersen et al. 2019). Application of this type of complex as a catalyst has become an attractive protocol as it does not require excess of oxidants. Roelfes and co-workers designed and synthesized water-soluble

66

G. Kalita et al.

(a)

CF3

F

(b)

N

N PF6 N

F N

F 3C

N

N Cl

F

Ir

F 3C

CF3

F

N

Ir N

N N

F F [Ir(dF(CF3)ppy)2(dNMe3bpy)]Cl3

F F [Ir(dF(CF3)ppy)2(dtbbpy)]PF6 R N H

R' O

O S O

Zn 2

Ir- catalyst Aqueous media blue LED

R'

R N H

O

Scheme 3.14 Ir-catalyzed modification of the amino acid, a commercially available photoredox catalyst, and b charged Ir(III)-based photoredox catalyst

photocatalyst [Ir(dF(CF3 )ppy)2 (dNMe3 bpy)]Cl3 via ligand modification to boost the complex’s water solubility (Lier et al. 2021). In the design of newly synthesized photocatalyst, the tert-butyl group on the ligand was substituted with quaternary ammonium group. The developed catalyst was shown to be promising to modify the dehydroalnine (Dha) containing natural products in aqueous environment under physiological circumstances at a wide range of pH (Scheme 3.14). Next, Conrad et al. designed similar heteroleptic Ir-complexes by introducing carboxylate group on the bipyridyl ligands which prompted a catalyst [Ir(dF(CF3 )ppy)2 (dCO2 Hbpy)]CO2 CF3 (4) with improved water solubility. The efficiency of this photocatalyst was tested in the trifluoromethylation reaction of polar molecules and peptides in phosphate-buffered saline solvent using Langlois reagent (CF3 SO2 Na) as CF3 • radical precursor in the presence of a light source for photoexcitation (Scheme 3.15) (Nguyen et al. 2021).

3.9 Metallacarboranes as Photoredox Catalyst in Water A metallacarborane of cobalt, [3,3’-Co(1,2-C2 B9 H11 )2 ]Na, with an unconventional pattern compared to known photoredox catalysts produces hydrogen and dihydrogen bonding which is advantageous in self-assembling, (Brusselle et al. 2013) water solubility (Tarrés et al. 2014), and micelle formation (Uchman et al. 2015). The application of cobaltabisdicarbollide, [3,3’-Co(1,2-C2 B9 H11 )2 ]− , and its chloro derivatives, as photoredox catalyst has been studied by Teixidor et al. in the oxidation reaction of alcohols in water via SET processes (Scheme 3.16) (Guerrero et al. 2020a).

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

67 O

O O HO

O

OH

H N

NH2

4 (10 mol%), CF3SO2Na (4.0 equiv) DPBS buffer (10 mM), blue LEDs

O HO F3C

CF3

F

O

F3C

O

NH2

OH

N

F

OH

H N

HO

O

N

O

HO

Ir

F

N

OH

N O

F

CF3

[Ir(dF(CF3)ppy)2(dCO2Hbpy)]CO2CF3 (4)

Scheme 3.15 Trifluoromethylation of biomolecule substrates

O

OH R1

[Co(C2B9H11)2]Na (0.01-0.1 mol%)

R2

H2O/K2CO3 pH = 7 Na2S2O8, 300 nm

R1

R2

8 examples 93-99% yield O

O CH3 99%

O H3 C

O Cl

97%

94%

99%

Scheme 3.16 Metallacarborane catalyzed oxidation reaction of alcohols

The efficiency of the same photocatalyst was also explored in the epoxidation of aromatic and aliphatic alkenes in water (Guerrero et al. 2021a). Elevated conversion toward epoxide formation was achieved after a short reaction time with extremely low catalyst loading. The proposed mechanism revealed that the photoredox [CoIII (C2 B9 H11 )2 ]− catalyst in the presence of water and S2 O8 2− ion generates the oxidized [CoIV (C2 B9 H11 )2 ] with OH• radical, and H+ and SO4 2− ions by absorption of light. The subsequent oxidation of the alkene by [CoIV (C2 B9 H11 )2 ] and the double bond being augmented to the hydroxyl radical (OH• ) led to the formation of the corresponding epoxide (Scheme 3.17). This metallacarborane was also covalently bonded to silica-coated magnetic nanoparticles (MNPs), resulting in an easily separable heterogeneous catalyst by an external magnet (Guerrero et al. 2020b). A cooperative photoredox catalytic system based on ruthenium-cobaltabis(dicarbollide), [RuII (tryp)(bpy)(H2 O)][3,3 Co(1,2-C2 B9 H11 )2 ]2 , in which the metallacarborane (as the photoredox catalyst) and Ru(II) (as the oxidation catalyst) were coupled by noncovalent interaction, has

68

G. Kalita et al.

R2 R1

O [Co(C2B9H11)2]Na (0.01-0.1 mol%) Na2S2O8, H2O/K2CO3 pH = 7

R1

R2

7 examples 66-99% yield

light

Scheme 3.17 Alkene epoxidation

been developed for photooxidation of alcohols under UV light irradiation (Guerrero et al. 2021b). Moreover, a homogeneous, reusable, and water-soluble cobaltbased phthalocyanine photoredox catalyst (5) allowed the oxidative dehydrogenation of tetrahydro-(iso)quinoline, tetrahydro-β-carboline, and indoline derivatives in a biphasic medium (Scheme 3.18) (Srinath et al. 2020). The biphasic system has the benefit of facile product separation and helps the catalyst to be used up to 5 times by maintaining similar reactivity levels. R3 NH N H

R3

5 (1 mol%) H2O/EtOAc, RT, air, blue LED

N

R1

N H

R1

SO3Na

N NaO3S

N

N

Co

N

N

CoPc(SO3Na)4

N N SO3Na N

(5)

NaO3S

CO2Me N H

92%

N

N H

89%

N

OMe

N

N H

91% NO 2

88%

N H

Scheme 3.18 A photoredox catalyzed oxidative dehydrogenation N-heterocycles

N

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

69

3.10 Photoredox-Micellar Catalysis Development of water-soluble photocatalysts has been receiving increasing attention in synthetic organic chemistry. Most of the substrates used in drugs and some photocatalysts are not water-soluble which limit the green chemistry features. A solution to this problem could arise by merging photoredox catalysis with micellar catalysis. Micelles is formed by adding surfactants to the water and enable organic transformations to run in water medium. In 2018, Lipshutz and the group (Bu 2018) designed PQS–[Ir] photocatalyst formed via covalent binding of PQS (polyethyleneglycol ubiquinol succinate, reduced form of dietary supplement CoQ10 ) with photocatalyst Ir(ppy)3 undergoing self-aggregation in aqueous medium to produce nanomicelles. The amphiphilic species PQS contains a hydrophilic group (MPEG), a lipophilic (50 carbon containing) side chain, and a –OH group which is situated within the hydrophobic inner core where catalysis occurs. The catalytic efficiency of newly designed PQS–[Ir] photocatalyst is explored in sulfonylation of alkenes and enol acetates yielding the required product in good yield (Scheme 3.19). Notably, the catalyst can be recycled for multiple times without compromising the product yield in the reaction. The organic dyes are often used as photoredox catalysts and are much more affordable than precious metal-polypyridyl complexes (Romero and Nicewicz 2016; Hari and König 2014; Margrey and Nicewicz 2016; Majek 2016). Cai and Jiang’s group developed a micellar photocatalytic system by combining with organic photoredox catalyst to arylate the aniline nitrosated in situ (Bu and Lu 2018). The commercially available Triton X-100 and Eosin B were used as the surfactant and photocatalyst, respectively, in the reaction under the influence of 20 W CFL. The reaction proceeded smoothly without any organic cosolvent at room temperature. Moreover, R1 Ar

O +

O S

Cl

HO Ar

PQS-[Ir] (1 mol%)

sulfonylation of alkenes

O O

OAc

O +

O S

Cl

R2

selected examples

O O O S 86%

PQS-attached photocatalyst O N

N

O-MPEG

O

Ir

MeO

N

MeO

O R2

O 10 H

O

15 examples 73-99% yield

PQS-[Ir] (6)

O

from alkene

O O S 90%

O

S

PQS-[Ir] (1 mol%) H2O, blue LED, RT

sulfonylation of enol acetate

HO

S

R2 20 examples 51-91% yield

H2O, blue LED, RT

R2

R1 O

O O S

HO

Me

from enol acetate

Me

72%

HO

O O S

O O S

HO

69%

76%

O O O S 83%

O O O S

O O O S

99%

Scheme 3.19 Sulfonylation of alkenes and enol acetates catalyzed by the PQS-[Ir]

95%

70

G. Kalita et al. NH2 R1

+

X

R2

X = O, S, NBoc

R1

NH2 + AcO

2 wt% TX100/H2O, 20 W CFL, RT

+

R2

R2

Eosin B (1 mol%), t-BuONO (2 equiv.)

R2 2 wt% TX100/H2O, 20 W CFL, RT

O

R1

4 examples 43-91% yield X

Eosin B (1 mol%), t-BuONO (2 equiv.)

X X

X = S, Se

R2

X

R1

14 examples 32-91% yield

2 wt% TX100/H2O, 20 W CFL, RT NH2

R1

R2

Eosin B (1 mol%), t-BuONO (2 equiv.)

R2

R1 7 examples 74-87% yield

Scheme 3.20 Arylation in photocatalytic conditions

the author has also explored (i) the synthesis of unsymmetrical sulfides and selenides from substituted disulfides/diselenides and anilines and (ii) the [4+2] benzannulation of 2-aminobiphenyl with alkynes under their developed photocatalytic conditions (Scheme 3.20).

3.11 Dual Hypervalent Iodine Reagent and Photocatalyst-Enabled Decarboxylation Organic carboxylates are easily available and are removable carboxylates, which act as a latent activating group to build various organic motifs (Gooßen et al. 2008). Generally, transition metal catalyst activates the carboxylates by the coordination of transition metal to the carboxylate group which require strong oxidant or high temperature to facilitate the CO2 extrusion (Mai et al. 2013; Yang et al. 2013). Hypervalent iodine reagents (HIR) have gained great interest because of having similar activation properties to that of transition metals which allows radical addition followed by subsequent decarboxylation under mild reaction conditions. Based on this hypothesis, researchers established a photoredox system with HIR having dual catalytic properties which promotes the decaboxylative radical alkenylation and ynonylation reaction (Huang et al. 2015a; 2015b). Chen’s group (Huang et al. 2015a) reported hypervalent iodine photocatalyst-mediated alkyl-alkene synthesis via the coupling of alkyl trifluoroborate with aryl- or acyl-substituted vinyl carboxylic acids. The use of blue LED irradiation with BI-OAc as iodinating reagent under DCE:H2 O medium at 25 °C gives the best yield for the desired product (Scheme 3.21).

3 Photoredox Strategies in Green and Sustainable Organic Synthesis Ph

Ph R BF3K + HOOC

71

R

[Ru(bpy)3](PF6)2 (2 mol%), BI-OAc (1.5 equiv) Ph

Ph 29 examples 58-87% yield

DCE/H2O, 4 W blue LED, 25 °C

BI = O O

Scheme 3.21 Decaboxylative radical alkenylation reaction

O

O N

N

COOH [Ru(bpy)3](PF6)2 (2 mol%), BI-OAc BI Ph aqueous condition, blue LED

Ph mGlu5 receptor inhibitor

10 mM, pH 7.4 PBS, 83% yield 10 mM, cell lysates, 81% yield 1 mM, cell lysates, 75% yield Scheme 3.22 Synthesis of bioactive molecules in neutral aqueous medium

Additionally, they have shown the biological applications of hypervalent iodine photoredox system to synthesize biomolecules (mGlu5 receptor inhibitor) in neutral aqueous conditions (Scheme 3.22) (Mizuta et al. 2013).

3.12 Photoredox Catalyst-Mediated Trifluoromethylation in Alcoholic Medium The trifluoromethylation method of allylsilanes established by Gouverneur et al. via photoredox catalysis yielded enantio-rich branched allylic-CF3 products. Togni reagent was used as the source of CF3 • radical for the trifluoromethylation reaction with photocatalyst Ru(bpy)3 Cl2 .6H2 O in an methanolic or ethanolic medium on exposure to household 14 W light bulb (Scheme 3.23; Kölmel et al. 2018).

3.13 Merging Nickel with Photoredox Catalysis in Water The amalgamation of transition metals with photoredox catalysts called metallaphotoredox catalysis has emerged as an intriguing platform for the facile synthesis of complicated structures relevant to discovery of drug. Metallaphotoredox catalysis might be another useful tool for DNA-encoded chemistry. Recently, amino acids were successfully decarboxylated in water using an iridium-based photocatalyst,

72

G. Kalita et al. SiMe3

R'

R

R' Togni reagent, MeOH, RT

CF3

CO2Et

OCOAr 46%

R

O Togni reagent

16 examples upto 83% yield CF3

CF3

CF3 I O

CF3

[Ru(bpy)3]Cl2.6H2O (5 mol%) 14 W bulb

65%

CF3 CO2Et Bn

CO2Me OMe

83%

73%

Scheme 3.23 Trifluoromethylation of allylsilanes

Ir[dF(F)ppy]2(dtbbpy)PF6 Ni catalyst, pyridyl igand

X Z DNA-tagged ary halide

+ HO2C

N Boc

amino acid

K2HPO4, DMSO/H2O, RT Blue LED

Z 2

N Boc

3

C(sp )-C(sp ) coupled product

Scheme 3.24 Decarboxylative arylation in aqueous medium

yielding the appropriate C-centered radicals, which were then added to different DNA-tagged radical acceptors (Kölmel et al. 2019). Then, the same group merged photoredox catalysts with nickel in water promoting DNA-compatible decarboxylative arylation reaction. A novel nickel precatalyst with pyridyl carboxamidine ligand combined with iridium-based photocatalyst enabled the structurally diverse DNAencoded libraries from readily available amino acids and various DNA-tagged aryl halides (Scheme 3.24) (Kölmel et al. 2019).

3.14 Supramolecular Photoredox Catalysis in Water Supramolecular photoredox catalysis has been introduced as a metal-free platform in water for various photoredox reactions. A nanosized supramolecular capsule comprising V-shaped aromatic amphiphiles with pentamethylphenyl groups can absorb an organic photoredox catalyst in aqueous condition effectively, and the host–guest combination may be changed. This catalyst effectively reduces organic compounds when exposed to visible light and creates diverse carbon-centered radicals, like aryl, ketyl, and trifluoromethyl radicals in water (Scheme 3.25; Noto et al. 2020). The ketyl radicals were employed to synthesize a series of pinacol derivatives (Scheme 3.25a); the in situ generated aryl radical gave intramolecular cyclization through 1,5-hydrogen atom transfer reaction (Scheme 3.25b) and the CF3 • radical lead to trifluoromethylation of 1,3-dimethyluracil (Scheme 3.25c).

3 Photoredox Strategies in Green and Sustainable Organic Synthesis O Ar

Supramolecular photocatalyst

I CF3SO2Cl

R

O Ar

visible light air, RT

R

73

CF3

R

R

Components of supramolecular photoredox catalyst host monomer (supramolecular capsule) O3S SO3 O

O

Guest (photoredox catalyst)

2.Na N R

(a)

1 mol% supramolecular photocatalyst 2 equiv. Et3N

O

R O R = 4-Ph-C6H4 OH Ph

H2O, air, RT, 425 nm blue LEDs

Ph

Ph OH 90%

(b) 2 mol% supramolecular photocatalyst 2 equiv. Et3N

N I

N

H2O, air, RT, 425 nm blue LEDs

O

47% O

(c) O

O N

N

+ O

O Cl

O S

CF3

2 mol% supramolecular photocatalyst H2O, air, RT, 425 nm blue LEDs

F 3C

N N

O 65%

Scheme 3.25 Supramolecular photoredox catalyst generates carbon-centered radicals in water

3.15 Dual Catalysis for C−H Bond Activation Diazonium salts under photoredox conditions have gained increased importance in recent years, particularly for the C–H bond activation. Sanford et al. merged a visible light-assisted photoredox catalysis of [Ru(bpy)3 ]Cl2 .6H2 O with Pd(OAc)2 catalyzed C−H functionalization to arylate the phenylpyridine derivatives at 25 °C (Kalyani et al. 2011). A broad range of phenylpyridine with various functionalities and substituted aryl diazonium salts were successfully afforded the desired product in the reaction (Scheme 3.26). Following this work, a method has been developed for ortho C−H Arylation of 6-arylpurine nucleosides using photoredox catalyst, Pd(OAc)2 , and diazonium salts under irradiation of visible light (Scheme 3.27) (Liang et al. 2017). This arylation

74

G. Kalita et al.

R1

N

+

H

Pd(OAc)2 (10 mol%) [Ru(bpy)3]Cl2.6H2O (2.5 mol%)

Ar N2BF4

R1

Ar

MeOH, 25 °C Household light (26 W)

R2

N

R2

selected examples N

N

OH N

N

76%

44% Me

Me

N

Ph

Ph

Ph

O

50%

72%

Scheme 3.26 Arylation of phenylpyridines

method offered a diverse range of substrates including functionalized purines which may be very significant in medicinal chemistry. Recently, Xu et al. developed dual catalytic system (consisting of Pd(OAc)2 catalyst and 9,10-dihydro-10-ethylacridine (AcrH2 -A) as an organic photoredox catalyst) for the ortho-directed arylation of acetanilides and benzamides under mild reaction conditions (Scheme 3.28; Jiang et al. 2017). It is also to be noted that the arylation of N-heteroarenes can be achieved using [Ru(bpy)3 ]2 .6H2 O photosensitizer and aryldiazonium salts as the arylating agent in the presence of household light bulb under argon atmosphere (Xue et al. 2014).

R1

H

+

N

N

Ar

N2BF4

Pd(OAc)2 (5 mol%) [Ru(bpy)3]Cl2.6H2O (2.5 mol%) MeOH, 25 °C Blue LEDs, N2

N

N

R1

Ar N

N

N

N

R2

R2

selected examples Ph Ph N

N N

N

N N

Ph

Ph

N

N

N

N

N

N

N

N

Br

HO

N

N O

Bn 73%

83%

Scheme 3.27 C−H arylation of purine nucleosides

74%

63% O O

3 Photoredox Strategies in Green and Sustainable Organic Synthesis NHAc H R

+

Ar

NHAc Ar

Pd(OAc) - 2 (15 mol%) [AcrH2 A] (2.5 mol%)

N2BF4

R

MeOH, 25 °C Blue LEDs (36 W)

selected examples Me

NHAc

Cl

NHAc

88%

CF3

NHAc

59%

75

N Et AcrH2 A

tBu

NHAc

77%

52%

Scheme 3.28 C–H Arylation of acetanilides

3.16 Au Catalysis A dimeric gold(I) photoredox catalyst, [Au2 (dppm)2 ]Cl2 in MeOH under argon environment, effectively generates alkyl radicals from unactivated bromoalkanes, which subsequently leads to direct C–H alkylation of various heteroarenes. This approach is effective for alkylation of heteroarenes in the absence of directing groups (McCallum and Barriault 2016). They first developed the 2-alkylation of lepidine-TFA salt with various bromoalkanes in the presence of MeOH as a green solvent with 5 mol% of [Au2 (dppm)2 ]Cl2 catalyst under UVA LEDs (365 nm) (Scheme 3.29). They also extended the generality of the heterocyclic coupling partners, such as benzofuran, indole, and pyridine for the alkylation with bromoalkanes (Scheme 3.30) (McCallum and Barriault 2016). Moreover, lepidine can be alkylated in a multicomponent manner with an alkene and α-bromoester under the same greener conditions. The alkene is combined with the radical produced by the α-bromoester, resulting in an alkylation at the C-2 position

+

N H CF3CO2-

[Au2(dppm)2]Cl2 (5 mol %)

R Br

MeOH (0.5M), Ar UVA LEDs

(3 equiv)

N

selected examples CO2Et N 90%

N 93%

Scheme 3.29 2-Alkylation of lepidine-TFA salt

N 45%

N 64%

R

76

G. Kalita et al.

+

Het

X

[Au2(dppm)2]Cl2 (5 mol %)

R Br

CF3CO2H ( 1 equiv) MeOH (0.5M), Ar UVA LEDs

(3 equiv)

selected entries

N

O

N H

Me

99%

Cy Cy

Cy Cl

X

Me

CO2Me

Cy

R

Het

N

Me 98%

76%

Me

66%

Scheme 3.30 Alkylation of heterocycles

+ R N

+ Br

CO2Et

[Au2(dppm)2]Cl (5 mol%) CF3CO2H (3 equiv) MeOH (0.5 M) UVA LEDs

CO2Et N R

Scheme 3.31 Multicomponent reaction of lepidine

of heteroarenes unless this position is substituted (Scheme 3.31) (McCallum and Barriault 2016).

3.17 Cross-Coupling with EDA Complex The metal-free unique photoredox strategy, employing an electron donor–acceptor complex (EDA) between substituted indoles and electron-accepting benzyl or phenacyl bromides, was developed by Melchiorre and colleagues to facilitate the direct alkylation of indoles (Kandukuri et al. 2015). They were able to distinguish and identify the reactive EDA complex that is generated by the interaction of 3methylindole and 2, 4-dinitrobenzyl bromide by the X-ray single-crystallographic technique. When exposed to visible light, this EDA complex further produced a radical ion pair, allowing easy access to the benzyl radical anion, which subsequently reacted with the indole unit to generate benzylated indole in good yields without the need for an additional photosensitizer. The scope relied on the substitution pattern of indole, with C-2 substituted indole providing the C-3 alkylated indole and vice versa (Scheme 3.32).

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

77 R

R

N H

2-6 lutitine (2 equiv)

Br

+ EWG

N H

MeOH, RT 23 W CFL

R

N H

R

Br

Br

hv e

EWG

EDA complex Me

EWG

N H

EWG

Radical ion pair Me

OH

NO2

N H

N H

81%

O 53%

NO2

N H O2N

Br

71%

NO2

Scheme 3.32 2-Benzylation of indoles

3.18 Double C–H Functionalization One of the subtle ways to construct C–C bonds is to functionalize two different C– H bonds. The production of α-oxyalkyl radicals from a range of extensively used ethers by hydrogen atom transfer (HAT) was reported in 2015 by MacMillan and coworkers. These radicals were then paired with a variety of heteroarenes in a Miniscitype procedure. HAT on dialkyl ethers using [Ir{dF(CF3 )ppy}2 (dtbbpy)]PF6 as a photoredox catalyst, (NH4 )2 S2 O8 as the oxidant, and TFA in CH3 CN/H2 O under a 26 W CFL irradiation facilitates the production of α-oxyalkyl radicals which leads to α-heteroarylation of ethers (Scheme 3.33) (Jin and MacMillan 2015). A robust, sustainable cascade process for the difunctionalization of Narylacrylamides with aryldiazonium salts was described by Fu et al. (Scheme 3.34).

R1

O

R2 +

(25-30 equiv.)

Het N

[Ir{dF(CF3)ppy}2(dtbbpy)]PF6(2 mol%) Na 2S2O8 (2 equiv) CF3CO2H (1 equiv) CH3CN/H2O, RT 26 W CFL

Scheme 3.33 2-Alkylation of heteroarenes

Het

R 2O R1

N

78

G. Kalita et al.

O

R1

+

N

Ar N2BF4

[Ru(bpy)3]Cl2.6H2O (5 mol%) MeOH, RT visible light

(2.5 equiv)

R2

Ar O R1

Ph O

Ph O N

N iPr

Me 80%

NR2

67%

O

Br

Me

76%

N

Scheme 3.34 Difunctionalization of N-arylacrylamides

[Ru(bpy)3 ]Cl2 acts as a photoredox catalyst in methanol under visible light irradiation allowing the synthesis of 3,3-disubstituted oxindoles with a wide range of functionalities (e.g., F, Br, Cl, OMe, CN, CF3 , and pyridine). Notably, no additional substance, such as base or reductant, was required for the reaction to proceed (Fu et al. 2013).

3.19 Conclusion Photoredox catalysis has been proven as a powerful tool in organic synthesis in recent times and has boosted a quickly developing field in the past few decades. Overall, photoredox catalysis permits the execution of numerous coupling reactions under widely milder conditions, frequently at room temperature, with extensive functional group tolerance. This chapter highlights the basic concept of photoredox chemistry along with several metal-based and organo-photocatalysts, followed by various reactions, including trifluoromethylation, Cyanation, C–H functionalizations, supramolecular catalysis, and heterogeneous catalysis in aqueous and alcoholic medium. In upcoming years, the design and development of new photoredoxmediated sustainable greener approaches for cascades and multicomponent reactions concerning the generation of multiple C–C and C–hetero atom bonds will be a significant research area for the basic planning of complex organic molecular architecture.

References Aycock RA, Wang H, Jui NT (2017) Chem Sci 8:3121–3125 Bera M, Lee D, Cho EJ (2021) Trends Chem 3:877–891

3 Photoredox Strategies in Green and Sustainable Organic Synthesis

79

Brusselle D, Bauduin P, Girard L, Zaulet A, Viñas C, Teixidor F, Ly I, Diat O (2013) Angew Chem Int Ed 52:12114–12118 Bu M-j, Cai C, Gallou F, Lipshutz BH (2018) Green Chem 20:1233−1237 Bu M-J Lu G-P, Jiang J, Cai C (2018) Catal Sci Technol 8:3728−3732 Call A, Casadevall C, Acuña-Parés F, Casitas A, Lloret-Fillol J (2017) Chem Sci 8:4739–4749 Chen F, Xu X-H, Qing F-L (2021) Org Lett 23:2364–2369 Crisenza GEM, Melchiorre P (2020) Nat Commun 803 Dai J-J, Zhang W-M, Shu Y-J, Sun Y-Y, Xu J, Feng Y-S, Xu H-J (2016) Chem Commun 52:6793– 6796 Fu W, Xu F, Fu Y, Zhu M, Yu J, Xu C, Zou D (2013) J Org Chem 78:12202–12206 Ghosh T, Slanina T, König B (2015) Chem Sci 6:2027–2034 Goez M, Schiewek M, Musa MHO (2002) Angew Chem Int Ed 41:1535–1538 Goez M, von Ramin-Marro D, Othman Musa MH, Schiewek M (2004) J Phys Chem A 108:1090– 1100 Gooßen LJ, Rodríguez N, Gooßen K (2008) Angew Chem Int Ed 47:3100–3120 Guerrero I, Kelemen Z, Viñas C, Romero I, Teixidor F (2020a) Chem-A Eur J 26:5027–5036 Guerrero I, Saha A, Xavier JAM, Viñas C, Romero I, Teixidor F (2020b) ACS Appl Mater Interfaces 12:56372–56384 Guerrero I, Viñas C, Romero I, Teixidor F (2021a) Green Chem 23:10123–10131 Guerrero I, Viñas C, Fontrodona X, Romero I, Teixidor F (2021b) Inorg Chem 60:8898–8907 Hari DP, König B (2014) Chem Commun 50:6688–6699 Hou Y, Wan P (2008) Photochem Photobiol Sci 7:588–596 Hou Y, Huck LA, Wan P (2009) Photochem Photobiol Sci 8:1408–1415 Hou H, Zhu S, Pan F, Rueping M (2014) Org Lett 16:2872–2875 Huang H, Jia K, Chen Y (2015a) Angew Chem Int Ed 54:1881–1884 Huang H, Zhang G, Chen Y (2015b) Angew Chem Int Ed 54:7872–7876 Jespersen D, Keen B, Day JI, Singh A, Briles J, Mullins D, Weaver JD III (2019) Org Process Res Dev 23:1087–1095 Jiang J, Zhang W-M, Dai J-J, Xu J, Xu H-J (2017) J Org Chem 82:3622–3630 Jin J, MacMillan DWC (2015) Angew Chem Int Ed 54:1565–1569 Kalyani D, McMurtrey KB, Neufeldt SR, Sanford MS (2011) J Am Chem Soc 133:18566–18569 Kandukuri SR, Bahamonde A, Chatterjee I, Jurberg ID, Escudero-Adan EC, Melchiorre P (2015) Angew Chem Int Ed 54:1485–1489 Kölmel DK, Loach RP, Knauber T, Flanagan ME (2018) ChemMedChem 13:2159–2165 Kölmel DK, Meng J, Tsai M-H, Que J, Loach RP, Knauber T, Wan J, Flanagan ME (2019) ACS Comb Sci 21:588–597 Lennox AJJ, Lloyd-Jones GC (2012) J Am Chem Soc 134:7431–7441 Liang L, Xie M-S, Wang H-X, Niu H-Y, Qu G-R, Guo H-M (2017) J Org Chem 82:5966–5973 Liu J, Lu L, Wood D, Lin S (2020) ACS Cent Sci 6:1317–1340 Mai W-P, Song G, Sun G-C, Yang L-R, Yuan J-W, Xiao Y-M, Mao P, Qu L-B (2013) RSC Adv 3:19264–19267 Majek M (2016) Jacobi von Wangelin A. Acc Chem Res 49:2316–2327 Margrey KA, Nicewicz DA (2016) Acc Chem Res 49:1997–2006 McCallum T, Barriault L (2016) Chem Sci 7:4754–4758 Mizuta S, Engle KM, Verhoog S, Galicia-López O, O’Duill M, Médebielle M, Wheelhouse K, Rassias G, Thompson AL, Gouverneur V (2013) Org Lett 15:1250–1253 Nguyen T-TH, O’Brien CJ, Tran MLN, Olson SH, Settineri NS, Prusiner SB, Paras NA, Conrad J (2021) Org Lett 23:3823–3827 Noto N, Hyodo Y, Yoshizawa M, Koike T, Akita M (2020) ACS Catal 10:14283–14289 Qiao H, Sun S, Yang F, Zhu Y, Kang J, Wu Y, Wu Y (2017) Adv Synth Catal 359:1976–1980 Romero NA, Nicewicz DA (2016) Chem Rev 116:10075–10166 Speckmeier E, Fuchs PJW, Zeitler K (2018) Chem Sci 9:7096–7103

80

G. Kalita et al.

Srinath S, Abinaya R, Prasanth A, Mariappan M, Sridhar R, Baskar B (2020) Green Chem 22:2575– 2587 Tarrés M, Viñas C, González-Cardoso P, Hänninen MM, Sillanpää R, Ďorďovič V, Uchman M, Teixidor F, Matějíček P (2014) Chem-A Eur J 20:6786–6794 Uchman M, Ďorďovič V, Tošner Z, Matějíček P (2015) Angew Chem Int Ed 127:14319–14323 van Lier RCW, de Bruijn AD, Roelfes G (2021) Chem-A Eur J 27:1430–1437 Wang C-S, Dixneuf PH, Souľe J-F (2018) Chem Rev 118:7532–7585 Xu Z-J, Zhu D, Zeng X, Wang F, Tan B, Hou Y, Lv Y, Zhong G (2010) Chem Commun 46:2504–2506 Xue D, Jia Z-H, Zhao C-J, Zhang Y-Y, Wang C, Xiao J (2014) Chem-A Eur J 20:2960–2965 Yang H, Yan H, Sun P, Zhu Y, Lu L, Liu D, Rong G, Mao J (2013) Green Chem 15:976–981 Yoon TP, Ischay MA, Du J (2010) Nat Chem 2:527–532 Zhang J, Chen J, Zhang X, Lei X (2014) J Org Chem 79:10682–10688

Chapter 4

The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed C−H Bond Functionalization Subhash Chandra Ghosh, Dharmik M. Patel, and Sachinkumar D. Patel

4.1 Introduction Visible-light photoredox catalysis is going through a renaissance and has started to flourish as a safer and more user-friendly method in organic synthesis. It converts visible light into chemical energy, and synthetic chemists potentially use it in various organic transformations (Narayanam and Stephenson 2011; Xuan and Xiao 2012). The photocatalyst when excited under visible light serves as a one-electron oxidant or reductant that allows the transfer of one electron from the catalyst to the substrates and generates a radical species from the stable organic molecules (Prier et al. 2013). Despite the photochemical transformations that have been well-known over the past century, the majority of the organic compounds are not photoactive in highenergy visible light, which has hampered the general photochemical reactions. Recent discoveries on various photosensitizers (organometallic complexes, organic dyes, and inorganic semiconductors) can absorb photons in the visible light region to form exited species that are capable of activating substrates irrespective of their photophysical properties (Shaw et al. 2016a; Romero and Nicewicz 2016). The photochemical reactions mainly proceed by single-electron transfer (SET) and energy transfer (ET) pathways. By the irradiation of visible-light excitation, photocatalysts can engage in single-electron transfer (SET) from HOMO to LUMO. In this scenario, the resulting energized species can function as both a potent reducer and a potent oxidizer concurrently. Photoredox catalysts possess the unique capability of being stronger oxidants and reductants in their excited states compared to their ground

S. C. Ghosh (B) · D. M. Patel · S. D. Patel Natural Products and Green Chemistry Division, Central Salt and Marine Chemicals Research Institute (CSIR), G. B. Marg, Bhavnagar, 364002 Gujarat, India e-mail: [email protected] Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India 81

82

S. C. Ghosh et al.

states and their capacity to convert photonic energy into significant levels of chemical energy (Skubi et al. 2016). The interaction between excited photocatalyst and organic substrate can result in the generation of radical anion and radical cation under remarkably mild conditions. During the past decades, transition metal-catalyzed unactivated C–H bond functionalization has emerged as an increasingly powerful tool for the site-selective construction of C–C and C-heteroatom bonds, which enables chemists an atom and step economical route for natural product synthesis, late-stage modification of API and the incorporation of native functional group in the small molecule, among others. In the past decade, considerable attention was received by organic and organometallic chemists by the merging of photoredox and transition metal catalysis in small molecule synthesis. The merger of a transition metal catalyst and photocatalyst in a reaction, termed as metallaphotoredox catalysis, has recently emerged as a unique approach that enables the creation of new bonds in organic chemistry (Twilton et al. 2017; Chan et al. 2022). The potential of dual photoredox-transition metal catalysis to unveil novel mechanistic pathways has only begun to be investigated in recent times. In 2011, the first application of metallaphotocatalysis for C–H activation was reported by Sanford and co-workers and they performed the arylation of unactivated arene with aryldiazonium salt by the merger of Pd catalyst with photocatalys (Kalyani et al. 2011). This chapter will provide an overview of the merger of inexpensive 3d transition metal with photocatalyst over the past decades on C–H activation and functionalization.

4.2 Merger of Cobalt Catalyst with Photoredox Catalyst In 1941, Karash and Fields first discovered the cobalt-catalyzed homocoupling of Grignard reagents (Kharasch and Fields 1941). After these ground-breaking findings, cobalt has undergone 80 years of research to become one of the most promising metals for use in homogeneous catalysis in the future, with important applications including hydroformylation (Moselage et al. 2016). The combination of photoredox catalysis and Co catalysis is the most promising and powerful strategy for constructing C—C and C—Het bond. Mostly, the Co/photoredox dual catalytic system works well for cross-dehydrogenative coupling (CDC) (Li 2009; Yeung and Dong 2011).

4.2.1 C–C Bond Formation In 2015, Wu and co-workers reported (Gao et al. 2015) a site-specific modification of α-amino acids via C−H bond functionalization using Co(dmgH)2 pyCl as a catalyst and Ru(bpy)3 (PF6 )2 as a photosensitizer (Scheme 4.1). A variety of glycine esters (1) with β-keto esters (2) or indole derivatives (5) were converted into the desired

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

83

Scheme 4.1 Cross-dehydrogenative coupling of amines via metallophotoredox catalysis

cross-coupling products (3). The advantages of this reaction are the reaction proceeds without any external oxidant or base and hydrogen gas is evolved as a sole by-product. This is the inaugural example of site-specific functionalization of α-amino acids using metallaphotoredox catalysis. They have proposed a tentative mechanism as depicted in Scheme 4.2. Initially, photocatalyst Ru(bpy)3 2+ upon visible light irradiation went to excited state Ru(bpy)3 2+ * and an initial SET takes place; the amino acid derivative converted to amine radical cation (I) and reduced Ru+ . This Ru I is oxidized by Co (III) to regenerate reactive Ru(II) species and self-oxidized to Co (II) complex. Further amine radical cation (I) converted to intermediate II or III which reacts with β-keto esters to yield the desired product. In 2016, the same research team (Wu et al. 2016) introduced an oxidant-free approach for synthesizing indoles through intramolecular C—C bond formation under visible light irradiation utilizing Ir(III) photosensitizer in a combination with cobaloxime catalyst (Scheme 4.3). This method transforms various N-aryl enamines

84

S. C. Ghosh et al.

Scheme 4.2 Mechanism of cross-dehydrogenative coupling of amines via metallophotoredox catalysis

(7) into their corresponding indoles with high efficiency under mild reaction conditions, yielding good to excellent results. Importantly, it generates hydrogen gas (H2 ) as the sole by-product.

Scheme 4.3 Oxidant-free synthesis of indole via intramolecular C–C bond formation

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

85

In the following year, again Wu reported (Yang et al. 2017) another visible-lightpromoted asymmetric cross-dehydrogenative coupling reaction between tertiary amine and simple ketones which was enabled by a tri-catalytic system, i.e. a chiral primary amine, Ru photocatalyst, and Cobalt catalyst system (Scheme 4.4). In this process, a sub-stoichiometric amount of nitro compound was added, which acts as a hydrogen acceptor, which supresses the need for an extra oxidant and avoids the oxidative consumption of the chiral amine catalyst. In 2017, Rovis and Thullen (Thullen and Rovis 2017) reported the first instance of hydroaminoalkylation of conjugated dienes utilizing a dual catalytic system comprising cobalt and Ir photoredox catalysts (Scheme 4.4). Here, both electronrich as well as electron-poor dienes demonstrated excellent reactivity in the reaction. In the proposed mechanism, dienes undergo migratory insertion into the Co–H bond to form a Co (III)-allyl species (I). Subsequently, the Co(III)-allyl species can be reduced by the photocatalyst, resulting in the generation of a Co(II)-allyl species (II). The Co-generated α-amino alkyl radical from the deprotonation of the oxidized tertiary amine may attack the Co(II)-allyl species. This species then undergoes reductive elimination, leading to the formation of the product and regeneration of Co(I), completing the catalytic cycle (Scheme 4.5). In the same year, C. Ranu and co-workers (Ghosh et al. 2018) reported a remote C-4 functionalization of 8-aminoquinoline with a variety of ethers under dual Co/ eosin Y photoredox catalytic system by the irradiation with CFL lamp (Scheme 4.6). In this reaction, a series of quinoline amide substituted with electron-donating and electron-withdrawing group gives good to excellent yield. The uniqueness of this reaction is it offers C-4 functionalization of 8-aminoquinoline amide 17 in contrast to C-5 functionalization. In 2018, Wu and co-workers (Yang et al. 2018) developed a redox-neutral oxidative cyclization of tertiary aniline 18 and maleimides 19 to tetrahydroquinoline derivatives 20 in good to excellent yields by merging a cobaloxime catalyst with Ru photocatalyst in good to excellent yield. In this reaction cycle, surplus maleimides were employed to capture the electrons and protons released from tertiary anilines (Scheme 4.7). While C–H and N–H bond annulation of benzamides 22 with alkynes 23 leading to the formation of isoquinolones 24 by merging a Co-catalyst with Na2 [Eosin Y] photocatalyst was reported by Sundararaju and co-workers (Kalsi et al. 2018) (Scheme 4.8), this dual catalytic strategy for directed oxidative C—H bond functionalization operated efficiently at mild conditions. This annulation reaction required only oxygen as a sole oxidant under redox-neutral conditions and operated at room temperature. The reaction was applicable to various benzamides with different substituents at ortho-, meta-, and para-position having electron-withdrawing and electron-donating groups that give the product in good to excellent yield. It is important to note that the reaction was found to be unaffected by the presence of other chelating directing groups such as pyridyl, pyrimidyl, pyrazoles, thienyl, and 7-azaindolyl. Both symmetrical and unsymmetrical alkynes with alkyl and aryl were employed successfully. As proposed by the author, the reaction mechanism is depicted in Scheme 4.9; first of all, Co(II) undergoes ligand exchange followed by oxidative e− transfer from eosin Y forming a reactive Co(III) complex. Following this, cyclometallation

O

N

11a

73% yield 99% ee, 5:1 d.r.

9

H

O

10

N

11b

F

O

CF3

11c

51% yield 96% ee, 3:1 d.r

N

m-NO2C6H4COOH (40 mol%) Blue LEDs

72% yield 97% ee, 12:1 d.r

H

Ru(bpy) 3Cl2·6H2O (3 mol%) Co(dmgH2)2Cl2 (8 mol%) ligand/HOTf

Scheme 4.4 Asymmetric CDC reaction between tertiary amine and ketones under multi-catalytic system

R1

N

R2

O

MeO

MeO

R1 O

N

11

11d

R2

88% yield 96% ee, 6:1 d.r

O

N

86 S. C. Ghosh et al.

CoIII

H

14a

I

N

66% yield 20:1 trans/cis

SET

13

12

CoIII -H

R3

R

N

R1

R2

COOEt

R4

II

CoII

14b

H

75% yield 20:1 trans/cis

N

NR2

COOEt

R2N

Blue LEDs CsOPiv, MeCN, 12-20h

CoIII

[Ir(dF-CF 3 ppy) 2dtbbpy]PF6(5 mol%) CoBr2 (10 mol%) dppp

Scheme 4.5 Hydroaminoalkylation of conjugated dienes by metallophotoredox catalysis

R

R

III

14c

H

N

R

N

NR2

R2

IV

CoI

R1

45% yield 20:1 trans/cis

Or

R

R

H

COOEt

14

R3

R4

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 87

15

N H

N H

N

H

17a R = Me 74% yield 17b R = t-Bu 71% yield 17c R = F 73% yield 17d R = Cl 74% yield 17e R = CF3 76% yield

O

N

H

O

16

O

tBu

O N H

17f 55% yield

N

O

Cs2CO3 (2 equiv.) DMSO, N2, 32W CFL Light, r.t., 4h

Co(acac)2(10 mol %) TBHP

Scheme 4.6 Remote C-4 functionalization of 8-aminoquinoline with variety of ethers via C–H activation

R

R

O

Eosin Y (2 mol %)

O

R 17

17g

N H

N H

N

N

71% yield

O

O

O

O

88 S. C. Ghosh et al.

H

O

F

20b

H

89% yield

Me

O

O

Me

H

Ph

R

N

N

19

O

N

N

H

Ph

O

O

H

O

Me

N

N

R1

30% yield

20c

MeCN Blue LEDs, r.t., 24h

Ru(bpy) 3Cl2 (1 mol%) Co(dmgH) 2pyCl (10 mol%)

N

81% yield

20a

18

R2

N

O

H

Ph

O

20

Scheme 4.7 Oxidative cyclization of tertiary anilines with maleimides to under Redox-Neutral Conditions

Me

R1

H H

O

Me

R2

N

N

H

R

H

O

Me

N

H

50% yield

20d

Me

O

H

N

H

Ph

21

O

O

N

O R

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 89

Scheme 4.8 C–H and N–H bond annulation of benzamide with alkynes via metallopotoredox catalysis under mild reaction condition

90 S. C. Ghosh et al.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

91

occurs through a concerted deprotonation pathway, resulting in the formation of a Co(III)-amide complex. Alternatively, Co(II) may undergo aerobic oxidation to Co(III), followed by coordination and cyclometallation. Coordination of the alkyne to the carbocycle is succeeded by regioselective insertion and reductive elimination, yielding the desired product and Co(I). Oxidation of Co(I) by eosin Y regenerates the Co(II) species and forms eosin Y radical anion. In the same vein, in the following year Sundararaju’s group (Kalsi et al. 2019) further expanded the C—H and N—H bond annulation of benzamides with unactivate olefins leading to dihydroisoquinolones under mild reaction condition (Scheme 4.10). The method was found to be compatible with various benzamides and compares favorably with previously reported annulations using unactivated olefins, which required stoichiometric amounts of oxidants. This method works well specifically for terminal alkenes and fails to work with internal alkenes. Thereafter, the same group reported (Mandal et al. 2021) mono-, bis-ortho-C— H alkynylation of benzamides derivatives with alkynyl bromides under dual cobalt and photoredox catalysis at room temperature (Scheme 4.11). In this method, the amount of NaOPiv differs with the formation of mono-and bis alkylated product. Mono alkylated product formed when 1 equiv. of NaOPiv was used as a base while bis alkylated product formed when 2 equiv. of NaOPiv along with 2.5 equiv. bromo

Scheme 4.9 Proposed mechanism of C–H and N–H bond annulation of benzamide with alkynes

Scheme 4.10 C–H and N–H bond annulation of benzamides with unactivate olefins

92 S. C. Ghosh et al.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

93

alkynes was used. Various ortho-and meta-substituted benzamides give moderate to good yield. For meta-substituted benzamides, alkylation preferably took place at the less sterically hindered position, resulting in the isolation of the corresponding mono-alkynylated products with decent yields. In 2020, Ghosh and co-workers reported (Sen et al. 2020) a room temperature C— H bond functionalization of benzamides (30) with maleimides (19); by combining a photocatalyst with a cobalt catalyst, the synthesis of isoindolone spirosuccinimides 31 was achieved. The reaction occurs under aerobic conditions, eliminating the necessity for sacrificial external oxidants like Ag(I) or Mn(III) salts. Upon exposure to visible light, the activated photocatalyst acts as an electron transfer agent, enabling the adjustment of the oxidation state of the active cobalt complex. This method of C–H bond functionalization and spirocyclization exhibits a wide substrate scope and remarkable tolerance toward diverse functional groups (Scheme 4.12). A proposed mechanism is illustrated in Scheme 4.13. Initially, ligand exchange occurs with the Cobalt complex (A), followed by the photocatalytic single-electron transfer (SET) oxidation by Eosin Y, yielding the Co(III) complex (B). This Co(III) complex then undergoes concerted metalation deprotonation (CMD) to form the cobaltacycle intermediate (C). Subsequently, maleimide insertion occurs with the Co–C bond of intermediate C, yielding intermediate D. Syn β-hydride elimination followed by intramolecular insertion of the amide nitrogen into the double bond leads to intermediate F. Finally, reductive elimination furnishes the desired spirocyclic product 31 alongside the Co(I) species. In 2020, Song Wu and co-workers (Li et al. 2021a) reported dual cobalt and eosin Y photoredox catalytic C–H Annulation of benzamides with allenes leading to the formation of isoquinolone scaffold under mild reaction condition. Various aryl amides having different substituents at ortho-, meta-, and para-positions were compatible. Para-substituted carboxamides having electron-donating or electronwithdrawing group give excellent yield while meta-substituted benzamides furnished two regioisomers in good yields. Ortho-substituted electron-withdrawing group gives excellent yield while ortho-methoxy substrate takes a short time but gives slightly reduced yield (Scheme 4.14). In 2021, Qiang Liu and co-workers (Ban et al. 2021) reported a dual Co/Ir photoredox catalyzed de-aromatization of indoles under mild reaction condition. This reaction allows the C–H and N–H bond annulation of N-quinolyl benzamides and regioselective C-2 and C-3 dual functionalization of indoles which leads to the formation of diverse array of indolo[2,3-c]isoquinolin-5-ones by metallaphotoredox catalysis. Numerous para-substituted benzamides, whether containing electron-donating or electron-withdrawing groups, exhibited robust reactivity, yielding moderate to excellent yields. Di-and tri-substituted N-quinolyl benzamides also reacted efficiently which offers moderate yield (Scheme 4.15). In the same year, Teskey and co-workers (Bergamaschi et al. 2021) reported cross-dehydrogenative coupling between benzothiazole and various amines under blue light irradiation (Scheme 4.16). This method is furnished by low loading of dual cobalt catalyst and Ir photoredox catalyst. The group explored the range of

Scheme 4.11 Mono-and bis-ortho-C–H alkynylation of benzamide derivatives under dual catalyst

94 S. C. Ghosh et al.

Me

N

O

N

30

N

31aR = OMe 91% yield 31bR = Cl 88% yield 31cR = Br 91% yield 31dR = I 89% yield 31eR = NO2 51% yield

O

N

O

H

N H

R O O

31f 85% yield

Me

N

N COOMe F3C O

N

O

89% yield

31g

Me

N

N

N

O

N

O

N

O

Me

TFE, 36h 3 W green-LED, RT

R1

R3 O

R3

Eosin Y (10 mol%) Co(acac)2 (10 mol%) KOAc (3 equiv.)

19

O

N

O

Scheme 4.12 Synthesis of spirocyclic succinamide s under metallaphotocatalysis conditions

R

1

O

R2

O

N

31

R

R2

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 95

96

S. C. Ghosh et al.

Scheme 4.13 Proposed mechanism for the synthesis of isoindolone spirosuccinimides

heterocycles having both electron-donating or electron-withdrawing group resulting in the desired product in moderate to good yield. In 2021, Sebastin and co-workers (Yerien et al. 2021) developed a novel strategy for the fluoroalkylation of electron rich arenes by combining vitamin B12 and Rose Bengal as the co-catalyst and catalyst respectively (Scheme 4.17). The role of RB catalyst in this reaction is to produce the super-nucleophilic Co(I) species, which helps to generate perfluoroalkyl radicals from perfluoroalkyl bromides in oxidative photoredox cycles. The method is found to be superb in photocatalytic perfluoroalkylation, electron rich substrates provided excellent yield while substrate with electron withdrawing group such as a nitro, fluoro gives moderate to good yield of the desired product. In the proposed mechanism (Scheme 4.18), initially, Vitamin B12 undergoes one electron reduction promoted by a RB oxidative photocatalytic cycle to afford Co(II).

O

N

COOEt

Q

35aR = Me 65% yield 35bR = OMe 76% yield 35cR = CN 72% yield

32

N H

Q

33

C

R

R

O

Ph

N

P

Q

TFE 15W CFL, O2, r.t., 24h

Ph O 35dR = OMe 92% yield 35eR = CyH 85% yield 35f R = NO2 91% yield

R,

Eosin Y (5 mol%) Co(acac) 2 (20 mol%) KOTf (20 mol%)

R

O

34

N

O

Ph

Q

N

R

Q

35gR = OMe 61% yield 35hR = CyH 57% yield 35i R = CN 55% yield

R

Scheme 4.14 Dual catalytic annulation of benzamides with allenes leading to isoquinolone scaffold

R

R

O R

O N

N

35j 56% yield

35

O

Q

R,

Q R

F

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 97

R

O

N

Q

N

H

Q

N

N

36

37aR = Me 79% yield 37bR = t-Bu 91% yield 37cR = F 73% yield 37dR = Cl 53% yield 37eR = Br 62% yield

H

32

N H N

N

Me

N

Me

N N

H

Q

37f 74% yield

H

O

N

N

PivONa·H2O TFE, r.t., 48h 6 W Blue LEDs

Ir Photocatalyst (1 mol%) Co(OAc)2 (20 mol%) Benzoylacetone (22 mol%)

Scheme 4.15 Metallophotoredox catalyzed de-aromatization of indoles

R

O

O

Me

R

O N

N

37g 55% yield

Me

H

37

H

O

N

H

Q

N

H

Q

N

N

N

N

98 S. C. Ghosh et al.

23% yield

37% yield

S

76% yield

N

N

40c

S

N

40b

N

MeO

39

DMF, r.t., 48h 24W Blue LEDs

N

Co(dmgH)2PyCl (1 mol %) [Ir(df(CF3)ppy)2dtbbpy]PF6 (1 mol %) DABCO(1 equiv.)

40a

S

N

38

S

H

N

Scheme 4.16 CDC between benzothiazole and various amines

R

N

H R

40d 53% yield

S

N

40

S

N

N

N

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 99

100

S. C. Ghosh et al.

The reaction pathway continues with the further reduction of Co(II) by an additional RB oxidative photocatalytic cycle to afford reactive Co(I) species, which instantly reacts with n-C6 F13 Br providing the Co(III)-C6 F13 complex and a bromide anion. The Co(III)-C6 F13 complex upon light irradiation releases a n-C6 F13 • radical and regenerates the Co(II) species to continue the cycle. The n-C6 F13 • radical formed reacts with the arene to afford the desired perfluorohexylated product. In the same year, Li and co-workers by taking an example of Minisci alkylation (Minisci et al. 1985) reported visible light-mediated dehydrogenative cross-coupling between heteroarene and various carbon radical precursors leading to various C–C Vitamin B12 (5 mol%) Rose Bengal (5 mol%) TMEDA (3 equiv.)

NH2 RF

R

Br

R H2O, Ar Green LED

RF = n-C6F13

RF 43

42

41

NH2

NH2 F

F

OMe

OMe

NH2

OMe

NO2

MeO

C6F17 C6F17 43a 99% yield

NH2

C6F17 43b 70% yield

43c 4-RF/6-RF 65% yield

OMe

C6F13

C6F13

43d 55% yield

43e 99% yield

Scheme 4.17 Fluoroalkylation of activated arenes in water under green light irradiation

Scheme 4.18 Proposed mechanism of fluoroalkylation of activated arenes

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

R

KF3B

[Co(dmgH)2(py)]Cl (5 mol%) DPQN (PC)

R

H

N 44

R N

TFA, dioxane -37 0C, Ar, 20h,h

45 Me

101

R

46

Me OMe

N

O

N

46a 70% yield

46b 62% yield

Me O

N

N OMe

N 46c 91% yield

O

Cy

Cy

DPQN

46d 32% yield

Scheme 4.19 C—C bond formation via dehydrogenative cross-coupling between arene and carbon radical precursor

bond formation reactions in unique quinoline-based organophotoredox catalyst, 2,4bis(4-methoxyphenyl) quinoline (DPQN2,4-di-OMe) and cobaloxime catalyst (Li et al. 2021b) (Scheme 4.19). In transition metal-catalyzed carbene, migratory insertion diazo compounds are widely explored as a coupling partner (Jha et al. 2021). In the following year, Manmohan and co-workers (Khot et al. 2022) demonstrated the C–H allylation of benzamides with vinyl diazo ester by dual cobalt and Na2 Eosin Y photocatalyst under mild reaction condition (Scheme 4.20). This transformation showed a wide range of functional group tolerance and good substrate scope. Moreover, the author showed the application of this transformation by late-stage functionalization of bio-active molecule.

4.2.2 C–N Bond Formation In 2016, Xiao and co-workers (Zhao et al. 2016) reported a N-Radical 5-exo cyclization/addition/aromatization cascade of β, γ-unsaturated hydrazones leading to biologically interesting dihydropyrazole-fused benzosultams (Scheme 4.21). This transformation occurred via Ru photocatalysis and cobalt catalyst without any external oxidant. In this transformation, a wide range of γ-unsaturated hydrazones

102

S. C. Ghosh et al. O N H

R

Co(acac) 2 (20 mol%) NaOPiv.H2O

OR

H

Me

Me

O

MeO

N H

OR

Q

Me

62% yield

O

O N H

COO

Q

48

O

Q tBu

N H

R

TFE, r.t., O2 Green LED

O 47

32

48a

O

Na2[Eosin Y] (20 mol%) N2

Q

N H

COOtBu

Q COOMe

48b 61% yield

48c 61% yield

Scheme 4.20 C–H allylation of benzamides with vinyl diazo ester

well tolerated and various substituents on aromatic ring-like electron-donating or electron-withdrawing group showed a good reactivity. Aromatic C—H bonds are relatively inert compared to active methylene and amino acid C—H bonds. By direct functionalization of this inert aromatic C—H bond in 2016, Wu and co-workers (Zheng et al. 2016) reported an amination and hydroxylation of benzene leading to anilines and phenols respectively (Scheme 4.22). Using amine and water as a nucleophile, this challenging amination and hydroxylation of benzene were successfully developed by the merger of cobalt catalyst and organophotoredox catalyst. This transformation is oxidant-free and proceeds smoothly under mild reaction conditions. In this reaction, H2 is generated as the only by-product. In the proposed mechanism (Scheme 4.23), initially by the irradiation of light photocatalyst was excited followed by a single-electron transfer from the aryl ring which generates aryl radical cation and radical photocatalyst. This aryl radical cation reacts with anionic nucleophiles and generates a corresponding dienyl radical. The photocatalyst radical may transfer one electron to Co(III) to produce Co(II) followed

Ts HN

N

H

R1

S N

N

R1

3 W Blue LEDs MeCN, Ar, r.t.

50

49 O

O

O

S N

O

O

Ru(bpy) 3Cl2.6H2O (2.0 mol%), [Co(dmgH)2PyCl] (8.0 mol%) K 2CO3 (1.5 equiv.)

O O

S

N

N

N

Ph

N

N

Cl S 50a 53% yield

50b 34%yield

Scheme 4.21 Oxidant-free synthesis of benzosultams

O S

Cl

50c 46% yield

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … Co(dmgBF 2)2(MeCN)2 (3 mol%) PC

H H

R

103

X

X R

H2

> 300 nm, MeCN, r.t.

X= NH2, OH

53

52

51

MeC N

N

N

Me

Me

QuH+

CN

F F

O B

N Co

O

N

QuCN+

N

O

N

O

F B

F

N CMe

Photocatalyst

Co(dmgBF2)2(MeCN)2

NH2

H N

O

tBu

OH

O 53a 40% conv. 90% select with QuH+, Co(OAc)2

53b 80% conv. 99% select with QuCN+

O

OH

53c 90% conv. 100% select with QuCN+

NH2

53d 63% conv. 84% select with QuCN+ (o:m:p = 55:12:17)

Scheme 4.22 Amination and hydroxylation of the aromatic inert C–H bond

by one electron transfer from dienyl radical Co(II) to produce Co(I), and dienyl cation upon deprotonation gives the desired product. The Co(I) species in each cycle received two electrons uses them to reduce the two protons generated from X−H and benzene C−H cleavage into H2 and oxidized to Co(III), and completed the catalytic cycle. In the same year, with a similar strategy Lei and co-workers (Niu 2017) reported selective amination of aryl Csp2 –H bond between simple arene and heterocyclic azoles (Scheme 4.24). This transformation is oxidant-free and utilizes cobalt-oxime catalyst and photocatalyst under mild reaction condition. A range of alkyl-substituted benzene, biphenyl, and anisole derivatives underwent smooth conversion into Narylazoles, yielding moderate to excellent yields. In the same vein, in the same year, Lei’s group (Yi et al. 2017) further expanded the dehydrogenative cross-coupling leading to amination and alkoxylation of alkene via C–N and C–O bond formation (Scheme 4.25). This transformation provides a new route for the synthesis of N-vinyl azole and enol ether. A series of alcohol and even long chain alcohol are well tolerated in this system.

104

S. C. Ghosh et al.

Scheme 4.23 Proposed mechanism of amination and hydroxylation of aryl

Scheme 4.24 Selective amination of aryl Csp2 –H bond between arene and azole

4.2.3 C–O Bond Formation In 2018, Zhu and co-workers (Zhang et al. 2018) reported the formation of lactone from 2-aryl benzoic acid utilizing dual cobalt catalyst and photoredox catalyst (Scheme 4.26). This transformation provides a new route for the construction of lactone. A wide range of lactones were synthesized under oxidant-free conditions. This transformation also furnished a facile route to remote hydroxylated arene and chromene.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

105

Scheme 4.25 Amination and alkoxylation of alkene via C–N and C–O bond formation

Scheme 4.26 Formation of lactone from 2-aryl benzoic acid

In 2021, Pinhua Li and co-workers (Xu et al. 2021) developed a novel strategy to furnish C8 -alkoxylation of 1-naphthaylamine with alcohol via dual cobalt catalyst and rose Bengal photocatalyst (Scheme 4.27). This novel strategy has the advantages of simple operation, broad functional group tolerance, a wide range of substrate scope, and high efficiency.

MeO

N H

22

61a 73% yield

N

O

N

N H H

N H O n

61b n = 0 70% yield 61c n = 1 68% yield 61d n = 2 66% yield 61e n = 3 65% yield 61f n = 4 67% yield

N

O

57

RO

61g 62% yield

N

O

DBN (base) 36W Green LEDs,

N H

Co(OAc)2·4H2O (20 mol%) Rose Bengal (3 mol%)

Scheme 4.27 C8 -alkoxylation of 1-naphthaylamine with various alcohols

R

O

O

R

N

O

61

RO

MeO

N H

N H

61h R = Me 71% yield 61i R = Cl 75% yield 61j R = Br 78% yield

R

N

O

106 S. C. Ghosh et al.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

107

4.2.4 C–S Bond Formation In 2016, Wu, Lei, and co-workers (Zhang et al. 2015) developed an oxidant-free strategy to construct C–S bond via thiolation of aryl C–H bond under dual cobalt catalyst and Ru photoredox catalysis (Scheme 4.28). In this transformation, H2 is generated as the only by-product. The role of the base is crucial for the synthesis. Various aryls transformed into their corresponding benzothiazoles, and these reactions exhibit a wide range of functional group tolerance and broad substrate scope. In particular, the author noted that 2-alkyl benzothiazoles provided good to excellent yields when catalytic TBAOH was employed as the base.

4.3 Merging Nickel Catalysis with Photoredox Catalysis In cross-coupling processes, nickel catalysts are commonly used and have proved very powerful for the activation of inert bonds. For this, generally harsh reaction conditions such as high reaction temperatures are required. As a result, these newly proposed photoredox catalytic techniques may be ideal replacements for established approaches for achieving difficult C–H bond transformations under mild reaction circumstances.

4.3.1 C–C Bond Functionalization In 2014, MacMillan and Doyle reported (Zuo et al. 2014) cross-couplings of dimethylaniline 64 with a variety of aryl halides 65 in the presence of [Ir(dFCF3 ppy)2 (dtbbpy)]PF6 and NiCl2 •glyme (Scheme 4.29). Electron-rich and electron-deficient aryl iodides give moderate to high yields (66a to 66c, 72 to 93% yield). Additionally, aryl bromides are capable coupling partners, allowing the incorporation of medicinally important heterocyclic motifs (66d, 60% yield). In 2016, the Doyle group (Joe and Doyle 2016) successfully achieved the direct synthesis of amino-ketones 70 from simple N-aryl amines 67 and acyl electrophiles 68 and 69, such as anhydrides and thioesters, by using Ir photocatalyst, and Ni(cod)2 as the transition metal catalyst (Scheme 4.30). The yield of various α-amino ketones using this method was moderate to good. Furthermore, this methodology has the potential to be further elaborated and expanded in the late-stage coupling of complex and biologically significant partners. In the same year, the MacMillan group (Shaw et al. 2016b) developed a triple catalytic system that can selectively functionalize α-amino and α-oxy sp3 C–H bonds in a wide range of both cyclic and acyclic systems (Scheme 4.31). In this catalytic system, the homolytic cleavage of strong C–H bonds is achieved in a manner by the matching of electronic polarities between a C–H bond and a HAT catalyst; the

Scheme 4.28 Synthesis of benzothiazoles via thiolation of aryl C–H bond

108 S. C. Ghosh et al.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … H

N

NiCl 2.glyme (10 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6(1 mol%)

X +

109

N

R

R dtbbpy (15 mol%),KOH (2 equiv) DMF,26 W CFL light, 23 oC

64

66

65

N

N

N

OMe

Cl

X = I, 84% yield

X = I, 72% yield

66a

66b

N

N

X = I, 93% yield 66c

CF3

X = Br, 60% yield 66d

Scheme 4.29 Arylation of C–H bonds of anilines via dual catalysis

O

R1 R2

R N

R1

O R

O

H

R2

R

N O

or 68

+

quinuclidine (1.5 equiv) dtbbpy (7 mol%), DMF (0.04 M) 34 W blue LEDs, 25 oC, 16 h

O

67

[Ni(cod) 2 ] (5 mol%) [Ir(ppy)2(dtbbpy)]PF6 (1 mol%)

X

R

X = Cl,SR

69

57-86% yield 34 examples 70

Scheme 4.30 Arylation of C–H bonds of arylamines with carbonyl-based electrophiles

optimal catalytic system involves an Ir photocatalyst and NiBr2 .3H2 O as the nickel catalyst. Additionally, 3-acetoxy quinuclidine serves as both the HAT catalyst and the base. The formation of the Ir*(III) catalyst takes place after the excitation of the Ir(II) photocatalyst by visible light, which has enough oxidizing power to undergo a singleelectron transfer (SET) process with a tertiary amine HAT catalyst. This SET process generates both Ir(II) and amine radical cations. Subsequently, the N-Boc-pyrrolidine and 3-acetoxyquinuclidine radical cations undergo a HAT process, leading to the formation of reactive α-amino carbon-centered radicals. Afterward, these carboncentered radicals enter the nickel catalytic cycle and interact with Ni(II) complexes, which are formed through the oxidative addition of aryl bromides to Ni(0) resulting in the production of Ni(III) species. After that, reductive elimination leads to the formation of a Ni(I) complex and coupling product by creating the desired C–C bond. Both the Ni catalyst and the Ir catalyst are regenerated via another SET process for the next catalytic cycle (Scheme 4.32).

Scheme 4.31 C–H arylation using triple catalytic system

110 S. C. Ghosh et al.

Scheme 4.32 Plausible mechanisms for C–H arylation using a triple catalytic system

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 111

112

S. C. Ghosh et al.

After that, the Doyle group (Ahneman and Doyle 2016) reported a ligandaccelerated C–H arylation reaction for the synthesis of various benzylic amines using the dual catalysis method (Scheme 4.33). This process entails the arylation of α-amino C(sp3 )–H bonds 67 with aryl iodides 74 utilizing photoredox nickel catalysis, although this methodology is used to couple β-hydrogen-containing amines with aryl halides, which was not possible in their previous work. Moreover, the steric characteristics of the BiOx ligand have been shown to significantly impact the efficiency of the reaction. The use of the chiral (S, S)-Bn-BiOx ligand resulted in an optically active product 75 g with a modest enantiomeric excess (ee) value of 30% (Scheme 4.34). The reduction of Ni(I) to Ni(0) through single-electron transfer by Ir(II) photocatalyst, followed by the oxidative addition of aryl halide, results in the generation of Ni(ii) aryl halide complex. Simultaneously, when the photocatalyst is excited by visible light irradiation, the exited Ir(III) catalyst reacts with an amine to produce αamino radical. This radical then reacts with Ni(II) aryl complex to form Ni(III) intermediate. Subsequently, reductive elimination takes place to yield the final arylated product and precatalyst Ni(I). In 2016, the Molander group (Heitz et al. 2016) reported on the process of arylating α-heteroatom-substituted 76 or benzylic C(sp3 )–H bonds using aryl bromides 77 (Scheme 4.35). This reaction was facilitated by the presence of an iridium photocatalyst and Ni(NO3 )2 .6H2 O as a transition metal catalyst. Additionally, stoichiometric amounts of 4,4’-dimethoxybenzophenone (DMBP) additives were utilized in conjunction with visible light. Also, the MacMillan group had previously conducted similar research, as demonstrated in (Scheme 4.31). In a similar vein, the Doyal group (Shields and Doyle 2016) reported an alkylaryl cross-coupling utilizing a distinct mechanism. The reaction is thought to advance through a direct Csp3 –H arylation instigated by a chlorine radical (Scheme 4.36). Aryl chlorides function both as cross-coupling partners and suppliers of chlorine radicals for the C(sp3 )–H arylation of ethers. Doyle proposed that the initiation of the Csp3 –H bond takes place through a single-electron transfer (SET) process. In 2017, the group led by Da-Gang Yu (Gui et al. 2017a) reported a method for arylation of α-amino-and α-oxy C(sp3 )–H bonds 64 using aryl tosylates or aryl triflates 82 (Scheme 4.37). This reaction produces allylic/benzylic amines 83 of significant value in moderate to excellent yields using a relatively more affordable ruthenium photocatalyst, Ru(bpy)3 Cl2 .6H2 O. In 2017, the Doyle group (Nielsen et al. 2017) successfully utilized the dual catalysis method to carry out the formylation of aryl chlorides 80 by selectively modifying 1,3-dioxolane 84 (Scheme 4.38). This versatile laboratory-based method offers a significant advantage compared to the traditional process of carbonylation reduction. This is because it does not involve the use of carbon monoxide, pressurized gas, or reducing substances. The aryl chlorides with electron deficiencies exhibited higher yields and faster reaction times compared to the substrates with electron richness. In the same year, the MacMillan group (Le et al. 2017) has reported a highly selective sp3 C–H alkylation (Scheme 4.39) using their previously developed method

113

Scheme 4.33 Ligand-accelerated C–H arylation via dual catalysis

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

114

S. C. Ghosh et al.

Scheme 4.34 Plausible mechanisms for ligand-accelerated C–H arylation via dual catalysis

that is based on polarity matching (Scheme 4.31). This method effectively combines photoredox, nickel, and hydrogen-atom transfer catalysis to simultaneously utilize three catalytic cycles. During the same year, the Shibakashi group (Sun et al. 2017) disclosed the direct coupling of ethers 79 with acyl halides employing a dual catalytic system. This system comprises an Ir-based photocatalyst and a nickel complex, in conjunction with blue-light irradiation (Scheme 4.40). Besides acyl chlorides 69 and anhydrides 68, both cyclic and acyclic ethers can be employed to synthesize acylated ethers. Control experiments have indicated that the primary factor in generating chlorine radicals, crucial for the α-C(sp3 )−H activation of ethers, is the triplet–triplet energy transfer. Subsequently, the Dixon group (Franchino et al. 2017) achieved the α-alkylation of N-diphenylphosphine ketimines 91 with bromocarbonyl compounds 92 using lightpromoted ruthenium and nickel catalysts (Scheme 4.41). They observed up to 59% yield in over 15 examples. The substrates containing electron-withdrawing groups on the aromatic ring were more reactive. In the same year, the Wu group (Deng et al. 2017) developed a novel reaction that combines photocatalysis and Ni catalysis to achieve hydroalkylation of internal

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

H R1

R3

+

R2

Ni(NO3)2.6H2O (5 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%) dtbbpy (5 mol%)

Br

76

CF3

R3

R1

DMBP (25 mol%) K2HPO4(2 equiv),26 W CFLs, rt

77

115

R2 78

CN

CN

N

O O O

S

O

63% yield

32% yield

21% yield

49% yield

78a

78b

78c

78d

CN CN

CHO N

S

MeO

MeO

O

O

87% yield

54% yield

43% yield

91% yield

78e

78f

78g

78h

Scheme 4.35 Arylation of α-heteroatom-substituted or benzylic C(sp3 )–H bonds using aryl bromides

H R3

+ R2

R1

O

Ni(cod)2 (10 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%) dtbbpy (15 mol%)

Cl

79

K3PO4 (2 equiv) 34 W blue LEDs, 23 0 C, rt

80

R3

R2O R1 81 EtO

O N

Ac OMe

Ac N

O O O

78% yeild 81a

N O

OMe

91% yeild

85% yeild

93% yeild

81b

81c

81d

Scheme 4.36 Direct C(sp3 )−H cross-coupling enabled by catalytic generation of chlorine radicals

116

S. C. Ghosh et al. NiCl2.glyme (2 mol%)

R 1O

H

N

N

Ru(bpy)3Cl2.6H2O (1 mol%)

+

Ar

Ar dtbbpy (2 mol%),Cs2CO3 (2 equiv) R1=Ts, Tf,P(O)Ph2

64

DMF(0.1 M),30 W blue LEDs, rt,12 h,

82

83

N

N

N

R

N

n

R

88% yield

N

83a

n=1, 85% yield n=2, 71% yeild n=3, 71% yeild

83b 83c 83d

R = H, 49% yield R =Ph, 96% yeild

R = Ac, 80% yield 83g 81% yeild 83h R = CF3, R = SO2Me, 94% yield 83i

83e 83f

N H

H

N

O

N

H

Ph O

Me O 68% yield 83j

62% yield 83k

64% yield 83l

Scheme 4.37 Coupling of C(sp3 )–H bonds with C(sp2 )–O electrophiles

alkenes 23 using α-hetero C(sp3 )–H bonds 16 as coupling partners (Scheme 4.42). The reaction involves various ethers or amides with internal alkynes, resulting in good yields of alkenylation products. Alkyl-substituted alkynes produce a mixture of regioisomeric allylic ethers. However, increasing steric hindrance improves the selectivity for alkylation, resulting in the production of cis-olefin products. Additionally, trimethylsilyl-substituted alkynes exhibit a regioselectivity ratio of > 20:1. In 2017, the MacMillan group (Zhang and MacMillan 2017) published an approach to synthesizing ketones through the utilization of a photoredox nickelcatalyzed aldehyde C–H arylation, vinylation, or alkylation using their developed triple catalysis system (Scheme 4.43). This specific reaction involves the combination of aldehydes 100 with aryl, alkenyl, or alkyl bromides 77 in the presence of dual catalysts and under blue light irradiation at room temperature. The researchers have demonstrated that this method can accommodate a wide range of substrates, including aryl bromides, alkenyl bromides, and alkyl bromides. In 2017, the Da-Gang Yu group (Gui et al. 2018) developed a new and effective method for adding aryl groups to anilines (Scheme 4.44). They achieved this by using free phenols as latent electrophiles, with the help of photoredox/nickel dual catalysis. Previously, preactivated phenols (tosylate) were required for the arylation of aniline (Scheme 4.37), but this new approach eliminates that need. Furthermore, it has been demonstrated that this method works well with a wide range of substrates (Scheme 4.45).

O

84

O

85c

O

H

85b

H

OH

85a

80

dtbbpy (15 mol%) K 2HPO4(2 equiv), 34 W CFLs, 23 0C, 72 h then1 M HCl

70% yield

Cl

64% yield

+

74% yield

O

NiCl 2.DME (10 mol%) [Ir(dFCF3ppy) 2(dtbbpy)]PF6(1 mol%)

Scheme 4.38 Formylation of aryl chlorides through the photocatalytic generation of chlorine radicals

H

O

H

N

S

H O

H

85

O

O

85d

N

86

O

59% yield

HO

Vi a

N

Ph

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 117

118

S. C. Ghosh et al. NiBr 2.4,4'-dOMebpy (2 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (1 mol%) K2CO3 (1 equiv)

R2 R1

N

H

+

R

Br

R2 R1

quinuclidine (10 mol%)

Boc MeCN/H2O (1/1), blue LEDs,h

88

89

CN

O

N

N

N

Boc

Boc

Boc

89a

R

Boc

87

43% yield

N

82% yield 89b

75% yield 89c

N

N

59% yield 89d

Scheme 4.39 Selective sp3 C–H alkylation via polarity-match-based cross-coupling

In the same year, again the Da-Gang Yu group (Gui et al. 2017b) performed arylation of amide 105 and urea C(sp3 )–H bonds at room temperature using aryl tosylates, which were created in situ from phenols 106 as latent arylation reagents. This is achieved by combining the use of visible-light photoredox catalysis, hydrogen atom transfer catalysis, and nickel catalysis (Scheme 4.46). In 2018, the MacMillan group (Twilton et al. 2018) developed a new method to facilitate arylation reactions on α-oxy Csp3 –H bonds using triple catalytic methodology. This triple catalytic methodology is different from their previous work; this method uses zinc salts as Lewis acids to activate α-hydroxy C–H bonds and generate alkoxide. They found that the use of zinc-based Lewis acid inhibits the formation of a nickel alkoxide compound and deactivates other types of hydridic bonds, including α-amino and α-oxy C–H bonds. In 2018, Rupping and co-workers (Huang and Rueping 2018) developed a method for directly coupling allylic C−H bonds with unactivated tri-and tetrasubstituted alkenes 110 using the organic photocatalyst 9-mesityl-10-methylacridinium perchlorate ([Acr-Mes]+ ClO4 − ) (Scheme 4.47). This protocol also allows for the functionalization of these alkenes with aryl-and vinyl bromides. In 2018, the Soon Hyeok Hong group (Go et al. 2018) developed a new method for synthesizing tri-substituted enones 114 using a photoredox-mediated Ni/Ir dual catalysis process. The reaction involves highly regioselective and E/ Z-selective hydroalkylation of activated alkynes (Scheme 4.48). The TIPS-groupinduced process promotes the α-selective Z isomer with excellent control and selectivity, which is attributed to the distinctive steric properties of the TIPS group. In the same year, the Doyle group (Ackerman et al. 2018) reported a method for the conversion of cyclohexane into esters by employing chloroformate derivatives in the presence of Ir/Ni catalysts (Scheme 4.49). The reaction takes place via the intermediacy of chlorine radicals, which act as hydrogen atom abstractors. This

79

O

H

+

Cl

R

69

O

68 or

O

R

O

R

blue LEDs, 24 h

K3PO4 (1.5 equiv)

NiCl2 .ligand (10 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (1 mol%)

Scheme 4.40 α-Acylation of ethers via dual catalysis

R2

R1

O

R2 O

90

R1

O

R

t Bu

N Ligand

N

t Bu

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … 119

120

S. C. Ghosh et al.

NP(O)Ph 2

NP(O)Ph 2

NiCl 2.(PPh3)2 (2 mol%) Ru(bpy) 3Cl2.6H 2 O (5 mol%)

R3

R1

+

Br

R2

R3 EWG

R1

H

R2

DIPEA or TEOA (2 equiv) DMF(0.2 M),1 W blue LEDs, 35 0C,20 h,

EWG

93 91

92

15 examples up to 59% yield

Scheme 4.41 α-alkylation of N-diphenylphosphine ketimines with bromocarbonyl compounds NiCl2 (10 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%) dtbbpy (12 mol%)

R2 + O

R2

p

p'

tBu

Ph O

O

nBu 94a 72% yield,(5:1), (>20:1)

O

94b 52% yield, (>20:1), (>20:1)

tBu 94d

94c 65% yield, (>20:1), (>20:1)

NiCl2 (10 mol%) SiMe3

O

Me3Si

OH

73% yield, (>20:1), (>20:1)

SiMe3

Ph

[Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%)

Ph 97

96

+

X

+ X

R1 95

yield, (p:p'), (E:Z)

S Ph

O

94

THF(0.05 M) 18 W Blue LED strip, 24 h, 60 0C

23

+

O

R1

16

R2

R1

dtbbpy (12 mol%) Benzene, 18 W Blue LED strip, 24 h, 60 0C

Me3Si

X

p

Ph

p'

98

99 yield, (p:p'), (E:Z)

O Ph

Ph

Ph O

Me3Si 98a 49% yield,(20:1), (>20:1)

O

Ph O

O Me3Si

Me3Si

98b 53% yield, (>20:1), (>20:1)

98c 61% yield, (>20:1), (>20:1)

N Me3Si 98d 96% yield, (>20:1), (>20:1)

Scheme 4.42 Regioselective hydroalkylation of internal alkynes with α-hetero C(sp3 )−H bonds of ethers and amides

method is useful for synthesizing ketones from unactivated C–H bonds, as well as benzylic and α-heteroatom C–H bonds. Tambar pioneered (Xu and Tambar 2019) a δ-selective C(sp3 )–H allylation of aliphatic amides utilizing allyl chlorides under visible-light photoredox nickel catalysis (Scheme 4.50). This approach accommodates cyclic and acyclic substrates featuring heteroatoms or electron-donating groups. The reaction has produced a

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … O

Br R

O

NiBr 2.dtbbpy (10 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (0.4 mol%)

H

R

quinuclidine (10 mol %) ,K3CO3 (2 equiv) dioxane,34 W blue LEDs,rt , 20 h

+ 77

121

100

101 O

O

O

Cl R

F3C

NBoc 101a

101b

72% yield

N H 101c 81% yeild

77% yield

Scheme 4.43 Direct aldehyde C−H arylation and alkylation via the combination of nickel, hydrogen atom transfer, and photoredox catalysis

R1

N

NiBr2.glyme (2 mol%)

H

+

Ar-OH

Me4Phen (3 mol%) TsCl (1.5 equiv),DABCO (4 equiv) DMF(0.1 M),30 W blue LEDs, rt,24 h

103

102

N

Ph

Ph

N

104a 48% yield

Ar

N

Ru(bpy)3Cl2.6H2O (1 mol%)

Ph

iPr

N

N

Ph

Ph

104b 40% yield

Ac

104

N Ac 104c 45% yield

Ph R = Ac, R = CF3, R = CN,

R 86% yield 104d 80% yeild 104e 61% yield 104f

Scheme 4.44 Arylation of aniline C(sp3 )–H bonds with phenols

range of amide products substituted with allyl groups, with good yields and high δ-selectivity. In 2019, Martin’s group (Rand et al. 2020) demonstrated an sp3 α-arylation and sp3 α-alkylation of α-amino C–H bonds of benzamides with unactivated alkyl halides. The combination of NiBr2 ·diglyme, along with the iridium photocatalyst Ir[dF(CF3 )ppy]2 (dtbbpy)PF6 , and a bipyridine ligand can be used under blue light irradiation to get the best yields. Additionally, the team developed an enantioselective sp3 α C−H functionalization of aliphatic secondary amides with aryl halides, which can be achieved using a chiral ligand called iPrBiOx (Scheme 4.51). In 2020, the Huo group (Shu et al. 2020) reported the development of a new method that can directly and selectively modify α-amino C(sp3 )−H bonds with carboxylic acids (Scheme 4.52). This method utilizes a combination of transition metal and photoredox catalysis, making it easy to execute. It enables the cross-coupling of a wide range of carboxylic acids with readily available N-alkyl benzamides, resulting

122

R1

S. C. Ghosh et al. TsCl (1.5 equiv),Cs 2CO3(2 equiv) 30 min, then filter

OH N

H +

O

R2

R1

NiBr 2.glyme (2 mol%) [IrdF(CF3)ppy2(dtbbpy)].PF6(4 mol%) Li 2CO 3(2 equiv), Me 4Phen (3 mol%) 3-acetoxyquinuclidine (1.1 equiv) 30 W blue LEDs, rt ,36 h

R2

N O

O

O

O

N N

N N Bz

Bz 65% yield

OMe

90% yield

67% yield

Scheme 4.45 Arylation of C(sp3 )–H bonds in amides and ureas using aryl tosylates generated in situ from phenols

H R2

+

R1

OH

R2

HO

ZnCl2, K3PO 4(2 equiv) DMSO(0.25 M) 34 W blue LEDs, fan, 24 h

Br

108

NiBr 2·Me 4 phen (1.5 mol%) [Ir(dFCF3 ppy) 2(dtbbpy)]PF6 0.(2 mol%) quinuclidine (30 mol%)

R1

77

109

O CF3 HO

CF3 HO

HO

HO

Bu n -

CF3

O

Bu n ph

109a 51% yeild

109b 75% yeild

109c 71% yeild

109d 66% yeild

Scheme 4.46 Direct a-arylation of alcohols through photoredox, HAT, and nickel catalysis

in the production of valuable α-amino ketones under mild conditions. The resulting α-amino ketones exhibit a high degree of enantioselectivity. In 2021, the Stahl group (Vasilopoulos et al. 2021) developed a method for the methylation of benzylic and α-amino C(sp3 )–H bonds using alkyl peroxides as hydrogen atom transfer (HAT) and methylating agents (Scheme 4.53). The reaction was carried out under mild conditions using a photoredox nickel-catalyzed mechanism. The peroxyl O–O bond undergoes homolysis when exposed to visible light, creating an alkoxy radical that can act as a hydrogen atom transfer agent. This method is useful for direct methylation of C(sp3 )–H bonds in various drug-like molecules and

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

H

NiCl 2.glyme (10 mol%) [Mes-Acr]ClO4 (5 mol%) dtbbpy (15 mol%)

R

+ Br

R

2,6-lutudune(2 equiv) 1,2-DCE, blue LEDs, rt 111

77

110

123

O N CHO

N

CN

O N

111a 88% yeild

111b 73% yeild

111c 31% yeild

111d 63% yeild

Scheme 4.47 Direct cross-coupling of allylic C(sp3 )–H bonds with aryl-and vinyl bromides

OEt

NiCl2.glyme (20 mol%)

TIPS

[Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%)

O

dtbbpy (30 mol%) Benzene (0.1 M), 35 W Blue LED strip, 23 0C, 20 h

TIPS

EtO

X

+ X

O

112

113

H 114 O

OEt

OEt

O O TIPS

H

114a 87% yield,

OEt

OEt

O

Ph

OPh TIPS

H

114b 63% yield

N

O

O TIPS

H

114c 87% yield

TIPS

H

114d 77% yield

Scheme 4.48 Regioselective and E/Z-selective hydroalkylation of Ynone, Ynoate, and Ynamide

pharmaceutical building blocks, especially significant is its application in late-stage functionalization of pharmaceutical and natural product derivatives.

4.3.2 Benzophenone as a Photosensitizer Benzophenone is a widely used photosensitizer that effectively harnesses light energy for photochemical processes, as supported by scientific evidence. Its strong absorption of ultraviolet (UV) light in the 300–350 nm range has been well-documented. This absorption leads to the formation of highly reactive excited states, which can

124

S. C. Ghosh et al.

O R

H

R

+

Cl

O

Ni(cod) (4 mol%) [Ir(dFCF3ppy)2(dtbbpy)]PF6 (0.4 mol%) Na2WO4.2H2O (1 equiv) dtbbpy (5.2 mol%),K3PO4 (2 equiv)

69

o

PhH(0.1 M), 34 W blue LEDs, 34 C

115

116

O

O

O O

C8H15

O

O

O

O

O

116a 52% yield

116b 18% yield

116c 48% yield

Scheme 4.49 Direct cross-coupling between unactivated C(sp3 )−H bonds and chloroformates

R1

Ni(COD)2 (1v0 mol%)

Cl

R2 NHTFA

R3

+

H

[Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%)

R2 NHTFA

R3

Ligand (11 mol%) K2PO4 (2 equiv) MeCN, Blue LED, 25 0C, 48 h

118

117

R1

119

R1

PC

H

R1 1,5-HAT

Cl

N R2

R3

R

118

R2

R

Me

NH

Me n-Bu

n-Bu

O

O

N

N

NHTFA

NHTFA

Ligand 119b 70% yield

119a 72% yield,

n-Bu

Me

Me

Me

Me

NHTFA

Me NHTFA

Me

Si

NHTFA

Me 119c 64% yield,

119d 66% yield,

119e 64% yield,

Scheme 4.50 Allylation of unactivated C(sp3 )−H bonds triggered by photogenerated amidyl radicals

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … NiBr2.diglyme (10 mol%)

H

O R1

125

[Ir(dFCF3ppy)2(dtbbpy)]PF6 (1 mol%) +

R2

N H

R3

Br

R2

N H

Ligand (15 mol%),K3PO4 (1.5 equiv) dioxane, Kessil blue LEDs, 20h

88

120

R3

O R1

N

N

bipyridine (Ligand)

121

NiBr2.diglyme (5 mol%) O

H

R1

[Ir(dFCF3ppy)2(dtbbpy)]PF6 (2 mol%) +

N H

R3

Br

122

R3

O R1

N H

Ligand (15 mol%),K3PO4 (2.0equiv) EtOAc, Kessil blue LEDs, -15 0C, 48 h

88

R2

i-Pr

O

O

N

N

i-Pr

iPrBiOx.(Ligand)

123

Scheme 4.51 sp3 α-C−H arylation and alkylation of benzamides with organic halides

R1

NiBr 2.glyme (5 mol%) [Ir(dFCF3ppy) 2(dtbbpy)]PF6 (1 mol%)

R2

O +

OH

H

NHBz

Ligand (7 mol%) DMDC (1.5 equiv), NH4Cl (1 equiv) Na 2HPO4 (1 equiv) iPrOAc (1 equiv) Blue LED, 150 C, 22 h

125

124

O R2

R1

O

O

Ph

Ph N

NHBz

N

Ph

Ph Ligand

126

O n-Bu

R1

Ph N

H

O

O

70% yield 85% ee 126j

R = 4-MeOPh, 86%yield 90% ee 126f R = 3-MeOPh, 74%yield 91% ee 126g R = 4-CF3Ph, 83%yield 92% ee 126h R = 2-Thiophene, 82%yield 89% ee 126i

55%yield 92% ee 126e

O

Me

NH O

Cl

NH

R

NHBz

Ph

R1 = Ph, 77% yield 95% ee 126a R1 = Me, 88% yield 90% ee 126b R1 = i-Pr, 63% yield 87% ee 126c R1 = Cy, 63% yield 88% ee 126d

O

n-Bu

n-Bu

O

NHBz

O

O

O

O

Me Me

n-Bu

O O NHBz O H

H

H

O

Me

O

Me

H

n-Bu

O

H O

NHBz

(R-S)-L: 50% yield 5:95 dr 126k (S-R)-L: 60% yield 95:5 dr 126l

H

TBSO

(R-S)-L: 76% yield 5:95 dr 126m (S-R)-L: 76% yield 94:6 dr 126n

Scheme 4.52 Direct enantioselective C(sp3 )−H acylation for the synthesis of α-amino ketones

126

S. C. Ghosh et al.

O

+

O

76

Me

O

O N H

N

Ph

R2

MeB(OH)2 (50 mol%) MeCN:DMSO (1:1), 400nm LEDs, rt, 16 h

127

Me

Me R1

Me

R2

R1

NiCl2.dimethoxethen [tButpy] (4 mol%) [Ir(dFCF3ppy)2(tBubpy)]PF6 (1 mol%)

Me

H

O H 2N

128

O S

Me

O

O

O O 128a

128c 43% yield, 6.7:1 d.r

128b 49% yield 2.5:1 r.r

59% yield,

O Me

Me

Me Boc

N

N H

O

Boc

N N

HN Me O

Ph

CF3

HN

O N

N

F

F3C F

128d 44% yield, 1.3:1 d.r

128e 53% yield

129f

F

61% yield, 1.6:1 d.r

Scheme 4.53 C(sp3 )–H methylation enabled by peroxide photosensitization and Ni-mediated radical coupling

efficiently transfer their energy to nearby molecules, initiating various photochemical reactions. This property has been demonstrated in numerous studies, making benzophenone a reliable and scientifically supported choice for enhancing controlled light-induced reactions in various fields of chemistry and photobiology. Diaryl ketones have excellent photochemical properties that make them suitable for various applications. These properties arise due to the creation of a long-lasting triplet state, which is produced when an electron is excited from a nonbonding orbital at the C–O bond to a corresponding π*orbital (n,π*). The process of intersystem crossing (ISC) follows this. The triplet excited state of diaryl ketones has significant potential for building molecular complexity. This state acts as a 1,2-biradical, leading to a substantial amount of spin density on the oxygen atom. Consequently, the (n,π*) triplet excited state exhibits distinctive electrophilic and radical-like properties, rendering it highly receptive to radical addition. The triplet excited states of diaryl ketones have the potential to initiate diverse mechanisms, such as hydrogenatom transfer (HAT) and single-electron transfer (SET). It helps in the formation of C–C bond formation (Scheme 4.54). In 2018, the Martin group (Shen et al. 2018) reported sp3 C−H arylation and alkylation reactions using a synergistic combination of nickel and diaryl ketone

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … O

127

O light

ISC O

130

129

131 singnal exicted state

Energy Transfer, HAT & SET

Scheme 4.54 Triplet photoexcited diaryl ketones

catalysts. This process is facilitated by the participation of triplet excited ketones, acting as both hydrogen atom transfer (HAT) and single-electron transfer (SET) catalysts (Scheme 4.55). The proposed catalytic cycle involves the cleavage of C–H bonds through a process of hydrogen atom transfer (HAT) between the triplet-excited ketone photocatalyst and the C(sp3 )–H substrates. At the same time, adding an organic halide to a lowvalent Ni(0)Ln complex results in the formation of an electrophilic Ni(II) species. Afterward, the carbon-centered radical species combines with the nickel(II)-aryl intermediate, resulting in the formation of a nickel(III) species. This is followed by Ni(acac)2 (10 mol%) photosensitizer (10 mol%)

Br O

H

+

16

O

R

R

ligand (10 mol%),Na2CO3 (1 equiv) 32 W CFL light, rt,18 h

77

132

O

MeO photosensitizer

Ligand

O

O

O

H H CO2Me N

CO2Me O 132a 74% yield

N

N

CF3

132b 96% yield

N

Ph 132c 53% yield

Scheme 4.55 sp3 C−H arylation and alkylation reactions using a synergistic combination of nickel and diaryl ketone catalysts

128

S. C. Ghosh et al. H O

O

HAT

Ar2 O

Ar2

Ar1

HO Ar1

O

NiILn

Br

I h

SET

O Ar1

Ar2 Ni0L

Transition metal Catalytic Cylcle

NiIII Br

n

Ln Br

A

Br

Br NiIII

L L

O

Scheme 4.56 Photochemical C(sp3 )–H arylation utilizing the synergy of ketone HAT catalysis and nickel catalysis: proposed mechanism

reductive elimination, which produces the desired C–H functionalization product and a Ni(I) intermediate (Scheme 4.56). In 2019, Rueping and his colleagues (Dewanji et al. 2019) reported a new method for the direct arylation of benzylic C–H bonds with aryl bromides. The process utilized 4,4’-dichlorobenzophenone as a photocatalyst, which played a dual role as a hydrogen atom transfer (HAT) catalyst and energy transfer catalyst. Through visible light irradiation, the photocatalyst reacted with toluene, forming a benzylic radical via hydrogen atom transfer. This radical then reacted with a Ni(0) catalyst to create a Ni(I) species that underwent oxidative addition and reductive elimination, resulting in the desired product. The reduced photocatalyst would then reduce the Ni(I) species and undergo deprotonation, closing both catalytic cycles (Scheme 4.57). In 2020, the Ruping group (Krach et al. 2020) reported a successful synthesis of unsymmetrical ketones by acylating the benzylic C–H bond using a photoactive benzophenone derivative and a nickel complex. Both acid chlorides and anhydrides are viable options for acylation at the benzylic position of toluene and methylbenzenes derivatives. However, the authors found that acid chlorides are more effective than acid anhydrides for this purpose (Scheme 4.58).

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … NiCl2.6H2O (5 mol%)

Br

H

photosensitizer (25 mol%)

+ 133

OH Ar

129

R

R dtbbpy (5 mol%),K2HPO4 (2 equiv) 2 * 23W CFL light,35 0C rt,18 h

76

134

-

PS-H + B

Ar Ln-Ni0

[ PS ]

Br-NiILn PS + BH + Br

-

[ PS ] h

Ar

Br

Ln Ni Ln

N

NiI

Br

Ar

O

O

CN

CF3

Cl

134a 53% yield

134b 99% yield

134c 66% yield

Cl photosensitizer

Scheme 4.57 Dual catalytic protocol for the direct arylation of non-activated C(sp3 )–H bonds

+ 133

NiCl2.6H2O (5 mol%) photosensitizer (25 mol%)

O

H

R

X

dtbbpy (5 mol%),K2HPO4 (2 equiv) 2 * 23W CFL light,35 0C rt,48 h

64

R O 135

O

O

O

O OAc

135a 39% yield

135b 61% yield

135c 44% yield

photosensitizer

Scheme 4.58 Synthesis of unsymmetrical ketones by applying visible-light benzophenone/nickel dual catalysis

In 2019, the Hashmi group (Si et al. 2019) discovered that by combining nickel catalysis and benzaldehyde, they were able to alkylate and arylate C(sp3 )–H bonds next to a heteroatom in amides and thioethers when exposed to UVA light irradiation. This method offers a straightforward and economical approach to directly functionalize amides and thioethers under mild reaction conditions (Scheme 4.59).

130

S. C. Ghosh et al. NiBr 2.glyme (10 mol%) photosensitizer (50 mol%)

H +

N

R

Br

R N

dtbbpy (10 mol%),K 2HPO4 (2 equiv) acetone, UVA light, rt

Boc 136

Boc 137

88 F

O N N CO2Me

Boc

Boc

Boc

137a 69% yield

137b 25% yield

S 16

R

Br 88

photosensitizer

R

dtbbpy (10 mol%),K2HPO4 (2 equiv) CH3CN, UVA light, rt

S 138

CN

S

S

S

Ph 138a 73% yield

137c 74% yield

NiBr 2.glyme (10 mol%) photosensitizer (50 mol%)

H +

H

N

N

OTBS 138b 53% yield

138c 71% yield

Scheme 4.59 Sp3 C—H arylation/alkylation of amide and thioethers

4.4 Merger of Copper Catalyst with Photoredox Catalyst In 2012, Rueping and co-workers (Rueping et al. 2012) developed copper catalyzed first C–H bond alkynylation reaction between N-aryl tetrahydroisoquinolines and terminal alkynes (Scheme 4.60a). By a combination of Ru photocatalyst and copper catalyst, various glycine ester and tetrahydroisoquinolines were investigated, yielding the desired product in good yield. In the same vein, Li (Perepichka et al. 2015) and co-workers reported similar dual copper/Ir photoredox-catalyzed highly efficient asymmetric cross-dehydrogenative coupling reaction (Scheme 4.60b). In this protocol under aerobic oxidative condition, optically active 1-Alkynyltetrahydroisoquinolines were synthesized in good yield and showed excellent enantioselectivity. In 2013, Wu and co-workers (Gao et al. 2013) developed a dual catalytic C–C bond-forming method via C–H bond alkylation of secondary amine under visible light irradiation (Scheme 4.61). Functionalization of secondary amine with β-keto

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

R

N

(MeCN)4CuPF6 [Ru(bpy) 3](PF6)2

CuBr [Ir(ppy)2(dtbbpy)]PF6 ligand, (BzO)2

H

DCM 5 W lamp

A 141

N

R

140

R

R

131

139

R

N

THF/MeCN -20 0C, 48h, Visible light

B

R

141

Scheme 4.60 Copper catalyzed C–H bond alkylation

ester as a coupling partner employing Ru as a photocatalyst and copper co-catalyst under aerobic oxidative conditions. A series of N-substituted glycine esters having electron-donating or electron-withdrawing groups on para-position of the phenyl ring showed good reactivity and furnished the desire product in moderate to excellent yield. In this synthesis, β-keto ester also showed a wide range of applicability. In 2016, Wang and co-workers (Chen et al. 2016) developed a novel synthesis for perfluoroalkylation of ortho C–H bond of benzamides by merging copper catalyst with eosin Y photocatalyst (Scheme 4.62). 8-aminoquinoline directing group assisted benzamide with perfluoroalkyl iodides leading to ortho-perfluoroalkyl-substituted acid in good to moderate yield. In the same year, Ackermann and co-workers (Yang et al. 2016) reported the merging of copper catalyzed and Ir photoredox catalyzed direct C–H arylation between nonaromatic oxazolines and aromatic halide leading to naturally occurring alkaloids under visible light irradiation (Scheme 4.63). In 2019, Guangming and co-workers (Tian et al. 2019) developed synthesis to perform ortho C–H bond trifluoromethylation of aniline derivatives by using low-cost and stable CF3 SO2 Na (langlois reagent) as a CF3 source by dual cobalt co-catalyst and eosin Y photoredox catalyst (Scheme 4.64). A series of aniline derivatives with electron-releasing or electron-withdrawing group employing the desired product in moderate yield.

HN H

Ar

O

COOR 1 O

R1 R2 2

OR3

O

142a 93% yield d.r. = 2:1

HN

R1 R2

O

COOR COOR3 142

O

O

OBn

OEt N H

Ar O

toluene Blue LEDs, r.t, air

H

O

MeOOC

Ru(bpy)3Cl2 (1 mol%) Cu(OTf)2 (10 mol%)

O

OMe

H N COOEt 142b 80% yield d.r. = 2:1

OEt OMe EtOOC

N H

142c 50% yield

Scheme 4.61 C–H bond alkylation of secondary amine under visible light

O

132

S. C. Ghosh et al. O

Cu(OAc)2.H2O (3 mmol%) Cs 2CO 3 (1.0 equiv.) Eosin Y

AQ

R

n-Cn-F(2n+1) I H

O AQ

R

DMAc, 60 0C, 12h Visible light

AQ = 8-Aminoquinoline

nCnF(2n+1)

143

32

144 O

O

AQ

AQ Me

n-C4F9

Et

O

O

AQ

AQ

n-C4F9

Ph

n-C4F9

O F

AQ

n-C4F9

F3C

n-C4F9

144a

144b

144c

144d

144e

68% yield

65% yield

70% yield

54% yield

69% yield

Scheme 4.62 Perfluoroalkylation of ortho C–H bond of benzamides

N

I

Me

H S

Me N S

DMF, 35 0C, 16h Blue LED

146

145

Ir Photocatalyst (2 mol%) CuI (20 mol%) Base

147

Scheme 4.63 Synthesis of naturally occurring alkaloids

O R

CuCl2 (10 mol %) Eosin Y (5 mol %) (NH4)2S2O8 (2 equiv.)

R

O

CF3SO2 Na

N H H

148

MeCN, air, Blue LED

149

O

O N H

N 150a 65% yield

CF3

R

R

Me

150b 40% yield

CF3

150 O

O

N H

N H

N H N

N H

CF3

CF3

CF3

150d

150c 60% yield

62% yield

Scheme 4.64 Trifluoromethylation of aniline derivatives by merger of dual catalyst

In 2020, Ying Li and co-workers (Zhang et al. 2020) reported Lewis acid-catalyzed methodology to construct a variety of 1,3-benzoxamine under mild reaction conditions (Scheme 4.65). By a combination of the copper catalyst with Ru photocatalyst, an aerobic dehydrogenative coupling of glycine esters with β-naphthol leads to a series of 1,3-benzoxamine in good yield with excellent diastereoselectivity. A series of glycine esters having an electron donation group on the ortho-, meta-, and para-position of benzene ring gives good yield.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

133 R1

H R1 N H

CO2R2

R2O2C

N

OR 2 O

DCE, r.t.,air 23 W Blue LEDs

152

151

153 OMe

OMe

R

O EtO

O

Cu(OTf) 2 (10 mol%) Ru(bpy)3Cl2.6H2O (1 mol%)

OH

O

O N

EtO

OEt O

R

O

O N

EtO

OEt

O N

OEt O

O R

153aR = OMe, 79% yield, 20:1 dr 153bR = OEt, 82% yield, 20:1 dr 153cR = Oi Pr, 84% yield, 12:1 dr 153dR = OtBu, 81% yield, 5:1 dr

153eR = Br, 77% yield, 20:1 dr 153f R = OH, 79% yield, 20:1 dr 153gR = OMe, 81% yield, 6:1 dr 153hR = OEt, 85% yield, 20:1 dr

153i R = Br, 73% yield, 20:1 dr 153j R = CN, 82% yield, 20:1 dr 153kR = COOH, 73% yield, 20:1 dr 153l R = CH2OH, 65% yield, 20:1 dr

Scheme 4.65 Synthesis of various 1,3-benzoxamine by merger of dual catalyst

In the same year, Zhang and co-workers (Yang et al. 2020) developed a visible light-mediated first cross-dehydrogenative coupling between glycine derivatives and simple ketone or aldehyde by a combination of copper catalyst with Ru photoredox catalyst (Scheme 4.66). This protocol offers an enantioselective aerobic oxidative coupling method for synthesizing enantiopure unnatural α-alkyl α-amino derivatives. The process delivers good yields with outstanding diastereoselectivities and enantioselectivities. Subsequently, Yu and co-workers (Chen et al. 2020) reported remote (Csp3 –H) asymmetric cyanation of carboxamide with TMSCN by merger of copper co-catalyst with Ir photocatalyst. In this protocol, O-acyl hydroxamides are employed as internal oxidants and precursors of NCRs. This strategy gives a wide array of cyanated amides in good to excellent yield with excellent enantioselectivity. Carboxamide with electron-donating group or electron-withdrawing group gives good to excellent yield (Scheme 4.67). In 2020, MacMillians group (Sarver et al. 2020) reported trifluoromethylation of a general C(sp3 )–H bond by merging a decatungstate photocatalysis with copper catalyst using a widely available CF3 source and requiring only a single equivalent of the C(sp3 )–H-bearing substrate (Scheme 4.68). This methodology performs the direct conversion of aliphatic and benzylic C–H bond yielding (Csp3 )-CF3 product. The synthetic utility of this methodology is exemplified in late-stage functionalization to the direct C–H trifluoromethylation of natural products and medicinal agents. In the following year, Huo and co-workers (Wang et al. 2021) reported visible light-irradiated α-alkylation of glycine derivatives with alkyl boronic acid leading

134

S. C. Ghosh et al.

O

H

H N H

R1

Cu(OAc)2.H2O (5 mol%) Ru(bpy)3Cl2.6H2O (2 mol%) Chiral catalyst (20mol%)

R1

CO2R2

O

CO2R2

MeCN. r.t., air 5W blue LEDs 154

152

10

HN

OMe

OMe

OMe NHTf

HN

O

HN

O

O

HN

O

O

O

O

O

O

N H

O Chiral Catalyst

R 154a 76% yield, 96% ee

154d 75% yield, 96% ee

154bR = Me 67% yield, 97% ee 154cR = tBu 73% yield 97% ee

Scheme 4.66 Synthesis of enantiopure unnatural α-alkyl α-amino derivatives Me

H

O N

O N

156

157 Me

O N H

CN

O

O

R N H R

157aR = t-Bu 97% yield 157bR = Me 99% yield 157cR = Et 99% yield 157dR = i-Pr 94% yield 157eR = Cy 98% yield

t-Bu

OCOAr

Ligand 40 W Blue LEDs,

Ar = p-CF3C6H4 155 CN

CN

TMSCN

OCOAr

Me

Me

Ir(ppy)3 (0.5 mol %) Cu(CH3CN)4BF4 (2.0 mol %) MTBE

t-Bu

O

t-Bu N

N Ligand

157f R = Cl 97% yield 157gR = F 90% yield

Scheme 4.67 Remote (Csp3 –H) asymmetric cyanation of carboxamide with TMSCN

to the desired product in good yield by the merger of copper catalyst with Ru as a photocatalyst (Scheme 4.69).

4.4.1 C–N Bond Formation In 2020, Nagib and co-workers (Nakafuku et al. 2020) reported a strategy to construct C–N bond by asymmetric radical C–H amination of alcohol by the merger of copper catalyst and Ir photocatalyst. A variety of alcohol containing alkyl, allyl, benzyl, and propargyl C–H bonds were readily converted to an imidate radical that undergoes

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … H

F 3C

I

135

CuCl 2 (5 mol%) NaDT(1mol%) H2SO4 (1.2 equiv.)

O

CF3

O N H 159

158 CF3

N H 160

H2O/MeCN 390 nm Kessil lamp O

CF3

CF3

CF3

O

H 2N

HN N H 160c 45% yield

NH2 160b 52% yield

160a 83% yield

OMe 160d 55% yield

Scheme 4.68 Trifluoromethylation of alkyl C–H bond by merger dual of Cu/decatungstate catalyst

CuCl (10 mol%) Ru(bpy)3 (PF3)2 (1 mol%)

H

R1

CO2R2

N H 152

R2 B(OH)2

H N

O

O

H N

O

CO2R2

N H

DCM O2, r.t.

161 O

R2

R1

162 H N

O O

H N

O O

n n

162a n = 0 42% yield 162b n = 1 58% yield 162c n = 2 71% yield

162d n = 0 52% yield 162e n = 1 64% yield 162f n = 2 65% yield

162g 62% yield

162h 50% yield

Scheme 4.69 α-alkylation of glycine derivatives with alkyl boronic acid

intramolecular H-atom transfer (HAT) to furnish chiral β-amino alcohol in good to excellent yield with excellent enantioselectivity (Scheme 4.70).

4.4.2 C–O Bond Formation In 2020, Yoon and co-workers reported (Lee et al. 2020) a methodology to construct C–O bond via site-selective C–H bond alkoxylation of benzylic C–H bond (Scheme 4.71). By a combination of a copper catalyst with Ir photocatalyst, this protocol evolved the functionalization of the benzylic C–H bond via a wide range of oxygen nucleophiles. This strategy allows high site selectivity, and chemoselectivity and shows a broad functional group tolerance. In the following year, Le and co-workers (Zhu et al. 2021) reported Csp3 –H functionalization of glycine derivative by merging of dual copper co-catalyst and Ru

136

S. C. Ghosh et al. Ir photocatalst (1 mol%) CuBAr4 (2 mol%) camphoric acid (4 mol%)

OPh N

Ph N

H

NH2

HCL

O R

163

165

164

Ph

Ph

OH

R

R

ligand (25 mol%) pentane:ether Blue LEDs

MeO N

N O

O

OMe

R 165a R = H 80% yield 165b R = Me 89% yield 165c R = F 98% yield 165d R = Cl 87% yield 165e R = Br 89% yield 165f R = I 79% yield

N O

F 165g

165h

90% yield

75% yield

Scheme 4.70 Enantioselective C–H amination of for synthesis of β-amino alcohol

H R

166

O

O

MeCN Blue LEDs

57

Me O

Me

167 Me

Me

O

Me Me

O Me

R1

R

OR1

H

O Me

O

Cu(TFA)2(MeCN) (1.2 equiv.) Ir photocatalyst (1 mol%) K 2HPO4 (3 equiv.)

Me

OH

Me O Me

O

O 167a 70% yield

Me

167b 68% yield

Me

167c 58% yield

O Me

167d 23% yield

Scheme 4.71 Site-selective C–H bond alkoxylation of benzylic C–H bond

photocatalyst to afford various 2-substituted benzoxazoles (Scheme 4.72). A series of glycine derivatives reacts via intramolecular C—H/O—H dehydrogenative coupling to afford structurally diverse benzoxazole derivatives. In the proposed mechanism (Scheme 4.73), initially, photocatalyst was excited by visible light irradiation, followed by SET from glycine ester to generate glycine ester radical cation and Ru(I). Ru(I) is then oxidized by O2 to generate Ru(II) and active species O2 − which abstracts hydrogen from α-amino radical cation to give imine intermediate and HO2 − . After that, imine intermediate forms a complex with Cu salt followed by cyclization complex molecule giving the desired product.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed … Ru(bpy)3Cl2 · 6H2O (5 mol %) CuI (15 mol%) MeCN

O H N

XR2

R1 168

N

O

O

OR

169aR = Me 70 % yield 169bR = Et 77% yield 169cR = i Pr 72% yield 169dR = Bn 60% yield

R

N

O

O

XR2

R1

Blue LEDs air, r.t.

OH

137

169

N

O

N

O

N

O

O

OEt

O

HN

O

N

169eR = Me 64% yield 169f R = CF3 42% yield

169g65% yield

169h35% yield

Scheme 4.72 Photocatalytic Oxidative Csp3 —H Functionalization of Glycine Derivatives for 2Substituted Benzoxazoles OH

OH

SET N H

CO2Me

N H

CO2Me

Ru(I) Ru(II)

*

O2

SET h

O

O

N

OMe

O2 Ru(II) OH N

OMe

Cu(I)

Cu O

HO2

-

OH N H

CO2Me

Scheme 4.73 Proposed mechanism of synthesis of various 2-substituted benzoxazoles

4.5 Other Catalysts with Photoredox Catalyst Mitsunuma and Kanai (Peng et al. 2023) introduce a threefold hybrid catalyst system that consists of three components: a thiophosphoric imide (TPI) catalyst, an acridinium photoredox catalyst, and a titanium catalyst. This system activates sp3 C—H bonds and enables the alkylation of ketones. It provides a straightforward and efficient method for synthesizing a wide range of tertiary alcohols, including aliphatic ketones. Furthermore, it can also be used for the late-stage modification of drugs and their derivatives (Schemes 4.74 and 4.75).

138

S. C. Ghosh et al.

Scheme 4.74 Ternary hybrid catalysis for the intermolecular addition of feedstock organic molecules to ketones

h Ph PC H

O O

R2

PC

NTf P

OH R1

*

Photoredox catalysis

SH

Ti(IV )

HAT Caalysis PC

H

Titanium catalysis Ti(III)

Ti(IV )

O

Ph 1

R

2

R

Ti(III) O O

NTf P

S

O

O H R1

R2

R1

R2

Scheme 4.75 A catalytic alkylation of ketones via sp3 C–H bond activation

Heng Li proposed (Ouyang 2019) a method that involves combining three components to achieve dialkylation (Scheme 4.76). This method involves the synthesis of modified 1,3-dicarbonyl compounds through the combined use of photoredox catalysis and iron catalysis. The modified compounds can be derived from alkenes, alkanes, and 1,3-dicarbonyl compounds. The investigation revealed

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

139

Scheme 4.76 Cooperative photoredox and iron catalysis for intermolecular unsymmetrical 1,2dialkylation of alkenes with two distinct C(sp3 )–H bonds

that the photoredox catalysis system effectively reduces the oxidation and reduction potentials of the iron intermediates and reaction partners, leading to enhanced reactivity. Consequently, the dialkylation reaction can be successfully conducted under mild conditions. In 2023, Matsunaga and co-workers (Kato et al. 2023) reported iron/ photosensitizer-catalyzed C–H alkenylation of amide derivatives through the in situ formation of an iron metallacycle (Scheme 4.77). This suggests a novel approach for iron-catalyzed C–H activation. In 2018, the Glorious groups reported (Schwarz et al. 2018) the successful integration of photoredox and chromium catalysis (Scheme 4.78). This technique allows for the allylation of aldehydes with unfunctionalized (hetero-)arenes, arenes, β-alkyl styrenes, and allyl-diarylamines. It can selectively allylate aliphatic and aromatic aldehydes even in the presence of ketones and esters. In 2020, Yahata and group (Yahata et al. 2020) detailed the formation of an organochromium-type carbanion species from an unactivated C−H bond, followed by its nucleophilic addition to aldehydes, resulting in the synthesis of the corresponding alcohols (Scheme 4.79). Here, carbanion was generated by decatungstatecatalyzed hydrogen abstraction followed by reductive radical-polar crossover (RRPCO) reactions with a chromium salt.

140

S. C. Ghosh et al.

Scheme 4.77 Iron/photosensitizer-catalyzed directed C−H activation

Scheme 4.78 Diastereoselective allylation of aldehydes by dual photoredox and chromium catalysis

In the same year, Mitsunuma and Kanai reported (Tanabe et al. 2020) the catalytic allylation of aldehydes using unactivated alkenes achieved through a ternary hybrid catalyst system. This system includes a photoredox catalyst, a hydrogen-atomtransfer catalyst, and a chromium complex catalyst (Scheme 4.80). The reaction has high chemoselectivity and by introducing a chiral ligand to the chromium catalyst, it offers the enantiomerically and diastereomerically enriched homoallylic alcohols.

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

141

Scheme 4.79 Coupling of aldehydes and non-activated hydrocarbons through the reductive radicalpolar crossover pathway

Scheme 4.80 Catalytic allylation of aldehydes using unactivated alkenes

4.6 Conclusions The merger of 3d transition metal and photoredox catalysis displayed exceptional growth in less than 15 years on C–H activation and functionalization. Significant progress has been made by successfully combining visible-light photoredox and 3d transition metal catalysis to create a dual catalysis platform for modular C–C bond formation by several pioneering groups in this field. As summarized in this chapter, methods have been developed to use cheap 3d transition metals, e.g. Co, Ni, Cu. Fe, and Cr instead of using expensive Pd, Ru, Rh, Ir, etc. catalysts. These methodologies are highly appealing due to their operational simplicity and exceedingly

142

S. C. Ghosh et al.

mild conditions. The utilization of dual catalysis signifies a noteworthy advancement in C–C and C-heteroatom bond-forming reactions, showcasing substantial synthetic potential. The synthetic community will be awaiting the next developments in this area, for example, the exploration of asymmetric versions of these reactions. To improve the quantum efficiencies of many photoredox catalysts and to shorten the reaction time, many reactions need very long reaction times (24–72 h). Most importantly, the mechanistic details of most photoredox reactions are very little explored, but this knowledge is essential for the rational design of metallaphotoredoxmediated cross-coupling reactions. The arrival of metallaphotoredox catalysis has brought numerous opportunities for chemists to explore syntheses to uncover novel fundamental reactivity.

References Ackerman LKG, Martinez Alvarado JI, Doyle AG (2018) Direct C-C bond formation from alkanes using Ni-Photoredox catalysis. J Am Chem Soc 140:14059–14063 Ahneman DT, Doyle AG (2016) C-H functionalization of amines with aryl halides by nickelphotoredox catalysis. Chem Sci 7:7002–7006 Ban YL, You L, Wang T, Wu LZ, Liu Q (2021) Metallaphotoredox dearomatization of indoles by a benzamide-empowered [4 + 2] annulation: facile access to indolo[2,3-c]isoquinolin-5-ones. ACS Catal 11:5054–5060 Bergamaschi E, Weike C, Mayerhofer VJ, Funes-Ardoiz I, Teskey CJ (2021) Dual photoredox/ cobaloxime catalysis for cross-dehydrogenative α-heteroarylation of amines. Org Lett 23:5378– 5382 Chan AY et al (2022) Metallaphotoredox: the merger of photoredox and transition metal catalysis. Chem Rev 122:1485–1542. https://doi.org/10.1021/acs.chemrev.1c00383 Chen H, Jin W, Yu S (2020) Enantioselective remote C(sp3 )-H cyanation via dual photoredox and copper catalysis. Org Lett 22:5910–5914 Chen X et al (2016) Photocatalytic/Cu-promoted C−H activations: visible-light-induced orthoselective Perfluoroalkylation of Benzamides. Chem–Eur J 22:6218–6222 Deng HP, Fan XZ, Chen ZH, Xu QH, Wu J (2017) Photoinduced nickel-catalyzed chemo-and regioselective hydroalkylation of internal alkynes with ether and amide α-hetero C(sp3)-H bonds. J Am Chem Soc 139:13579–13584 Dewanji A, Krach PE, Rueping M (2019) The dual role of benzophenone in visible-light/nickel photoredox-catalyzed C−H arylations: hydrogen-atom transfer and energy transfer. Angew Chem Int Ed 58:3566–3570 Franchino A, Rinaldi A, Dixon DJ (2017) α-Alkylation of ketimines using visible light photoredox catalysis. RSC Adv 7:43655–43659 Gao X et al (2013) Combining visible light catalysis and transition metal catalysis for the alkylation of secondary amines. Adv Synth Catal 355:2158–2164 Gao XW et al (2015) Visible light catalysis assisted site-specific functionalization of amino acid derivatives by C-H bond activation without oxidant: cross-coupling hydrogen evolution reaction. ACS Catal 5:2391–2396 Ghosh T, Maity P, Ranu BC (2018) Cobalt-catalyzed remote C-4 functionalization of 8aminoquinoline amides with ethers via C-H activation under visible-light irradiation. Access to α-heteroarylated ether derivatives. Org Lett 20:1011–1014 Go SY, Lee GS, Hong SH (2018) Highly regioselective and E/ Z-selective hydroalkylation of Ynone, Ynoate, and Ynamide via photoredox mediated Ni/Ir dual catalysis. Org Lett 20:4691–4694

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

143

Gui YY et al (2017a) Coupling of C(sp3)-H bonds with C(sp2)-O electrophiles: mild, general and selective. Chem Commun 53:1192–1195 Gui YY, Chen XW, Zhou WJ, Yu DG (2017b) Arylation of amide and urea C(sp 3)-H bonds with aryl tosylates generated in situ from phenols. Synlett 28:2581–2586 Gui YY et al (2018) Arylation of aniline C(sp3)−H bonds with phenols via an in situ activation strategy. Asian J Org Chem 7:537–541 Heitz DR, Tellis JC, Molander GA (2016) Photochemical nickel-catalyzed C-H arylation: synthetic scope and mechanistic investigations. J Am Chem Soc 138:12715–12718 Huang L, Rueping M (2018) Direct cross-coupling of allylic C(sp 3)−H bonds with aryl-and vinylbromides by combined nickel and visible-light catalysis. Angew Chem Int Ed 57:10333– 10337 Jha N, Khot NP, Kapur M (2021) Transition-Metal-Catalyzed C−H bond functionalization of Arenes/Heteroarenes via tandem C−H activation and subsequent carbene migratory insertion strategy. Chem Rec 21:4088–4122 Joe CL, Doyle AG (2016) Direct acylation of C(sp 3)−H bonds enabled by nickel and photoredox catalysis. Angew Chem Int Ed 55:4040–4043 Kalsi D, Dutta S, Barsu N, Rueping M, Sundararaju B (2018) Room-temperature C-H bond functionalization by merging cobalt and photoredox catalysis. ACS Catal 8:8115–8120 Kalsi D et al (2019) C-H and N-H bond annulation of aryl amides with unactivated olefins by merging cobalt(III) and photoredox catalysis. Chem Commun 55:11626–11629 Kalyani D, McMurtrey KB, Neufeldt SR, Sanford MS (2011) Room-temperature C-H arylation: merger of Pd-catalyzed C-H functionalization and visible-light photocatalysis. J Am Chem Soc 133:18566–18569 Kato Y, Yoshino T, Matsunaga S (2023) Iron/photosensitizer-catalyzed directed C-H activation triggered by the formation of an iron metallacycle. ACS Catal 13:4552–4559 Kharasch MS, Fields EK (1941) Factors determining the course and mechanisms of Grignard reactions. IV. The effect of metallic halides on the reaction of aryl Grignard reagents and organic halides1 . J Am Chem Soc 63:2316–2320 Khot NP, Deo NK, Kapur M (2022) A switch to vinylogous reactivity of vinyl diazo esters for the C-H allylation of benzamides by merging cobalt and photoredox catalysis. Chem Commun 58:13967–13970 Krach PE, Dewanji A, Yuan T, Rueping M (2020) Synthesis of unsymmetrical ketones by applying visible-light benzophenone/nickel dual catalysis for direct benzylic acylation. Chem Commun 56:6082–6085 Le C, Liang Y, Evans RW, Li X, MacMillan DWC (2017) Selective sp3 C-H alkylation via polaritymatch-based cross-coupling. Nature 547:79–83 Lee BJ, DeGlopper KS, Yoon TP (2020) Site-selective alkoxylation of benzylic C−H bonds by photoredox catalysis. Angew Chem Int Ed 59:197–202 Li CJ (2009) Cross-dehydrogenative coupling (CDC): exploring C-C bond formations beyond functional group transformations. Acc Chem Res 42:335–344 Li T et al (2021a) Metallaphotoredox-catalyzed C-H activation: regio-selective annulation of allenes with benzamide. Org Chem Front 8:928–935 Li J, Huang CY, Han JT, Li CJ (2021b) Development of a quinolinium/cobaloxime dual photocatalytic system for oxidative C-C cross-couplings via H2Release. ACS Catal 11:14148–14158 Mandal R et al (2021) Room-temperature C-H bond alkynylation by merging cobalt and photocatalysts. Chem Commun 57:12167–12170 Minisci F, Citterio A, Vismara E, Giordano C, (1985) Polar effects in free-radical reactions. New synthetic developments in the functionalization of heteroaromatic bases by nucleophilic radicals. Tetrahedron 41:4157–4170 (1985) Moselage M, Li J, Ackermann L (2016) Cobalt-catalyzed C-H Activation. ACS Catal 6:498−525 Nakafuku KM et al (2020) Enantioselective radical C-H amination for the synthesis of β-amino alcohols. Nat Chem 12:697–704

144

S. C. Ghosh et al.

Narayanam JMR, Stephenson CRJ (2011) Visible light photoredox catalysis: applications in organic synthesis. Chem Soc Rev 40:102–113 Nielsen MK et al (2017) Mild, redox-neutral formylation of aryl chlorides through the photocatalytic generation of chlorine radicals. Angew Chem Int Ed 56:7191–7194 Niu L et al (2017) Photo-induced oxidant-free oxidative C-H/N-H cross-coupling between arenes and azoles. Nat Commun 8 Ouyang XH et al (2019) Intermolecular dialkylation of alkenes with two distinct C(sp 3 ) H bonds enabled by synergistic photoredox catalysis and iron catalysis. Sci Adv 5 Peng X et al (2023) A catalytic alkylation of ketones via sp3 C-H bond activation. J Org Chem 88:6333–6346 Perepichka I, Kundu S, Hearne Z, Li CJ (2015) Efficient merging of copper and photoredox catalysis for the asymmetric cross-dehydrogenative-coupling of alkynes and tetrahydroisoquinolines. Org Biomol Chem 13:447–451 Prier CK, Rankic DA, MacMillan DWC (2013) Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis. Chem Rev 113:5322–5363. https://doi.org/ 10.1021/cr300503r Rand AW et al (2020) Dual catalytic platform for enabling sp3 α C-H arylation and alkylation of benzamides. ACS Catal 10:4671–4676 Romero NA, Nicewicz DA (2016) Organic photoredox catalysis. Chem Rev 116:10075–10166. https://doi.org/10.1021/acs.chemrev.6b00057 Rueping M et al (2012) Dual catalysis: combination of photocatalytic aerobic oxidation and metal catalyzed alkynylation reactions—C-C bond formation using visible light. Chem–Eur J 18:5170–5174 Sarver PJ et al (2020) The merger of decatungstate and copper catalysis to enable aliphatic C(sp3)–H trifluoromethylation. Nat Chem 12:459–467 Schwarz JL, Schäfers F, Tlahuext-Aca A, Lückemeier L, Glorius F (2018) Diastereoselective allylation of aldehydes by dual photoredox and chromium catalysis. J Am Chem Soc 140:12705–12709 Sen C, Sarvaiya B, Sarkar S, Ghosh SC (2020) Room-temperature synthesis of isoindolone spirosuccinimides: merger of visible-light photocatalysis and cobalt-catalyzed C-H activation. J Org Chem 85:15287–15304 Shaw MH, Shurtleff VW, Terrett JA, Cuthbertson JD, MacMillan DWC (2016b) Native functionality in triple catalytic cross-coupling: sp3 C-H bonds as latent nucleophiles. Science 1979(352):1304–1308 Shaw MH, Twilton J, MacMillan DWC (2016) Photoredox catalysis in organic chemistry. J Org Chem 81:6898–6926. https://doi.org/10.1021/acs.joc.6b01449 Shen Y, Gu Y, Martin R (2018) Sp 3 C-H arylation and alkylation enabled by the synergy of triplet excited ketones and nickel catalysts. J Am Chem Soc 140:12200–12209 Shields BJ, Doyle AG (2016) Direct C(sp3)-H cross coupling enabled by catalytic generation of chlorine radicals. J Am Chem Soc 138:12719–12722 Shu X, Huan L, Huang Q, Huo H (2020) Direct enantioselective C(sp3)-H acylation for the synthesis of α-amino ketones. J Am Chem Soc 142:19058–19064 Si X, Zhang L, Hashmi ASK (2019) Benzaldehyde-and nickel-catalyzed photoredox C(sp3)-H alkylation/arylation with amides and thioethers. Org Lett 21:6329–6332 Skubi KL, Blum TR Yoon TP (2016) Dual catalysis strategies in photochemical synthesis. Chem Rev 116:10035–10074. https://doi.org/10.1021/acs.chemrev.6b00018 Sun Z, Kumagai N, Shibasaki M (2017) Photocatalytic α-acylation of ethers. Org Lett 19:3727–3730 Tanabe S, Mitsunuma H, Kanai M (2020) Catalytic allylation of aldehydes using unactivated alkenes. J Am Chem Soc 142:12374–12381 Thullen SM, Rovis T (2017) A mild hydroaminoalkylation of conjugated dienes using a unified cobalt and photoredox catalytic system. J Am Chem Soc 139:15504–15508 Tian C, Wang Q, Wang X, An G, Li G (2019) Visible-light mediated ortho-trifluoromethylation of aniline derivatives. J Org Chem 84:14241–14247

4 The Merger of Photoredox Catalysis and 3d Transition Metal-Catalyzed …

145

Twilton J et al (2018) Selective hydrogen atom abstraction through induced bond polarization: direct α-arylation of alcohols through photoredox, HAT, and nickel catalysis. Angew Chem Int Ed 57:5369–5373 Twilton J et al (2017) The merger of transition metal and photocatalysis. Nat Rev Chem 1. https:// doi.org/10.1038/s41570-017-0052 Vasilopoulos A, Krska SW, Stahl SS (2021) C(sp 3)–H methylation enabled by peroxide photosensitization and Ni-mediated radical coupling. Science 1979(372):398–403 Wang J et al (2021) Visible-light promoted α-alkylation of glycine derivatives with alkyl boronic acids. Chem Commun 57:1959–1962 Wu CJ et al (2016) An oxidant-free strategy for indole synthesis via intramolecular C-C bond construction under visible light irradiation: cross-coupling hydrogen evolution reaction. ACS Catal 6:4635–4639 Xu B, Tambar UK (2019) Remote allylation of unactivated C(sp3)-H bonds triggered by photogenerated amidyl radicals. ACS Catal 9:4627–4631 Xu Z, Hu Y, Wang L, Sun M, Li P (2021) Merging cobalt and photoredox catalysis for the C8-H alkoxylation of 1-naphthylamine derivatives with alcohols. Org Biomol Chem 19:10112–10119 Xuan J, Xiao WJ (2012) Visible-light photoredox catalysis. Angew Chem-Int Ed 51:6828–6838. https://doi.org/10.1002/anie.201200223 Yahata K et al (2020) Coupling reaction between aldehydes and non-activated hydrocarbons via the reductive radical-polar crossover pathway. Org Lett 22:1199–1203 Yang F, Koeller J, Ackermann L (2016) Photoinduced copper-catalyzed C−H arylation at room temperature. Angew Chem Int Ed 55:4759–4762 Yang Q et al (2017) Visible-light-promoted asymmetric cross-dehydrogenative coupling of tertiary amines to ketones by synergistic multiple catalysis. Angew Chem Int Ed 56:3694–3698 Yang XL et al (2018) Oxidative cyclization synthesis of tetrahydroquinolines and reductive hydrogenation of maleimides under redox-neutral conditions. Org Lett 20:2916–2920 Yang X, Xie Z, Li Y, Zhang Y (2020) Enantioselective aerobic oxidative cross-dehydrogenative coupling of glycine derivatives with ketones and aldehydes: via cooperative photoredox catalysis and organocatalysis. Chem Sci 11:4741–4746 Yerien DE, Postigo A, Baroncini M, Barata-Vallejo S (2021) Bioinspired photocatalysed C-H fluoroalkylation of arenes in water promoted by native vitamin B12and rose Bengal. Green Chem 23:8147–8153 Yeung CS, Dong VM (2011) Catalytic dehydrogenative cross-coupling: forming carbon-carbon bonds by oxidizing two carbon-hydrogen bonds. Chem Rev 111:1215–1292. https://doi.org/10. 1021/cr100280d Yi H et al (2017) Photocatalytic dehydrogenative cross-coupling of alkenes with alcohols or azoles without external oxidant. Angew Chem Int Ed 56:1120–1124 Zhang X, MacMillan DWC (2017) Direct aldehyde C-H arylation and alkylation via the combination of nickel, hydrogen atom transfer, and photoredox catalysis. J Am Chem Soc 139:11353–11356 Zhang G et al (2015) External oxidant-free oxidative cross-coupling: a photoredox cobalt-catalyzed aromatic C-H thiolation for constructing C-S bonds. J Am Chem Soc 137:9273–9280 Zhang M, Ruzi R, Li N, Xie J, Zhu C (2018) Photoredox and cobalt co-catalyzed C(sp2)-H functionalization/C-O bond formation for synthesis of lactones under oxidant-and acceptor-free conditions. Org Chem Front 5:749–752 Zhang Y et al (2020) Visible light-induced oxidative cross dehydrogenative coupling of glycine esters with β-Naphthols: access to 1,3-benzoxazines. J Org Chem 85:6261–6270 Zhao QQ, Hu XQ, Yang MN, Chen JR, Xiao WJ (2016) A visible-light photocatalytic N-radical cascade of hydrazones for the synthesis of dihydropyrazole-fused benzosultams. Chem Commun 52:12749–12752 Zheng YW et al (2016) Photocatalytic hydrogen-evolution cross-couplings: benzene C-H amination and hydroxylation. J Am Chem Soc 138:10080–10083 Zhu Z et al (2021) Visible-light-induced aerobic oxidative C sp3 −H functionalization of glycine derivatives for 2-substituted benzoxazoles. Adv Synth Catal 363:2568–2572 Zuo Z et al (2014) Merging photoredox with nickel catalysis: coupling of α-carboxyl sp3 -carbons with aryl halides. Science 1979(345):437–440

Chapter 5

Photocatalysis: Application in Drugs and Analogues Synthesis Shikha Sharma

5.1 Introduction Recent advances in photoredox catalysis have made it a safe and effective way to produce radicals. This technique takes advantage of the unique photophysical properties of transition metal complexes and organic dyes (Nicewicz and MacMillan 2008; Yoon et al. 2010; Narayanam and Stephenson 2011). The rates of reactions in photocatalysed processes are entirely governed by the intensity of light, providing precise control over radical generation, making it an attractive tool for synthetic chemists. Recent reviews have highlighted the potential of light-driven catalysis in numerous synthetic transformations (Romero and Nicewicz 2016), encompassing the intricate structures found in natural products (Kärkäs et al. 2016) and certain pharmaceuticals (Douglas et al. 2016). This chapter aims to organise and present instances of employing visible-light photoredox catalysis in the creation of intricate bond formations, especially those essential for the synthesis of pharmaceuticals and analogues, with a focus on literature from the past five years. The focus lies on catalysing the creation of fresh carbon–carbon, carbon–nitrogen, or carbon– oxygen bonds. Iridium- and ruthenium-based complexes are the most commonly used photocatalysts for this purpose. However, a few examples utilising highly desirable metal-free photocatalysts, such as Eosin Y, are also covered.

S. Sharma (B) Department of Pharmaceutical Science, Lords University, Chikani, Alwar, Rajasthan 301028, India e-mail: [email protected] 147

148

S. Sharma

5.1.1 Functionalization Involves the Formation of Carbon–Carbon Bonds In drug development, the formation of C-H bonds stands as a crucial technique, in the past time potent oxidants and elevated heat levels to generate requisite radical species. However, our study introduces a novel method for the direct methyl-, ethyl-, and cyclopropylation of various physiologically active heterocycles. This breakthrough is achieved through the utilisation of stable organic peroxides activated by Photonic oxidative-reductive catalysis. This approach emerges as a valuable tool in drug discovery due to its distinctive tolerability, gentle reaction conditions, and straightforward procedural steps. In case of C-H functionalization in substituted indoles, pyrroles, and furans using diethyl bromomalonate for direct intermolecular conversation (Furst et al. 2010). This strategy depends on the visible light-triggered reductive quenching route of Ru(bpy)3 Cl2 (Scheme 5.1). The method shows exceptional yields and regioselectivity. Important features include working in normal conditions, carrying at regular temperatures, using a small amount of catalyst, being able to handle different functional groups well, and showing high selectivity in chemical reactions. Utilising visible-light photoredox catalysis facilitated the construction of a carbon–carbon bond during the total synthesis of gliocladine, an intermediate in the synthesis of hexahydropyrroloindoline alkaloids derived from two tryptophan molecules (Furst et al. 2011) (Scheme 5.2). Trifluoromethylated was used for variations of heteroarenes, like pyrroles, furans, thiophenes, and thiazoles, as well as heteroaromatics such as pyrazine, pyrimidine, pyridine, and pyrone, consistently yield good to excellent results without the necessity for pre-activation of the aryl ring. The introduction of highly electron-withdrawing trifluoromethyl groups. Researchers have discovered gentle methods that allow for making changes to a molecule at a later stage in the synthesis process. These methods R

R

CO2Et H

CO2Et

Ru(bpy)3Cl2

+Br

blue LED

X

CO2Et

X

CO2Et

Scheme 5.1 Intermolecular C-H functionalization of electron-rich heterocycles with malonates NH

COR

Br N N

H

Ru(bpy)3Cl2 R'

+ R

N H

CHO

HN

H R'

blue LEDs

R

Scheme 5.2 Coupling of pyrrolidones with indolones

CO2Me

COR N N R

H

N R

N Cbz

Boc

H Intermediate in the synthesis of Gliocladin C (72%)

5 Photocatalysis: Application in Drugs and Analogues Synthesis

149 CF3

b.

A

Y

B

Ru(phen)Cl2

H

H

X

B

CF3

CF3

O

OMe

CF2SO2CI

26 W fluorescent light H

A

Y

X

CF3

OMe C

C

Alzheimer's drug precursor (94%)

Scheme 5.3 Radical trifluoromethylation of five- and six-membered heteroarenes

involve exposing the reaction mixture to light. Ru(phen)3 Cl2 in the presence of triflyl chloride (Scheme 5.3) (Nagib and MacMillan 2011). A series of reactions utilises ethyl 2-(3,4-dihydroisoquinolin-2(1H)-yl)acetates with various electron-deficient alkenes and alkynes. This sequence provides a fast and efficient pathway to pyrrolo[2,1-a]isoquinolines, as shown in (Scheme 5.4). This method introduces an innovative approach for directly and effectively synthesising central structures present in naturally occurring lamellarin alkaloids (Zou et al. 2011). A method has been devised as a metal-free option for creating bonds between aryl and heteroaryl compounds. This technique utilises visible light alongside a 1 mol % eosin Y catalyst. Through this photoredox process, it becomes possible to directly form aryl-heteroaryl bonds by arylating C–H bonds in heteroarenes using aryl diazonium salts. The study of this reaction’s applicability encompasses diverse aryl diazonium salts and heteroarenes (Hari et al. 2012a) (Scheme 5.5). N-aryltetrahydroisoquinoline and Michael acceptors were successfully coupled by a photoredox-catalysed procedure by employing Ru(bpy)3Cl2 or [Ir(ppy)2(dtbbpy)]PF6 in conjunction with 455 nm blue LED irradiation. This technique efficiently absorbs α-amino radicals produced by visible light. Products arise from O

Ru(bpy),Cl2

+

N H

H

H

O OEt

HO

H

N

O

N

OEt

visible light

Ar

O

N

O

Ar

Scheme 5.4 Arylation of 5-membered N-heteroarenes using aryl diazonium salts

N2BF4

H

R +

Eosin Y 530 nm LED

R X

X

X= NBoc, O, S

Scheme 5.5 Pyrrole synthesis has been achieved using aryldiazonium salts and the metal-free photocatalyst Eosin Y under green light irradiation

150

S. Sharma R

R

Ar

+

X

R'

N

[Ir(ppy)2(dtbbpy)]PF6 R'

N

Ar

Blue LED

H

X Ph

O

Immunosupressant against IL-2, IL-10 and IFN-y (36%)

Scheme 5.6 Blue-light irradiation of [Ir(ppy)2 (dtbbpy)]PF6 with aryl tertiary amines generates α-amino radicals

conjugate addition in intermolecular processes, whereas intramolecular variations immediately lead to 5,6-dihydroindolo[2,1-a]tetrahydroisoquinolines through further dehydrogenation. These substances are important because they may act as immunosuppressive agents (Kohls et al. 2012) (Scheme 5.6). The coupling reaction of N-aryltetrahydroisoquinoline and Michael acceptors through a photoredox-catalysed process was successfully gained using either Ru(bpy)3Cl2 or [Ir(ppy)2(dtb-bpy)]PF6, in combination with irradiation at 455 nm from a blue LED. This method effectively used visible light-generated α-amino radicals and intermolecular reactions, products arise from conjugate addition, while intramolecular variations undergo further dehydrogenation, leading to the direct formation of 5,6-dihydroindolo[2,1-a]tetrahydroisoquinolines (Hari et al. 2012b). These compounds hold significance as potential immunosuppressive agents (Scheme 5.7). Revealed that photoredox catalysts aid in the visible light-mediated direct amination of sp3 C–H bonds in benzocyclic amines via α-aminoalkyl radicals. When carbon nucleophiles are included, the resultant N,N-acetals have shown efficacy in carbon– carbon bond formation processes. This process works well for late-stage C–H bond modification, which results in the production of C–C bonds (Miyake et al. 2012) (Scheme 5.8). EWG N2BF4

Eosin Y

R

+

EWG

GWE

OMe S

Meo

S

530 nm LED

SMe

EWG

R

Intermediate in the synthesis of raloxifene (70%) Current Opinion in Green and Sustainable Chemistry

Scheme 5.7 In the presence of a fluorescent bulb, aryldiazonium salts with electron-withdrawing groups react with N-heteroarenes, such as 4-substituted pyridines

Boc

or N Ar

H

N Ar

H

+

Boc

[Ir(ppy) 2 (dtbbpy)]BF4

N

14 W white LED

N Boc

Boc N Ar

N NHBoc

or

N

N NHBoc

Ar

Scheme 5.8 Direct α-C–H amination of 1,2,3,4-tetrahydroquinolines and indolines, resulting in the formation of N,N-acetals

5 Photocatalysis: Application in Drugs and Analogues Synthesis

151 O

N N Cl

R

H

+

N

R

N H

N

O

R

Ir(ppy)3, imidazole R''

N H

blue LEDs

R

N

S

R''

X = O, S

N

Nizatidine precursor (69%)

Scheme 5.9 The optimal reaction conditions use Ir(ppy)3 as the photocatalyst and imidazole as the base in an argon atmosphere, with blue LED irradiation

The synthesis of tertiary aliphatic amines and their subsequent coupling with several 2-chloroazole derivatives. Tris-fac-Ir(ppy)3 catalyses the process at convenient and mild conditions when paired with blue light irradiation. Remarkably, the majority of couplings show outstanding regioselectivity. The reaction exhibits tolerance towards several functional groups, offering a fast method of accessing α-azole carbinamines frequently found in peptides that have undergone post-translational modification (Singh et al. 2013) (Scheme 5.9). Reported photocatalysis mediated by visible light for a difficult bond formation inside a complicated pharmaceutical target. N-methylmorpholine and an unfunctionalized pyridazine were able to be directly coupled through reaction optimisation, producing good yield and selectivity outcomes. Through crystallisation, the product was separated and found to be extremely pure. This reaction is a useful tool for medicinal chemistry because it also makes efficient use of other commercially available N-methyl substituted tertiary amines to synthesise a variety of analogues. Moreover, this investigation revealed a number of fascinating photoredox reactions, such as an iminium ion reduction driven by visible light, the functionalization of C-H bonds alpha to amides, and a formal methylation reaction through C–N bond breaking (Douglas et al. 2014) (Scheme 5.10). Visible-light-mediated photoredox catalysis has successfully enabled the direct decarboxylative arylation of α-amino acids. This approach provides a quick route to common benzylic amine structures using readily available biomass, particularly α-amino acid precursors. The method demonstrates substantial versatility in terms of both the amino acid and arene components, expanding the scope of potential substrates (Zuo and MacMillan 2014) (Scheme 5.11). R O

N H H 3C

N

Cl

N

+

CH3

N

F

N R

Cl O

Ir(ppy)3 R'

R

N N

1 W white LED Cl

N

N

CH3

N

Cl O

F

Cl

N

CH3

N

Cl O

F

JAK2 inhibitor LY2784544 (56%)

Scheme 5.10 N-methyl tertiary amines have been utilized to introduce aminomethyl radicals into various non-functionalized pyridazine scaffold complexes

152

S. Sharma Y CN

X

O

Ir[p-F(t-Bu)-ppy]3

R

+

OH

Y

R

26 W fluorescent light NHBoc

X

NHBoc

Scheme 5.11 Moreover, α-oxygenated acids treated with this methodology yield heteroaryl ethers in high yields Me O

H

+

Het

O O

O

or R

X

R O

O

N

Ir (III) photocatalyst or

Het O

450 nm hv TFA/ACN

Het

O

N

O

X

X

Me

R = Me, Et

OH

O

Camptothecin (77%)

Scheme 5.12 Mild conditions using cyclometalated Ir(III) catalysts, such as [Ir(dF-CF3 ppy)2 (dtbpy)]PF6 or [Ir(ppy)2 (dtbpy)]PF6 , along with blue light irradiation

Application of cyclometalated catalysts, such as [Ir(dF-CF3-ppy)2-(dtbpy)]PF6 or [Ir(ppy)2(dtbpy)], in combination with blue light. Findings showed that when the photocatalyst and tert-butyl peracetic acid, tert-amyl peracetate, or biscyclopropanecarbonyl peroxide (serving as sources of methyl, ethyl, or cyclopropyl radicals, respectively) were exposed to blue light, the anticancer medication camptothecin was synthesised (DiRocco et al. 2014) (Scheme 5.12). Through photoredox organocatalysis, benzyl ethers have been directly functionalized on the C–H bond and arylated. In the presence of ambient light, the efficient combination of a thiol catalyst with a commercially available iridium photoredox catalyst yields good to exceptional yields of benzylic arylation products. This methodology’s usefulness is further illustrated by the formation of a single regioisomer through direct arylation of 2,5-dihydrofuran (Qvortrup et al. 2014) (Scheme 5.13). Highly efficient and environmentally friendly visible light-induced “radical-type” coupling method has been developed for N-heteroarenes with aryldiazonium salts. The reaction, occurring at room temperature, utilises [Ru(bpy)3 ]Cl2 ·6 H2 O as a photosensitizer and a standard household light bulb. Various substituted pyridines are effective substrates, yielding exclusively monosubstituted products with distinct

O Ar

Ir(ppy)3, octanal

+ H

O

CN

R

Y X

26 W fluorescent light

R Y

Ar

O

CN

X

Dihydrofuran derivative (82%)

Scheme 5.13 N-methyl tertiary amines have been utilized to introduce aminomethyl radicals into various non-functionalized pyridazine-based scaffolds

5 Photocatalysis: Application in Drugs and Analogues Synthesis

153 O

N2BF4

R

+

R'

Ru(bpy)3Cl2 N

5 W Fluorescent light

H

N

R'

O

R

N

N

N

N

Antagonists of human A2B adenosine receptors (60-70%)

Scheme 5.14 In the presence of aryldiazonium salts with electron-withdrawing groups and Nheteroarenes such as 4-substituted pyridines, 2-arylated products

O

R

Cl

Ru(phen)3cl2

R'

+

R

2

R''

Cl

S

CF3

CF3

R

visible light

O

R''

Scheme 5.15 Visible-light irradiation of photocatalysts

regioselectivities. Many chemicals, such as xanthenes, thiazole, pyrazine, and pyridazine, are compatible with this arylation method when aqueous formic acid is utilised as the solvent. The broad substrate scope, mild conditions, and the use of water as a solvent make this method practical for synthesising compounds with aryl-heteroaryl motifs (Xue et al. 2014) (Scheme 5.14). A method for adding a chlorotrifluoromethyl group to adjacent carbon atoms in alkenes using light is discussed. With the help of a catalyst, Ru(Phen)3Cl2 , CF3 SO2 Cl is used to generate CF3 radicals and chloride ions when exposed to visible light. This process successfully transforms different types of alkenes, both at the end and in the middle of the molecule, into compounds with added chlorotrifluoromethyl groups. The method is versatile enough to be applied to biologically active compounds, making it suitable for modifying drugs during late-stage development (Oh et al. 2014) (Scheme 5.15). Carboxylic acids have been effectively used directly as a traceless activating group for radical Michael additions by visible-light-mediated photoredox catalysis. Without requiring organometallic activation or propagation, a wide range of carboxylic acids, including hydrocarbon-substituted, α-oxy, and α-amino acids, can be photo-inducedly oxidised to generate Michael donors. It becomes a versatile platform for CO2 -extrusion as a result. The new conjugate addition technique is compatible with a large class of Michael acceptors. The three-step synthesis of pregabalin, a medication marketed by Pfizer under the Lyrica brand, offers more proof of the technology’s effectiveness (Chu et al. 2014) (Scheme 5.16). NHBoc Y Z

[Ir(dF(CF3)ppy)2(dtbpy)]PF6

O +

R

OH X

EWG

26 W fluorescent light

Y

Scheme 5.16 Michael addition of carboxylic acid

CO2Me

EWG

R X

Z

Me

Me

CO2Me

Intermediate in the synthesis of (±)pregabalin (96%)

154

S. Sharma Cl H

H

Ir(dF(CF3)ppy)2(bpy)PF6 N

BF3K

PG

+

R

blue LEDs or solar light

R

N PG

Boc

H N

CO2Et CO2Et

Intermediate in the synthesis of (±)baclofen (89%)

Scheme 5.17 Blue LEDs or solar light irradiation of [Ir(dF(CF3 ) ppy)2 (bpy)]PF6 , allows synthesizing primary amines with good yields

N

9-mesityl-10-methyl-acridinium +

GWE

R

H N

F

R'

H N

EWG

blue LED

R'

EWG

EWG CO2Me

CO2Me

Intermediate in the synthesis of a HMG-CoA reductase inhibitor (42%)

Scheme 5.18 Tetrasubstituted pyrrole, a key intermediate in the synthesis of a HMGCoA reductase inhibitor

A novel photocatalytic hydroaminomethylation of olefins using N-protected aminomethyltrifluoroborates has been established. This method offers a fresh approach for incorporating a primary aminomethyl group onto electron-deficient C–C bonds. The reaction serves as a straightforward entry point to synthetically valuable γ-aminobutyric acid (GABA) derivatives, including compounds like baclofen (Miyazawa et al. 2014) (Scheme 5.17). A visible light-induced photocatalytic formal [3 + 2] cycloaddition of 2H-azirines with alkynes has been successfully accomplished using organic dye photocatalysts. This process offers a streamlined route to highly functionalized pyrroles in good yields and has been utilised in the synthesis of drug analogues. The initial attempt at photocascade catalysis, combining energy transfer with redox-neutral reactions, proved to be successful (Xuan et al. 2014) (Scheme 5.18). Researchers have developed a method to add nitrogen atoms to aromatic compounds at room temperature using visible light. A crucial improvement in this technique involves using N-acyloxyphthalimides as starting materials to create nitrogen-based radicals. The method works with a wide range of compounds, even allowing selective addition of nitrogen to specific positions in pyridine derivatives. The proposed mechanism involves a process called radical aromatic substitution (Allen et al. 2014) (Scheme 5.19). O N O

O OCOCF3

Ar

H

Ir(ppy)3

N

visible LED

O

Scheme 5.19 Nacyloxyphthalimides in the presence of Ir(ppy)3 and visible light

Ar

5 Photocatalysis: Application in Drugs and Analogues Synthesis

155

Researchers have successfully developed a method for directly adding aryl groups to α-oxo acids using a combination of visible-light-mediated photoredox and nickel catalysis. This approach provides a quick way to create aryl and alkyl ketone structures from basic α-oxo acid starting materials through the formation of acyl radicals. The method is versatile, allowing for a wide range of α-oxo acids and arene coupling partners. Additionally, this mild decarboxylative arylation can be applied to efficiently produce medicinal agents, as illustrated by the rapid synthesis of fenofibrate (Chu et al. 2015) (Scheme 5.20). A study demonstrates that molecular fragments, easily coupled through a straightforward, in situ RO–C OR bond-forming reaction, can undergo metal insertion–decarboxylation–recombination under metallaphotoredox catalysis to generate Csp2–Csp3 bonds. In this context, the conversion of various mixed anhydrides (formed in situ from carboxylic acids and acyl chlorides) to fragment-coupled ketones is achieved with good to high yields. Additionally, a three-step synthesis of the medicinal agent edivoxetine is detailed using this novel decarboxylation–recombination protocol (Le and MacMillan 2015) (Scheme 5.21). A radical Smiles rearrangement mediated by visible light has been developed to overcome the synthetic challenges in creating the gem-difluoro group found in an opioid receptor-like 1 (ORL-1) antagonist currently under development for treating depression and/or obesity. This method facilitates the direct and efficient incorporation of the difluoroethanol motif into various aryl and heteroaryl systems, providing a novel disconnection for synthesising this versatile moiety. When applied to the target compound, the photochemical step could be performed on a 15 g scale using industrially relevant [Ru(bpy)3Cl2] catalyst loadings of 0.01 mol %. This transformation is a key component of a five-step route to the antagonist, offering advantages over the existing synthetic sequence and highlighting a strategic benefit of photocatalysis in this specific case (Douglas et al. 2015) (Scheme 5.22). The effective α-allylation of amines was achieved using the combination of palladium catalysis and visible-light photoredox catalysis. This dual catalysis technique

O

R HO

X

Ir[(dF(CF3)ppy)2(dtbbpy)]PF6 NiCl2dtbbpy R'

+

O

O R'

34 W blue LED

O

A

O

A

R

O O

Cl

Fenofibrate (71 % )

Scheme 5.20 γ-Moreover, α-oxygenated acids subjected to this methodology provide heteroaryl ethers with high yields O O Cl

OH X

R

+ O

Ir[dF(OMe)ppy]2 (dtbbpy)PF6 NiCl2'glyme

R X

O

blue LED O

X = N, O

Scheme 5.21 Anhydrides to ketones upon decarboxylation

O

N Boc

Intermediate in the synthesis of Edivoxetine (68%)

156

S. Sharma F

F

OH O

O

Ru(bpy)3Cl2 Br

S

Ar

O

F

F

Cl OH

Ar

Blue LED

S

Intermediate in the synthesis of an ORL-1 antagonist (3 steps, 28% overall yield)

F

F

Scheme 5.22 Visible light driven radical rearrangement

is redox-neutral since it generated allyl radicals catalytically from the matching πallylpalladium intermediate without the requirement for additional metal reducing reagents. Via radical cross-coupling, amines underwent modest reaction conditions to give a wide range of allylation products. Moreover, the formal synthesis of derivatives of 8-oxoprotoberberine was carried out using this transition, demonstrating possible anticancer characteristics (Xuan et al. 2015) (Scheme 5.23). Enamine catalysis in conjunction with photoredox catalysis has made it possible to produce an enantioselective α-cyanoalkylation of aldehydes. Through the coupling of two extremely adaptable yet orthogonal functions, this synergistic catalysis procedure enables the rapid diversification of the oxonitrile products to a wide range of derivatives and heterocycles with medical significance. Additionally, the complete synthesis of the lignan natural product (−)-bursehernin has been carried out using this technology (Welin et al. 2015) (Scheme 5.24). (±)-Tetrabenazine was created using substances that were readily available in the market in six steps. The Baylis–Hillman and aza–Michael reactions were utilised to quickly build the essential cyclization substrate. Through visible light photocatalysis, the last ring was annulated. The oxidation of a tertiary amine fueled the creation of carbon–carbon bonds. The photoredox cyclization outcome was largely dependent on the solvent used. While methanol produced a mixed ketal, acetonitrile/water (10:1)

R N

Ar

R

Pd(PPh3)4 [Ir(ppy)2(dtbbpy)]PF

X

Ar

+

R'

R'

OMe

N

R'

N

OMe

3 W Blue LED

H

R

N O

X = Br, OH, OAc, OP(O)(OEt)2 Intermediate in the synthesis of 8oxoprotoberberine derivatives (78%)

Scheme 5.23 A dual palladium and [Ir(ppy)2(dtbbpy)]PF6 photoredox catalysis has been used for performing redox-neutral a-allylation of amines O NOH O

O

Y H

H

or

N

Ir(ppy)3 or Ru(bpy)3Cl2

+ Br

X

R

Bn

26 W fluorescent light N H

H

Y

O H

H X

R

X = Ar, CN

Scheme 5.24 Enantioselective α-alkylation of aldehydes

CN O

N O Intermediate in the synthesis of an angiogenesis inhibitor (82% yield, 93% ee)

Intermediate in the synthesis of (-) - bursehernin (94% yield, 94% ee)

5 Photocatalysis: Application in Drugs and Analogues Synthesis

157

gave rise to a more fast and direct cyclization of (±)-tetrabenazine (Orgren et al. 2015) (Scheme 5.25). An extensive approach has been successfully used for biologically active compounds, including as an analogue of vitamin P (85% yield), a precursor to an Alzheimer’s medication, and a CF3-uracil derivative with antiviral and cancertreating capabilities (92% yield). Furthermore, mixes are produced by trifluoromethylating ibuprofen, lidocaine, or Lipitor (a statin that lowers cholesterol), producing 74–78%. The resulting isomers are then separated, allowing for quick access to analogues in the late-stage synthesis of lead compounds. Using a unique visible light photoredox approach for indoline oxidation, elbasvir, a powerful NS5A antagonist for treating chronic hepatitis C, is synthesised. By using this method, the hemiaminal stereocenter is not epimerized. To be more precise, when Ir[(dF(CF3 )ppy)2 (dtbbpy)]PF6 is exposed to radiation, 85% of the indoline moiety may be extracted with a 99.8% yield when tert-butylperbenzoate is used as the terminal oxidant (Yayla et al. 2016) (Scheme 5.26). A straightforward intramolecular cyclization of benzimidazole to 2-amino benzimidazole hybrid, mediated by visible light. The method that has been revealed is a quick and easy way to create benzimidazole-amine hybrids using readily accessible substituted cyclic and acyclic amines and benzimidazole in a clean environment with catalyst tris(2,2-bipyridine)ruthenium(II) chloride. Without a doubt, this approach provides an easy and uncomplicated strategy to create environmentally acceptable benzimidazole–amine hybrid compounds. Under solvent-free conditions, the process demonstrated low catalyst loading and cost-effective intermediates of product yield. Industrial research places a great deal of weight on the solvent-free approach. This new green method is far more efficient and has a larger scope than the previous ones (Siddiqui et al. 2016) (Scheme 5.27). The synthesis of isochromanones and isochromenones using visible-light RuII photoredox Meerwein is described, beginning with diazonium salts of variously OMe OMe

H

Ru(bpy)3Cl2 455 nm LED

N

N

OMe

OMe H O

(+-)-tetrabenazine (57%)

OTIPS

Scheme 5.25 Annulation of tertiary alkyl benzyl amine to synthesis Br

H Br

H Br

N Ph

Ir[(dF(CF3)ppy)2(dtbbpy)]PF6 tert-butylperbenzoate

O

Scheme 5.26 Dehydrogenation

Br

N

blue LED Ph

O

Intermediate in the synthesis of Elbasvir (85%, 99.8% ee)

158

S. Sharma

R H

+

N

N

N

or

CH3 R

Ir(ppy)3 or Ru(bpy)3Cl2

H

H

OBs

Bs

R N

white LED

R

Bs N

NHAc

Meo

Bs

N N

CH3

N

R''

CH3

N

R'

R'

R"

H

N

or

Me

indole melatonin derivative (97%)

Bs = Benzenesulfon

Scheme 5.27 C-H amination of (hetero)arenes from hydroxylamine derivatives or amines

substituted anthranilic acids and alkenes. This methodology has facilitated the dependable and effective extraction of structures included in numerous physiologically active compounds or employed in materials science (Crespi et al. 2017) (Scheme 5.28). Functionalization Through Carbon–Nitrogen Bond Formation N-producing 1,2,3,4-tetrahydroquinolines and indolines can be directly aminated, which is a helpful method for preparing uses of photoredox catalysts in the direct sp3 C–H amination of benzocyclic amines via α-aminoalkyl radicals under visible light. The N, N-acetals that were synthesised were also effectively used in carbon–carbon bond formation processes involving carbon nucleophiles. The process works well for late-stage C–H bond to C–C bond modifications (Miyake et al. 2012) (Scheme 5.29). The invention of N-acyloxyphthalimides as precursors to nitrogen-based radical intermediates for these transformations represents a major breakthrough in this work. A variety of substrates are offered, such as pyridine derivatives that are selectively meta-aminated. A mechanism of radical aromatic substitution is suggested. This work describes a photocatalysed room temperature visible light approach for arene and heteroarene C–H amination (Allen et al. 2014) (Scheme 5.30). It has been possible to establish a redox neutral direct C–H amidation of heteroarenes at room temperature. The readily available hydroxylamine derivatives have been used as adjustable sources of nitrogen. A single-electron transfer channel without a guiding group that was stimulated by visible light allowed for these events to occur. A wide range of heteroarenes, including furans, pyrroles, and indoles, could R

R

N2BF4

Ru(bpy)3Cl2

+ R'

OH

R'

R

O

455 nm LED O

O

Scheme 5.28 Cyclization of o-phenolic amidines or N-substituted-2-hydroxyphenylthioureas to 2-aminobenzoxazoles Boc

or N Ar

H

N Ar

H

+

Boc

[Ir(ppy)2(dtbbpy)]BF4 N

14 W white LED

N Boc

Boc N Ar

N NHBoc

or

N Ar

Scheme 5.29 C–H amination of benzocyclic amines with di-tert-butyl azodicarboxylate

N NHBoc

5 Photocatalysis: Application in Drugs and Analogues Synthesis

159

O

O

Ir(ppy)3 N

Ar

OCOCF3

H

N

visible LED

Ar

O

O

Scheme 5.30 C–H amination of (hetero)arenes from N-acyloxyphthalimides

undergo this amidation with yields as high as 98%. All of the products were separated as a single regioisomer, demonstrating the great regioselectivity of these reactions (Qin and Yu 2014) (Scheme 5.31). This article describes an effective visible light photocatalytic process that produces various biologically interesting dihydropyrazole-fused benzosultams in satisfactory yields. It also eliminates the need for external oxidants and facilitates the N-radical 5-exo cyclization/addition/aromatization cascade of β,γ-unsaturated hydrazones (Hu et al. 2016) (Scheme 5.32). A highly effective visible light photocatalytic method, free from external oxidants, is outlined for the N-radical 5-exo cyclization/addition/aromatization cascade of β,γ-unsaturated hydrazones. This approach offers a practical pathway to diverse biologically relevant dihydropyrazole-fused benzosultams with satisfactory yields. (Zhao et al. 2016) (Scheme 5.33).

R H

N

+

N

or

CH3 R

Ir(ppy)3 or Ru(bpy)3Cl2

H

H

OBs

Bs

N

R

R

Bs N

white LED

NHAc

Meo

Bs

N

or N

CH3

N

R''

N

R'

R'

R"

H

N

N

CH3

Me

indole melatonin derivative (97%)

Bs = Benzenesulfon

Scheme 5.31 C–H amination of (hetero)arenes from hydroxylamine derivatives or amines Ts Ts Ts H

N

Ts

Ts N

R

N N

Ru(bpy)3Cl2

visible LED

R'

N

or R

R

N

Ph Ph

with TEMPO

R' = H, Ph

N

N N

N

Intermediate in the synthesis of a biologically active pyrazole (70%)

Intermediate in the synthesis of antifungal derivatives (81%)

Scheme 5.32 N-radical hydroamination of α, β-unsaturated hydrazones O

Ts H

N

N

O

Ru(bpy)3Cl2 CoIII(dmgH)2PyCl blue LED

R

S

N N R

Scheme 5.33 Cooperative photocatalyzed N-radical 5-exo cyclization/addition/aromatization of, β,γ-unsaturated hydrazones

160

S. Sharma O

NO2

R'

Ru(bpy)3Cl2 R''

+

R'''

R'''

N,N-diisopropylisobutylamine

CHO

H

blue LED

R' R''

N R

R

Scheme 5.34 Alkylnitrones from nitroalkanes upon photoredox catalysis and in situ condensation

Br

OH

+

R

Ir[dF(CF3)ppy]2(dtbbpy)PF6 NiCl2(dtbbpy)

O

O R

blue LED

N Boc

N-Boc fluoxetine (82%)

Current Opinion in Green and Sustainable Chemistry

Scheme 5.35 Aryl ethers upon dual photoredox and nickel catalysis

Visible light photoredox catalysis has been documented as a viable method for producing indazolo[2,3-a]quinoline derivatives from 2-(2-nitrophenyl)-1,2,3,4tetrahydroquinolines with moderate to good yields. This process involves a novel intramolecular synthesis of the indazole ring’s N–N bond, facilitated by ruthenium catalysis (Lin and Yang 2013) (Scheme 5.34). Functionalization Through Carbon–Oxygen Bond Formation There are many examples of the utilisation of photocatalysis for forming C–O bonds in drug or pharmacophore synthesis in the literature. In this regard, 2aminobenzoxazoles are a crucial component of medicinal chemistry, and research is being done on their potential use in the treatment of a wide range of illnesses, including HIV, degenerative neurological conditions, and immune-mediated diseases (Terrett et al. 2015) (Scheme 5.35).

References Allen LJ, Cabrera PJ, Lee M, Sanford MS (2014) J Am Chem Soc 136:5607–5610 Chu L, Ohta C, Zuo Z, MacMillan DWC (2014) J Am Chem Soc 136:10886–10889 Chu L, Lipshultz JM, MacMillan DWC (2015) Angew Chem Int Ed 54:7929–7933 Crespi S, Jäger S, König B, Fagnoni M (2017) Eur J Org Chem 2147–2153 DiRocco DA, Dykstra K, Krska S, Vachal P, Conway DV, Tudge M (2014) Angew Chem Int Ed 53:4802–4806 Douglas JJ, Cole KP, Stephenson CRJ (2014) J Org Chem 79:11631–11643 Douglas JJ, Albright H, Sevrin MJ, Cole KP, Stephenson CRJ (2015) Angew Chem Int Ed 54:14898– 14902 Douglas JJ, Sevrin MJ, Stephenson CRJ (2016) Org Process Res Dev 20:1134–1147 Furst L, Matsuura BS, Narayanam JMR, Tucker JW, Stephenson CRJ (2010) Org Lett 12:3104–3107 Furst L, Narayanam JMR, Stephenson CRJ (2011) Angew Chem Int Ed 50:9655–9659 Hari DP, Schroll P, König B (2012a) J Am Chem Soc 134:2958–2961

5 Photocatalysis: Application in Drugs and Analogues Synthesis

161

Hari DP, Hering T, König B (2012b) Org Lett 14:5334–5337 Hu XQ, Qi XT, Chen JR, Zhao QQ, Wei Q, Lan Y, Xiao WJ (2016) Nat Commun 7:11188 Kärkäs MD, Porco JA, Stephenson CRJ (2016) Chem Rev 116:9683–9747 Kohls P, Jadhav D, Pandey G, Reiser O (2012) Org Lett 14:672–675 Le CC, MacMillan DWC (2015) J Am Chem Soc 137:11938–11941 Lin WC, Yang DY (2013) Org Lett 15:4862–4865 Miyake Y, Nakajima K, Nishibayashi Y (2012) Chem Eur J 18:16473–16477 Miyazawa K, Koike T, Akita M (2014) Adv Synth Catal 356(13):2749–2755 Nagib DA, MacMillan DWC (2011) Nature 480:224–228 Narayanam JMR, Stephenson CRJ (2011) Chem Soc Rev 40:102–113 Nicewicz DA, MacMillan DW (2008) Science 322:77–80 Oh SH, Malpani YR, Ha N, Jung YS, Han SB (2014) Org Lett 16(5):1310–1313 Orgren LR, Maverick EE, Marvin CC (2015) J Org Chem 80:12635–12640 Qin Q, Yu S (2014) Org Lett 16:3504–3507 Qvortrup K, Rankic DA, MacMillan DWC (2014) J Am Chem Soc 136:626–629 Romero NA, Nicewicz DA (2016) Chem Rev 116:10075–10166 Siddiqui IR, Ibad F, Ibad A, Waseem MA, Watal G (2016) Tetrahedron Lett 2016(57):5–10 Singh A, Arora A, Weaver JD (2013) Org Lett 15:5390–5393 Terrett JA, Cuthbertson JD, Shurtleff VW, MacMillan DWC (2015) Nature 524:330–334 Welin ER, Warkentin AA, Conrad JC, MacMillan DWC (2015) Angew Chem Int Ed 54:9668–9672 Xuan J, Xia X-D, Zeng T-T, Feng Z-J, Chen J-R, Lu L-Q, Xiao WJ (2014) Angew Chem Int Ed 53:5653–5656 Xuan J, Zeng T-T, Feng Z-J, Deng Q-H, Chen J-R, Lu L-Q, Xiao W-J, Alper H (2015) Angew Chem Int Ed 54:1625–1628 Xue D, Jia Z-H, Zhao C-J, Zhang Y-Y, Wang C, Xiao J (2014) Chem Eur J 20:2960–2965 Yayla HG, Peng F, Mangion IK, McLaughlin M, Campeau L-C, Davies IW, DiRocco DA, Knowles RR (2016) Chem Sci 7:2066–2073 Yoon TP, Ischay MA, Du J (2010) Nat Chem 2:527–532 Zhao QQ, Hu XQ, Yang MN, Chen JR, Xiao WJ (2016) Chem Commun 52:12749–12752 Zou Y-Q, Lu L-Q, Fu L, Chang N-J, Rong J, Chen J-R, Xiao W-J (2011) Angew Chem Int Ed 50:7171–7175 Zuo ZW, MacMillan DWC (2014) J Am Chem Soc 136:5257–5260

Chapter 6

Photocatalysis: Application in Drug Derivatization Priyanka Chaudhary and Sureshbabu Popuri

6.1 Background and Introduction Photocatalysis has been lately advanced as an effective and greener method for the establishment of drug derivatization through visible-light-mediated reactions which is an advancement within the synthetic methodology for the investigation of versatility and utility across the broad spectrum of the chemical structures (Wencel-Delord and Glorius 2013). Photocatalysis has acquired its name from the amalgamation of photons and the catalysts which play vital in a reaction to occur. It has been exclusively studied which has gathered information in the application of pharmaceutical drug development since they have huge potential. This recent attention of the scientists is motivated in both the capacity and feasibility of visible-light-mediated reactions which has categorized it into a defined research area. The unique property of different compounds has been identified through the solicitation of light radiation in the form of visible-light-mediated reactions which lead to pharmaceutical products. Therefore, the synthetic as well as biological properties are investigated. Photocatalysis has newly developed as an effective method for the formation of radicals upon using the unique photophysical properties of various pharmaceutical drugs. Photocatalysis is an advanced aspect which is based on free radical chemistry (Harry and Gunning 1957). Since, free radical chemistry plays a significant role transversely in numerous branches, especially in synthetic organic, material, and biological chemistry (Renaud and Sibi 2001). Conventionally, radical chemistry was investigated P. Chaudhary (B) Amity Institute of Applied Sciences, Amity University, Uttar Pradesh, Noida 201303, India e-mail: [email protected] S. Popuri University of Oklahoma, Norman, OK 73019, USA e-mail: [email protected] P. Chaudhary Department of Chemistry, University of Lucknow, 226007, Lucknow, India 163

164

P. Chaudhary and S. Popuri

through the usage of oxidizing or reducing reagents for the synthetic application or derivatization of the synthesized compounds. The UV light radiation (Andrew 2013) was also one of the sources to study the radical chemistry, but it involved the usage of high energy UV light absorbance for the initiation of the reactions (Lorthioir et al. 2021). It causes the generation of undesirable byproducts since it is difficult to monitor and control. Hence, the alternative, safe, and efficient method for photocatalysis was investigated over the high energy UV light and the critical chemicals which provided a great catalytic platform for the chemistry of radicals. This chapter is dedicated on the application of visible-light-mediated reactions for the construction of different bond construction and late-stage functionalization of pharmaceutical products. This provides an energetically sustainable path for radical based chemical drug modification. In general, the synthetic organic photocatalysis the catalysts or reactants are activated with the absorption of suitable visible light, followed by the electron transfer progressions into or from the reactants which leads to photoredox reactions (Narayanam and Stephenson 2011). The irradiation of visible light on the photocatalysts leads to an absorbance of the low energy to form a stable with longstanding excited state species which opens access to react with organic or organometallic substrates. Upon excitation, they are engaged in two modes of processes: (a) Single electron transfer (SET), (b) Energy Transfer (ET). The SET process involves the absorbance of light source by the photocatalyst (PC) and forms the photoexcited species (*PC) (Wang et al. 2021). The resultant excited species acts as both a strong oxidizing and reducing agent which provides a suitable organic reaction accessibility through oxidative and reductive cycles (Fig. 6.1a). In the occurrence of a cycle of oxidative, *PC acts as a reductant in an oxidation cycle which reduces the electron acceptor (EA) through SET to form A.− and oxidizes the photocatalyst as PC.+ . This would lead to a recipient of an electron forming an electron-donor (ED) to form D.− and the stable ground state PC which leads to the end of this cycle. Whereas *PC also role as an oxidant in a reductive cycle, initially it accepts an electron from ED to furnish the photocatalyst in its reduced form and then, gives an electron to EA to give PC. Later, the degeneration of a photocatalyst from the excited state is through the energy transfer (ET) (Fig. 6.1b). Later, *PC involves the straight energy transfer with an organic substrate (OS) which leads to the generation of a raised higher energy state of the substrate *OS and comes back to the PC to its low energy level. The detailed ET has been studied through two distinctive approaches called Dexter and Förster energy transfer (Cravcenco et al. 2020). This has opened an avenue for industries to access unique analogues of pharmaceutical drugs through sustainable photocatalysts which could undergo various transformations such as late-stage functionalization. Furthermore, beyond the use of flow, numerous photocatalytic pathways have been demonstrated on high scale, emphasizing the potential of these methods to impact not only drug discovery but also drug manufacturing (Noe¨ and Zysman-Colman 2020). The foremost aim of this chapter is to include a collection of visible-light photoredox catalysis-based examples which are applicable to the reports involving

6 Photocatalysis: Application in Drug Derivatization Electron ED Donor ED

Electron EA Acceptor EA *PC

PC

EA Electron Acceptor

165

PC Oxidative cycle

Reductive cycle

EA PC

PC ED Electron Donor

*PC

Organic *OS substrate OS

ED (b) Energy Transfer

(a) Single electron transfer (SET)

Fig. 6.1 Mechanistic studies of photocatalysts

the construction of the challenging bonds. Its application has been used to produce drugs and their analogs, primarily reporting the published information in recent years. This has incorporated direct functionalization of C–H to C-heteroatom which provides diversity in its structural and physical properties. The most commonly used photocatalysts for this specific objective, ruthenium, and iridium-based complexes are used ones (Kumagai et al. 2022). Nevertheless, a few examples of metal-free photocatalysts for example Rose Bengal, Eosin Y, etc, are also included (Qian et al. 2018). There has been nowadays, availability of new methodologies based on photocatalysts have been developed for their robustness in demonstrative functionalities of pharmaceutical compounds. This signifies an embrace and simple screening to study the effectiveness of a visible-light-mediated method, eventually important to the superior approval of such types of transformations transversely to the medicinal and chemical production industries (Peng et al 2019). Besides these, the implementation of well-studied photocatalysts and to manufacture novel and potent photocatalyst materials which would give a better understanding of the primary approach towards photocatalytic mechanisms, and is of paramount significance. The best approach would be the isotopic method for the exploration of the mechanistic approach which is considered as a powerful tool. Although this is not involved in the discussion of the photocatalytic reactions here.

6.2 Photocatalysts They are carbon-based or mineral-based compounds which have the ability to absorb light and get excited to a higher energy state. This would lead to transfer of energy to a coupling partner which leads to a reaction. The commonly used photocatalysts have been mentioned here (Fig. 6.2). They can be categorized into two sections.

166

P. Chaudhary and S. Popuri 2+

Cl Cl

Cl

Cl

CO2Na I

I O

N

N

Ir

Ru N

N

N

N

ONa I I Rose Bengal A Me

2+

Ru(bpy)3 B

O

O

fac-Ir(ppy)3 C

CH3

tBu

Me

Benzophenone E

Me

Acetophenone F

CN

N

N Ir

N N

N Me BF4 Mes-Acr-MeBF4 D

CN 9,10-Dicyanoanthracene (DCA) G

COOH Br

Br

Me

PF6

-

tBu

Ir(ppy)2(dtbpy)PF6 H

N

Me

O HO

O

O Br

Br Eosin Y I

N Me

B

F

N F

Me

BODIPY J

Ph

Ph 3,7-di([1,1'-biphenyl]-4-yl)-10(naphthalen-1-yl)-10H-phenoxazine (Miyaka phenoxazine) K

Fig. 6.2 Commonly used Photocatalysts in recent years

6.2.1 Metallo-Photocatalysts The amalgamation of transition-metal catalysts and visible light which is termed as metallo-photocatalysts (Chan et al. 2022) gave a useful approach for the formation of new synthetic methodologies. The most used visible-light-mediated photocatalysts are Ir-cyclometalated derivatives or ruthenium (II) polypyridine complexes. These catalysts in the presence of a visible light source give redox reactions due to SET under the mild reaction conditions.

6.2.2 Organic Dye Photocatalysts The formation of carbon heteroatom bonds has been considered as the center of attraction for vital synthetic chemistry. Organic dyes using visible light have been considered as green approach for the formation of new bonds which could be used

6 Photocatalysis: Application in Drug Derivatization

167

in late-stage functionalization. They have proved to undergo reaction under mild and efficient reaction circumstances as they use low power source of visible light and henceforth, various organic dyes (Gualandi et al. 2021) have been investigated and then, employed as photoredox catalysts.

6.3 Minisci-Type Radical Reactions Minisci-type reactions (Proctor and Phipps 2019) are known for the reaction of a radical substitution (nucleophilic) to an electron deficient aromatic compound where an alkyl group is introduced in a nitrogen containing heterocycle. Specifically, this is one of the C–H functionalizations where alkyl radicals are introduced to a heteroaromatic system. The traditional methods for this transformation and its applications in medicinal industry could be opted but have drawbacks such as functional tolerance, harsh conditions such as acid usage, and high temperature. Therefore, the potential of Minisci-type radical addition has been investigated using visible-light photocatalysis where the substrate scope and productivity of the Minisci reaction have been intensely established. Visible-light photocatalysis has benefitted the synthetic medicinal chemists to overcome the drawbacks and explore the mild and controlled approaches to improve and enhance the yields of these transformations. Hence, the academic and industrial collaborations have led the adaption and investigation of Minisci-type radical chemistry to heterocycles (Bosset et al. 2018). This has led to the understand the late-stage functionalization of medicinal compounds (Cannalire et al. 2021). The modern synthetic photochemistry has gathered a significant interest and momentous attention with various photocatalysts. The impact of light photons over the photocatalysts and radical generation has a great potential which gave a scaleup development of pharmaceutical drugs which exhibit photophysical and different reactivity profiles.

6.3.1 Functionalization Through Carbon–Carbon Bond Formation 6.3.1.1

Photoredox Catalysis with Organic Dye Rose Bengal

X. Li et al. disclosed an efficient and direct Rose Bengal (RB) (Sharma and Sharma 2019) mediated conversion of different heterocycles to difluoro methylated heterocycles which has great scope as ant cancerous agents (Zhang et al. 2020). This investigated methodology does not involve application of any poisonous or costly metal catalyst or an external oxidant which clearly indicates the advantages over the

168

P. Chaudhary and S. Popuri Cl

Rose bengal NaSO2CF2H

1

Het

DMSO, air, rt 2*3 W green LEDS

2a

Cl

Cl

CO2Na I

I

(2-5 mol%) Het

Cl

CF2H O

ONa

3, 4, & 5

A I I Rose bengal

X. Li et al 2019 (A) Scope of quinoxalin-2(1H)-ones: N CF2H Cl N

O 2N

O

Cl

3a: 40%

N

CF2H

N

CF2H

N

O

N

O

3b: 75%

N N Bn 3d: 52%

3c: 34%

CF2H O

(B) Scope of heteroaromatics: O

Cl O

N

S O

N

O

CF2H

O

O

N CF2H N N H Caffeine 5a: 74% O H

4d: 65%

O

O

O

HN

CF2H

4c: 42%

(C) Scope of Drugs Molecules:

O

O

N

4b: 70%

4a: 41%

HN

O CF2H

N

CF2H N

Cl

O N

NHAc CF2H N H Melanotin

O

Flavorant 5e: 28% O

H

N

5c: 72% HF2C HF2C

NH

N CF2H N N H Threophylline 5b: 70%

O

N O H Uracil 5d: 57%

O

HF2C

CF2H

F N

O O

N N

N F N HO

HN

F

N S

Oral antidiabetic sulfonylures agent's precursor 5f: 31%

OH

N

F CF2H

Voriconazole 5g:25%

OH 2'-Fluoro-2'deoxyuridine 5h: 62%

Scheme 6.1 Substrate scope of direct C–H difluoromethylation of quinoxaline-2(1H)-ones, heteroaromatics, and late-stage functionalization of drug molecules

conventional methods. The authors have actively used Hu’s reagent sodium difluoromethane sulfonate (CF2 HSO2 Na) (He et al. 2015) which is used as a radical precursor for heterocycle functionalization in the occurrence of photocatalyst, i.e, RB to produce difluoroethylation product (Sakamoto et al. 2017) (Fig. 6.4). The optimized reaction conditions revealed tremendous compatibility with an extensive array of various heterocycles substituted differently involving pyridines, pyrazoles, quioxalines, and further to be explored later. They have examined the substrate scope of bioactive molecules with optimized conditions and obtained quantitative yields. It was noticed that the synthesis of different difluoromethylated caffeine derivatives,

6 Photocatalysis: Application in Drug Derivatization

169

nucleoside derivatives with good yields, along with these, several difluoromethylated drug compounds comprising of free secondary amino functionality and further bioactive aromatic heterocycles (Fig. 6.4c). This methodology has been found to have great substrate scope which makes this transformation a brilliant means for the advancement of drug library (Scheme 6.1). The substrate scope was detailed and inspected with the optimized conditions of a variation of quinoxalin-2(1H)-ones, heterocycles, and bioactive drug molecules. The reactions went smoothly, and the desired products formed with quantitative yields. The methodology was well tolerated different functionalities such as hydroxyl (–OH), amine (–NH), or aldehyde (–CHO) with the reaction conditions. Besides these, the viability of the methodology was found to be proceeded well with voriconazole, uracil, melatonin, flavorant, and sulfonylureas giving good yields of difluoromethylated products. The contributors of this protocol have also investigated control experiments to propose a plausible mechanism. The thorough mechanism has been investigated for the reaction (Fig. 6.2). The visible light was absorbed by the photocatalyst RB which led to excited state RB* and a single electron is transferred from CF2 HSO2 Na to RB*, which furnished CF2 H• and generated an RB•− . This photocatalytic cycle was finished with the oxidation of RB•− in the presence of O2 along with the RB and O2 •− . Later, the CF2 H• added to 3e led to intermediary A, that underwent a 1,2-H shift to form B as a radical intermediate. The loss of an H atom from the intermediate B to O2 •− which afforded the product 3e. Therefore, they have developed a practical approach for difluoromethylation reactions with cheap reagent CF2 HSO2 Na which produces CF2 precursor in optimized standard circumstances. This reaction involves the catalytic system of CF2 HSO2 Na in DMSO with organic photocatalysis, i.e, Rose Bengal (2–5 mol%) which gives a viable route for the preparation of different classes of heterocycles (Sessler, et al.

N

H

CF2H

H N

O

N

CF2H

N

CF2H

O

N

O

N N N

A

O

3e

CF2H Na + SO2

O2 RB SET

NaSO2CF2H

B

HO2

-

H2O 2 SET

O 2 H 2O

Visible RB RB* light

Scheme 6.2 Mechanism of C–H difluoromethylation of heterocycles

170

P. Chaudhary and S. Popuri

2017). Outstandingly, 2 -deoxy-5-difluoromethyluridine (F2 TDR) which is a difluoromethylation product significantly can inhibit the production of cancer cells such as MCF-7 (Scheme 6.2).

6.3.1.2

Photoredox Catalysis with Metallophotocatalyst

The alkyl-arylation of alkenes was reported by X. L. Lv group with the combination of fac-Ir(ppy)3 and copper(I) catalysis (CuI) (Lv et al. 2019). This is a multicomponent relay approach which involves the occurrence of the reaction in the incidence of blue LEDs (30 W) irradiation of d-bromocarbonyls and boronic acids at RT. The optimized reaction was conducted with 1 mol % of fac-Ir(ppy)3 in the support of irradiation of visible light, cost-effective CuI or CuBr·Me2 S, and Cs2 CO3 as a base with dichloromethane has delivered the ϒ-arylated esters with quantitative yields (Fig. 6). The visible-light photocatalysis gave an insight into an extensive range of amides, ketones, and ϒ-arylated esters with great tolerance of functional group as demonstrated in the late-stage amendment of ϒ-tocopherol (Jiang et al. 2000) having alkene (Fig. 6). The authors have designed to interpret the mechanistic approach for the reaction. The reactions were performed using radical scavenger TEMPO (Li et al. 2023) where the product was not formed to confirm the free radical mechanistic pathway and no use of PhB(OH)2 gives bromoalkylation product was obtained which signifies that benzyl radical intermediate is present in the catalytic cycle (Schemes 6.3 and 6.4). The mechanism was suggested with the help of mechanistic studies (Fig. 7). The irradiation of light with the Iridium photocatalyst gives the Ir*(III) photocatalyst (excited). The contact of α-bromocarbonyl starting material with photocatalyst Ir*(III) with SET provided the sensitive radical intermediate C1 along with the oxidation from Ir*(III) to photocatalyst Ir(IV). C1 would be imprisoned by alkene to produce a C2 alkyl radical intermediate. The arylcopper intermediate C3 was formed by the combination Cu(I) with aryl boronic acid that might with base, and later recombine with C2 to give C4. C4 would form reduced Ir(III) from Ir(IV) and underwent reductive elimination which gave the ultimate product and restored Cu(I).

6.3.2 Functionalization Through Carbon–Oxygen Bond Formation 6.3.2.1

Photoredox Catalysis with Metallophotocatalyst

Ming-Yu Ngai et al have developed the notable coupling reaction of N-(hetero)arylN-hydroxylamides with alkyl fluoro iodide radically where O-alkyl fluoro migrates to give a range of perfluoroalkoxylated (hetero)arenes (Fig. 8) (Wright and English 2003). The reaction underwent photocatalysis followed by the O-alkyl fluoro groups

6 Photocatalysis: Application in Drug Derivatization

171

Scheme 6.3 Substrate Scope of alkyl-arylation of alkenes and late-stage functionalization

for selective C-O construction of bond. The optimized conditions were 3W blue LEDs which irradiated evident light in the presence of [Ru(bpy)3 (PF6 )2 with 3.00 equiv. K2 CO3 in 0.100 M of CH3 CN at 0 °C for 12 h which gave the best yields. The scope of perfluoroisopropylation was well evaluated through the wide approach of the substrate scope where an array of functional groups and molecular frameworks were found to be compatible. The chemo-selectivity of the reaction was proved since the benzylic substrates are more prone to free radical reaction whereas the radical coupling of O- and RF -radical coupling was established to be faster comparatively. The perfluoroisopropylation of arenes and heteroarenes including the heterocyclic N-hydroxylamides such as thiophene and benzofuran gave high regioselectivity with good yields. It was also proven that pharmaceutically important molecules can also

172

P. Chaudhary and S. Popuri O

Ar 3

Visible light

R1 R R3

R1 Cu (I)

O Ir* (III) Ir (III)

Br R3

R4

C1 ArB(OH)2

R2

R3

O

R4 C1

R2 Br

R2

base Ir (IV) O Cu Ar (III

R C4

1 R3

R3

R2

Ar Cu (I) C3 R1

R1

O R3 R 3 C2

R2

Cu

Br O R3 R 3

R2

Scheme 6.4 Mechanism of photocatalytic radical relay alkyl-arylation of alkenes

be synthesized such as perfluoroisopropylated analogs of estrone and diacetone-Dglucose. Also, polyfluoisopropylation of arenes gave best results with the optimized conditions with good yields. The mechanism of the photocatalytic cycle for the discerning O-fluorinated alkyl bond formation and the consequential O-fluorinated alkyl migration is described in Fig. 8. In the incidence of visible light, Ru(bpy)3 2+ photocatalyst goes to the excited state *Ru(bpy)3 2+ (1.10 ms). The perfluoroalkyl iodide (RF I) (13) was reduced through the single electron with Ru(bpy)3 + forms a per-fluoroalkyl radical (cRF ) and produces Ru(bpy)3 2+ which subsequently undergoes a combination between 12 and cRF gives O-per-fluoroalkylated N-Phenyl-N-hydroxylamide (14), that undertakes heterolytic Nitrogen-O-fluorinated alkyl bond cleavage (Porzelle et al. 2010; Tabolin and Ioffe 2014) followed by of the short-lived ion pair which tautomerizes to produce the perfluoroalkoxylated arene product 14 (Schemes 6.5 and 6.6).

6.3.2.2

Photoredox Catalysis with Organic Dye Eosin Y

In 2020 Xing et al. has reported a visible-light-mediated Csp3 − H activation which is a highly efficient benzylic hydroperoxidation. The reaction was found to be feasible using eosin Y which is a metal-free organic dye catalyst and a cost-effective blue LED with a molecular O2 as an oxidant (Inoa et al. 2020). The extensive investigation of various metal and metal-free catalysts, eosin Y was found to be suitable to serve the purpose (Hari and Konig 2014). Wang group has already explored and reported that the neutral eosin Y-derived photoexcited states can be served as photoacids (Zhao and Wang 2018). It was also believed that the reaction undergoes through direct HAT catalysts (Fan et al. 2018). Also, it was observed that a range of 1°, 2°,

6 Photocatalysis: Application in Drug Derivatization

Ac N R

Het

OH

RF

Ru(bpy)3(PF)2 (0.500 mol%) K2CO3 (3.00 equiv.)

I

R

12 13 Ming-Yu Ngai et al 2017 (A) Perfluoroisopropylation of arenes:

CF3 CF3

iPr

14a: 76% Cl

H N O NH 14d: 74%

Het O 14, 15

NHAc F

NHAc F O

Ac NH

MeCN (0.100 M) 3 W Blue LEDs Temp ∞C, 12 h

H

tBu

173

O

Boc

NHAc F

NH

MeO

CF3 CF3

14b: 73% NHAc F CF3 O CF3

RF

O O

CF3 CF3

14c : 72%

NHAc F CF3 CF3

O

S O

14e: 57% OEt

(B) Perfluoroisopropylation of hetero-arenes: O

Me Me O

Me

O

NHAc F

Me

H H

Me

H O

N

NHAc F CF3 CF3 O

O

(C) Polyfluoroalkoxylation of arenes: NHAc F F F F F F tBu O CF3 F F F F 15a: 58%

Me Me

O

NHAc F F Cl

tBu

O

Br F F

F F 15b: 59%

CF3 CF3

14g: 84%

NHAc F F tBu

O

O

O

14f: 51%

N

15c: 27%

Scheme 6.5 Substrate scope of perfluoroisopropylation and polyfluoroalkoxylation of arenes, hetero-arenes

and 3° hydroperoxides as well as benzyl, silyl, and acyl peroxides were smoothly synthesized with optimum yields and great functionalities tolerance in substrates was also found. Remarkably, the approach demonstrated a wide approach for latestage functionalization for drug derivatization, for example, the amendment in the C−H bond of benzylic group, Celecoxib (Scholtz and Riley 2021) which is an antiinflammatory drug (17e) has been reported.

174

P. Chaudhary and S. Popuri RF Ru(bpy)3

2+

I

12

SET RF

I

+ Ru(bpy)3

I

2+

*Ru(bpy)3

SET Ac N

O

Ac

RF 13

NH

O O

-

14

-H+ +H+

Ac N

Ac N

Ac N

RF

Ac

Radical Coupling

O

N H R O F

OH Ac N

14

RF

O

RF

Ac N

O

RF

Ac NH O

RF

Short-Lived Ion Pair

Scheme 6.6 Mechanism of perfluoroisopropylation of arenes

The peroxides containing the hydroperoxides and endoperoxides exist in different natural compounds which are seized from plants, mushrooms, endophytes, and additional creatures (Scholtz and Riley 2021b, c). Such compounds possess antibacterial, antimalarial, and cytotoxic also. Especially the hydroperoxides have been found to be of significant usefulness in material science chemistry also (Cheng and Loh 2015) (Schemes 6.7 and 6.8). The description of the mechanism is mentioned in Fig. 11. Eosin Y drives to the excited level as eosin Y* upon irradiation of light which is directed to the removal of a hydrogen atom from the respective C−H bond benzylic group to furnish a benzylic radical 16’ with eosin Y-H. The molecular O2 traps 16’ radical to form a peroxy radical. Finally, a retro-HAT from eosin Y−H to peroxy radical forms hydroperoxide product 17 and re-establishes eosin Y into the catalytic cycle. After Wu’s development, a great advancement towards the Eosin Y as a direct HAT catalyst has been published in the works (Fan et al. 2018).

6 Photocatalysis: Application in Drug Derivatization

R2 R1

H R3

175 R2

2 mol% Eosin Y O2

R1

CH3CN Blue LED

16

H O O R3

17

Xing et al 2020 OOH

HOO

OOH 17b: (65%)

17a: (80%)

17c: (70%)

NH2

O S

O

O N N OOH

F3C

OOH

17d: (55%)

17e: (43%) Celecoxib

Scheme 6.7 Substrate scope of Benzylic Hydroperoxidation R2 R1

H R3

16 Blue LEDs

R2

COOH Br

Br HO

O

O

R3

R1

.

16'

HAT

Br Br Eosin Y* COOH Br

Br HO

O

COOH Br

Br

O

HO

Br Br Eosin Y

O

O2

OH

Br Br Eosin Y+1

R2 R1

R2 O OH R3

Scheme 6.8 Mechanism of Benzylic Hydroperoxidation

R1

O O R3

176

P. Chaudhary and S. Popuri

6.3.3 Functionalization Through Carbon–Nitrogen Bond Formation 6.3.3.1

Photoredox Catalysis with Organic Photocatalyst 9-Mesityl-10-Methylacridinium Tetrafluoroborate (Mes-Acr-MeBF4 )

One of the cardinal functional entity is an amide bond is found in diverse natural products and pharmaceutical drugs (Walsh et al. 2013). The survey conducted in 2006 stated 2/3rd of the drugs possess the amide moiety such as etazolamide, moclobemide, and paracetamol (Carey et al. 2006). The green approach for the formation of amide bond via photochemical reaction has mimicked the photosynthesis process. Since, the chemical transformation has been achieved through the energy transfer by light. The standard conditions opted were acridinium-based catalysts which is Mes-AcrMeBF4 [2 mol %] in 0.1 M of acetonitrile with 36 W blue LED for 5 h led to the establishment of preferred products in quantifiable yields. The alternative of metal catalysts by a photocatalyst especially acridinium-based catalyst had outstanding reacting abilities in the excited level (Ered = 2.06 V vs SCE, MeCN) (Nicewicz and Nguyen 2014), that disclosed a great efficacy of more than 90% yield for Mes-AcrMeBF4 . Here, thioacids are used as the effective acyl group sources which has an important part in amide bond construction due to the formation of thioacid radicals. The metal-free and base free amide (-CONH2 ) bond construction was established by Wangze Song et al. with an organic photocatalyst (Song et al. 2020). This approach has shown an excellent functional stability under the standard conditions. All the functionalities such as ethers, esters, alcohols, phenols, halogens, or heterocycles were stable. This methodology has led to substrate scope that were compatible in the presence of water and air. The broad substrate scope of aliphatic and aromatic thioacid with high yields showed a great potential for the modification in amino acids as illustrated in Scheme 6.9. All the amino acids with the protecting groups such as Fmoc, Boc, and Cbz in the reaction participated well. The production of significant medication molecules for example paracetamol, melatonin, and moclobemide was also attempted without affecting the heterocycles, thioethers, and secondary alcohols. Moclobemide was synthesized with chlorobenzothio acid and alkyl amine with 89% yield which is an alterable monoamine oxidase inhibitor (MAOI) utilized for the treatment of melancholy and communal anxiety (Scheme 6.10) (Bonnet 2003). The N-acetylation of indole alkyl amine has acquired Melatonin with selective amide formation of alkyl amine with 92% yield which regulates the sleep—wake cycle (Boutin et al. 2005). The chlorobenzothio acid with amine 5-amino-1,3,4-thiadiazole-2-sulfonamide produced acetazolamide with selective amide formation which is a carbonic anhydrase inhibitor (Lindskog 1997). The photoredox catalytic cycle was proposed through the amide bond formation mechanism in Scheme 6.11. The deprotonation of thioacid in the existence of amine results in intermediate A. The irradiation of blue LED photoexcite [MesAcrMeBF4 ] to form the excited form of respective photocatalyst that promoted to

6 Photocatalysis: Application in Drug Derivatization

177 Mes

O 2 SH R NH2 19 18 Wangze Song et al 2020

R1

Mes-Acr-MeBF4 O Open in air R2 R1 N Blue LED H 20

N BF Me 4

(A) Scope of Aromatic thioamides: O Me

N Me H 20a: 95%

NH2

CH2OH O

O

Me

N H

Me

N H 20b: 79%

O N H

20c: 75% N

O Me

20d: 86%

N H 20e: 71%

(B) Scope of Alphatic thioamides: O

O

O

5

N H 20g: 83%

N H 20f: 78%

N H 20h: 84%

O

O

N H

N H

F

20i: 77%

20j: 88%

(C) Scope of Modified Amino acid: Fmoc

NH

Cbz H N

Me

NH

N H N

O 21c: 76%

O 21b: 87%

O 21a: 84% Fmoc

NH

Me

Boc H N

OH O 21d: 77%

Fmoc H N

NH

H N

O 21e: 84%

Scheme 6.9 Substrate scope of amide bond formation using Mes-Acr-MeBF4

178

P. Chaudhary and S. Popuri N H2 N

O

O

Open in air 19f Blue LED

O N

N H Cl

Moclobemide (89%) OMe

H2N O

N H Open in air 19g Blue LED

SH Cl

O OMe

N H

Me

N H Melatonin (92%)

18f N N

NH2 S O O 19g Open in air Blue LED

H 2N

O

S

Me

N N HN S

O S NH2 O

Acetazolamide (76%)

Scheme 6.10 Synthesis of drug molecules through amide linkage construction

undergo reduction to form [Mes-Acr-MeBF4 ]. by electron-rich anion of thioacid I. Later, the same radical undergoes oxidation gave [Mes-Acr-MeBF4 ] which terminates the photoredox cycle. The SET from thioacid anion I to thioacid radical II catalyzed through the photocatalyst. The attained disulfide was via the di-radical combination of thioacid radical II which was tracked by its lysis with the help of an RNH2 to furnish amide 20 and per thioacid IV. The lysis of amino for each and every thioacid IV would result in amide 20 (Liu and Orgel 1997).

6.3.3.2

Photoredox Catalysis with Metallophotocatalyst

There are well developed transition-metal mediated sp2 C-N couplings of haloarenes with amine nucleophiles, such as Buchwald–Hartwig reaction (Ruiz-Castillo and Buchwald 2016), Ullmann coupling (Sambiagio et al. 2014), and Chan–Lam amination (Sambiagio et al. 2014). Xu et al. have developed a green combination of C–N amid N-(tert-butyl)-N-fluoro-2-methylbenzamide derived and aniline alternatives in the existence of the photocatalyst [Ir(ppy)2 (dtbpy)](PF6 ) regioselectively (Fig. 6.3). The tertiary amine has been obtained as the desired product which has wide range of pharmaceuticals. The tertiary amines bearing EWG’s and EDG’s at ortho, meta, or para-point of the aromatic ring remained well tolerated with quantitative yields synthesized from respective carboxylamides and anilines under the standard reaction conditions (Scheme 6.12). But the amines with alkyl-substitution, for example, nBu2 NH, and CyNH2 do not give the respective amination products. Besides this,

6 Photocatalysis: Application in Drug Derivatization

179

O R1

O O R1

S

R1 S S

III

II O R1

[Mes-Acr-MeBF4]

O

R2NH2 R1

SH -R2NH 3

I

S

.

O2

SET

R2NH2

O2

[Mes-Acr-MeBF4]*

[Mes-Acr-MeBF4] O

Blue LED O R1

R1

R2 NH

R2NH2

R2 NH

20

O

20 R1

S

SH

IV

Scheme 6.11 Mechanism for amide formation O O

O NHR1 NHAr

ArNH2

NFR1 R2

Ir

R2

NHR1

ArNHCH3 or alkyl Hantzsch esters

NHAr or

Ir

R2 O

H 3

sp3 C-N cross-coupling

NHR1 alkyl

3

C(sp )-C(sp ) cross-coupling R2

Fig. 6.3 C–N (sp3 ) cross-coupling of alkyl and N-center radically

O =

H N

20% H2SO4

N 28: 95% yield

CONHtBu

COOH

N =

Ph

20% H2SO4

Ph

Fig. 6.4 Synthetic applications of the protocol

Ph N

Ph

29: 93% yield

180

P. Chaudhary and S. Popuri

the alkyl amide alkylation was also explored which gave a noble yield of the product (25a). The high valent Ir photocatalyst accepts an e− from amine and concurrently, produces radical cation of an amino I, upon irradiation (SET) (Scheme 6.12). The α-amino alkyl radical I’ was achieved by deprotonation from amino radical cation. Later, the intermediary I’ might be seized by radical of C-center II’ which produced via 1,5-HAT from 22 and hence, the coupling of (sp3 ) C–C (24) was achieved. Stimulated by the accomplishment of photoredox sp3 Carbon–Nitrogen coupling, an alternate approach to accomplish regioselective C(sp3 )-C(sp3 ) combination between 30 amines α-substituted C(sp3 )-H and C(sp3 )-H (unactivated) utilizing the

Ir(ppy)2(dtbpy)PF6 (1 mol%) K2CO3 (3 equiv)

CONFtBu

H

R1

NH R3 DMF (0.1 M), rt, 12 h Violet LED (24 W, 390-410 nm)

R2 23

22

t Bu

CONHtBu

R3

R1

N

N

N R2

PF6-

Ir N

tBu

N 24

Condition A

Z. Xu et al 2020

Ir(ppy)2(dtbpy)PF6

Substrate scope of

sp3

C-N coupling:

CONHt Bu

CONHt Bu

N H

N H

23a : 73%

CF3

CONHt Bu

CONHt Bu N H

23b: 66%

N N 24d: 72%

23c: 57%

Amination of alkyl amide: O

NH2

O

N H

Condition A

N F

NH

F3C 25a: 51%

CF3 Mechanism for sp3 C-N coupling: H 23 NR2R3 SET Ir(III)*

I

Ir(II)

O

F hv

Ir(III)

NR3R2

H

SET O tBu

H

H

-H

O 3R2RN

I' O

tBu

N R1

base

N

1,5-HAT

tBu

II'

II R1

N F R1 22

Scheme 6.12 Scope of substrate of sp3 C–N coupling and its mechanism

tBu N H R1 2 3 24 NR R

6 Photocatalysis: Application in Drug Derivatization

181

photoredox 1,5-HAT strategy (Löffler and Freytag 1909) under the same conditions. The protocol was followed for the alkylation of andersterone derivative which was successfully performed and a yield of 56% was achieved (27f) (Scheme 6.13). The mechanism proposed was initiated through the excitement of the Ir(III)* photocatalyst where the oxidation of aniline takes place due to the formation of Ncentered radical III in the presence of base and Ir(II) photocatalyst was reduced. This Ir (II) undertakes one more SET with reactant to give radical of amidyl IV, and consequently 1,5-HAT, forms radical V as an intermediate. Lastly, a coupling among the radicals as III and V generates C (sp3 )-N coupled product 27 (Scheme 6.14). Basically, in this reaction amino groups led to form the nitrogen centered radical which combines with the alkyl radicals with the irradiation of the visible light. They are produced from Hofmann-Löffler-Freytag (HLF) category 1,5-HAT (Schemes 6.12 and 6.14).

CONFtBu R2 H

R1

R3

22 Substrate scope of

Ir(ppy)2(dtbpy)PF6 (1 mol%) K2CO3 (3 equiv)

H

sp3

CONHtBu

t BuHNOC

N DMF (0.1 M), rt, 12 h R4 Violet LED (24 W, 390-410 nm) 26 Condition A

R2

R4 N R3

R1 27

C-N coupling CONHtBu

N

tBuHNOC

tBuHNOC

N

27a : 73%

N

N

27b : 76%

COOEt

27d : 71%

27c : 59%

C-H alkylation of alkyl amide: O

O

H N F

N Ph

Ph Condition A

O

CONFtBu

N

O

H O

H

Ph

27e: 47%

Alkylation of andersterone derivative:

H

N Ph

N H

H O

H

H

Condition A

O

CONHtBu

H O

N 27f: 56%

Scheme 6.13 Scope of Substrate of alkylation of C–H bonds of 3° amines

H

182

P. Chaudhary and S. Popuri Visible light

O tBu

Ir (III)

N F

Ir (III)* -

F

SET

SET

R1 O tBu

Ir (II)

N

base R1

IV 1,5-HAT

NH III

O t Bu

N H R1

O tBu

radical-radical cross coupling

N H

27 R1

NH

V

Scheme 6.14 Plausible mechanism for C(sp3 )–N coupling reactions

In 1881, A. R. Hantzsch synthesized Hantzsch esters (Li et al. 2013) were first synthesized which are broadly used in pharmaceutical chemistry. Later, the regioselective C(sp3 )-C(sp3 ) cross-coupling was attempted by the utilization of cyclohexyl, 10 , 20 , and 30 alkyl Hantzsch esters as radical alkylating agents (Scheme 6.15). All the reactions were feasible and gave satisfactory results. The photoredox strategy opted showed the vital versatility for the construction of sp3 hybridized C–C bonds in the organic syntheses. The application of the reported method in synthesis of lactam (28) and acid (29) was achieved from the corresponding synthesized amination and alkylation products via mild processes with outstanding yields, respectively (Fig. 6.4).

6.4 Peptide Functionalization and Protein Bioconjugation The growing and promising attention in peptides has grabbed the attention towards the importance of antibody and drug conjugates (Tsuchikama et al. 2018). The protein modification via photocatalysis was attentive towards the peptide crosslinking which is the base for the bioconjugation methods (Taylor 2022). There are several transformations have been reported which are used for the implication of visible-light

6 Photocatalysis: Application in Drug Derivatization R5

CONFt Bu

MeOOC +

R1

(1 mol%) H COOMe CH OK (2.5 3 equiv.)

N H 28 R5 = Cy/ 1 /2 /3 alkyl

R2 22

183

groups

tBuHNOC

R2 R5

18 W blue LED CH2Cl2 (0.1

R1

M), rt, 12 h Condition B

29

Substrate scope of carboxylamides with cyclohexyl/primary/secondary/tertiary Hantzsch ester: CONHtBu

CONHtBu

CONHtBu

CONHtBu

S 29a: 71% CONHtBu

29c: 65%

29b: 55% CONHtBu

29e: 70%

CONH

29d: 65% tBu

29g: 52%

29f: 70%

CONHtBu

Cl 29h: 43%

C-H alkylation of alkyl amides O O Ph

N H

Ph

N H

29i: 64%

29j: 56%

Scheme 6.15 Scope of Substrate of alkyl Hantzsch-esters

photocatalysis for protein modification (Bottecchia and Noël 2019) and protein bioconjugation (Younong et al. 2018) at selective sites.

6.4.1 Photoredox Catalysis Using Visible Catalysis in the Presence of Blue LEDs and 4-Alkyl-1,4-Dihydropyridine (DHP) Chemicals The structure of Histidine (His) has a side chain of heteroaromatic imidazole which is electron deficient and displays an exceptional role in the functioning of protein involving coordination of metal ion, H-bond acceptor/donor, transfer of proton, and nucleophilic catalysis (Agostini et al. 2017). Ping Wang and group demonstrated an effective and widely applicable synthetic approach for Histidine centered peptide amendment through radical routed C2-selective C–H alkylation of imidazole with

184

P. Chaudhary and S. Popuri

differently substituted DHP chemicals (Chen et al. 2019) with the irradiation of visible light (Gutiérrez-Bonet et al. 2016). The critical and important nitrogen functionality of His is preserved in the products where alkylation was attempted. This protocol proceeded with moderate circumstances and illustrated wide possibility for both (peptides and DHP reagents). The scope was investigated of this alkylation method with varied length and composition of the peptide substrates (Scheme 6.16). The authors reported that all the proteinogenic amino acids (Fichtner et al. 2017) with the exception of free Cysteine were consistent with opted methodology with DHP-a (Scheme 6.16A). The C−H alkylation of Histidine was accomplished selectively in satisfactory yields for 32b to 32d. Similarly, various amino acids have been explored which gave rise to interesting results. Further, the protocol was explored with an arrangement of trifled-sized Histidine-comprising peptide drugs of < 10 AA residues, such as leuprorelin (Plosker and Brogden 1994) (breast cancer cure), gonadorelin (Hoitink et al. 1997) (cure of hypogonadism) and angiotensin II (Horiuchi et al. 1999) (a cardiovascular drug) (Scheme 6.16B). All the peptides reacted smoothly and gave quantitative yields. Besides these, Cosyntropin (David 2010) (a synthetic adrenocorticotropic hormone), Secretin (Afroze et al. 2013) (an investigative agent for the functioning of pancreatic diagnosis) and Exenatide (Clegg et al. 2019) (curing drug for Type-2 diabetes) were also investigated (Scheme 6.17). The mechanistic route began with the irradiation of visible light to DHP-R substrate which produced the R. (alkyl radical) and DHP. intermediate I by homolytic cleavage of carbon-carbon bond. DHP cation II and radical III are formed when I intermediate could be oxidized by SET or HAT with the other DHP-R reactant. Later, the aromatization of pyridine product A formed from the deprotonation of II. Later, radical cation intermediate VI was formed by the Nu-alkyl radical R. combined with the protonated Histidine reactant V. The HAT/SET oxidation of VI by III results in the ultimate alkylated product 32 alongside tetrahydropyridine IV. Hence, DHP-R reagents played an important role as oxidant and alkyl radical donors both in the visible-light-irradiated Minisci-type C–H alkylation of Histidine.

6.5 Miscellaneous Photocatalytic Reactions 6.5.1 Selective Photocatalytic C − F Functionalization of Unactivated Trifluoromethylarene Using Miyake Photocatalyst The trifluoromethylaromatic (Sanz-Vidal et al. 2021) (Ar−CF3 ) moiety is regularly exploited in pharmaceutics and agrichemical industries (Ogawa et al. 2020), since its assimilation can considerably amend the features of conferred biologically effective molecules. The effective formation of Aromatic−CF3 compounds has been found to be explored in recent years (Zhu et al. 2014).

6 Photocatalysis: Application in Drug Derivatization Ping Wang et al 2019

R EtO2C

H N

N H

H N

R N NH peptide

Blue LEDs (10 W) TFA, TFE, 35 OC, 3h

peptide

O 30

CO2Et

N H 31 (10 equiv.)

NH peptide

185

N H

H N peptide

O 32

(A) Scope of tolerance of AA Side Chains with DHP-a [R = Cyclohexyl] R H2N M D W R F S Y K L COOH H2N M H D W R F S Y K L COOH 32a: (0%) 32b: (40%) R R H 2N

G R L Y H S P K E COOH

V H L T P E E K S COOH

H 2N

32d: (59%)

32c: (52%)

(B) Chemoselective His C2-Position Functionalization of Bioactive Peptides R Lueprorelin Angiotensin II O R H2N D R V Y I H P F COOH HN H W S Y L L R P CONHEt N O OH H 32e: (36%)

32g: (55%)

R=

R= N3 OH 32f: (54%)

O

32h: (47%)

Gonadorelin O R O

N H

HN

H W S Y G L

L R P CONHEt OH

32i: (55%)

O

R=

(C) Chemoselective His C2-Position Functionalization of Cyclic Peptide Bremelanotide and Bleomycin Glycopeptide R

N NH

Bremelanotide 32j: (56%) 32k: (92%)

NH O O O HN

HN NH

O

O

HN

32j: (47%)

NH

NH2

NH NH

O O NH HO2C NH

NH O

Scheme 6.16 Peptide-labelling: scope of reactants for C−H Alkylation of His: (A) Scope of reactants of amino acid side chains, (B) Chemo-selectivity for the His C2-position functionalization of bioactive peptides, (C) Chemo-selectivity for the His C2-position functionalization of cyclic peptide bleomycin glycopeptide

186

P. Chaudhary and S. Popuri H

R H E

E

E

SET/H or

E

light N H

DHP-R

R'

N V H

EE

E E

E N H

N H

III

H

H N

R H addition

H R'

N VI H

H E

N II H R H

R H

R H

H N

E

HAT

N H I

Homolytic R C-C cleavage

H

+

E N

H

DHP-R as R donor E DHP-R as oxidant

N IV H H HAT

E

H N

R or N Minsci alkylation + R' SET/H 32 H

Scheme 6.17 Proposed route of C−H Alkylation of Histidine

Jui and co-workers in 2019, explained an approach for the difluoro-alkylation and hydro-defluorination of unactivated trifluoromethyl arenes utilizing a Miyake phenoxazine photocatalyst under irradiation of visible light (Scheme 6.18) (Vogt et al. 2019). The Miyake phenoxazine photocatalyst (McCarthy et al. 2018) has been found to be the most efficient catalyst which showed the highest absorbent in the visible spectrum which led to the formation of extensive existing triplet excited levels which were found to be strong reducing (Du et al. 2017). This de-fluorinative radical procedure had been opted to produce a varied range of Aromatic-CF2 R and Aromatic-CF2 H compounds, specifically products with electron giving groups. The functionalization of sold medications such as cinacalcet and travoprost were performed under the designed and standard conditions to afford derivatives 35c and 35d in 61% and 73% yield respectively, demonstrating that basic functionalities such as internal alkenes and alcohols were compatible. A broad range of functionalities and heterocyclic moieties were found in building blocks of medicinal drugs that were compatible under the standard defluorination conditions. Both the substrate scope of unactivated trifluoromethyl aromatic substrates and olefinic coupling partners were well accepted under the optimized conditions. The mechanism proposed showed the transformation which is initiated with the excitation of Miyake phenoxazine photocatalyst under visible light radiation using commercially available blue LEDs and led to the reductant PC*. Then, SET to the Aromatic-CF3 reactant leads to the respective radical anion and radical cation which is ground level catalyst. The strategic and important intermediate of difluorobenzylic is then, formed via either homolytic or heterolytic C-F cleavage consequently. The intermolecular addition to the olefinic reactant regioselectively gave an alkyl radical which underwent HAT with thiophenol to provide the defluoro-alkylation products. Later, the thiol and photoredox catalysts in the presence of formate are regenerated as stoichiometric reductant producing CO2 and as a metal fluoride salt byproduct (Scheme 6.19).

6 Photocatalysis: Application in Drug Derivatization Jui et al 2019 F FG

34 X Miyaka phenoxazine [2 mol%] HCOOK (5 mol %) PhSH (10 mol%) FG DMSO, 100 O C Blue LEDs

F F

33

F

187

N

F X

O

35

Ph

Ph

Miyaka phenoxazine

(A) Catalytic Defluoroalkylation: Scope of Unactivated Trifluoromethylaromatic Substrates

R

F F N

Me

35a: (64%) R=

O

HO

F F

F

R N H

35b:(62%)

F R HO

35c: (61%) {from cinacalcet}

OH

O

35d: (73%) {from travoprost}

O

Me Me

(B) Scope of Olefinic Coupling Partner for Photocatalytic Difluoroalkylaromatic Synthesis F F F F O F F Ph F F N OEt OAc Ph N 35g: (71%) OEt 35e: (64%) 35h: (89%) 35f: (75%)

Scheme 6.18 Substrate scope of catalytic difluoro-alkylation F F

PhSH F

R

PC

PC* catalytic SET

F F

H

35

catalytic HAT HAT

HAT

SET OM

33

PC

CO2

H

O

PhS

M F F F

F F

F R

-F F

F

R

H F

36 Hydro defluorination

Scheme 6.19 Catalytic SET or HAT mechanism for difluoro-functionalization of Aromatic-CF3

188

P. Chaudhary and S. Popuri

The syntheses of different bioactive difluoroalkylaromatic molecules have been illustrated using the photocatalytic difluoro-alkylation in medicinal chemistry, (as mentioned in Scheme 6.20). The traditional and patented routes followed through difluorobenzylarene intermediates 38, 40, and 42, all of which were prepared via deoxy fluorination of the respective carbonyl compounds. Therefore, growth hormone secretagogue (John 2018) (39) was achieved in 63% yield over the three steps previous method (Ewing et al. 2006) with only 4% yield. The stated synthesis of a Retinoid-related orphan receptor gamma (RORγt) modulator (Ahmed 2014) was accomplished with 67% yield whereas the previous method (Das et al. 2017) gave on 4% yield. In the described synthetic protocol of a pioneer to β2 adrenergic receptor agonist (Das et al. 2017) 43 was accomplished with 91% yield as reported (Peterson et al. 2014) only with 4% yield in 5 steps. All the mentioned examples demonstrated the capability of the photocatalytic procedure to rationalize the formulation of pharmaceutically relevant Aromatic–CF2 R building blocks.

Scheme 6.20 Catalytic difluoro-alkylation in the syntheses of pharmaceutical building blocks with comparison of previous methods

6 Photocatalysis: Application in Drug Derivatization

189

6.6 Conclusions In summary, with the context of drug derivatization the modern advancement of visible-light-mediated photocatalysis has been exhibited through its applications to different arenas such as C(sp3 )-C(sp2 ) cross-coupling reactions including CarbonCarbon, Carbon-Nitrogen, or Carbon-Oxygen bonds, late-stage functionalization, and protein bioconjugation. In this chapter, new approaches have been utilized where visible-lightphotocatalysis is found to be an innovative platform in reactivity where standard 2e- reaction aspects were not observed. This is essential because of the benign environment of visible-light irradiation and their tolerance towards the biologically related solvents. Furthermore, this greener approach to this type of catalysis requires only a minor quantity of catalyst for the reaction to occur via radical pathway. There is no requirement of the harmful or toxic oxidants/reductants or Ultra-Violet radiation of high energy which is one of the advantages of such protocols. This attractive technology attributed towards the inherent challenges that need to be enquired. The large-scale reactions are difficult to be handled where the light penetration into the reaction container is a challenge. Therefore, this drawback has been overcome by solutions such as flow reactor synthesis and immersion-well-photochemical reactors (Porta et al. 2016; Jonathan 2012; Chen et al. 2016). The application in drug discovery/derivatization is established through synthetic chemistry. The photocatalytic platform has guided the promising capability in drug discovery representing a prototype transferal towards single electron transfer pathways.

References Abdel-Magid AF (2014) RORγt modulators are potentially useful for the treatment of the immunemediated inflammatory diseases. ACS Med Chem Lett 5(8):844–845 Afroze S, Meng F, Jensen K, McDaniel K, Rahal K, Onori P, Gaudio E, Alpini G, Glaser SS (2013) Ann Transl Med. 1(3):29 Agostini F, Völler J-S, Koksch B, Acevedo-Rocha CG, Kubyshkin V, Budisa N (2017) Biocatalysis with unnatural amino acids: enzymology meets Xenobiology. Angew Chem Int Ed 56:9680−9703. (b) Liao S-M, Du Q-S, Meng J-Z, Pang Z-W, Huang R-B (2013) The multiple roles of histidine in protein interactions. Chem Cent J 7:44−55 Blaustein AR (2013) Catherine searle, ultraviolet radiation, encyclopedia of biodiversity, 2nd edn, pp 296–303 Bonnet U (2003) Moclobemide: therapeutic use and clinical studies. CNS Drug Rev 9:97–140 (a) Bosset C, Beucher H, Bretel G, Pasquier E, Queguiner L, Henry C, Vos A, Edwards JP, Meerpoel L, Berthelot D (2018) Minisci-Photoredox-mediated α-Heteroarylation of N-protected secondary amines: remarkable selectivity of Azetidines. Org Lett 20(19):6003–6006. (b) David Bacoş P, Lahdenperä ASK, Phipps RJ (2023) Discovery, and development of the enantioselective minisci reaction. Acc Chem Res 56(14):2037–2049 Bottecchia C, Noël T (2019) Photocatalytic modification of amino acids, peptides, and proteins. Chemistry25(1):26–42 Boutin JA, Audinot V, Ferry G, Delagrange P (2005) Molecular tools to study melatonin pathways and actions. Trends Pharmacol Sci 26:412–419

190

P. Chaudhary and S. Popuri

(a) Cannalire R, Pelliccia S, Sancineto L, Novellino E, Tron GC, Gustavian M (2021) Visible light photocatalysis in the late-stage functionalization of pharmaceutically relevant compounds. Chem Soc Rev50:766–897. (b) Hota SK, Jinan D, Panda SP, Pan R, Sahoo B, Murarka S (2021) Organophotoredox-Catalyzed late-stage functionalization of heterocycles. Asian J Org Chem 10(8):1848–1860 Carey JS, Laffan D, Thomson C, Williams MT (2006) Analysis of the reactions used for the preparation of drug candidate molecules. Org Biomol Chem 4:2337–2347 (a) Chan AY, Perry IB, Bissonnette NB, Buksh BF, Edwards GA, Frye LI, Garry OL, Lavagnino MN, Li BX, Liang Y, Mao E, Millet A, Oakley JV, Reed NL, Sakai HA, Seath CP, MacMillan DWC (2022) Metallaphotoredox: the merger of photoredox and transition metal catalysis. Chem Rev 122(2):1485–1542. (b) Lu F-D, He G-F, Lu L-Q, Xiao W-J (2021) Metallaphotoredox catalysis for multicomponent coupling reactions. Green Chem 23:5379–5393 Chen K, Zhang S, He P, Li P (2016) Efficient metal-free photochemical borylation of aryl halides under batch and continuous-flow conditions. Chem Sci 7:3676–3681 Chen X, Ye F, Luo X, Liu X, Zhao J, Wang S, Zhou Q, Chen G, Wang P (2019) Histidine-specific peptide modification via visible-light-promoted C−H Alkylation. J Am Chem Soc 141:18230– 18237 (a) Cheng J-K, Loh T-P (2015) Copper-and Cobalt-catalyzed direct coupling of sp3 α-Carbon of Alcohols with Alkenes and hydroperoxides. J Am Chem Soc137:42−45. (b) Kong D-L, Cheng L, Yue T, Wu H.-R, Feng W-C, Wang D, Liu L (2016) Cobalt-catalyzed peroxidation of 2-oxindoles with hydroperoxides. J Org Chem 81:5337−5344. (c) Chaudhari MB, Moorthy S, Patil S, Bisht GS, Mohamed H, Basu S, Gnanaprakasam B (2018) Iron-catalyzed batch/continuous flow C–H functionalization module for the synthesis of anticancer peroxides. J Org Chem 83:1358−1368 Clegg LE, Penland RC, Bachina S et al (2019) Effects of exenatide and open-label SGLT2 inhibitor treatment, given in parallel or sequentially, on mortality and cardiovascular and renal outcomes in type 2 diabetes: insights from the EXSCEL trial. Cardiovasc Diabetol 18:138 (a) Cravcenco A, Ye C, Gräfenstein J, Börjesson K (2020) Interplay between Förster and dexter energy transfer rates in isomeric donor-bridge-acceptor systems. J Phys Chem A 124(36):7219– 7227. (b) Sun J, Shu M, Wang N, Wang Q, Cao H, Zhang X, Wang B, Zhao J (2022) Förster and Dexter energy transfer boosted and weakened respectively by host−guest complexations between cyano-containing perylene diimide and BODIPY/diiodo-BODIPY functionalized pillar [5] arenes. Dyes Pigments 202:110297–110301. (c) Olaya-Castro A, Scholes GD (2011) Energy transfer from Förster–Dexter theory to quantum coherent light-harvesting. Int Rev Phys Chem 30(1):49–77 Das S, Gharat LA, Harde RL, Shelke DE, Pardeshi SR, Thomas A, Khairatkar-Joshi N, Shah DM, Bajpai M (2017) Preparation of carbocyclic compounds as ror gamma modulators. WO 2017037595, March 9, 2017 Du Y, Pearson RM, Lim C-H, Sartor SM, Ryan MD, Yang H, Damrauer NH, Miyake GM (2017) Strongly reducing, visible-light organic photoredox catalysts as sustainable alternatives to precious metals. Chem.-Eur. J. 23:10962–11096 Ewing W, Li J, Sulsky RB, Hernandez AS (2006) Preparation of azoles as growth hormone secretagogues. US 20060079562, April 13, 2006 Fan X, Rong J, Wu H, Zhou Q, Deng H, Tan J, Xue C, Wu L, Tao H, Wu J (2018) Eosin Y as a direct hydrogen-atom transfer photocatalyst for the functionalization of C-H bonds. Angew Chem Int Ed 57:8514−8518 Fichtner M, Voigt K, Schuster S (2017) The tip and hidden part of the iceberg: Proteinogenic and non-proteinogenic aliphatic amino acids. Biochim Biophys Acta Gen Subj 1861:3258–3269 (a) Gualandi A, Anselmi M, Calogero F, Potenti S, Bassan E, Ceroni P, Cozzi PG (2021) Metallaphotoredox catalysis with organic dyes. Org Biomol Chem 19:3527–3550. (b) Duong La D, Tran CV, Hoang NTT, Duyen Doan Ngoc M, Phuong Nguyen TH, Tung Vo H, Hien Ho P, Anh Nguyen T, Bhosale SV, Cuong Nguyen X, Woong Chang S, Chung WJ, Duc Nguyen D (2020) Efficient photocatalysis of organic dyes under simulated sunlight irradiation by a novel magnetic CuFe2 O4 @porphyrin nanofiber hybrid material fabricated via self-assembly. Fuel

6 Photocatalysis: Application in Drug Derivatization

191

281:118655. (c) Ravelli D, Fagnoni M (2012) Dyes as visible light photoredox organocatalysts. ChemCatChem 4(2):169–171 Gutiérrez-Bonet Á, Tellis JC, Matsui JK, Vara BA, Molander GA (2016) 1,4-Dihydropyridines as Alkyl radical precursors: introducing the Aldehyde feedstock to Nickel/photoredox dual catalysis. ACS Catal 6(12):8004–8008 Hamilton DD, Cotton BA (2010) Cosyntropin as a diagnostic agent in the screening of patients for adrenocortical insufficiency. Clin Pharmacol 2:77–82 (a) Hari DP, Konig B (2014) Synthetic applications of eosin Y in photoredox catalysis. Chem Commun50:6688−6699. (b) Srivastava V, Singh PP (2017) Eosin Y catalysed photoredox synthesis: a review. RSC Adv 7:31377−31392. (c) Yan DM, Chen JR, Xiao WJ (2019) New roles for photoexcited Eosin Y in photochemical reactions. Angew Chem Int Ed 58:378−380 (a) Harry E, Gunning J (1957) The study of free radical reactions through photochemistry. Chem Educ 34(3):121. (b) Fischer H, Baer R, Hany R, Verhoolen I, Walbiner M (1990) 2,2-Dimethoxy-2-phenylacetophenone: photochemistry and free radical photofragmentation. J Chem Soc, Perkin Trans 2:787–798. (c) Avery HE (1974) Photochemical reactions. In: Basic reaction kinetics and mechanisms. Palgrave, London. (d) Wong NGK, Berenbeim JA, Dessent CEH (2019) Direct observation of photochemical free radical production from the sunscreen 2-phenylbenzimidazole-5-sulfonic acid via laser-interfaced mass spectrometry. Chem. Photo, Chem 3(12):1231–1237. (e) Petersen RC, Reddy MS, Liu P-R (2018) Advancements in freeradical pathologies and an important treatment solution with a free-radical inhibitor. SF J Biotechnol Biomed Eng 1(1):1003 He Z, Tan P, Ni C, Hu J (2015) Fluoroalkylative aryl migration of conjugated N-arylsulfonylated amides using easily accessible sodium Di- and monofluoroalkanesulfinates. Org Lett 17:1838– 1841 Hoitink MA, Beijnen JH, Boschma MU, Bult A, Hop E, Nijholt J, Versluis C, Wiese G, Underberg WJ (1997) Identification of the degradation products of Gonadorelin and three analogues in aqueous solution. Anal Chem69(24):4972–4978 Horiuchi M, Akishita M, Dzau VJ (1999) Recent progress in Angiotensin II Type 2 receptor research in the cardiovascular system. Hypertension 33:613–621 Inoa J, Patel M, Dominici G, Eldabagh R, Patel A, Lee J, Xing Y (2020) Benzylic Hydroperoxidation via visible-light-induced Csp3 −H activation. J Org Chem 85:6181–6187 (a) Ji P, Zhang Y, Wei Y, Huang H, Hu W, Mariano PA, Wang W (2019) Visible-light-mediated, chemo- and stereoselective radical process for the synthesis of C-Glycoamino Acids. Org Lett 21(9):3086–3092. (b) Cuadros S, Horwitz MA, Schweitzer-Chaput B, Melchiorre P (2019) A visible-light mediated three-component radical process using dithiocarbamate anion catalysis. Chem Sci 10:5484–5488 (2019). (c) Kim SD, Lee J, Kim N-J, Park BY (2019) Visible-lightmediated cross-couplings and C−H activation via dual photoredox/transition-metal catalysis in continuous-flow processes. Asian J Org Chem 8(9):1578–1587. (d) Lechner VM, Nappi M, Deneny PJ, Folliet S, Chu JCK, Gaunt MJ (2022) Visible-light-mediated modification and manipulation of biomacromolecules. Chem Rev 122(2):1752–1829. (e) Roy S, Chatterjee I (2022) Visible-light-mediated (sp3 )Cα–H functionalization of ethers enabled by electron donor– acceptor complex. ACS Org Inorg Au 2(4):306–311 Jiang Q, Elson-Schwab I, Courtemanche C, Ames BN (2000) γ-Tocopherol and its major metabolite, in contrast to α-tocopherol, inhibit cyclooxygenase activity in macrophages and epithelial cells. Biol Sci 97(21):11494–11499 Sigalos JT, Pastuszak AW (2018) The safety and efficacy of growth hormone secretagogues. Sex Med Rev 6(1):45–53 John Wright P, English AM (2003) Scavenging with TEMPO• to identify peptide- and protein-based radicals by mass spectrometry: advantages of spin scavenging over spin trapping. J Am Chem Soc 125(28):8655–8665 Knowles JP, Elliott LD, Booker-Milburn KI (2012) Flow photochemistry: old light through new windows. Beilstein J Org Chem 8:2025–2052

192

P. Chaudhary and S. Popuri

(a) Kumagai H, Tamaki Y, Ishitani O (2022) Photocatalytic systems for CO2 reduction: metalcomplex photocatalysts and their hybrids with photofunctional solid materials. Acc Chem Res 55(7):978–990. (b) Madec H, Figueiredo F, Cariou K, Roland S, Sollogoub M, Gasser G (2023) Metal complexes for catalytic and photocatalytic reactions in living cells and organisms. Chem Sci 14:409–442. (c) Prier CK, Rankic DA, MacMillan DWC (2013) Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis. Chem Rev 113(7):5322–5363. (d) Dumur F (2019) Recent advances on visible light metal-based photocatalysts for polymerization under low light intensity. Catalysts 9(9):736. https://doi.org/ 10.3390/catal9090736 Li L, Hao C, Zhai R, He W, Deng C (2023) Study on the mechanism of free radical scavenger TEMPO blocking in coal oxidation chain reaction. Fuel331:125853 Li G et al (2013) Alkyl transfer from C-C cleavage. Angew Chem Int Ed 52:8432–8436. (b) Leeuwen TV, Buzzetti L, Perego LA, Melchiorre P (2019) A redox-active nickel complex that acts as an electron mediator in photochemical Giese reactions. Angew Chem Int Ed 58:4953–4957 Lindskog S (1997) Structure and mechanism of carbonic anhydrase. Pharmacol Ther 74:1–20 Liu RH, Orgel LE (1997) Oxidative acylation using thioacids. Nature 389:52–54 (a) Löffler K, Freytag C (1909) Über das ω-Oxy-α-propyl-piperidin und eine neue synthese des piperolidins (δ-coniceins). Ber. Dtsch. Chem Ges42:3427–3431. (b) Hlrnández R, Rivera A, Salazar JA, Suárez E (1980) Nitroamine radicals as intermediates in the functionalization of non-activated carbon atoms. J Chem Soc Chem Commun 20:958–959 (a) Lorthioir O, Corner T, Demanze S, Greenwood R, Proctor K, Stokes S, Turner P (2021) Transfer of photochemistry from UV to visible: an expedient access to a bridged pyrrolidine. Tetrahed Lett 84(9):153447. (b) Green NJ, Xu J, Sutherland JD (2021) Illuminating life’s origins: UV photochemistry in abiotic synthesis of biomolecules. J Am Chem Soc 143(19):7219–7236. (c) Blatchley ER III (2022) Photochemical reactors: theory, methods, and applications of ultraviolet radiation. Wiley. Lv X-L, Wang C, Wang Q-L, Shu W (2019) Rapid synthesis of γ-Arylated Carbonyls enabled by the merge of copper- and photocatalytic radical relay Alkylarylation of Alkenes. Org Lett 21(1):56–59 McCarthy BG, Pearson RM, Lim C-H, Sartor SM, Damrauer NH, Miyake GM (2018) Structureproperty relationships for tailoring Phenoxazines as reducing Photoredox catalysts. J Am Chem Soc 140(15):5088–5101 (a) Narayanam JMR, Stephenson CRJ (2011) Visible light photoredox catalysis: applications in organic synthesis. Chem Soc Rev 40:102−113. (b) Xuan J, Xiao W-J (2012) Visible-light photoredox catalysis. Angew Chem, Int Ed 51:6828–6838. (c) Reckenthaler M, Griesbeck AG (2013) Photoredox catalysis for organic syntheses. Adv Synth Catal 355:2727−2744. (d) Prier CK, Rankic DA, MacMillan DWC (2013) Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis. Chem Rev 113:5322−5363. (e) Schultz DM, Yoon TP (2014) Solar synthesis: prospects in visible light photocatalysis. Science 343:1239176−1−1239176−8. (f) Skubi KL, Blum TR, Yoon TP (2016) Dual catalysis strategies in photochemical synthesis. Chem Rev 116(17)10035–10074. (g) Romero NA, Nicewicz DA (2016) Organic photoredox catalysis. Chem Rev 116(17):10075–10166 (a) Nicewicz DA, Nguyen TM (2014) Recent applications of organic dyes as photoredox catalysts in organic synthesis. ACS Catal4:355−360. (b) Romero NA, Nicewicz DA (2016) Organic photoredox catalysis. Chem Rev 116:10075−10166 (a) Noe¨ T, Zysman-Colman E, The promise, and pitfalls of photocatalysis for organic synthesis. Chem Catal 2:468–476. (b) Li P, Terrett JA, Zbieg JR (2020) Visible-light photocatalysis as an enabling technology for drug discovery: a paradigm shift for chemical reactivity. ACS Med Chem Lett 11(11):2120–2130. (c) Baran W, Masternak E, Sapińska D, Sobczak A, Adamek E (2021) Synthesis of new antibiotics derivatives by the photocatalytic method: a screening research. Catalysts 11(9):1102. (d) König B (2018) Photocatalysis in organic synthesis, science of synthesis, 2018/6. https://doi.org/10.1055/sos-SD-229-00341. (d) Chen Y, Lu L-Q, Yu D-G,

6 Photocatalysis: Application in Drug Derivatization

193

Zhu C-J, Xiao W-J (2019) Visible light-driven organic photochemical synthesis in China. Sci China Chem 62:24–57 (a) Ogawa Y, Tokunaga E, Kobayashi O, Hirai K, Shibata N (2020) Current contributions of organofluorine compounds to the agrochemical industry. iScience 23(9):101467. (c) Nair AS, Singh AK, Kumar A, Kumar S, Sukumaran S, Sukumaran S, Koyiparambath VP, Pappachen LK, Rangarajan TM, Kim H, Mathew B (2022) FDA-approved Trifluoromethyl group-containing drugs: a review of 20 years. Processes 10(10):2054 Peterson L, Ismond KP, Chapman E, Flood P (2014) Potential benefits of therapeutic use of β2Adrenergic receptor agonists in neuroprotection and Parkinson’s disease. J Immunol Res 103780 Plosker GL, Brogden RN (1994) Leuprorelin. A Review of Its Pharmacology and Therapeutic Use in Prostatic Cancer, Endometriosis and Other Sex Hormone-Related Disorders. Drugs 48(6):930– 967 Porta R, Benaglia M, Puglisi A, Chemistry F (2016) Recent developments in the synthesis of pharmaceutical products. Org Process Res Dev 20(1):2–25 Porzelle A, Cooper AWJ, Woodrow MD, Tomkinson NCO (2010) 2-aminophenols containing electron-withdrawing groups from N-Aryl Hydroxylamines. Synlett 2471–2473 (a) Qian H-F, Li C-K, Zhou Z-H, Tao Z-K, Shoberu A, Zou J-P (2018) Visible light-mediated photocatalytic metal-free cross-coupling reaction of Alkenyl Carboxylic Acids with Diarylphosphine Oxides leading to β-Ketophosphine Oxides. Org Lett 20(18):5947–5951. (b) Lu B, Xiao W-J, Chen J-R (2022) Recent advances in visible-light-mediated amide synthesis. Molecules 27(2):517. (c) Liu Q, Wu L-Z (2017) Recent advances in visible-light-driven organic reactions. Nat Sci Rev 4(3):359–380 (a) Renaud P, Sibi MP (2001) Radicals in organic synthesis. Wiley-VCH Verlag GmbH. (b) Rowlands GJ (2011) Synthetic methods. Part (i): free-radical reactions. Ann Rep Prog Chem, Sect B: Org Chem 107:19–33. (c) Phaniendra A, Jestadi DB, Periyasamy L (2015) Free radicals: properties, sources, targets, and their implication in various diseases. Indian J Clin Biochem 30(1):11–26. (d) Gritter RJ (1958) Free radical chemistry in solution. J Chem Educ 35(9):475. (e) Neumann WP, Harendza M, Junggebauer J et al (1993) Applied photochemistry for free radical organic synthesis by means of distannane reagents. J Chem Sci 105:591–601. Kalyanasundaram K, Gratzel M (1998) Coord Chem Rev 177:347−414. (f) Takeda H, Ishitani O (2010) Development of efficient photocatalytic systems for CO2 reduction using mononuclear and multinuclear metal complexes based on mechanistic studies. Coord Chem Rev 254:346−354. (g) Kalyanasundaram K, Gratzel M (1998) Applications of functionalized transition metal complexes in photonic and optoelectronic devices. Coord Chem Rev 177:347−414 (a) Proctor RSJ, Phipps RJ (2019) Recent advances in minisci-type reactions. Angew Chem Int Ed 58(39):13666–13699. (b) Matthew A, Duncton J (2011) Minisci reactions: versatile CHfunctionalizations for medicinal chemists. Med Chem Commun 2:1135–1161 Ruiz-Castillo P, Buchwald SL (2016) Applications of palladium-catalyzed C-N cross-coupling reactions. Chem Rev 116:12564–12649 (a) Sakamoto R, Kashiwagi H, Maruoka K (2017) The direct C–H difluoromethylation of heteroarenes based on the photolysis of hypervalent iodine(III) reagents that contain difluoroacetoxy ligands. Org Lett19:5126–5129. (b) Tung T, Christensen SB, Nielsen J (2017) Difluoroacetic acid as a new reagent for direct C-H difluoromethylation of heteroaromatic compounds. Chemistry 23:18125–18128. (c) Fujiwara Y et al (2012) A new reagent for direct difluoromethylation. J Am Chem Soc 134:1494–1497 (a) Sambiagio C, Marsden SP, Blacker AJ, McGowan PC (2014) Copper catalysed Ullmann type chemistry: from mechanistic aspects to modern development. Chem Soc Rev 43:3525–3550. (b) Qiao JX, Lam PYS (2011) Copper-promoted carbon-heteroatom bond cross-coupling with boronic acids and derivatives. Synthesis6:829–856 Sanz-Vidal A, Gaviña D, Sotorríos L, Gómez-Bengoa E, Ortiz FL, Sánchez-Roselló M, Del Pozo C (2021) Unexpected metal-free synthesis of trifluoromethyl arenes via tandem coupling of dicyanoalkenes and conjugated fluorinated sulfinyl imines. Chem Commun 57:8023–8026

194

P. Chaudhary and S. Popuri

(a) Scholtz C, Riley DL (2021) Improved batch, and flow syntheses of the nonsteroidal antiinflammatory COX-2 inhibitor celecoxib. React Chem Eng6:138–146. (b) Dembitsky VM (2014) Astonishing diversity of natural peroxides as potential therapeutic agents. J Mol Genet Med 9(1). (c) Norris MD, Perkins MV (2016) Structural diversity and chemical synthesis of peroxide and peroxide-derived polyketide metabolites from marine sponges. Nat Prod Rep 33:861−880 (a) Sessler CD et al (2017) CF2H, a hydrogen bond donor. J Am Chem Soc139:9325–9332. (b) Studer AA (2012) Renaissance” in radical trifluoromethylation. Angew Chem Int Ed 51:8950– 8958 Sharma S, Sharma A (2019) Recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis. Org Biomol Chem 17:4384–4405 Song W, Dong K, Li M (2020) Visible light-induced amide bond formation. Org Lett 22(2):371–375 Tabolin AA, Ioffe SL (2014) Rearrangement of N-Oxyenamines and related reactions. Chem Rev 114:5426–5476 (a) Tana JB, Crespo MIC, Duran CP, Roig SG, Munoz AO (2008) Derivatives of 4-(2-Amino-1Hydroxyethyl) Phenol as agonists of the Β2 Adrenergic receptor. WO 2008046598, April 30, 2008 (a) Taylor MT (2022) Photochemical protein modification in complex biological environments: recent advances and considerations for future chemical methods development. Biol Chem403(4):413–420. (b) Xiao F, Zhang X, Lei X (2018) Recent developments and applications of photoconjugation chemistry. Chimia (Aarau) 72(11):782–790 (a) Tsuchikama K, An Z (2018) Antibody-drug conjugates: recent advances in conjugation and linker chemistries. Protein Cell 9(1):33–46. (b) Pettinato MC (2021) Introduction to antibody-drug conjugates. Antibodies (Basel) 10(4):42 Vogt DB, Seath CP, Wang H, Jui NT (2019) Selective C−F functionalization of unactivated Trifluoromethylarenes. J Am Chem Soc 141:13203–13211 (a) Walsh CT, O’Brien RV, Khosla C (2013) Nonproteinogenic Amino acid building blocks for nonribosomal peptide and hybrid polyketide scaffolds. Angew Chem Int Ed52:7098−7124. (b) Humphrey JM, Chamberlin AR (1997) Chemical synthesis of natural product peptides: coupling methods for the incorporation of noncoded amino acids into peptides. Chem Rev 97:2243−2266 (a) Wang S, Wang H, König B (2021) Light-induced single-electron transfer processes involving sulfur anions as catalysts. J Am Chem Soc 143(38):15530–15537. (b) Yang Y, Liu L, Fang W-H, Shen L, Chen X (2022) Theoretical exploration of energy transfer and single electron transfer mechanisms to understand the generation of triplet nitrene and the C(sp3 )-H Amidation with photocatalysts. JACS Au 2(11):2596–2606. (c) Zhang X, Liu L, Li W, Wang C, Wang J, Fang WH, Chen X (2023) Extended single-electron transfer model and dynamically associated energy transfer event in a dual-functional catalyst system. JACS Au 3(5):1452–1463. (d) Li H, Chiba S (2022) Synthesis of α-tertiary amines by polysulfide anions photocatalysis via single-electron transfer and hydrogen atom transfer in relays. Chem Catal 2(5):1128–1142 (a) Wencel-Delord J, Glorius F (2013) C–H bond activation enables the rapid construction and late-stage diversification of functional molecules. Nat Chem 5:369–375. (b) Karka¨s MD, Porco JA Jr, Stephenson CRJ (2016) Photochemical approaches to complex chemotypes: applications in natural product synthesis. Chem Rev 116:17, 9683–9747. (c) Bach T, Hehn JP (2011) Photochemical reactions as key steps in natural product synthesis. Angew Chem Int Ed 50:1000−1045. (d) Hoffmann N (2008) Photochemical reactions as key steps in organic synthesis. Chem Rev 108:1052−1103. Early history of organic photochemistry, see: (e) Roth HD (1989) The beginnings of organic photochemistry. Angew Chem Int Ed Engl 28:1193−1207. (f) Barton DHR, De Mayo P, Shafiq M (1958) Photochemical transformations. Part II. the constitution of Lumisantonin. J Chem Soc 140−145. (g) Ciamician G, Silber P (1908) Introduction: photochemical catalytic processes. Ber Dtsch Chem Ges 41:1928−1935. (h) Barber J (2009) Photosynthetic energy conversion: natural and artificial. Chem Soc Rev 38:185−196. (i) Shaw MH, Twilton J, MacMillan DWC (2016) Photoredox catalysis in organic chemistry. J Org Chem 81(16):6898– 6926. (j) Gratzel M (1981) Artificial photosynthesis: water cleavage into hydrogen and oxygen

6 Photocatalysis: Application in Drug Derivatization

195

by visible light. Acc Chem Res 14:376−384. (k) Meyer T (1989) Optical and thermal electron transfer in metal complexes. J Acc Chem Res 22:163−170 Yu Y, Zhang L-K, Buevich AV, Li G, Tang H, Vachal P, Colletti SL, Shi Z-C (2018) Chemoselective peptide modification via photocatalytic Tryptophan β-Position conjugation. J Am Chem Soc140(22):6797–6800 Zhang W, Xiang XX, Chen J et al (2020) Direct C-H difluoromethylation of heterocycles via organic photoredox catalysis. Nat Commun 11:638 Zhao G, Wang T (2018) Stereoselective synthesis of 2-Deoxyglycosides from Glycals by visiblelight-induced Photoacid catalysis. Angew Chem Int Ed 57:6120−6124 (a) Zhu W, Wang J, Wang S, Gu Z, Aceña JL, Izawa K, Liu H, Soloshonok VA (2014) Recent advances in the Trifluoromethylation methodology and new CF3 -containing drugs. J Fluorine Chem 167:37−54. (b) Morimoto H, Tsubogo T, Litvinas ND, Hartwig JF (2011) A broadly applicable copper reagent for Trifluoromethylations and Perfluoroalkylations of Aryl Iodides and Bromides. Angew Chem Int Ed 50:3793−3798. (c) Le C, Chen TQ, Liang T, Zhang P, MacMillan DWC (2018) A radical approach to the copper oxidative addition problem: Trifluoromethylation of bromoarenes. Science 360:1010−1014. (d) Nagib DA, MacMillan DWC (2011) Trifluoromethylation of arenes and heteroarenes by means of photoredox catalysis. Nature 480:224

Chapter 7

Catalytic Degradation of Drugs Vinod Kumar Yadav, Siddharth Baranwal, and Jeyakumar Kandasamy

7.1 Introduction 7.1.1 Overview of Drug Contamination in the Environment Water pollution creates adverse impact on the environment and animal lives all over the world (Appannagari 2017a, b). Toxic and hazardous pollutants like detergents, pesticides, plasticizers, phenolic compounds, industrial solvents, cosmetic type anthropogenic organic materials, and heavy metals are obtained in high concentrations in the water bodies (Ali 2012). Pharmaceutically active compounds have been a class of emerging water pollutants and they are potentially hazardous to human health and the environment as they are hardly decomposed completely, hence posing a significant challenge to water quality control (Patel 2019a, b). The ubiquity of pharmaceuticals in aquatic systems raises concerns about potential risks to living beings and the environment (Haddaoui and Mateo-Sagasta 2021a–c). These drugs, known for their refractory and stability, can persist in water for extended periods and even their metabolites can remain active. However, the extent of their toxicity and effects on the environment are still under studies (de Andrade et al. 2018). Pharmaceuticals are widely involved to target the diseases and for the betterment of human beings, flora, and fauna; the most frequently detected active pharmaceutical ingredients in water and wastewater effluents include mainly antibiotics, analgesics, anti-inflammatories, antiepileptics, antihypertensives, among others (Lindberg et al. 2014a–d). These substances can have noxious effects such as toxicity to V. K. Yadav · S. Baranwal (B) Kashi Naresh Government Postgraduate College, Gyanpur Bhadohi, UP 221304, India e-mail: [email protected] J. Kandasamy Department of Chemistry, School of Physical, Chemical and Applied Sciences, Pondicherry University, Kalapet, India 197

198

V. K. Yadav et al.

aquatic systems, the development of resistance in pathogenic microorganisms, genotoxicity, and endocrine disruption (Lindberg et al. 2014a). Few of the most useful medicinal compounds including antibiotics, antifungals, and NSIDs are mentioned in Table 7.1. Of particular concern, highly water-soluble compounds are non-steroidal anti-inflammatory drugs (NSAIDs) (Table 7.1-C); their affordability and availability make them commonly prescribed for analgesics, antipyretics, and the treatment of inflammatory disorders, contributing to their high consumption and subsequent presence in water bodies (Izadi et al. 2020). Due to their widespread occurrence, large consumption, potential bioactivity, and toxicity in water make their persistence in the environment and impose potentially harmful impacts on human life and water resources including hospital wastewaters, STP effluents, rivers, lakes, marine water, and soil matrices (Parolini 2020). Moreover, antibiotics (Table 7.1-A) are extensively used to control diseases and improve health in humans, flora and fauna (Walsh 2003). Antibiotics, in particular, are highly consumed in countries such as India, China, Brazil, Russia, and South Africa (Kovalakova et al. 2020a, b). The excessive uptake of antibiotics has led to adverse effects on human health and the development of antibiotic-resistant microbes (Serwecińska 2020). The same way fungicides can be effective in preventing and treating fungal diseases, their widespread use can have several consequences. Fungicides are highly water soluble and persistent in nature, their accumulation over time in soil and water, increasing the likelihood of exposure to living organisms, including humans (Ali et al. 2021). Prolonged exposure or high levels of exposure to certain fungicides have been associated with various health issues, including skin irritation, respiratory problems, and even more severe conditions like cancer (Mostafalou and Abdollahi 2017). The fungicides Thiram, Carbendazim, and Propiconazole (Table 7.1-B) are heavily used in crop production. Recently the mutagenity of thiram and its toxicity is well explored (Gómez-Ortíz et al. 2020). In crop production, the pesticide demand has also increased due to extensive usage in agriculture. However, the removal of pesticides from wastewater poses challenges, resulting in the persistent and toxic nature of these contaminants in various water bodies (Syafrudin et al. 2021a, b). In addition, phenol and phenolic chemicals, commonly used in the manufacturing of pharmaceuticals and other industries including pesticides, textiles, plastics, and pulp and paper, have significantly impacted the environment due to their carcinogenic and toxic properties (Sable et al. 2018). Bisphenol A (BPA), a widely used phenol derivative found in epoxy resins, drinking water bottles, and consumer products, is considered an endocrine-disrupting chemical (EDC) that disrupts hormone function and adversely affects living organisms (Teh and Mohamed 2011).

7 Catalytic Degradation of Drugs

199

Table 7.1 Some common medicines in different classes

7.2 Role of Catalysis in Drug Degradation With the growing concern over the presence of drug and drug related materials in industrial wastewater and other sources, there is a pressing need to address their detrimental effects on the ecosystem (Knopp et al. 2016). Existing physicochemical and biochemical treatment processes have been widely employed however; their design and strategies were not specifically targeted for such contaminants at considerable concentrations (Crini and Lichtfouse 2019). Consequently, there is a critical demand to develop efficient treatment processes tailored to address the challenges posed by hard-to-remove contaminants, particularly drug related materials (Tambosi et al. 2009). Among the array of advanced treatment methods available (Fig. 7.1), including membrane-based, advanced oxidation processes (AOPs), UV-illuminated, electrochemical, ultrasonic, ion exchange, photo-Fenton processes, and biological methods, each has its drawbacks such as leaving residues, requiring longer reaction times, and generating byproducts as contaminants (Zhou and Smith 2001a–f). In light of this, the chapter aims to focus on the catalytic degradation of pharmaceutical drugs as a potential solution for mitigating their presence in water bodies. By thoroughly exploring various catalytic strategies and their effectiveness in degrading pharmaceuticals, our review seeks to contribute to the understanding of this emerging field and underscore the importance of developing environmentally friendly approaches to address the challenges posed by pharmaceutical pollutants in water resources. By shedding light on the promising potential of catalytic drug degradation, we hope to pave the way for the implementation of more effective and eco-friendly solutions in the field of wastewater treatment.

200

V. K. Yadav et al.

Fig. 7.1 Pictorial presentation of catalytic degradation

7.3 Nanoparticle Based Photon Assisted Catalytic Degradation The fundamental process of photocatalysis involves the photo-excitation of a solid semiconductor caused by the absorption of electromagnetic energy. Photocatalysis is a process of breaking down substances using light energy. This happens when a photon of light becomes energetic enough to surpass the energy barrier of 3.2 electronvolts (eV) in anatase TiO2 (titanium dioxide). As a result, an electron is elevated from the lower energy valence band (VB) to the higher energy conduction band (CB). This movement of the electron creates an empty space, known as a hole (h+ ), in the valence band (Opoku et al. 2017a, b). These charge carriers have the capacity to trigger oxidation or reduction, respectively. Typically, the process of using photocatalysis to break down water-based pollutants involves employing air. This encourages the creation of super-oxide ions (O2 −• ) at the conduction band (CB) through the interaction of free electrons with oxygen (O2 ). Simultaneously, hydroxyl radicals (HO• ) are produced at the valence band (VB) due to the presence of water (H2 O). The breakdown of pollutants happens at the active sites of TiO2 nanomaterials, leading to the formation of CO2 , H2 O, and other intermediate products. This is primarily due to the highly reactive nature of hydroxyl radicals. Doping within the TiO2 material involves introducing dopant atoms into its structure as illustrated in Fig. 7.2. The incorporation of metal dopants alongside TiO2 has been documented as a means to modify the rate at which charge carriers recombine, the energy of the band gap, and the physical characteristics. Metal dopants play a critical role in capturing electrons, facilitating the separation of charge carriers, and slowing down the recombination process. The inclusion of metal dopants has resulted in a shift of the band gap’s edge towards longer wavelengths by reducing the energy band gap of pure TiO2 by altering the energy level of the conduction band towards higher values (Fig. 7.2). Frequently, TiO2 nanomaterials doped with metals exhibit

7 Catalytic Degradation of Drugs

201

Fig. 7.2 Photocatalytic degradation of pollutant using TiO2 NPs showing reduction in band gap by metals or nonmetals doping

improved performance under visible and solar light in comparison to undoped TiO2 . Similarly, the introduction of non-metal dopants significantly reduces the energy band gap of pure TiO2 by shifting the energy level of the valence band towards lower values. The substitution of oxygen with non-metal dopants leads to the creation of oxygen defects, which in turn decreases the energy band gap of non-metal doped TiO2 nanomaterials (Fig. 7.2) (Bahnemann et al. 1991a, b). There are a few examples from nanopartical based with doped TiO2 , other than doped TiO2 and tetrapyrrolic macrocycle (TPM) based photocatalyst are discussed below.

7.4 Doped TiO2 Nanomaterials as Photocatalyst Titanium dioxide (TiO2 ) is potentially used for different applications, as it is chemically stable, non-toxic, and also comparatively economical (Opoku et al. 2017). Under various light sources, the use of different metal- and non-metal doped TiO2 nanoparticles against pharmaceutical degradation has been well studied. Metal and non-metal doping on TiO2 has been found to be an excellent method for creating nanophotocatalysts because it makes it easier to separate charge carriers and improves photocatalyst performance (Teoh et al. 2012). In both metal and non-metal doping the band gap energy is reduced, improving the performance of the photocatalyst when exposed to UV, visible, and solar light (Rauf et al. 2011). TiO2 is a substance that numerous researchers frequently employ for degradation of many drug and drug based molecules, including oflaxacin, ibuprofen, carbendazim, propiconazole, acetaphate, metronidazole, amoxicillin, 2,4-dichloro-phenoxyacetic acid

202

V. K. Yadav et al.

thiram, phthalic acid, diclofenac, chloramphenicol and many others. There is a brief discussion on the use of doped TiO2 nanoparticles under different light sources in the photocatalytic degradation of some drugs. Ofloxacin, ibuprofen, carbendazim, propiconazole, and acephate, all are photocatalytically degraded under natural solar light irradiation utilizing metal/non-metal doped TiO2 NPs, as shown in Table 7.1. Ni doped TiO2 nanomaterial (Table 7.2 entry 1) is reported by using a hydrothermal process (Kundu et al. 2014). In a doublewalled photocatalytic reactor using natural sunlight, the photocatalytic degradation of ofloxacin is examined (Kundu et al. 2014). It is discovered that significant aqueous pollutant degradation is seen with the use of Ni-TiO2 nanomaterial. Preparation of NiTiO2 nanomaterials is well-known through sol–gel method with Ni dopant concentration of 0.5 wt.%. Under natural solar light illumination, significant photocatalytic degradation efficiency against aqueous ibuprofen (Table 7.2 entry 1) solution is found upto 78% (Kundu et al. 2014). Similarly, Bi-TiO2 (Table 7.2 entry 2) nanomaterial is prepared using the sol–gel technique and 89% of degradation efficiency against the ibuprofen solution is seen (Bhatia and Dhir 2016). Fe doped TiO2 nanomaterials with Fe doping are prepared through impregnation method and the optimized concentration of 2 wt.% obtained (Kaur et al. 2016). Photocatalytic degradation performance is checked against two model aqueous drugs, i.e., carbendazim and propiconazole (Table 7.2 entry 3). Under solar light illumination, the individual degradation of carbendazim and propiconazole, the requirement of optimized FeTiO2 (2 wt.%) is 1 g/L and 0.25 g/L respectively. Furthermore non-metal N doped TiO2 nanotube is prepared for photocatalytic degradation of acephate (Table 7.2 entry 4) under natural solar light illumination (Zhang et al. 2015). It is observed that N-TiO2 nanotube arrays have shown noticeably higher photocatalytic performance efficiency upto 84%. Under visible light radiation source, metal/non-metal doped TiO2 nanomaterials are performed against drug and drug like molecules (Table 7.2 entries 5–8). Visible light assisting Ni doped TiO2 NPs are synthesized through ultrasonic mediated sol–gel method. Photocatalytic drug degradation experiment is carried out against Bisphenol A (Blanco-Vega et al. 2017). Optimum photocatalytic degradation efficiency is observed in 1 wt.% Ni doped TiO2 nanomaterials upto 93% (Table 7.2 entry 5). Silver doped hollow TiO2 NPs are synthesized through sol–gel method. The photocatalytic degradation of metronidazole is examined through the synthesized NP and its performance is reported upto 96% (Boxi and Paria 2015). Moreover, Ag doped TiO2 NPs are also utilized to break down amoxicillin under a visible light source. Ag doping concentration of 3 wt.% has shown significantly better photocatalytic activity against the amoxicillin drug (Table 7.1 entry 6) (Leong et al. 2014). Similarly, Chromium doped TiO2 nanoparticles were produced using the flame spray pyrolysis process (Tian et al. 2012). The 2,4-dichlorophenol is subjected to photocatalytic degradation (Table 7.1 entry 7). In comparison to undoped TiO2 nanomaterial, 1 atom% Cr-TiO2 nano-photocatalysts demonstrated nearly three times the photoactivity against aqueous drug solution. Furthermore, non-metal S doped TiO2 nanotube is prepared for photocatalytic degradation of diclofenac (Table 7.2 entry 8) under visible light illumination. It is observed that S-TiO2 nanotube arrays have

7 Catalytic Degradation of Drugs

203

Table 7.2 Doped TiO2 NPs under different light sources in the photocatalytic degradation of some drugs and related molecules Sn.

Doped TiO2 NP

Drug for degradation

Performance (%)

Photocatalytic drug degradation by doped TiO2 under solar irradiation 1

Ni-TiO2 (3/0.5 wt.% Ni)

Oflaxacin/Ibuprofen

70/78

2

Bi-TiO2 (0.25 wt.% Bi)

Ibuprofen

89

3

Fe-TiO2 (2 wt.% Fe)

Carbendazim/Propiconazole

98/90

4

N-TiO2

Acephate

84

Photocatalytic drug degradation by doped TiO2 under visible light radiation 5

Ni-TiO2 (*wt.% Ni)

Bisphenol A

93

6

Ag-TiO2 (*/3 wt.% Ag)

Metronidazole/Amoxicillin

96/63

7

Cr-TiO2 (1 wt.% Cr)

2,4 dichlorophenol

63

8

S-TiO2

Diclofenac

93

Photocatalytic drug degradation by doped TiO2 under UV light irradiation 9

Ni/Fe/Cu-TiO2 (1 wt.% Ni)

Neproxen sodium

84/99/87

10

Ag-TiO2 (0.96 wt.% Ag)

Chloramphenicol

~100

11

Sn-TiO2 (1.5 mol.% Sn)

Amoxicillin trihydrate

0.25a

12

N-TiO2

Malathion

97

* a

Ag doped hollow TiO2 pseudo-first order reaction min−1

shown noticeably higher photocatalytic performance efficiency upto 93% (Yi et al. 2019). Neproxen sodium, chloramphenicol, amoxicillin trihydrate, and malathion drug all are photocatalytically degraded under ultraviolet light irradiation, utilizing metal/ non-metal doped TiO2 NPs (Table 7.2 entries 9–12). Ni, Cu, and Fe doped TiO2 is prepared using sol–gel process. Utilizing prepared metal doped TiO2 NPs, the photocatalytic performance is monitored against aqueous solution of naproxen sodium drug molecule individually in the presence of UV light (Hinojosa-Reyes et al. 2019). Among these metals; Fe doped TiO2 NPs show maximum degradation efficiency upto 99% with 1 wt.% dopant concentration (Table 7.2 entry 9). Furthermore, Silver doped TiO2 NPs is prepared through photodeposition method (Table 7.2 entry 10). Nearly complete degradation of chloramphenicol drug with Ag-TiO2 NP is reported at optimum silver doping conditions (Shokri et al. 2013). Thereafter Sn-TiO2 NPs for the degradation of antibiotic, amoxicillin trihydrate drug is well demonstrated in laboratory quartz photoreactor under UV radiation (Mohammadi et al. 2012). At 1.5 mol.% Sn-TiO2, the optimum photocatalytic performance is mentioned against the amoxicillin (Table 7.2 entry 13). The non-metal N doped TiO2 nanotube is prepared through microwave mediated method for photocatalytic degradation of malathion (Table 7.2 entry 14) under UV light illumination. It is observed that NTiO2 NPs have shown noticeably higher photocatalytic performance efficiency upto 97% (Kadam et al. 2014).

204

V. K. Yadav et al.

Table 7.3 Nanoparticles under different light sources in the photocatalytic degradation of drugs SN

Doped NP

Drug for degradation

Performance (%)

1

Cu–ZnO/Fe-ZnO (Vis light)

Amlodipine besylate

90

2

ZnFe2 O4 -PCz (MW)

Amoxicillin

80

3

BiVO4 -GQDs (Solar)

Carbamazepine

98/90

7.5 Nanomaterials as Photocatalyst Other Than TiO2 There are several methods designed to prepare photocatalysts using nanomaterials other than TiO2 . The synthesis of Cu doped ZnO, and Fe doped ZnO nanocatalysts have been synthesized by a co-precipitation method (Table 7.3 entry 1). These nanocatalysts are treated for the degradation of amlodipine besylate drug which is generally used for the prevention of high blood pressure and angina. Here the optimum degradation efficiency of amlodipine besylate (approximately 90%) is observed using Fe doped ZnO as the nanocatalyst under visible-light irradiation with 100 mL of H2 O2 (Alizadeh and Baseri 2018). Moreover microwave-assisted the catalytic degradation of antibiotic amoxicillin drug using ZnFe2 O4 nanoparticles hybrid with polycarbazole (PCz) is demonstrated (Table 7.3 entry 2) (Zia et al. 2020). The degradation efficiency of amoxicillin drug is performed with exposure to microwave irradiation. The UV peaks related to the drug are found at 276 and 350 nm. The degradation efficiency of amoxicillin drug without catalyst was observed at 52% (for 276 nm) and 58% (for 350 nm) while in the presence of catalyst it led to 77% (for 276 nm) and 80% (for 350 nm). Similarly, the development of an effective and sustainable method for environmentally persisting psychiatric carbamazepine drug degradation is demonstrated using solar-driven catalysis (Table 7.3 entry 3) (Tang et al. 2017). The application of advanced materials like graphene quantum dots (GQDs) and BiVO4 heterostructures offers promising possibilities for addressing water pollution caused by such environmentally recalcitrant drugs. They conveyed the potential degradation of the drug with minimum residues of transformation products during the photocatalytic process.

7.6 Tetrapyrrolic Macrocycle (TPM) as Photocatalyst Tetrapyrrolic macrocycle (TPM), is a large ring-like structure consisting of four pyrrole units linked together (Piccirillo et al. 2021). TPM based catalysts have shown promising applications in oxidative degradation of different classes of drugs (Silvestri et al. 2022). The mechanistic perspective is well studied for the photochemical degradation of pharmaceuticals using tetrapyrrole-based catalysts (Yin et al. 2015). Tetrapyrroles are a class of organic compounds known for their ability to act as photosensitizers, which means they can efficiently capture light energy and transfer it to other molecules. The role of tetrapyrrole-based catalysts in this context

7 Catalytic Degradation of Drugs

205

is to enhance the degradation of pharmaceuticals through the generation of reactive oxygen species (ROS) upon exposure to light. These ROS, such as hydroxyl radicals (OH• ) and singlet oxygen (1 O2 ), are highly reactive and can break down the chemical bonds in pharmaceutical compounds, leading to their degradation into smaller, less harmful byproducts (Nonell and Flors 2016). One of the most wellknown and widely studied examples of tetrapyrrolic macrocycle-based catalysts is heme, which is the active component in hemoglobin and plays a crucial role in biological oxidation reactions (Fernández et al. 2016). The unique electronic and structural properties of tetrapyrrolic macrocycles lead to act as a photosensitizer hence it makes TPM attractive for photocatalysis as well. It is noteworthy that hybrid materials incorporating semiconductors frequently employ tetrapyrrolebased photodegradation catalysts to benefit from their absorption in the UV area and complementing methods of drug degradation (Anucha et al. 2021). There are several reports of drug degradation by TPM based catalyst. Among these, the antibiotics of the tetracycline family, i.e., tetracycline, oxytetracycline, and their corresponding hydrochloride salts are the most studied regarding their photodegradation (Li et al. 2019; He et al. 2019; Liu et al. 2020; Yao et al. 2016). The synthesis of CeO2 /Bi2 MoO6 nanofibers is achieved by sensitizing them with 2,9,16,23-tetranitro copper(II) phthalocyanine (TNCuPc) through a simple two-step electrospinningsolvothermal method (Li et al. 2019). This leads to the arrayed growth of TNCuPc granules on the surface of CeO2 /Bi2 MoO6 nanofibers. The resulting one-dimensional TNCuPc/CeO2 /Bi2 MoO6 photocatalysts exhibit rapid separation of photogenerated carriers, respond to a wide range of solar light, and display outstanding photocatalytic efficiency, recyclability, and long-term stability for tetracycline (TC) degradation under simulated sunlight. This impressive performance is attributed to the sensitization effect of TNCuPc and the synergistic interactions among TNCuPc, CeO2 , and Bi2 MoO6 . The TNCuPc/CeO2 /Bi2 MoO6 nanofibers achieve a high degradation rate of up to 94.6%. This improved photocatalytic performance is a result of the combined influence of TNCuPc, CeO2 , and Bi2 MoO6 , working together synergistically. TPM based α-substituted zinc(II) 1, 8(11),15(18),22(25)-tetrakis(4carboxylphenoxy) phthalocyanine (α-ZnTcPc) is used as a sensitizer and derive a catalyst on a graphitic carbon nitride (g-C3 N4 ) for a semiconducting photocatalyst through polycondensation process to degrade the tetracycline in the presence of visible light (Table 7.4 entry 1). At optimum conditions, the degradation of tetracycline is investigated approx 91% (He et al. 2019). Similarly, zinc(II) β-tetraaminophthalocyanine (ZnTAPc) associated with semiconducting Cu2 O–TiO2 layer derived TPM catalyst is used under visible-light irradiation (Table 7.4 entry 2). The experiment has shown efficiencies in the full degradation of tetracycline-hydrochloride (TC•HCl) (Liu et al. 2020). Furthermore copper-porphyrin metal–organic frameworks based photocatalyst is utilized to encourage the degradation of norfloxacin under visible-light irradiation, reaching 44% degradation at 100 min of irradiation. Additionally, microsphere (FeTCPP–TDI–TiO2 ) is successfully prepared by toluene disocyanate (TDI) as a bridging molecule, for grafting tetra-(carboxyphenyl) porphyrin iron (FeTCPP) on the surface of TiO2 microspheres (Table 7.4 entry 3)

206

V. K. Yadav et al.

Table 7.4 TPM based photocatalytic degradation of drugs in presence of visible light sources Sn.

Doped NP

Drug for degradation

Performance (%)

1

TNCuPc/CeO2 /Bi2 MoO6

Tetracycline

94.6

2

α-ZnTcPc/g-C3 N4

Tetracycline

91

3

ZnTAPc/Cu2 O-TiO2

Tetracycline•HCl

100

4

FeTCPP–TDI–TiO2

Norfloxacin

100

(Yao et al. 2016). The photocatalyst is utilized to break down norfloxacin completely in just 2 h of visible-light irradiation.

7.7 Oxidative Degradation Based Catalysts Advanced oxidation processes (AOPs) are one of the most prominent ways to degrade organic materials and drug molecules as well. It is carried out at temperatures close to ambient using extremely reactive radicals as their main oxidants, particularly the hydroxyl radical (OH• ) (Glaze et al. 1991). It is obvious that the OH• radical is one of the most potent oxidizing species employed in the treatment of water and wastewater and has the potential to significantly speed up the oxidation of drug materials. AOPs are broadly divided into two parts for the generations of hydroxyl radical such as photochemical catalytic and non-photochemical catalytic methods (Ikehata et al. 2006a, b). In both ways, catalysts are required for the degradation of drug materials. The photochemical nanomaterials and TiO2 based catalysts are discussed earlier in detail here some other classes of examples are shown.

7.8 Photocatalytic Ozonation Reactions The study of photocatalytic ozonation reactions focuses by A. Hassani et al. on the simultaneous degradation of a mixture of three pharmaceuticals (metronidazole (MET), ciprofloxacin (CIP), and acetaminophen (ACP) using a photocatalytic ozonation system (Table 7.5 entry 1) (Hassani et al. 2017). Titanium dioxide is served as the nanoparticles based catalyst, immobilized onto montmorillonite support and irradiated with ultraviolet-A light in the presence of ozone. Under optimized conditions with various operational parameters to achieve the highest degradation of each pharmaceutical: MET degradation reached 64%, CIP degradation reached 80%, and ACP degradation reached 50%. The optimized conditions have enabled the maximum simultaneous degradation of all three pharmaceuticals. Furthermore, a mixture of eight emerging contaminants of pharmaceutical origin (acetaminophen, antipyrine, caffeine, hydrochlorothiazide, sulfamethoxazole, ketorolac, metoprolol, and diclofenac,) is treated using ozonation with visible LED

7 Catalytic Degradation of Drugs

207

Table 7.5 Oxidative degradation based photocatalytic ozonation reactions of drugs SN

Doped NP

Drug for degradation

Performance (%)

1

O3 /TiO2 -montmorillonite (UV-A)

MET/CIP/ACP

64/80/50

2

O3 /GO/TiO2 (visible)

8 drugs

Upto 92

3

O3 /UVC/chlorination

Paracetamol

~100 (3 h)

4

O3 /4% Ag-g-C3 N4 /solar

Acetaminophen

~83 (2 h)

radiation and a graphene oxide/titania (GO/TiO2 ) catalyst (Table 7.5 entry 2) (Checa et al. 2020). The study remarks the degradation and mineralization of all contaminants are enhanced in the following sequence: O3 /GO/TiO2 < O3 /visible < O3 /GO/ TiO2 /visible. This enhancement is attributed to the production of more OH from O3 reduction. Overall, the study demonstrates the benefits of using composites of TiO2 with high adsorbent materials for the remediation of wastewaters contaminated with pharmaceuticals and other drugs, especially when combined with visible light upto 92% of the drug degradation is achieved. In addition, there is a notable application involving a hybrid approach combining O3 /UVC and chlorination (with 15% NaClO) (Table 7.5 entry 3) (Ekowati et al. 2019). The results show that the initial concentration of paracetamol is at 5 μgL−1 is completely eliminated after a 3 h treatment involving O3 /UVC/chlorination. However, substances like caffeine and ibuprofen necessitated a longer hybrid treatment of 24 h. In addition, a straightforward calcination approach is established by a successful synthesis of 4% Ag-g-C3 N4 (Table 7.5 entry 4) (Ling et al. 2019). This composite exhibits enhanced catalytic performance when subject to simulated solar light. This is attributed to the incorporation of Ag nanoparticles, which act as efficient carriers for photon-generated electrons. The Ag component within the 4% Ag-g-C3 N4 composite serves as the site for ozone decomposition, yielding an increased electron supply for ozone degradation and generating a higher percentage of hydroxyl radicals (OH• ) compared to pure g-C3 N4 . This elevated presence of both OH• radicals and electron holes contribute synergistically and results in heightened catalytic efficiency by which the concentration of acetaminophen is degraded upto 83% at 120 min of exposure under solar irradiation.

7.9 Non-photochemical Catalysts 7.9.1 Fenton System (H2 O2 /Fe2+ ) Over a hundred years ago Fenton reported the degradation of maleic acid through oxidation process (Brillas et al. 1998). In this method, ferrous ion and hydrogen peroxide are used as catalysts and oxidants respectively which react together and generate hydroxyl radicals (Skoumal et al. 2006). Ferrous (II) ion oxidizes to ferric (III) ion in a matter of seconds to minutes in the presence of sufficient hydrogen

208

V. K. Yadav et al.

peroxide due to the high rate constant for the interaction of ferrous ion with hydrogen peroxide. However, Hydrogen peroxide is catalytically decomposed by ferric (III) ion and produces hydroxyl radicals once more. It is believed that most waste destruction catalyzed by Fenton’s reagent is simply a Fe (III)–H2 O2 system catalyzed destruction process, and Fenton’s reagent with an excess of hydrogen peroxide is essentially a Fe(III)–H2 O2 process known as a Fenton-like reagent. By employing several phthalocyanine (TPM) based catalysts and H2 O2 as the oxidant, Lu’s group continues their thorough investigation of carbamazepine (CBZ) degradation under Fentonlike oxidation conditions (Zhu et al. 2016). In the first investigation, the FePc-PAN nanofibers are created by blending iron phthalocyanine (FePc) onto polyacrylonitrile (PAN). The degradation of CBZ in the presence of oxidants H2 O2 is carried out using the catalyst (Zhu et al. 2016). The reusability of the catalyst is eight times of the catalyst and it is not a discernible decrease in activity. Afterwards, the same group used H2 O2 as an oxidant once more to test the iron(II) hexadecafluorinated phthalocyanine µ-oxo dimer (FePcF16 )2 O as a catalyst for CBZ degradation (Zhou et al. 2017). The degradation of carbamazepine (CBZ) solution in the presence of oxidants H2 O2 and the catalyst is completely destroyed in 40 min.

7.9.2 Catalytic Ozonation Reactions Ozone is a toxic and unstable gaseous compound that is rapidly transformed into O2 . The rate of decomposition of ozone in water increases as pH rises. Ozone in water, for instance, might have a half-life of less than 1 min at pH 10. Organic species may oxidize as a result of the interactions between molecular ozone and OH• radicals (Andreozzi et al. 2003). Super-oxide anion radical O2 •− and hydroperoxyl radical HO2 • are produced when hydroxide ions and ozone react (I). This super-oxide anion radical O2 •− further reacts with ozone to produce ozonide anion radical O3 •− (II) and it rapidly forms hydrogen ozonide radical (III) which breaks down to finally produce the hydroxy radical OH• (IV) (see Scheme 7.1). Utilizing heterogeneous or homogeneous catalysts in the above chain reaction is another way to quicken ozonation reactions. To enhance the catalytic ozonation process (COP) for the elimination of Acetaminophen (ACT) Hormuz Red Soil (HRS), a naturally occurring mineral rich in hematite (α-Fe2 O3 ), is utilized (Table 7.6 entry 1) (Kohantorabi et al. 2022). The surface properties and particle size of HRS through calcinations have been modified, resulting in a catalyst named C-HRS, which reveals significant catalytic activity. The catalytic activity of C-HRS has been assessed for the ozonation of ACT under various conditions. Remarkably, complete degradation of 50 mg L−1 ACT is achieved within just 10 min at natural conditions when using Scheme 7.1 Generation of hydroxyl radical through catalytic ozonation reaction

7 Catalytic Degradation of Drugs

209

1.0 g L−1 of C-HRS. This rate is more than ten times faster than the single ozonation process (SOP) without the catalyst. Overall, this study introduces a novel and efficient catalyst, C-HRS, derived from Hormuz Red Soil, which enhances the ozone-based degradation of ACT and potentially other pollutants, offering a promising approach for pollutant removal in wastewater treatment. Further, a modified thermal/sol–gel method is demonstrated to prepare a magnesium oxide (MgO) powder as a heterogeneous catalyst in the ozonation of acetaminophen (ACT) (Table 7.6 entry 2) (Mashayekh-Salehi et al. 2017). For this purpose, anhydrous magnesium acetate (Mg(C2 H3 O2 )2 ) is used as the precursor for magnesium along with ammonium hydroxide as an alkaline and gelation agent and sodium dodecyl sulfate (SDS) surfactant which acts as a capping agent. The optimized condition is proposed calcinations at 500 °C where modified MgO catalyst performs with a high percentage of catalytic activity. Overall, the modified MgO catalyst exhibits high catalytic activity for the ozonation of ACT, suggesting its potential as an effective catalyst for pollutant removal in wastewater treatment. Similarly, iron and manganese ions are investigated as heterogeneous catalysts for accelerated oxidation of chlorobenzenes in effluents (Cortes et al. 2000). They conclude that the ozone/catalyst system is more effective in reducing total organic carbon (TOC) and chemical oxygen demand (COD) from effluents than oxidation with ozone at high pH levels. The elimination of organochloride is more efficient using the O3 / Mn(II) and O3 /Fe(II) systems. Furthermore, there is exploration of a hybrid catalytic ozonation strategy involving SnO2 nanoparticles (Table 7.6 entry 3) (Rashidashmagh et al. 2021). The experimental procedures involve 250 mL of a solution containing 50 ppm of a drug and 30 g L−1 of the catalyst in pure water, maintaining a pH of 7.0. The system is operated with the introduction of 1.3 g O3 per hour. Notably, the utilization of a catalyst with a substantial quantity of SnO2 nanoparticles yields significant enhancements in the degradation and mineralization of paracetamol. The ozonation process increased to 98% when employing O3 /SnO2 NPs for 20 min. Correspondingly, the mineralization at the 30-min mark shows a considerable rise to 83% in the O3 /SnO2 NPs scenario, underscoring the potent catalytic capability of the SnO2 nanoparticle catalyst. The researchers note the remarkable stability of the catalytic activity of SnO2 NPs even after four consecutive runs. Moreover, a study was conducted to synthesize a sophisticated catalyst termed Fe3 O4 /Ce-MOF (Ce-UiO-66) for integration with ozonation using 50 mL of pure water containing 25 ppm of a drug and 0.16 g L−1 of the catalyst (Table 7.6 entry 4) (Mohebali et al. 2022). Notably, at optimized pH of 5.6 with the 10-min mark, the progression of Table 7.6 Oxidative degradation based non-photocatalytic ozonation reactions of drugs Sn.

Doped NP

Drug for degradation

Performance (%)

1

O3 /HRS NPs/H2 O2

Acetaminophen

86

2

O3 /MgO/SDS

Acetaminophen

94

3

O3 /SnO2 NPs

Paracetamol

98

4

O3 /Fe3 O4 /Ce-MOF

Paracetamol

87

210

V. K. Yadav et al.

PCT degradation stands as follows: 51% for O3 /Fe3 O4 < 70% for O3 /Ce-MOF < 87% for O3 /Fe3 O4 /Ce-MOF. The remarkable superiority of the O3 /Fe3 O4 /Ce-MOF treatment becomes evident through the elimination of 55% of total organic carbon (TOC). The researchers validated the Fe3 O4 /Ce-MOF catalyst’s reusability for five cycles.

7.9.3 Oxidants Assisted Tetrapyrrolic Macrocycle-Based Catalysts In the absence of light, metal complexes of tetrapyrrolic macrocycles can also promote substrate oxidation in the presence of oxidants such as O2 or H2 O2 (Piccirillo et al. 2021). These catalysts often possess a central metal ion, such as iron (Fe), cobalt (Co), or manganese (Mn), coordinated within the macrocycle, which enhances their catalytic activity. An eco-friendly heterogeneous catalyst is developed (CoPcGO-PMS) by graphene oxide (GO) supported cobalt phthalocyanine (CoPc) to activate peroxymonosulfate (PMS), generating hydroxyl and sulfate radicals for efficient degradation of norfloxacin (NOR) in water. The degradation of NOR is reported 100% in 1 h (Zhang et al. 2018). Similarly, hybrid catalysts FePc-P4VP-PAN are prepared by adsorbing iron phthalocyanine (FePc) onto poly(4-vinylpyridine)polyacrylonitrile (P4VP-PAN) nanofibers (Zhu et al. 2017). Using a catalyst concentration of 1000 ppm, in the presence of a 10 mM hydrogen peroxide solution as an oxidant, 95% of sulfaquinoxaline (SQX) was degraded in 2 h. Moreover, the chemical degradation of diclofenac is catalyzed by iron(II) octacarboxyphthalocyanine (FeC8Pc) using hydrogen peroxide or sodium periodate (NaIO4 ) as oxidants (Nackiewicz et al. 2021). The complete degradation is observed using H2 O2 (in 35 min) and NaIO4 (25 min) at a substrate catalyst 50:1 molar ratio. Interestingly FeC8Pc also entirely decomposes by itself as a result of the generation of hydroxyl radicals from the oxidants. Cobalt (II) tetracarboxyphthalocyanine (CoC4Pc) is prepared by electrostatically linking it to an amino-functionalized manganese octahedral molecular sieve (CNOMS) (Wu et al. 2019). The catalytic performance of CoC4Pc-CNOMS on the degradation of a 10 ppm, diclofenac aqueous solution is investigated using peroxymonosulfate (PMS) as an oxidant. Upto 99% of the diclofenac is degraded after 20 min of action. It is noteworthy that catalyst reusability is also conducted that is monitored at four cycles (see Table 7.7).

7.10 Conclusion In summary, this chapter focuses on the catalytic degradation of drugs as a means of environmentally friendly drug removal. The main objective is to counteract the negative effects of drug contamination in the environment by employing advanced

7 Catalytic Degradation of Drugs

211

Table 7.7 Oxidants assisted metal complexed tetrapyrrolic macrocycles based catalytic reaction of drugs Sn.

Doped NP

Drug for degradation

Performance (%)

1

CoPc-GO/PMS

Norfloxacin

100

2

FePc-P4VP-PAN/H2 O2

Sulfaquinoxaline

3

FeC8Pc/NaIO4

Paracetamol

100

4

CoC4Pc-CNOMS/PMS

Diclofenac

99

95

catalytic processes. This method shows promise in tackling the issues of drug stability and effectiveness. The significance of catalytic degradation in mitigating environmental drug pollution is highlighted. The purpose of this review is to comprehensively examine recent progress in catalytic drug degradation, covering different types of catalysts and their applications in pharmaceutical research and development. By utilizing diverse catalytic systems such as photocatalysts, oxidative degradation catalysts, and non-photochemical catalysts, substantial progress can be achieved in sustainably eliminating drug residues from ecosystems. The wide array of discussed catalysts reflects the extensive research and innovation in this domain, providing hopeful avenues for addressing the pressing problem of drug pollution. In essence, catalytic drug degradation holds significant potential as an advanced technique in the realm of drug utilization, with far-reaching implications for improving drug safety and optimizing therapeutic results.

References Appannagari RR (2017) Environmental pollution causes and consequences: a study. North Asian Int Res J Soc Sci Hum 3(8):151–161; (b) Rajak J (2021) A preliminary review on impact of climate change and our environment with reference to global warming. Int J Environ Sci 10:11–14 (a) Ali I (2012) New generation adsorbents for water treatment. Chem Rev 112(10):5073–5091; (b) Sharma BM, Bečanová J, Scheringer M, Sharma A, Bharat GK, Whitehead PG, Klánová J, Nizzetto L (2019) Health and ecological risk assessment of emerging contaminants (pharmaceuticals, personal care products, and artificial sweeteners) in surface and groundwater (drinking water) in the Ganges River Basin, India. Sci Total Environ 646:1459–1467 Ali S, Ullah MI, Sajjad A, Shakeel Q, Hussain A (2021) Environmental and health effects of pesticide residues. In: Inamuddin, Ahamed MI, Lichtfouse E (eds) Sustainable agriculture reviews, vol 48. Springer, Cham, pp 311–336 Alizadeh E, Baseri H (2018) Catalytic degradation of Amlodipine Besylate using ZnO, Cu doped ZnO, and Fe doped ZnO nanoparticles from an aqueous solution: Investigating the effect of different parameters on degradation efficiency. Solid State Sci 78:86–94 Andreozzi R, Caprio V, Marotta R, Vogna D (2003) Paracetamol oxidation from aqueous solutions by means of ozonation and H2 O2 /UV system. Water Res 37(5):993–1004 Anucha CB, Altin I, Bacaksiz E, Degirmencioglu I, Kucukomeroglu T, Yilmaz S, Stathopoulos VN (2021) Immobilized TiO2 /ZnO sensitized copper (II) phthalocyanine heterostructure for the degradation of ibuprofen under UV irradiation. Separations 8:24 a) Bahnemann D, Bockelmann D, Goslich R (1991) Mechanistic studies of water detoxification in illuminated TiO2 suspensions. Sol Energy Mater 24:564–583; (b) Kumar SG, Devi LG (2011)

212

V. K. Yadav et al.

Review on modified TiO2 photocatalysis under UV/visible light: selected results and related mechanisms on interfacial charge carrier transfer dynamics. J Phys Chem A 115:13211–13241 Bhatia V, Dhir A (2016) Transition metal doped TiO2 mediated photocatalytic degradation of anti-inflammatory drug under solar irradiations. J Environ Chem Eng 4:1267–1273 Blanco-Vega MP, Guzmán-Mar JL, Villanueva-Rodríguez M, Maya-Treviño L, Garza-Tovar LL, Hernández-Ramírez A, Hinojosa-Reyes L (2017) Photocatalytic elimination of bisphenol A under visible light using Ni-doped TiO2 synthesized by microwave assisted sol-gel method. Mater Sci Semicond Process 71:275–282 Boxi SS, Paria S (2015) Visible light induced enhanced photocatalytic degradation of organic pollutants in aqueous media using Ag doped hollow TiO2 nanospheres. RSC Adv 5:37657– 37668 Brillas E, Sauleda R, Casado J (1998) Degradation of 4-chlorophenol by anodic oxidation, electroFenton, photoelectro-Fenton, and peroxi-coagulation processes. J Electrochem Soc 145(3):759 Checa M, Beltrán FJ, Rivas FJ, Cordero E (2020) On the role of a graphene oxide/titania catalyst, visible LED and ozone in removing mixtures of pharmaceutical contaminants from water and wastewater. Environ Sci Water Res Technol 6(9):2352–2364 Cortes S, Sarasa J, Ormad P, Gracia R, Ovelleiro JL (2000) Comparative efficiency of the systems O3 /High pH And O3 /catalyst for the oxidation of chlorobenzenes in water. Ozone Sci Eng 22(4):415–426 Crini G, Lichtfouse E (2019) Advantages and disadvantages of techniques used for wastewater treatment. Environ Chem Lett 17:145–155 (a) de Andrade JR, Oliveira MF, da Silva MGC, Vieira MGA (2018) Adsorption of pharmaceuticals from water and wastewater using nonconventional low-cost materials: a review. Ind Eng Chem Res 57(9):3103–3127; (b) Fatta-Kassinos D, Meric S, Nikolaou A (2011) Pharmaceutical residues in environmental waters and wastewater: current state of knowledge and future research. Anal Bioanal Chem 399:251–275 Ekowati Y, Ferrero G, Farré MJ, Kennedy MD, Buttiglieri G (2019) Application of UVOX Redox® for swimming pool water treatment: Microbial inactivation, disinfection byproduct formation and micropollutant removal. Chemosphere 220:176–184 Fernández L, Esteves VI, Cunha Â, Schneider RJ, Tomé JPC (2016) Photodegradation of organic pollutants in water by immobilized porphyrins and phthalocyanines. J Porphyr Phthalocyanines 20:150–166 Glaze WH, Kang JW, Ziegler SS (Mar 1991) Treatment of hazardous waste chemicals using AOPs. In: Proceedings of the 10th Ozone world congress, March 1991, Monaco, vol 1, pp 261–279 Gómez-Ortíz N, De la Rosa-García S, González-Gómez W, Soria-Castro M, Quintana P, Oskam G, Ortega-Morales B (2013) Antifungal coatings based on Ca(OH)2 mixed with ZnO/TiO2 nanomaterials for protection of limestone monuments. ACS Appl Mater Interfaces 5(5):1556– 1565; (b) Mukherjee K, Acharya K, Biswas A, Jana NR (2020) TiO2 nanoparticles co-doped with nitrogen and fluorine as visible-light-activated antifungal agents. ACS Appl Nano Mater 3(2):2016–2025 (a) Haddaoui I, Mateo-Sagasta J (2021) A review on occurrence of emerging pollutants in waters of the MENA region. Environ Sci Pollut Res 28:68090–68110; (b) Mezzelani M, Gorbi S, Regoli F (2018) Pharmaceuticals in the aquatic environments: evidence of emerged threat and future challenges for marine organisms. Mar Environ Res 140:41–60; (c) Costa F, Lago A, Rocha V, Barros O, Costa L, Vipotnik Z, Silva B, Tavares T (2019) A review on biological processes for pharmaceuticals wastes abatement–a growing threat to modern society. Environ Sci Technol 53:7185–7202 Hassani A, Khataee A, Karaca S, Fathinia M (2017) Degradation of mixture of three pharmaceuticals by photocatalytic ozonation in the presence of TiO2 /montmorillonite nanocomposite: simultaneous determination and intermediates identification. J Environ Chem Eng 5(2):1964–1976

7 Catalytic Degradation of Drugs

213

He Y, Huang Z, Ma Z, Yao B, Liu H, Hu L, Zhao Q, Yang Q, Liu D, Du D (2019) Highly efficient photocatalytic performance and mechanism of A-ZnTcPc/G-C3 N4 composites for methylene blue and tetracycline degradation under visible light irradiation. Appl Surf Sci 498:143834 Hinojosa-Reyes M, Camposeco-Solis R, Ruiz F, Rodríguez-González V, Moctezuma E (2019) Promotional effect of metal doping on nanostructured TiO2 during the photocatalytic degradation of 4-chlorophenol and naproxen sodium as pollutants. Mater Sci Semicond Process 100:130–139 (a) Ikehata K, Jodeiri Naghashkar N, Gamal El-Din M (2006) Degradation of aqueous pharmaceuticals by ozonation and advanced oxidation processes: a review. Ozone Sci Eng 28(6):353–414; (b) Peralta-Hernández JM, Brillas E (2022) A critical review over the removal of paracetamol (acetaminophen) from synthetic waters and real wastewaters by direct, hybrid catalytic, and sequential ozonation proceses. Chemosphere, p 137411 Izadi P, Izadi P, Salem R, Papry SA, Magdouli S, Pulicharla R, Brar SK (2020) Non-steroidal antiinflammatory drugs in the environment: Where were we and how far we have come? Environ Pollut 267:115370 Kadam AN, Dhabbe RS, Kokate MR, Gaikwad YB, Garadkar KM (2014) Preparation of N doped TiO2 via microwave-assisted method and its photocatalytic activity for degradation of Malathion. Spectrochim Acta Part A 133:669–676 Kaur T, Sraw A, Toor AP, Wanchoo RK (2016) Utilization of solar energy for the degradation of carbendazim and propiconazole by Fe doped TiO2 . Sol Energy 125:65–76 Knopp G, Prasse C, Ternes TA, Cornel P (2016) Elimination of micropollutants and transformation products from a wastewater treatment plant effluent through pilot scale ozonation followed by various activated carbon and biological filters. Water Res 100:580–592 Kohantorabi M, Moussavi G, Oulego P, Giannakis S (2022) Heterogeneous catalytic ozonation and peroxone-mediated removal of Acetaminophen using natural and modified hematite-rich soil, as efficient and environmentally friendly catalysts. Appl Catal b: Environ 301:120786 (a) Kovalakova P, Cizmas L, McDonald TJ, Marsalek B, Feng M, Sharma VK (2020) Occurrence and toxicity of antibiotics in the aquatic environment: a review. Chemosphere 251:126351. (b) Mendez E, González-Fuentes MA, Rebollar-Perez G, Méndez-Albores A, Torres E (2017) Emerging pollutant treatments in wastewater: cases of antibiotics and hormones. J Environ Sci Health A 52(3):235–253 Kundu P, Kaur A, Mehta S, Kansal S (2014) Removal of ofloxacin from aqueous phase using Ni-doped TiO2 nanoparticles under solar irradiation. J Nanosci Nanotechnol 14:6991–6995 Leong KH, Gan BL, Ibrahim S, Saravanan P (2014) Synthesis of surface plasmon resonance (SPR) triggered Ag/TiO2 photocatalyst for degradation of endocrine disturbing compounds. Appl Surf Sci 319:128–135 Li K, Pang Y, Lu Q (2019) In situ growth of copper(II) phthalocyanine-sensitized electrospun CeO2 / Bi2 MoO6 nanofibers: a highly efficient photoelectrocatalyst towards degradation of tetracycline. Inorg Chem Front 6:3215–3224 (a) Lindberg RH, Östman M, Olofsson U, Grabic R, Fick J (2014) Occurrence and behaviour of 105 active pharmaceutical ingredients in sewage waters of a municipal sewer collection system. Water Res. 58:221–229; (b) Schröder P, Helmreich B, Škrbić B, Carballa M, Papa M, Pastore C, Emre Z, Oehmen A, Langenhoff A, Molinos M, Dvarioniene J(2016) Status of hormones and painkillers in wastewater effluents across several European states—considerations for the EU watch list concerning estradiols and diclofenac. Environ Sci Pollut Res 23:12835– 12866; (c) Kookana RS, Williams M, Boxall AB, Larsson DJ, Gaw S, Choi K, Yamamoto H, Thatikonda S, Zhu YG, Carriquiriborde P (2014) Potential ecological footprints of active pharmaceutical ingredients: an examination of risk factors in low, middle-and high-income countries. Philos Trans R Soc Lond B Biol Sci 369(1656):05–86; (d) Batt AL, Kincaid TM, Kostich MS, Lazorchak JM, Olsen AR (2016) Evaluating the extent of pharmaceuticals in surface waters of the United States using a National-scale Rivers and Streams Assessment survey. Environ Toxicol Chem 35(4):874–881 Ling Y, Liao G, Xu P, Li L (2019) Fast mineralization of acetaminophen by highly dispersed Ag-g-C3 N4 hybrid assisted photocatalytic ozonation. Sep Purif Technol 216:1–8

214

V. K. Yadav et al.

Liu C, Cui X, Li Y, Duan Q (2020) A hybrid hollow spheres Cu2 O@TiO2 -G-ZnTAPc with spatially separated structure as an efficient and energy-saving day-night photocatalyst for Cr(VI) reduction and organic pollutants removal. Chem Eng J 399:125807 Mashayekh-Salehi A, Moussavi G, Yaghmaeian K (2017) Preparation, characterization and catalytic activity of a novel mesoporous nanocrystalline MgO nanoparticle for ozonation of acetaminophen as an emerging water contaminant. J Chem Eng 310:157–169 Mohammadi R, Massoumi B, Rabani M (2012) Photocatalytic decomposition of amoxicillin trihydrate antibiotic in aqueous solutions under UV irradiation using Sn/TiO2 nanoparticles. Int J Photoenergy 2012 Mohebali H, Moussavi G, Karimi M, Giannakis S (2022) Catalytic ozonation of acetaminophen with a magnetic, cerium-based metal organic framework as a novel, easily-separable nanocomposite. J Chem Eng 434:134614 Mostafalou S, Abdollahi M (2017) Pesticides: an update of human exposure and toxicity. Arch Toxicol 91(2):549–599 Nackiewicz J, Kołodziej Ł, Poliwoda A, Broda MA (2021) Oxidation of diclofenac in the presence of iron (II) octacarboxyphthalocyanine. Chemosphere 265:129145 Nonell S, Flors C (eds) (2016) Singlet oxygen: applications in biosciences and nanosciences; comprehensive series in photochemical & photobiological sciences, vol 1. RSC Books, Cambridge, UK Opoku F, Govender KK, van Sittert CGCE, Govender PP (2017) Recent progress in the development of semiconductor-based photocatalyst materials for applications in photocatalytic water splitting and degradation of pollutants. Adv Sustain Syst 1:1700006 (a) Opoku F, Govender KK, van Sittert CGCE, Govender PP (2017) Recent progress in the development of semiconductor-based photocatalyst materials for applications in photocatalytic water splitting and degradation of pollutants. Adv Sustain Syst 1:1700006; (b) Nonell S, Flors C (2016) (eds) Singlet oxygen: applications in biosciences and nanosciences; comprehensive series in photochemical & photobiological sciences, vol 1. RSC Books, Cambridge, UK Parolini M (2020) Toxicity of the non-steroidal anti-inflammatory drugs (NSAIDs) acetylsalicylic acid, paracetamol, diclofenac, ibuprofen and naproxen towards freshwater invertebrates: a review. Sci Total Environ 740:140043 (a) Patel M, Kumar R, Kishor K, Mlsna T, Pittman Jr CU, Mohan D (2019) Pharmaceuticals of emerging concern in aquatic systems: chemistry, occurrence, effects, and removal methods. Chem Rev 119(6):3510–3673; (b) Chopra S, Kumar D (2018) Pharmaceuticals and personal care products (PPCPs) as emerging environmental pollutants: toxicity and risk assessment. In: Advances in animal biotechnology and its applications, pp 337–353 Piccirillo G, Aroso RT, Rodrigues FM, Carrilho RM, Pinto SM, Calvete MJ, Pereira MM (2021) Oxidative degradation of pharmaceuticals: The role of tetrapyrrole-based catalysts. Catalysts 11(11):1335 Rashidashmagh F, Doekhi-Bennani Y, Tizghadam-Ghazani M, van der Hoek JP, Mashayekh-Salehi A, Heijman BS, Yaghmaeian K (2021) Synthesis and characterization of SnO2 crystalline nanoparticles: a new approach for enhancing the catalytic ozonation of acetaminophen. J Hazard Mater 404:124154 Rauf MA, Meetani MA, Hisaindee S (2011) An overview on the photocatalytic degradation of azo dyes in the presence of TiO2 doped with selective transition metals. Desalination 276:13–27 Sable SS, Shah KJ, Chiang PC, Lo S-L (2018) Catalytic oxidative degradation of phenol using iron oxide promoted sulfonated-ZrO2 by advanced oxidation processes (AOPs). J Taiwan Inst Chem E 91:434–440 Serwecińska L (2020) Antimicrobials and antibiotic-resistant bacteria: a risk to the environment and to public health. Water 12(12):3313 Shokri M, Jodat A, Modirshahla N, Behnajady M (2013) Photocatalytic degradation of chloramphenicol in an aqueous suspension of silver-doped TiO2 nanoparticles. Environ Technol 34:1161–1166

7 Catalytic Degradation of Drugs

215

Silvestri S, Fajardo AR, Iglesias BA (2022) Supported porphyrins for the photocatalytic degradation of organic contaminants in water: a review. Environ Chem Lett 1–41 Skoumal M, Cabot PL, Centellas F, Arias C, Rodríguez RM, Garrido JA, Brillas E (2006) Mineralization of paracetamol by ozonation catalyzed with Fe2+ , Cu2+ and UVA light. Appl Catal b: Environ 66(3–4):228–240 a) Syafrudin M, Kristanti RA, Yuniarto A, Hadibarata T, Rhee J, Al-Onazi WA, Algarni TS, Almarri AH, Al-Mohaimeed AM (2021) Pesticides in drinking water—a review Int J Environ Res Public Health 18(2):468. (b) Mitsika EE, Christophoridis C, Fytianos K (2013) Fenton and Fentonlike oxidation of pesticide acetamiprid in water samples: kinetic study of the degradation and optimization using response surface methodology. Chemosphere 93:1818–1825 a) Tambosi JL, de Sena RF, Gebhardt W, Moreira RFPM, José HJ, Schröder HF (2009) Physicochemical and advanced oxidation processes-a comparison of elimination results of antibiotic compounds following an MBR treatment. Ozone Sci Eng 31:428–435; (b) Lapworth DJ, Baran N, Stuart ME, Ward RS (2012) Emerging organic contaminants in groundwater: a review of sources, fate and occurrence. Environ Pollut 163:287–303 Tang L, Wang JJ, Jia CT, Lv GX, Xu G, Li WT, Wang L, Zhang JY, Wu MH (2017) Simulated solar driven catalytic degradation of psychiatric drug carbamazepine with binary BiVO4 heterostructures sensitized by graphene quantum dots. Appl Catal b: Environ 205:587–596 Teh CM, Mohamed AR (2011) Roles of titanium dioxide and ion-doped titanium dioxide on photocatalytic degradation of organic pollutants (phenolic compounds and dyes) in aqueous solutions: a review. J Alloys Compd 509:1648–1660 Teoh WY, Scott JA, Amal R (2012) Progress in heterogeneous photocatalysis: from classical radical chemistry to engineering nanomaterials and solar reactors. J Phys Chem Lett 3:629–639 Tian B, Li C, Zhang J (2012) One-step preparation, characterization and visible light photo-catalytic activity of Cr-doped TiO2 with anatase and rutile bicrystalline phases. Chem Eng J 191:402–409 Walsh C (2003) Antibiotics: actions, origins, resistance. ASM Press, Washington, DC, USA Wu M, Fu K, Deng H, Shi J (2019) Cobalt tetracarboxyl phthalocya-nine-manganese octahedral molecular sieve (OMS-2) as a heterogeneous catalyst of peroxymonosulfate for degradation of diclofenac. Chemosphe-Re 219:756–765 Yao B, Peng C, He Y, Zhang W, Zhang Q, Zhang T (2016) Conjugated microspheres FeTCPP– TDI–TiO2 with enhanced photocatalytic performance for antibiotics degradation under visible light irradiation. Catal Lett 146:2543–2554 Yi C, Liao Q, Deng W, Huang Y, Mao J, Zhang B, Wu G (2019) The preparation of amorphous TiO2 doped with cationic S and its application to the degradation of DCFss under visible light irradiation. Sci Total Environ 684:527–536 Yin R, Hamblin MR (2015) Antimicrobial photosensitizers: drug discovery under the spotlight. Curr Med Chem 22(18):2159–2185 Zhang X, Zhou J, Gu Y, Fan D (2015) Visible-light photocatalytic activity of N-doped TiO2 nanotube arrays on acephate degradation. J Nanomater 16(1):42–42 Zhang Y, Li H, Huang H, Zhang Q, Guo Q (2018) Graphene oxide–supported cobalt phthalocyanine as heterogeneous catalyst to activate peroxymonosulfate for efficient degradation of norfloxacin antibiotics. J Environ Eng 144(7):04018052 Zhou J, Wu F, Zhu Z, Xu T, Lu W (2017) Identification of O-bridge iron perfluorophthalocyanine dimer and generation of high-valent diiron-oxo species for the oxidation of organic pollutants. J Chem Eng 328:915–926 (a) Zhou H, Smith DW (2001) Advanced technologies in water and wastewater treatment. Can J Civ Eng 28(S1):49–66; (b) Glaze WH (1987) Drinking-water treatment with ozone. Environ Sci Technol 21:224–230; (c) Cheng M, Zeng G, Huang D, Lai C, Xu P, Zhang C, Liu Y (2016) Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: a review. Chem Eng J 284:582–598; (d) Munter R (2001) Advanced oxidation processes–current status and prospects. Proc Estonian Acad Sci

216

V. K. Yadav et al.

Chem50(2):59–80; (e) Andreozzi R, Caprio V, Marotta R, Vogna D (2003) Paracetamol oxidation from aqueous solutions by means of ozonation and H2 O2 /UV system. Water Res 37:993– 1004; (f) Brillas E (2022) Fenton, photo-Fenton, electro-Fenton, and their combined treatments for the removal of insecticides from waters and soils. A review. Sep Purif Technol 284:120290 Zhu Z, Chen Y, Gu Y, Wu F, Lu W, Xu T, Chen W (2016) Catalytic degradation of recalcitrant pollutants by Fenton-like process using polyacrylonitrile-supported iron (II) phthalocyanine nanofibers: Intermediates and pathway. Water Res 93:296–305 Zhu Z, Lu W, Li N, Xu T, Chen W (2017) Pyridyl-containing polymer blends stabilized iron phthalocyanine to degrade sulfonamides by enzyme-like process. Chem Eng J 321:58–66 Zia J, Riyazuddin M, Aazam ES, Riaz U (2020) Rapid catalytic degradation of amoxicillin drug using ZnFe2 O4 /PCz nanohybrids under microwave irradiation. Mater Sci Eng B 261:114713

Chapter 8

Synthesis and Functionalization of Natural Products with Light-Driven Reactions Suman Majee, Km. Anjali, Sonu Yadav, and Devalina Ray

8.1 Introduction The semi and total synthesis of natural products encounter an important role in medicinal chemistry and drug discovery (Baran 2018; Hale 2013; Natural 2014; Ball 2015; Lourenco et al. 2012; Wang and Hui 2021). Past decades have witnessed the design and development of a myriad of novel transformation strategies for the synthesis and derivatization of natural products (Majhi and Das 2021; Lin et al. 2022; Hong et al. 2020; Robles and Romo 2014).They have emerged as effective therapeutic agents for improvement of existing drug molecules (Mushtaq et al. 2018; Newman and Cragg 2020; Ramana et al. 2014). The incredible contribution of natural products in drug discovery has prompted the chemists to profoundly explore structurally intricate assemblies. In this regard, the synthesis of natural product-inspired bioactive small molecules portrays a commendable aspect in the early phases of drug development (Kim et al. 2022; Singh et al. 2023; Cordier et al. 2008). The late-stage diversification of natural products contributes both to the enhanced exploration of SAR (structure–activity relationship) studies and improvization of pharmacological properties. On the other hand, the elevated environmental concerns have led to the resurgence of synthetic strategies resulting in the development of green and sustainable protocols eliminating the hazardous approach (Ganesh et al. 2021; Sheldon 2019; Sheldon and Brady 2019). The new methods demand to address a couple of S. Majee · Km. Anjali · D. Ray (B) Amity Institute of Biotechnology, Amity University, Noida, Uttar Pradesh, India e-mail: [email protected] Amity Institute of Click Chemistry Research and Studies, Amity University, Noida, Uttar Pradesh, India S. Yadav Indira Gandhi University, Meerpur, Rewari, Haryana, India 217

218

S. Majee et al.

constraints involving atom economy, energy efficiency, and minimal discharge of wastes. Various intervening approaches to satisfy these practical aspects consist of organocatalysis (Antenucci et al. 2021), electrochemistry (Sbei et al. 2021), bioenzymatic reactions (Jaiswal and Rathod 2020), photocatalysis (Liu et al. 2022), etc. Among them, photochemical reactions have gained enormous attention due to their vast application in generating complex or strained architecture (Holland et al. 2020). The budding applications of photocatalytic reactions as key steps in the total synthesis of natural products contributed significantly to the recent advancements (Kärkäs et al. 2016). In this aspect, the identification of suitable photocatalyst critically influences the reaction outcome (Pitre and Overman 2022; Revol et al. 2013; Cannillo et al. 2016; Gravatt et al. 2021). Various photocatalysts (PCs) required in the total synthesis of natural products have been emphasized (Fig. 8.1). In general, the photochemical reactions proceed through the excitation of the molecules to generate a transient intermediate which can be controlled to end up with intended products in high yield and selectivity. The reactions venture for a more favourable radical pathway through a set of SET (single electron transfer) mechanisms (Gravatt et al. 2021). The thermodynamic feasibility of SET which in turn relies on redox potentials of the species involved certainly dictates the viability of photoredox catalysis. In this context, the excited photocatalyst generated by absorption of suitable wavelength light initiates the photoredox catalytic cycle through SET to the reactant. Notably, the Gibbs free energy change (GSET ) for the SET process can be calculated by the Rehm–Weller equation. The equation considers redox potential and excited state energies of electron donors and electron acceptors (Rehm and Weller 1970). The choice of photocatalyst with appropriate redox potential is crucial to confirm the SET from PC·− or PC·+ to the substrate or sacrificial reagent to be exothermic. It is essential for regeneration of ground-state photocatalyst with the completion of catalytic cycle. It is noteworthy to mention that the kinetics of excited state is crucial for ensuring the overall efficiency of the reaction, in spite of a thermodynamically feasible SET process. Additionally, the selection of efficient photocatalyst emphasizes the role of high quantum yield in the formation of the triplet excited state possessing longer lifetime. The triplet excited state enhances the probability of successful SET promoted quenching events leading to efficient photoredox reactions (Pitre and Overman 2021). Notably, molecular oxygen is a potent quencher of triplet excited states. Hence, amendments in the reaction conditions are essential to subside the competitive unwanted quenching events (Fig. 8.2). In this regard, the application of UV light has been vastly explored and authenticated in past few decades (Wu et al. 2023). However, the visible light-mediated breakthroughs in photochemical transformations have gained its momentum since past decade and contributed efficiently to many important transformations involving natural products (Srivastava et al. 2022; Yoon et al. 2010; He and Koenigs 2019; Festa et al. 2019). The photochemical reactions can be performed in one step under simple reaction conditions even in the absence of metal activation, oxidant, or additives unlike thermal

F

N

F

N

Ir

CF3

N

N

F

Bu

t

tBu

+

I

O

O

Cl

O

N

I

I

OH

Cl

Cl

Cl

Br

N

Ir

N N N

PF6

N

Ir N

N

O Br

OH

R

[Ir(ppy)2(dpbpy)] (PF6)

N

+

Bu

t

F

O

Rhodamine 6G

HCl EtN

tBu

tBu

t Bu [Ir(dtppy)2(bpy)] (PF6)

N

N

R = Br Eosin Y R = NO2 Eosin B

OH

HO2C R

Bu

t

Bu

t

Bu

t

Fig. 8.1 a Metal-based photoredox catalysts. b Organic photoredox catalysts

Rose Bengal

HO

I

b)

Ir

fac -[Ir(ppy)3]

N

N

[Ir{dF(CF3)ppy}2(dtbpy)] (PF6)

F3C F

a)

N

Bu

Ir

N

t

F

N

F

t

Bu

F

N

N

Ru N

N

S

N

F

N

Ir

N N N

PF6

t-Bu

t-Bu

tBu

BF4

Mes - Acr+- Ph

NH+

or Ru(phen)3Cl2 Ru(phen)3(PF6)2

N Ru N N N N N

2+

tBu

[Ir{dF(Me)ppy}2(dtbpy)] (PF6)

F F

F

10-Phenylphenothiazine

NHEt

CO2Et

or Ru(bpy)3Cl2 Ru(bpy)3(PF6)2

N

N

2+

fac-Ir[dF(p-t-Bu)ppy]3

F

F

8 Synthesis and Functionalization of Natural Products with Light-Driven … 219

220

S. Majee et al. Sub (EA)

Sub (ED) 3PC*

Sub

Sub 1PC*

ISC Reductive Quenching Cycle

3PC*

PC

hγ

PC

Sub = Substrate ED = Electron donor EA = Electron Acceptor

Oxidative Quenching Cycle

Non Radiative decay or Phosphorescence

Sub (ED)

Sub (EA) PC Sub

Sub

Fig. 8.2 Photoredox cycle with reductive and oxidative quenching cycle of photocatalyst

reactions. Therefore, the contribution of photochemistry in the synthesis and modification of natural products have profoundly taken it forward (Lackner et al. 2018; Liu and Wu 2017). The present chapter not only intends to furnish a thorough accumulation of extensive achievements but also to display innovative ideas in expanding the field through the utilization of photoredox approach.

8.2 Synthesis of Natural Products via Photochemical Reactions 8.2.1 Ir-Catalyzed Photochemical Reaction A highly enantioselective sp2 C–H functionalization of β-carbolines was achieved by Wang and co-workers through Minisci-type radical process in a cooperative catalytic system using photoredox reaction and chiral phosphoric acid (Luo et al. 2022). An extensive array of C1 aminoalkylated β-carbolines (3) were generated using this method directly from easily accessible β-carboline (1) and alanine-derived redoxactive esters (2) in presence of 1 mol% [Ir(dF(CF3 )ppy)2 (dtbpy)]PF6 as photocatalyst and 10 mol% of chiral phosphoric acid catalyst in 0.05 M THF solvent under 3 W blue LED irradiation at −40 °C for 3 days with high degrees of enantioselectivities and 65–95% yields (Scheme 8.1). Highly valuable enantioenriched β-carbolines, a fascinating structural motif in both natural product and synthesized bioactive chemicals, are easily accessible through this transition. For the rapid, asymmetric total synthesis of the marine alkaloids eudistomin X, (+)-eudistomidin B, and (+)-eudistomidin I,

8 Synthesis and Functionalization of Natural Products with Light-Driven …

221

this technique has proven to be an extremely effective synthetic method. 6-hydroxy1-aminoalkylated β-carboline (3a) was treated with acid hydrolysis for deacetylation followed by aminomethylation yield eudistomin X (4) in 82% yield and 99% e.e. 5-bromo-1-aminoalkylated β-carboline (3b) was further treated in several steps to form (+)-eudistomidin B (5) with 66% yields. Then (+)-eudistomidin B reacted with formaldehyde in toluene solvent at 90 °C to form (+)-eudistomidin I (6) in 82% yields. The asymmetric total synthesis of marine alkaloids has been accomplished with great efficiency by using this technique as a synthetic method. Additional research on other plans directs to catalytically functionalize N-heteroarenes with asymmetric radical C–H in this field. (±)-Millpuline A has a unique biflavone skeleton. The low yield, poor physicochemical qualities, and lack of target definition in the complete synthesis of (±)-millpuline A, whose bioactivity is still unknown, were addressed by Li et al. via building an intermolecular [2 + 2] photocycloaddition of disubstituted alkene (7) and flavonoid (8) in presence of 1 mol% of photocatalyst [IrdF(CF3 )ppy]2 (dtbbpy)]PF6 driven by 455 nm visible light irradiation in chloroform for 8 h with good yields (Scheme 8.2) (Zhang et al. 2023). Consequently, twenty derivatives of (±)-millpuline A (9a–u) were synthesized for assessment of bioactivity. The stereoconfiguration of the cyclobutane moiety was essential to these compounds’ ability to protect normal lung cells from NNK. Furthermore, addressing (±)-millpuline A’s protective activity against NNK-induced lung cell damage, SRC was shown to be the target-by-target prediction and experimental verification in MLE-12 cells. R2 R1 N 1 H

(R)-STRIP (10 mol%) [Ir(dF(CF3)ppy)2(dtbpy)]PF6 (1 mol%) NHAc 3W Blue LED (455-465 nm) THF (0.05 M), -40 °C, 3 d

O O

N

+

N O

O 2 R1, R2 = Alkyl, Aryl, -H, -Cl, -Br, -F, -OH, -OMe R3 = Alkyl, Aryl HO

1. HCl, MeOH, 80 °C, 4 h N H AcHN 3a

N

Br N Ph

5 Steps

R1

N N H 3 AcHN R 3 65-95 %

HO

N N H Me2N 4, 82%, 99% e.e.Ph eudistomin X Br Formaldehyde N N H Ph toluene, 90 °C N

2. HCOH, HOAc, NaBH3CN

Ph

Br N H AcHN 3b

R2

R3

N H MeHN

5, 66% (+)-eudistomidin B

N H

Ph

6, 82% (+)-eudistomidin I

Scheme 8.1 Photochemical total synthesis of eudistomin X, (+)-eudistomidin B, and (+)eudistomidin I

222

S. Majee et al.

O

O Ir[dF(CF3)ppy]2(dtb-bpy)PF6 (1 mol%) R2 455 nm LED R1 CH2Cl2, 8 h

O

O OR1

+

O

R2

O

O O

7

8

9 (±)-millpuline A derivatves

O O H H

O HO

O H H

O R

O H H

O R

O H H

MeO RO

O

RO

OH H 9a, R = Me, 57% 9b, R = Et, 53% 9c, R = n-Pr, 49% 9d, R = n-Bu, 50% 9e, R = i-Pr, 56% 9f, R = i-Bu, 52% 9g, R = i-Pentyl, 50%

O

EtO

OH H

O

O H H

OH H 9r, 59%

MeO

O H H

O O

NC O

O

O

F O H H MeO

O

OH H 9m, R = F, 58% 9n, R = Cl, 60% 9o, R = Br, 57% 9p, R = CF3, 50% 9q, R = Me, 50%

9j, R = Br, 59% 9k, R = CN, 56% 9l, R = OMe, 52%

9h, R = Me, 57% 9i, R = Et, 55%

O

F

MeO

OH H

O OH H 9t, 56%

EtO

O OH H 9u, 50%

Scheme 8.2 Photochemical synthesis of (±)-millpuline A derivatives

Nitrogen-containing spirocyclic scaffolds are prevalent structural elements found in a large number of naturally occurring alkaloid as medicinal prospects and products. The inflexibility of the powerful bioactive capabilities of these spirocyclic frameworks are frequently attributed to their ability to project polar functionality in well-defined orientations, hence facilitating interactions with protein receptor sites. The di-tyrosine-derived alkaloids (−)-FR901483 and (+)-TAN1251C, which exhibit a unique type of amino-substituted aza-spirocyclic framework, are related through biosynthesis and have garnered considerable interest from the synthetic community due to their biological activity and the difficulties presented by their comparatively small but intricate structures. Fujisawa Pharmaceutical Co. first isolated FR901483 from the fermentation broth of Cladobotryum sp. No. 11231 in 1996 (Sakamoto et al. 1996) and Takeda identified the TAN1251 family of natural chemicals for the first time in 1991 (Shirafuji et al. 1991). The divergent complete synthesis of (−)-FR901483 and (+)-TAN1251C was described by Reich et al. in order to

8 Synthesis and Functionalization of Natural Products with Light-Driven …

223

get the two natural products on gram scale by means of a crucial spirolactam intermediate. The three-component reaction of L-tyrosine methyl ester (10), dehydroalanine derived cyclic compound (11), and 1,4-cyclohexanedione monoethylene acetal (12) underwent photocatalytic irradiation by 40 W blue LED in presence of 1 mol% fac-Ir(ppy)3 as photocatalyst, 1.5 equivalent of Hantzsch ester, 20 mol% of TFA in dichloromethane solvent at room temperature for 4 h, followed by treatement with 3 M HCl to afford the spirolactam (13) precursor in 73% yields. The spirolactum precursor was then consecutively treated in seven and three steps to afford the natural product (+)-TAN1251C (14) and (−)-FR901483 (15), respectively (Scheme 8.3) (Reich et al. 2020). Thus, this highly modular three-component photocatalytic hydroaminoalkylation approach allowed the divergent synthetic strategy to afford di-tyrosine-derived alkaloids. A diverse spectrum of marine diterpenoids are believed to be produced by the breaking apart and reorganization of the steroid-like skeleton. One significant rearranged spongian diterpenoid is (−)-macfarlandin C wherein the large hydrocarbon fragment is connected to the highly hindered concave face of the cis-2,8dioxabicyclo[3.3.0]octan-3-one moiety via a quaternary carbon. The enantioselective complete synthesis of (−)-macfarlandin C was reported by Overman and collaborators. A tertiary carbon radical and an electrophilic butenolide engage in a late-stage fragment coupling as part of the approach, which yields the creation of vicinal quaternary and tertiary stereocentres in a stereoselective manner. Creating the difficult concave-substituted cis-dioxabicyclo-[3.3.0]octanone fragment required a stereoselective Mukaiyama hydration that aligns a pendant carboxymethyl side chain cis to the large octahydronapthalene substituent. The oxalate radical precursor fac-Ir(ppy)3 (1 mol%) Hantzsch ester (1.5 equiv.) TFA (20 mol%), CH2Cl2 Molecular Sieves, rt, 4 h 40 W Blue LED

O

HO

MeO O 10

NH2 +

O

O

Cbz

N 11

O

HO

MeO2C

O N NHCbz

then, 3M HCl, THF, 50 °C, 20 h 12

O 13, 73%

O 3 Steps

t-Bu

7 Steps O

OMe

HO N O

H 14, 24% (+)-TAN1251C

N

H

N

.HCl

O

O P HO OH

NHMe

15, 85% (-)-FR901483

Scheme 8.3 Total synthesis of (−)-FR901483 and (+)-TAN1251C photochemically

224

S. Majee et al. D-Menth O O O 18

OCs O

O 11 Steps

16

O O

H 17, 95%

D-Menth O O

Cl [Ir{df(CF3)ppy}2(dtbbpy)]PF6 (2 mol%) H2O, THF, Bu3N, 60 °C 34 W Blue LEDs

O

H H 19, 74% >20:1 d.r.

6 Steps D-Menth AcO O

H O

HH H

O 20, 38% macfarlandin C

Scheme 8.4 Total synthesis of macfarlandin C

(17) was synthesized in eleven steps from 4,4-dimethylcyclohexen-1-one (16) with 95% overall yields. The key photochemical step was screened by 34 W blue light irradiation on oxalate radical precursor (17) and D-menthol derived chlorobutenolide (18) in presence of 2 mol% of [Ir{df(CF3 )ppy}2 (dtbbpy)]PF6 as photocatalyst, water, tributylammonia in solvent THF at 60 °C for 20 h to afford the cyclized lactone (19) in 74% yield with > 20:1 d.r. The cyclized lactone was consecutively treated in six several steps to afford (20) macfarlandin C (20) in 38% of the overall yield (Scheme 8.4) (Allred et al. 2020). Thus, this comprehensive synthesis of the structurally complex diterpenoid (−)-macfarlandin C, an example of this series enantioselective synthesis that meticulously determines the natural product’s exact structure. Zephycarinatines were classified as a plicamine-type alkaloid with 6,6-spirocyclic core structure, having multiple stereogenic centres, which were isolated from Zephyranthes carinata Herbert by Zhan et al. (2017). Ohno and Inuki reported total synthesis of the plicamine-type alkaloids zephycarinatines C and D via nonbiomimetic synthetic strategy. The key step of this total synthesis is stereoselective reductive radical ipso-cyclization using visible light-mediated photoredox catalysis. This cyclization enables the construction of 6,6-spirocyclic core structure through the addition of a carbon-centred radical onto the aromatic ring. The key intermediate was synthesized by the reaction of biphenyl-2-carboxylic acid derivative (21) and oxazolidine derived from L-serine (22) in the presence of base triethylamine in dichloromethane followed by reaction with mesityl chloride afforded product with 66% yield and which was then furnished with LiOH · H2 O afford the single diastereomer (23) with 92% yield. The diastereomer (23) then underwent ipso-cyclization

8 Synthesis and Functionalization of Natural Products with Light-Driven …

225

O O COOH 1. Et3N, CH2Cl2 OH t-Bu t-Bu K2CO3, MeCN then MsCl, 0 °C to rt N N O O Ph 40 W Blue LED 66%, >95:5 d.r. O + 21 O O OMe 2. LiOH.H2O [Ir{dF(CF3)ppy}2(dtbpy)]PF6 O O Ph CH3OH, 40 °C O (2 mol%) O t-Bu N 24, 58% O 23, 92% H d.r. = 58:42 22 8 steps O

O H R N

Me NH OMe

O O O 25, R = isopentyl, 23%, Zephycarinatine C 26, R = methyl, 52%, Zephycarinatine D

Scheme 8.5 Total synthesis of Zephycarinatine C and D

in the presence of 2 mol% of [Ir{dF(CF3 )ppy}2 (dtbpy)]PF6 as photocatalyst and weak base potassium carbonate under 40 W blue light irradiation in acetonitrile solvent to afford the product (24) with 58% yields. This cyclized product was then undergoing eight consecutive steps to afford the natural product Zephycarinatine C and D (25, 26) with 23% and 52% yield, respectively (Scheme 8.5) (Takeuchi et al. 2020). The keto group in zephycarinatine alkaloid is the main responsible group to display moderate inhibitory activity against LPS-induced NO production. This synthetic approach enables the future opportunities to expand the chemical diversity of plicamine-type alkaloids. The dimeric pyrrole-imidazole alkaloid sceptrin is synthesized in four major steps by Jamison and Nguyen. The route’s shortness is based on a straightforward method created for the selective construction of core of the natural product that is cyclobutane. A practical hymenidin surrogate’s photochemical intermolecular [2+2] dimerization provides direct access to this mysterious family of physiologically active marine secondary metabolites. Initial hydroboration of commercially available N-Boc-propargylamine (27) with dicyclohexylborane (Cy2 BH) and pinacolborane (HBpin) was used to synthesize pinacol ester of vinylboronic (28). By reacting aqueous potassium carbonate (K2 CO3 ), 3-bromoimidazopyrimidine (29), and bis(triphenylphosphine)palladium(II) dichloride (5 mol%) in refluxing tetrahydrofuran (THF), a tandem Suzuki–Miyaura cross-coupling was carried out to produce monomer (30) in 63% yield. The most effective way to achieve the crucial dimerization was to use blue LEDs (440–450 nm) to irradiate a methanolic solution of (30) in the presence of catalytic Ir[dF(CF3 )ppy]2 (dtbbpy)PF6 (1.8 mol %), followed by flash column chromatography, the C2-symmetric dimer (31) was extracted as a single regioisomer and diastereomer in 41% yield. Following that, dimer (31) was treated with TFA for Boc-deprotection. The crude mixture was then reacted with substituted

226

S. Majee et al.

Scheme 8.6 Total synthesis of (±)-Sceptrin

bromopyrrole (32) and Hunig’s base (i-PrNEt) in acetonitrile solvent, after which protected sceptrin precipitated from the solution. The direct addition of hydrazine in DMF in this solution was gently warmed and purified by flash chromatography to afford 96% of (±)-Sceptrin (33) (Scheme 8.6) (Nguyen and Jamison 2020). Strychnine is an important well-known alkaloid natural product which was first isolated in 1818. The heptacyclic strychnine is a typical member of the broad family of monoterpenoid indole alkaloids and is biogenetically connected to the Corynanthe alkaloid geissoschizine and its less complex congener norfluorocurarine. The Strychnos alkaloid strychnine is specifically produced by biosynthetic transformations that include skeletal reorganization and subsequent oxidation and cyclization processes. The organic synthesis community finds strychnine to be a fascinating target for synthetic organic chemists due to its unique chemical structure. A novel synthetic approach was reported by He et al. for the catalytic asymmetric total synthesis of (+)-strychnine. An organocatalytic enantioselective Michael addition to determine the chirality of the initial building block, a photoinduced radical cascade reaction to obtain the Corynanthe alkaloid intermediate, and a bioinspired cascade rearrangement are important aspects of this synthesis to produce the Strychnos alkaloids’ core. The cyclic enamides (35) were synthesized by consecutive three-step reaction from chiral aldehyde ester derivative (34) with 64% overall yields. The key photocatalytic radical cascade step was screened from the cyclic enamides (35) in the presence of 0.5 mol% [Ir(dtbbpy)(ppy)2 ]PF6 as photocatalyst and potassium bicarbonate as a base in THF solvent under blue light irradiation at 37 °C to afford the isomer (36) with 80% yields. Therefore, the isomer was treated with several

8 Synthesis and Functionalization of Natural Products with Light-Driven … CO2Me

H

CHO NO2

34

3 Steps

H NH Ts

CHO O [Ir(dtbbpy)(ppy)2]PF6 (0.5 mol%) KHCO3 (5 equiv.), THF, 37 °C N Blue LEDs

35, 64%

227

H

O N H

N H Ts 36, 80% HO

O

OH 13 Steps N N O

H

H O

H

H 37, 38% (+)-strychnine

Scheme 8.7 Total synthesis of (+)-strychnine

(13) steps consisting of major key steps—reduction of hemiacetal, protection of allylic alcohol, oxidation of indoline, mesylation, substation by cyanation, reduction of amide followed by bioinspired oxidation-rearrangement reaction to afford (+)strychnine (37) as single isomer in 38% overall yield (Scheme 8.7) (He et al. 2019). Thus, this protocol provided a good catalytic asymmetric total synthesis of indole alkaloid (+)-strychnine. (+)-Flavisiamine F was isolated from the leaves of Kopsia flavida by Hiroshi Morita in 2008 (Morita et al. 2008). Due to caged and strained polycyclic scaffolds with multiple all-carbon quaternary stereocentres, Kopsia alkaloids pose particular challenges for enantioselective synthesis. Xia and co-workers first reported the asymmetric total synthesis of (+)-flavisiamine F. The synthetic approach included visible light-induced cyclization to connect the all-quaternary carbon stereocentres at C7 and C20. The total synthesis was started with N-protected carbazolone (38) to afford the photochemical precursor (39) in 83% yield after seven consecutive reactions. This precursor (39) was then undergoing radical cyclization reaction in the presence of 5 mol% of [Ir{df(CF3 )ppy}2 (dtbbpy)]PF6 as photocatalyst and 10 equivalent of triethyl amine as a base under blue light irradiation and air in DMF solvent to afford hexacyclic imine (40) in 77% yield. Therefore, the hexacyclic imine reacted with imidazole and MAC reagent in methanol followed by treatment with firstly hydrogen peroxide in the presence of a weak base and secondly with reflux by acid to afford (+)-flavisiamine F (41) in 43% yield (Scheme 8.8) (Tong et al. 2019). Hence, this synthetic route provided a template for the construction of highly strained and bridged cyclic alkaloids. Lycopodium alkaloids have interesting structural units which have been fascinating targets for synthetic chemists. In 2003, Kobayashi and co-workers first isolated (−)-himeredine A, which is a lycopodium alkaloid. (−)-Himeredine A contains seven rings, ten stereoisomers, a quinolizidine moiety to the caged pentacyclic core

228

S. Majee et al. O N SO2Ph 38

7 Steps

I

ON

[Ir{df(CF3)ppy}2(dtbbpy)]PF6 (5 mol%) Et3N (10 equiv.), DMF, air

N SO2Ph 39

ON

Blue LEDs N 40, 77% 1. imidazole, CH(CN)2OAc MeOH, 25 °C, 1 h 2. a)K2CO3, H2O2,DMSO, 25 °C, 3 h b) HCl, MeOH, reflux, 30 h ON

N H CO2Me 41, 43% (+)-flavisiamine F

Scheme 8.8 Total synthesis of (+)-flavisiamine F

via a single methylene linker, and three nitrogen atoms. The five-membered ring was unlike lycodine that included a significant amount of strain and complexity in the total core structure. The cyclic enone intermediate (43) was synthesized in twelve steps starting from 1,4-dibromopyridine (42). Then, aminomethyl fragment was installed at the C3 position photochemically. The cyclic enone (43) reacting with N-Bocglycine (44) was then decarboxylated photochemically in the presence of [Ir{df(CF3 )ppy}2 (dtbbpy)]PF6 as photocatalyst to form α-amino radical which reacted with cyclic enone via 1,4-addition stereoselectivity to afford inseparable diastereomers in 60% yield. Therefore, this diastereomer was then treated with tetrabutylammonium fluoride to afford separable diastereomers (45) and (46) in 31% and 60% yield, respectively. The diastereomer was then treated in different four consecutive steps to afford (−)-himeredine A (47) in 84% isolated yield (Scheme 8.9) (Burtea et al. 2019). Hence this enantioselective total synthesis of (−)-himeredine A was achieved in 17 steps in the longest linear sequence.

8.2.2 Ru-Catalyzed Photochemical Reaction The selective synthesis of 4-hydroperoxy-2,5-cyclohexadienones from para-alkyl phenols is revealed through the use of photocatalysis by Kozlowski and co-workers. Using a photosensitized singlet oxygen method, many electrically varied para-alkyl phenols were functionalized in 27–99% isolated yields. Using this dearomative oxidation, commercially accessible starting materials were subjected to the synthesis of (±)-stemenone B and (±)-parvistilbine B in 9 and 11 steps, respectively. From the readily accessible organic compounds, 3-bromo-5-methoxy-2,4-dimethylphenol and

8 Synthesis and Functionalization of Natural Products with Light-Driven …

229

OTBDPS N

Br

Boc

Br 42

O

H

12 Steps

TBSO

NH Boc N

H

HO

O

H BocHN

BocHN

COOH 44

H

43 1.[Ir{df(CF3)ppy}2(dtbbpy)]PF6 DMF, K2HPO4 Blue LED 2. TBAF, THF, 35 °C OH Boc O NH Boc N

OH Boc

+

H

NH Boc N

H HO BocHN

45 , 31%

46, 60%

4 Steps

N

N

N O

47 (-)-himeradine A

Scheme 8.9 Total synthesis of (−)-himeredine A

2-methoxy-3-substituted phenyl acetylene were first synthesized. Then Sonogashira cross-coupling of (48) and (49) produced a coupled product which was simultaneously reduced by Pd/C, H2 to afford the condensed product (50). It was then treated in the presence of Ru(bpy)3 (PF6 )2 as photocatalyst, oxygen as oxidant, and pyridine as a base in visible light irradiation followed by reaction with sodium thiosulfate to afford (±)-stemenone B in 86% yield and (±)-parvistilbine B in 90% yield (Scheme 8.10) (Carson et al. 2022). Further investigations shed light on the mechanism underlying this change and demonstrated the significant impact of the base and solvent on the selectivity. A technique is disclosed by Laha and Pandey for heterocyclization that is both generic and efficient which involves the functionalization of benzylic C(sp3 )–H by visible light photoredox catalysis that opens up a wide variety of structurally varied oxygen and nitrogen heterocycles up to the gram scale. The complete synthesis of (+)-centrolobine and (−)-codonopsinine demonstrates the possible applicability of this innovative approach. Here, it is suggested that selectfluor functions as an acceptor of hydrogen radicals and an oxidative quencher in contrast to fluorinating reagents.

230

S. Majee et al.

Scheme 8.10 Photochemical synthesis of (±)-stemenone B and (±)-parvistilbine B

The production of highly functionalized (−)-codonopsinine (15), which was separated from Codonopsis clematidea, has notable hypotensive and antibacterial properties without having an impact on the central nervous system. The total synthesis of (−)-codonopsinine was carried out by the synthesis of pivotal intermediate (54) from benzyl (R,E)-(5-(4-methoxyphenyl)pent-3-en-2-yl)carbamate (53) in presence of 2.5 mol% of Ru(bpy)3 (PF6 )2 as photocatalyst, three equivalents of selectfluor as oxidative quencher, and three equivalents of sodium hydrogenphosphate as base in 0.025 M dry acetonitrile under 454 nm blue light irradiation at room temperature for 24 h to afford 55% yield of (55) with 1.9:1 diastereomeric ratio. The epoxidation of pivotal intermediate (54) using m-CPBA, followed by sulphuric acid-mediated ring opening, and lastly reduction by lithium aluminium hydride produced 22% of (−)-codonopsinine (55). The oxygen-containing heterocycle (+)-centrolobine was isolated from Centrolobium robustum. It was synthesized by direct photoredox cyclization of (S)-4-(3-hydroxy-7-(4-methoxyphenyl)heptyl)phenyl acetate (56) in the presence of 2.5 mol% of Ru(bpy)3 (PF6 )2 , three equivalents of selectfluor, and three equivalents of sodium hydrogenphosphate in 0.025 M dry acetonitrile under 454 nm blue light irradiation at room temperature for 24 h, followed by base-mediated O-acetate deprotection to afford (+)-centrolobine (57) in 85% yield (Scheme 8.11) (Pandey et al. 2019).

8.2.3 Organophoto Catalyzed Reaction Using pyridinium salts produced from amino acids as alkylating reagents, Yetra et al. had devised a chiral amine catalyzed enantioselective α-alkylation of aldehydes via a light-activated charge-transfer complex, the process proceeds in the presence of visible light and in the absence of a photocatalyst (Scheme 8.12) (Yetra et al. 2022). This photochemical stereoconvergent approach was utilized in the total synthesis of natural lignan derivatives, namely (−)-enterolactone and (−)-enterodiol. The 3(3-hydroxyphenyl) propanal (58) and pyridinium salt of racemic m-tyrosine (59) underwent a stereoconvergent reaction in the presence of 20 mol% of catalyst A, 1.0

8 Synthesis and Functionalization of Natural Products with Light-Driven … Ru(bpy)3(PF6)2 (2.5 mol%) Selectfluor (3 equiv.) Na2HPO4 (3 equiv.) Dry CH3CN (0.025 M), rt, 24 h PMP 53

NHCbz

Blue LED (454 nm)

OAc PMP HO

2

56 PMP = p-methoxyphenyl

231

1. m-CPBA 2. H2SO4, dioxane/H2O 3. LiAlH4, THF N Cbz 54, 55% d.r. = 1.9:1

OH

HO

N

PMP

Ru(bpy)3(PF6)2 (2.5 mol%) Selectfluor (3 equiv.) Na2HPO4 (3 equiv.) Dry CH3CN (0.025 M), rt, 24 h Blue LED (454 nm) then, NaOH/MeOH

MeO

55, 22% (-)-Codonopsinine

OH PMP

O

2

57, 85% (+)-centrolobine

Scheme 8.11 Photochemical synthesis of (−)-codonopsinine and (+)-centrolobine

equivalent of 2,6-lutidine, 1.0 equivalent of sodium iodide, 10 equivalent of water, and 0.1 M DMA solvent under 390 nm kessil lamp irradiation at 4 °C for 24 h to generate the α-alkylated product, which underwent reductive conditions in presence of sodium borohydride without purification, yielding 46% yield of lactone (60) in two steps. Despite the fact that the diastereomeric lactones had low diastereoselectivity (3:2) but good e.e. (97, 96%), the combination could be epimerized to create more complicated compounds with high diastereoselectivity. The diastereomeric lactones were subjected to LHMDS and TMSCl in THF to yield (−)-enterolactone (61) in 81% yield, 12:1 d.r. and 97% e.e. Reduction of (−)-enterolactone by lithium aluminium hydride in THF produced single diastereomer of (−)-enterodiol (62) in 70% yield with 97% e.e. The absolute stereochemistry of the alkylation products generated in this enantioselective process was further confirmed by optical rotations of the synthetic samples of the two natural compounds. The ground-state complexation of the reactive components, followed by divergent charge, was supported by mechanistic investigations suggesting transfer procedures including in-cage radical combination phases and catalyst-controlled radical chain.

8.2.4 Miscellaneous Photochemical Reaction Srinath et al. reported an efficient and simple oxidative dehydrogenation strategy of β-carbolines by using a homogenous and reusable cobalt-phthalocyanine photoredox catalyst in a biphasic medium, which provided easy separation of product and an efficient reusability of the homogenous catalyst (Scheme 8.13) (Srinath et al. 2020). The synthesis of many biologically active N-heterocycles, including indoles, (iso)quinolines, and β-carbolines, as well as natural compounds like eudistomin U, norharmane, and harmane, as well as precursors to perlolyrine and flazin, highlight its potential applicability to organic transformations. The catalytic oxidative

232

S. Majee et al. 1. Catalyst A (20 mol%)

OH 2,6-lutidine (1 equiv.) Me O OH NaI, H2O, DMA (0.1 M) N Me N Ph Kessil Lamp (390 nm) Bn N O 4 °C, 24 h O H Me HCl OCH2CF3 2. NaBH4, CH2Cl2/MeOH, 15 min O Catalyst A 60, 46%, 3:2 d.r. 59 OH 97% e.e, 96% e.e. Ph

BF4

OH +

Ph

CHO 58

OH HO

OH OH

LiAlH4 OH THF, 0 °C, 1 h

62, 70%, 97% e.e. (-)-Enterodiol

OH THF, 23 °C, 16 h O

LiHMDS, TMSCl O 61, 81%, 12:1 d.r., 97% e.e (-)-Enterolactone

Scheme 8.12 Synthesis of (−)-enterolactone and (−)-enterodiol

dehydrogenation was optimized from carbazole derivative (63) in the presence of commercially available 1 mol% of cobalt phthalocyanine as photoredox catalyst in 1:1 mixture of water and ethyl acetate under 3 W blue light irradiation at room temperature for 24 h in the air to afford oxidized product carbazole derivatives (64, 65) eudistomin U (64a) (85%), norharmane (64b) (82%), and harmane (64c) (82%) in good yields. The furans containing C-3 substituted β-carboline precursor for perlolyrine (66a) and flazin (66b) were also synthesized with 88 and 90% yield, respectively. The furan containing C-3 substituted β-carboline (66a-b) was then reduced by sodium borohydride to afford Perlolyrine (67a) and Flazin (67b). Using reactants that comprise nitrile and diazo, Maiti and co-workers reported a photoinduced technique for the synthesis of pharmaceutically significant oxazole compounds. First, the diazo compound (68) was photolyzed to produce singlet carbenes, which are then used in a [3+2] cycloaddition way by nitriles (69) to produce substituted oxazoles (70a–c) under blue light irradiation and nitrogen atmosphere in dichloroethane solvent for 24 h (Scheme 8.14) (Saha et al. 2023). This synthetic procedure is able to obtain useful bis-oxazoles with di-nitrile compounds. Felibinac, pimprinine, texamine, ugnenazole, and other small-molecule medications and medically significant compounds are quickly synthesized, demonstrating the transformation’s utility. For the purpose of creating 2 H and 13 C isotope-labelled pimprinine (70a–b) and uguenenazole (70c) alkaloid, the technique was also helpful with good yields. It was shown that photolysis and continuous-flow chemistry might be used to scale up the reaction. The use of blue light to harvest light energy suffices the execution of photosynthesis without the need for metal catalysis or photosensitizers.

8 Synthesis and Functionalization of Natural Products with Light-Driven … R2

R2

CoPc(SO3Na)4 (1 mol%) Water/EtOAc, rt, 24 h, air

NH 63 N H

N N H 64 R1

3 W Blue LED

R1

233

CO2H N

CO2H

N

N H

N

N H

N H 64a, 85% Eudistomin U

N H 64c, 82% Harmane

64b, 82% Norharmane

R

R

CoPc(SO3Na)4 (1 mol%) NH Water/EtOAc, rt, 24 h, air N H

N H

3 W Blue LED

O

Reduction

N O

R

66a, R = H, 88% 66b, R = CO2Me, 90%

65

N N H

O

67a, R = H, Perlolyrine HO 67b, R = CO2Me, Flazin

Scheme 8.13 Photochemical synthesis of β-carboline-derived natural products N2 R1

OR2 +

O 68

R3

Blue LEDs DCE, N2 , 24 h

N

R2O

O

R1

N

R3

70a-c

69 MeO

HN

O N

HN C13H3

70a, 72%

D O N

CD3

70b, 73% Pimprinine alkaloid

D

O N

D

D D 70c, 88% Uguenenazole alkaloid

Scheme 8.14 Photochemical synthesis of deuterated pimprinine and uguenenazole alkaloid

234

S. Majee et al.

8.3 Photochemical Functionalization of Natural Products 8.3.1 Ir-Catalyzed Photochemical Reaction Among the most widely used, synthetically adaptable, and practical functional groups in organic chemistry are alcohols and carboxylic acids. These native synthetic handles rapidly undergo radical activation under visible light photoredox catalysis, and the resultant open-shell intermediates can then take part in transition metal catalysis. Sakai et al. reported the dual combination of hypervalent iodine-mediated decarboxylation and heterocyclic carbene (NHC)-mediated deoxygenation that results in the Csp3 −Csp3 cross-coupling of alcohols and carboxylic acids. A variety of alkyl−alkyl cross-coupled compounds, including extremely congested quaternary carbon centres from the appropriate tertiary alcohols or tertiary carboxylic acids, were prepared using this gentle and useful Ni-catalyzed radical-coupling technique. The reaction was screened by the reaction of aliphatic alcohol (71) and benzoxazolium salt (72) in presence of 1 mol% iridium catalyst with nickel co-catalyst and 2 equivalents of iodomesitylene diacetate and pyridine as base in 1:1 mixture of methyl tert-butyl ether and dimethyl sulfoxide under blue light irradiation at room temperature for 1 h with good to excellent yields. Furthermore, the methodology’s synthetic applications to formal homologation, alcohol C1-alkylation, and late-stage functionalization of D-gluocopyranose (73a) and isoandrosterone (73b) with 44–80% yield (Scheme 8.15) (Sakai and Macmillan 2022). t-Bu OH

Pyridine MTBE (0.10 M), rt, 15 min

Cbz N + t-Bu

R

MesI(OAc)2 (2 equiv.) Cbz N Ni-catalyst (10 mol%) 73 Ir- catalyst (1 mol%) MTBE/DMSO (1:1, 0.02 M) Blue LEDs, 1 h, rt

71 R N

t-Bu

t-Bu

F

PF6 t-Bu

N F F

O BF4 t-Bu 72

Ir N

N N t-Bu

F H N

BnO BnO

t-Bu O O Ni O O

O Cbz

OBn OBn

73a, 44% From D-glucopyranose

Cbz

H N H

H

H 73b, 80% From Isoandrosterone

Scheme 8.15 Late-stage alkylation of D-glucopyranose and isoandrosterone under blue light irradiation

8 Synthesis and Functionalization of Natural Products with Light-Driven …

235

Larger libraries of bioactive compounds are now accessible due to the development of novel functionalization processes spurred by the widespread availability of azaarene moieties in natural products. The production of cyclobutanes using the light-promoted [2+2] photocycloaddition process has been in-depth research in the field of photochemistry. Specifically, De Mayo described the synthesis of 1,5-dicarbonyls via [2+2] cycloaddition between the enols of 1,3-dicarbonyls and double bonds, followed by retroaldol condensation. Here, Salaverri et al. reported a ring-opening rearomatization reaction involving electron-deficient 2-methyleneazaarenes (74) and trisubstituted double bonds (75), which is followed by a [2+2] photocycloaddition in presence of 2 mol% photocatalyst [Ir{dF(CF3 )ppy}2 bpy]PF6 and 50 mol% of DBU as a base in tetrahydrofuran solvent under 455 nm visible light irradiation and nitrogen atmosphere at room temperature with good to excellent yields. This reaction is possible because the heterocyclic derivatives may generate the appropriate pseudo-enamine intermediate. The process permits the inclusion of various electron-withdrawing groups and exhibits a high functional group tolerance on both the heteroarene and double bond sides. Furthermore, the reaction’s broad application has been shown by the late-stage derivatization of natural compounds (76a–c) with 85–92% yield (Scheme 8.16) (Salaverri et al. 2020). In conjunction with theoretical computations, photochemical investigations affirm a process that involves the pseudo-enamine intermediate’s photosensitization. Polyfluoroarenes are helpful building blocks for a variety of applications, including crop protection, materials, and medication development. Ritter and Sun reported the first polyfluoroarylation by photoredox decarboxylation of aliphatic carboxylic acids. The polyfluoroarylation was screened by the reaction of substituted carboxylic acid (77) and hexafluorobenzene (78) in the presence of 0.5 mol% of [Ir(dFFppy)2 (dtbpy)]PF6 as catalyst and 2.0 equivalent of lithium carbonate as base

R4

EWG + 74

R1

[Ir{dF(CF3)ppy}2bpy]PF6 (2 mol%) R3 R4 DBU (50 mol%)

R2 75

THF, N2, rt 455 nm

R3 EWG 76

R1

R2

O O

H H

MeO2C

O NHBOc

H MeO2C

3 2

N

N N

76a, 85%, d.r. = 50:50 from Estrone derivative

O

76b, 89%, d.r. = 50:50 MeO2C 76c, 92%, d.r. = 50:50 from Trosine derivative from δ-Tocopherol derivative

Scheme 8.16 Late-stage functionalization of natural products under visible light irradiation

236

S. Majee et al. [Ir(dFFppy)2(dtbpy)]PF6 (0.5 mol%) O R

F +

F5

OH 77

Li2CO3 (2.0 equiv.) DMSO (0.5 M) Blue LEDs, 35 °C

R F5 79

78 5-10 equiv.

O

F H H

F

H

F

S F

O

N

N O

F

79a, 67%, d.r. = 1:1 F from Estrone

F

F

F

H N

F F

79b, 63% from MTV III

F

F F

O F

HO H H

H

79c, 83%, d.r. > 20:1 from glycyrrhetic acid

Scheme 8.17 Perfuoroarylation of natural products under blue light irradiation

in 0.5 M DMSO solvent under blue light irradiation at 35 °C with good to excellent yields. The process works with a wide range of substrates and a high tolerance for functional groups. A platform for the synthesis of polyfluoroaromatics using different carbon radical precursors may be established via the radical route of carbon radical addition to polyfluoroarenes in conjunction with photocatalysis. Furthermore, latestage modification may be used to change tiny, complicated compounds like estrone, MTV III, and glycyrrhetic acid, those found in natural products (79a–c) with 63–83% yield (Scheme 8.17) (Sun and Ritter 2021). Chemical biology, materials science, and drug development are three areas that heavily rely on sulfonyl fluorides. In this line, the very active SO2F radical has been used to create sulfonyl fluorides; however, the laborious and dangerous synthesis of gaseous ClSO2 F as a radical precursor limits its use. Concurrently, the synthesis of fluorosulfonyl radical (SO2 F) approach to produce fluorides from inert SO2 F2 gas has encountered unavoidable challenges because of the high homolytic bond dissociation energy of the S(VI)-F bond. Wang and co-workers reported a radical fluorosulfonylation method using an air-stable crystalline benzimidazolium fluorosulfonate cationic salt reagent for the stereoselective synthesis of alkenyl sulfonyl fluorides and functional alkyl sulfonyl fluorides. The reaction was optimized with different alkenes (80) and benzimidazolium fluorosulfonate triflate (81) in the presence of 2 mol% fac-Ir[dF(p–t-Bu)ppy]3 as a photocatalyst, 2.0 equivalent of 1,4-cyclohexadiene and 9:1 mixture of 2-methyltetrahydrofuran and acetone under 60 W blue light irradiation and argon atmosphere with good yields. For the purpose of radical fluorosulfonylation

8 Synthesis and Functionalization of Natural Products with Light-Driven …

OTf R

+

n

80

N

fac-Ir[dF(p-t-Bu)ppy]3 (2 mol%) 1,4-cyclohexadiene (2.0 equiv.) 2-Me-THF:acetone = 9:1 (0.1 M), Ar

Ar N 81 SO F 2 Ar = Ph, p-CF3-C6H4

237

R

n

60 W Blue LEDs

SO2F

82

O

O O

H H H 82a, 58% from Estrone

4

O O

H 4

SO2F

H O

82b, 34% from Testosterone SO2F

O O

H

SO2F

O

82c, 25% from Vitamin E

Scheme 8.18 Late-stage fluorosulfonylation of natural products under blue light irradiation

of unsaturated hydrocarbons with strong stereoselectivity and good yield, this benchstable redox-active reagent provides an effective and practical approach that may be further changed into beneficial functional SO2 F molecules. The cationic character of this radical fluorosulfonylating reagent is a crucial design element that promotes the progressive production of fluorosulfonyl radical (· SO2 F) through photocatalytic conditions via a SET reduction process. It is possible for this SO2 F radical reservoir to react with different alkenes to create migratory fluorosulfonylating products, alkylsulfonyl fluoride, and alkenyl sulfonyl fluoride. The late-stage derivatization of estrone, testosterone, and vitamin E produced SO2 F functionalized natural products (82a–c) in 25–58% yields (Scheme 8.18) (Zhang et al. 2022).

8.3.2 Tungsten-Catalyzed Photochemical Reaction Lu et al. reported a unique visible light photoredox approach for the effective dehydroxylative Sulfones that are not just a class of preferred structural motifs, but also major building blocks found in a wide range of biologically active natural compounds and compounds used in pharmaceuticals. Jing and Yang reported a one-pot, threecomponent technique for producing alkyl–alkyl sulfones by photoinduced TBADTcatalyzed Csp3 –H sulfonylation of unactivated hydrocarbon molecules. A wide variety of commercially available hydrocarbon compounds and bioactive molecules can be successfully applied to the catalytic system, resulting in the corresponding alkyl–alkyl sulfones in the process with excellent to good yields. The sulfonylation reaction was screened by the reaction of Aryl acrylate (83) and hydrocarbon (84) in the presence of DABCO · (SO2 )2 as SO2 source and 5 mol% tetrabutylammonium

238

S. Majee et al.

decatungstate as photocatalyst in solvent acetonitrile under visible light irradiation (385–395 nm) at room temperature for 48 h with moderate to excellent yields. From a molecular perspective, photoexcitation of TBADT caused the Csp3 –H sulfonylation of inactive hydrocarbon molecules through a radical mechanism. The late-stage functionalization of this process showed its usefulness because sulfones are commonly found in medicinally active natural analogues (Scheme 8.19) (Lu et al. 2023). This technique worked well with amino alcohol derivatives with a stereocentre, yielding the required products in synthetically usable yields (60–68% yield). With a 60–74% yield, the monoterpene molecules were converted into the matching sulfone (85a–d). Estrone (85e) and its polycyclic counterparts (85f–g) were later shown to be very compatible with the current catalytic system, providing the significant value-added alkyl–alkyl sulfones in yields ranging from 57 to 75%. Using the decatungstate anion as the only catalyst, a widely applicable approach is provided for the trifluoromethylthiolation of methylene C(sp3 )−H, methine C(sp3 )−H, α-oxygen C(sp3 )−H, and formyl C(sp2 )−H bonds. Modifying this approach, which included the derivatization of natural compounds, was applied with good reproducibility, taking into account the substrate ratio and reaction concentration. Moreover, the SCF3 products were functionalized again to create

Scheme 8.19 Late-stage sulfonylation of natural products under visible light irradiation

8 Synthesis and Functionalization of Natural Products with Light-Driven …

239

O N SCF3 (0.4 equiv.) R H or

R O 87

86

F3CS

O

H

R R SCF3 or

TBADT (2.5 mol%) rt, 385 nm LED 6-16 h, N2, Dry CH3CN

O

SCF3

O

O

H H

88a, 55% From Sclareolide

88b, 67%, d.r. = 60:40 From Sclareolide

H

89

O O

H

H

88 O

SCF3 O

H O

H

H O

SCF3 O

89a, 45% from dehydrocholic asid ester

Scheme 8.20 Late-stage photocatalytic trifluoromethylation of natural products

SCF3 -drug equivalents, demonstrating the significance of this photocatalyzed C– H functionalization. Burkhard and co-workers optimized the trifluoromethylthiolation of alkane (86) or substituted aldehyde (87) in presence of 0.4 equivalent of N-(trifluoromethylthio)phthalimide as -SCF3 source and 2.5 mol% tetrabutylammonium decatungstate as photocatalyst in dry acetonitrile solvent under 385 nm visible light irradiation and nitrogen atmosphere at room temperature for 6–16 h to afford trifluoromethylthiolated product (88 or 89) with good to excellent yields. Furthermore, this C–H trifluoromethylthiolation was shown to be profoundly applicable in the late-stage functionalization of natural products to afford products with good yields (Scheme 8.20) (Schirmer et al. 2021).

8.3.3 Organophoto-Catalyzed Reaction Enones are preferred structural motifs in medicines and bioactive natural compounds, although γ-hydroxylation of enones is difficult. Yue and Zheng demonstrated a gentle and effective technique for the direct hydroxylation of C(sp3 )–H bond. Enones under visible light-induced hydrogen-atom transfer (HAT) enable the γ-hydroxylation of various enones namely primary, secondary, and tertiary C–H bonds without the need for metal or peroxide. The γ-hydroxylation of substituted enones (90) was screened in the presence of 4–8 mol% of Na2 -eosin Y in acetonitrile solvent under 455 nm visible light irradiation and oxygen atmosphere as sustainable oxidant at room temperature for 12 h. This was followed by a reaction with thiourea in methanol at room temperature to afford the hydroxylated product (91) with moderate to excellent yields. In the HAT-based catalytic cycle, Na2 -eosin Y functions as both the photocatalyst and the source of catalytic bromine radical species, as indicated by the mechanistic study.

240

S. Majee et al.

Ultimately, it completely sacrifices itself through oxidative degradation to produce bromine radical and the primary product, phthalic anhydride, in an environmentally benign manner. The benefits of this beneficial technique included wide substrate compatibility, high functional group tolerance, and simple experimental operation— all of which make it very easy to incorporate hydroxy group for late-stage functionalization into complex natural products with an enone moiety. Moreover, this scalable and practical technique may find its way into large-scale industrial production. Numerous natural materials (91a–g) were used to illustrate this scalable technique with 21–86% yield (Scheme 8.21) (Zheng and Yue 2023). Chemists are becoming more and more interested in developing innovative synthetic techniques for chroman frameworks due to their significance in medicinal and natural product chemistry. A novel (4+2) radical annulation method for photocatalytically creating these useful six-membered frameworks was reported by Lei and Huang with its moderate reaction conditions. The approach enables the highly selective conversion of widely accessible N-hydroxyphthalimide esters (92) and electron-deficient olefins (93) into a variety of useful chromans (94) in the presence of organo photocatalyst eosin Y in dimethylacrylate under nitrogen atmosphere and blue light irradiation at room temperature for 12 h. Additionally, the synthetic route had the potential to be applied in the late-stage functionalization of physiologically active molecules and derivatives of natural products (94a–c). The electron-rich O R2 R3 H 90 O

R1 R5 R4

O

1.Na2-Eosin Y (4-8 mol%) O2, CH3CN, rt, 12 h 455 nm LEDs

R2 R3

2. Thiourea, CH3OH, rt

R1 R5 R4 OH 91

O

HO

OH

O

O OH

H

OH

91a, 58% from Isophorone

O

CHO

O

91b, 55%, d.r. = 1:2 91c, 27% + 50% racemic mix. from myrtenal from Piperitone

91d, 86% from Hedyosumin B

O OH H

OAc

O

H

H

OH

OH HO O 91e, 35%, d.r. = 1.1:1 from neoacolamone

AcO

H 91f, 18% + 72% racemic mix. from betulin derivative

HO 91g, 21% + 64% racemic mix. from Kilodenoid G

Scheme 8.21 Visible light-mediated allylic hydroxylation of natural products

8 Synthesis and Functionalization of Natural Products with Light-Driven …

241

Scheme 8.22 Late-stage derivatization of natural products into different chromans under photocatalytic irradiation

dienophiles and orthoquinone methides in the classic Diels–Alder [4+2] cycloaddition process was enhanced by this approach because electron-deficient dienophiles were easily converted into the chromans (Scheme 8.22) (Guan et al. 2022). Alkylation of a diverse range of α-hydroxy carboxylic acid derivatives was employed by producing in-situ diaryl boron radical. The reaction has widely available starting analogues, a broad substrate scope, great functionality tolerance, and eliminated the time-consuming process of generating a free radical initiator. Preliminary mechanistic studies show that the spin-centre shift process is responsible for the activation of the C–O bond, which was aided by the diaryl boron radical created by bench-stable and commercially available tetraphenyl borate (NaBPh4 ). The alkylation was screened by the reaction of lactic derived acid-derived amides (95) with mono-substituted alkene (96) in the presence of tetraphenyl borate (NaBPh4 ) as boron radical sources using 2 mol% 4-CzIPN as photocatalyst, H2 O as additives in DMF solvent under violet light irradiation and nitrogen atmosphere. The alkylation proceeded via the SET process, where tetraphenyl borate was used as the radical initiator. The efficacy of this approach was most notably proved by the latestage functionalization of natural compounds (97a–c) (e.g. leucine, menthol, and cholesterol) in good yields (Scheme 8.23) (Liu et al. 2023). The present photoredox approach empowered the synthesis of a diverse range of important compounds of α-hydroxy carboxylic acid derivatives.

242

S. Majee et al.

R2 X R1

OY +

R3

O 95 96 X = N, O Y = Ac or Ms R1, R2, R3 = Ar or Alkyl

R1

O

t-Bu

O

N H 97a, 61%, d.r. = 1:1 from Menthol

O N

H N O

97b, 56%, d.r. = 1:1 from Leucine

H N O

R3 O 97

O

H

X

NaBPh4 (2 equiv.) rt, N2, Violet LED

O O

R2

4-CzIPN (2 mol%) H2O (4 equiv.), DMF

O

OMe

O

H 97c, 65%, d.r. = 1:1 from Cholesterol

Scheme 8.23 Visible light-mediated dehydroxylative alkylation of α-hydroxy carboxylic acids

8.3.4 Miscellaneous Photocatalyzed Reaction Shen et al. presented a visible light-induced photocatalytic approach that used a thiolate-based EDA complex as a bifunctional reagent to thiolate and pyridylate styenes with a wide range of substrates. The reaction took place in mild circumstances without the need for a photocatalyst, metal, or external redox agent. The reaction was optimized with substituted styrene (98), aryl thiol (100), and substituted 4-cyanopyridine (99) in the presence of 3 equivalents of HCO2 Li · H2 O in dimethyl sulfoxide at room temperature for 24 h under 10 W blue light irradiation and nitrogen atmosphere. Under the influence of visible light, the reaction proceeded through a SET step in the EDA complex, which in turn was generated by thiophenol deprotonation and subsequent condensation with substituted 4-cyanopyridine. On the gram scale, the technique could be applied, and complex compounds produced from natural products can also be functionalized at a later stage. The late-stage functionalization was successfully compiled for L-proline (101a), L-menthol (101b), and estrone (101c) with a 45–66% yield (Scheme 8.24) (Shen et al. 2023).

8 Synthesis and Functionalization of Natural Products with Light-Driven … N R2 CN + R1

HCO2Li.H2O (3.0 equiv.)

99 HS

98

R3

R2

S

N

DMSO N2, rt, 24 h 10 W Blue LEDs

R3

R1 101

100

S

N

N

243

S O H H

Boc N

O

O

O

S

O

101a, 45% from L-Proline

101b, 46% from L-Menthol

N

101c, 66% from Estrone

Scheme 8.24 Visible light-induced late-stage C–H functionalization of natural products

8.4 Conclusion In summary, the present chapter outlines a comprehensive approach to various aspects and applications of photochemical reactions in natural product synthesis and derivatizations. The underlying mechanisms mostly follow the SET process where the consideration of the energy for excited states, redox potentials, coulombic interactions, and the importance of appropriate photocatalyst have been prioritized. Enhanced efficiencies in photochemical reactions are expected by using photocatalyst with longer excited state lifetimes. The longer excited-state lifetime results in a higher likelihood of successful SET quenching events. These considerations aim to enhance the overall efficiency of photochemical reactions, especially under those circumstances where time constraints and competition with other reagents may pose challenges. The synthetic schemes in this chapter started with the commercially accessible substrates in some cases; otherwise, its origin is given in the text to provide the reader an idea of how concisely the whole syntheses presented are covered. The photocatalytic reactions are either utilized as a key step in the total synthesis of natural products or in their late-stage derivatization. The chapter aims to provide important insights into the pros and cons related to the application of photochemical reactions in the field of natural products which will be beneficial to the readers. Acknowledgements Devalina Ray, Suman Majee, and Km. Anjali are thankful to DST-SERB (CRG/2019/002333) and UP CST (Project Id: 1818) for financial support.

244

S. Majee et al.

Authors’ Contribution Suman Majee and Km Anjali wrote the paper. Devalina Ray supervised the work and edited the manuscript. All the authors have read and approved the final manuscript. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References Allred TK, Dieskau AP, Zhao P, Lackner GL, Overman LE (2020) Enantioselective total synthesis of Macfarlandin C, a spongian diterpenoid harboring a concave-substituted cisdioxabicyclo[3.3.0]octanone fragment. Angew Chemie—Int Ed 59:6268–6272. https://doi.org/ 10.1002/anie.201916753 Antenucci A, Dughera S, Renzi P (2021) Green chemistry meets asymmetric organocatalysis: a critical overview on catalysts synthesis. Chemsuschem 14:2785–2853. https://doi.org/10.1002/ cssc.202100573 Ball P (2015) Chemistry: Why synthesize? Nature 528:327–329. https://doi.org/10.1038/528327a Baran PS (2018) Natural product total synthesis: as exciting as ever and here to stay. J Am Chem Soc 140:4751–4755. https://doi.org/10.1021/jacs.8b02266 Burtea A, DeForest J, Li X, Rychnovsky SD (2019) Total synthesis of (−)-himeradine A. Angew Chemie—Int Ed 58:16193–16197. https://doi.org/10.1002/anie.201910129 Cannillo A, Schwantje TR, Bégin M, Barabé F, Barriault L (2016) Gold-catalyzed photoredox C(Sp 2) cyclization: formal synthesis of (±)-triptolide. Org Lett 18:2592–2595. https://doi.org/ 10.1021/acs.orglett.6b00968 Carson MC, Orzolek BJ, Kozlowski MC (2022) Photocatalytic synthesis of para-peroxyquinols: total synthesis of (±)-Stemenone B and (±)-Parvistilbine B. Org Lett 24:7250–7254. https:// doi.org/10.1021/acs.orglett.2c02640 Cordier C, Morton D, Murrison S, Nelson A, O’Leary-Steele C (2008) Natural products as an inspiration in the diversity-oriented synthesis of bioactive compound libraries. Nat Prod Rep 25:719. https://doi.org/10.1039/b706296f Festa AA, Voskressensky LG, Van der Eycken EV (2019) Visible light-mediated chemistry of indoles and related heterocycles. Chem Soc Rev 48:4401–4423. https://doi.org/10.1039/C8C S00790J Ganesh KN, Zhang D, Miller SJ, Rossen K, Chirik PJ, Kozlowski MC, Zimmerman JB, Brooks BW, Savage PE, Allen DT et al (2021) Green chemistry: a framework for a sustainable future. Org Process Res Dev 25:1455–1459. https://doi.org/10.1021/acs.oprd.1c00216 Gravatt CS, Melecio-Zambrano L, Yoon TP (2021) Olefin-supported cationic copper catalysts for photochemical synthesis of structurally complex cyclobutanes. Angew Chemie—Int Ed 60:3989–3993. https://doi.org/10.1002/anie.202013067 Guan Z, Zhong X, Ye Y, Li X, Cong H, Yi H, Zhang H, Huang Z, Lei A (2022) Selective radical cascade (4+2) annulation with olefins towards the synthesis of chroman derivatives via organophotoredox catalysis. Chem Sci 13(21):6316–6321. https://doi.org/10.1039/D2SC00903J Hale KJ (2013) Terpenoid- and shikimate-derived natural product total synthesis: a personal analysis and commentary on the importance of the papers that appear in this virtual issue. Org Lett 15:3181–3198. https://doi.org/10.1021/ol401788y He F, Koenigs RM (2019) Visible light mediated, metal-free carbene transfer reactions of diazoalkanes with propargylic alcohols. Chem Commun 55:4881–4884. https://doi.org/10.1039/ C9CC00927B He L, Wang X, Wu X, Meng Z, Peng X, Liu XY, Qin Y (2019) Asymmetric total synthesis of (+)-strychnine. Org Lett 21:252–255. https://doi.org/10.1021/acs.orglett.8b03686 Holland JP, Gut M, Klingler S, Fay R, Guillou A (2020) Photochemical reactions in the synthesis of protein–drug conjugates. Chem A Eur J 26:33–48. https://doi.org/10.1002/chem.201904059

8 Synthesis and Functionalization of Natural Products with Light-Driven …

245

Hong B, Luo T, Lei X (2020) Late-stage diversification of natural products. ACS Cent Sci 6:622–635. https://doi.org/10.1021/acscentsci.9b00916 Jaiswal KS, Rathod VK (2020) Bioenzyme-assisted green organic synthesis. In: Green sustainable process for chemical and environmental engineering and science. Elsevier, pp 303–349 Kärkäs MD, Porco JA, Stephenson CRJ (2016) Photochemical approaches to complex chemotypes: applications in natural product synthesis. Chem Rev 116:9683–9747. https://doi.org/10.1021/ acs.chemrev.5b00760 Kim S, Lim S-W, Choi J (2022) Drug discovery inspired by bioactive small molecules from nature. Ani Cells Syst (Seoul) 26:254–265. https://doi.org/10.1080/19768354.2022.2157480 Lackner GL, Quasdorf KW, Overman LE (2018) Visible-light photocatalysis in the synthesis of natural products. In: Visible light photocatalysis in organic chemistry. Wiley, pp 283–297 Lin D, Jiang S, Zhang A, Wu T, Qian Y, Shao Q (2022) Structural derivatization strategies of natural phenols by semi-synthesis and total-synthesis. Nat Products Bioprospect 12:8. https://doi.org/ 10.1007/s13659-022-00331-6 Liu Q, Wu L-Z (2017) Recent advances in visible-light-driven organic reactions. Natl Sci Rev 4:359–380. https://doi.org/10.1093/nsr/nwx039 Liu Q, Huo C, Fu Y, Du Z (2022) Recent progress in organophotoredox reaction. Org Biomol Chem 20:6721–6740. https://doi.org/10.1039/D2OB00807F Liu X, Lu M, Guo X, Xu H, Xu J (2023) Visible-light enabled dehydroxylative alkylation of αhydroxy carboxylic acid derivatives via C À O Bond cleavage 202302041:1–5. https://doi.org/ 10.1002/chem.202302041 Lourenco AM, Ferreira L M, Branco PS (2012) Molecules of natural origin, semi-synthesis and synthesis with anti-inflammatory and anticancer utilities. Curr Pharm Des 18:3979–4046. https:// doi.org/10.2174/138161212802083644 Lu W, Yang D, Jing L, Wang G, Wang T, Zhou Y (2023) Photocatalytic synthesis of alkyl–alkyl sulfones via direct C(sp3)–H bond functionalization. Org Biomol Chem 2822–2827. https://doi. org/10.1039/d3ob00276d Luo MP, Gu YJ, Wang SG (2022) Photocatalytic enantioselective minisci reaction of β-carbolines and application to natural product synthesis. Chem Sci 14:251–256. https://doi.org/10.1039/d2s c05313f Majhi S, Das D (2021) Chemical derivatization of natural products: semisynthesis and pharmacological aspects—decade update. Tetrahedron 78:131801. https://doi.org/10.1016/j.tet.2020. 131801 Morita H, Sekiguchi M, Hirasawa Y, Zaima K, Hoe TC, Chan KL, Flavislamines EF, Fruticoslamine A (2008) New methyl chanofruticosinate-and aspidofractinine-type indole alkaloids, from two species of kopsia. Heterocycles 76(1):867. https://doi.org/10.3987/com-08-s(n)48 Mushtaq S, Abbasi BH, Uzair B, Abbasi R (2018) Natural products as reservoirs of novel therapeutic agents. EXCLI J 17:420–451. https://doi.org/10.17179/excli2018-1174 Natural A (2014) The renaissance of natural products chemistry. Org Lett 16:3849–3855. https:// doi.org/10.1021/ol501917g Newman DJ, Cragg GM (2020) Natural products as sources of new drugs over the nearly four decades from 01/1981 to 09/2019. J Nat Prod 83:770–803. https://doi.org/10.1021/acs.jnatprod. 9b01285 Nguyen LV, Jamison TF (2020) Total synthesis of (±)-sceptrin. Org Lett 22:6698–6702. https:// doi.org/10.1021/acs.orglett.0c01381 Pandey G, Laha R, Mondal PK (2019) Heterocyclization involving benzylic C(Sp3)-H functionalization enabled by visible light photoredox catalysis. Chem Commun 55:9689–9692. https:// doi.org/10.1039/c9cc04287c Pitre SP, Overman LE (2021) Strategic use of visible-light photoredox catalysis in natural product synthesis. Chem Rev 122:1717–1751. https://doi.org/10.1021/acs.chemrev.1c00247 Pitre SP, Overman LE (2022) Strategic use of visible-light photoredox catalysis in natural product synthesis. Chem Rev 122:1717–1751. https://doi.org/10.1021/acs.chemrev.1c00247

246

S. Majee et al.

Ramana KV, Singhal SS, Reddy AB (2014) Therapeutic potential of natural pharmacological agents in the treatment of human diseases. Biomed Res Int 2014:1–4. https://doi.org/10.1155/2014/ 573452 Rehm D, Weller A (1970) Kinetics of fluorescence quenching by electron and h-atom transfer. Isr J Chem 8:259–271. https://doi.org/10.1002/ijch.197000029 Reich D, Trowbridge A, Gaunt MJ (2020) Rapid syntheses of (−)-FR901483 and (+)TAN1251C enabled by complexity-generating photocatalytic olefin hydroaminoalkylation. Angew Chemie—Int Ed 59:2256–2261. https://doi.org/10.1002/anie.201912010 Revol G, McCallum T, Morin M, Gagosz F, Barriault L (2013) Photoredox transformations with dimeric gold complexes. Angew. Chemie 125:13584–13587. https://doi.org/10.1002/ange.201 306727 Robles O, Romo D (2014) Chemo- and site-selective derivatizations of natural products enabling biological studies. Nat Prod Rep 31:318–334. https://doi.org/10.1039/C3NP70087A Saha A, Sen C, Guin S, Das C, Maiti D, Sen S, Maiti D (2023) Photoinduced [3+2] cycloaddition of carbenes and nitriles: a versatile approach to oxazole synthesis. Angew Chemie—Int Ed 62:1–8. https://doi.org/10.1002/anie.202308916 Sakai HA, Macmillan DWC (2022) Nontraditional fragment couplings of alcohols and carboxylic acids: C(sp3 )–C(sp3 ) cross-coupling via radical sorting. Am Chem Soc 144:6185–6192. https:// doi.org/10.1021/jacs.2c02062 Sakamoto K, Tsujii E, Abe F, Nakanishi T, Yamashita M, Shigematsu N, Izumi S, Okuhara M (1996) FR901483, a Novel Immunosuppressant Isolated from Cladobotryum Sp. No. 11231. Taxonomy of the producing organism, fermentation, isolation, physico-chemical properties and biological activities. J Antibiot (Tokyo) 49:37–44. https://doi.org/10.7164/antibiotics.49.37 Salaverri N, Mas-ballesté R, Marzo L, Alemán J (2020) Visible light mediated photocatalytic [2+2] cycloaddition/ring-opening rearomatization cascade of electron-deficient azaarenes and vinylarenes. Commun Chem 1–8. https://doi.org/10.1038/s42004-020-00378-x Sbei N, Hardwick T, Ahmed N (2021) Green Chemistry: electrochemical organic transformations via paired electrolysis. ACS Sustain Chem Eng 9:6148–6169. https://doi.org/10.1021/acssusche meng.1c00665 Schirmer TE, Rolka AB, Karl TA, Holzhausen F, Burkhard K (2021) Photocatalytic C–H Tri Fl uoromethylthiolation by the decatungstate anion. Org Lett 23:5729–5733. https://doi.org/10. 1021/acs.orglett.1c01870 Sheldon RA (2019) The greening of solvents: towards sustainable organic synthesis. Curr Opin Green Sustain Chem 18:13–19. https://doi.org/10.1016/j.cogsc.2018.11.006 Sheldon RA, Brady D (2019) Broadening the scope of biocatalysis in sustainable organic synthesis. Chemsuschem 12:2859–2881. https://doi.org/10.1002/cssc.201900351 Shen J, Li J, Chen M, Chen Y (2023) Organic chemistry an electron donor—acceptor complex as a bifunctional reagent. Org Chem Front 10:1166–1172. https://doi.org/10.1039/d2qo01889f Shirafuji H, Tsubotani S, Ishimaru T, Harada S (1991) WO1991013887A1 Singh K, Sharma S, Tyagi R, Sagar R (2023) Recent progress in the synthesis of natural product inspired bioactive glycohybrids. Carbohydr Res 534:108975. https://doi.org/10.1016/j.carres. 2023.108975 Srinath S, Abinaya R, Prasanth A, Mariappan M, Sridhar R, Baskar B (2020) Reusable, homogeneous water soluble photoredox catalyzed oxidative dehydrogenation of N-heterocycles in a biphasic system: application to the synthesis of biologically active natural products. Green Chem 22:2575–2587. https://doi.org/10.1039/D0GC00569J Srivastava V, Singh PK, Singh PP (2022) Recent advances of visible-light photocatalysis in the functionalization of organic compounds. J Photochem Photobiol C Photochem Rev 50:100488. https://doi.org/10.1016/j.jphotochemrev.2022.100488 Sun X, Ritter T (2021) Decarboxylative polyfluoroarylation of alkylcarboxylic acids. Angewandte Chemie, 133:10651–10656. https://doi.org/10.1002/anie.202015596

8 Synthesis and Functionalization of Natural Products with Light-Driven …

247

Takeuchi H, Inuki S, Nakagawa K, Kawabe T, Ichimura A, Oishi S, Ohno H (2020) Total synthesis of zephycarinatines via photocatalytic reductive radical ipso-cyclization. Angew Chemie—Int Ed 59:21210–21215. https://doi.org/10.1002/anie.202009399 Tong X, Shi B, Liang K, Liu Q, Xia C (2019) Enantioselective total synthesis of (+)-flavisiamine F via late-stage visible-light-induced photochemical cyclization. Angew Chemie—Int Ed 58:5443– 5446. https://doi.org/10.1002/anie.201901241 Wang Z, Hui C (2021) Contemporary advancements in the semi-synthesis of bioactive terpenoids and steroids. Org Biomol Chem 19:3791–3812. https://doi.org/10.1039/D1OB00448D Wu J, Li S-J, Jiang L, Ma X-C, Lan Y, Shen L (2023) UV light–driven late-stage skeletal reorganization to diverse limonoid frameworks: a proof of concept for photobiosynthesis. Sci Adv 9. https://doi.org/10.1126/sciadv.ade2981 Yetra SR, Schmitt N, Tambar UK (2022) Catalytic photochemical enantioselective α-alkylation with pyridinium salts. Chem Sci 14:586–592. https://doi.org/10.1039/d2sc05654b Yoon TP, Ischay MA, Du J (2010) Visible light photocatalysis as a greener approach to photochemical synthesis. Nat Chem 2:527–532. https://doi.org/10.1038/nchem.687 Zhan G, Zhou J, Liu J, Huang J, Zhang H, Liu R, Yao G (2017) Acetylcholinesterase inhibitory alkaloids from the whole plants of zephyranthes carinata. J Nat Prod 80:2462–2471. https://doi. org/10.1021/acs.jnatprod.7b00301 Zhang W, Li H, Li X, Zou Z, Huang M, Liu J, Wang X, Ni S, Pan Y, Wang Y (2022) A practical fluorosulfonylating platform via photocatalytic imidazolium-based SO2 F radical reagent. Nat Commun 13. https://doi.org/10.1038/s41467-022-31296-2 Zhang H, Guo X, Zhou D, Wen J, Tang Y, Wang J, Liu Y, Chen G, Li N (2023) Design, synthesis of (±)-Millpuline A, and biological evaluation for the lung cell protective effects through SRC. ChemMedChem 18. https://doi.org/10.1002/cmdc.202300219 Zheng C, Yue J (2023) Allylic hydroxylation of Enones useful for the functionalization of relevant drugs and natural products, 1–9, https://doi.org/10.1038/s41467-023-38154-9.

Chapter 9

Photoremediation—An Emerging Approach for Dye Degradation in Wastewater Treatment Ramuel John I. Tamargo and Juniper V. Magallanes-Nava

9.1 Introduction What would the world look like without color? Humans have been fascinated with colors. Since ancient times, natural sources such as plants, insects, animals, and minerals have been used as colorants. Colorants are substances that are used to impart color because of their wavelength-selective absorption. The major forms of colorants are dyes and pigments. Dyes are water soluble while pigments are insoluble in water and other solvents. The chemical properties of the dyes make them adhere to the material, while pigments require a binder to attach to the material. Due to the demand for dyes as colorants for various applications, it has evolved from home use in ancient times, to industrial scale in modern times. Industrialization comes at a cost, often at the expense of the environment. No matter how beautiful colors are, once they are introduced into systems that they are not naturally a part of, they are considered contaminants or pollutants. Wastewater coming from industries that use dye, when left untreated, poses a threat to human life, and the environment. There are various approaches to treating dye-contaminated wastewater that aim to minimize its impact on human health and the environment. This book section discusses emerging approaches to the degradation of dye in wastewater treatment.

R. J. I. Tamargo (B) Department of Chemical Engineering, College of Engineering, University of the Philippines Diliman, 1101 Quezon City, Philippines e-mail: [email protected] J. V. Magallanes-Nava School of Technology, University of the Philippines Visayas, 5023 Miagao, Iloilo, Philippines e-mail: [email protected] 249

250

R. J. I. Tamargo and J. V. Magallanes-Nava

9.1.1 Definition Dyes are compounds that impart color. They are absorbed in the pores of the materials due to their size and their strong affinity to the material due to intermolecular forces. It is classified into two major categories (a) natural dyes and (b) synthetic dyes. Natural dyes are dyes that are directly obtained from the natural and biological environment which includes plants, animals, and minerals. Synthetic dyes are derived indirectly from natural sources or those that are synthesized in laboratories. There are more than 10,000 dyes that are commercially available at present (Sardar et al. 2021).

9.1.2 Chemistry of Dye Dyes impart colors to a material due to the chemical bonding of colored substances to surfaces or substrates they are applied to (Roy and Saha 2021). Dyes radiate colors due to the following reasons (a) they absorb visible light at 400–700 nm (b) they have at least one chromophore (color-bearing group) (c) they have a conjugated system, and (d) they exhibit resonance of electrons (IARC 2010). Chromophores are molecules that absorb certain wavelengths of visible light and, in the process, give off color to the material (Millington 2009). Examples of chromophores are the nitro group (–NO2 ), nitroso group (–NO), carbonyl group (– CO–), ethylenic bond (–C = C), and acetylenic bond among others. Auxochromes (atoms attached to a chromophore) give depth to the color of the dye (Kumar et al. 2021).

9.1.3 Major Types of Dyes There are different ways to classify dyes, they may be classified (a) according to their origin—synthetic or natural; (b) according to their chemical structure—cationic or anionic dyes (Rafiq et al. 2021); (c) according to their usage; or (d) according to the method of application on fiber (Kiron 2021). There are major classifications of dyes according to the mode of application (Kiron 2021). Direct or substantive dyes are soluble dyes that are directly applied to the fabrics. They are strongly polar. This may be acidic or basic dyes. Examples of these are nitrosonaphthol, acid orange-7, Malachite green, and magenta among others. Vat dyes are insoluble dyes that can be applied to cotton and rayon. It is called vat for it is carried out in a large vessel called vat. The process, called vatting, involves converting the dyes into their soluble form in a strong alkaline medium. The converted form is called the leuco compound where the materials are dropped in. Examples of which are Indigo Blue, and Tyrian purple.

9 Photoremediation—An Emerging Approach for Dye Degradation …

251

Table 9.1 Commonly used dyes for some materials Material

Commonly used dyes

Cellulose fiber

Direct dyes, reactive dyes, vat dyes, sulfide dyes, azo dyes

Wool

Acid dyes

Silk

Direct dyes, acid dyes

Polyester

Azo dyes, disperse dyes

Mordant dyes are insoluble dyes in which mordants are needed as binding material. Alizarin is an example of a mordant dye. Azo dyes constitute the largest chunk of the world’s dye production and are widely used in textile, printing, and paper manufacturing (Benkhaya et al. 2020). These are dyes with at least one azo group (−N ≡ N −) attached to at least one aromatic ring. This is directly applied to the fiber at low temperatures, where it develops. The material is soaked in phenol first, dried, and immersed in a low-temperature solution of diazonium salt. Examples of azo dyes are methyl orange and methyl red. Disperse dyes are insoluble in water, usually applied in a material as dispersion of small dye particles in a high-temperature dye bath solution. This type of dye is usually used in polyester, nylon, acrylic, and acetate rayon. An example of disperse dye is Celliton. The specific type of material used in the textile industry requires specific types of dye. Based on Kiron (2021), Table 9.1 shows commonly used dyes for some materials.

9.2 Examples of Industries Using Dyes Several industries use dyes for their operation. Some examples of these industries are described in Sects. 2.1 and 2.2.

9.2.1 Textile Industry The textile and fashion industry is an industry that involves the designing, manufacturing, research and development, and distribution of textile and fabric materials. Its history dates back to prehistoric times when pieces of clothing worn by humans have been discovered. It has since been evolving into what the modern textile industry is now. It is one of the most popular industries in the global setting. It has greatly impacted the world’s economy, even serving as a source of revenue for some economies.

252

R. J. I. Tamargo and J. V. Magallanes-Nava

As with other major industries, this development also caused a major impact on the environment. It is considered one of the largest generators of pollutants in the world. Dyeing, which gives color to textiles and clothing, requires a large amount of water and produces a large quantity of wastewater in its production and subsequent processes. One of the major contributors to wastewater in the manufacturing of textiles is the dyeing process. It is defined as the process of applying dyes or pigments to the textile material which is a value-adding process. It is the interaction between the dye and the fiber. The process involves the adsorption of the dye from the solution to the surface of the fiber, and the diffusion of the dye into the surface (Shang 2013).

9.2.2 Pulp and Paper Industry The pulp and paper industry is a manufacturing industry that involves the production of pulp and paper for various applications and products. It is one of the most important industries in the world (Bajpai 2015). The processes involved in the industry are pulp production and processing, and paper/paperboard production. In the production of paper and paperboard, dyes are one of the key materials (Athalye 2012). It is considered one of the largest polluting industries. The process involves the usage of a large quantity of water; thus, a large quantity of wastewater is also generated. The wastewater generated from this industry is considered one of the highly polluting effluents (Narayana and Kariyazzanavar 2016). The effluent is highly colored and contains suspended solids, dissolved colloidal organics, coloring (from lignin and dyes), dissolved inorganics, microorganisms, and toxic chemicals (Gopal et al. 2019; Narayana and Kariyajjanavar 2019). This dark-colored effluent brought about mainly by dyes raises concerns since these are highly visible, may inhibit photosynthesis, and are toxic to the marine environment (Narayana and Kariyajjanavar 2019; El Haddad et al. 2013).

9.3 Wastewater Treatment Approaches The dyes should be removed before discharge for environmental impact reduction. Thus, its removal or degradation constitutes a major part of the wastewater treatment of industries incorporating dyes in their processes.

9 Photoremediation—An Emerging Approach for Dye Degradation …

253

9.3.1 Wastewater Characteristics Wastewater coming from different stages of processes in dye industries contains mixtures of metals, dyes that have not settled on the fiber, and other pollutants (Shindhal et al. 2020). These effluents have varying degrees of chemical oxygen demand (COD), pH, total dissolved solids (TDS), biological oxygen demand (BOD), salt content, quantity, and color. This is based on the types of raw materials, chemicals and processes involved, and types of dyes used. Generally, wastewater from dye industries has low biodegradability, high color, and high BOD and COD (Shindhal et al. 2020).

9.3.2 Effects of Dye Pollutants on the Health and Environment There are types of dyes that are insoluble in water, such as vat, azoic, and disperse dyes. Insoluble dyes are easily removed in water. However, some dyes are highly soluble in water such as reactive, direct, basic, and acid dyes. Because of this property, it is difficult to separate and remove from wastewater (Hassan and Carr 2018). Dyes, even in small quantities, are visible to the naked eye and are undesirable indicators of contamination of the wastewater. It is aesthetically unpleasant. Its resistance to degradation poses threats to the aquatic environment by preventing the penetration of sunlight, decreasing aeration of the water body, and impeding photochemical reactions (Ruan et al. 2019; Hussain et al. 2019). Its effect in photosynthesis reactions affects aquatic plants and animals. Moreover, some dyes are metal complexes that are considered toxic, carcinogenic (can cause cancer), and mutagenic (can cause mutation). When released into the environment, it is incorporated into the food chain through bioaccumulation and affects human and animal health. They can cause allergic reactions, and respiratory problems (Rapo and Tonk 2021). Dyes also affect agricultural fields, showing inhibition effects on seed germination and plant growth (Alsukaibi 2022).

9.3.3 Conventional Wastewater Treatment Method Treatment of wastewater is essential. In some countries, it is even mandatory to treat wastewater before its discharge to the receiving bodies of water, or on land. Due to the scarcity of water experienced worldwide, it is important to optimize usage and find ways to improve the quality of the wastewater for potential reuse and to mitigate its impact on the environment. Typical wastewater setup of dye industries includes the following treatment processes: preliminary treatment, primary treatment, secondary treatment, and

254

R. J. I. Tamargo and J. V. Magallanes-Nava

tertiary treatment (Shindhal et al. 2020; Xiaoxu et al. 2017). Preliminary treatment aims to protect the wastewater treatment facility and to remove oil, grease, waves, large solid particles, and debris. The primary treatment employs physical processes to remove settleable solids and inorganic solids. Secondary treatment uses biological processes to remove dissolved and suspended organic pollutants in the wastewater. This is carried out with the aid of microorganisms. Tertiary treatment, also known as chemical treatment, uses chemicals to further improve the quality of wastewater to meet environmental standards and other qualifications (Perry et al. 2018; Metcalf and Eddy 2014). The specific type of process employed depends upon the volume, quality, and strength of the wastewater, the space available for the wastewater treatment facility, and the governing regulations and environmental policies. In dye wastewater management, the goal of the treatment is to reduce the pollution load, decolorize, degrade, and detoxify the dye present in the wastewater. Dye decolorization refers to the removal of color in the wastewater. Dye degradation is the term used to describe a method where large color atoms are decomposed or broken down into smaller size particles (Menon et al. 2021). The performance of dye treatment processes is measured by the percent removal or percent degradation of dye. The values are generated using a UV–Vis spectrophotometer. Absorption peaks monitor the degradation of dye. The disappearance of the main absorption peak of the dye, or the appearance of new peaks suggests the degradation of the dye (Chen et al. 2021) The absorbance before and after light irradiation is measured and the equation is given as (Khan et al. 2023a, b):  %Degradation (%Removal) Efficiency =

 A0 − A x100 A0

(9.1)

where A0 = absorbance before irradiation A = absorbance after irradiation It can also be expressed with respect to the concentration (Hira et al. 2020):  %Degradation (%Removal) Efficiency =

 C0 − C x100 C0

(9.2)

where C0 = initial concentration C = concentration after irradiation Conventional dye treatment includes physicochemical and biological treatment approaches. Examples of these are stated in the following subsections.

9 Photoremediation—An Emerging Approach for Dye Degradation …

9.3.3.1

255

Coagulation–Flocculation

Coagulation–flocculation (CF) is a sequential wastewater treatment process that involves the addition of chemical compounds to destabilize colloidal particles, and then binding or clumping of particles together to form flocs (Butani and Mane 2017). These clumped particles become heavier and settle at the bottom. In this approach, both synthetic and natural coagulants can be used. In particular, the most frequently used coagulants are iron or aluminum salts (Srivatsav et al. 2020). Polyaluminum chloride (PACl) is used as a coagulant, and commercial-grade anionic polyacrylamide as a coagulant aid effectively removes 99% of the color of industrial-grade wastewater (Wong et al. 2007). Methylene blue and methyl orange dyes were successfully degraded using a natural coagulant–laterite soil (with high silica content, aluminum, and iron contents). The removal efficiency is 99.61% for methylene blue and 92.11% for methyl orange (Lau et al. 2015). It hastens the settling time of the suspended solids, facilitates the removal of fine particles, and is shown to effectively remove bacteria, protozoa, and viruses (Srivatsav et al. 2020). The major disadvantage of coagulation–flocculation is the production of a high volume of sludge (Golob et al. 2005). This is one of the most used treatments in most industries (Butani and Mane 2017). This should be combined with other processes to have a more efficient removal and improvement of the quality of wastewater.

9.3.3.2

Adsorption

Adsorption is a mass transfer process that describes the interaction between two different phases where a liquid binds to a solid surface. It occurs at the interface between the solid adsorbent and the wastewater to be treated (El-Baz et al. 2020). The solute that has accumulated in the solid surface is called the adsorbate. Adsorption can be physical (dye molecules attaching to the adsorbent surface) or a chemical process (dye molecules attaching via chemical reaction or by chemical bond). The choice of adsorbent is crucial in dye degradation efficiency. Desirable properties of a good adsorbent include stability, large surface area, high adsorption capacity, large porosity, availability, compatibility, selectivity, eco-friendliness, and reusability (Nasar and Mashkoor 2019; Yagub et al. 2014). Lanthanum-incorporated carboxymethylcellulose—bentonite (LCB) composite is used as an adsorbent for the removal of Indigo Carmine (IC), Acid Blue 158 (AB), and Reactive Blue 4 (RB) aqueous solutions. Results showed effective removal of dye molecules in aqueous solutions using LCB composite (Sirajudheen et al. 2020). A study by Tan et al. (2023) shows a magnetic starch-based adsorbent (MSBA) as a promising candidate adsorbent for dye degradation at 83.04% removal of crystal violet dye. The MSBA was synthesized using a copolymer solution of starch-grafted acrylic acid, alkali homogeneous phase, and Fe3 O4 @SiO2 particles.

256

R. J. I. Tamargo and J. V. Magallanes-Nava

Biomass and natural sources have also been tested as low-cost, eco-friendly, and good surface characteristics adsorbents for the removal of dyes in wastewater (Aragaw and Bogale 2021). Lignocellulosic biomass has become one of the most widely used starting materials to produce activated carbon using different activating agents (Husien et al. 2022). Activated carbon is typically used for the adsorption of dyes due to its high carbon content, reusability, simplicity, convenience, and ease of operation (Nizam et al. 2021a, b). Carrot waste-derived activated carbon (AC) was used for the degradation of toxic Rhodamine B (RhB) dye activated by ZnCl2 . A degradation efficiency of 87% is achieved after 2 h showing the potential of AC to remove RhB dye (Hira et al. 2020). Rice husk residue-based activated carbon has been found effective in removing methylene blue dye, neutral dye, and methyl orange (Li et al. 2016). Other biomass with or without modification has been utilized for dye removal. Anchote peel-based agricultural waste achieved a removal efficiency of methyl orange dye of up to 94.47% (Hambisa et al. 2022). Coffee waste modified with polyethylenimine has the potential to adsorb anionic textile dyes (Reactive Black 5 and Congo Red) (Wong et al. 2020). Due to its cost, efficiency, and operation requirements, adsorption is considered one of the best treatment processes for dye degradation (Sirajudheen et al. 2020).

9.3.3.3

Filtration

Filtration shows promising results in the elimination of color (Alsukaibi 2022). The membranes used have small pores, thus solutes with larger pores are left behind, resulting in dye removal. This can be microfiltration (0.1–10 µm), nanofiltration (0.5–0.2 nm), and ultrafiltration (0.1–0.001 µm) (Al-Tohamy et al. 2022). The ultrafiltration process was performed using ultrafiltration membranes made of polyethersulfone (PES), and regenerated cellulose (C) to remove five reactive dyes—Reactive Orange 16, Remazol Brilliant Blue R, Reactive Orange 20, Reactive Black 5, Reactive Red 120). This study showed that reactive dye removal percentages are 80–97% for PES, while the regenerated cellulose was able to remove by 45–89% (Ahmed et al. 2021). David et al. (2020) studied the filtration efficiency for dye removal of keratinpolyamide blend nanofibrous membranes. Very fine nanofibers produced and enhanced porosity of the membrane resulted in 83–100% dye removal efficiencies of dark green color tannery dye at different member blends. Polymer blends of polyphenyl sulfone (PPSU) and polyether sulfone (PES) were used for ultrafiltration application for the removal of drupel black NT dye. PPSU– PES membrane blend achieved 96.62% dye removal efficiency (Ghadhban et al. 2020).

9 Photoremediation—An Emerging Approach for Dye Degradation …

9.3.3.4

257

Coagulation–Flocculation Combined with Other Processes

As mentioned, the coagulation–flocculation method can be paired with other treatment processes to remove dye contaminants efficiently. Adsorption–coagulation combined system using Hibiscus sabdariffa as coagulant and activated carbon as adsorbent proves to be a highly efficient system for the removal of up to 96.67% of Congo red dye powder (Hoong and Ismail 2018). In the study of Puchana-Rosero et al. (2018), the stock dye solution of Acid Black 210 dye (AB-210) undergoes a combination of CF and adsorption treatment. The coagulant used is aluminum sulfate and the anionic polyelectrolyte FX AS1. The adsorbent used is activated carbon from sludge. The result showed efficient dye removal of up to 85.2%. The removal of solophenyl blue (SB) dye in an aqueous solution by CF followed by microfiltration (MF) was studied. The natural coagulant, potato starch, is modified using titanium dioxide. The result showed 100% removal of SB for CF followed by MF (Januario et al. 2021).

9.3.3.5

Biological Treatment Processes

Fungus, algae, yeast, bacteria, and enzymes have been utilized to treat dye wastewater. This biodegradation to a less harmful form is based on the biotransformation enzymes such as tyrosinase, hexane oxidase, demethylase, laccase, or lignin peroxidase (Soltani et al. 2021). Thermophilic bacterial strain (Anoxybacillus sp.PDR2) has the potential to detoxify azo dye—Direct Black G (DBG) (Chen et al. 2021). The photocatalytic activity of fungi (Aspergillus spp.) assisted silver nanoparticles has been effectively used for the removal of reactive yellow dye. Moreover, the biomass retentate was proven effective in removing yellow dye (Gola et al. 2021). Five bacteria [Bacillus pumilus/safensis, Bacillus thuringiensis, Enterococcus faecium, Pseudomonas aeruginosa (Lab1), and Pseudomonas aeruginosa (Lab2)] were isolated from textile effluent have the potential ability for the decolorization of Novacron dyes (Afrin et al. 2021). Kanagaraj et al. (2012) studied the decolorization of azo dyes using B.cereus bacteria. The decolorization rate of dye in agitated conditions is 80% and 96% in static conditions. Of these treatment processes, adsorption is by far the more effective and cheaper method (Ruan et al. 2019).

9.4 Modern Wastewater Treatment Approaches The knowledge of conventional wastewater treatment paved the way for the development of other treatment approaches which are designed to overcome disadvantages of the conventional processes. Limitations of physicochemical treatments include high cost, high energy requirements, low environmental effectiveness, and high sludge

258

R. J. I. Tamargo and J. V. Magallanes-Nava

production (Rawat et al. 2016). Innovative treatment approaches target specific pollutants, more efficiently or cost-effectively. Current wastewater treatment methods include chemical, electrochemical, and physical treatments. Graphite electrodes (anode and cathode) were used for the removal of methylene blue (MB) at pH, initial MB concentration, electrolyte concentration, electrolyte concentration, and operating time. The maximum removal efficiency of 99.9% was observed at an initial pH of 4, initial MB concentration of 26.5 mg/L, electrolyte concentration of 0.6 g/L, electric potential of 3 V, and operating time of 30 min (Goren et al. 2022). The emergence of advanced oxidation processes (AOPS) is a welcome development in the field of wastewater treatment. It is considered the most attractive and favorable option for the removal of recalcitrant pollutants in wastewater (Ghime and Ghosh 2019). The Fenton process is an example of an advanced oxidation process. Fenton reagent was used for the degradation of methylene blue (MB) dye. It was proven to be most effective with a decolorization efficiency of 98.8% at pH 3, 30-min reaction, and a ratio of 0.05 M Fe2+/ H2 O2 . Chemical oxygen demand (COD) removal of 85% was noted. It was noted that the process is thermodynamically feasible, spontaneous, and endothermic (Giwa et al. 2020).

9.5 Photo Remediation as an Emerging Approach in Wastewater Treatment Photoremediation comes from the words, “photo” which means light, and “remediation” which is the process of removing or minimizing the contaminants or pollutants from the environment. Thus, photoremediation is the use of light to eliminate or inhibit the effect of hazardous or toxic substances in the environment. A strategy employed in this area is called photocatalytic degradation. Some of the advantages of photocatalysis include low energy consumption, relatively simple operation, no production of secondary pollutants from the process, can be carried out under mild reaction conditions, and solar energy can be utilized (Guo et al. 2023). Photoremediation is highly considered in dye degradation due to its stability, availability, low cost, eco-friendliness, and reusability (Kumari et al. 2023; Ramli et al. 2014). Photocatalytic degradation is an advanced light-induced oxidation process in the presence of catalysts (Alsukaibi 2022). It degrades highly concentrated, complex, and recalcitrant pollutants (Guo et al. 2017). The pollutant molecules undergo oxidation and hydrolysis through the absorption of photons in visible, ultraviolet, and infrared light spectra (da Silva Alves et al. 2022). The wavelengths (Klijn and Hubbuch 2021) are reflected in Fig. 9.1. Photocatalysis is defined as the speeding up of a photoreaction through the action of semiconductor catalysts. The type of irradiation employed will depend on the type

9 Photoremediation—An Emerging Approach for Dye Degradation …

259

Fig. 9.1 Light spectra

of catalyst used in the process (Ajmal et al. 2014). In photoremediation, dyes degrade when the light source interacts with the photocatalyst. The photocatalysis system may be homogeneous or heterogeneous (Pirhashemi et al. 2018). It is homogeneous when both the catalysts and the reactant are in the same phase; when it is in different phases, it is called heterogeneous (Ameta et al. 2018). One of the most important aspects of photocatalytic degradation of dye is the choice of the photocatalyst for the process.

9.5.1 Photocatalysts Photocatalysts are materials that absorb light to speed up and improve light-induced reactions (Qutub et al. 2022). It alters the rate of the reaction upon exposure to light. All semiconductors are photocatalysts since they conduct electricity at ambient temperature provided that a light source is present (Ameta et al. 2018). Photocatalysts are categorized as first-generation (single-component materials), second-generation (multiple components in a suspension), and third-generation (single or multiple components immobilized on solid substrates) (Anwer et al. 2019). Pirhashemi et al. (2018) described the major properties of good photocatalysts. These properties are appropriate band gap, good chemical stability, high carrier mobility, high surface area, and efficient light absorption. • The band gap refers to the energy difference between the valence band (VB) and the conduction band (CB) (Ameta et al. 2018). This is illustrated in Fig. 9.2. Semiconductor has a discontinuous electron band with a moderate band gap. This gap must be just enough that exposure to a certain amount of energy will excite the electron in the valence band to move to the conduction band (Pennington 2015). • The valence band is the highest occupied energy band from the energy levels of valence electrons. The conduction band is the lowest unoccupied energy band (or partially occupied by electrons) in which electrons move freely, causing the flow

260

R. J. I. Tamargo and J. V. Magallanes-Nava

Fig. 9.2 The band gap of the semiconductor

• •

•

•

of current (conduction). It serves as the electron acceptor (from the valence band) in semiconductors. Chemical stability is the resistance of the photocatalyst to undergo a chemical reaction. The photocatalyst must not be converted into other forms during the photocatalytic process. Carrier mobility is one of the most important parameters of semiconductors which determines their subsequent applications. It determines the speed of a carrier (electron or hole) in a solid material under an applied electric field. High carrier mobility has a higher frequency response and higher current (Myronov 2018). Surface area refers to the total area of the catalyst surfaces. The surface area greatly influences the activity of a photocatalyst. The surface area is directly proportional to the number of active photocatalytic sites and adsorption capacity. The higher the surface area, the more active sites for catalytic activities are available, thus, the higher the adsorption capacity of the catalyst (Nayan et al. 2019). Light absorption plays an important role in the photocatalytic process which affects the rate of the reaction (Calza et al. 2018). Ideal photocatalysts display efficient light absorption capacity.

Considering the properties of the ideal photocatalyst, semiconductors such as titanium dioxide (TiO2 ) or zinc oxide (ZnO) reflect these properties, thus they are the usual choice for a photocatalyst. Due to the excellent features of TiO2 , it is the most common and widely used photocatalyst. However, some of its limitations such as the low utilization rate of solar energy (poor response to visible light), wide band gap, issues in the degradation efficiency, and difficulty in recovery inhibit large-scale application (Liu et al. 2023a, b; Zheng et al. 2022; Mamba and Mishra 2016).

9.5.2 Mechanism of the Photocatalytic Degradation of Dye This subsection will discuss different mechanisms for dye degradation using different types of catalysts under various light spectra. The basic principle of photocatalysis involves the absorption of energy (hv) by the photocatalyst which results in the excitation of the electrons (e− ) This leads to the transfer of excited electrons from the valence band (VB) to the conduction band

9 Photoremediation—An Emerging Approach for Dye Degradation …

261

(Mamba and Mishra 2016). The transfer leads to the formation of holes (h+ ) in the valence band (Ameta et al. 2018). Ameta et al. (2018) described four possible outcomes of this process based on the relative positions of the conduction and valence bands of the semiconductor, and the redox levels of the substrate. The possible outcomes are as follows: (a) Redox level < conduction band → reduction of the substrate. (b) Redox level > valence band → oxidation of the substrate. (c) Conduction band < redox level substrate < valence band → neither oxidation nor reduction. (d) Valence band < redox level substrate < conduction band → both oxidation and reduction. The complex nature of the photocatalytic process makes it difficult to propose a single mechanism to describe the processes and reactions involved in the degradation of dye using a photocatalyst. Navidpour et al. (2023) enumerated the reactions involved in the mechanism of an ideal heterogeneous photocatalytic process (Fig. 9.3). The generation of electron and hole pairs through the excitation of the electrons in the presence of light subsequently produces highly reactive oxygen species (ROSs) such as hydroxyl radicals (. OH), superoxide radical ions (. O2 − ), hydrogen peroxide (H2 O2 ), hydroperoxyl radicals (. HO2 ), and singlet oxygen (1 O2 ). These ROSs are responsible for various subsequent reactions. The performance of the photocatalysts is determined by the lifeline of the electrons and the holes that form the ROSs. The efficiency of the catalysts is also affected by the rate of recombination of the electrons (Tahir and Saad 2021). These ROSs, free electrons, and holes react with the organic pollutants (molecules) adsorbed in the surface of the catalysts and convert these to degraded and less harmful (or safe) products (Pavel et al. 2023). The potential products are carbon dioxide and water (Tahir and Saad 2021). The proposed general photocatalytic mechanism for dye degradation is as follows (Navidpour et al. 2023; Mamba and Mishra 2016;): (1) Adsorption of the dye to the catalysts. (2) Photogenerated electrons (trapped by a recipient) in the conduction band give ROSs such as superoxide radicals (O2 • − ). Superoxide is one of the four known oxidation states of O2 . It is considered both a radical and an anion. Its highly reactive property makes it a strong oxidizing agent and initiator of radical reactions which is ideal for the oxidation of organic pollutants (Hayyan et al. 2016). (3) Photogenerated holes (due to the migration of electrons to the conduction band) in the valence band as occupied by the donors (can be dye organics or OH− ). (4) Radicals react with the adsorbed dye to give the degraded product(s). (5) The degraded products undergo desorption to the surface, giving less toxic or decolorized products. Reza et al. (2017) mentioned three possible reaction mechanisms for dye degradation under photocatalytic influence which include (1) hydroxyl radical attack, (2)

262

R. J. I. Tamargo and J. V. Magallanes-Nava

Fig. 9.3 Reaction mechanism for an ideal heterogeneous photocatalytic process

9 Photoremediation—An Emerging Approach for Dye Degradation …

263

Fig. 9.3 (continued)

direct oxidation by the positive hole, and (3) direct reduction by the electron in the conducting band. Ajmal et al. (2014) classified the mechanisms for the degradation of dyes using TiO2 -based photocatalysts as indirect or direct. The direct mechanism is visible light—initiated while the indirect process uses semiconductors. Direct dye degradation under visible light involves dye excitation from the ground state (Dye) to a triple-excited state (Dye*). This is further converted into a semi-oxidized radical cation (Dye+ ) through an electron injection into the TiO2 conduction band. The superoxide radical anions (O2 • − ) are formed from these trapped electrons and dissolved oxygen, which is converted into hydroxyl radicals ( . OH). These •OH oxidize the organic compounds. The proposed reactions are shown in Fig. 9.4. Mishra et al. (2021) reported the mechanism for the reductive transformation of rhodamine B (RhB) and congo red (CR) using metal nanoparticles (NPs)/oxide core–shell nanocomposites, specifically, Au@CeO2 -rGO nanohybrids (NH). The reductive transformation of RhB is illustrated in Fig. 9.5. For CR, the degradation yielded 3,4-diaminonaphthalene-1-sulfonic acid which can potentially be used as an anti-AIDS agent.

264

R. J. I. Tamargo and J. V. Magallanes-Nava

Fig. 9.4 Reaction mechanism for the degradation of dyes using TiO2 -based photocatalysts

Fig. 9.5 Reductive transformation of RhB

9.5.3 Factors Affecting Photocatalysis Several factors affect the performance of the photocatalytic degradation of dyes. These parameters are pH, initial concentration of dyes, the size, type, and amount of photocatalyst, the reaction time, and the intensity of the irradiation (Gusain et al. 2020; Rafiq et al. 2021; Reza et al. 2017). The pH of the solution has a direct effect on the electrical double layer of the solid interface. This affects the adsorption–desorption processes, and the separation of the electron–hole pairs in the catalysts surface (Reza et al. 2017). Further, it affects the adsorption characteristics of the materials due to its effect on the surface charge of the photocatalytic membrane (Sakarkar et al. 2020). The agglomeration of particles at a certain pH may reduce surface to volume ratio that limits the amount of light available (Josephine et al. 2019). In general, degradation efficiency increases with the increase in the generation of OH, but above pH 11, these compete with the pollutants, reducing the amount of adsorbed pollutants on the surface of the catalyst. This consequently reduces the removal efficiency (Gusain et al. 2020). An increase in the dye concentration generally reduces the efficiency of dye degradation due to the increased adsorption of the pollutant in the active sites of the catalyst,

9 Photoremediation—An Emerging Approach for Dye Degradation …

265

reducing the active sites available for the adsorption of OH− . The reduction in the amount of OH− affects the formation of other radicals. For the catalyst loading, more catalysts ensure more active sites for photocatalysis, thus increasing its efficiency. However, after reaching a certain amount, this might cause turbidity of the solution, thus blocking the light source, and causing a light scattering phenomenon (Josephine et al. 2020). Another possible cause is the agglomeration of nanoparticles which will result in a decrease in the number of active sites available (Gusain et al. 2020). Vasiljevic et al. (2020) studied the effects of different factors on the dye degradation efficiency of methylene blue using iron titanate (Fe2 TiO5 ) under visible light. It was noted that the degradation efficiency increased with the increase in pH (pH 7–11), decreased with the increase in dye concentration, and initially increased with the increase in catalyst loading but decreased above 50 mg. In a study by Sakarkat et al. (2020), modified TiO2 -entrapped polyvinylidene fluoride (PVDF) membranes were used to investigate its efficiency for the removal of Remazol Turquoise Blue (RTB) under UV light. It was observed that the removal efficiency was high at acidic conditions, then declined at higher pH. Lower dye concentration also resulted in higher removal efficiency. The efficiency of the bismuth vanadate (BiVO4 ) catalyst for the removal of Rhodamine B under visible light was investigated. It was noted that there was an initial increase in the removal efficiency with the increase in pH (pH 9–10), then a further increase in the pH (pH 11) lower degradation efficiency. Though these studies follow the general trend for the behavior of the photocatalysts at different conditions, it is still necessary to investigate different factors specific to the conditions (photocatalyst used, light source, and target dye) to establish the efficiency of the photocatalyst in the dye degradation process.

9.5.4 Titanium-Based Photocatalysts To overcome the disadvantages and improve the efficiency of the photocatalysts, modifications in TiO2 and other nanocomposites are studied for their photocatalytic degradation performance. The following subsections discuss studies involving TiO2 based, ZnO-based, and other nanoparticle-based photocatalysts. Li et al. (2016) prepared titanium dioxide/corn straw biochar (TiO2 /BC) for the removal of methyl orange (MO) in an aqueous solution. A Xenon lamp (for simulated sunlight effect) was used for the irradiation. The photocatalytic degradation performance of TiO2 /BC composite was at 97.98% attributed to BC acting as an MO dye adsorbent, its promotion of the absorption of light, and the narrowing of bandgap. Liu et al. (2023a, b) synthesized TiO2 and nitrogen-rich graphite-based carbon nitride (g-C3 N5 ) heterojunction for the removal of methylene blue (MB) in aqueous solution under visible light. TiO2 /g-C3 N5 showed improved degradation performance at 97.4% compared to that of TiO2 alone and g-C3 N5 alone.

266

R. J. I. Tamargo and J. V. Magallanes-Nava

The photocatalytic degradation performances of TiO2 , its binary CdTiO2 , and its ternary NiCdTiO2 were investigated for methylene blue (MB) and methyl green (MG). The degradation rates (%) of TiO2 for MB and MG are 76.59% and 63.5%, respectively. For CdTiO2 , the MB degradation rate is at 82% and the MG degradation rate is at 88%. The most efficient photocatalyst is proven to be a ternary NiCdTiO2 at 86% MB degradation, and 97.5% MG degradation at 100 min irradiation time (Khan et al. 2023a, b). Cadmium sulfide (CdS) is doped with Titanium oxide (CdS/TiO2 ) for removal of the Acid Blue –29 dye. As prepared CdS/ TiO2 exhibits the highest dye degradation efficiency at 84% (Qutub et al. 2022). Vasiljevic et al. (2020) synthesized iron titanate (Fe2 TiO5 ) nanoparticles and tested these as-prepared Fe2 TiO5 nanoparticles for the photocatalytic degradation of methylene blue under visible light. It showed moderate degradation efficiency which is affected by the particle-specific surface area, catalyst loading, and pH of the solution. In a study by Ambaye and Hagos (2020), photoremediation as a pre-treatment of textile effluent containing azo dyes, followed by biological treatment showed the highest color removal and chemical oxygen demand (COD) reduction. This is in comparison with photocatalytic treatment alone, and aerobic treatment alone. Titanium dioxide (TiO2 ), hydrogen peroxide (H2 O2 ), and UV lamp system were used for the photocatalytic degradation and Providencia rettgeri strain HSL1 bacteria culture was used for the aerobic treatment. This is an example of the combination of chemical and biological treatment to degrade dye. A combined flocculation–photocatalysis system was used to remove crystal violet, reactive red X-3B, and acid orange II dye. The flocculant used is polyaluminum chloride (PAC) and for the photocatalysis, TiO2 was used under UV light. It is proven to be an effective system for dye concentration reduction (Wang et al. 2020). Sirirerkratana et al. (2019) coated glass, ceramic tile, and stainless-steel sheets with TiO2 to make an innovative reactor for dye removal in synthetic (methylene blue) and actual wastewater from the textile industry (with reactive purple as the main component). This is exposed to UVA and UVC light inside a chamber. Results showed the highest color removal efficiency at about 93% using transparent glass and a UVC light source. TiO2 – NH2 NPs cross-linked to cellulose acetate (CA)/carbon nanotube (CNT) composite nanofibers achieved 100% degradation of indigo carmine (IC) and methylene blue (MB) dyes at 10 ppm dye concentration, pH 2, 80 °C temperature, and 40 W UV lamp. These were achieved at 180 min (for IC) and 300 min (for MB) (Salama et al. 2018).

9 Photoremediation—An Emerging Approach for Dye Degradation …

267

9.5.5 Zinc-Based Photocatalysts Due to its wide band gap (at approximately 3.3 eV), ZnO is considered a good photocatalyst (Lau et al. 2020). This subsection discusses studies using zinc-based photocatalysts for dye degradation. Silver and zinc oxide nanoparticles were phytofabricated with Plumbago auriculata leaf extract (PALE) and were used for photocatalytic methylene blue (MB) dye degradation under UV light. The results showed that the ZnO combined with silver nanoparticles at 10:1 (10 mM of ZnCH4 H6 O4 and 1 mM of AgNO3 ) had a maximum MB degradation of 95.7% (Bloch et al. 2022). Nguyen et al. (2021) investigated the use of Canna indica flowers as a capping and stabilizing source for the fabrication of ZnO nanoparticles (ZnONPs) for dye removal. Using solar light, it was reported that using the ZnONPs showed 94.23% photocatalytic degradation of methylene blue. Zinc oxide nanoparticles (ZnONPs) synthesized with roselle flower and oil palm leaf extract effectively degrade 10 ppm of methyl orange (MO) in 5 h and methylene blue (MB) in 3 h in the presence of 10 W of UV light. It also exhibited high antioxidant properties and low toxicity (Lau et al. 2020). Chauhan et al. (2020) synthesized pure ZnO and Ag-doped ZnO using Cannabis sativa for photocatalytic dye degradation under solar light. It showed that Ag-doped ZnO exhibited higher degradation efficiency compared to pure ZnO under solar lights in 80 min. The reported values are as follows: ZnO and Ag-ZnO nanoparticles removed 38% and 96% of congo red, and 35% and 94% for methyl orange. The photocatalytic degradation potentials of ZnO and 2% Fe-ZnO nanomaterial prepared via sol–gel method were investigated using methylene blue (MB) under UV light irradiation. At pH = 2 and a dye concentration of 10 mg/L, the maximum degradation of MB dye was 86% for ZnO and 92% for 2% Fe-ZnO (Isai and Shrivastava 2019). Scutellaria baicalensis—ZnO nanoparticles were synthesized for photocatalytic degradation activity using methylene blue under UV irradiation. At 210 min and 0.05 mg/ml concentration of Sb-ZnO NP (powder to deionized water), the degradation was around 98.6% (Chen et al. 2019).

9.5.6 Other Photocatalysts Aside from TiO2 -based and ZnO-based materials, other composite materials were also explored for their dye degradation performance. These include nanocomposites and quantum dots among others. Graphite-phase carbon nitride (g-C3 N4 ) and nitrogen-rich graphite-based carbon nitride (g-C3 N5 ) semiconductor materials were evaluated for their photocatalytic degradation efficiency using methyl orange (MO) dye. Pure forms (g-C3 N4 and gC3 N5 ) showed 41.7% and 28.9% dye removal, respectively. Significant improvement

268

R. J. I. Tamargo and J. V. Magallanes-Nava

in the dye removal was observed for the heterojunction (1D/2D–N5 /N4 ) at 92.20%. This showed that 1D/2D–N5 /N4 is an efficient photocatalyst for MO removal (Liu et al. 2023a, b). Highly fluorescent carbon quantum dots from rubber seed shells were synthesized and their potential for photocatalytic degradation of congo red (CR) and methylene blue (MB) were studied. This was conducted under the influence of sunlight irradiation. Results showed a 93% degradation for CR and 94% degradation for MB (Nizam et al. 2023). Kalaycioglu et al. (2023) synthesized cerium oxide nanoparticles (CeO2 -NPs)/ graphene oxide (GO)/polyacrylamide (PAM) ternary composite for the photocatalytic degradation of methylene blue (MB) from aqueous solution. At 90 min under UVA light irradiation, 90% of the MB dye degraded. Akram et al. (2023) studied the photocatalytic degradation effect of pure and manganese (Mn)-doped zinc oxide (ZnO) nanoparticles on methyl green (MG) under natural sunlight. After 60 min of irradiation, the pure and Mn-doped ZnO photocatalysts were found to achieve 62.78% and 66.44% photocatalytic degradation of the MG aqueous solution, respectively. Das et al. (2022) investigated the performance of zinc telluride (ZnTe) and reduced graphene oxide (rGO-ZnTe) nanoparticles for photocatalytic degradation of Rhodamine B (azo dye) under solar light. The percent degradation of rGO-ZnTE and ZnTe nanoparticles are 66% and 23%, respectively. Cheng et al. (2022) showed that magnetic separation photocatalyst-adsorbent (MSPA) prepared from cotton stem pyrolysis with FeCl3 and ZnCl2 can effectively remove rhodamine B and malachite green in aqueous solution. MSPA displayed photocatalytic removal close to 100% due to the excellent adsorption capacity and photocatalytic activity of MSPA. Bismuth molybdate (Bi2 MoO6 ) was effectively used for the photocatalytic degradation of Orange G (ORG) under UV light. The maximum ORG removal of 96% was carried out at 1 g L−1 catalyst loading, 50 mg L−1 ORG concentration, 1.4 mol L−1 H2 O2 concentration, pH 7.0, and 30°C (Shukla et al. 2022). Maruthapandi et al. (2021) prepared nitrogen-doped carbon nanodots (N@CDs) from bovine serum albumin. This was used for polyaniline nanocomposites (PANIN@CDs) synthesis. PANI-N@CDs were studied for the degradation of congo red (CR), methylene blue (MB), Rhodamine B (RhB), and crystal violet (CV) Under visible light illumination, it was noted that at 20 min, CR was completely degraded, MB reported 60% degradation, RhB at 20% degradation, and 2–3% CV degradation. Nanoparticles of copper (Cu), nickel (Ni), and silver (Ag), collectively called MNPs, were synthesized using polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP). The synthesized M-NPs were used for catalytic degradation of methylene blue (MB), bromocresol green (BCG), and crystal violet (CV) under solar and UV irradiations. UV irradiation showed higher degradation of dyes compared to solar irradiation. Moreover, the M-NPs removal rate for MB is 80% at 30–60 min, while the same removal rates were observed for both CV and BCG but at a longer time of 90–120 min (Kanchana and Vijayalakshmi 2020).

9 Photoremediation—An Emerging Approach for Dye Degradation …

269

Peng et al. (2020) synthesized boron-doped carbon dots (C-dots) from citric acid and 1,2-diboranyethane via hydrothermal method. Rhodamine B (RhB) and methylene blue (MB) were selected to test the photocatalytic performance for C-dots under visible light (mercury-xenon light). C-dots exhibited excellent performance with 100% RhB and MB degradation. Fabricated “red-emitting magnesium-nitrogen-embedded carbon dots” (r-Mg-NCD) from Bougainvillea plant leaves extract were investigated as a potential photocatalytic material for the degradation of methylene blue under sunlight and artificial visible light (100 W tungsten bulb). At 120 min, sunlight irradiation exhibited 99.1% photocatalytic degradation. This is much higher compared to the 45% degradation by 100 W tungsten bulb (Bhati et al. 2018). Sharma et al. (2018) studied the dye degradation performance of oxidized graphite-supported La2 O3 /ZrO2 nanocomposite for the photoremediation of toxic fast green dye. Dye degradation of 89% is recorded under visible light irradiation. Iron nanoparticles (Fe NPs), monometallic Fe@carbon quantum dots (Fe@CQDS), and bimetallic Fe/Ag@carbon quantum dots (Fe/Ag@CQDS) nanocomposites were used to investigate the removal efficiency of fast green (FG) dye under sodium light for combined adsorption/photocatalytic degradation. The nanocomposites have proven to be potential photocatalysts for FG dye degradation (Sharma et al. 2017). In a study by Baeissa (2016), In/ZnO nanoparticles were able to oxidize 100% of the methylene blue dye after 30 min of irradiation using a xenon lamp. Iron (III)- salen complex has been used as catalysts with H2 O2 and UV light to degrade persistent organic dyes [Rhodamine B( RhB), Malachite Green Oxalate (MG), and Crystal Violet 10B (CV)]. Complete removal of RhB is reportedly reached at 60 min (Gazi et al. 2010). These new composite photocatalysts exhibit excellent performance in dye degradation. The summary of the photocatalyst used for specific dyes and light sources, and the corresponding removal efficiency is reflected in Table 9.2.

9.6 Challenges and Future Prospects The practical applications of photoremediation to dye industries’ wastewater is still subject to extensive research and feasibility studies. Future studies for the broader practical applications of the highly efficient photocatalysts should consider the compatibility, suitability, loading of dopants onto the surface of the photocatalyst for optimization and surface modification, the establishment of in-depth photocatalytic mechanism, efficient use of solar energy, and large-scale production of photocatalysts while maintaining its mechanical properties and photocatalytic performance (Khan et al. 2023a, b; Wang et al. 2020).

270

R. J. I. Tamargo and J. V. Magallanes-Nava

Table 9.2 Photocatalysts with the corresponding removal efficiency for different dyes Material

Dye

Light source

%Removal Efficiency

Ref

TiO2 /BC

Methyl Orange (MO)

Visible Light

97.98%

Li et al. (2023)

TiO2 /g-C3 N5

Methylene Blue (MB)

Visible Light

97.4%

Liu et al. (2023a, b)

NiCdTiO2

MB, Methyl UV Light 86%(MB) Green (MG) 97.5%(MG)

Khan et al. (2023a, b)

CdS/TiO2

Acid Blue – 29 dye

84%

Qutub et al. (2022)

Transparent glass with TiO2

MB and Actual Wastewater

UVC

93.03 ± 0.66%

Sirirerkratana et al. (2019)

TiO2 - NH2 NPs cross-linked to cellulose acetate (CA)/carbon nanotube (CNT) composite nanofibers

Indigo Carmine (IC), MB

UV Light 100%

Salama et al. 2018

ZnO10Ag1Ps with Plumbago auriculata leaf extract

MB

UV Light 95.7%

Bloch et al. (2022)

ZnONPs with Canna indica flower extract

MB

Sunlight

94.23%

Nguyen et al. (2021)

ZnO and Ag-doped ZnO using Cannabis sativa leaf extract

Congo Red (CR), MO

Sunlight

Pure ZnO: CR – 38%; MO – 35% Ag-doped ZnO: CR – 94%; MO – 96%

Chauhan et al. (2020)

Titanium-based Photocatalyst

Zinc-based Photocatalyst

ZnONPs with roselle flower and MO, MB oil palm

UV Light 100%

Lau et al. (2020)

ZnO and 2%Fe-ZnO

MB

UV Light ZnO: 86% Isai & 2%Fe-ZnO: 92% Shrivastava (2019)

ZnO with Scutellaria baicalensis root extract

MB

UV Light 98.6%

Chen et al. (2019)

Other Photocatalysts g-C3 N4 and g-C3 N5

MO

Carbon quantum dots from rubber seed shells

CR, MB

CeO2 -NPs)/graphene oxide (GO)/polyacrylamide (PAM) ternary composite

MB

92.20%

Liu et al. (2023a, b)

Sunlight

CR: 93% MB: 94%

Nizam et al. (2023)

UVA

90%

Kalaycioglu et al. (2023) (continued)

9 Photoremediation—An Emerging Approach for Dye Degradation …

271

Table 9.2 (continued) Material

Dye

Light source

%Removal Efficiency

Ref

Manganese (Mn)-doped zinc oxide (ZnO) nanoparticles

Methyl Green

Sunlight

66.44%

Akram et al. (2023)

Reduced graphene oxide (rGO-ZnTe)

Rhodamine B (RhB)

Sunlight

66%

Das et al. (2022)

Magnetic separation photocatalyst-adsorbent with FeCl3 and ZnCl2

RhB, Malachite Green

100%

Cheng et al. (2022)

Bi2 MoO6

Orange G

Polyaniline-nitrogen-doped carbon dot nanocomposite

CR, MB, Visible RhB, Crystal Light Violet (CV)

M-NPs (NP of Cu, Ni and Ag)

MB

UV Light 80%

Kanchana and Vijayalakshmi (2020)

Boron-doped carbon dots

RhB, MB

Visible Light

RhB and MB: 100%

Peng et al. (2020)

Mg-N-Embedded carbon dots (Bougainvillea plant leaves extract as carbon source)

MB

Sunlight

99.1%

Bhati et al. (2018)

Oxidized graphite-supported La2 O3 /ZrO2 nanocomposite

Fast Green Dye

Visible Light

89%

Sharma et al. (2018)

In/ZnO nanoparticles

MB

Visible Light

100%

Baeissa (2016)

Iron (III)- salen complex

RhB

UV Light 100%

UV Light 96% CR: 100% MB: 60% RhB: 20% CV: 2–3%

Shukla et al. (2022) Maruthapandi et al. (2021)

Gazi et al. (2010)

Third-generation photocatalysts have great potential for industrial application, however, there is a need to develop or improve immobilization techniques for more efficient performance (Anwer et al. 2019). Studies have already been initiated that will overcome these challenges. The photoremediation technique has great potential for industrial-scale application.

9.7 Summary In summary, the harmful effects of effluents containing dyes can be remediated through various wastewater treatment approaches. Among the various approaches to dye degradation, photoremediation has become a promising strategy that harnesses light and photocatalysts to reduce or remove pollutants from the wastewater, thus,

272

R. J. I. Tamargo and J. V. Magallanes-Nava

mitigating the effect of dye-containing industrial effluents on the receiving bodies of water. Photocatalysis can be carried out under solar irradiation, thus, taking advantage of natural and renewable sources of energy, and reducing our dependence on non-renewable energy sources. There are several factors affecting the photocatalytic degradation process which include pH of the solution, catalyst loading, and initial dye concentration. Among the several factors, the key component of an effective photoremediation process is the choice of photocatalyst. The most used photocatalysts are TiO2 and ZnO. However, due to their limitations, there are emerging materials developed that incorporate the advantages of these photocatalysts and overcome their limitations. TiO2 -based, ZnO-based, and other nanoparticles are extensively studied for their photocatalytic properties and the subsequent degradation of different types of dyes. These studies show promising performance of these catalysts for the dye degradation application. Photoremediation can be the future of dye wastewater treatment. Acknowledgements This work was funded by the UP System Balik PhD Program (OVPAABPhD-2020-01).

References Afrin S, Shuvo H, Sultana B, Islam F, Rus’d A, Begum S, Hossain M (2021) The degradation of textile industry dyes using the effective bacterial consortium. Heliyon Ahmed A, Majewska-Nowak K, Grzegorzek M (2021) Removal of reactive dyes from aqueous solutions using ultrafiltration membranes. In: Environment protection engineering. Ajmal A, Majeed I, Malik RN, Idriss H, Nadeem MA (2014) Principles and mechanisms of photocatalytic dye degradation on TiO2 based photocatalysts: comparative review. RSC Adv 4:37003–37026 Akram RF (2023) Photocatalytic degradation of methyl green dye mediated by pure and Mn-doped zinc oxide nanoparticles under solar light irradiation. Adsorpt Sci Technol Alsukaibi A (2022) Various approaches for the detoxification of toxic dyes in wastewater. Processes 10 Al-Tohamy R, Ali S, Li F, Okasha K, Mahmoud Y, Elsamahy T, Fu YS (2022) A critical review on the treatment of dye-containing wastewater: Ecotoxicological and health concerns of textile dyes and possible remediation approaches for environmental safety. Ecotoxicol Environ Safety 231 Ambaye T, Hagos K (2020) Photocatalytic and biological oxidation treatment of real textile wastewater. Nanotechnol Environ Engin 5(28) Ameta R, Solanki M, Benjamin S, Ameta S (2018) Photocatalysis. In: Ameta S, Ameta R (eds) Advanced oxidation process for wastewater treatment, pp 135–175 Anwer H, Mahmood A, Lee J, Kim K-H, Park J-W, Yip ACK (2019) Photocatalysts for degradation of dyes in industrial effluents: opportunities and challenges. Nano Res Aragaw T, Bogale F (2021) Biomass-based adsorbents for removal of dyes from wastewater: a review. Front Environ Sci 9 Athalye A, Chakrabarti A, Tailor H (2012) The art and craft of paper dyeing. Dye Chem Pharma Business News

9 Photoremediation—An Emerging Approach for Dye Degradation …

273

Baeissa E (2016) Photocatalytic degradation of methylene blue dye under visible light irradiation using In/ZnO nanocomposite. Front Nanosci Nanotech 2 Bajpai P (2015) Basic overview of pulp and paper manufacturing process. In: Green chemistry and sustainability in pulp and paper industry, pp 11–39 Benkhaya S, M’rabet S, El Harfi A (2020) Classifications, properties, recent synthesis and applications of azo dyes. Heliyon Bhati A, Anand SR, Gunture G, AK, Khare P, Sonkar SK (2018) Sunlight-induced photocatalytic degradation of pollutant dye by highly fluorescent red-emitting Mg-N-embedded carbon dots. ACS Sustain Chem Eng 6:9246–9256 Bloch K, Mohammed SM, Karmakar S, Shukla S, Asok A, Banerjee K, Patil-Sawant R, Kaus NHM, Thongmee S, Ghosh S (2022) Catalytic dye degradation of novel phytofabricated silver/ zinc oxide composites. Front Chem Sec Nanosci 10 Butani S, Mane S (2017) Coagulation/flocculation process for cationic, anionic dye removal using water treatment residuals- a review. Int J Sci Technol Manage 6(4). Calza P, Minella M, Demarchis L, Sordello F, Minero C (2018) Photocatalytic rate dependence on light absorption properties of different TiO2 specimens. Catal Today Chauhan A, Verma R, Kumari S, Sharma A, Shandilya P, Li X, Batoo KM, Imran A, Kulshrestha S, Kumar R (2020) Photocatalytic dye degradation and anti- microbial activities of pure and Ag-doped ZnO using cannabis sativa leaf extract. Sci Rep 10:7881 Chen L, Batjikh I, Hurh H, Han Y, Huo Y, Ali H, Li JF, Rupa EJ, Ahn JC, Mathiyalagan R, Yang DC (2019) Green synthesis of zinc oxide nanoparticles from root extract of Scutellaria baicalensis and its photocatalytic degradation activity using methylene blue. Optik- Int J Light Electron Opt 184:324–329 Chen G, An X, Li H, Lai FY, Xia X, Zhang Q (2021) Detoxification of azo dye Direct Black G by thermophilic Anoxybacillus sp. PDR2 and its application potential in bioremediation. Ecotoxicol Environ Safety Cheng SZ (2022) Facile one-pot green synthesis of magnetic separation photocatalyst-adsorbent and its application. J Water Process Engin 47 Das D, Das M, Sil S, Sahu P, Ray PP (2022) Effect of higher carrier mobility of the reduced graphene oxide—zinc telluride nanocomposite on efficient charge transfer facility and the photodecomposition of rhodamine B. ACS Omega 7:26843–26494 David P, Karunanithi A, Fathima N (2020) Improved filtration for dye removal using keratin– polyamide blend nanofibrous membranes. Environ Sci Pollut Res Metcalf, Eddy Inc (2014) Wastewater engineering: treatment and resource recovery, 5th edn. McGraw-Hill Higher Education, pp 10–12 El Haddad M, Regti A, Laamari M, Mamouni R, Saffaj N (2013) Use of Fenton reagent as advanced oxidative process for removing textile dyes from aqueous solutions. J Mater Environ Sci 5(3):668–674 El-Baz A, Hendy I, Dohdoh A, Srour M (2020) Adsorption technique for pollutants removal; current new trends and future challenges – a review. Egyptian Int J Engin Sci Technol 1–24 Gazi S, Ananthakrishnan R, Singh N (2010) Photodegradation of organic dyes in the presence of [Fe(III)-salen]Cl complex and H2O2 under visible light irradiation. J Hazardous Mater 894–901 Ghadhban M, Majdi H, Rashid K, Alsalhy Q, Lakshmi D, Salih I, Figoli A (2020) Removal of dye from a leather tanning factory by flat-sheet blend ultrafiltration (UF) membrane. Membranes Ghime D, Ghosh P (2019) Advanced oxidation processes: a powerful treatment option for the removal of recalcitrant organic compounds. In C. Bustillo-Lecompte, Adv Oxidat Process Giwa A, Bello I, Olabintan A, Bello O, Saleh T (2020) Kinetic and thermodynamic studies of fenton oxidative decolorization of methylene blue. Heliyon 6(8) Gola D, Tyagi P, Arya A, Gupta D, Raghav J, Kaushik A, Chauhan N (2021) Antimicrobial and dye degradation application of fungi-assisted silver nanoparticles and utilization of fungal retentate biomass for dye removal. Water Golob V, Vinder A, Simonic M (2005) Efficiency of the coagulation/flocculation method for the treatment of dyebath effluents. Dyes Pigments 93–97

274

R. J. I. Tamargo and J. V. Magallanes-Nava

Gopal P, Sivaram N, Barik D (2019) Paper industry wastes and energy generation from wastes. In: Energy from toxic organic waste for heat and power generation, pp 83–97 Goren A, Recepoglu Y, Edebali O, Sahin C, Genisoglu M, Okten H (2022) Electrochemical degradation of methylene blue by a flexible graphite electrode: Techno-economic evaluation. In: ACS Omega, pp 32640–32652 Guo, Y, Qi, P, Liu, Y. (2017) A review on advanced treatment of pharmaceutical wastewater. IPO Conf Ser Earth Environ Sci 63(1) Guo W, Guo T, Zhang Y, Yin L, Dai Y (2023) Progress on simultaneous photocatalytic degradation of pollutants and production of clean energy: a review. Chemosphere 339 Gusain R, Kumar N, Ray SS (2020) Factors influencing the photocatalytic activity of photocatalysts in wastewater treatment. In: Photocatalysts in advanced oxidation processes for wastewater treatment, pp 229–270. https://doi.org/10.1002/9781119631422.ch8 Hambisa A, Regasa M, Ejigu H, Senbeto C (2022) Adsorption studies of methyl orange dye removal from aqueous solution using Anchote peel-based agricultural waste adsorbent. Appl Water Sci 13 Hassan M, Carr C (2018) A critical review on recent advancements of the removal of reactive dyes from dyehouse effluent by ion-exchange adsorbents. Chemosphere 201–219 Hayyan M, Hashim MA, Alnashef IM (2016) Superoxide ion: Generation and chemical implications. Chem Rev 116(5):3029–3085 Hira S, Yusuf M, Annas D, Hui HP (2020) Biomass-derived activated carbon as a catalyst for the Effective Degradation of Rhodamine B dye. Processes 8(8) Hoong H, Ismail N (2018) Removal of dye in wastewater by adsorption coagulation combined system with Hibiscus sabdariffa as the coagulant. In: MATEC web of conferences, p 152 Husein S, El-taweel R, Salim A, Fahim I, Said L, Radwan A (2022) Review of activated carbon adsorbent material for textile dyes removal: preparation, and modelling Author links open overlay panel. Current Res Green Sustain Chem 5 Hussain S, Khan N, Gul S, Khan S, Khan H (2019) Contamination of water resources by food dyes and its removal technologies. In: Eyvaz M (ed) Water chemistry Isai KA, Shrivastava VS (2019) Photocatalytic degradation of methylene blue using ZnO and 2%FeZnO semiconductor nanomaterials synthesized by sol-gel method: a comparative study. SN Appl Sci 1:1247 Januario E, Vidovix T, Bergamasco R, Vieira A (2021) Performance of a hybrid coagulation/ flocculation process followed by modified microfiltration membranes for the removal of solophenyl blue dye. In: Chemical engineering and processing - process intensification Josephine AJ, Dhas CR, Venkatesh R, Arivukarasan D, Christy AJ, Monica SES, Keethana S (2020) Effect of pH on visible-light-driven photocatalytic degradation of facile synthesized bismuth vanadate nanoparticles. Mater Res Express 7 Kalaycioglu Z, Uysal B, Pekcan O, Erim FB (2023) Efficient photocatalytic degradation of methylene blue dye from aqueous solution with cerium oxide nanoparticles and graphene oxide-doped polyacrylamide. ACS Omega 8:13004–13015 Kanagaraj J, Velan T, Mandal A (2012) Biological method for decolourisation of an azo dye:clean technology to reduce pollution load in dye wastewater. Clean Techn Environ Policy 565–572 Kanchana S, Vijayalakshmi R (2020) Photocatalytic degradation of organic dyes by PEG and PVP capped Cu, Ni and Ag nanoparticles in the presence of NaBH4 in aqueous medium. J Water Environ Nanotechnol 5(4) Khan KA, Shah A, Nisar J, Haleem A, Shah I (2023) Photocatalytic degradation of food and juices dyes via photocatalytic nanomaterials synthesized through green synthetic route: a systematic review. Molecules 28(12) Khan S, Noor A, Khan I, Muhammad M, Sadiq M, Muhammad N (2023) Photocatalytic degradation of organic dyes contaminated aqueous solution using binary CdTiO2 and ternary NiCdTiO2 nanocomposites. Catalysts 13(1) Kiron M (2021) Classification and characteristics of dyes. Accessed from Textile Learner: https:// textilelearner.net/classification-and-characteristics-of-dyes/

9 Photoremediation—An Emerging Approach for Dye Degradation …

275

Klijn M, Hubbuch J (2021) Application of ultraviolet, visible, and infrared light imaging in proteinbased biopharmaceutical formulation characterization and development studies. European J Pharmaceut Biopharmaceut 319–336. Kumar A, Dixit U, Singh K, Gupta S, Jamal Beg M (2021) Structure and properties of dyes and pigments. In: Papadakis R (ed) Dyes and pigments Kumari H, Suman S, Ranga R, Chahal S, Devi S, Sharma S.; Kumar S, Kumar P, Kumar S, Kumar A, Parmar R (2023) A review on photocatalysis used for waste-water treatment: Dye degradation. Water, Air, Soil Pollut 234 Lau GE, Che Abdullah CA, Wan Ahmad WAN, Assaw S, Zheng ALT (2020) Eco-friendly photocatalyst for degradation of dyes. Catalysts 10:1129 Lau Y, Wong Y, Teng T, Morad N, Rafatullah M, Ong S (2015) Degradation of cationic and anionic dyes in coagulation–flocculation process using bi-functionalized silica hybrid with aluminumferric as auxiliary agent. Royal Soc Chem 34206–34215. Li Y, Zhang X, Yang R, Li G, Hu C (2016) Removal of dyes from aqueous solutions using activated carbon prepared from rice husk residue. Water Sci Technol 73(5) Liang S, An M, Xia S, Zhang B. Xue B, Xu G (2023) Enhanced photocatalytic degradation of methyl orange by TiO2/biochar composites under simulated sunlight irradiation. Opt Mater 142 Liu S, Bu Y, Cheng S, Tao Y, Hong W (2023) Preparation of g-C3N5/g-C3N4 heterojunction for methyl orange photocatalytic degradation: Mechanism analysis. J Water Process Engin Liu S, Bu Y, Cheng S, Tao R (2023) Synthesis of TiO2/g-C3N5 heterojunction for photocatalytic degradation of methylene blue wastewater under visible light irradiation: mechanism analysis. Diamond Related Mater 136 Mamba G, Mishra A (2016) Graphitic carbon nitride (g-C3N4) nanocomposites: a new and exciting generation of visible light driven photocatalysts for environmental pollution remediation. Appl Catal B 198:347–377 Maruthapandi M, Saravanan A, Manohar P, Luong JHT, Gedanken A (2021) Photocatalytic degradation of organic dyes and antimicrobial activities by poly-aniline-nitrogen-doped carbon dot nanocomposite. Nanomaterials 11 Menon S, Agarwal H, Shanmugam V (2021) Catalytical degradation of industrial dyes using biosynthesized selenium nanoparticles and evaluating its antimicrobial activities. Sustain Environ Res 31 Millington K (2009) Improving the whiteness and photostability of wool. In: Advances in wool technology. Woodhead Publishing, pp 217–247 Mishra K, Pradhan S, Akhtar MS, Yang W-G, Kim SH, Lee YR (2021) Catalytic synergy of Au@CeO2-rGO nanohybrids for the reductive transformation of antibiotics and dyes. New J Chem 45(20) Myronov M (2018) Molecular beam epitaxy of high mobility silicon, silicon germanium, and germanium quantum well heterostructures. Molecul Beam Epitaxy 37–54 Narayana S, Kariyajjanavar P (2019) Studies on degradation of pulp and paper mill industrial dye fast red by indirect electrochemical method. Nat Environ Pollut Technol 657–662 Narayana S, Kariyazzanavar P (2016) Pulp and paper mill dye effluent treatment by electrochemical degradation. In: Lake 2016: conference on conservation and sustainable management of ecologically sensitive regions in Western. Ghats, pp 398–403 Nasar A, Mashkoor F (2019) Application of polyaniline-based adsorbents for dye removal from water and wastewater- a review. Environ Sci Pollut Res 26:5333–5356 Navidpour AH, Abassi S, Li D, Mojiri A, Zhou JL (2023) Investigation of advanced oxidation process in the presence of TiO2 semiconductor as photocatalyst:property, principle, kinetic analysis, and photocatalytic activity. Catalyst 13(2) Nayan M, Jagadish K, Abhilash M, Namratha K, Srikantaswamy S (2019) Comparative study on the effects of surface area, conduction band and valence band positions on the photocatalytic activity of ZnO-MxOy heterostructures. J Water Resour Protect 11(3)

276

R. J. I. Tamargo and J. V. Magallanes-Nava

Nguyen DTC, Le HTN, Nguyen TT, Nguyen TTT, Bach LG, Nguyen TD, Tran TV (2021) Multifunctional ZnO nanoparticles biofabricated from CannaIndica L. flowers for seed germination, adsorption, and photocatalytic degradation oforganic dyes. J Hazardous Mater 420(15) Nizam N, Hanafiah M, Mahmoudi E, Halim A, Mohammad AW (2021) Synthesis of highly fluorescent carbon quantum dots from rubber seed shells for the adsorption and photocatalytic degradation of dyes. Sci Rep 13 Nizam N, Hanafiah M, Mahmoudi E, Halim A, Mohammad AW (2021) The removal of anionic and cationic dyes from an aqueous solution using biomass-based activated carbon. Sci Rep 11 Pavel M, Anastesescu C, State R-N, Vasile A, Papa F, Balint I (2023) Photocatalytic degradation of organic and inorganic pollutants to harmless end products: assessment of practical application potential for water and air cleaning.Catalysts 13(2) Peng Z, Zhou Y, Ji C, Pardo J, Mintz KJ, Pandey RP, Chusuei CC, Graham RM,Yan G, Leblanc RM (2020) Facile synthesis of “boron-doped” carbon dots and their application in visible-light-driven photocatalytic degradation of organic dyes. Nanomaterials 10 Pennington A (2015) Increased visible-light photocatalytic activity of TiO2 via band gap manipulation. Accessed from Rutgers University: https://rucore.libraries.rutgers.edu/rutgers-lib/48623/ PDF/1/play/ Perry RH, Green DW, Southard MZ (2018) Perry’s chemical engineer’s handbook, 9th edn. McGraw-Hill Education, New York, pp 22–52–22–69 Pirhashemi M, Habibi-Yangyeh A, Pouran S (2018) Review on the criteria anticipated for the fabrication of highly efficient ZnO-based visible-light-driven photocatalysts. J Ind Engin Chem 62 Puchana-Rosero M, Lima E, Mella B, da Costa D, Poll E, Gutteres M (2018) A coagulationflocculation process combined with adsorption using activated carbon obtained from sludge for dye removal from tannery wastewater. J Chilean Chem Soc Qutub N, Singh P, Sabir S, Sagadevan S, Oh W (2022) Enhanced photocatalytic degradation of Acid Blue dye using CdS/TiO2 nanocomposite. Sci Rep Rafiq A, Ikram M, Ali S, Niaz F, Khan M, Khan Q, Maqbool M (2021) Photocatalytic degradation of dyes using semiconductor photocatalysts to clean industrial water pollution. J Ind Eng Chem 97:111–128 Ramli ZAC, Asim N, Isahak WNRW, Emdadi Z, Ahmad-Ludin N, Yarmo MA, Sopian K (2014) Photocatalytic degradation of methylene blue under UV light irradiation on prepared carbonaceous TiO2 . Sci World J Rapo E, Tonk S (2021) Factors affecting synthetic dye adsorption; desorption studies: a review of results from the last five years (2017–2021) Molecules 26(17) Rawat D, Mishra V, Sharma R (2016) Detoxification of azo dyes in the context of environmental processes. Chemosphere 591–605 Reza K, Kurny A, Gulshan F (2017) Parameters affecting the photocatalytic degradation of dyes using TiO2: a review. Appl Water Sci 7:1569–1578 Roy M, Saha R (2021) Dyes and their removal technologies from wastewater: a critical review. In: Bhattacharyya S, Kumar Mondal N, Platos J, Snášel V, Krömer P (eds) Intelligent data-centric systems, intelligent environmental data monitoring for pollution management. Academic Ruan W, Hu J, Qi J, Hou YZ, Wei X (2019) Removal of dyes from wastewater by nanomaterials: a review. Adv Mater Lett 10(1):19–20 Sakarkar S, Muthukumran S, Jegatheesan V (2020) Factors affecting the degradation of remazol turquoise blue (RTB) bytitanium dioxide (TiO2 ) entrapped photocatalytic membrane. J Environ Manag 272 Salama A, Mohamed A, Aboamera NM, Osman TA, Khattab A (2018) Photocatalytic degradation of organic dyes using composite nanofibers under UV irradiation. Appl Nanosci 8:155–161 Sardar M, Manna M, Maharana M, Sen S (2021) Remediation of dyes from industrial wastewater using low-cost adsorbents. In: Inamuddin M, Ahamed E, Lichtfouse, Asiri A (eds) Green adsorbents to remove metals, dyes, and boron Springer, pp 377–403

9 Photoremediation—An Emerging Approach for Dye Degradation …

277

Shang SM (2013) Process control in dyeing of textiles. In: Process control in textile manufacturing. Woodhead publishing series in textiles: pp 300–338 Sharma G, Kumar A, Naushad M, Kumar A, Al-Muhtaseb A, Dhiman P, Khan M (2017) Photoremediation of toxic dye from aqueous environment using monometallic and bimetallic quantum dots based nanocomposites. J Cleaner Product 2919–2930 Sharma G, Kumar A, Sharma S, Al-Saeedi S, Al-Senani G, Nafady A, Stadler F (2019) Fabrication of oxidized graphite supported La2O3/ZrO2 nanocomposite for the photoremediation of toxic fast green dye. J Molecul Liquids 738–748 Shindhal T, Rakholiya P, Varjani S, Pandey A, Ngo H, Guo W, Taherzadeh M (2020) A critical review on advances in the practices and perspectives for the treatment of dye industry wastewater. Bioengineered 12(1):70–87 Shukla B, Rawat S, Gautam MK, Bhandari H, Garg S, Singh J (2022) Photocatalytic degradation of Orange G dye by using bismuth molybdate: Photocatalysis optimization and modeling via definitive screening designs. Molecules 27(7) da Silva Alves D, de Farias B, Breslin dA, Sant’Anna Cadaval T (2022) Carbon nanotubebased materials for environmental remediation processes. In: Giannakoudakis D, Meili L (eds) Anastopoulos, Advanced materials for sustainable environmental remediation, pp 475–513 Sirajudheen P, Karthikeyan P, Vigneshwaran S, Meenakshi S (2020) Synthesis and characterization of La(III) supported carboxymethylcellulose-clay composite for toxic dyes removal: evaluation of adsorption kinetics, isotherms and thermodynamics. Int J Biolog Macromolecul Sirirerkratana K, Kemacheevakul P, Chuangchote S (2019) Color removal from wastewater by photocatalytic process using titanium dioxide-coated glass, ceramic tile, and stainless steel sheets. J Cleaner Product 123–130 Soltani A, Faramarzi M, Parsa S (2021) A review on adsorbent parameters for removal of dye products from industrial wastewater. Water Quality Res J 56(4):181–193 International Agency for Research on Cancer (2010) Some aromatic amines, organic dyes, and related exposures. In: IARC monographs on the evaluation of carcinogenic risks to humans, p 99 Spoorthi J, Kariyazzanavar N, Kariyazzanar P (2016) Pulp and paper mill dye effluent treatment by electrochemical degradation. In: Lake 2016: conference on conservation and sustainable management of ecologically sensitive regions in Western Ghats Srivatsav P, Bhargav B, Shanmugasundaran V, Arun J, Gopinath K, Bhatnagar A (2020 ) Biochar as an eco-friendly and economical adsorbent for the removal of colorants (dyes) from aqueous environment: a review. Water 12(12). Tahir H, Saad M (2021) Using dyes to evaluate the photocatalytic activity. In: Ghaedi M (ed) Photocatalysis: fundamental processes and applications, vol 32. Elsevier, pp 125–224 Tan Q, Jia X, Dai R, Chang H, Woo M, Chen H (2023) Synthesis of a novel magnetically recyclable starch-based adsorbent for efficient adsorption of crystal violet dye. Separat Purificat Technol Vasiljevic ZZ, Dojcinovic MP, Vujancevic JD, Jankovic- Castvan I, Ognjanovic M, Tadic NB, Stojadinovic S,Brankovic GO, Nikolic MV (2020) Photocatalytic degradation of methylene blue under natural sunlight using iron titanate nanoparticles prepared by a modified sol-gel method. Royal Soc Open Sci 7. Wang X. Zhang X, Zhang Y, Wang Y, Sun SP, Wu WD, Wu Z (2020) Nanostructured semiconductor supported iron catalysts for heterogeneous photo-Fenton oxidation: a review. J Mater Chem 8:15513–15546 Wang Y, Geng Q, Yang J, Liu Y, Liu C (2020) Hybrid system of flocculation−photocatalysis for the decolorization of crystal violet, reactive red X-3B, and acid orange II dye. ACS Omega 31137–31145 Wong P, Teng T, Norulaini N (2007) Efficiency of the coagulation-flocculation method for the treatment of dye mixtures containing disperse and reactive dye. Water Qual Res J Can 42(1):54– 62 Wong S, Ghafar N, Ngadi N, Razmi F, Inuwa I, Mat R, Amin N (2020) Effective removal of anionic textile dyes using adsorbent synthesized from coffee waste. Sci Rep 10

278

R. J. I. Tamargo and J. V. Magallanes-Nava

Xiaoxu S, Jin X, Xingyu L (2017) Experimental study on treatment of dyeing wastewater by activated carbon adsorption, coagulation, and fenton oxidation. In: IOP conference series: earth and environmental science, p 100 Yagub MT, Sen TK, Afroze S, Ang HM (2014) Dye and its removal from aqueous solution by adsorption: a review. Adv Coll Interface Sci 209:172–184 Zheng Y, Qi H, Zhang L, Zhang Y, Zhong L, Zhang X, Feng Y, Xue J (2022) Photocatalytic degradation of dye wastewater by stepwise assembling PVA aerogel/TiO2/MoS2/Au composites in visible light. Water Sci Technol 85(9):2625–2638

Chapter 10

Detoxification of Industrial Waste Water by Photocatalytic Techniques Pratibha Sharma and Amit Kumar

10.1 Introduction “Waste water”, which is additionally coined as sewage, refers to the polluted form of water, which is a result of imprudent human activities. The issue is really concerning as the waste which is eluted specifically by the industries is highly toxic, and exhibits potential to cause irreversible damage to the environment. Depending on the type of industry, the eluted waste water may be comprised of contaminants such as dyes, antibiotics, personal care products, heavy metal ions, metalloids, nitrates, sulfates, and heavy metal complexes (Table 10.1) (Ranade and Bhandari 2014). Typically, detoxification of industrial waste water is initiated by performing its characterization to identify its source. This is followed by the investigation regarding the nature of the pollutants, as well as the detection of a priority pollutant, where the waste water containing the latter is treated separately. In general, the waste water which is discharged from industry is first subjected to primary operations (such as screening, sedimentation, thickening, precipitations, centrifugation, cyclone separations, and filtration), which improves the quality of water for next-stage treatments. Further, waste water is treated using either physio-chemical techniques or biological methods in the secondary stage of treatment, where the intent is to reduce the BOD (biochemical oxygen demand)/COD (chemical oxygen demand) by ~85–95%. Furthermore, the toxicity of the water is removed up to the prescribed level in the tertiary stage of treatment. The advanced separation techniques which include evaporation, distillation, absorption, extraction, ion exchange, crystallization, cavitation, biological P. Sharma (B) Department of Chemistry, Amity Institute of Applied Sciences, Amity University, Noida, Uttar Pradesh 201301, India e-mail: [email protected] A. Kumar Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, Delhi 110016, India 279

280

P. Sharma and A. Kumar

processes, and membrane separations, are usually employed in either secondary or tertiary stages of water treatment. It is to be noted that techniques such as adsorption or coagulation merely result in the concentration of the pollutants, and do not exhibit potential to destroy them. Further, membrane treatment technologies are cost-intensive, and can possibly generate secondary pollutants in the ecosystem (Gaya and Abdullah 2008; Chong et al. 2010). Interestingly, advanced oxidation processes (AOPs) are considered as economically viable, as well as environmentfriendly method for waste water treatment, where highly reactive species (such as H2 O2 , OH• , O2 •− , O3 , SO4 •− ) are generated, which have potential to mineralize organic pollutants, as well as to destroy pathogenic bacteria. Among advanced oxidation processes, photocatalysis has gained enormous research interest in the detoxification of industrial waste water, which can be ascribed to its favorable characteristics, such as the utilization of solar light, mild operation conditions, and efficient mineralization of pollutants (Lu et al. 2022; Saianand et al. 2022). Further, employing photocatalytic technology in the treatment of industrial discharge does not lead to the generation of any secondary waste (Crini and Lichtfouse 2019), and offers reusability of water. Photocatalytic degradation of toxic chemicals is performed under light illumination in the presence of a photocatalyst (Chong et al. 2010), where the reactive system can be either heterogenous or homogenous. Treatment of waste water performed via heterogenous photocatalysis is a multiple-step process (Fig. 10.1) and is initiated with the adsorption of toxic species on the photocatalyst. Further, the photocatalyst (a semiconductor material) absorbs photons of energy equal to its band gap width (energy required for transition from valence to conduction band) and leads to formation of photoinduced charge carriers (electrons and holes). After absorbing the light (usually, UV–visible–near infrared), electron travels to the conduction band leaving behind the positive hole vacancies in valence band. It is to be noted that the possibility of recombination of charge carriers is avoided by the presence of electron scavengers, such as dissolved oxygen and water molecules, otherwise recombination of electrons with hole vacancies in valence band will takes place in nanoseconds, with simultaneous dissipation of heat energy. Further, in aqueous medium, hole vacancies react with hydroxyl group (OH− ) and produce hydroxyl radical species (• OH), which then degrades pollutants. Electrons present in the conduction band react with the oxygen to produce superoxide radical (O2 •− ) species, which gets protonated and produce hydroperoxyl radical (HO2 • ) and is followed by the generation of H2 O2 . It is worth mentioning that hydroperoxyl radical (HO2 • ) has been additionally considered for electron scavenging and provides contribution in delaying the recombination of charge carriers. One of the highly efficient photocatalysts is TiO2 , which is commercially referred to as Degussa P25, and comprises of 70:30 mixture of anatase/rutile crystal phase. The performance of TiO2 in degrading pollutants has been credited to its strong oxidation potential (3.2 eV for anatase and 3.0 eV for rutile), easy lab-scale as well as large-scale production, chemical stability, and strong resistance against acids as well as alkalis (Lee and Park 2013; Horikoshi and Serpone 2020). However, there are some drawbacks associated with TiO2 as a photocatalyst, which include low visible light utilization, low quantum efficiency, and weak photoreduction ability

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

281

Table 10.1 List of industries and their respective pollutants (reported by Ranade et al. and reproduced with permission from Ranade and Bhandari (2014)) Type of industry Pollutants

Reference

Cement

Alkali, sulfur oxides, nitrogen oxides, heavy metals, waste soil, byproduct gypsum

Ranade and Bhandari (2014)

Sugar

Washing waste, sugar cane juice, molasses

Thermal power

Fly ash, heavy metals, coal, oil

Fertilizer

Organics, ammonia, nitrate, phosphorus, fluoride, cadmium and other heavy metals

Petrochemicals

Oil, acid, sludge, hydrogen sulfide, lead sludge, hydrocarbons, clay, ethylene glycol, 1,4-dioxane

Mining

Metals oxides such as copper, lead, zinc, mercury, cadmium oxide, calcium oxide, sodium oxide, barium oxide, cuprous oxide, zinc oxide, sulfates, chlorine, lithium oxide, manganese oxide, magnesium oxide, silica, gypsum, hydroxides, carbonates, cyanide, sulfur

Metallurgy

Ammonia, cyanide, benzene, naphthalene, anthracene, phenol, cresol, heavy metals

Paper

Sodium hydroxide, sodium carbonate, sodium sulfide, bisulfide, elemental chlorine, chlorine dioxide, calcium oxide, HCl, organic halides, toxic pollutants, lime mud, wood processing residuals, traces of heavy metals, pathogens

Tanneries

Organics, heavy metals such as Cr, ammoniacal nitrogen, acids, salts, sulfides, suspended solids, dyes, fats, oil

Pharmaceutical

Polycyclic aromatic hydrocarbons, arsenic trioxide, chlorambucil, epinephrine, cyclophosphamide, nicotine, daunomycin, nitroglycerin, melphalan, physostigmine, mitomycin C, physostigmine salicylate, streptozotocin, warfarin over 0.3%, uracil mustard, halogenated/ nonhalogenated solvents, organic chemicals, sludge and tars, heavy metals, test animal remains

Textile

Complex mixture of salts, acids, heavy metals, organochlorine-based pesticides, pigments, dyes, polycyclic aromatic hydrocarbons

Pesticide

Volatile aromatics, halomethanes, cyanides, haloethers, heavy metals, chlorinated ethane, phthalates, polycyclic aromatic hydrocarbons

(Miklos et al. 2018). It is to be noted that the photocatalytic efficiency of TiO2 can be improved by non-metal doping, which can modify the band gap energy level, and shift its absorption characteristics to visible range (Yan et al. 2013). Alternatively, researchers have reported the potential of various semiconductor materials as photocatalyst which includes ZnO, WO3 , V2 O5 , BiVO4 , Ag3 VO4 , SrTiO3 , Fe2 O3 , CuO, SnO2 , MoS2 , CdS, ZnS, g-C3 N4 , BiOCl, BiOBr, BiOI to treat variety of organic as

282

P. Sharma and A. Kumar

Fig. 10.1 Graphical representation showing the photocatalytic degradation of pollutants through heterogenous photocatalysis

well as inorganic pollutants (Long et al. 2020). Further, employing a single semiconductor material (n- or p-type) as a photocatalyst is considered as ineffective for waste water treatment (Bayan et al. 2021), while the heterostructures containing two or more types of photocatalytic materials have displayed appreciable performance. This has been ascribed to their charge separation capacity, resistance against photocorrosion, and their significant tendency for light harvesting (Suresh et al. 2023). In this direction, a variety of binary (n-n type, p-p type, p-n type) (Kuang et al. 2023; Wang et al. 2022a, 2019a) and tertiary (n-p-n type and p-n-p type) (Rajendran et al. 2022; Wang et al. 2022b) photocatalysts have been explored for their potential in degrading pollutants present in the industrial waste water. Degradation of pollutants is additionally performed in a homogenous environment and is referred to as a homogenous Fenton process. The basis of the Fenton process is the generation of reactive hydroxyl radicals (• OH), by the reaction of Fe2+ and H2 O2 in an acidic medium. The process comprises two stages (Fig. 10.2), where the first stage involves the reaction of Fe2+ with H2 O2 , leading to the formation of • OH radicals, which act as strong oxidants and result in the fast degradation of pollutants. In the second stage Fe3+ (generated in the first stage) reacts with H2 O2 resulting in the formation of HO2 • radicals which are weaker oxidants, as well as exhibit a slow rate of production (Mirzaei et al. 2017). It is worth mentioning that the performance of this process can be improved by irradiation with UV–visible light, and the process is then referred to as the photo-Fenton process. On exposure to light irradiation, the second stage of the process which involves the photoreduction of Fe3+ to Fe2+ gets accelerated, and a cyclic reaction is established, which generates extra reactive radical species (• OH) (Koltsakidou et al. 2019; Perini et al. 2018). Many excellent review articles are available where advancements made in photocatalytic degradation of pollutants in past years have been summarized (Chong et al.

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

283

Fig. 10.2 Reaction scheme representing Fe(II)/Fe(III) cycle in photo-Fenton process

2010; Musial et al. 2023; Samuel et al. 2023; Sharma et al. 2023; Ali et al. 2023). Further, the efficiency of a photocatalytic system toward degrading a pollutant has been found to be influenced by a variety of factors, which includes, the amount of pollutant, loading of catalyst, doping, presence of oxidants, pH, temperature, reaction light intensity, concentration of oxygen (Gopinath et al. 2020; Gusain et al. 2020). Apart from this, photocatalysis has been integrated with a variety of technologies, such as adsorption, sonocatalysis, piezo-catalysis, ozonization, biofilm (Suresh et al. 2023), for improved degradation of pollutants, and the recent advancements made in these modified systems, have been discussed in this chapter.

10.2 Advancements in Photocatalytic Techniques for the Degradation of Pollutants The photocatalysis process, as already mentioned, offers several advantages in the detoxification of industrial waste water; however, it is associated with a few downsides, such as a short life span of photoinduced charges, low degradation efficiency, and inadequate utilization of solar energy. In view of the same, innovative treatment methods have been developed by integrating photocatalysis with several effective technologies, which has resulted in increased production of reactive radical species, and consequently, has enhanced the kinetics of pollutant degradation.

10.2.1 Integration of Photocatalysis with Adsorption Technique Pollutants such as organic dyes, chemicals, and heavy metal ions can be conveniently removed from the water by using adsorbents that exhibit high surface area, however, this method does not result in the mineralization of the pollutants, as well as requires an additional regeneration step for the reusability of the adsorbent. Interestingly, designing photocatalysts by immobilizing the semiconductor catalytic material over an adsorbent with a high surface area, has been reported to be effective in the mineralization of pollutants. This has been ascribed to the instant adsorption of pollutants

284

P. Sharma and A. Kumar

which is generally performed in the dark, followed by its degradation by the semiconductor material under light illumination. Further, it has been reported that the efficiency of photocatalytic treatment can be additionally enhanced by designing the catalyst with appropriate bandgap, as well as band edge energy levels, obstructing the recombination of photoinduced charge carriers, controlled as well as beneficial point defects, edged and dangling bonds, and ability to interact with the molecules (Yang and Wang 2018). Conventionally, photocatalysts are employed in the form of suspended particulates, and the separation of these fine particles is performed either via conventional filtration technique or sedimentation method, which makes the catalyst recovery as well as its reuse ineffectual (Kagaya et al. 1999; Rachel et al. 2002; Wang et al. 2013). Immobilization of photocatalyst on a solid support can overcome this issue (Alhaji et al. 2017; Adnan et al. 2019), however, the nature of solid support can alter the catalytic efficiency of the active material (Rao et al. 2004; Ramos et al. 2021; Levchuk et al. 2016). In addition, the photocatalytic performance of the semiconductor materials can be improved by combining the catalyst with carbon materials, such as graphene, carbon dots, carbon nanotubes, and biochar (Zhang et al. 2020). Among these, biochar has been considered as a promising candidate, due to its high specific surface area, easily tunable functional groups, and excellent electronic conductivity. Recently, Tian et al. utilized the biochar derived from lignin (LC) using H3 PO4 activation, to prepare the oxygen vacancies enriched LC/Bi2 MoO6 composite, which was employed for degradation of methylene blue under visible light irradiation. A variety of Bi-based semiconductors have been explored for remediation of organic pollutants such as Bi2 MoO6 , Bi2 WO6 , BiVO4 , and BiOBr; however, Aurivillius structure of Bi2 MoO6 , has been found to exhibit great potential to detox the industrial waste water, due to its wide-light utilization range, layered structure, chemical and thermal stability (Tian et al. 2020; Hu et al. 2020). Nevertheless, photocatalytic degradation of pollutants using Bi2 MoO6 as a photocatalyst has been obstructed by the poor separation of photogenerated charge carriers, low surface area, and consequently, low adsorption characteristics (Hu et al. 2020; Li et al. 2022a), which can be overcome by immobilizing the catalyst on biochar derived from lignin (Tian et al. 2023). Results of investigations revealed that LC/Bi2 MoO6 composite was able to reduce methylene blue by 95.43% in 1 h, which was found to be ~7 times higher than the reduction observed for treatment employing Bi2 MoO6 photocatalyst without any support. It is to be noted that the performance of the LC/Bi2 MoO6 composite was credited to the oxygen vacancies and enhanced absorption of pollutants. Moreover, the LC/Bi2 MoO6 composite was additionally explored for the degradation of bamboo ECF bleaching effluent, where 75.72% reduction was observed in CODCr (chemical oxygen demand determined using potassium dichromate oxidation method) and 69.64% reduction was observed for AOX (absorbable organic halogen) (Tian et al. 2023). Further, clay has been found to be another promising support for the immobilization of photocatalysts, due to its inexpensiveness, environment compatibility, thermal, chemical as well as mechanical stability (Garrido-Ramírez et al. 2010). Moreover, the textural characteristics of clay such as high surface area, porosity,

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

285

and large volume of surface-active sites, are expected to contribute in enhancing the performance of the composite particles of clay with photocatalyst (Mishra et al. 2018). In this direction, Aguilar et al. reported the photodegradation of pollutants using TiO2 /clay macro-composites, with an aim to facilitate the easy catalyst recovery as well as its reuse. It is to be noted that the nanoparticles of photocatalyst can be toxic to the environment (Canesi et al. 2015; Nogueira et al. 2015) and necessitate their complete separation from the medium post-treatment. In view of the same, the photocatalyst was prepared in the form of pellets by uniform mixing of Ecuadorian clay (P1 M2 ) and commercial form of TiO2 (P25), which is followed by molding, drying, and calcination. The photocatalytic degradation of phenol was performed in a flow reactor (Fig. 10.3), which comprises a tube-lamp assembly, where photocatalytic pellets were placed in a single layer, and the phenolic solution (10 mg/L) was circulated over the pellets in a laminar fashion. It was observed that exposing the contaminant solution to UVA-Vis radiation in the absence of a photocatalyst, resulted in only 11% reduction of phenol. In addition, experiments were performed with clay sample (without photocatalyst), where insignificant photocatalytic degradation of pollutants was observed. Further, bulky pellets prepared only with TiO2 demonstrated inferior photocatalytic degradation of phenol, relative to the pellets prepared using a combination of clay and TiO2 , which was attributed to a lower anastase:rutile ratio in the former sample. It was revealed that pellets fabricated using 60% TiO2 and 40% clay displayed approximately 85% reduction in the pollutant (phenol) concentration. It is worth mentioning that due to the bulky nature of the photocatalyst, the recovery and reuse of this catalytic system was convenient. Moreover, the production cost of this photocatalyst was reported to be low (Aguilar et al. 2023). Fig. 10.3 Representation of flow photoreactor (reproduced with permission from Aguilar et al. (2023))

286

P. Sharma and A. Kumar

Furthermore, mesoporous silica can be additionally considered for its candidature to act as a support for the immobilization of photocatalytic particles for the treatment of industrial waste water. Wei et al. evaluated the performance of TiO2 loaded on mesoporous SiO2 as a photocatalyst for the treatment of waste water containing cyanide. It is to be noted that cyanide contamination in water, which is leached from the gold refining industry is a significant problem that needs attention, as cyanide is considered highly toxic for health. In view of the same, a photocatalytic material with a specific surface area of 1011 m2 /g and pore size of 5.3 nm, was prepared by using the optimized feed concentration of precursors. It was mentioned that cyanide waste water was sourced from the Hexi gold mine located in the Shandong region of China and the developed catalyst was able to display a reduction of 95.98% in total cyanide content. In addition, copper as well as zinc in cyanide waste water were removed by 92.07%, and 98.69%, respectively. Furthermore, detailed investigations on the mechanism of degradation revealed that cyanide was first chemisorbed on the surface of the catalyst and was removed in the form of CO2 and NO3 − , while copper, as well as zinc, were removed in the form of their oxides (Wei et al. 2023).

10.2.2 Integration of Photocatalysis with Fenton Process The homogenous photo-Fenton process is usually performed in an acidic medium (pH–3), to avoid precipitation of iron, thereby increasing the operating costs of waste water treatment, due to additional steps of acidification and basification. After the reaction, iron is removed through sludge precipitation, and the mandatory high concentration (50–80 mg/L) of Fen+ employed in the Fenton process leads to inescapable contamination of water. Furthermore, industrial discharge is expected to be contaminated with ions, such as phosphates, halogens, and sulfates which can either lead to the precipitation of the ferric ions or promote the formation of less reactive radicals. It is worth mentioning that integrating the Fenton process with photocatalysis has displayed enhancement in charge separation efficiency, as the Fe3+ /H2 O2 of the Fenton system acts as an electron scavenger, and thus hinders the recombination of induced charge species (Yang et al. 2021a). Further, the catalyzed photo-Fenton process utilizes a limited amount of ferrous catalyst and the iron sludge produced is relatively lower than produced in the Fenton process (Mirzaei et al. 2017). In addition, performing photo-Fenton process in the presence of a complexing agent can obviate the requirement of acidic pH, as well as the issue of stability of iron is resolved, as iron-based complexes are expected to display activity in the visible region and will not alter the rate of reaction (Malato et al. 2009). Moreover, employing a solid photo-catalyst (heterogenous photo-Fenton process) has been additionally reported to overcome the above-mentioned concerns of the Fenton process. However, the suspension of catalyst in the waste water medium poses difficulties, such as catalyst aggregation, formation of slurries, and cost of catalyst separation (Sampaio et al. 2011). These limitations can be overcome by either immobilization of catalyst on solid supports such as films (Sampaio et al. 2011), glass slides (Píšťková et al. 2015),

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

287

and polymers (Curcio et al. 2015) or by using magnetically recoverable catalysts (Lima et al. 2014). Recently, Zhang et al. reported the use of a Fe2+ /Fe3+ co-doped BiVO4 /Ag3 PO4 catalyst for the efficient degradation of antibiotics via the photo-Fenton technique. It is to be noted that BiVO4 (Bismuth Vanadate), exhibits a band gap of 2.4–2.9 eV, as well as offers flexibility in band energy, and therefore has been widely explored for the construction of heterojunction. However, BiVO4 has been reported to display recombination of surface charges as well as the light absorption range has been found to be insufficient, which hinders its applicability (Nguyen et al. 2020). Further, modification of BiVO4 with Ag3 PO4 has been reported to promote carrier migration, reduce charge transfer resistance, as well as can improve the photo-corrosion defects of Ag3 PO4 (Li et al. 2013; Gao et al. 2020; Chen et al. 2020). Furthermore, incorporating Fe as an electronic medium can lead to the formation of high-quality junctions (Baba et al. 2015), as well as has been reported to widen the light absorption range of BiVO4 and increase the charge carrier density (Wei et al. 2021). In addition, Fe doping in BiVO4 results in the generation of oxygen vacancies on the catalyst surface, which can reportedly accelerate electron scavenging (Ma et al. 2020). Results of the photo-Fenton experiments with the developed catalysts revealed that the degradation efficiency of the developed catalyst was found to be 99.7% for tetracycline (antibiotic) and displayed high stability in cyclic experiments. In addition, the system retained high degradation efficiency when subjected to changes in pH, electrolytes, and sources of water. The catalyst was additionally explored for mineralization of ciprofloxacin, doxycycline, levofloxacin, norfloxacin, and enrofloxacin, where the degradation efficiency was found to be 91.69%, 86.33%, 85.64%, 79.43%, and 78.66%, respectively (Zhang et al. 2023).

10.2.3 Integration of Photocatalysis with Electrochemical Process Integrated photo-electrochemical technology has demonstrated promising results in the detoxification of industrial saline sewage (Dai et al. 2020; Wang et al. 2020), which generally poses difficulty in treatment via conventional methods. Photoelectrochemical treatment of saline waste water involves the generation of reactive oxygen species and reactive chlorine species, which are collectively strong oxidants and can effectively degrade a variety of organic pollutants (Fig. 10.4b) (Mei et al. 2021; Li et al. 2020). Several investigations have been reported to evaluate the potential of TiO2 , WO3, and BiVO4 as photoanodes in the photoelectrochemical treatments (Kim et al. 2018; Koo et al. 2019; Li et al. 2021a); however, issues such as the inferior potential to activate chloride ions and generation of toxic chlorates as side products, have been encountered (Chen et al. 2017; Hou et al. 2018; Coates and Achenbach 2004), which has obstructed their use in waste water treatment on large scale. The

288

P. Sharma and A. Kumar

activation of chloride ions is expected to be enhanced by incorporating oxygen vacancies in the metal oxide photocatalyst, as it improves the adsorption characteristics of the photoelectrode, reduces the band gap to improve the light absorption characteristics, intensifies carrier concentration, conductivity as well as charge separation efficiency (Wang et al. 2012, 2018, 2019b). Recently, Wu et al., highlighted the importance of oxygen vacancies in the photo-electrochemical performance of photoelectrodes based on TiO2 nanorods, where the oxygen vacancies were introduced via electrochemical reduction of TiO2 at a constant current of 0.003 A in the sodium sulfate (0.1 M) electrolyte solution for 180 s (Fig. 10.4a) (Wu et al. 2023a). The presence of oxygen vacancies in TiO2 nanorods was confirmed by deconvolution of XPS peak associated with O1s, where the ratio of oxygen defect (Ov ) peak was observed to be higher in the Ov -TiO2 crystals (TiO2 nanorods with oxygen vacancies) relative to the TiO2 nanorods. The degradation efficiency of the developed photoanodes toward 4-chlorophenol, phenol, and bisphenol-A was determined in an H-type double cell, and the results revealed that the system containing Ov -TiO2 photoanode (enriched with oxygen vacancies) is able to degrade these pollutants significantly (~99.9%), in the presence of chloride ions (sourced from saline water). In addition, the hydrogen generation was found to be in the range of 192.5 to 198.2 μmol h−1 . Further, a low concentration of chlorate ions (toxic by-product) was detected in this approach, which ensures negligible negative impact on environment. Moreover, it was mentioned that electrical consumption in this method is less, relative to other electrochemical processes and solar energy (~100 mW cm−2 ) is sufficient to meet the energy requirement. In view of the same, additional set of experiments were performed by utilizing solar energy, and 98% degradation of 4-chlorophenol (pollutant) was observed, which was retained in cyclic treatments. Moreover, LC– MS investigation revealed that the degradation of 4-chlorophenol proceeds through multiple stages of oxidation, ring opening, fragmentation, which finally resulted in mineralization of the pollutant in the form of CO2 and H2 O (Fig. 10.4c) (Wu et al. 2023a). Further, several integrated techniques including microbial electrocatalytic cells (MEC), photoelectrocatalytic cells (PEC), and photocatalytic desalination cells (PDC), are able to perform detoxification of waste water and simultaneously can generate hydrogen, however, these methods require electrical energy from an external source to overcome the HER potential to generate hydrogen. It is believed that industrial waste water contains enormous energy, which can be extracted effectively and can compensate for the energy consumption in waste water treatment. Recently, Tian et al. reported the construction of a new photoelectrochemical cell referred to as a photocatalytic reverse cell (PRC), which can perform the detoxification of waste water, as well as generate hydrogen and electricity (Fig. 10.5) (Tian and Wang 2023). The cell was constructed by employing TiO2 /Ti mesh weaved onto a titanium wire as anode, while cathode material was fabricated by loading Ni-doped carbonitride (NiN-C) on cobalt phosphide (CoP) immobilized on nickel foam. It is to be noted that cobalt phosphide (CoP) is conventionally employed in the fabrication of hydrogen evolution cathodes, due to its high durability, high activity, and is inexpensive (Ma et al. 2017; Pan et al. 2016, 2018). However, CoP exhibits high overpotential, displays

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

289

Fig. 10.4 a Representation showing the fabrication of photoanode based on oxygen vacancies enriched Ov -TiO2 nanorods, b proposed mechanism for the generation of reactive species in the photoelectrochemical treatment of saline water, c proposed mechanism for the photoelectrochemical degradation of 4-chlorophenol in presence of saline water (reproduced with permission (Wu et al. 2023a))

low charge transfer, and exhibits inferior electrical conductivity (Tian et al. 2014), which can be enhanced by doping with iron (Lin et al. 2019), N-doped carbon (Ma et al. 2018), manganese (Maosen Wang et al. 2020), and nickel (Zhang et al. 2021). Further, to provide power to the external circuit, PRC was integrated with a reverse electrodialysis (RED) stack having different compartments (HC solution and LC solution) with different concentrations of ions separated by the membranes, where the ionic movement generates a flux, which is utilized in generating electricity. To maintain the salinity gradient, the RED feed solution (ammonium carbonate) can undergo decomposition in the LC tank and can be regenerated in the HC tank via a distillation column, where the heating can be sourced from industrial waste heat. Overall, this technology was able to generate hydrogen as well as produce electricity using solar energy and heat from industrial waste. Further, it was reported that the developed cell was able to provide output current in the range of 2.2–3.0 mA, while the cumulative hydrogen generation was found to be 500 μmol/L. In addition, the cell was able to display ~81% degradation of ampicillin. It was further reported that the electricity and hydrogen generation can be enhanced by increasing pollutant concentration, HC, and flow rate of ammonium carbonate.

290

P. Sharma and A. Kumar

Fig. 10.5 Representation of photocatalytic reverse cell which is able to degrade the pollutants (ampicillin in the present case), as well as generate hydrogen and electricity (reproduced with permission from Tian and Wang (2023))

10.2.4 Integration of Photocatalysis with Sonocatalysis Technique Sonocatalysis technique for waste water treatment involves ultrasound waves assisted homolytic cleavage of water molecules to generate active radical species such as • H and • OH, which have the potential to non-selectively mineralize the organic pollutants present in the water (Qiu et al. 2018). However, the technique has been found to display ineffective mineralization of organic pollutants, which can be enhanced by integrating it with photo-catalysis. Recently, Tannaz et al. reported the degradation of Rifadin (antibiotic) using a NiCr-based layered double hydroxide (labeled as NC) as well as its immobilized versions over carbon nanotubes (NC/CNT) and biochar (NC/BC), as photocatalysts. Results revealed that the integration of sonocatalysis with photocatalysis displayed higher efficiency in degrading the antibiotic relative to the sonocatalysis and photocatalysis alone (Fig. 10.6a–c). Further, in comparison of the performance displayed by the developed catalysts, it was observed that NC/BC (based on biochar) photocatalyst displayed a high degradation efficiency of ~80.3% in natural pH conditions of antibiotic (concentration 15 mg/L) when assisted with an ultrasonic bath of 150 W, as well as exposure to 50 W LED light for 90 min (Rad et al. 2023). Furthermore, GC–MS investigations were performed to propose a degradation pathway of Rifadin which has been represented in Fig. 10.6d. It was suggested that degradation of the antibiotic initiated with cleavage of C–C, C–N, and N–N bonds, and is followed by collapse of complicated rings leading to the generation of basic aromatic rings. Further, aliphatic species with a low number of

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

291

carbon atoms were detected which can undergo mineralization into carbon dioxide and water molecules (Rad et al. 2023). Integrated sono-photocatalytic treatment has been additionally found to be an efficient technique for the degradation of plasticizers, dyes, and pharmaceuticals. Parisa et al. reported the use of sporopollenin/zinc oxide (SP/ZnO) as an environment friendly photocatalyst for the degradation of contaminants such as direct blue 25 (dye containing-N=N-bonds), levofloxacin (antibiotic), and dimethyl phthalate (plasticizer). It was mentioned that the intent behind opting for ZnO as a semiconductor material was its stability, biodegradability, and low toxicity (Dihom et al. 2022). In addition, sporopollenin (SP) which comprises oxygenated aromatic and long-chain fatty acids, was chosen as a catalyst support due to its porous structure (Fig. 10.7), high surface area, low cost, stability, and eco-friendly nature (Chen et al.

Fig. 10.6 Degradation efficiencies of photocatalyst labeled as a NC, b NC/BC, and c NC/CNT, for Rifadin (antibiotic), d Possible degradation mechanism of Rifadin through integrated sonophotocatalysis technique (reproduced with permission from Rad et al. (2023))

292

P. Sharma and A. Kumar

Fig. 10.7 SEM images showing the surface morphology of a–c sporopollenin and d–f sporopollenin/zinc oxide (SP/ZnO) catalyst at different magnifications (reproduced with permission from Motlagh et al. (2023))

2021). The SP/ZnO catalyst was found to exhibit porosity (Fig. 10.7) and displayed a surface area of 9.81 m2 /g, while the results of diffuse reflectance spectroscopy revealed a bandgap value of 2.65 eV for the catalyst. Further, 0.1 g/L of catalyst displayed a reduction of 86.41% for direct blue 25, 75.88% for levofloxacin, and 62.54% was observed for dimethyl phthalate, at 10 mg/L of pollutant concentration, under natural pH conditions. The performance of this integrated technique was found to be relatively higher than the individual treatment methods, which was ascribed to the decreased recombination rate of photo-induced charges as well as the generation of large amounts of reactive oxygen species. Moreover, the results of GC–MS analysis revealed that the rigid structures of contaminants were converted to cyclic compounds, which were further converted to simple aliphatic compounds (Motlagh et al. 2023).

10.2.5 Integration of Photocatalysis with Ozonization Technique The integrated photocatalytic-ozonation technique is emerging as an effective hybrid advanced oxidation process for the degradation of refractory pollutants. Integration of photocatalysis with ozonization generates a variety of reactive oxygen species

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

293

(• OH, • O3− , • O2− , surface O) which synergistically mineralize the pollutants with recalcitrant structures. Ozone (O3 ) is already established as a strong oxidant and is typically used for water disinfection process, however, the instability associated with the molecule in an aqueous environment as well as its preferred reaction with aromatic structures does not result in the effective mineralization of organic pollutants. Recently, Ling et al. integrated the photocatalysis and ozonization techniques to achieve efficient degradation of a widely used antibiotic azithromycin, which is known for its lowest removal efficiency, and the concentration of the same can easily reach up to mg/L level in waste water eluted from the pharmaceutical industry. For this, the catalyst was developed by doping Fe atoms in the framework of MCM-48, followed by its wrapping with g-C3 N4 nanosheets, resulting in a photocatalyst with excellent magnetic characteristics to offer easy separation. The catalyst was found to exhibit a specific surface area of 165 m2 /g with a pore volume of 0.35 cm3 /g and pore diameter was found to be in the range of 1.5–8 nm. Further, the band gap energy value was determined as 2.27 eV. Moreover, PL studies were conducted to investigate the migration, transfer, and recombination rate of photo-induced charge carriers, where the lowest PL intensity was observed for the hybrid catalyst. It was suggested that the recombination rate of photo-induced charge carriers is minimal in the hybrid catalyst relative to its individual components. The degradation of azithromycin (at a concentration of 50 mg/L) was performed in a reactor (sketch presented in Fig. 10.8a) which was equipped with simulated solar light as well as an ozone generator (flow rate 1 L/min). Results revealed that g-C3 N4 was able to display a reduction of 37% in the concentration of pollutant, while degradation efficiency for hybrid catalyst designated as g-C3 N4 /Fe doped MCM-48 was found to be 98.8% in 11 min. Further, it was suggested that treatment of the contaminated water should be performed in alkaline conditions, as the medium allows the conversion of O3 to • OH. In addition, a higher percentage of hydroxide ions is expected to react with holes generated on the surface of the catalyst, thereby additionally generating • OH radical species (Fig. 10.8b) (Ling et al. 2023).

10.2.6 Integration of Photocatalysis with Piezo-Catalysis Technique On exposure to mechanical force, piezoelectric materials are able to produce an electric field through the separation of positive and negative charges on their surface. Consequently, these electrons and holes can react with oxygen or water to generate reactive oxygen species and can therefore be applied to degrade the organic pollutants present in the water. The integration of the piezo-catalysis technique with photocatalysis has been found to display synergism in enhancing the photodegradation of pollutants by preventing carrier recombination. The internal electric field generated by mechanical stimuli is able to induce polarization, thereby facilitating the separation of photo-induced charge carriers, which catalyzes the degradation of pollutants. Reports

294

P. Sharma and A. Kumar

Fig. 10.8 a Sketch representation of reactor utilized to perform the degradation of azithromycin using integrated photocatalytic ozonation technique, b proposed mechanism of degradation of azithromycin (reproduced with permission from Ling et al. (2023))

are available where exploring piezoelectric materials, such as BaTiO3 − @TiO2 micro-flowers, Bi0.5 Na0.5 TiO3 /MWCNTs, 0.67BiFeO3 -0.33BaTiO3 , ZnO-GO, Ag/ PbBiO2 I and Bi2 MoO6 /BiOBr, have been explored for the degradation of variety of organic pollutants (Liu et al. 2022; Wang et al. 2022c; Muduli et al. 2022; Ma et al. 2022; Li et al. 2021b; Yao et al. 2021). Recently, Wu et al. designed a catalyst designated as ZIF-67N@BiFeO3 @CdS, where two ferroelectric materials BiFeO3 and CdS were integrated, as well as the incorporation of ZIF-67N (MOF having hollow nanostructures and cobalt as well as sintered in nitrogen atmosphere), was expected to contribute in catalyzing the degradation of pollutant. It is to be noted that photocatalysis mainly consumes the ultraviolet and visible range, while infrared light having lower phototoxicity has rarely been utilized (Yang et al. 2021b). In view of the same, this catalyst was designed with an aim to degrade pollutants such as Bisphenol-A, by consuming visible as well as near infra-red light, and thus the issue of short wavelength absorption associated with the pure components of the developed catalysts was resolved. It was suggested that excitation of the catalyst by using dual stimuli (visible light irradiation for photocatalysis and ultrasonic vibration for piezo-catalysis) displayed better degradation efficiency than subjecting the catalyst to a single stimulus. Results revealed the impressive degradation efficiency of ZIF-67N@BiFeO3 @CdS, which was found to be 91.2% under visible light irradiation and in the presence of ultrasonic vibration. Further, the appreciable degradation of Bisphenol-A was mainly ascribed to the generation of • O2− species during the photocatalysis process (Wu et al. 2023b). It is to be noted that piezoelectric materials are generally based on heavy metals, and thus are associated with a risk of metal leaching in the water treatment, which is a serious concern and poses obstruction in the large-scale applicability of this technique. In this direction, Cheng et al. explored nitrogen-rich carbon nitrides (C3 N5 )

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

295

for the degradation of tetracycline, rhodamine B, ciprofloxacin, and methylene blue, as this carbon nitride has been reported to display better electrocatalytical and photocatalytical performance relative to C3 N4 . Further, the framework of semiconductor material C3 N5 was modified with dual defects including cyano groups and nitrogen vacancies. The potential of C3 N5 -xCN (doped with cyano and nitrogen vacancies) was highlighted with the highest kinetic constant of 0.1218 min−1 determined for rhodamine B removal, relative to C3 N5 , CN-modified C3 N5 , as well as commercially available piezo-photocatalyst BaTiO3 and ZnO. Further, the degradation efficiency of the developed catalyst was additionally investigated for ciprofloxacin, tetracycline, and methylene blue, where the kinetic constants were determined as 0.0161, 0.0342, and 0.0401 min−1 (Fu et al. 2023).

10.2.7 Integration of Photocatalysts with Biofilm Reactor Sewage water contaminated with biodegradable organic pollutants is conventionally detoxed via biological waste water treatment processes, such as the activated sludge process, and biofilm process (Palatsi et al. 2021). It is to be noted that emerging pollutants such as antibiotics, which are usually detected in significant amounts, are considered as a threat to the ecological environment as well as to human health (Soni et al. 2022). In addition, these chemicals pose obstructions in their degradation using biological waste water treatment processes due to their recalcitrant chemical structure and toxicity (Sun et al. 2022; Oberoi et al. 2019). Methodologies, such as microalgae-bacteria consortium (Wang et al. 2022d), cometabolic biodegradation (Li et al. 2022b), and wetlands (Hazra et al. 2022) are employed for removing antibiotics, however, these techniques are associated with certain limitations such as long operational duration, and instability associated with the treatment. In view of the same, it has become necessary to modify and enhance the efficiency of the biological treatment process to remove antibiotics. In this direction, biological treatments have been integrated with photocatalysis, where the generated strong oxidizing species are able to mineralize the antibiotics such as tetracycline (Xiong et al. 2017), amoxicillin (Wang et al. 2019c), and ciprofloxacin (Li et al. 2021c). Recently, Liu et al. reported the integration of photocatalytic technology with the biological treatment method for mineralization of sulfamethoxazole (SMX) pollutant and additionally evaluated the performance of the integrated system for the reduction of chemical oxygen demand (COD) (Liu et al. 2023). It was observed that the removal efficiency of MBBR toward SMX was only between 51 and 55% and was ascribed to the low biodegradability of the pollutant due to its antibacterial nature. Further, the degradation of the pollutant was better in the presence of light relative to dark, which was due to the higher reaction temperature resulting in higher mass transfer rate and microbial activity. Interestingly, the integration of MBBR with Fe3+ /g-C3 N4 photocatalyst resulted in the complete removal of the SMX. Furthermore, the COD removal efficiencies were determined in the MBBR system which was found to be in the range of 69–75% and remained unaltered in the integrated photocatalytic-biofilm system.

296

P. Sharma and A. Kumar

10.3 Conclusion Photocatalysis has emerged as an efficient technology for the degradation of a variety of toxic pollutants detected in industrial discharge. Photocatalysis has been integrated with techniques including adsorption, Fenton, sonocatalysis, electrocatalysis, ozonation, piezo-catalysis, and biological treatments, with an aim to enhance the degradation efficiency of pollutants exhibiting recalcitrant structures. Several nanomaterials as well as their hybrids have been explored as photocatalysts in the integrated photocatalytic treatments. The synergism observed in the integrated system has been primarily attributed to the reduction in the rate of recombination of photoinduced charges at the surface of the photocatalyst. It is interesting to note that the degradation efficiency of the integrated system is essentially dependent on the characteristics of nanomaterials, which are believed to exert a negative environmental impact. In view of the same, researchers have reported environment friendly and cost-effective approaches for designing photocatalysts. Surprisingly, reports on integrated systems such as piezo-photocatalytic technology, and photocatalytic biofilms reactors are limited, as well as the integration of more than two technologies should be explored in the degradation of pollutants that are detected at higher concentrations.

References Adnan MAM, Julkapli NM, Amir MNI, Maamor A (2019) Effect on different TiO2 photocatalyst supports on photodecolorization of synthetic dyes: a review. Int J Environ Sci Technol 16:547– 566. https://doi.org/10.1007/s13762-018-1857-x Aguilar SD, Ramos DR, Santaballa JA, Canle M (2023) Preparation, characterization and testing of a bulky non-supported photocatalyst for water pollution abatement. Catal Today 413–415:113992. https://doi.org/10.1016/j.cattod.2022.12.023 Alhaji MH, Sanaullah K, Khan A, Hamza A, Muhammad A, Ishola MS, Rigit ARH, Bhawani SA (2017) Recent developments in immobilizing titanium dioxide on supports for degradation of organic pollutants in wastewater—a review. Int J Environ Sci Technol 14:2039–2052. https:// doi.org/10.1007/s13762-017-1349-4 Ali HM, Roghabadi FA, Ahmadi V (2023) Solid-supported photocatalysts for wastewater treatment: supports contribution in the photocatalysis process. Sol Energy 255:99–125. https://doi.org/10. 1016/j.solener.2023.03.032 Baba Y, Yatagai T, Harada T, Kawase Y (2015) Hydroxyl radical generation in the photo-Fenton process: effects of carboxylic acids on iron redox cycling. Chem Eng J 277:229–241. https:// doi.org/10.1016/j.cej.2015.04.103 Bayan EM, Pustovaya LE, Volkova MG (2021) Recent advances in TiO2 -based materials for photocatalytic degradation of antibiotics in aqueous systems. Environ Technol Innov 24:101822. https://doi.org/10.1016/j.eti.2021.101822 Canesi L, Ciacci C, Balbi T (2015) Interactive effects of nanoparticles with other contaminants in aquatic organisms: friend or foe? Mar Environ Res 111:128–134. https://doi.org/10.1016/j.mar envres.2015.03.010 Chen X, Huo X, Liu J, Wang Y, Werth CJ, Strathmann TJ (2017) Exploring beyond palladium: catalytic reduction of aqueous oxyanion pollutants with alternative platinum group metals and new mechanistic implications. Chem Eng J 313:745–752. https://doi.org/10.1016/j.cej.2016. 12.058

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

297

Chen S, Huang D, Zeng G, Xue W, Lei L, Xu P, Deng R, Li J, Cheng M (2020) In-situ synthesis of facet-dependent BiVO4 /Ag3 PO4 /PANI photocatalyst with enhanced visible-light-induced photocatalytic degradation performance: synergism of interfacial coupling and hole-transfer. Chem Eng J 382:122840. https://doi.org/10.1016/j.cej.2019.122840 Chen S, Shi Q, Jang T, Bin Ibrahim MS, Deng J, Ferracci G, Tan WS, Cho N-J, Song J (2021) Engineering natural pollen grains as multifunctional 3D printing materials. Adv Funct Mater 31:2106276. https://doi.org/10.1002/adfm.202106276 Chong MN, Jin B, Chow CWK, Saint C (2010) Recent developments in photocatalytic water treatment technology: a review. Water Res 44:2997–3027. https://doi.org/10.1016/j.watres.2010. 02.039 Coates JD, Achenbach LA (2004) Microbial perchlorate reduction: rocket-fuelled metabolismMicrobial perchlorate reduction: rocket-fuelled metabolismMicrobial perchlorate reduction: rocket-fuelled metabolism. Nat Rev Microbiol 2:569–580 Crini G, Lichtfouse E (2019) Advantages and disadvantages of techniques used for wastewater treatment. Environ Chem Lett 17:145–155. https://doi.org/10.1007/s10311-018-0785-9 Curcio MS, Oliveira MP, Waldman WR, Sánchez B, Canela MC (2015) TiO2 sol-gel for formaldehyde photodegradation using polymeric support: photocatalysis efficiency versus material stability. Environ Sci Pollut Res 22:800–809. https://doi.org/10.1007/s11356-014-2683-4 Dai W, Tao Y, Zou H, Xiao S, Li G, Zhang D, Li H (2020) Gas-phase photoelectrocatalytic oxidation of NO via TiO2 nanorod array/FTO photoanodes. Environ Sci Technol 54:5902–5912. https:// doi.org/10.1021/acs.est.9b07757 Dihom HR, Al-Shaibani MM, Mohamed RMSR, Al-Gheethi AA, Sharma A, Bin Khamidun MH (2022) Photocatalytic degradation of disperse azo dyes in textile wastewater using green zinc oxide nanoparticles synthesized in plant extract: a critical review. J Water Process Eng 47:102705. https://doi.org/10.1016/j.jwpe.2022.102705 Fu C, Zhao M, Chen X, Sun G, Wang C, Song Q (2023) Unraveling the dual defect effects in C3 N5 for piezo-photocatalytic degradation and H2 O2 generation. Appl Catal B Environ 332:122752. https://doi.org/10.1016/j.apcatb.2023.122752 Gao X, Liang C, Gao K, Li X, Liu J, Li Q (2020) Z-scheme heterojunction Ag3 PO4 /BiVO4 with exposing high-active facets and stretching spatial charge separation ability for photocatalytic organic pollutants degradation. Appl Surf Sci 524:146506. https://doi.org/10.1016/j.aps usc.2020.146506 Garrido-Ramírez EG, Theng BK, Mora ML (2010) Clays and oxide minerals as catalysts and nanocatalysts in Fenton-like reactions—a review. Appl Clay Sci 47:182–192. https://doi.org/ 10.1016/j.clay.2009.11.044 Gaya UI, Abdullah AH (2008) Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress and problems. J Photochem Photobiol C Photochem Rev 9:1–12. https://doi.org/10.1016/j.jphotochemrev.2007.12.003 Gopinath KP, Madhav NV, Krishnan A, Malolan R, Rangarajan G (2020) Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: a review. J Environ Manag 270:110906. https://doi.org/10.1016/j.jenvman.2020.110906 Gusain R, Kumar N, Ray SS (2020) Factors influencing the photocatalytic activity of photocatalysts in wastewater treatment. In: Photocatalysts in advanced oxidation processes for wastewater treatment, pp 229–270. https://doi.org/10.1002/9781119631422.ch8 Hazra M, Joshi H, Williams JB, Watts JEM (2022) Antibiotics and antibiotic resistant bacteria/ genes in urban wastewater: a comparison of their fate in conventional treatment systems and constructed wetlands. Chemosphere 303:135148. https://doi.org/10.1016/j.chemosphere.2022. 135148 Horikoshi S, Serpone N (2020) Can the photocatalyst TiO2 be incorporated into a wastewater treatment method? Background and prospects. Catal Today 340:334–346. https://doi.org/10. 1016/j.cattod.2018.10.020

298

P. Sharma and A. Kumar

Hou S, Ling L, Dionysiou DD, Wang Y, Huang J, Guo K, Li X, Fang J (2018) Chlorate formation mechanism in the presence of sulfate radical, chloride, bromide and natural organic matter. Environ Sci Technol 52:6317–6325. https://doi.org/10.1021/acs.est.8b00576 Hu J, Li J, Cui J, An W, Liu L, Liang Y, Cui W (2020) Surface oxygen vacancies enriched FeOOH/ Bi2 MoO6 photocatalysis-fenton synergy degradation of organic pollutants. J Hazard Mater 384:121399. https://doi.org/10.1016/j.jhazmat.2019.121399 Kagaya S, Shimizu K, Arai R, Hasegawa K (1999) Separation of titanium dioxide photocatalyst in its aqueous suspensions by coagulation with basic aluminium chloride. Water Res 33:1753–1755. https://doi.org/10.1016/S0043-1354(99)00004-4 Kim S, Piao G, Han DS, Shon HK, Park H (2018) Solar desalination coupled with water remediation and molecular hydrogen production: a novel solar water-energy nexus. Energy Environ Sci 11:344–353. https://doi.org/10.1039/C7EE02640D Koltsakidou A, Antonopoulou M, Evgenidou E, Konstantinou I, Lambropoulou D (2019) A comparative study on the photo-catalytic degradation of Cytarabine anticancer drug under Fe3+ /H2 O2 , Fe3+ /S2 O8 2− , and [Fe(C2 O4 )3 ]3− /H2 O2 processes. Kinetics, identification, and in silico toxicity assessment of generated transformation products. Environ Sci Pollut Res 26:7772–7784. https://doi.org/10.1007/s11356-018-4019-2 Koo MS, Chen X, Cho K, An T, Choi W (2019) In situ photoelectrochemical chloride activation using a WO3 electrode for oxidative treatment with simultaneous H2 evolution under visible light. Environ Sci Technol Sci Technol 53:9926–9936. https://doi.org/10.1021/acs.est.9b02401 Kuang X, Min Fu HK, Peng Lu JB, Yang Y, Gao S (2023) A BiOIO3 /BiOBr n-n heterojunction was constructed to enhance the photocatalytic degradation of TC. Opt Mater (Amst) 138:113690. https://doi.org/10.1016/j.optmat.2023.113690 Lee S-Y, Park S-J (2013) TiO2 photocatalyst for water treatment applications. J Ind Eng Chem 19:1761–1769. https://doi.org/10.1016/j.jiec.2013.07.012 Levchuk I, Guillard C, Dappozze F, Parola S, Leonard D, Sillanpää M (2016) Photocatalytic activity of TiO2 films immobilized on aluminum foam by atomic layer deposition technique. J Photochem Photobiol A Chem 328:16–23. https://doi.org/10.1016/j.jphotochem.2016.03.034 Li C, Zhang P, Lv R, Lu J, Wang T, Wang S, Wang H, Gong J (2013) Selective deposition of Ag3 PO4 on monoclinic BiVO4 (04 0) for highly efficient photocatalysis. Small 9:3951–3956. https://doi. org/10.1002/smll.201301276 Li F, Sun L, Liu Y, Fang X, Shen C, Huang M, Wang Z, Dionysiou DD (2020) A ClOradical dotmediated photoelectrochemical filtration system for highly-efficient and complete ammonia conversion. J Hazard Mater 400:123246. https://doi.org/10.1016/j.jhazmat.2020.123246 Li X, Kan M, Wang T, Qin Z, Zhang T, Qian X, Kuwahara Y, Mori K, Yamashita H, Zhao Y (2021a) The ClO generation and chlorate suppression in photoelectrochemical reactive chlorine species systems on BiVO4 photoanodes. Appl Catal B Environ 296:120387. https://doi.org/10.1016/j. jhazmat.2020.123246 Li Z, Zhang Q, Wang L, Yang J, Wu Y, He Y (2021b) Novel application of Ag/PbBiO2 I nanocomposite in piezocatalytic degradation of rhodamine B via harvesting ultrasonic vibration energy. Ultrason Sonochem 78:105729. https://doi.org/10.1016/j.ultsonch.2021.105729 Li Y, Chen L, Tian X, Lin L, Ding R, Yan W, Zhao F (2021c) Functional role of mixedculture microbe in photocatalysis coupled with biodegradation: total organic carbon removal of ciprofloxacin. Sci Total Environ 784:147049. https://doi.org/10.1016/j.scitotenv.2021.147049 Li S, Wang C, Liu Y, Cai M, Wang Y, Zhang H, Guo Y, Zhao W, Wang Z, Chen X (2022a) Photocatalytic degradation of tetracycline antibiotic by a novel Bi2 Sn2 O7 /Bi2 MoO6 S-scheme heterojunction: performance, mechanism insight and toxicity assessment. Chem Eng J 429:132519. https://doi.org/10.1016/j.cej.2021.132519 Li S, Peng L, Yang C, Song S, Xu Y (2022b) Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms during wastewater treatment processes. J Environ Manag 305:114336. https://doi.org/10.1016/j.jenvman.2021.114336 Lima MJ, Leblebici ME, Dias MM, Lopes JCB, Silva CG, Silva AMT, Faria JL (2014) Continuous flow photo-Fenton treatment of ciprofloxacin in aqueous solutions using homogeneous and

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

299

magnetically recoverable catalysts. Environ Sci Pollut Res 21:11116–11125. https://doi.org/10. 1007/s11356-014-2515-6 Lin C, Wang P, Jin H, Zhao J, Chen D, Liu S, Zhang C, Mu S (2019) An iron-doped cobalt phosphide nano-electrocatalyst derived from a metal–organic framework for efficient water splitting. Dalt Trans 48:16555. https://doi.org/10.1039/c9dt03619a Ling Y, Liu H, Li B, Zhang B, Wu Y, Hu H, Yu D, Huang S (2023) Efficient photocatalytic ozonation of azithromycin by three-dimensional g-C3 N4 nanosheet loaded magnetic Fe-MCM-48 under simulated solar light. Appl Catal B Environ 324:122208. https://doi.org/10.1016/j.apcatb.2022. 122208 Liu Q, Zhan F, Luo H, Zhai D, Xiao Z, Sun Q, Yi Q, Yang Y, Zhang D (2022) Mechanism of interface engineering for ultrahigh piezo-photoelectric catalytic coupling effect of BaTiO3 @TiO2 microflowers. Appl Catal B Environ 318:121817. https://doi.org/10.1016/j.apcatb.2022.121817 Liu Q, Hou J, Zeng Y, Xia J, Miao L, Wu J (2023) Integrated photocatalysis and moving bed biofilm reactor (MBBR) for treating conventional and emerging organic pollutants from synthetic wastewater: performances and microbial community responses. Bioresour Technol 370:128530. https://doi.org/10.1016/j.biortech.2022.128530 Long Z, Li Q, Wei T, Zhang G, Ren Z (2020) Historical development and prospects of photocatalysts for pollutant removal in water. J Hazard Mater 395:122599. https://doi.org/10.1016/j.jhazmat. 2020.122599 Lu Y, Zhang H, Fan D, Chen Z, Yang X (2022) Coupling solar-driven photothermal effect into photocatalysis for sustainable water treatment. J Hazard Mater 423:127128. https://doi.org/10. 1016/j.jhazmat.2021.127128 Ma M, Zhu G, Xie F, Qu F, Liu Z, Du G, Asiri AM, Yao Y, Sun X (2017) Homologous catalysts based on Fe-doped CoP nanoarrays for high-performance full water splitting under benign conditions. ChemSusChem 10:3188–3192. https://doi.org/10.1002/cssc.201700693 Ma J, Wang M, Lei G, Zhang G, Zhang F, Peng W, Fan X, Li Y (2018) Polyaniline derived N-doped carbon-coated cobalt phosphide nanoparticles deposited on N-doped graphene as an efficient electrocatalyst for hydrogen evolution reaction. Small 14:1702895. https://doi.org/10.1002/smll. 201702895 Ma N, Xu J, Bian Z, Yang Y, Zhang L, Wang H (2020) BiVO4 plate with Fe and Ni oxyhydroxide cocatalysts for the photodegradation of sulfadimethoxine antibiotics under visible-light irradiation. Chem Eng J 389:123426. https://doi.org/10.1016/j.cej.2019.123426 Ma W, Lv M, Cao F, Fang Z, Feng Y, Zhang G, Yang Y, Liu H (2022) Synthesis and characterization of ZnO-GO composites with their piezoelectric catalytic and antibacterial properties. J Environ Chem Eng 10:107840. https://doi.org/10.1016/j.jece.2022.107840 Malato S, Fernández-Ibáñez P, Maldonado MI, Blanco J, Gernjak W (2009) Decontamination and disinfection of water by solar photocatalysis: recent overview and trends. Catal Today 147:1–59. https://doi.org/10.1016/j.cattod.2009.06.018 Wang M, Fu W, Du L, Wei Y, Rao P, Wei L, Zhao X, Wang Y, Sun S (2020) Surface engineering by doping manganese into cobalt phosphide towards highly efficient bifunctional HER and OER electrocatalysis. Appl Surf Sci 515:146059. https://doi.org/10.1016/j.apsusc.2020.146059 Mei J, Tao Y, Gao C, Zhu Q, Zhang H, Yu J, Fang Z, Xu H, Wang Y, Li G (2021) Photo-induced dye-sensitized BiPO4 /BiOCl system for stably treating persistent organic pollutants. Appl Catal B Environ 285. https://doi.org/10.1016/j.apcatb.2020.119841 Miklos DB, Remy C, Jekel M, Linden KG, Drewes JE, Hübner U (2018) Evaluation of advanced oxidation processes for water and wastewater treatment—a critical review. Water Res 139:118– 131. https://doi.org/10.1016/j.watres.2018.03.042 Mirzaei A, Chen Z, Haghighat F, Yerushalmi L (2017) Removal of pharmaceuticals from water by homo/heterogonous Fenton-type processes—a review. Chemosphere 174:665–688. https://doi. org/10.1016/j.chemosphere.2017.02.019 Mishra A, Mehta A, Basu S (2018) Clay supported TiO2 nanoparticles for photocatalytic degradation of environmental pollutants: a review. J Environ Chem Eng 6:6088–6107. https://doi.org/10. 1016/j.jece.2018.09.029

300

P. Sharma and A. Kumar

Motlagh PY, Vahid B, Akay S, Kayan B, Yoon Y, Khataee A (2023) Ultrasonic-assisted photocatalytic degradation of various organic contaminants using ZnO supported on a natural polymer of sporopollenin. Ultrason Sonochem 98:106486. https://doi.org/10.1016/j.ultsonch.2023.106486 Muduli SP, Veeralingam S, Badhulika S (2022) Free-standing, non-toxic and reusable 0.67BiFeO3 – 0.33BaTiO3 based polymeric piezo-catalyst for organic dye wastewater treatment. J Water Process Eng 48:102934. https://doi.org/10.1016/j.jwpe.2022.102934 Musial J, Mlynarczyk DT, Stanisz DT (2023) Photocatalytic degradation of sulfamethoxazole using TiO2 -based materials—perspectives for the development of a sustainable water treatment technology. Sci Total Environ 856:159122. https://doi.org/10.1016/j.scitotenv.2022.159122 Nguyen TDV-HN, Nanda S, Vo D-VN, Nguyen VH, Van Tran T, Nong LX, Nguyen TT, Bach L-G, Abdullah B, Hong S-S, Van Nguyen T (2020) BiVO4 photocatalysis design and applications to oxygen production and degradation of organic compounds: a review. Environ Chem Lett 18:1779–1801. https://doi.org/10.1007/s10311-020-01039-0 Nogueira V, Lopes I, Rocha-Santos T, Gonçalves F, Pereira R (2015) Toxicity of solid residues resulting from wastewater treatment with nanomaterials. Aquat Toxicol 165:172–178. https:// doi.org/10.1016/j.aquatox.2015.05.021 Oberoi AS, Jia Y, Zhang H, Khanal SK, Lu H (2019) Insights into the fate and removal of antibiotics in engineered biological treatment systems: a critical review. Environ Sci Technol 53:7234–7264. https://doi.org/10.1021/acs.est.9b01131 Palatsi J, Ripoll F, Benzal A, Pijuan M, Romero-Güiza MS (2021) Enhancement of biological nutrient removal process with advanced process control tools in full-scale wastewater treatment plant. Water Res 200:117212. https://doi.org/10.1016/j.watres.2021.117212 Pan Y, Liu Y, Lin Y, Liu C (2016) Metal doping effect of the M–Co2 P/nitrogen-doped carbon nanotubes (M=Fe, Ni, Cu) hydrogen evolution hybrid catalysts. ACS Appl Mater Interfaces 8:13890–13901. https://doi.org/10.1021/acsami.6b02023 Pan Y, Sun K, Liu S, Cao X, Wu K, Cheong W-C, Chen Z, Wang Y, Li Y, Liu Y, Wang D, Peng Q, Chen C, Li Y (2018) Core–Shell ZIF-8@ZIF-67-derived CoP nanoparticle-embedded Ndoped carbon nanotube hollow polyhedron for efficient overall water splitting. J Am Chem Soc 140:2610–2618. https://doi.org/10.1021/jacs.7b12420 Perini JAL, Tonetti AL, Vidal C, Montagner CC, Nogueira RFP (2018) Simultaneous degradation of ciprofloxacin, amoxicillin, sulfathiazole and sulfamethazine, and disinfection of hospital effluent after biological treatment via photo-Fenton process under ultraviolet germicidal irradiation. Appl Catal B Environ 224:761–771. https://doi.org/10.1016/j.apcatb.2017.11.021 Píšťková V, Tasbihi M, Vávrová M, Štangar UL (2015) Photocatalytic degradation of β-blockers by using immobilized titania/silica on glass slides. J Photochem Photobiol A Chem 305:19–28. https://doi.org/10.1016/j.jphotochem.2015.02.014 Qiu P, Park B, Choi J, Thokchom B, Pandit AB, Khim J (2018) A review on heterogeneous sonocatalyst for treatment of organic pollutants in aqueous phase based on catalytic mechanism. Ultrason Sonochem 45:29–49. https://doi.org/10.1016/j.ultsonch.2018.03.003 Rachel A, Subrahmanyam M, Boule P (2002) Comparison of photocatalytic efficiencies of TiO2 in suspended and immobilised form for the photocatalytic degradation of nitrobenzenesulfonic acids. Appl Catal B Environ 37:301–308. https://doi.org/10.1016/S0926-3373(02)00007-3 Rad TS, Yazici ES, Khataee A, Gengec E, Kobya M (2023) Ultrasound-assisted photocatalytic decomposition of rifadin with biochar and CNT-based NiCr layered double hydroxides. Surf Interfaces 36:102628. https://doi.org/10.1016/j.surfin.2022.102628 Rajendran S, Hoang TKA, Trudeau ML, Jalil AA, Naushad M, Awual MR (2022) Generation of novel n-p-n (CeO2 -PPy-ZnO) heterojunction for photocatalytic degradation of micro-organic pollutants. Environ Pollut 292:118375. https://doi.org/10.1016/j.envpol.2021.118375 Ramos DR, Iazykov M, Fernandez MI, Santaballa JA, Canle M (2021) Mechanical stability is key for large-scale implementation of photocatalytic surface-attached film technologies in water treatment. Front Chem Eng 3. https://doi.org/10.3389/fceng.2021.688498 Ranade VV, Bhandari VM (2014) Chapter 1—Industrial wastewater treatment, recycling, and reuse: an overview, pp 1–80. https://doi.org/10.1016/B978-0-08-099968-5.00001-5

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

301

Rao KVS, Subrahmanyam M, Boule P (2004) Immobilized TiO2 photocatalyst during long-term use: decrease of its activity. Appl Catal B Environ 49:239–249. https://doi.org/10.1016/j.apcatb. 2003.12.017 Saianand G, Gopalan A-I, Wang L, Venkatramanan K, Roy VAL, Sonar P, Lee D-E, Naidu R (2022) Conducting polymer based visible light photocatalytic composites for pollutant removal: progress and prospects. Environ Technol Innov 28:102698. https://doi.org/10.1016/j.eti.2022. 102698 Sampaio MJ, Silva CG, Marques RRN, Silva AMT, Faria JL (2011) Carbon nanotube–TiO2 thin films for photocatalytic applications. Catal Today 161:91–96. https://doi.org/10.1016/j.cattod. 2010.11.081 Samuel O, Othman MHD, Kamaludin R, Dzinun H, Imtiaz A, Li T, El-badawy T, Khan AU, Puteh MH, Yuliwati E, Kurniawan TA (2023) Photocatalytic degradation of recalcitrant aromatic hydrocarbon compounds in oilfield-produced water: a critical review. J Clean Prod 415:137567. https://doi.org/10.1016/j.jclepro.2023.137567 Sharma K, Vaya D, Prasad G, Surolia PK (2023) Photocatalytic process for oily wastewater treatment: a review. Int J. Environ Sci Technol 20:4615–4634. https://doi.org/10.1007/s13762-02103874-2 Soni K, Jyoti K, Chandra H, Chandra H (2022) Bacterial antibiotic resistance in municipal wastewater treatment plant; mechanism and its impacts on human health and economy. Bioresour Technol Rep 19:101080. https://doi.org/10.1016/j.biteb.2022.101080 Sun C, Hu E, Liu S, Wen L, Yang F, Li M (2022) Spatial distribution and risk assessment of certain antibiotics in 51 urban wastewater treatment plants in the transition zone between North and South China. J Hazard Mater 437:129307. https://doi.org/10.1016/j.jhazmat.2022.129307 Suresh R, Gnanasekaran L, Rajendran S, Soto-Moscoso M, Chen W-H, Show PL, Khoo KS (2023) Application of nanocomposites in integrated photocatalytic techniques for water pollution remediation. Environ Technol Innov 31:103149. https://doi.org/10.1016/j.eti.2023.103149 Tian H, Wang Y (2023) A reverse electrodialysis cell-modified photocatalytic fuel cell for efficient electricity and hydrogen generation from the degradation of refractory organic pollutants. J Hazard Mater 444:130443. https://doi.org/10.1016/j.jhazmat.2022.130443 Tian J, Liu Q, Asiri AM, Sun X (2014) Self-supported nanoporous cobalt phosphide nanowire arrays: an efficient 3D hydrogen-evolving cathode over the wide range of pH 0–14. J Am Chem Soc 136:7587–7590. https://doi.org/10.1021/ja503372r Tian Q, Fang G, Ding L, Ran M, Zhang H, Pan A, Shen K, Deng Y (2020) ZnAl2 O4 /Bi2 MoO6 heterostructures with enhanced photocatalytic activity for the treatment of organic pollutants and eucalyptus chemimechanical pulp wastewater. Mater Chem Phys 241:122299. https://doi. org/10.1016/j.matchemphys.2019.122299 Tian Q, Yang Q, Guo W, Li X, Fang G, Ge Y, Liu CX, Yin H, Pan A, Li N (2023) Synergy of adsorption-photocatalysis and enriched surface oxygen vacancies over lignin-biochar/Bi2 MoO6 nanocomposites for organic pollutant removal and bamboo ECF bleaching effluent treatment. Ind Crops Prod 191:115966. https://doi.org/10.1016/j.indcrop.2022.115966 Wang G, Ling Y, Wang H, Yang X, Wang C, Zhang JZ, Li Y (2012) Hydrogen-treated WO3 nanoflakes show enhanced photostability. Energy Environ Sci 5:6180–6187. https://doi.org/10. 1039/C2EE03158B Wang HT, Ye YY, Qi J, Li FT, Tang YL (2013) Removal of titanium dioxide nanoparticles by coagulation: effects of coagulants, typical ions, alkalinity and natural organic matters. Water Sci Technol 68:1137–1143. https://doi.org/10.2166/wst.2013.356 Wang S, Chen P, Bai Y, Yun J-H, Liu G, Wang L (2018) New BiVO4 dual photoanodes with enriched oxygen vacancies for efficient solar-driven water splitting. Adv Mater 30:1800486. https://doi. org/10.1002/adma.201800486 Wang X, Ma J, Kong Y, Fan C, Peng M, Komarneni S (2019a) Synthesis of p-n heterojunction Ag3 PO4 /NaTaO3 composite photocatalyst for enhanced visible-light-driven photocatalytic performance. Mater Lett 251:192–195. https://doi.org/10.1016/j.matlet.2019.05.078

302

P. Sharma and A. Kumar

Wang Z, Mao X, Chen P, Xiao M, Monny SA, Wang S, Konarova M, Du A, Wang L (2019b) Understanding the roles of oxygen vacancies in hematite-based photoelectrochemical processes. Angew Chemie 131:1042–1046. https://doi.org/10.1002/ange.201810583 Wang Y, Chen C, Zhou D, Xiong H, Zhou Y, Dong S, Rittmann BE (2019c) Eliminating partialtransformation products and mitigating residual toxicity of amoxicillin through intimately coupled photocatalysis and biodegradation. Chemosphere 237:124491. https://doi.org/10.1016/ j.chemosphere.2019.124491 Wang W, Xu M, Xu X, Zhou W, Shao Z (2020) Perovskite oxide based electrodes for highperformance photoelectrochemical water splitting. Angew Chemie 59:136–152. https://doi.org/ 10.1002/anie.201900292 Wang F, Ma N, Zheng L, Zhang L, Bian Z, Wang H (2022a) Interface engineering of p-p Zscheme BiOBr/Bi12 O17 Br2 for sulfamethoxazole photocatalytic degradation. Chemosphere 307:135666. https://doi.org/10.1016/j.chemosphere.2022.135666 Wang X, Li Z, Zhang Y, Li Q, Du H, Liu F, Zhang X, Mu H, Duan J (2022b) Enhanced photocatalytic antibacterial and degradation performance by p-n-p type CoFe2 O4 /CoFe2 S4 /MgBi2 O6 photocatalyst under visible light irradiation. Chem Eng J 429:132270. https://doi.org/10.1016/ j.cej.2021.132270 Wang P, Zhong S, Lin M, Lin C, Lin T, Gao M, Zhao C, Li X, Wu X (2022c) Signally enhanced piezo-photocatalysis of Bi0.5 Na0.5 TiO3 /MWCNTs composite for degradation of rhodamine B. Chemosphere 308:136596. https://doi.org/10.1016/j.chemosphere.2022.136596 Wang Y, Li J, Lei Y, Li X, Nagarajan D, Lee D-J, Chang J-S (2022d) Bioremediation of sulfonamides by a microalgae-bacteria consortium—analysis of pollutants removal efficiency, cellular composition, and bacterial community. Bioresour Technol 351:126964. https://doi.org/10.1016/ j.biortech.2022.126964 Wei Y, Zhang Y, Miao J, Geng W, Long M (2021) In-situ utilization of piezo-generated hydrogen peroxide for efficient p-chlorophenol degradation by Fe loading bismuth vanadate. Appl Surf Sci 543:148791. https://doi.org/10.1016/j.apsusc.2020.148791 Wei P, Zhang Y, Huang Y, Chen L (2023) Structural design of SiO2 /TiO2 materials and their adsorptionphotocatalytic activities and mechanism of treating cyanide wastewater. J Mol Liq 377:121519. https://doi.org/10.1016/j.molliq.2023.121519 Wu J, Tao Y, Zhang C, Zhu Q, Zhang D, Li G (2023a) Activation of chloride by oxygen vacanciesenriched TiO2 photoanode for efficient photoelectrochemical treatment of persistent organic pollutants and simultaneous H2 generation. J Hazard Mater 443:130363. https://doi.org/10. 1016/j.jhazmat.2022.130363 Wu Y, Gao Z, Jiao S, Zhou G (2023b) Piezo-photo coupling effect and extended optical absorption of piezoelectric-based hybrids for efficient bisphenol A degradation. Chem Eng J 452:139456. https://doi.org/10.1016/j.cej.2022.139456 Xiong H, Zou D, Zhou D, Dong S, Wang J, Rittmann BE (2017) Enhancing degradation and mineralization of tetracycline using intimately coupled photocatalysis and biodegradation (ICPB). Chem Eng J 316:7–14. https://doi.org/10.1016/j.cej.2017.01.083 Yan H, Wang X, Yao M, Yao X (2013) Band structure design of semiconductors for enhanced photocatalytic activity: the case of TiO2 . Prog Nat Sci Mater Int 23:402–407. https://doi.org/10. 1016/j.pnsc.2013.06.002 Yang X, Wang D (2018) Photocatalysis: from fundamental principles to materials and applications. ACS Appl Energy Mater 1:6657–6693. https://doi.org/10.1021/acsaem.8b01345 Yang L, Xiang Y, Jia F, Xia L, Gao C, Wu X, Peng L, Liu J, Song S (2021a) Photo-thermal synergy for boosting photo-Fenton activity with rGO-ZnFe2 O4 : novel photo-activation process and mechanism toward environment remediation. Appl Catal B Environ 292:120198. https:// doi.org/10.1016/j.apcatb.2021.120198 Yang Y-Y, Feng H-P, Niu C-G, Huang D-W, Guo H, Liang C, Liu H-Y, Chen S, Tang N, Li L (2021b) Constructing a plasma-based Schottky heterojunction for near-infrared-driven photothermal synergistic water disinfection: synergetic effects and antibacterial mechanisms. Chem Eng J 426:131902. https://doi.org/10.1016/j.cej.2021.131902

10 Detoxification of Industrial Waste Water by Photocatalytic Techniques

303

Yao Z, Sun H, Xiao S, Hu Y, Liu X, Zhang Y (2021) Synergetic piezo-photocatalytic effect in a Bi2 MoO6 /BiOBr composite for decomposing organic pollutants. Appl Surf Sci 560:150037. https://doi.org/10.1016/j.apsusc.2021.150037 Zhang B, Yang D, Qian Y, Pang Y, Li Q, Qiu X (2020) Engineering a lignin-based hollow carbon with opening structure for highly improving the photocatalytic activity and recyclability of ZnO. Ind Crops Prod 155:112773. https://doi.org/10.1016/j.indcrop.2020.112773 Zhang X, Liu W-X, Zhou Y-W, Meng Z-D, Luo L, Liu S-Q (2021) Single-atom nickel anchored on surface of molybdenum disulfide for efficient hydrogen evolution. J Electroanal Chem 894:115359. https://doi.org/10.1016/j.jelechem.2021.115359 Zhang X, Chen Z, Li X, Wu Y, Zheng J, Li Y, Wang D, Yang Q, Duan A, Fan Y (2023) Promoted electron transfer in Fe2+ /Fe3+ co-doped BiVO4 /Ag3 PO4 S-scheme heterojunction for efficient photo-Fenton oxidation of antibiotics. Sep Purif Technol 310:123116. https://doi.org/10.1016/ j.seppur.2023.123116

Chapter 11

Waste Management: Nano Photocatalysis as an Efficient Future Pathway Abhishek Tiwari, Varsha Tiwari, and Bimal Krishna Banik

11.1 Introduction Waste management and its environmental implications: Waste management is a critical aspect of maintaining environmental sustainability. Improper management of waste can have detrimental effects on ecosystems, human health, and overall environmental quality. The release of pollutants into water bodies, such as industrial effluents, agricultural runoff, and domestic sewage, poses significant risks to aquatic life and can contaminate water resources. These pollutants include heavy metals, organic compounds, nutrients, pharmaceuticals, and pathogens, among others. It is imperative to develop effective and sustainable methods for treating wastewater to minimize environmental damage and protect human well-being. Importance of photocatalysis in wastewater treatment: Photocatalysis has emerged as a promising technology for wastewater treatment due to its ability to degrade a wide range of pollutants under mild conditions. This process involves the use of a photocatalyst that, upon exposure to light, initiates a series of chemical reactions that break down organic and inorganic contaminants A. Tiwari (B) Department of Pharmaceutical Chemistry, Amity Institute of Pharmacy, Lucknow Campus, Amity University, Sector 125, Noida-201313, Uttar Pradesh, India e-mail: [email protected] V. Tiwari Department of Pharmacognosy, Amity Institute of Pharmacy, Lucknow, Amity University, Sector 125, Noida-201313, Uttar Pradesh, India B. K. Banik Department of Mathematics and Natural Sciences, College of Sciences and Human Studies, Prince Mohammad Bin Fahd University, Al Khobar 31952, Kingdom of Saudi Arabia 305

306

A. Tiwari et al.

into harmless byproducts. The photocatalytic degradation process is highly efficient, selective, and environmentally friendly, making it an attractive option for wastewater treatment. Figure 11.1 illustrates waste management within the built environment and its alignment with the Sustainable Development Goals (SDGs). The key component of photocatalysis is the photocatalyst, which absorbs light energy and utilizes it to generate reactive species, such as hydroxyl radicals (•OH) and superoxide radicals (•O−2 ). Semiconductor nanoparticles have shown great potential as photocatalysts due to their unique properties, such as large surface area, tunable bandgap, and high reactivity. These nanoparticles can be synthesized using various methods, including sol–gel, hydrothermal, and precipitation techniques, allowing for control over their size, morphology, and surface properties (Chong et al. 2010; Dionysiou et al. 2013; Pablos and Rey 2016; Khan and Ahmed 2018). Environmental issues: The presence of plastic pollution in both marine and terrestrial environments poses a significant threat to various forms of life. In addition, it has been observed that the byproducts resulting from natural degradation have the potential to generate a greater quantity of hazardous chemicals. Throughout the lifespan of plastic, several detrimental substances can come into contact with microorganisms, plants, animals, and humans. For example, the presence of polystyrene (PS) fragments in the environment is facilitated by wind dispersion, posing a significant threat to avian and other animal species in terms of mortality. Plastic waste is deposited in both aquatic and terrestrial environments, subsequently entering the food chain as depicted in Fig. 11.2. Microplastics have been identified in several sources, including food, salt, and bottled water. As a result, microplastics have the potential to be present in the gastrointestinal tract or respiratory system of mammals when they are consumed through food or water ingestion, or inhaled from the surrounding air. Upon reaching the organism, plastics exhibit an enhanced affinity for lipophilic tissues such as the brain or liver due to their hydrophobic properties. This affinity leads to the accumulation of plastics in these tissues, hence promoting the onset and progression of various disorders. Furthermore, it is worth noting that microplastics often contain other chemicals, such as bisphenol A, phthalates, and flame retardants, which have been identified as having endocrine-disrupting properties (Chong et al. 2010; Chen and Dionysiou 2016; Pablos and Rey 2016; Khan and Ahmed 2018). For example, the emission of vinyl chloride, a potentially carcinogenic chemical, might occur through the use of polyvinyl chloride (PVC). Plastics and microplastics have been identified in soil samples, indicating the potential for ingestion by animals. This occurrence is likely to have implications for the health of the animals involved and the subsequent entry of these contaminants into the food chain (Fig. 11.2). In this particular situation, it should be noted that the soil is also impacted due to the presence of microplastics. It is worth mentioning that the severity of this impact increases with the decreasing size of the microplastics. This presence of microplastics contributes to the evaporation of soil water and subsequent cracking, which in turn facilitates the release of additional pollutants.

Fig. 11.1 The graphical depiction illustrates the interconnectedness between several aspects of waste management within the Built Environment and its alignment with the Sustainable Development Goals

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway 307

308

A. Tiwari et al.

Fig. 11.2 A schematic illustration depicting the trajectory of microplastics within the food chain

11.1.1 Waste Management and Its Environmental Implications Waste management is the process of collecting, treating, and disposing of waste materials in a manner that minimizes its impact on the environment and human health. The management of waste is crucial for maintaining a sustainable environment and preventing pollution. Improper waste management practices can have significant environmental implications, including the following: (a) Water pollution: Inadequate treatment and disposal of wastewater can lead to the contamination of water bodies, such as rivers, lakes, and oceans. Industrial effluents, agricultural runoff, and untreated sewage can introduce pollutants, including toxic chemicals, heavy metals, pathogens, and nutrients, into water sources. This pollution not only affects aquatic ecosystems but also poses risks to human health when contaminated water is consumed or used for recreational purposes.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

309

(b) Soil contamination: Improper disposal of solid waste, such as landfilling, can result in the leaching of harmful substances into the soil. Landfills can release pollutants into the surrounding soil, including hazardous chemicals, heavy metals, and organic compounds. These contaminants can negatively impact soil fertility, plant growth, and ultimately enter the food chain, posing risks to both ecosystems and human health. (c) Air pollution: Improper waste management practices, such as open burning of waste or inadequate incineration processes, can release harmful gases and particulate matter into the air. These emissions contribute to air pollution, leading to respiratory problems, cardiovascular diseases, and other adverse health effects. In addition, the release of greenhouse gases from decomposing organic waste in landfills contributes to climate change. (d) Habitat destruction and biodiversity loss: Irresponsible waste disposal, such as illegal dumping or littering, can lead to the destruction of natural habitats. Wildlife may ingest or become entangled in waste materials, causing harm or death. The loss of biodiversity can disrupt ecosystems and have far-reaching ecological consequences. (e) Resource depletion: Waste management is closely linked to resource conservation. Proper waste management practices, such as recycling and waste-to-energy processes, help recover valuable resources from waste streams. By reducing the need for raw materials extraction, waste management contributes to the conservation of natural resources and reduces energy consumption associated with resource extraction and manufacturing (Tchobanoglous et al. 2014; UNEP 2021; World Health Organization 2016).

11.1.2 Importance of Photocatalysis in Wastewater Treatment Photocatalysis has gained significant attention as a promising technology for wastewater treatment due to its potential to effectively degrade a wide range of pollutants. This section highlights the importance of photocatalysis in addressing the challenges of wastewater treatment and references supporting its significance. (a) Efficient pollutant degradation: Photocatalysis offers an efficient and sustainable approach for the degradation of various pollutants present in wastewater. Semiconductor nanoparticles, such as titanium dioxide (TiO2 ), zinc oxide (ZnO), and other metal oxides, act as photocatalysts when exposed to light, initiating redox reactions that break down organic and inorganic pollutants into harmless byproducts. (b) Versatility and broad applicability: Photocatalysis can be applied to a diverse range of pollutants and wastewater types. It is effective in treating both industrial and municipal wastewaters, enabling the removal of pollutants originating from various sources, including industries, households, and agriculture.

310

A. Tiwari et al.

(c) Environmental friendliness: One of the key advantages of photocatalysis is its environmentally friendly nature. The process utilizes light energy, typically from solar radiation, as the driving force for pollutant degradation. As a result, it does not require the addition of harsh chemicals or generate harmful byproducts, reducing the potential for secondary pollution. (d) Potential for water reuse: With the increasing scarcity of freshwater resources, the need for water reuse and recycling is becoming crucial. Photocatalysis has shown promise in enabling the treatment of wastewater to a quality suitable for reuse in various applications, such as irrigation, industrial processes, and even potable water production. Waste management in the built environment will be discussed in relation to the Sustainable Development Goals (SDGs) The objective of examining waste management in relation to sustainable development goals is to highlight the significant role that waste management will play in achieving the objective of establishing a sustainable built environment in the foreseeable future. When considering the significance of Sustainable Development Goals (SDGs) in the context of waste management, it becomes evident that adopting the SDG framework provides a comprehensive perspective on this subject, as previously illustrated (see Fig. 11.1). The perception of waste management in the BE, including its various qualities such as the economic position of workers and critical environmental elements, becomes more comprehensive when examined from the perspective of each SDG. This is because a multi-faceted vision emerges, highlighting the interconnectedness of waste management with different sustainable development goals. The subsequent sections give an illustration of how Sustainable Development Goals (SDGs) might serve as a framework for addressing waste management in contemporary contexts across various regions (Roy et al. 2023; Mills and Hunte 1997; Li and Dionysiou 2019; Gaya and Abdullah 2008a, b; Wang et al. 2012; Chen and Dionysiou 2016). The life cycle of materials in the environment is shown in the Fig. 11.4.

11.1.3 SDG 1: Waste and Waste Workers The aims encompassed by Sustainable Development Goal 1 pertain to ensuring universal access to essential services, enhancing individuals’ capacity to withstand adversity, and mitigating the vulnerability of populations to extreme climate-related occurrences, as well as other economic, social, and environmental disasters that may be deemed exceptional. An effectively functioning waste management system plays a significant role in the achievement of Sustainable Development Goal 1 by mitigating poverty and enhancing the well-being of individuals and their communities. In order to progress toward the achievement of Sustainable Development Goal 1 (SDG 1), it is of particular significance that policymakers and government officials, who bear

311

Fig. 11.3 Social determinants of health

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

Fig. 11.4 Life cycle of materials in the environment

312 A. Tiwari et al.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

313

the responsibility of formulating policies and legislation pertaining to waste management, prioritize the enhancement of the well-being and occupational circumstances of trash employees. Trash management personnel play a crucial role in the collaborative production of several urban services, thereby contributing significantly to the achievement of various Sustainable Development Goals (SDGs). Among these goals, SDG 1 holds particular importance, and attending to the needs of trash employees contributes to the enhancement of waste management efficiency. Figure 11.5 provides a detailed overview of waste management practices within environmentally sustainable buildings. It highlights strategies for minimizing waste generation, promoting recycling and reuse, and efficiently handling waste disposal processes. These practices aim to reduce the environmental impact of buildings, contributing to sustainability goals by lowering resource consumption, reducing pollution, and encouraging circular economy principles. The figure underscores the integration of waste management protocols in building design and operation, aligning with green building standards and sustainable development objectives.

Fig. 11.5 Management of waste in environmental building

314

A. Tiwari et al.

11.2 Photocatalysis: Principles and Mechanisms The mechanism of photocatalysis semiconducting materials serve as photocatalysts, enhancing the rate of redox reactions by virtue of their electronic structure characterized by a valence band (VB) populated by electrons and a conduction band (CB) that remains unoccupied. If the band gap (BG) of the nano-photocatalyst is equal to or lower than the energy of the incident radiation, the electrons in the valence band (VB) will absorb the photon and transition to the conduction band (CB). In the context of VB (valence bond) theory, the presence of holes plays a crucial role as they facilitate the oxidation of donor molecules, leading to the generation of hydroxyl species upon their reaction with water (H2 O). The absorption of an electron by water in the conduction band (CB) leads to the creation of a superoxide ion, which acts as a reducing agent. When a contaminant interacts with the photocatalyst, it can engage in a redox reaction with the available electrons and holes, resulting in the transformation of the contaminant into carbon dioxide (CO2 ) and water (H2 O), which are fewer complex compounds. The formation of electron–hole (e− –h+ ) pairs occurs when photocatalysts are exposed to photons of light with a wavelength that is equal to or greater than the bandgap width. If the band gap (BG) of the nano-photocatalyst is equal to or lower than the energy of the incident radiation, the electrons in the valence band (VB) will absorb the photon and transition to the conduction band (CB) (see Fig. 11.6). Nano-photocatlyst + (EBG ≤ hν) → h+ VB + e− CB 2. Photooxidation involves the generation of excess positive charges (h+ ) due to the presence of the photocatalyst VB. In the context of Visual Basic (VB), the presence of holes holds significant importance. When the hydrogen ion (H+ ) in the valence band (VB) engages with water (H2 O) molecules, it has the ability to oxidize donor molecules, resulting in the formation of hydroxyl (OH) radicals. H2 O + h+ → H+ + OH 3. Photoreduction: When an electron in the conduction band combines with dissolved oxygen, the result is the production of superoxide ions. This electronic entity is accountable for instigating photoreduction processes on the surfaces of photocatalysts. O2 + e− → O− 2 H2 O + O− → HO2 2 H2 O2 + e− → OH

The absorption of an electron by water in the conduction band leads to the generation of a superoxide ion, which functions as a reducing agent.

315

Fig. 11.6 Mechanism of photocatalysis

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

316

A. Tiwari et al.

4. The degradation of pollutants occurs through the simulation of photoreduction and photooxidation events on the photocatalyst’s surface, resulting in the generation of electron–hole (e− –h+ ) pairs that form superoxide radicals. Subsequently, these radicals engage in chemical reactions with impurities, resulting in their degradation into carbon dioxide (CO2 ), water (H2 O), and byproducts or simpler molecules. Oxidizing Species + contaminates → Byproduct/Simpler compound + CO2 + H2 O Recombination of e− –h+ pair → radiation less decay + energy When a contaminant interacts with the photocatalyst, it can engage in a redox reaction with the available electrons and holes, resulting in the conversion of the contaminant into carbon dioxide (CO2 ) and water (H2 O), which are simpler compounds. 1. A diverse array of organic pollutants can be found in water. Dyes are present in several industries such as the food industry, printing and dyeing factories, and dyestuff factories, among others. These industrial businesses contribute to the generation of dye wastewater, which is responsible for the presence of dyes in water sources. Several dyes that are known to contaminate water bodies are methyl blue, eosin, methylene orange, congo red, and rhodamine B. Photocatalytic degradation has the potential to destroy methylene blue (see Fig. 11.7). Personal care and pharmaceutical waste In recent years, there has been a growing worry regarding new pollutants, including personal care items and pharmaceutical waste, due to their adverse environmental impacts. In contrast, conventional treatment methods have limitations in their capacity to effectively manage such waste. The photocatalytic process is considered one of the most efficient methods for the elimination of harmful pollutants. Table 11.1 presents the results of a study on the photocatalytic degradation of a diverse array of personal care products, pharmaceutical waste, and antibodies found in wastewater. This investigation utilized different types of nanoparticles and nanocomposites.

11.2.1 Role of Semiconductor Nanoparticles as Photocatalysts Semiconductor nanoparticles have emerged as highly effective photocatalysts in wastewater treatment and pollutant degradation processes. Their unique properties and characteristics make them ideal for harnessing light energy and initiating photocatalytic reactions. This section discusses the role of semiconductor nanoparticles as photocatalysts and highlights their key attributes. Large surface area: Semiconductor nanoparticles possess a high surface area-tovolume ratio due to their small size. This increased surface area provides a larger number of active sites for pollutant adsorption and facilitates efficient interaction

317

Fig. 11.7 Photocatalytic degradation of Methylene blue

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

318

A. Tiwari et al.

Table 11.1 Photocatalytic elimination of a wide range of personal care and pharmaceutical waste Photocatalyst

Synthesis method Light source

Contaminant

Removal efficiency

Graphite-C3 N4

Polycondensation UV–visible

Tetracycline (Te), Ciprofloxacin (CP), Salicylic acid (SA)

Te = 86%; CP = 60% SA = 36%

CuO/TiO2 /MCM-41

Hydrothermal UV

Te

70.52%

BaTiO3 /TiO2

One step Calcination, UV

Acetaminophen

Ibuprofen = 20%; BaTiO3 /TiO2

BiVO4 /TiO2 /Reduced GO

Hydrothermal Visible

Doxycycline Tetracycline(Te)

Doxycycline = 99.6% Tetracycline = 96.2%

Graphite-C3 N4 /AgBr/ Reduced GO

Hydrothermal Visible

2,4-Dichlorophenol Tetracycline

2,4-Dichlorophenol = 68.2% Tetracycline = 78.4%

TiO2 /ZrO2

Sol–gel UV

Metformin

50%

Ag3 PO4 /GO/Ni

Dip coating Method, Visible

Norfloxacin

83.68%

between the photocatalyst and the target pollutants. The enhanced surface area enhances the overall photocatalytic activity and pollutant degradation efficiency. Bandgap engineering: The bandgap of semiconductor nanoparticles can be tailored by controlling their size, composition, and surface modifications. This ability to engineer the bandgap allows the semiconductor nanoparticles to absorb a broader range of light wavelengths, including ultraviolet (UV) and visible light. By tuning the bandgap, the photocatalyst can utilize a larger portion of the solar spectrum, making the photocatalytic process more efficient and effective. Photogenerated charge carriers: Semiconductor nanoparticles, when illuminated, generate photoexcited charge carriers, including electrons and holes. These charge carriers play a vital role in the photocatalytic reaction pathways. The photoexcited electrons in the conduction band are involved in the reduction reactions, while the holes in the valence band participate in the oxidation reactions. The high reactivity of these charge carriers enables efficient pollutant degradation and mineralization. Redox potential: Semiconductor nanoparticles possess suitable redox potentials, allowing them to participate in the generation of reactive oxygen species (ROS) during photocatalysis. The photoexcited electrons can reduce oxygen molecules, generating superoxide radicals (•O−2 ), while the holes can oxidize water molecules, producing hydroxyl radicals (•OH). These ROS are powerful oxidants that react with adsorbed pollutants, leading to their degradation.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

319

Photostability: Semiconductor nanoparticles exhibit excellent photostability, meaning they can endure prolonged exposure to light without significant degradation or loss of catalytic activity. This property ensures the longevity and stability of the photocatalyst, enabling its repeated use in wastewater treatment applications. The high photostability of semiconductor nanoparticles contributes to their cost-effectiveness and long-term viability as photocatalysts. Versatility: Semiconductor nanoparticles can be synthesized with various compositions and morphologies, such as metal oxides (e.g., TiO2 , ZnO), metal sulfides (e.g., CdS), and metal chalcogenides (e.g., MoS2 ). This versatility allows the selection of an appropriate photocatalyst based on the specific pollutants to be treated and the desired reaction conditions. Furthermore, semiconductor nanoparticles can be integrated into different forms, including films, powders, coatings, or immobilized on support materials, to enhance their practical applicability in wastewater treatment systems. The utilization of semiconductor nanoparticles as photocatalysts in wastewater treatment offers numerous advantages, including high reactivity, cost-effectiveness, stability, and versatility. These attributes make them promising candidates for addressing pollution challenges and developing sustainable solutions for water purification and environmental remediation (Chen and Mao 2007; Peral and Ollis 1992; Linsebigler et al. 1995).

11.3 Nanoparticles for Wastewater Treatment Nanoparticles have gained significant attention in the field of wastewater treatment due to their unique properties and capabilities to address various pollutants. This section discusses the utilization of nanoparticles for wastewater treatment and highlights their effectiveness in pollutant removal (see Fig. 11.8). Metal-based nanoparticles: Metal-based nanoparticles, such as iron nanoparticles, silver nanoparticles (AgNPs), and zero-valent iron nanoparticles (ZVIs), have been widely studied for their ability to remove various contaminants from wastewater. These nanoparticles exhibit high reactivity and catalytic activity, enabling them to effectively degrade organic pollutants, heavy metals, and even recalcitrant compounds. Metal-based nanoparticles can undergo redox reactions, adsorption, and surface catalysis, leading to the degradation and transformation of pollutants into less harmful forms. Metal oxide nanoparticles: Metal oxide nanoparticles, such as titanium dioxide (TiO2 ), zinc oxide (ZnO), and cerium oxide (CeO2 ), have shown remarkable photocatalytic activity in wastewater treatment. These nanoparticles can be activated by UV or visible light to generate reactive oxygen species (ROS), such as hydroxyl radicals (•OH), which are highly

Fig. 11.8 Nanotechnology in water technology

320 A. Tiwari et al.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

321

effective in degrading organic pollutants. Metal oxide nanoparticles are also capable of adsorbing heavy metals and metalloids, removing them from wastewater through surface interactions. Carbon-based nanoparticles: Carbon-based nanoparticles, including carbon nanotubes (CNTs) and graphene oxide (GO), have demonstrated promising potential for wastewater treatment applications. CNTs possess high adsorption capacity and can effectively remove organic pollutants, heavy metals, and even emerging contaminants. GO, with its large surface area and unique properties, has been utilized for adsorption, catalysis, and membranebased separation processes, offering effective removal of various pollutants from wastewater. Magnetic nanoparticles: Magnetic nanoparticles, such as magnetite (Fe3 O4 ) nanoparticles, have been widely explored for wastewater treatment due to their magnetic properties. These nanoparticles can be easily separated from the treated wastewater using magnetic fields, facilitating their reusability. Magnetic nanoparticles can be functionalized or coated with other materials to enhance their adsorption capacity for contaminants such as heavy metals, dyes, and organic compounds. Hybrid nanoparticles: Hybrid nanoparticles, formed by combining different types of nanoparticles or incorporating nanoparticles into other materials, offer enhanced properties and multifunctionality for wastewater treatment. For example, hybrid nanocomposites consisting of metal/metal oxide nanoparticles combined with carbon-based materials can synergistically combine adsorption, catalysis, and other mechanisms to remove a wide range of pollutants effectively. The utilization of nanoparticles in wastewater treatment offers several advantages, including high reactivity, large surface area, tunable properties, and potential for regeneration and reuse. However, challenges such as nanoparticle stability, the potential release of nanoparticles into the environment, and the need for scalable and cost-effective synthesis methods need to be addressed for their practical implementation (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019; Ge and Fang 2020).

322

A. Tiwari et al.

11.4 Synthesis of Semiconductor Nanoparticles 11.4.1 Semiconductor Nanocomposites Transition metal oxides and transition metal dichalcogenides are often synthesized nanocomposites that have demonstrated exceptional characteristics. These nanocomposites are typically fabricated employing diverse techniques. Therefore, the development of nanocomposites could potentially provide a solution for effectively controlling the properties of individual nanoparticles. In the realm of semiconductor materials, there is a prevalent practice of engineering nanocomposites consisting of many materials in order to modify their electrical and optical characteristics. The synthesis of nanocomposites involves the incorporation of nanoparticles into other functional materials by either surface decorating or intercalation methods. The surface decorating of nanoparticles is a significant problem due to the limitations of existing synthetic approaches in achieving precise allocation of nanoparticles to desired places. Various indirect methods have been employed to put solutionbased nanoparticles onto material surfaces, with the solvent subsequently evaporating throughout the assembly process (see Fig. 11.9). Various types of semiconductor nanocomposites may be found in the field of materials science. These include noble metal–metal oxides, carbon materials-metal oxides, and polymer-metal oxides, among others. The utilization of two distinct materials in the composition of nanocomposites presents an intriguing approach for modifying the band gap energy of semiconductors. The preparation of ZnO/CuO mixed semiconductor nanocomposites is undertaken, whereby ZnO, characterized as a broadband gap n-type semiconductor, is combined with CuO, known as a narrow band gap p-type semiconductor. This combination is intended to yield nanocomposites with enhanced electrical, optoelectronic, photovoltaic, piezoelectric, and catalytic capabilities. The conventional techniques employed for the synthesis of nanoparticles are similarly utilized in the production of nanocomposites. The photo-deposition approach is considered one of the more straightforward techniques employed in the synthesis of noble metal/semiconductor nanocomposites. This method capitalizes on the semiconductor’s band gap to facilitate the synthesis process. In contrast to many other techniques that necessitate high temperatures, additional redox agents, potential drops, or multi-step procedures, the photoinduced reduction approach solely relies on the irradiation of a lightweight source. Moreover, using the process of photo-deposition, noble nanoparticles can be effectively deposited onto two-dimensional substrates. This allows for precise control over the dimensions of metallic nanoparticles by altering factors such as the concentration of the metal precursor, irradiation time, and power. Additionally, this approach facilitates the achievement of material selectivity, wherein nanoparticles composed of metallic elements are exclusively deposited onto the semiconductor templates. Certain conductive polymers, such as polyaniline (PAni), have the capability to combine with semiconductor nanoparticles, resulting in the enhancement of the

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

323

Fig. 11.9 Synthetic pathway of organic semiconductors

radiative recombination of electron–hole pairs. This improvement holds significant potential for advancing the performance of optoelectronic applications. Hydrothermal/Solvothermal Synthesis: In hydrothermal or solvothermal synthesis, the precursors are reacted under high-pressure and high-temperature conditions in a closed system. This method enables the formation of highly crystalline nanoparticles with controlled sizes and shapes. The use of organic solvents or water as the reaction medium influences the properties of the nanoparticles obtained. Microwave-Assisted Synthesis: Microwave irradiation can be employed to enhance the synthesis of semiconductor nanoparticles by providing rapid and uniform heating. This method offers advantages such as shorter reaction times, energy efficiency, and

324

A. Tiwari et al.

improved control over particle size and morphology (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019). Application of Nanoparticles in Wastewater Treatment Nanoparticles have emerged as promising tools for various applications in wastewater treatment due to their unique properties and high surface-to-volume ratios. A few applications of nanoparticles in wastewater treatment are as follows: Adsorption: Nanoparticles, such as activated carbon nanoparticles, graphene oxide, and magnetic nanoparticles, can be used for the adsorption of various pollutants present in wastewater. They have large surface areas and can effectively adsorb heavy metals, organic compounds, dyes, and emerging contaminants. Nanoparticles with functionalized surfaces can enhance their adsorption capacity and selectivity for specific pollutants. Catalysis: Semiconductor nanoparticles, particularly titanium dioxide (TiO2 ) and zinc oxide (ZnO), exhibit photocatalytic activity when exposed to light. This property allows them to degrade organic pollutants through the generation of reactive oxygen species (ROS) such as hydroxyl radicals (•OH). Photocatalysis using nanoparticles has shown promise in the removal of organic dyes, pharmaceuticals, pesticides, and other persistent organic pollutants (see Fig. 11.10). Disinfection: Silver nanoparticles (AgNPs) possess strong antimicrobial properties and can be used for disinfection in wastewater treatment. They have been shown to effectively inhibit the growth and kill bacteria, viruses, and other microorganisms present in wastewater. AgNPs can be added directly to wastewater or incorporated into filtration membranes for continuous disinfection. Membrane Filtration: Nanoparticles can be used to enhance the performance of membrane filtration processes. By incorporating nanoparticles into membranes or modifying their surfaces, the filtration efficiency can be improved, fouling can be reduced, and the removal of specific contaminants can be enhanced. Nanoparticles like titanium dioxide, carbon nanotubes, and zeolites have been used to enhance membrane filtration in wastewater treatment. Advanced Oxidation Processes (AOPs): Nanoparticles can be utilized in advanced oxidation processes, such as Fenton and photo-Fenton reactions, to enhance the degradation of refractory pollutants in wastewater. Nanoparticles, such as iron-based nanoparticles or zero-valent iron (ZVI), can generate ROS and promote the oxidation of recalcitrant organic compounds. These processes are effective in the degradation of pharmaceuticals, pesticides, and other persistent organic pollutants. Nutrient Removal: Nanoparticles can be used for the removal of nutrients like phosphorus and nitrogen from wastewater. Nanostructured materials, such as ironbased nanoparticles or zeolites, can adsorb or catalytically convert these nutrients into less harmful forms, reducing their environmental impact when discharged into water bodies.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

325

Fig. 11.10 Structure of nanocomposite on the cell membrane of the bacteria

It is worth noting that the application of nanoparticles in wastewater treatment requires careful consideration of factors such as nanoparticle stability, potential release into the environment, cost-effectiveness, and potential toxicity. Further research and development are needed to optimize the synthesis, performance, and safety of nanoparticles for effective and sustainable wastewater treatment (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019). Removal of heavy metal-containing compounds The removal of heavy metal-containing compounds from wastewater is a critical concern due to their toxic nature and potential harm to the environment and human health. Nanoparticles have shown promise in the effective removal of heavy metals through various mechanisms. Adsorption: Nanoparticles with high surface area and specific functional groups can adsorb heavy metal ions from wastewater through ion exchange or complexation

326

A. Tiwari et al.

reactions. Various nanoparticles, such as activated carbon nanoparticles, magnetic nanoparticles, graphene oxide, and metal oxide nanoparticles, have been used for the adsorption of heavy metals. The large surface area and functionalized surfaces of nanoparticles enhance their adsorption capacity and selectivity for heavy metal ions. Precipitation: Nanoparticles can induce the precipitation of heavy metal ions by providing nucleation sites for the formation of insoluble metal compounds. For example, nanoparticles of iron-based materials, such as zero-valent iron (ZVI) nanoparticles, can be used to precipitate heavy metals as metal hydroxides or metal sulfides. The formed precipitates can be subsequently separated from the wastewater through sedimentation or filtration. Ion Exchange: Nanoparticles with ion exchange properties can selectively remove heavy metal ions from wastewater by exchanging them with less toxic or harmless ions. For instance, zeolite nanoparticles and certain clay nanoparticles have shown effective ion exchange capabilities for heavy metal removal. Redox Reactions: Nanoparticles with redox-active properties can facilitate the reduction or oxidation of heavy metal ions in wastewater. Zero-valent iron nanoparticles, for example, can reduce certain heavy metal ions to their fewer toxic forms through redox reactions. This method can transform highly toxic heavy metal ions into less harmful species or facilitate their removal through precipitation. Membrane Filtration: Nanoparticles can be incorporated into membranes to enhance their heavy metal removal efficiency. Nanoparticles can modify the surface properties of membranes, reducing fouling and enhancing selectivity for heavy metal ions. Functionalized nanoparticles, such as carbon nanotubes and polymer-based nanoparticles, have been used in membrane filtration for the removal of heavy metals. Chelation: Nanoparticles can be modified or coated with chelating agents that have a high affinity for heavy metal ions. Chelating agents can form stable complexes with heavy metal ions, facilitating their removal from wastewater. Nanoparticles functionalized with chelating ligands, such as thiol groups or amino groups, have shown effective heavy metal chelation properties. Nanoparticles offer several advantages for the removal of heavy metal-containing compounds, including their high surface area, tunable surface properties, and potential for regeneration and reusability. However, factors such as nanoparticle stability, the release of nanoparticles into the environment, and potential toxicity should be carefully evaluated to ensure their safe and effective application in heavy metal removal from wastewater (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019). Degradation of biological substances The degradation of biological substances, including bacteria, viruses, and other organic contaminants, is an essential aspect of wastewater treatment to ensure the removal of harmful pathogens and potential sources of waterborne diseases. Nanoparticles have shown promise in the degradation of biological substances through various

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

327

mechanisms. Here are some common methods employed for the degradation of biological substances using nanoparticles: Photocatalysis: Semiconductor nanoparticles, such as titanium dioxide (TiO2 ) and zinc oxide (ZnO), possess photocatalytic properties and can be activated by light to generate reactive oxygen species (ROS), such as hydroxyl radicals (•OH). These ROS can effectively oxidize and degrade organic contaminants, including bacteria, viruses, and other biological substances, present in wastewater. Photocatalytic nanoparticles can be incorporated into wastewater treatment systems or immobilized on surfaces to enhance the degradation of biological substances. Metal-Based Nanoparticles: Metal-based nanoparticles, such as silver nanoparticles (AgNPs), copper nanoparticles (CuNPs), and zinc nanoparticles (ZnNPs), exhibit antimicrobial properties and can effectively inhibit the growth and activity of bacteria and viruses. These nanoparticles can interact with biological substances and disrupt their cellular structures or metabolic processes, leading to their degradation. AgNPs, in particular, have shown broad-spectrum antimicrobial activity and are commonly used for disinfection purposes in wastewater treatment. Enzyme-Mediated Degradation: Nanoparticles can serve as carriers or supports for enzymes that have the capability to degrade biological substances. Enzymefunctionalized nanoparticles can facilitate the enzymatic degradation of organic contaminants, such as proteins, lipids, carbohydrates, and nucleic acids. This approach can enhance the efficiency and stability of enzymes, allowing for the effective degradation of biological substances in wastewater. Membrane Filtration: Nanoparticles can be incorporated into filtration membranes to enhance their antimicrobial properties and facilitate the removal of biological substances. Nanoparticles can modify the surface properties of membranes, reducing the adhesion and growth of bacteria and viruses. Functionalized nanoparticles, such as silver nanoparticles or graphene oxide, have been used to enhance the antimicrobial properties of membranes and improve their performance in the removal of biological substances. Advanced Oxidation Processes (AOPs): Nanoparticles can participate in advanced oxidation processes, such as Fenton and photo-Fenton reactions, to generate ROS and promote the degradation of organic contaminants, including biological substances. The ROS generated by nanoparticles can attack and degrade the cellular structures and components of microorganisms, leading to their inactivation and degradation. The application of nanoparticles for the degradation of biological substances in wastewater treatment offers several advantages, including their high surface area, catalytic properties, and potential for targeted and selective degradation. However, it is essential to consider factors such as nanoparticle stability, the potential release of nanoparticles into the environment, and the need for appropriate dosage and control to ensure the safe and effective degradation of biological substances in wastewater (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019).

328

A. Tiwari et al.

Inactivation of algae, bacteria, and viruses The inactivation of algae, bacteria, and viruses is a crucial step in wastewater treatment to prevent the spread of waterborne diseases and ensure the safety of water resources. Nanoparticles have demonstrated efficacy in the inactivation of algae, bacteria, and viruses through various mechanisms. Here are some common methods employed for the inactivation of these microorganisms using nanoparticles: Silver Nanoparticles (AgNPs): AgNPs possess strong antimicrobial properties and have been extensively studied for the inactivation of algae, bacteria, and viruses. The silver ions released from AgNPs can interact with the cell membranes and components of microorganisms, leading to membrane damage, disruption of cellular functions, and ultimately, microbial inactivation. AgNPs can be directly added to wastewater or incorporated into filtration membranes to continuously inhibit the growth and activity of microorganisms. Copper Nanoparticles (CuNPs): CuNPs have also shown antimicrobial activity against algae, bacteria, and viruses. Similar to AgNPs, the copper ions released from CuNPs can interact with the cellular structures of microorganisms, disrupting their functions and causing inactivation. CuNPs can be applied in a similar manner as AgNPs for the inactivation of microorganisms in wastewater. Photocatalysis: Semiconductor nanoparticles, such as titanium dioxide (TiO2 ) and zinc oxide (ZnO), exhibit photocatalytic properties and can be activated by light to generate reactive oxygen species (ROS), including hydroxyl radicals (•OH). These ROS can effectively oxidize and degrade the cell membranes and genetic material of microorganisms, leading to their inactivation. Photocatalytic nanoparticles can be used in wastewater treatment systems to continuously inactivate algae, bacteria, and viruses. Graphene Oxide (GO): GO nanoparticles have demonstrated antimicrobial properties against a wide range of microorganisms, including algae, bacteria, and viruses. The unique structure of GO nanoparticles allows them to interact with microbial cells, leading to membrane disruption and intracellular damage. GO nanoparticles can be applied directly to wastewater or incorporated into filtration membranes to enhance the inactivation of microorganisms. Other Nanoparticles: Besides silver, copper, titanium dioxide, and graphene oxide nanoparticles, other nanomaterials, such as zinc peroxide (ZnO2 ), zinc sulfide (ZnS), and iron oxide (Fe3 O4 ) nanoparticles, have also shown antimicrobial activity against algae, bacteria, and viruses. These nanoparticles can interact with microorganisms through various mechanisms, including membrane disruption, oxidative stress, and enzyme inhibition, leading to their inactivation (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019). Elimination of organic pollutants The elimination of organic pollutants from wastewater is a crucial step in wastewater treatment to ensure the removal of harmful compounds that can have adverse effects

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

329

on the environment and human health. Nanoparticles have shown great potential in the elimination of organic pollutants through various mechanisms. Adsorption: Nanoparticles with high surface area and specific functional groups can effectively adsorb organic pollutants from wastewater. The large surface area of nanoparticles provides ample sites for the adsorption of organic compounds, while functional groups on the nanoparticle surface enhance the affinity for specific pollutants. Examples of nanoparticles used for adsorption include activated carbon nanoparticles, magnetic nanoparticles, and metal oxide nanoparticles. Photocatalysis: Semiconductor nanoparticles, such as titanium dioxide (TiO2 ) and zinc oxide (ZnO), exhibit photocatalytic properties and can be activated by light to generate reactive oxygen species (ROS), such as hydroxyl radicals (•OH). These ROS have strong oxidative capabilities and can effectively degrade organic pollutants into smaller, less toxic molecules through oxidation reactions. Photocatalytic nanoparticles are particularly effective for the degradation of organic pollutants that are resistant to conventional treatment methods (see Fig. 11.11). Advanced Oxidation Processes (AOPs): Nanoparticles can participate in advanced oxidation processes, such as Fenton and photo-Fenton reactions, to generate ROS and promote the oxidation and degradation of organic pollutants. The generated ROS, such as hydroxyl radicals (•OH) and superoxide radicals (•O2− ), can attack and break down the chemical bonds of organic compounds, leading to their degradation. Metalbased nanoparticles, such as zero-valent iron (ZVI) nanoparticles, are commonly used in AOPs for the elimination of organic pollutants. Catalysis: Nanoparticles with catalytic properties can facilitate the degradation of organic pollutants through catalytic reactions. For example, palladium nanoparticles can catalyze the hydrogenation or dehalogenation of organic compounds, leading to their conversion into less toxic or more easily degradable substances. Other metal nanoparticles, such as platinum (Pt) and gold (Au) nanoparticles, have also shown catalytic activity in the degradation of organic pollutants. Membrane Filtration: Nanoparticles can be incorporated into filtration membranes to enhance their organic pollutant removal efficiency. Functionalized nanoparticles, such as carbon nanotubes and polymer-based nanoparticles, can modify the surface properties of membranes, improving their adsorption and separation capabilities for organic pollutants. Nanoparticle-modified membranes can effectively remove organic pollutants through size exclusion, adsorption, and filtration mechanisms (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019). Nanofiltration and Reverse Osmosis: Nanoparticles can be incorporated into filtration membranes, such as nanofiltration and reverse osmosis membranes, to enhance their nutrient removal efficiency. These membranes have selective permeability and can effectively separate and concentrate nutrients, such as nitrogen and phosphorus, from the wastewater. Functionalized nanoparticles, such as zeolites or carbon nanotubes, can modify the membrane surface and improve the nutrient removal performance.

330

A. Tiwari et al.

Fig. 11.11 Waste management through photocatalytic materials

Biological Processes: Nanoparticles can be used as carriers for microorganisms in biological processes for nutrient removal and recovery. For instance, nanoparticles can be functionalized with specific enzymes or microbial cells that have the ability to metabolize or assimilate nutrients. These functionalized nanoparticles can enhance the activity and stability of the microorganisms, promoting efficient nutrient removal and recovery. Controlled Release Fertilizers: Nanoparticles can be utilized as carriers for controlled release fertilizers, allowing for the targeted and controlled delivery of nutrients in agricultural applications. Nanoparticles can encapsulate nutrients, such as nitrogen and phosphorus, and slowly release them over time, reducing nutrient leaching and optimizing nutrient uptake by plants. This approach helps in reducing nutrient runoff and environmental pollution. The application of nanoparticles for nutrient removal and recovery offers several advantages, including high surface area, selectivity, and potential for controlled

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

331

release. However, it is crucial to consider factors such as nanoparticle stability, the potential release of nanoparticles into the environment, and the overall efficiency and cost-effectiveness of the nanoparticle-based methods for nutrient removal and recovery (Zhang et al. 2018; Yang et al. 2017; Malakootian et al. 2019). Antibiotic degradation using nanoparticles The degradation of antibiotics in wastewater is of significant importance to prevent the release of these compounds into the environment, as their presence can contribute to the development of antibiotic-resistant bacteria and pose risks to ecosystems and human health. Nanoparticles have shown promise in the degradation of antibiotics through various mechanisms. Figure 11.12 presents an in-depth exploration of advanced nanotechnology-based methods in industrial wastewater treatment, showcasing their effectiveness in pollutant removal through improved adsorption, filtration, and catalytic degradation. Among the key nanomaterials featured, carbon nanoparticles stand out for their high surface area and adsorptive properties, making them ideal for capturing organic pollutants and toxic metals. Green synthesis, an eco-friendly method of producing nanoparticles using sustainable resources, aligns with green chemistry principles, reducing harmful by-products and making these nanoparticles valuable for environmental applications. Metal-organic frameworks (MOFs), with their porous structures and large surface areas, are highly effective for selective pollutant adsorption and can be tailored to target specific contaminants, boosting the efficiency of wastewater treatment. Enzyme nanotechnology leverages enzymes immobilized on nanomaterials to facilitate the biocatalytic degradation of organic pollutants, enabling precise and efficient breakdown of complex contaminants. Microwave-assisted nanotechnology utilizes microwave energy to enhance the synthesis and activation of nanomaterials, speeding up pollutant degradation and improving treatment efficiency. Multi-walled carbon nanotubes (MWCNTs), known for their unique tubular structure and high adsorptive capacity, excel at trapping heavy metals and organic toxins within their layered walls. Together, these nanotechnologybased approaches offer powerful and sustainable solutions for managing industrial wastewater, helping to mitigate pollution and advance environmentally responsible practices. Some common methods employed for antibiotic degradation using nanoparticles: Photocatalysis: Semiconductor nanoparticles, such as titanium dioxide (TiO2 ) and zinc oxide (ZnO), possess photocatalytic properties and can be activated by light to generate reactive oxygen species (ROS), including hydroxyl radicals (•OH). These ROS have strong oxidative capabilities and can effectively degrade antibiotics by breaking down their chemical bonds. Photocatalytic nanoparticles can be used in wastewater treatment systems to degrade a wide range of antibiotics. Advanced Oxidation Processes (AOPs): Nanoparticles can participate in advanced oxidation processes, such as Fenton and photo-Fenton reactions, to generate ROS and promote the oxidation and degradation of antibiotics. Metal-based nanoparticles, such as zero-valent iron (ZVI) nanoparticles or iron oxide nanoparticles, can react with hydrogen peroxide or other oxidizing agents to produce highly reactive radicals

332

A. Tiwari et al.

that can degrade antibiotics. AOPs involving nanoparticles are effective in breaking down complex antibiotic structures. Enzymatic Degradation: Nanoparticles can be functionalized with specific enzymes that possess antibiotic-degrading capabilities. These enzyme-functionalized nanoparticles can selectively bind to antibiotics and facilitate their degradation through enzymatic reactions. For example, nanoparticles coated with laccase or peroxidase enzymes have been used to degrade various antibiotics, including sulfonamides and tetracyclines. Catalysis: Nanoparticles with catalytic properties, such as palladium (Pd) or platinum (Pt) nanoparticles, can catalyze the degradation of antibiotics through various reactions, including hydrogenation, oxidation, or hydrolysis. These nanoparticles can break down the chemical structure of antibiotics and convert them into less harmful substances. Catalytic nanoparticles offer the advantage of high efficiency and selectivity in antibiotic degradation. Adsorption and Filtration: Nanoparticles with high surface area, such as activated carbon nanoparticles, can adsorb antibiotics from wastewater. The adsorption process involves the binding of antibiotics to the nanoparticle surface, effectively removing them from the water. Nanoparticle-based filtration membranes can also be employed to physically separate antibiotics from wastewater through size exclusion and adsorption mechanisms (Bhattacharya and Sharma 2021). Overview of AOPs for wastewater treatment Advanced Oxidation Processes (AOPs) are a class of treatment techniques used in wastewater treatment for the removal of organic and inorganic pollutants that are resistant to conventional treatment methods. AOPs involve the generation of highly reactive oxidizing species, such as hydroxyl radicals (•OH), which can effectively degrade and mineralize various pollutants. These processes are characterized by their ability to generate and utilize powerful oxidants to promote the degradation of contaminants. Combination of photocatalysis with other AOPs Combining photocatalysis with other Advanced Oxidation Processes (AOPs) can lead to synergistic effects and improved treatment efficiency for wastewater treatment. By integrating multiple AOPs, the generation of reactive species can be enhanced, and the degradation of various pollutants can be effectively achieved (see Fig. 11.13). Photocatalysis-Ozonation: The combination of photocatalysis and ozonation (photocatalytic ozonation) has been widely studied. In this approach, photocatalysis using semiconductor nanoparticles (e.g., TiO2 ) is employed to generate reactive species, such as hydroxyl radicals (•OH), which can initiate the degradation of pollutants. Ozone (O3 ) is then introduced into the system to react with the intermediates or byproducts generated during photocatalysis, thereby enhancing the overall degradation process.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

333

Fig. 11.12 Utilization of various nanotechnology approaches

Photocatalysis-Fenton/Photo-Fenton: Fenton and Photo-Fenton processes involve the use of ferrous ions (Fe2+ ) and hydrogen peroxide (H2 O2 ) to generate hydroxyl radicals (•OH). When combined with photocatalysis, the process is referred to as photocatalytic Fenton or photocatalytic photo-Fenton. The photocatalyst (e.g., TiO2 ) acts as a catalyst to promote the decomposition of H2 O2 , leading to the generation of •OH radicals for enhanced pollutant degradation. Photocatalysis-Sonolysis: The combination of photocatalysis with sonolysis (ultrasound treatment) can enhance the degradation of pollutants. Ultrasonic waves induce cavitation, which generates microbubbles that collapse and produce intense local heating and high-pressure conditions. This promotes the generation of reactive species and enhances the mass transfer of pollutants to the photocatalyst surface, leading to improved degradation efficiency. Photocatalysis-Electrochemical Oxidation: Electrochemical oxidation involves the application of an electric potential to induce oxidation reactions. When combined with photocatalysis, the electrochemical oxidation process can enhance the degradation of pollutants. The photocatalyst facilitates the formation of reactive species, while the applied electric potential promotes the oxidation reactions, resulting in

334

A. Tiwari et al.

synergistic effects for pollutant degradation (Zhang and Crittenden 2014; Dong et al. 2015; Wang et al. 2014; Chen and Pignatello 1997). Challenges and future prospects of AOPs in wastewater treatment Advanced Oxidation Processes (AOPs) have shown great potential for wastewater treatment due to their ability to degrade recalcitrant pollutants. However, several challenges and future prospects need to be considered for their widespread implementation and improvement. Some of these challenges and prospects are outlined below: Efficiency and Energy Consumption: AOPs often require significant energy inputs, especially in processes like ozonation and electrochemical oxidation. Improving process efficiency and reducing energy consumption are critical aspects of the practical application of AOPs. Development of novel catalysts, optimization of reaction conditions, and integration with renewable energy sources can help address these challenges. Catalyst Stability and Reactor Design: The stability of catalysts used in AOPs is crucial for long-term operation. Catalyst deactivation, aggregation, and loss can

Fig. 11.13 Various AOPs and the ROS

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

335

occur over time, reducing treatment efficiency. Furthermore, reactor design plays a vital role in achieving effective mass transfer and maximizing catalyst utilization. Ongoing research is focused on developing stable catalysts and innovative reactor designs to enhance AOP performance. Cost Considerations: The implementation of AOPs in large-scale wastewater treatment systems should be economically viable. The cost of catalysts, energy consumption, and maintenance should be considered. Advancements in catalyst synthesis techniques, catalyst recovery and reuse methods, and process optimization can help reduce costs and make AOPs more economically attractive. By-Product Formation: AOPs can generate byproducts during the oxidation process, which may have toxicity or persistence concerns. The identification and characterization of byproducts and their potential environmental impacts are crucial for ensuring the overall safety and sustainability of AOPs. Strategies to minimize byproduct formation and develop appropriate post-treatment methods for their removal need to be explored. Treatment of Emerging Contaminants: AOPs need to be further investigated and optimized for the removal of emerging contaminants, such as pharmaceuticals, personal care products, and endocrine-disrupting compounds. These compounds often exhibit resistance to conventional treatment methods and pose challenges to wastewater treatment plants. AOPs have shown promise in degrading emerging contaminants, and future research should focus on their specific degradation mechanisms and optimization for efficient removal. Process Integration and Optimization: AOPs can be integrated with other treatment processes, such as biological treatment or adsorption, to achieve comprehensive and efficient wastewater treatment. The optimization of process conditions, such as pH, temperature, catalyst loading, and reaction time, is crucial for achieving optimal performance and minimizing costs. Process modeling and simulation can play a significant role in optimizing AOPs and their integration with other treatment technologies. The future prospects of AOPs in wastewater treatment are promising. With ongoing research and technological advancements, AOPs have the potential to become more energy-efficient, cost-effective, and reliable for the removal of various pollutants. Furthermore, the integration of AOPs with other treatment processes and the development of hybrid systems can lead to synergistic effects and improved treatment efficiency. Continued efforts in catalyst development, reactor design, optimization, and monitoring techniques will contribute to the successful application of AOPs in wastewater treatment (Pera-Titus et al. 2004; Crittenden et al. 2005; Klamerth et al. 2018). Nanocomposites in Photocatalytic Systems Nanocomposites play a crucial role in enhancing the performance of photocatalytic systems for wastewater treatment. These materials combine the properties

336

A. Tiwari et al.

of different components to create synergistic effects, resulting in improved photocatalytic activity, stability, and selectivity. Nanocomposites typically consist of a photocatalyst (e.g., semiconductor nanoparticles) and another material, such as graphene, carbon nanotubes, metal oxides, or polymers. The integration of these materials offers several advantages in photocatalysis. Enhanced Photocatalytic Activity: The incorporation of nanocomposite structures can significantly enhance the photocatalytic activity compared to pure photocatalysts. The synergistic effects arise from the combined properties of different materials, such as increased light absorption, improved charge separation and transfer, and enhanced surface area. These factors contribute to higher pollutant degradation rates and overall treatment efficiency. Extended Light Absorption Range: Nanocomposites can expand the light absorption range of photocatalysts. By incorporating materials with different bandgap energies, such as metal oxides or carbon-based materials, the nanocomposites can absorb a broader spectrum of light, including visible light. This expands the range of pollutants that can be effectively degraded, as many organic pollutants absorb in the visible light range. Improved Photocatalyst Stability: Nanocomposites can enhance the stability and durability of photocatalysts. The presence of additional materials can protect the photocatalyst from photocorrosion, aggregation, and surface contamination, leading to a prolonged catalyst lifespan. This is particularly important for long-term applications in wastewater treatment. Enhanced Charge Carrier Separation and Transfer: Efficient charge carrier separation and transfer are critical for photocatalytic reactions. The incorporation of nanocomposite structures can facilitate the separation of photogenerated electron– hole pairs, reducing the chance of recombination and increasing the availability of active species for pollutant degradation. This leads to improved overall photocatalytic efficiency. Synthesis and properties of nanocomposite materials Synthesis and properties of nanocomposite materials play a crucial role in determining their performance and suitability for various applications, including photocatalysis in wastewater treatment. Here is an overview of the synthesis methods and key properties of nanocomposite materials. Synthesis Methods: Sol–Gel Method: This method involves the hydrolysis and condensation of precursor materials to form a sol, which is then transformed into a gel and subsequently dried or calcined to obtain the nanocomposite. The sol–gel method allows for precise control over the composition, structure, and morphology of the nanocomposite by adjusting the precursor concentrations and reaction conditions.

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

337

Co-precipitation Method: In this method, the precursor materials are simultaneously precipitated from a solution, resulting in the formation of nanocomposite particles. The co-precipitation method enables the formation of homogeneous nanocomposites with well-defined compositions, and it is relatively simple and cost-effective. Hydrothermal/Solvothermal Method: This method involves the synthesis of nanocomposites under high-pressure and high-temperature conditions in a closed reactor. The hydrothermal/solvothermal method allows for the formation of highly crystalline nanocomposites with controlled sizes, shapes, and structures. It is particularly suitable for the synthesis of metal oxide-based nanocomposites. Chemical Vapor Deposition (CVD): CVD is a gas-phase synthesis method that involves the deposition of precursor molecules onto a substrate under controlled temperature and pressure conditions. It allows for the growth of nanocomposites with precise control over the film thickness, composition, and structure. CVD is often used for the synthesis of nanocomposite thin films (Chen et al. 2017; Zhang et al. 2012).

11.5 Conclusion Photocatalysis has emerged as a promising technology for wastewater treatment due to its ability to efficiently degrade pollutants and promote environmental sustainability. Semiconductor nanoparticles, such as titanium dioxide (TiO2 ), have demonstrated excellent photocatalytic properties and are widely used as photocatalysts in various wastewater treatment applications. Nanoparticles offer a large surface area, high reactivity, and tunable properties, making them effective in the degradation of diverse contaminants. Throughout this chapter, we have discussed the fundamentals of photocatalysis, including the principles, mechanisms, and photocatalytic reaction pathways involved. We explored the role of semiconductor nanoparticles as photocatalysts and their synthesis and characterization techniques. Additionally, we examined the application of nanoparticles in wastewater treatment, specifically their effectiveness in the removal of heavy metal-containing compounds, degradation of biological substances, inactivation of algae, bacteria, and viruses, elimination of organic pollutants, nutrient removal and recovery, and antibiotic degradation. Furthermore, we explored the integration of photocatalysis with advanced oxidation processes (AOPs), such as ozonation, hydrogen peroxide, and fenton processes, to enhance the overall efficiency of wastewater treatment. The combination of photocatalysis with other AOPs allows for synergistic effects and improved removal of persistent and refractory pollutants. We also discussed the use of nanocomposites in photocatalytic systems, where the incorporation of nanoparticles into matrices or supports enhances the photocatalytic activity, stability, and selectivity. Nanocomposites provide opportunities

338

A. Tiwari et al.

for tailoring the properties of photocatalysts and optimizing their performance for specific wastewater treatment applications. While photocatalysis shows great potential, there are challenges and considerations that need to be addressed. These include the scale-up and implementation of nanoparticle-based photocatalysis, photocatalyst recovery and reuse, costeffectiveness and sustainability of the processes, as well as potential environmental impacts and safety considerations. It is crucial to conduct comprehensive studies, including life cycle assessments and risk assessments, to ensure the safe and environmentally sound implementation of photocatalytic systems. Overall, the application of nanoparticles and nanocomposites in photocatalytic wastewater treatment offers significant advantages in terms of pollutant removal, energy efficiency, and environmental sustainability. Continued research, technological advancements, and collaboration among researchers, industry, and regulatory bodies are necessary to overcome the challenges and further enhance the effectiveness and practicality of photocatalytic processes for wastewater treatment (Gaya and Abdullah 2008a, b; Li et al. 2021; Zhang and Zhou 2020; Chong et al. 2010; Puma 2014).

References Bhattacharya SK, Sharma A (2021) Nanotechnology for antibiotics degradation: a state-of-the-art review. In: Emerging technologies in environmental biotechnology. Springer, pp 183–200 Chen B, Dionysiou DD (2016) Photocatalysis and nanotechnology for environmental applications. Environ Sci Technol Lett 3(7):243–254 Chen J, Pignatello JJ (1997) Role of quenchers in the photomineralization of organic pollutants by semiconductor particles. Environ Sci Technol 31(8):2399–2406 Chen X, Liu L, Yu P (2017) Nanostructured semiconductor materials for environmental applications. Chem Rev 117(12):9433–9520 Chen X, Mao SS (2007) Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications. Chem Rev 107(7):2891–2959 Chong MN, Jin B, Chow CWK, Saint C (2010) Recent developments in photocatalytic water treatment technology: a review. Water Res 44(10):2997–3027 Crittenden JC, Hand DW, Perram DL (eds) (2005) Advanced oxidation processes for water and wastewater treatment. IWA Publishing Dionysiou DD, Pillai SC, O’Shea KE (eds) (2013) Photocatalysis and water purification: from fundamentals to recent applications. Royal Society of Chemistry Dong T, Jiang J, Ji M, Liu F, Qu J (2015) Combination of photocatalysis and sonolysis: a hybrid technology for water treatment. Chem Eng J 279:712–725 Gaya UI, Abdullah AH (2008a) Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress, and problems. J Photochem Photobiol c: Photochem Rev 9(1):1–12 Gaya UI, Abdullah AH (2008b) Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: a review of fundamentals, progress and problems. J Photochem Photobiol c: Photochem Rev 9(1):1–12 Ge H, Fang J (2020) Recent advances in the application of nanoparticles for wastewater treatment. J Nanosci Nanotechnol 20(9):5365–5381

11 Waste Management: Nano Photocatalysis as an Efficient Future Pathway

339

Khan MA, Ahmed S (2018) Recent advancements in the utilization of semiconductor nanomaterials for photocatalytic water treatment. Chem Eng J 335:424–437 Klamerth N, Malato S, Maldonado MI (2018) Advanced oxidation processes: mechanisms and applications. IWA Publishing Li J, Wu J, Chen Z, Megharaj M (2021) Photocatalyst recovery and reuse for sustainable photocatalysis. J Clean Prod 313:127999 Li P, Dionysiou DD (2019) Emerging challenges in semiconductor photocatalysis for environmental applications. Environ Sci Technol 53(18):10670–10687 Linsebigler AL, Lu G, Yates Jr JT (1995) Photocatalysis on TiO2 surfaces: principles, mechanisms Malakootian M, Ameri E, Fatehizadeh A (2019) Nanotechnology in wastewater treatment: a review on the synthesis, modification, and application of nanomaterials. J Water Process Eng 32:100928 Mills A, Le Hunte S (1997) An overview of semiconductor photocatalysis. J Photochem Photobiol a: Chem 108(1):1–35 Pablos C, Rey A (eds) (2016) Semiconductor photocatalysis: materials, mechanisms, and applications. Wiley Peral J, Ollis DF (1992) Photocatalytic purification and treatment of water and air. Elsevier Pera-Titus M, García-Molina V, Baños MA, Giménez J, Esplugas S (2004) Degradation of chlorophenoxy herbicides by means of advanced oxidation processes: a general review. Appl Catal B: Environ 47(4):219–256 Puma GL (2014) Environmental applications of semiconductor photocatalysis. Chem Eng J 256:399–417 Roy S, Rautela R, Kumar S (2023) Towards a sustainable future: nexus between the sustainable development goals and waste management in the built environment. J Clean Prod 415:137865 Tchobanoglous G, Theisen H, Vigil S (2014) Integrated solid waste management: engineering principles and management issues. McGraw-Hill Education UNEP (2021) Waste management. United Nations Environment Programme. https://www.unep. org/what-we-do/cross-cutting-issues/resource-efficiency/waste-management Wang H, Li X, Yang Y, Qu J (2012) Photocatalytic disinfection capabilities of TiO2 -based nanomaterials: progress and prospects. Appl Microbiol Biotechnol 95(2):297–312 Wang P, Yu H, Zhang S, Zhu L (2014) Combination of photocatalysis and electrochemical oxidation for wastewater treatment: a review. J Hazard Mater 266:84–93 World Health Organization (2016) Waste and human health: evidence and needs. World Health Organization. https://www.who.int/ceh/publications/waste/en Yang Y, Qu Y, Lian J, Zhao H, Zhang H (2017) Recent advances in the application of nanomaterials in water treatment and remediation. Environ Sci Nano 4(3):656–677 Zhang L, Crittenden J (2014) Combination of photocatalysis and ozonation for water and wastewater treatment: A review. Crit Rev Environ Sci Technol 44(24):2577–2641 Zhang Y, Zhou M (2020) Recent advances and challenges in nanotechnology for water and wastewater treatment. Chem Eng J 402:126191 Zhang Y, Li H, Yu J, Jaroniec M (2012) Hierarchical photocatalysts. Chem Soc Rev 41(23):7529– 7551 Zhang Y, Zhou R, Fu L, Ji J (2018) Nanomaterials for water treatment: opportunities and challenges. NanoImpact 10:174–200

Chapter 12

Light-Induced Conversion of Waste Biomass to Value-Added Chemicals Swati Dhamija, Rafia Siddiqui, Kumar Shivam, and Ranjan Patra

12.1 Introduction Light-induced conversion of waste biomass to value-added chemicals is a promising approach to address the increasing concern over the depletion of fossil fuels and the need for sustainable production of chemicals. Waste biomass such as agricultural and forestry residues, municipal solid waste, and industrial waste is a potential feedstock for the production of value-added chemicals viz. lignin, carbohydrates, and glycerol (Fig. 12.1) (Nwosu 2021). Every year, the world produces a staggering amount of around 998 million metric tonnes of agricultural waste (Periyasamy et al. 2022). That’s enough to fill more than 200 million Olympic-sized swimming pools! The country that contributes the most to this pile of leftovers is India, followed by China and Egypt in second and third places, respectively. However, the conversion of waste biomass to value-added chemicals is a complex and energy-intensive process. In this regard, light-induced conversion is an emerging technology that offers a sustainable and energy-efficient alternative to traditional conversion methods. The use of light as an energy source for biomass conversion has several advantages over traditional conversion methods such as light being a clean and renewable energy source, which means that it does not contribute to greenhouse gas emissions or other environmental pollutants. To be noted is that the light-induced conversion is a highly selective process, which allows to produce specific chemicals or compounds from the biomass feedstock. This selectivity can help to reduce waste and enhance the efficiency of the conversion process. This approach uses light as a clean and renewable energy source to drive the conversion of waste biomass to value-added chemicals such as platform chemicals and biofuels. The mechanism of light-induced biomass

S. Dhamija · R. Siddiqui · K. Shivam · R. Patra (B) Amity Institute of Click Chemistry Research & Studies (AICCRS), Amity University, Sector-125, Noida, India e-mail: [email protected] 341

342

S. Dhamija et al.

Fig. 12.1 Representation of conversion of the waste biomass into lignin, carbohydrates, and glycerol

conversion involves the absorption of light by the photocatalyst that produces electron–hole pairs (Li et al. 2019a). These pairs can interact with the biomass feedstock, leading to the formation of reactive intermediates that can undergo further reactions to produce the desired chemicals. The process may involve multiple steps including the activation of catalyst, adsorption of the biomass feedstock, and the formation of intermediates (Dessie et al. 2020). One potential application of light-induced biomass conversion is the production of platform chemicals, which are intermediate chemicals that can be further processed into a diverse array of chemical compounds that can be produced from biomass including sugars, organic acids, and alcohols (Banerjee et al. 2017). Although lightinduced biomass conversion offers many advantages, there are several obstacles that require attention and resolution. One obstacle is the development of efficient and stable photocatalysts that can operate under different conditions. Another challenge is the development of scalable processes that can be used in industrial settings. Additionally, the economics of light-induced biomass conversion must be competitive with traditional conversion methods. Research into light-induced biomass conversion is actively pursued, with new developments and applications emerging regularly. For example, Myohwa Ko et al. created a fusion catalytic system that uses solar energy to selectively transform lignin, the main component of wood wastes, into higher value-added compounds (Ko et al. 2019). Some future directions for research in this area include the development of new photocatalysts, the optimization of conversion conditions, and the integration of light-induced conversion with other technologies, such as biorefineries. Additionally, the development of novel applications to produce value-added chemicals from waste materials may lead to the formation of new markets and opportunities for sustainable

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

343

chemical production. Overall, light-induced conversion of waste biomass to valueadded chemicals is a promising approach to sustainable chemical production. The technology offers several advantages over traditional conversion methods, including reduced environmental impact, increased selectivity, and the potential to create a circular economy for waste materials. As ongoing study in this field progresses, it is probable that novel and pioneering applications of this technology will emerge and hence enhance the scope for sustainable chemical production.

12.1.1 Photocatalyst Photocatalytic reactions have a unique advantage over many other catalytic processes due to their environmentally friendly nature. They can be conducted under regular atmospheric pressure and at room temperature, which is a significant departure from the often-demanding conditions required by other catalytic reactions. The International Union of Pure and Applied Chemistry (IUPAC) defines photocatalysis as a process where the rate of a chemical reaction is influenced or initiated by certain types of light, such as ultraviolet, visible, and infrared radiation. This occurs in the presence of a substance called a photocatalyst which has the remarkable ability to absorb light and actively participate in the chemical transformation of reactants. However, it’s essential to note that the term “photocatalysis” can also be used to describe other photochemical or photo-initiated thermal reactions which can create confusion in defining the concept precisely. In this chapter, we adopt a broad definition of photocatalysis that includes both ligand-to-metal charge transfer (LMCT) and photo-sensitized reactions, acknowledging the complexity in distinguishing these processes from traditional photocatalytic mechanisms. It’s important to recognize that a thorough exploration of the intricate mechanisms involved in photo-initiated or -assisted degradation is beyond the scope of this discussion. Photocatalysis is a promising technique for industrial processes as it offers both environmental and economic advantages. It uses solar energy as a clean and renewable source of power which can help restore the environment, lower the emission of greenhouse gases, and cut down the costs of production and maintenance compared to that of fossil fuels. Various materials can act as photocatalysts such as titanium dioxide, zinc oxide, cadmium sulfide, metal oxide, and perovskite. A good photocatalyst should be highly effective, stable, and durable for a long time. Photocatalysis has many applications, such as wastewater treatment, bacteria disinfection, hydrogen production, and carbon dioxide removal (Jiang and et al. 2012). Because of its versatility, photocatalysis also has great potential in a new application such as biogas production, aromatic chemicals from lignin, glycerol oxidation into different chemicals, and many more applications.

344

12.1.1.1

S. Dhamija et al.

Photocatalyst Mechanism

Photocatalysis relies on a type of material called a semiconductor which has a gap between two energy levels: the valence band (VB) and the conduction band (CB). The valence band is where the electrons (e) normally reside, while the conduction band is where they can move freely. When light energy with enough photons hits the semiconductor, some electrons get excited and jump from the VB to the CB, leaving behind holes (h). These charge carriers (e and h) then migrate to the semiconductor surface and undergo a chemical reaction with other substances by transferring or accepting electrons (Kumar et al. 2017). Usually, the electrons in the CB reduce the substances into positively charged ions, while the holes in the VB oxidize them into negatively charged ions. What makes photocatalysis so versatile is that the charge carriers can produce different kinds of active species depending on what substances they react with. These active species can then be used for various applications, such as cleaning water, making hydrogen, and converting carbon dioxide. The key to photocatalysis is to generate the right active species for each application.

12.1.1.2

Factors Affecting Photocatalyst

The performance and quality of a photocatalyst depend on several factors that need to be considered during its synthesis. One of these factors is the band gap which determines the light absorption of the photocatalyst. The band gap is the difference in energy between the VB, where the electrons are normally located, and the CB, where they can move freely. The photocatalyst can only absorb light that has enough energy to excite the electrons from the VB to the CB, where they can participate in redox reactions. Another factor is the crystallinity, which is the degree of order and alignment of the molecules in the photocatalyst. A higher crystallinity means a smoother and more uniform flow of charge carriers which reduces the chances of them getting trapped or recombined. This allows them to reach the surface of the photocatalyst faster and react with other substances. The specific surface area is also an important factor as it affects the number of substances that can be adsorbed on the photocatalyst (Granone et al. 2018). A larger surface area means more contact points and more opportunities for reactions to occur. The size of the photocatalyst particles also matters as it influences the resistance and diffusion length of the charge carriers. Smaller particles have lower resistance and shorter diffusion length which means less energy loss and more efficient charge transfer (Kumar et al. 2017). Finally, the reusability of the photocatalyst is a desirable factor, as it indicates how long the photocatalyst can maintain its activity and stability. A good photocatalyst must possess the capability to withstand recurring cycles of reactions without losing its effectiveness or requiring extensive treatment. By optimizing these factors, a photocatalyst can be a powerful tool for converting waste into useful energy sources.

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

12.1.1.3

345

Composition of Biomass

The wastage of farming practices and the processing of farm goods, such as poultry, fruits, vegetables, dairy, and crops, are composed of agricultural waste. Cellulose composition categorizes these wastes as lignocellulosic, for example, sugarcane bagasse, spent coffee grounds, spent grain, fiber of coconut, corn, and its by-products as non-lignocellulosic, exemplified by a membrane of eggshell waste materials (Agopyan et al. 2005; Viswanathan 2020; Wang et al. 2008; Gismatulina et al. 2022; Mathias et al. 2015). Plant biomass mainly consists two types of the polymers: one is carbohydrate polymer cellulose and hemicellulose and another is aromatic polymer, i.e., lignin (lignocellulose) (Fig. 12.2). Lignocellulose is a complex material with hemicellulose and cellulose which are encapsulated with the lignin matrix. Cellulose fibers stick to hemicellulose and lignin via H-bonds, while hemicellulose forms covalent bonds with lignin. On average, lignocellulose contains the approximate amount of lignin (10–25%), cellulose (30–45%), and hemicellulose (25–35%), but this proportion varies with different plants. However, less than 5–6% carbohydrates biomass is used by humans’ various purposes (Table 12.1). A substantial portion of these resources is often deemed waste and the remained is still unused. Typically, this waste is used in the paper and pulp industries, but generating large amounts of heat and energy from it has a negative impact on a global scale. Using a huge amount of edible plants for making certain kinds of biofuel such as (bioethanol and biodiesel) can take up a lot of land and harm the food availability worldwide. So, recent research has been looking into how to use non-edible or waste materials from growing food crops in a better way.

Fig. 12.2 Lignocellulose: An illustrated overview of its structure

346

S. Dhamija et al.

Table 12.1 Chemical Composition of Biomass Sources: Lipids, Carbohydrates, and Lignin Percentages Biomass sources

Lipids (%)

Carbohydrates (%)

Lignin (%)

Refrences

Coconut fiber

0.3

50.0

14.0

(Agopyan et al. 2005)

Hemp

4.2

37.8

18.5

(Viswanathan 2020)

Jute

1.5

55.0

15.0

(Wang et al. 2008)

Miscanthus

2.8

40.5

22.0

(Gismatulina et al. 2022)

Sunflower stalks

1.0

48.2

23.7

(Mathias et al. 2015)

Bamboo

0.6

45.0

30.5

(Yang et al. 2022)

Poplar wood

1.8

44.0

20.0

(Liu et al. 2022)

Peanut shells

3.5

38.0

18.5

(Sareena et al. 2013)

Bagasse (Sugarcane)

2.2

41.5

26.0

(Kim et al. 2010)

Corn cobs

1.2

46.8

21.3

(Prasad et al. 2007)

Apple pomace

0.7

50.5

24.0

(Lobo et al. 2019)

Olive pomace

6.0

35.5

14.2

(Skaltsounis et al. 2015)

Sorghum stalks

1.4

47.5

22.5

(Xu et al. 2020)

Water hyacinth

3.2

41.0

9.5

(Chaiwarit et al. 2022)

Cellulosic biomass

0.9

60.0

10.0

(Gutiérrez-Antonio et al. 2021)

Carbohydrates and lignin are the two main components of the composition of biomass, making them pivotal in the manufacturing of various components particularly in the context of photocatalytic biomass conversion. In crops, carbohydrates make up to 75% of the dry mass, while lignin comprises the second largest portion, accounting for 10% to 20% of the dry mass and the remaining mass consists mainly of glycerides (triglycerides), which are also known as lipids. The exact composition can vary substantially depending on the plant type. For instance, softwood conifers may contain approximately 40% mass of the lignin and relatively less amount of carbohydrates. Plants contain two primary types of carbohydrates such as starch and insulin (whose main function is to store energy) as well as structural polysaccharides (cellulose and hemicelluloses). Given concerns about using edible biomass as a feedstock due to its potential impact on food supply, recent research has shifted its focus toward non-edible biomass sources or waste stream-derived biomass. This shift represents significant progress in terms of sustainability because it avoids competition with food resources, a key argument against scaling up promising photocatalytic processes. Cellulose, the main carbohydrate source in plants, is mostly indigestible among humans and animals. Consequently, it has emerged as the best source used for the production of various chemical components and a variety of fuels. Thermal catalysis

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

347

and biotechnology have been used to convert cellulose into alcohols, sugars, and valuable chemicals. The production of sugars provides a foundation for synthesizing a variety of chemicals referred to as the sugar-derived stage for various molecules. These sugars can be produced via direct–indirect methods from the carbohydrates present in nature, which contribute to the bulk of biomass. The usage of edible crops in such large amounts poses a significant sustainability challenge to the industries. Nevertheless, the well-established saccharide molecules offer versatile raw materials for a variety of chemical synthesis, potentially mitigating this issue. Converting nonedible feedstocks like glycerol or lignin into sugar-derived molecules also offers a convenient solution to this dilemma. Lignin is a complex bio-polymeric molecule with a 3-D framework of polyphenols. Natural lignin structures are highly intricate, varying in molecular masses and their composition depends upon the material generated from the source. Lignin is an inherent part of shrub cells and is typically a by-product of pulp and paper manufacturing. Unlike starch, cellulose, and hemicelluloses which find various industrial applications, lignin has been underutilized due to its resistance to degradation. From the data, we have an overall production of 70 million tons of lignin annually, with the majority being used up for the paper industries and mills. However, the aromatic components derived from lignin produced a high-value variety of aromatic compounds that cannot be obtained from plants (such as cellulose and hemicelluloses). While the plants containing cellulose and other carbohydrates have been successfully converted into valuable non-aromatic chemicals, lignin’s industrial applications remain limited, mainly involving the formulation of adhesives (like glues, pastes, and gums) and dispersants. Nevertheless, lignocelluloses offer a substantial and renewable carbon source, potentially serving as an alternative to fossil resources. Lipids can be converted to biodiesel (it’s a fatty acid methyl ester), through a process called transesterification. Biodiesel production represents a substantial and growing application of biomass with imperative demand in the European Union alone. The first generation of biodiesel primarily focused on edible oils (such as vegetable oil), while the second generation shifted toward non-edible oils, and third generation was motivated to use sustainable sources like microalgae. The main byproduct obtained from biodiesel is glycerol with approximately 100 g of glycerol produced for every kilogram of biodiesel. However, challenges, such as removing the high amount of free fatty acid content, have limited use of glycerol. Recently, it has been demonstrated that these challenges can be overcome by using dual-functional catalysts and utilizing the second generation of lipids (microalgae or non-food crops as sustainable feedstocks). This purest glycerol can then be directly used in various chemical industries.

348

S. Dhamija et al.

12.2 Applications 12.2.1 Photocatalysis in Useful Chemicals The light-inducing conversion of residual and waste biomass into valuable chemicals is a promising technology for a range of potential applications across various industries.

12.2.1.1

Sugar

Sugar is the most affordable monosaccharide and highly abundant in nature, and polysaccharides like cellulose and starch can easily convert into glucose. Glucose, a hexose containing six carbon atoms, exists primarily in two forms: an open chain structure and a cyclic structure. In its open-chain configuration, the glucose exhibits a straight line and unbranching 6-carbon atoms. Carbon1 (C1 ) is associated with an aldehydic group, while the remaining 5-carbons each carry hydroxyl group. Consequently, the glucose molecule is commonly referred to as aldose or aldohexose. The presence of the aldehyde group in glucose classifies it as a reducing sugar leading to a positive reaction when exposed to Fehling’s solution. The cyclic form of glucose forms with an intra-molecular reaction between the aldehyde atom at C1 and the OH (hydroxyl group) at C5 , forming an intra-molecular hemiacetal molecule. The selective glucose oxidation can yield a diverse array of valuable chemicals, including arabinose, gluconic acid, formic acid, and xylitol (Fig. 12.4). These products serve as fundamental chemicals used across a wide range of applications. For example, gluconic acid is a versatile chemical with various uses, including as an edible additive, concrete retarder, medical usage intermediate, precursor for polymers (biodegradable), cleaning agent, water treatment chemical, cosmetic ingredient, and agricultural aid and in photography (Climent et al. 2010). Glucaric acid, seen as a valuable chemical derived from biomass, works as an important key in the production of biodegradable polymers particularly in the creation of unique plastics like new nylons and hyperbranched polyesters (Kiely et al. 2002). A few other applications are water treatment as a corrosion inhibitor, dietary supplements for health benefits, chemical synthesis, cosmetics, and potential pharmaceutical applications. Formic acid also acts as a precious intermediate that is often involved in various chemical synthesis. Furthermore, formic acid has great potential to be an outstanding hydrogen carrier due to its ability to release hydrogen through dehydrogenation under milder conditions using catalysts (Guerriero et al. 2014). The conventional oxidation of glucose molecules has been thoroughly examined via fermentation technique and aerobic catalytic oxidation processes (Suriyachai et al. 2020; Benkó et al. 2014). However, the fermentation of glucose is a slow process that highly depends upon the enzymatic activity. The nanoparticles of metals such as Au, Ag, Pd, and Pt are used for aerobic oxidation under high temperature and pressure conditions; due to these, the expensive metal catalysts

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

349

show low-performance activity under harsh temperature and pressure conditions. In recent years, heteroatomic photocatalysts have been used for transformation of glucose (Table 12.2). The photocatalysts incorporated solar energy under normal temperature and pressure conditions. TiO2 -based catalysts are used in large scale for light-induced conversion due to its non-toxic, stable under light irradiation and its chemical or biological inertness. A TiO2 photocatalyst in powdered form was created using a sol–gel method that was enhanced by ultrasound. This catalyst was specifically designed for the targeted conversion of glucose into three compounds: glucaric acid, gluconic acid, and arabitol Table 12.2 Photocatalytic conversion of glucose Photocatalyst

Light source

TiO2 powder

Conversion (%)

Products (%)

References

Hg-lamp (125 10 W)

11

Gluconic acid, glucaric acid, and arabitol (total 71.3)

(Colmenares et al. 2011)

Nano-TiO2

Hg-lamp (125 9 W)

~100

Formic acid (35)

(Jin et al. 2017)

AuNPs/TiO2 with 3 Wt% Gold

UV-light (λ 360–400 nm, 0.3 Wcm−2 )

99

Gluconic acid (94) (Zhou et al. 2017)

Visible-light irradiation (λ 430–780 nm, 0.3 Wcm−2 )

99

Gluconic acid (99)

H-ZSM-5/ FePz (SBu)8

Xe-lamp (1.70 4 W cm−2 , λ > 410 nm)

35.8

Gluconic acid (31.9), Glucaric acid (13.1), Arabinose (17.3), Glycerol (1.7), Formic acid (13)

(Chen, et al. 2019)

SnO2 / FePz(SBu)8

Xe-lamp (2 Wcm−2 )

3

34.2

Formic acid (6.4), Glucaric acid (12.9), Gluc-nic acid (32.9)

(Zhang et al. 2019)

TiO2 /HPW/ CoPz

Xe-lamp (1.70 3 Wcm−2 )

22.2

Glucaric acid (-16.9), Gluconic acid (63.5)

(Yin et al. 2020)

B/N-doped TiO2

Hg-lamp (450 3 W, 250–365 nm)

93.1

Arabinose (30), (Suriyachai Xylitol (6), Formic et al. 2020) acid (46) Gluconic acid (6.5)

97.7

Arabinose (30), Xylitol (9), Formic acid (35) Gluconic acid (6.5)

Ag/N-doped TiO2

Irradiation time (min)

4

350

S. Dhamija et al.

through a photo-oxidation process. To achieve desirable product results, Colemenras and co-workers utilized a solvent mixture consisting of acetonitrile and water in a 50:50 volume-to-volume (v/v) ratio. Acetonitrile played a crucial role as a “stabilizing agent” on the TiO2 surface, and the observed high selectivity for carboxylic acids can be attributed to these acids having a reduced affinity for the TiO2 surface in the presence of acetonitrile. Within a span of 10–15 min of irradiation, the yield of glucose conversion reached as high as 11%, accompanied by an impressive total organic selectivity of 71.3%. It’s worth to mention that an excess of water in the reaction mixture could lead to an elevated concentration of non-selective hydroxyl radicals (•OH) (Colmenares et al. 2013a). A new zeolite Y-TiO2 catalyst selectively produces gluconic and glucaric acids up to 68% yield. The desorption of organic acids over zeolite framework is facilitated by the electrostatic repulsion between the negatively charged sites and carboxylic acids. This repulsion effectively hinders the subsequent mineralization of these organic compounds (Colmenares et al. 2013a). Doping TiO2 zeolite with Fe3+ or Cr3+ ions slightly reduces the band gap to 2.3 eV and 3.04 eV respectively, compared to the generally accepted value of 3.2 eV for anatase TiO2 . This modification results in a 7% conversion of glucose into glucaric and gluconic acids. However, the key advantage is the significantly increased selectivity with Fe-doped zeolite achieving 94.3% selectivity and Cr-doped zeolite achieving 87% selectivity for these target products (Colmenares et al. 2013b). Co-doping of TiO2 zeolite with foreign elements like boron (B) and nitrogen (N) is not commonly reported. When such Co-doping occurs, it results in the formation of localized states near the conduction band (CB) and valence band (VB) in the band gap of TiO2 . This Co-doping can have interesting electronic effects on the TiO2 lattice: excitations to CB of TiO2 responsible for Shift of absorption band toward visible region (Suriyachai et al. 2020). In Ag/N doped on the TiO2 lattice, Ag plays a crucial role in enhancing the separation of charges between different energy bands. This improved charge separation, in turn, leads to an increased active surface area resulting in the formation of a higher number of hydroxyl radicals (•OH). These hydroxyl radicals, upon further oxidation, contribute to the production of desirable glucose-derived products (Benkó et al. 2014). In a study conducted by Chong et al., using a rutile TiO2 -based photocatalyst in an aqueous solution, which is a novel approach to directly convert glucose into sugar aldoses (such as erythrose and arabinose) and hydrogen (Chong et al. 2014a). Herein, the researchers achieved a glucose conversion rate of 65% and a total selectivity of 91% for sugar aldose. The selectivity of the products depended on the reactive oxygen species [hydroxy radicals and peroxy radicals] derived from water. To be noted, when highly oxidative hydroxyl radicals (•OH) were present, lower product selectivity was observed, whereas mild active peroxy species resulted in higher selectivity. A research led by Da Vi and co-workers conducted a study on the selective photooxidation of glucose using visible light (Vià et al. 2017). They observed that UVA light caused extensive mineralization of glucose through a non-selective pathway. However, when glucose was exposed to visible light, the mineralization process was completely suppressed, and products like formic acid, gluconic acid, arabinose, glyceraldehyde, and erythrose were obtained (Fig. 12.3); variation in product selectivity

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

351

may be attributed to the ligand-to-metal-charge-transfer (LMCT) effect, which arises from the light-induced activity generated by the adsorption of glucose on the surface of TiO2 under visible light. A similar effect was observed when TiO2 was replaced with zeolite (ZeY) and metals; it enhances the photocatalytic conversion of glucose to carboxylic acids (formic and gluconic acids) (Roongraung et al. 2020). After the reduction of the ratio of silica-alumina in the zeolite (ZeY) the product conversion for carboxylic compounds increases, primarily because of the increment of positive charge present in the zeolite structure. This increase in positive charge facilitated the enhanced conversion of glucose. Moreover, incorporating metal loading into the photocatalyst enhanced its electronic conductivity, resulting in improved charge separation and enhanced photocatalytic capabilities. Jin et al. demonstrated a remarkable level of selectivity in the photo-oxidation of glucose (or xylose) into formates by manipulating the surface charge of nanoTiO2 under ambient temperature conditions using an aqueous alkaline solution of NaOH (0.03 M) (Jin et al. 2017). The presence of OH ions played a crucial role in

Fig. 12.3 Photocatalytic conversion of glucose into various products

352

S. Dhamija et al.

Fig. 12.4 Chemical structure of TiO2 -glucose complexes

promoting the generation of active oxidative radicals, including hydroxyl radical (•OH) and (•O2 ), which promotes the higher yield of generating formate from glucose. Adjusting the surface charge for TiO2 facilitates effective adsorption of glucose and efficient desorption of formates. Chemical structures of monodentate and bidentate TiO2 -glucose complex responsible for the LMCT and photocatalytic degradation of glucose under visible light are shown in (Fig. 12.4) (Kim et al. 2015). The effectiveness of a photocatalyst is influenced by three key factors: the mobility of charges, the efficiency of separating electron–hole pairs, and the speed at which the active species are generated. Nevertheless, it’s important to note that the interaction between the substrate and the surface of the photocatalyst is occasionally neglected. Yet, this interaction is precisely what holds significant importance and can offer fresh insights into the reaction mechanism. Kim et al. concluded that the direct transfer of electrons from the highest occupied molecular orbital (HOMO) of glucose to the conduction band (CB) of TiO2 is more efficient when facilitated by the metal– organic framework (Kim et al. 2015). Under visible light absorption conditions, a glucose conversion rate of 42% was achieved with selectivity of 7% for gluconic acid and 93% for other oxidative products. Zhou et al. reported Au nanoparticle-infused TiO2 in aqueous solution of Na2 CO3 which gives selective and efficient oxidation of glucose under UV light as well as visible light (Fig. 12.5) (Zhou et al. 2017).

12.2.1.2

Cellulose

Cellulose is the principal component of non-edible lignocellulosic biomass along with hemicellulose and lignin, constituting 35–50% of its weight. It provides plant cell wall the strength, stability, and fiber. Cellulose (C6 H12 O5 )n is a known simple structural polysaccharide having β-1,4-glycosidic linkage bonds between the equatorial OH (hydroxyl group) groups of C4 and the C1 carbon atoms (Liu et al. 2019). The degree of polymerization (DP) in cellulose is determined by the quantity of homopolymer β-D anhydro glucopyranose units (AGUs) present. Cotton and other

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

353

Fig. 12.5 Glucose oxidation via Au/TiO2 under UV–Visible light

similar fibers exhibit a high degree of polymerization (DP), ranging from 800 to 10,000 while wood pulp possesses a lower DP, typically falling within the range of 300 to 700. A substantial quantity of hydroxyl groups positioned along the cellulose structure establishes both intra- and inter-molecular hydrogen bonds with oxygen atoms either on the same chain or on adjacent ones. These bonds make the chains stick together tightly, forming strong microfibrils. Consequently, dissolving cellulose without chemical alteration in typical solvents is a rather challenging endeavor. It was reported that concentration ZnCl2 successfully breaks the hydrogen bond between cellulose. It’s important to mention that breaking the β-1,4-glycosidic bonds between two anhydro glucose units to create glucose is the initial step for other chemical changes (Huang et al. 2013). This process is quite tough because of the cellulose’s strong crystalline structure and the strong bonding that happens between its molecules, both within and between them. More recently, it was found that, beyond the production of hydrogen, the direct hydrolysis of cellulose driven by photocatalysis offers a unique and sustainable method for fabricating valuable biochemicals including 5-hydroxymethylfurfural (HMF), arabinose, and glucose under milder conditions (Liu et al. 2019; Zhang et al. 2018a). In contrast to conventional heating techniques, localized surface plasmon resonance (LSPR) is inducing photo-thermal heating to facilitate the biomass conversion proves to be a more efficient and direct approach when targeting specific reaction sites. To promote the hydrolysis of cellulose, Zhang et al. reported an Ir/ HY (Iridium H-form Y-zeolites) photocatalyst, which was exposed to visible-light irradiation at temperatures below 100°C (Zhang et al. 2018a) (Table 12.3). In the photocatalyst, Ir-nanoparticles are the photo-thermal sources, which convert light energy into thermal energy, while the acidic site of HY (H-form Y-zeolites) served as the primary reaction center for hydrolysis. The combined effect of acidic sites and plasmonic Ir-nanoparticles simultaneously enhanced the breakdown of cellulose β-1,4-glycosidic linkages, enabling efficient and highly selective hydrolysis

354

S. Dhamija et al.

(>99%). This process under mild conditions has yielded value-added chemicals such as 5-hydroxymethylfurfural (HMF), cellobiose, and glucose. Similarly, a plasmonic nanostructure composed of Au-nanoparticles supported on TiO2 nanofibers with zeolite was developed by Wang et al. which is denoted as Au-HYT. The nanostructure effectively enhanced cellulose degradation with collective yield 60% of glucose and 5-hydroxymethylfurfural (HMF), and it represents as a potential pathway for cellulose hydrolysis to occur over Au-HYT (Wang et al. 2015) (Table 12.3). The presence of (Au) gold nanoparticles promotes the polarized E-field (electrical field) of extra-framework cations within the zeolite, thus inducing LSPR effect. Firstly, this leads to an increase in acidity and elongation of polarized bonds. Secondly, the elongation of these bonds results in a higher (-ve) negative charge on oxygen atom in the β-1,4-glycosidic bond, facilitating its cleavage and generating glucose along with a positively charged carbo-cation, and third this cation readily undergoes hydrolysis to produce a proton (H + ) and glucose. Subsequently, zeolite promotes dehydration of glucose to form (5-hydroxymethylfurfural)HMF. Overall, this proposed mechanism emphasizes the collaborative effect of acid catalysis and plasmonic nanoparticles, where the polarized E-fields of zeolites enhance acid strength through the LSPR effect of plasmonic gold nanoparticles. Their conclusion highlights that as the intensity of light increases, the conversion of cellulose into glucose also rises, providing evidence of the enhanced LSPR effect. Fan and co-workers conducted a separate investigation where they showcased the direct photodegradation of cellulose utilizing TiO2 in a concentrated ZnCl2 solution under UV irradiation (Fan et al. 2011). As a result, the main product obtained from this process was (5-hydroxymethylfurfural)HMF. ZnCl2 played a vital role in disrupting the hydrogen bonding network within cellulose, thereby promoting the cleavage of glycosidic linkages and facilitating the hydrolysis of monosaccharides derived from cellulose degradation. In addition, the combination of photocatalytic cellulose hydrolysis with H2 evolution through water splitting offers a significant enhancement in solar-driven hydrogen production. This approach eliminates the need for expensive sacrificial agents and simultaneously converts cellulose into valuable chemicals (Zhang et al. 2016, 2018b; Zou et al. 2018). During the photoconversion process, either cellulose or its intermediate compounds donate electrons to photoinduced holes, hydroxyl radicals, and O2 generated from water cleavage. As a result, cellulose undergoes oxidation, leading to the formation of valuable organic products such as sugars, (5-hydroxymethylfurfural)HMF, and formic acid. Consequently, the occurrence of recombination between photogenerated electrons and holes, as well as the reverse reaction between hydrogen and oxygen, can be significantly minimized, thereby allowing for more efficient photochemical processes.

12.2.1.3

Lignin

Lignin, constituting 15–30 wt% of biomass, is chemically composed of three phenolic units: p-hydroxyphenyl (H), syringyl (S), and guaiacyl (G). These units are cross-linked with various chemical bonds, including β-O-4, α-O-4, β-β, and β-5

Media

Water, EMIMCI

Water, EMIMCI

Water

Water

Photocatalyst

Au-HYT

Ir/HY3

P25-SO4 2− Nix Sy

TiO2 /NiO@Cg

N2

N2

NA

NA

Atmosphere

Table 12.3 Photocatalytic conversion of cellulose

Xenon lamp (500 W)

Xe lamp (500 W)

Xe lamp (300 W, 420–800 nm)

Visible light (0.5 W/cm2

Light source

5

3

8

16

Irradiation time (h)

80

80

90

140

temperature (C)

References

(Zhang et al. 2018a)

(Hao et al. 2018) (Zhang et al. 2018b)

Cellobiose (10.9), Glucose (40.4), HMF (24) H2 (181.2 μmol) H2 (82.9 μmol h−1

Glucose (yield (Wang et al. 2015) 48.1), HMF (yield 10.6)

Product (selectivity, %)

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals 355

356

S. Dhamija et al.

(Parthasarathi et al. 2011). Due to its abundance, lignin is considered as a valuable renewable resource for producing aromatic chemicals. Extensive reviews have been conducted on thermal and catalytic processes for lignin utilization (Parthasarathi et al. 2011). Additionally, discussions have taken place regarding cutting-edge innovations in catalyst development and photoreactor design for the photocatalytic conversion of lignin into valuable chemicals (Xiang et al. 2020; Li et al. 2016). Photocatalytic transformation of lignin involves two main steps: depolymerization of lignin into oligomeric fragments and subsequent conversion of functional groups. Among the inter-aromatic linkages in lignin, the β-O-4 linkage is the most predominant, accounting for 45–62% of ether moieties (Zakzeski et al. 2010). Therefore, the efficient and selective cleavage of the β-O-4 bond is the primary focus in most photocatalytic processes for lignin valorization. Mechanistic investigations have proposed three reaction pathways for selectively cleaving the C-O bond in the β-O-4 linkage: oxidative cleavage: (initiated by holes/oxidative species); reductive cleavage: (promoted by electrons/reducing agents); and redox-neutral cleavage: (using a combination of holes/oxidative species and electrons) (Xiang et al. 2020). In reductive lignin depolymerization, the cyclic lignin complex reacts with photogenerated e- or reducing agents, leading to the C-O bond breaking and the rearrangement of the complex. As an example, lignin is modified with nitrogen by Li and coworkers to construct oximes (acetyl) as a nucleophilic agent to selectively cleave the aryl ether bond (Li et al. 2019b). Herein, phenothiazine (PTH) acts as a photoexciting agent to reduce the N–O bond and generate iminyl radicals from acetyl oxime which attack the aryl C-O bond. Primary arylamine and α-hydroxy ketone are produced by the cleavage of aryl C-O further H-abstraction and hydrolysis. Also, ascorbic acid acts as a reducing agent thereby inhibiting further oxidation of the products. Notably, the β-O-4 bond in oxidative lignin is degraded by targeting the cleavage of C-O and/or C–C bonds leading to the formation of reactive oxidative products. Various mechanisms have been proposed based on specific photocatalytic systems, the first being light-induced conversion of a lignin compound (veratryl alcohol) forming veratraldehyde with high selectivity (76%) and the second being superoxide anion radicals formed due to the reduction of one electron between triplet chlorophyllin and oxygen (Pan 2020). Active species (pyridinium chlorochromate) formed by light-induced cleavage of β-O-4 bond in lignin over Ni/TiO2 oxidizes β-O-4 alcohol to produce ketone (Fig. 12.6). β-O-4 alcohol produces phenol and acetophenone derivatives via hydrogen atom abstraction and protonation. Sunlight-enhanced Fenton reactions selectively convert lignin compounds into valuable aromatic products. For example, using partially reduced graphene oxides (rGO) decorated with nanoparticles (CuFe2 O4 ) act as a photo-active catalyst to obtain high selectivity (72.6%) of guaiacol from lignin.

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

357

Fig. 12.6 Photocatalytic cleavage β-O-4 alcohol to produce bonds with ketone

12.2.1.4

Glycerol

Gu and Jérôme discussed the possibility to use glycerol as a green solvent as it exhibits low toxicity with high biodegradability. Recent progress in glycerol oxidation through thermo-, electro-, and photocatalysis was highlighted in a review by Dodekatos and co-workers (Dodekatos et al. 2018). Photocatalysis is an innovative strategy that holds significant promise for the production of fine chemicals from glycerol. Light-induced conversion offers a compelling avenue for selectively converting glycerol into a range of valuable chemical components, such as formic acid, glycolic acid, DHA (Dihydroxyacetone), and oxalic acid. The two photocatalysts (Evonik P25 and Merck) of TiO2 can follow different reaction pathways for glycerol oxidation over TiO2 as indicated through mechanistic studies. This can be utilized to control both product yield and selectivity (Minero et al. 2012). The mechanistic studies show that the Merck TiO2 oxidized glycerol into glyceraldehyde and DHA followed by hydroxyl radical (•OH)-mediated mechanism, whereas the substratemediated recombination mechanism leads to the production of glycolaldehyde and formaldehyde via Evonik P25 TiO2 (Minero et al. 2012). For the synthesis of lactic acid, Evonik P25 and Merck catalysts gives turnover number (TONs) of 30,000 and selectivity greater than 95% at 69% conversion of glycerol. Zhang et al. recently discovered light-induced oxidation of glycerol using sol–gel encapsulated, impermeable, and flower-shaped Bi2 WO6 microparticles decorated into silica-based material (SiO2 xerogels) (Fig. 12.7) (Zhang, et al. 2013). The research shows that glycerol. preferentially oxidized the secondary OH group under aerobic conditions showcasing the remarkable encapsulation effect of the silica material on the photocatalyst Bi2 WO6 thereby improving the yield of the resulting product hydroxyacetaldehyde (HAA) in an aqueous solution. The photocatalyst Bi2 WO6 (exhibiting high selectivity and activity) converts glycerol to DHA by giving 96% selectivity to glycerol over 91% selectivity to DHA. We can attribute this to the mild oxidation potential of Bi2 WO6 , the weaker adsorption capacity of DHA compared to glycerol, the absence of unselective OH radicals, DHA’s stability in the reaction system, and regioselective oxidation of glycerol’s secondary OH group. Mendoza et al. observed that the selectivity of glyceraldehyde or DHA from glycerol light-induced oxidation is enhanced

358

S. Dhamija et al.

Fig. 12.7 Reaction mechanism of formation of hydroxyacetone from glycerol via Bi2 WO6 (UVirradiation)

through the Fenton process using Fe-Pillared clay, in comparison to typical TiO2 (Mendoza et al. 2020). This also depends on catalyst loading, affecting the concentration of reactive oxidative species (e.g., hydroxy radicals) formed by the dissociation of in situ produced H2 O2 . Payormhorm et al. conducted a visible-light-induced conversion of aqueous glycerol over C-doped TiO2 , giving 67.5% conversion with nearly 100% selectivity of DHA, glyceraldehyde, and formic acid (Payormhorm 2020). The improved performance in photocatalyst glycerol oxidation is attributed to the presence of O2 vacancies and Ti3+ resulting from microwave irradiation and C-doping. The C-doping in TiO2 enhances the performance of the catalyst. The other non-metal doping such as nitrogen, sulfur, and phosphorus enhanced the activity of the catalyst in the visible region (Irie et al. 2003). A recent study by Xiao and Varma described the renovation of bio wastage glycerol into aromatic hydrocarbons in the occurrence of Pt/ZSM-5 and Pd/ZSM-5 bifunctional catalysts, achieving a yield of about 60% hydrocarbons at a conversion rate of 90% for glycerol (Xiao et al. 2016). Using zeolite catalysts, Corma et al. explored the synthesis of acrolein from the mixture of water and gas-phase-glycerol (Corma et al. 2008). In this regard, for supercritical water Bühler et al. investigated the breakdown of glycerol to acrolein, allyl alcohol, propionaldehyde, acetaldehyde, and methanol (Bühler et al. 2002). Konaka et al. investigated the ZrO2 FeOX (K/ZrO2 FeOX ) composite for allyl alcohol synthesis from glycerol (Konaka et al. 2014). Roy et al. investigated a lowtemperature selective hydrothermal process to produce lactic acid from the glycerol; Cu/Cu2 O is used with low amount of NaOH that demonstrated outstanding cyclability and selectivity (Roy et al. 2011). Yun et al. investigated sol–gel-prepared NiCu nanocomposite for catalytic synthesis of 1,2-propane diol from the glycerol (Yun et al. 2014). They looked at different catalyst Cu:Ni molar ratios (9:1, 7:3, and 5:5), with the 9:1 ratio displaying the highest activity. According to Nanda et al., crude glycerol was purified by acidification utilizing phosphoric, sulfuric, and hydrochloric acids. They also evaluated the hue of crude

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

359

and pure glycerol (Nanda et al. 2014). The three types of surface interactions relating glycerol and catalyst are separated based on surface charges: (1) negative, (2) positive, and (3) non-ionic. Three interactions between glycerol and the catalytic surfaces of Cu = Cu to Cu-Cu and Ni = Ni to Ni–N are depicted in Fig. 12.8. In this process, glycerol hydrogenolysis is tracked by the dehydration hydrogenation path (Fig. 12.9). In the catalytic acid sites, hydrogen pressure and a little volume of water in the feed are suitable circumstances for this route. The oxygen present on the terminal hydroxyl (OH) groups of the employed glycerol is adsorbed on the Cu metal and at the acid sites of Cu, which further dehydrates and forms acetol through the aid of alumina. Due to the lack of hydrogen, a minor amount of 1,2-propane diol is produced in the absence of Ni. Additionally, there are two routes to create hydrogen after adding Ni, using routes (1) and (2) for aqueous phase reforming (APR) of the glycerol present on the Ni metal. Finally, 1,2-propane diol is produced when glycerol is oxidized in the presence of Cu. According to Sun et al., the sort of reaction is determined using the composition of the acid sites (Sun et al. 2017). Lewis acid sites direct to the dehydration of the product of ketol (B), while Bronsted acid sites encourage the synthesis of acrolein (A).

Fig. 12.8 The reaction surface interaction routes for obtaining 1,2-propane diol from 1,2,3-propane triol

360

S. Dhamija et al.

Fig. 12.9 Glycerol dehydration reaction process over Lewis acid site (b) and Bronsted acid site (a)

12.2.2 Photocatalysis for Energy Generation As per the International Energy Agency (IEA), various biofuels hold the potential to make up 10% of the global primary energy supply by 2035 and could potentially replace up to 27% of the global transportation fuel by 2050. Hence, the responsible and sustainable utilization of the global plentiful bio-resources could play a crucial part in addressing the global energy crisis. Traditionally thermochemical methods have been used by lignocellulosic industries for the formation of biofuels with carbohydrates incorporating intensive temperature and pressure conditions. Using biochemical processes, despite their significance in converting carbohydrates into biogases, involves the use of expensive enzymes, bacteria, and microorganisms. Nowadays, photocatalysis replacing thermal energy is widely used in the carbohydrate biomass conversion into valuable fuels and chemicals.

12.2.2.1

Reforming of the Carbohydrate

In 1980, Kawai and Sakata pioneered research on the light-induced transformation of carbohydrates (cellulose, saccharose, and starch,) into H2 fuel (Kawai et al. 1980). They introduced a powerful photocatalyst composed of RuO2 , TiO2 , and Pt for the deprivation of cellulose, a filtrate paper into multiple pieces, and placed in (pH-7) water or a NaOH (6 M) solution together. Irradiation under a Xe-lamp (500 W) led to the observation of remarkable gas bubble formation primarily consisting of hydrogen and CO2 gas, along with trace amounts of methanol and ethanol, with the quantum yields of 0.35% and 1.0% in neutral H2 O and alkaline solution, respectively. Over extended periods of illumination, complete degradation of cellulose into CO2 and H2 was reported. Building upon this pioneering work, Zhang et al. investigated the light-induced conversion of the small crystalline cellulose into monosaccharides and CO2 while simultaneously producing molecular H2 (Zhang et al. 2016). They employed a

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

361

creative approach, immobilizing microcrystalline cellulose over TiO2 via the ballmilling method, followed by the addition of a Pt/TiO2, Pt (0.5%wt) suspension under continuous rousing and sonication. The photocatalytic process, conducted in a gasfree aqueous phase under UV-light or solar light, revealed the presence of formic acid, cellobiose, and glucose as products (Nair et al. 2016). Remarkably, after subjecting the cellulose@TiO2 (Pt) composites with varying cellulose content to repeated cycles of UV light irradiation, impressive yields of molecular hydrogen production ranging from 81.2% to 91.7% were achieved. Caravaca et al. explored the H2 production potential through light-induced reforming of raw biomass and cellulose utilizing various metal-loaded TiO2 photocatalysts, including Ni, Pd, Pt, and Au (Caravaca et al. 2016). Their investigations revealed H2 production rates ranging from 77–173 μmolh−1 g−1 of photocatalyst. Notably, they successfully addressed the issue of a long induction time for H2 evolution in Ni/TiO2 by pre-reducing the photocatalyst under an H2 /He flow. The authors emphasized the initial step in the photo-induced conversion of cellulose unit within glucose that was later photocatalytically converted to H2 and CO2 . Furthermore, Fu et al. conducted an extensive study on the de-aerobic photo-induced conversion of glucose utilizing noble-metal TiO2 photocatalysts (Fu et al. 2008). They observed significantly enhanced rates of H2 evolution by depositing metals such as Au, Pt, Pd, Rh, or Ru onto TiO2 . The highest level of H2 expansion was achieved with Pt/TiO2 and Pd/TiO2 catalysts. Numerous studies have focused on the photo-induced conversion of glucose employing modified TiO2 as a photocatalyst and other materials like ZnS-coated, ZnIn2 S4 , Platinum/Cd0.5 Zn0.5 S (Li et al. 2011), WO3 (Esposito et al. 2012), Cu2 O (Zhang et al. 2014), Er3+ :YAlO3 /Platinum–TiO2 membranes, LaFeO3 (Iervolino et al. 2016), and Fe2 O3 . These investigations have shown the highest photocatalytic process for glucose conversion, proposing various mechanisms to elucidate the complex reaction pathways.

12.2.2.2

Reforming of Lignin

Although the investigation of photocatalytic fuel generation has predominantly focused on the utilization of simple organic compounds, there have been remarkable instances where biomass raw materials have been directly employed. In 1995, Greenbaum et al. published a pioneering study on the photo-assisted transformation of biomass into hydrocarbons and molecular O2 whereas ZnO acts as the catalyst (Greenbaum et al. 1995). The cellulose fibers and woodstock are doped with ZnO catalyst and subjected to near-UV and visible light irradiation under high pressure. Consequently, the excited electrons in the conduction band (CB) effectively reduced biomass, whereas the light-induced holes oxidized H2 O to produce O2 or oxidized stock of biomass, resulting in a diverse array of oxygenated products and hydrocarbons. Furthermore, the group led by kale explored the simultaneous degradation of lignin and water splitting using various non-metal (C, N, S) doped ZnO nanomaterials under visible light induction (Kadam et al. 2014). They investigated the generation of H2 and the degradation of lignin utilizing Na-salt of lignosulfonate diffuse in

362

S. Dhamija et al.

H2 O whereas the sample consisting of C-, N-, and S-doped ZnO/ZnS showed exceptional activity in both H2 production and degradation of lignin, yielding products (3-hydroxy-2-methyl-3-phenyl-propionic acid, 1-phenyl-3-buten-1-ol, and methyl 4-hydroxyphenylacetate). In the context of lignin photodegradation, Ksibi et al. examined the degradation of lignin derived from black liquor (alfalfa) involving a TiO2 photocatalyst under UV light (Ksibi et al. 2003). Through comprehensive GC–MS analysis, they discovered a range of products, lignin monomers like coniferylic alcohol, and oxidation products such as syringaldehyde, p-coumaric acid, and vanillic acid. The diverse products obtained from this process are depicted in Fig. 12.10. Moreover, Kobayakawa and colleagues demonstrated the potential of TiO2 as a photocatalyst for achieving complete mineralization of lignin (Kobayakawa et al. 1989). Their investigation revealed the presence of various intermediates (phenol derivatives like vanillin and catechol), along with their dimers (oxalic acid, formaldehyde, methanol, ethanol), and even little amounts of methane and ethylene. Intriguingly, the utilization of photocatalysis also offered the advantage of reducing or replacing energy-intensive thermochemical pre-treatments.

Fig. 12.10 Products detected from degradation of lignin under UV-irradiation

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

363

In another study by Yasuda et al., they proposed a 2-step process formation of biofuel of ethanol from lignin (Yasuda et al. 2011). Their approach involved a photocatalytic conversion of lignin using TiO2 , which effectively reduced the time taken for fermentative and enzymatic reactions. These reports define that the photo-induced degradation of raw biomass (lignocellulosic) involves a complex procedure, encompassing a diverse range of electron acceptors and donors. As a result, the use of raw biomass of lignin as a sacrificial reagent in photo-induced H2 evolution reactions is not commonly explored, and conclusions drawn from experiments using simpler model compounds are often extrapolated to more intricate biomass systems.

12.2.2.3

Reforming of Glycerol

Glycerol is a readily available by-product generated during the esterification process of vegetable oil and animal fat. Due to the recent trend of increased replacement of petroleum-derived fuels with biofuels, glycerol cost has decreased substantially making it important to explore new applications for the same. One of the major promising applications is the use of glycerol as a sacrificial reagent for performing light-induced generation of H2 . Raw glycerol obtained from biofuel manufacturing contains different concentrations of impurities (esters, water, soap stock, and alcohol reagents). Since glycerol concentration is very high in the crude product, commercially available pure glycerol can be utilized to mimic it for the purpose of experimental research. Light-induced formation of aqueous glycerol was investigated by Kondarides et al. at ambient conditions by using a solar light-inducing source in an inert atmosphere with TiO2 as a photocatalyst (Kondarides et al. 2007). Results from the analysis showed that the absolute transition of glycerol to CO2 and H2 was achieved with a maximum rate of 2.7 mmolh−1 g−1 cat of photocatalyst for an initial glycerol concentration of 1.1 mol/L. The combination of CuO2 and TiO2 has also been investigated as a visible light photocatalyst for the generation of H2 from glycerol. Sufficiently high H2 production of 0.2 mmolh−1 g−1 cat of the photocatalyst was formed in 5% glycerol solution under a N2 atm. when utilizing 0.5 wt% of combination of CuO2 and TiO2 . After several hours of reaction, nearly 12.5% of the cocatalyst is degraded due to the dissolution of Cu ions into the solution at acidic conditions. Kinetic and mechanistic studies of photo-induced and -oxidation reactions of glycerol were performed by Panagiotopoulou et al. in aqueous suspensions of Pt/TiO2 and TiO2 (Panagiotopoulou et al. 2013). After the analysis of the reaction intermediates and products in the gas and liquid phases, it was observed that the initial steps involved the dehydration of glycerol and then followed by the oxidation of glycerol or hydrogenolysis to propylene glycol to glyceraldehyde. A variety of intermediates such as acetone, ethanol, 2-oxopropanol, glycolaldehyde, acetaldehyde, and methanol are generated subsequently through dehydration, dehydrogenation, and decarbonylation reactions and then transformed into CO2 . Under similar light-induced reaction conditions, CO is oxidized to CO2 over Pt/TiO2 . A reduction process facilitated via conduction band electrons is used to generate H2 . Platinum has two important roles in the light-induced conversion reaction: (i) reduce

364

S. Dhamija et al.

overpotential for hydrogen evolution and (ii) act as an electron trap center which improves charge carrier separation. Recent studies have demonstrated that these limitations can be surmounted by utilizing dual-functional photocatalysts for the formation of the glycerol with exceptional purity while harnessing the potential of second-generation lipids derived from non-food crops or microalgae as environmentally sustainable feedstocks (Roy et al. 2011; Yun et al. 2014; Nanda et al. 2014). The conversion of lipids into biodiesel stands as an exemplary practical application of biomass transformation. Consequently, there is considerable interest in exploring prospective routes for converting glycerol into high-value products. By producing chemicals derived from biomass, the profitability of biodiesel production can be significantly enhanced (Sun et al. 2017). Glycerol harbors the capacity to substitute numerous fossil-based feedstocks. Through the utilization of a diverse array of catalysts, glycerol can undergo conversion into a wide range of chemicals, such as propanediol, acrolein, epichlorohydrin, lactic acid, dihydroxyacetone, and glyceric acid (Kawai et al. 1980). According to Kumar et al., an efficient interaction connecting CuO and TiO2 nanotubes led to improved H2 generation of 99,823 μmolh−1 g−1 cat (Praveen Kumar, et al. 2013). They also explained the utilization of glycerol as a sacrificial agent. Another study showed that the presence of Cu2 O and CuO on TiO2 nanotubes worked as cocatalysts and photo-sensitizers, respectively, and were accountable for increased H2 generation (114,900 μmolh−1 g−1 cat ) when exposed to solar light (Sadanandam et al. 2017). The study also established that some intermediates are produced when glycerol is oxidized and that these intermediates then irreversibly oxidize to CO2 . In order to increase the production of H2 (Fig. 12.11), Lakshmana Reddy et al. displayed the aqueous solution of the crude glycerol generated from the biodiesel manufacturing thing that can be employed as an efficient hole scavenger (Lakshmana Reddy et al. 2018). Additionally, they demonstrated how Ni(OH)2 quantum dots present on the TiO2 nanotubes may be used to build an effective photocatalyst for the creation of H2 and demonstrated a 12-fold increase in productivity over pure TiO2 . By giving electrons to holes, glycerol initiates an irreversible oxidation reaction that produces H+ , oxidized intermediates, and an endless provision of electrons for the valence band. Those electrons are readily accessible from an appropriate energy level at the photocatalyst conduction band; the oxidation of glycerol pathway confirms the accessibility of H+ to create H2 gas. Lakshmana Reddy et al. report that using a tiny amount of the crude glycerol, a biodiesel by-product manufacturing can help to enhance the rate of H2 synthesis (Reddy et al. 2017). Additionally, they demonstrated how adding Ni(OH)2 quantum dots to TiO2 nanotubes produces an impactful photocatalyst for the production of H2 , with an efficiency increase of roughly 12 times when compared to pure TiO2 . Chong et al. looked at Cu-Ni/TiO2 nanocomposite for the evolution of hydrogen; they discovered that glycerol had a significant impact as the sacrificial agent (Chong et al. 2014b). Crude glycerol is acceptable for more operations, nevertheless, according to the cost–benefit analysis, as it may be obtained in significant quantities as a by-product from industries that process biomass (AlAzri et al. 2014). The catalyst’s surface characteristic and the way it interacts with the organic sacrificial agent determine the overall rate of H2 generation. The amount

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

365

Fig. 12.11 Illustration of the creation of H2 using crude glycerol from a biodiesel-producing facility. Praveen Kumar et al. 2013 Adapted from reference (), reproduced from permission from ACS

of the hydroxyl groups and carbon available in the sacrificial agent’s structure may affect how it interacts with the catalyst. The speed with which they can be oxidized and their potential to bind to the catalyst surface are crucial factors to consider when selecting sacrificial agents. Recently, to study the effect of pH, Zhou et al. checked Pt/TiO2 nanocomposites at separate pH times among 2 and 14 (Zhou et al. 2012). The authors accomplished the greatest rate of H2 construction at pH 11.2 because of the improved surface relations linking Pt and TiO2 . Additionally, Zhen et al. justified that a metal colloid complex catalyst-based reaction at pH of 7 exhibited remarkable quantum yield in the acidic pH due to isoelectric point of utilized photocatalyst (Fig. 12.12) (Zhen et al. 2017). In contrast, a current study that examined the impact of pH 5–9 solution on MoS2 /graphene at the MOF support found that alkaline circumstances increased H2 formation (Hao et al. 2017). After testing activity at a pH range of 0–14, the influence increased the frequency of pH on carbon quantum dot-based photocatalysts as well as revealed pH 8.5 of H2 production. It is evident from the literature studies that the best pH solution for greater hydrogen construction can differ based on the type of catalyst being used and other reaction-related factors. Therefore, managing the pH of the solution is crucial, particularly in the event of a particle system where each of the three dimensions are open for adsorption. The zero-charge point, below the surface of catalyst develops a positive-charge while above surface displays negative-charge, this whole process determines the effective production of H2 . It is made clear that

366

S. Dhamija et al.

Fig. 12. 12 Exhibiting generation of hydrogen at various pH levels. Adapted from reference (Zhen et al. 2017), reproduced from permission from Wiley

the catalyst’s positive charge causes the most significant reaction for the formation of H+ in the oxidation of the sacrificing agent. There are various experimental reports on how to increase hydrogen production by optimizing glycerol concentration. Glycerol content is known to influence the pH of the solution, band bending, and the catalyst’s surface-active sites, which in turn regulates the adsorption properties. The best glycerol adsorption is crucial, since both strong and weak adsorption on catalysts is demonstrated to have a detrimental effect on photocatalytic performance. The influence of glycerol concentration on the photocatalytic activity of CuO-NiO@TiO2 was studied by Ravi et al. (Ravi et al. 2020). The volume of H2 produced after a tiny quantity 5 vol% of the glycerol was added to water amplified significantly, and scientists attributed this to the fact that the amount of glycerol in water prevents photogenerated electron–hole recombination and promotes the generation of H2 . The rate of production of H2 is slowed by excessive glycerol formation because of competing catalyst’s ability to donate electrons which is constrained by the absorption of glycerol along with its intermediates over the catalyst surface. Recent research by Fujita et al. on NiO/TiO2 nanocomposite, in which they have evaluated glycerol quantity, i.e., 1—4 mol dm−3 , looked at five parameters for enhancing photocatalytic performance (Fujita et al. 2016). Due to optimal amounts of glycerol trapped on the photocatalyst and Langmuir-type adsorption, 2.5 mol dm−3 demonstrated greater performance in this instance. Lalitha et al. investigated the amount of glycerol (220 vol.%) affected the photocatalytic H2 development of a 0.5 wt.% CT-2 the photocatalyst when exposed to solar light (Lalitha et al. 2010). In this instance, it was discovered that a 5 vol.% glycerol content was ideal. The ideal volume percentage of the glycerol was discovered as proportional to the photocatalyst’s surface area that makes glycerol adsorption as well as the effective generation of H2 gas easier (Lalitha et al. 2010).

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

367

12.3 Conclusion Light-induced conversion of waste biomass to value-added chemicals is an innovative and sustainable methodology. This book chapter provides insight into various photocatalyst developments and versatile reaction conditions that play a significant role in the light-induced conversion of biomass into valuable chemicals. The goal is to create highly selective photocatalysts to avoid the formation of unwanted radicals (such as OH radicals). This involves adjusting electronic band structure and photochemical properties. External factors like solvent and pH significantly impact the interaction between the photocatalyst and biomass, influencing the overall efficiency and selectivity. External factors like solvent and pH significantly impact the interaction between the photocatalyst and biomass, influencing the overall efficiency and selectivity. Despite progress, challenges remain in scaling up selective biomass conversion to an industrial level. Understanding the detailed mechanisms of converting native biomass is a challenge, and research should focus on the complex nature of raw biomass. The development of efficient photocatalysts remains a challenge, and future research should concentrate on materials that effectively capture light and enhance interactions with biomass. To overcome current limitations, there is a need for precise engineering of the band gap structure through adjustments in chemical composition, space structure, crystal form, surface states, and morphology modification.

References Agopyan V et al (2005) Developments on vegetable fibre–cement based materials in São Paulo, Brazil: an overview. Cement Concr Compos 27(5):527–536 Al-Azri ZH et al (2014) Performance evaluation of Pd/TiO 2 and Pt/TiO 2 photocatalysts for hydrogen production from ethanol-water mixtures. Int J Nanotechnol 11(5–678):695–703 Banerjee J et al (2017) Bioactives from fruit processing wastes: Green approaches to valuable chemicals. Food Chem 225:10–22 Benkó T et al (2014) Bimetallic Ag–Au/SiO2 catalysts: formation, structure and synergistic activity in glucose oxidation. Appl Catal A 479:103–111 Bühler W et al (2002) Ionic reactions and pyrolysis of glycerol as competing reaction pathways in near- and supercritical water. J Supercrit Fluids 22(1):37–53 Caravaca A et al. (2016) H2 production by the photocatalytic reforming of cellulose and raw biomass using Ni, Pd, Pt and Au on titania. In: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 472(2191) Chaiwarit T et al. (2022) Fabrication and evaluation of water hyacinth cellulose-composited hydrogel containing quercetin for topical antibacterial applications. Gels, 8(12) Chen J et al. (2019) Polysaccharide monooxygenase-catalyzed oxidation of cellulose to glucuronic acid-containing cello-oligosaccharides. Biotechnol Biofuels, 12(1) Chong R et al (2014a) Selective conversion of aqueous glucose to value-added sugar aldose on TiO2-based photocatalysts. J Catal 314:101–108 Chong R et al (2014b) Selective photocatalytic conversion of glycerol to hydroxyacetaldehyde in aqueous solution on facet tuned TiO2-based catalysts. Chem Commun 50(2):165–167 Climent MJ et al (2010) Heterogeneous catalysts for the One-Pot synthesis of chemicals and fine chemicals. Chem Rev 111(2):1072–1133

368

S. Dhamija et al.

Colmenares JC et al (2011) High-value chemicals obtained from selective photo-oxidation of glucose in the presence of nanostructured titanium photocatalysts. Biores Technol 102(24):11254–11257 Colmenares JC et al (2013a) Room temperature versatile conversion of biomass-derived compounds by means of supported TiO2 photocatalysts. J Mol Catal a: Chem 366:156–162 Colmenares JC et al (2013b) Sonication-Assisted Low-Temperature routes for the synthesis of supported Fe–TiO2 econanomaterials: partial photooxidation of glucose and phenol aqueous degradation. Chem Cat Chem 5(8):2270–2277 Corma A et al (2008) Biomass to chemicals: Catalytic conversion of glycerol/water mixtures into acrolein, reaction network. J Catal 257(1):163–171 Da Vià L et al (2017) Visible light selective photocatalytic conversion of glucose by TiO2 . Appl Catal B 202:281–288 Dessie W et al (2020) Current advances on waste biomass transformation into value-added products. Appl Microbiol Biotechnol 104(11):4757–4770 Dodekatos G et al (2018) Recent advances in thermo-, photo-, and electrocatalytic glycerol oxidation. ACS Catal 8(7):6301–6333 Esposito DV et al. (2012) Photoelectrochemical reforming of glucose for hydrogen production using a WO3-based tandem cell device. Energy & Environ Sci, 5(10) Fan H et al (2011) Photodegradation of cellulose under UV light catalysed by TiO2. J Chem Technol Biotechnol 86(8):1107–1112 Fu X et al (2008) Photocatalytic reforming of biomass: A systematic study of hydrogen evolution from glucose solution. Int J Hydrogen Energy 33(22):6484–6491 Fujita S-I et al (2016) Photocatalytic hydrogen production from aqueous glycerol solution using NiO/TiO2 catalysts: Effects of preparation and reaction conditions. Appl Catal B 181:818–824 Gismatulina YA et al (2022) Evaluation of chemical composition of miscanthus × giganteus raised in different climate regions in Russia. Plants, 11(20) Granone LI et al (2018) Photocatalytic conversion of biomass into valuable products: a meaningful approach? Green Chem 20(6):1169–1192 Greenbaum E et al (1995) New Photosynthesis: direct photoconversion of biomass to molecular oxygen and volatile hydrocarbons. Energy Fuels 9(1):163–167 Guerriero A et al (2014) Hydrogen production by selective dehydrogenation of HCOOH catalyzed by Ru-biaryl sulfonated phosphines in aqueous solution. ACS Catal 4(9):3002–3012 Gutiérrez-Antonio C et al. (2021) Production processes from lignocellulosic feedstock, in Production Processes of Renewable Aviation Fuel. pp 129–169 Hao X et al (2017) Peculiar synergetic effect of MoS 2 quantum dots and graphene on Metal-Organic Frameworks for photocatalytic hydrogen evolution. Appl Catal B 210:45–56 Hao H et al (2018) Facile modification of titania with nickel sulfide and sulfate species for the photoreformation of cellulose into hydrogen. Chemsuschem 11(16):2810–2817 Huang Y-B. et al. (2013) Hydrolysis of cellulose to glucose by solid acid catalysts. Green Chem, 15(5) Iervolino G et al (2016) Production of hydrogen from glucose by LaFeO 3 based photocatalytic process during water treatment. Int J Hydrogen Energy 41(2):959–966 Irie H et al (2003) Carbon-doped Anatase TiO2 Powders as a Visible-light sensitive photocatalyst. Chem Lett 32(8):772–773 Jiang L et al. (2012) Application of photocatalytic technology in environmental safety. Procedia Eng, 45: pp 993–997 Jin B et al (2017) Photocatalytic oxidation of glucose into formate on nano TiO2 Catalyst. ACS Sustain Chem & Eng 5(8):6377–6381 Kadam SR et al (2014) A green process for efficient lignin (biomass) degradation and hydrogen production via water splitting using nanostructured C, N, S-doped ZnO under solar light. RSC Adv 4(105):60626–60635 Kawai T et al (1980) Conversion of carbohydrate into hydrogen fuel by a photocatalytic process. Nature 286(5772):474–476

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

369

Kiely DE et al (2002) Hydroxylated nylons based on unprotected esterified D-glucaric acid by simple condensation reactions. J Am Chem Soc 116(2):571–578 Kim M et al (2010) Composition of sugar cane, energy cane, and sweet sorghum suitable for ethanol production at Louisiana sugar mills. J Ind Microbiol Biotechnol 38(7):803–807 Kim G et al (2015) Glucose–TiO 2 charge transfer complex-mediated photocatalysis under visible light. Appl Catal B 162:463–469 Ko M et al. (2019) Unassisted solar lignin valorisation using a compartmented photo-electrobiochemical cell. Nat Commun. 10(1) Kobayakawa K et al (1989) Photodecomposition of kraft lignin catalyzed by titanium dioxide. Bull Chem Soc Jpn 62(11):3433–3436 Konaka A et al (2014) Conversion of glycerol into allyl alcohol over potassium-supported zirconia– iron oxide catalyst. Appl Catal B 146:267–273 Kondarides DI et al (2007) Hydrogen production by photo-induced reforming of biomass components and derivatives at ambient conditions. Catal Lett 122(1–2):26–32 Ksibi M et al (2003) Photodegradation of lignin from black liquor using a UV/TiO2 system. J Photochem Photobiol, A 154(2–3):211–218 Kumar A et al. (2017) A review on the factors affecting the photocatalytic degradation of hazardous materials. Mater Sci & Eng Int J, 1(3) Lakshmana Reddy N et al (2018) Photocatalytic Reforming of Biomass Derived Crude Glycerol in Water: A Sustainable Approach for Improved Hydrogen Generation Using Ni(OH)2 Decorated TiO2 Nanotubes under Solar Light Irradiation. ACS Sustain Chem & Eng 6(3):3754–3764 Lalitha K et al (2010) Highly stabilized and finely dispersed Cu2O/TiO2: a promising visible sensitive photocatalyst for continuous production of hydrogen from glycerol: water mixtures. J Phys Chem C 114(50):22181–22189 Li S-H et al (2016) A sustainable approach for lignin valorization by heterogeneous photocatalysis. Green Chem 18(3):594–607 Li J-Y et al (2019a) Visible light-induced conversion of biomass-derived chemicals integrated with hydrogen evolution over 2D Ni2P–graphene–TiO2. Res Chem Intermed 45(12):5935–5946 Li H et al (2019b) Photocatalytic cleavage of aryl ether in modified lignin to non-phenolic aromatics. ACS Catal 9(9):8843–8851 Li, Y., et al., Photocatalytic hydrogen evolution over Pt/Cd0.5Zn0.5S from saltwater using glucose as electron donor: An investigation of the influence of electrolyte NaCl. International Journal of Hydrogen Energy, 2011. 36(7): p. 4291–4297. Liu X et al (2019) Photocatalytic conversion of lignocellulosic biomass to valuable products. Green Chem 21(16):4266–4289 Liu M et al. (2022) Production of microfibrillated cellulose fibers and their application in polymeric composites, in Nanotechnology in paper and wood engineering. 2022. p. 197–229 Lobo MG et al (2019) Utilization and management of horticultural waste, in postharvest technology of perishable horticultural commodities. pp 639–666 Mathias J-D et al. (2015) Upcycling sunflower stems as natural fibers for biocomposite applications. BioResources, 10(4) Mendoza A et al (2020) Selective production of dihydroxyacetone and glyceraldehyde by photoassisted oxidation of glycerol. Catal Today 358:149–154 Minero C et al (2012) Glycerol as a probe molecule to uncover oxidation mechanism in photocatalysis. Appl Catal B 128:135–143 Nair V et al (2016) Production of phenolics via photocatalysis of ball milled lignin–TiO2 mixtures in aqueous suspension. RSC Adv 6(22):18204–18216 Nanda A et al. (2014) Retrosigmoid approach for resection of petroclival meningioma. Neurosurg Focus, 36(v1supplement) Nwosu U, et al. (2021) Selective biomass photoreforming for valuable chemicals and fuels: A critical review. Renew Sustain Energy Rev 148 Pan Y et al. (2020) Selective conversion of lignin model veratryl alcohol by photosynthetic pigment via photo-generated reactive oxygen species. Chem Eng J 393

370

S. Dhamija et al.

Panagiotopoulou P et al (2013) Kinetics and mechanism of glycerol photo-oxidation and photoreforming reactions in aqueous TiO2 and Pt/TiO2 suspensions. Catal Today 209:91–98 Parthasarathi R et al (2011) Theoretical study of the remarkably diverse linkages in lignin. J Phys Chem Lett 2(20):2660–2666 Payormhorm J et al. (2020) Synthesis of C-doped TiO2 by sol-microwave method for photocatalytic conversion of glycerol to value-added chemicals under visible light. Appl Catal A: Gen, 590 Periyasamy S et al (2022) Chemical, physical and biological methods to convert lignocellulosic waste into value-added products. A Review Environ Chem Lett 20(2):1129–1152 Prasad S et al (2007) Ethanol as an alternative fuel from agricultural, industrial and urban residues. Resour Conserv Recycl 50(1):1–39 Praveen Kumar D et al. (2013) Nano-size effects on CuO/TiO2 catalysts for highly efficient H2 production under solar light irradiation. Chem Commun, 49(82) Ravi P et al (2020) CuO@NiO core-shell nanoparticles decorated anatase TiO2 nanospheres for enhanced photocatalytic hydrogen production. Int J Hydrogen Energy 45(13):7517–7529 Reddy NL et al (2017) Multifunctional Cu/Ag quantum dots on TiO 2 nanotubes as highly efficient photocatalysts for enhanced solar hydrogen evolution. J Catal 350:226–239 Roongraung K et al. (2020) Enhancement of photocatalytic oxidation of glucose to value-added chemicals on TiO2 photocatalysts by A Zeolite (Type Y) support and metal loading. Catalysts, 10(4) Roy D et al (2011) Cu-Based catalysts show low temperature activity for glycerol conversion to lactic acid. ACS Catal 1(5):548–551 Sadanandam G et al (2017) Highly stabilized Ag2O-loaded nano TiO2 for hydrogen production from glycerol: Water mixtures under solar light irradiation. Int J Hydrogen Energy 42(2):807–820 Sareena C et al (2013) Biodegradation behaviour of natural rubber composites reinforced with natural resource fillers – monitoring by soil burial test. J Reinf Plast Compos 33(5):412–429 Skaltsounis A-L, et al. Recovery of high added value compounds from olive tree products and olive processing byproducts, in olive and olive oil bioactive constituents. pp 333–356 Sun D et al (2017) Glycerol as a potential renewable raw material for acrylic acid production. Green Chem 19(14):3186–3213 Suriyachai N et al (2020) Synergistic effects of Co-doping on photocatalytic activity of titanium dioxide on glucose conversion to value-added chemicals. ACS Omega 5(32):20373–20381 Viswanathan MB et al. (2020) Variability in structural carbohydrates, lipid composition, and cellulosic sugar production from industrial hemp varieties. Ind Crop Prod, 2020. 157. Wang L et al (2015) Sustainable conversion of cellulosic biomass to chemicals under visible-light irradiation. RSC Adv 5(104):85242–85247 Wang W-M et al. (2008) Study on the chemical modification process of jute fiber. J Eng Fibers Fabr, 3(2) Xiang Z et al (2020) Photocatalytic conversion of lignin into chemicals and fuels. Chemsuschem 13(17):4199–4213 Xiao Y et al (2016) Conversion of Glycerol to Hydrocarbon Fuels via Bifunctional Catalysts. ACS Energy Lett 1(5):963–968 Xu Y et al. (2020) Water-soluble sugars of pedigreed sorghum mutant stalks and their recovery after pretreatment. Appl Sci, 10(16) Yang GU et al (2022) Physical and chemical characteristics of the bamboo culm and wood carbonized at low temperature. BioResources 17(3):4837–4855 Yasuda M et al (2011) The effect of TiO2-photocatalytic pretreatment on the biological production of ethanol from lignocelluloses. J Photochem Photobiol, A 220(2–3):195–199 Yin J et al (2020) Highly selective oxidation of glucose to gluconic acid and glucaric acid in water catalyzed by an efficient synergistic photocatalytic system. Catal Sci Technol 10(7):2231–2241 Yun YS et al (2014) Effect of nickel on catalytic behaviour of bimetallic Cu–Ni catalyst supported on mesoporous alumina for the hydrogenolysis of glycerol to 1,2-propanediol. Catal Sci Technol 4(9):3191–3202

12 Light-Induced Conversion of Waste Biomass to Value-Added Chemicals

371

Zakzeski J et al (2010) The Catalytic Valorization of Lignin for the Production of Renewable Chemicals. Chem Rev 110(6):3552–3599 Zhang L et al (2014) Photocatalytic reforming of glucose under visible light over morphology controlled Cu2O: efficient charge separation by crystal facet engineering. Chem Commun 50(2):192–194 Zhang G et al (2016) Simultaneous cellulose conversion and hydrogen production assisted by cellulose decomposition under UV-light photocatalysis. Chem Commun 52(8):1673–1676 Zhang B et al (2018a) Photothermally promoted cleavage of β-1,4-glycosidic bonds of cellulosic biomass on Ir/HY catalyst under mild conditions. Appl Catal B 237:660–664 Zhang L et al (2018b) Enhanced H2 evolution from photocatalytic cellulose conversion based on graphitic carbon layers on TiO2 /NiOx. Green Chem 20(13):3008–3013 Zhang Q et al (2019) Enhanced photocatalytic performance for oxidation of glucose to value-added organic acids in water using iron thioporphyrazine modified SnO2. Green Chem 21(18):5019– 5029 Zhang Y et al. (2013) Identification of Bi2WO6 as a highly selective visible-light photocatalyst toward oxidation of glycerol to dihydroxyacetone in water. Chem Sci, 4(4) Zhen W et al (2017) The role of a metallic copper interlayer during visible photocatalytic hydrogen generation over a Cu/Cu2O/Cu/TiO2 catalyst. Catal Sci Technol 7(21):5028–5037 Zhou M et al (2012) Effect of epimerization of d-glucose on photocatalytic hydrogen generation over Pt/TiO2. Catal Commun 18:21–25 Zhou B et al (2017) Highly selective photocatalytic oxidation of biomass-derived chemicals to carboxyl compounds over Au/TiO2. Green Chem 19(4):1075–1081 Zou J et al (2018) One-pot photoreforming of cellulosic biomass waste to hydrogen by merging photocatalysis with acid hydrolysis. Appl Catal A 563:73–79

Chapter 13

Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic Applications to Important Chemicals Arindam Modak

13.1 Introduction In differentiation to fossil fuels, biomass could be an important and renewable asset of complex molecules found in plants and creatures. The method of photosynthesis, which uses water, carbon dioxide, and daylight to form plant biomass, happens normally. It can be divided into edible and non-edible biomass, with the previous being basically based on its appropriateness for human utilization. As a first-generation crude material, consumable biomass overwhelmingly comprises polysaccharides like starch, and is represented by crops including wheat, rice, maize, and potatoes (Lee and Lavoie 2013). Oppositely, non-edible biomass, in some cases referred to as lignocellulosic biomass or lignocellulose, which incorporates crop waste and wood, is regarded as a second-generation raw resource. These non-edible sources have a wide variety of applications in biofuels, biochemicals, and biocomposites and are high in cellulose, hemicellulose, and lignin. There’s a chance to produce fuels and chemicals from this abundant and renewable asset much obliged to the expanding accentuation on utilizing lignocellulosic biomass for feasible employment (Bohre et al. 2022). Since lignocellulosic biomass derived from plants, which contains cellulose, hemicelluloses, and lignin, is non-edible in differentiation to biomass derived from foods like starch and other disaccharides, its conversion is significant and has potential benefits (Jha et al. 2022). The utilization of starch as a first-generation biomass is an important polysaccharide to produce an array of chemicals which may be a critical matter since it is generally utilized as food (Hao et al. 2021a). As a result, the use of lignocelluloses as non-edible biomass might be significant for the conversion into platform chemicals. So far, methods like combustion, pyrolysis, gasification, supercritical treatment, and thermo-chemical (corrosive, A. Modak (B) Amity Institute of Applied Sciences; Amity University, Gautam Buddha Nagar; Amity Rd, Sector 125, Noida, Uttar Pradesh 201313, India e-mail: [email protected] 373

374

A. Modak

alkali) methods can be used to change the complex structures of di/polysaccharides for their transformations (Canabarro et al. 2013). However, the catalytic method manifests enough potential owing to the mild conversion protocol (Modak 2023). It is pertinent to mention that cellulose is a natural polymer and is the main component in the lignocellulose structure of plants. It is also one of the foremost copious biopolymers on our planet. The utilization of cellulose into chemicals and fuels has the potential to decrease the chemical industry’s reliance on fossil fuels (Mankar et al. 2021a). On the other hand, in difference to starch, cellulose does not constitute a human nourishment source, and its utilization isn’t draining consumable assets for the chemical union. In addition, since the CO2 produced by chemicals at the end of their life cycle, it is captured during by photosynthesis in the lignocellulosic biomass. Hence, cellulose produced from CO2 -utilization by plant, is considered as carbon– neutral feedstock. As a result, utilizing cellulose as an elective feedstock will reduce demand for fossil fuels and may help to moderate CO2 -induced climate alteration.

13.1.1 Potential Sources of Sugars and Fine Chemicals from Biomass Monosaccharides, often known as sugars, are assigned in two ways: (1) aldose for a monosaccharide containing an aldehyde group and (2) ketose for a monosaccharide having a ketone group. The foremost likely sources of C6 sugars are glucose, fructose, mannose, and galactose, whereas the foremost likely sources of C5 sugars are xylose, arabinose, and xylulose. The hydrolysis of their disaccharides yields monosaccharides (sugars). On hydrolysis, hemicellulose (polysaccharide comprising numerous C5 and C6 sugars) created from consumable and non-edible plant biomass can surrender sugars. As cellulose may be a huge component (45%) of lignocelluloses, its transformation into chemicals (generally sugars) is organized within the biorefinery (Sannigrahi et al. 2010). Nevertheless, sugars discover diverse applications in different industries such as fine chemicals and pharmaceuticals. They serve numerous purposes, including acting as a vitality source (glucose), low-calorie sweeteners (xylose), and as building blocks for the synthesis of imperative mechanical chemicals. For example, sugars can be utilized to create furans like 5-hydroxymethylfurfural and furfural, which are antecedents for fuels, tars, plastics, nylon, polyester, and fine chemicals. Also, sugars can be changed into sugar alcohols such as sorbitol, mannitol, xylitol, and arabitol. These sugar alcohols have applications as low-calorie sweeteners, cement, makeup, and vitality sources. Sugar acids like gluconic, xylonic, and arabinonic acids are utilized as chelating operators, cement retardants, makeup, and restorative compounds. Besides, sugars can be changed over into different acids counting succinic acid, itanoic acid, formic acid, and glycolic acid. These acids are utilized within the nourishment and polymer businesses. Sugars can too be changed into alcohols like ethanol and butanol, having applications in solvents (De et al.

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

375

2012). At last, the alkyl ethers of sugars, such as alkyl glucosides and alkyl xylosides, are being applied as biomass-derived surfactants. Generally, HMF (Mondal et al. 2015), pentose and hexose sugars, and other monosaccharides play a significant part in the generation of a wide run of mechanically critical chemicals over numerous segments. In this case, catalysts are required that they successfully break the stable glycosidic linkage display in disaccharides and polysaccharides, driving the formation of monosaccharides. Figure 13.1 shows the biomass conversion processes to valuable hydrocarbons and furan-based aromatics.

13.2 Biomass Pre-treatment The most favourable approach for the extraction of monosaccharides involves the direct utilization of lignocellulosic biomass, which is composed of abundant polysaccharides (approximately 45% cellulose and 25% hemicelluloses) (Mankar et al. 2022). However, the complex nature of lignocellulosic materials is challenging for their conversion into sugars. Factors such as intricate hydrogen bonding (including intra- and inter-molecular bonding) within cellulose, the presence of lignin (an aromatic polymer) in lignocellulose, and the multiple bonds between polysaccharides and lignin make the direct processing of lignocellulosic biomass into sugars very complicated (Mankar et al. 2022). During the process of converting of polysaccharides which include cellulose and hemicellulose into sugars, lignin stays unchanged due to its higher processing temperature requirements compared to polysaccharides. Simultaneous attempts to convert lignin alongside polysaccharides often lead to predominant degradation reactions of sugars. Furthermore, the unconverted lignin can interfere with the catalyst and inhibit the catalytically active sites, thereby affecting the overall efficiency of the process (Agbor et al. 2011). To determine the weight of unconverted lignin, the authors initially suspended the solid lignin in DMSO and stirred for 24 h at room temperature. After the reaction, it was filtered and the solid was washed with acetone, followed by drying at air. The difference in weight before and after the washing determines the weight of unconverted lignin. The presence of complex hydrogen bonding, lignin content, and challenges associated with lignin conversion, hinders the direct transformation of lignocellulosic biomass into sugars. The presence of multiple hydrogen bonds in cellulose leads to its highly rigid and crystalline structure, making it challenging to degrade. Additionally, due to the strong hydrogen bonding, cellulose remains insoluble in many common solvents. Moreover, cellulose possesses a high degree of polymerization, further complicating its hydrolysis. Furthermore, lignin, which acts as a protective layer covering the polysaccharides, hinders their catalytic conversion by shielding them from chemical and biological attacks. Therefore, it becomes essential to pretreat lignocellulosic materials before hydrolysis to remove lignin and to reduce the crystallinity of cellulose. Effective pre-treatment techniques are required to avoid

376

A. Modak

Fig. 13.1 Process for biomass conversion into platform chemicals; reproduced with permission from Ref. Coumans et al. (2022)

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

377

degradation or loss of saccharides and to ensure an economically and environmentally friendly process. Certain pre-treatment procedures reduce cellulose polymerization, which can enhance the solubility of cellulose parts in water, facilitating a successful hydrolysis process (Chen et al. 2017). In such a process, 72 wt.% sulphuric acid solution was utilized where the sulphate ions and hydronium ions present in the sulphuric acid form electron donor–acceptor complexes with the hydroxyl (OH) groups in cellulose. This interaction between cellulose and sulphuric acid causes the breakdown of both intra- and intermolecular hydrogen bonding among the hydroxyl groups in cellulose. Consequently, the molecular chains of cellulose undergo separation, resulting in the swelling of cellulose and eventually its dissolution. Remarkably, after only 15 min of pre-treatment in the 72 wt.% sulphuric acid solution, the yield of glucose exhibits a rapid increase, and subsequently, the glucose yield continues to rise, albeit at a slower rate, after 2 h of pre-treatment.

13.2.1 Biomass Treatment Pre-treatment is an essential step for biomass conversion process, where cellulose and hemicellulose components from biomass-feedstock are separated from lignin and have been identified as the major step which is economically advantageous. In the pre-treatment process, cell wall was depolymerized to reduce the crystallinity of cellulose, thus have potential in biorefineries (Hernández-Beltrán et al. 2019). List of several pre-treatment methods are discussed here: (i) mechanical method that considers reducing the particle size; (ii) chemical method which uses diluted acids, alkalis, and organic solvents; (iii) physicochemical method with steam explosion, and (iv) biological method that concerns the use of microbes and enzymes. The pre-treatment step is pictorially shown in Fig. 13.2.

13.2.1.1

Mechanical Method

Mechanical pre-treatment considers ball milling, grinding, and chipping that could improve biogas production from lignocellulose. However, it has a drawback regarding its high energy demand. The advantage of this process is that it increases processibility of the cellulose in the next step, by increasing the surface area, and reducing the size and crystallinity.

13.2.1.2

Chemical Method

Chemical treatment considers the use of acid, alkali, and organic solvents which is much milder than mechanical route as it is considered most effective for the degradation of complex substrates. Besides, chemical method improves bioavailability of

378

A. Modak

Fig. 13.2 Biomass pre-treatment processes. Reproduced with permission from Ref. Hashemi et al. (2021)

the carbohydrate while removing unwanted lignin and decreasing the degree of polymerization of cellulose. Considerable attention was paid to chemical method as it is less expensive, and has better efficiencies and faster rate of degradation of complex organics. Acid method: Acid method solubilizes hemicellulose and exposes cellulose fractions at low acid concentrations of 0.2% to 2.5% v/v. It is pertinent to mention that acid method creates corrosion issues of the reactor, simultaneously increasing purification issue. A study reported that pre-treatment with 2% H2 SO4 increases high methane yield, 175 mL/g, which proves the necessity of acid method (Song et al. 2014). Alkaline method: Alkaline method is highly efficient for delignification process because alkaline medium swells the cell wall while decreasing crystallinity and polymeric nature of cellulose. The advantage of this method consists of adjustment in the loading of alkali, temperature, where strong alkali may degrade polysaccharides. Nevertheless, low alkaline concentrations at low temperature does not produce HMF, while increasing biomethane production efficiency. Organic solvent: Methanol, ethanol, acetone, and peracetic acid are progressively used as organic solvents that could isolate pure lignin and separate each lignocellulosic component. Organic solvents along with mineral acids viz. HCl and H3 PO4 are acting as catalyst. Acid catalyst along with organic solvent increases delignification

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

379

rate, and decreases pre-treatment temperature as acid catalysts cleave labile arylether bonds (α-aryl ether, aryl glycerol-β-aryl ether bonds) present in lignin. Such techniques are quite useful in the production of value-added products as applied in biorefinery. Organic solvent hydrolyses the internal bonds between lignin and hemicellulose, as well as the glycosidic bonds in cellulose and hemicellulose. Thus, organic solvents are eventually useful as an alternative to inorganic acids that could avoid corrosion problem by decreasing energy demand. However, high volatility and concomitant rise in vapour pressure may be critical while operating at high pressure. Ionic liquid (IL): ILs are significant to traditional solvents as they have low vapour pressure, and thus avoid solvent loss by evaporation. Simultaneously, they have high recyclability that signifies minimum waste generation through ILs. Thus, IL-based solvents gained immense interest because of their easy scalability from small scale to pilot scale and their ability to depolymerize lignin and decrystallize cellulose, whereas cost of IL is only disadvantageous.

13.2.1.3

Steam Explosion

Steam explosion consists of explosive decompression of biomass and is an effective process to break the fibrous and rigid nature of woody biomass into water-soluble oligomers and individual sugars. It is reported by Nges et al. that steam explosion method with 0.3 M NaOH increases methane yield by 57% as compared to untreated substrates (Nges et al. 2016).

13.2.1.4

Hydrothermal Method

Hydrothermal pre-treatment has high potential as it is the efficient method for damaging cellulose and the removal of hemicellulose and lignin without using chemicals and materials. This method loses recalcitrant structure of woody biomass and solubilizes hemicellulose at the working temperature of 90–260 °C.

13.2.1.5

Enzymatic Pre-Treatment

Biological pre-treatment is attractive as compared to chemical method since it considers no use of chemicals, but the reaction rate is slow and is unattractive from the commercial point of view. In this regard, several fungi such as microorganisms are used for delignification reaction. It reports the use of laccase enzyme that could increase biomethane production by 25%. Meanwhile, it also showed that peroxidase could increase biomethane by 17% (Liu et al. 2017).

380

A. Modak

13.2.2 Catalytic Pyrolysis of Biomass Pyrolysis is a promising technology for obtaining renewable chemicals and fuels; however, commercialization is quite difficult owing to the high energy demand of this process to break the complex structure of lignin, cellulose, and hemicellulose. Hence, catalytic pyrolysis may be necessary that involves the production of a series of compounds, involving a much milder route. Hierarchical zeolites, alkaline metal oxides, and carbonaceous materials were investigated in this approach. Besides, plastics were also added as hydrogen donor during the pyrolysis process. Catalytic pyrolysis was accomplished through two experimental conditions like in situ and ex situ pyrolysis (Luna-Murillo et al. 2021). In situ pyrolysis considers mixing both feedstock and catalyst in a reactor and upgrading simultaneously both solid and vapour phases. Under such conditions, both biomass and catalyst particles came under contact of each other in a fluidized bed that favours faster decomposition of biomass. Under such conditions, the vapour diffused into the catalyst pores, followed by its cracking and other reactions. This process is disadvantageous regarding the pyrolysis temperature that cannot be optimized for catalyst activation. Also, high level of coking produced on the catalyst decreases bio-oil yield and quality. Owing to high char formation, catalyst particles are mixed with char and hence separation of catalyst from biochar is problematic. In ex situ pyrolysis, feedstock is kept into the reactor and after cracking, biomass is introduced there for pyrolysis. The pyrolytic vapour is then passed through catalytic bed for upgrading into bio-oil, gaseous product, and other solid by-products. This process has the potential since cracking temperature can be adjusted to optimize the bio-oil yield (Liu et al. 2020). Contemporary to saying that the product distribution depends on the type of catalyst, and catalyst-to-biomass ratio, additionally, process parameters such as temperature, reactor type, size of biomass particles, heating rate, and residence time, all are the predominating factors that determine product distribution. It has been observed that catalyst influences the yield of the main petrochemical products like toluene, benzene, xylene, propylene, etc. which considers designing of appropriate porous catalyst via controlling the pore structure and active sites. High catalyst/biomass ratio strengthens the diffusion of volatile organic compounds into the pores of catalyst prior to its decomposition into coke. Such a catalytic pyrolysis is subjected to ensure greater deoxygenated products in bio-oil with a high hydrogen-to-carbon (H/ C) ratio in the product, therefore decreasing the acidic quantities present in bio-oil while decreasing the corrosive nature of bio-oil. Also, char formation after catalytic pyrolysis can also be decreased by using a suitable catalyst (Rangel et al. 2023).

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

381

13.3 Heterogeneous Catalysis The pre-treated lignocellulosic biomass after removing lignin may contain a higher concentration of cellulose and hemicellulose that can be catalytically converted to platform chemicals. Among several solid catalysts, Bronsted acid and Lewis’s acidsites both are noteworthy. Cases of strong acid catalysts incorporate zeolites, Mishra et al. (2022), ion-exchanged resins, Harmer and Sun (2001), functionalized mesoporous silicas, Modak et al. (2023a), functionalized carbons, Modak and Bhaumik (2016), functionalized metal oxides, and heteropoly acids and phosphates (Kamata et al. 2024). These catalysts can impact the hydrolysis reaction of disaccharides (such as sucrose) and polysaccharides counting cellulose, starch, and inulin, by dissolving the glycosidic bonds and changing them into sugar monomers like glucose, fructose, and xylose. Solid acid catalysts offer points of interest over homogeneous acids, regularly mineral acids, in terms of selectivity, solidness, recuperation, and reusability. Also, solid acid catalysts have lower working costs and avoid reactor erosion. Earlier, zeolites, a sort of solid acid catalysts, were utilized for the change of different disaccharides (maltose, cellobiose, and sucrose) and polysaccharides (inulin, starch, and cellulose) into sugars (glucose and fructose) in a fluid medium. Strikingly, within the early works, faujasite (HY) zeolite, by changing Si/Al proportions for the hydrolysis of sucrose, illustrated that higher Si/Al proportions (coming about from dealumination reaction) could improve the catalytic rate (Coumans et al. 2022).

13.3.1 Oxidation Reactions 13.3.1.1

Glucose Conversion

Among other catalysts which consider oxidation, gold is significantly applied because of its high selectivity to products. Thus, glucose conversion by gold-based catalysts has attracted interest for its transformation into value-added chemicals. In this regard, cellulose or glucose can be used as a feedstock for the oxidation reaction to gluconic acid which is considered as important as food and beverage additives (An et al. 2012). Thus, gluconic acid obtained from catalytic oxidation is a good choice having been applied in industry although this process has serious drawbacks regarding low efficiency and stability (Zhang et al. 2012a). It is contemporary to mention that onepot glucose to gluconic acid has been used as a model reaction under liquid phase conditions (Fig. 13.3). Comotti and others observed the selective oxidation of D-glucose to D-gluconic acid in the aqueous phase at atmospheric pressure, within 30 °C to 60 °C, by using a colloidal gold catalyst (3.5 nm) as catalyst in an acidic pH range (Beltrame et al. 2006). However, the high activation energy (47.0 ± 1.7 kJ mol−1 ) of the reaction precludes the oxidation reaction. In this regard, plasma-reduced Au/C (7–8 nm)

382

A. Modak OH

OH

O 2 / H 2O 2

O HO

OH

HO OH

O

OH

HO

Supported Au pH (8.5) 50-60 oC

ONa OH

OH

Fig. 13.3 Oxidation of glucose to gluconic acid by gold catalyst

exhibits better efficiency and higher rate than it prepares through the incipient wetimpregnation method (Zhang et al. 2012b). This is because that plasma-modified support enables smaller Au NPs than the conventional synthesis route (Fig. 13.4) (Mohan et al. 2019). Vorlop and others showed that bead-shaped Au/γ-Al2 O3 (0.23 wt% Au) can oxidize glucose to gluconic acid in the presence of either gaseous oxygen or hydrogen peroxide as an oxidant (Prüße et al. 2012). On the other hand, trimetallic gold nanoparticles, Au60 Pt30 Rh10 nanoparticles (TNPs) having 99%) in FDCA. On the other hand, Au/Na-ZSM-5–25 contains much larger gold nanoparticles (15 nm) and promote high yield of HMFCA. TiO2 , CeO2 , and Mg(OH)2 have moderate activity. Table 13.3 shows oxidation reaction of HMF using several supported Au-catalysts. It reports that Au nanoparticles when deposited on conventional supports exhibit poor HMFC yield, in contrast to FDCA yield. However, the HMFC yield was surprisingly improved when Au/MOF and Au/zeolite were used. This result proves that acidic support is crucial for selective oxidation of HMF. Reaction condition: 0.30 g, Au 1.5 wt% catalyst, HMF (0.317 g), H2 O (4.6 g), NaOH (0.4 g), 0.3 MPa O2 , 60 °C, 6 h, molar ratio of Au/HMF = 1:110 (Cai et al. 2013). 3 mmol HMF was dissolved in 20 mL H2 O (mQ) containing 12 mmol NaOH and the corresponding Au catalyst. The reaction mixture was loaded into an autoclave bubbling 0.5 mLs−1 air at 10 bar and heated to 65 °C. Davis et al. reported that by increasing the NaOH/HMF ratio from 2 to 20, the selectivity for FDCA can be improved up to 65% over Au/TiO2 (Casanova et al. 2009a). In another research, the reaction shows an influential effect from the acidic –OH groups of HY zeolite cage to accelerate the oxidation of HMF by molecular oxygen. High conversion (>99%) of HMF as well as high yield of FDCA (>99%) might be because of the stabilization of Au nanoclusters by the hydroxy sites of the support (Table 13.3). Customarily, the size of Au nanoparticles is crucial in determining the selectivity in catalytic reactions, since larger nanoparticles (>15 nm)

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

389

Table 13.3 Comparative study for aerobic oxidation of HMF with supported-Au nanoparticles. Cai et al. 2013 Reproduced with permission from Ref. () Entry

Catalyst

Particle size (nm)

Conversion (%)

Yield (%) HMFCA

FDCA

Others

1

Au/Mg(OH)2

5–7

>99

10

76

14

2

Au/TiO2

10

>99

6

85

9

3

Au/CeO2

10

>99

25

73

2

4

Au/H-MOF

3–5

96

64

15

21

5

Au/Na-ZSM-5

15

92

90

1

15

6

Au/HY

1

>99

>99

0

7

Au-Fe2 O3

–

–

85

15

0

8

Au-C

–

–

56

44

0

0

may lead to wider distribution of products. Smaller Au nanoparticles (~1 nm) may show higher selectivity in oxidation product and thus efficiency of the catalytic reaction was improved. It is hereby noted that the rate of HMF oxidation is dependent on various factors such as the effect of base, temperature, pressure of oxygen, solvent as well as the composition of catalyst. At a high NaOH concentration, subsequent oxidation of HFCA to FDA can be facilitated. Gorbanev et al. observed high selectivity of monoacid HFCA at low NaOH concentration over Au/TiO2 catalyst where yield of HFCA (yield 12%) was drastically reduced in the absence of a base (Davis et al. 2012). Ebitani et al. reported basic hydrotalcite (HT) supported Au NP (3.2 nm) that resulted in an excellent yield to FDCA in the absence of any homogeneous base (Gorbanev et al. 2009). Casanova et al. reported HMF oxidation under base-free condition at 1000 kPa oxygen pressure over Au/CeO2 catalyst. The reaction produced di-ester of 99% yield after 5 h (Gupta et al. 2011). Furthermore, Au/TiO2 was inactive for HMF oxidation throughout 690–3000 kPa oxygen pressure. While alloying with Cu, gold shows high activity for HMF oxidation reaction and thus Au-Cu/TiO2 shows HMF oxidation to HFCA as a major product at 25–130 °C (Gorbanev et al. 2009). Also, there are few reports on HMF oxidation in non-aqueous condition using alcohol specially methanol as a solvent. The major advantage using methanol was that the solubility of FDCA in H2 O is very low, but the ester has high solubility in MeOH. Au/ZrO2 was explored as catalysts for effective oxidation of HMF to FDCA with 90% selectivity at 398 K temperature and 5 MPa pressure within 5 h in the presence of NaOH (Casanova et al. 2009). Conversely, the selectivity of FDCA was substantially decreased after higher regeneration cycles. It is important to note that the incorporation of Ce3+ and the utilization of Au/Cex Zr1-x O2 may rightly function between the Lewis and Brønsted acid sites to promote HMF oxidation (Megías-Sayago 2018). In another report, Wan et al. demonstrate CNT as a stable support while conjugating with Au–Pd nanoalloy catalyst for aerobic oxidation of HMF to FDCA and in the absence of a base (Schade et al. 2018). It has been said that the support could

390

A. Modak

Fig. 13.11 TEM images of a Au/AC, b Au/CNFs, c Au/CNTs, and d Au/Graphite. Stability tests for Au-based catalysts (right side figure). Reproduced with permission from Ref. Megías-Sayago et al. (2018)

enhance the adsorption, and the alloying of Au nanoparticles are the contributory factors for such base-free oxidation reaction of HMF to FDCA. Subsequently, the catalytic activity of Au–Pd/CNT is comparable with Au–Pd/MgO and Au–Pd/HT catalyst that shows a conversation of 100% HMF to FDCA with >99% selectivity. It is pertinent to mention that gold while deposited over carbon (activated carbon, graphite, carbon nanofiber, carbon nanotubes) is widely acknowledged as a catalyst for the oxidation reaction of HMF. On the other hand, Villa et al. prepared Aucatalysts viz. Au/AC (2.9 nm), Au/graphite (5.4 nm), Au/CNFs (3.8 nm), and Au/ CNT (4.6 nm) by sol–gel immobilization approach and manifested a very narrow size distribution of gold particles which proliferates HMF oxidation reaction (Fig. 13.11) (Megías-Sayago et al. 2018). The catalysts were prepared by the sol immobilization method in which the particle sizes increased in the following order: Au (2.9 nm) < Au/CNFs (3.8 nm) < Au/CNTs (4.6 nm) < Au/Graph (5.4 nm) (Fig. 13.11). It is important to note that the acidity and basicity of the surface groups also influence the oxidation process of HMF. The existence of basic functional group on the carbon material can aid in the adsorption of OH− and increase the concentration of OH− near Au species. This phenomenon facilitates the oxidation of HMF to HMFCA, FFCA, and FDCA. On the other hand, it has been reported that the acidic functional groups repel the OH− species resulting in the reduction of the catalytic activity. An alternate explanation was provided by Donoeva et al. where they depict that the catalytic superiority of basic functionalized carbon is attributed to the transfer of positive charge from the surface groups to Auδ+ species, which increases the attraction between the Auδ+ species and hydroxyl species (Wan et al. 2014). Alternatively, the acidic functional group reduces the positive charge on the Auδ+ species which decreases the interaction between Auδ+ species and hydroxyl species and the catalytic oxidation of HMF decreases.

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

391

In another study, Fe(III)-porous polymer was utilized for environmentally friendly synthesis of 2,5-furandicarboxylic acid (FDCA), which is well-known as a polyester building block derived from biomass in water by aerobic oxidation of 5hydroxymethylfurfural (HMF). In this regard, the authors used highly cross-linked, thermally stable robust FeIII-porous organic polymer (FeIII–POP-1) material (Saha et al., 2013). The advantage of metallo-porphyrin unit in FeIII-POP-1 shows high yield (79%) of FDCA at 100 °C and 10 bar air atmosphere. The authors suggested a plausible radical chain mechanism for HMF oxidation involving thermal autooxidation that forms the product via Fenton-type homolytic cleavage of peroxide bonds over iron. Figure 13.12 shows the oxidation profile of HMF from lignocellulosic biomass and the probable intermediates. Also, the reaction kinetics indicates a steady increase in conversion profile of HMF, followed by the highest FDCA yield achieved at 10 h of the reaction time. The above reactions are truly reflecting the oxidation potential of gold and iron for the highly effective conversion of biomass-feedstocks to value-added chemicals.

13.3.2 Hydrogenation Reaction Hydrogenation of biomass under a high-pressure reactor is a common protocol for the upgradation of lignocellulose to clean chemicals like xylitol, sorbitol, ethylene glycol, propylene glycol, etc. which are important as artificial sweeteners, additives, and precursors of polymer (Donoeva et al. 2017). It is customary to mention that high-pressure reactor is hazardous and is not desirable for green condition (Saha et al. 2013). An interesting work was done by Modak et al. while introducing a novel approach to reduce biomass under ambient reaction conditions and using a microwave reactor (Modak et al. 2022). They synthesized atomically dispersed rutheniumsingle-atom catalyst showing unprecedented activity for xylose and glucose hydrogenation to xylitol and sorbitol respectively (Fig. 13.13). In contrast, commercial catalysts that composed of ruthenium nanoparticles on activated carbon are exhibiting inferior activity. The authors showed that ordered mesoporous polymer based on Ru/triphenylphosphine group affords a high yield of reduced sugars, xylitol (yield ∼95%), and sorbitol (yield ∼65%) with formic acid as the only hydrogen donor in a microwave reactor, in contrast to Ru-catechol and Ru-triphenylamine catalysts. They established a unique structure–property relationship that shows an important ligandeffect. The tailored electronic properties in Ru/phosphine catalyst were studied using state-of-the-art techniques viz. X-ray absorption techniques (EXAFS, XANES), Xray photoelectron spectroscopy (XPS), operando in situ DRIFTS, and high-angle annular dark-field scanning transmission electron microscopic analysis (HAADFSTEM) and confirm a promotion in activity and selectivity towards less vulnerable aldehydes for hydrogenation which was again corroborated by DFT calculations. The same group did cellulose valorization under high pressure and showed hydrolytic hydrogenation of cellulose to ethylene glycol, and other polyols can be accomplished under harsh reaction conditions at 200 °C and 50 bar hydrogen pressure

392

A. Modak

Fig. 13.12 (Top) Oxidation pathway for the conversion of lignocellulosic biomass to FDCA; (Bottom) reaction kinetics for the conversion of HMF to FDCA over supported Fe(III) catalysts. Reproduced with permission from Ref. Villa et al. (2013)

(Mankar et al. 2021a). It is pertinent to mention that cellulose is an important biological feedstock which holds promise and potential towards a bio-based economy. Hence, it directs a one-pot process which used heteropolyacid (HPA)/zirconia and Ru/C catalyst (Fig. 13.14). The developed catalytic system exhibits high activity towards selective production of hexitols and ethylene glycol. Ball milling of cellulose for 900 rpm and 8 h proves significantly improvement in the catalytic performance because ball milling reduces crystallinity of cellulose. The current process shows almost complete conversion (100%) of cellulose giving hexitols and ethylene glycol yields of 26.2 and 40%, respectively. The authors demonstrated that heteropolyacid/

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

393

Fig. 13.13 Scheme for the preparation of sugar hydrogenation catalysts containing Ru as the active sites. Reproduced with permission from Ref. Modak et al. (2022)

zirconia catalyst promotes the hydrolysis of cellulose followed by Ru/C responsible for hydrogenation reaction, in this tandem catalysis. Another important application of biomass hydrogenation is to produce transportation fuels by a challenging hydrodeoxygenation reaction from heavily oxygenated lignocelluloses. Sun et al. 2018 describe that C5–C20 range of hydrocarbons of gasoline, diesel, and jet-fuel is formed from furfural (FA) through hydrogenation and hydrodeoxygenation reactions (Fig. 13.15). This process utilizes Raney nickel as catalyst under a batch reaction condition which could effectively decrease oxygen content from 22.1 wt.% to 0.58 wt.% in the products. On the other hand, hydrothermal liquefaction (HTL) of biomass produces crude bio-oil, and upgradation of biocrude oil to biofuel is necessary by catalytic hydrogenation which is considered a promising method to produce clean and pure biofuel. Effect of reaction temperature, residence time, and type of catalyst can predominately monitor the process as described by the authors.

394

A. Modak

Fig. 13.14 One-pot cellulose valorization using heteropolyacid/zirconia and Ru/C as catalyst. Reproduced with permission from Ref. Mankar et al. (2021a) Fig. 13.15 Hydrodeoxygenation of biomass to several ranges of alkane products at 6 MPa H2 , 170 °C, reaction 5 h in a batch reactor. Reproduced with permission from Ref. Sun et al. (2018)

Modak et al. showed a facile hydrogenolysis of sugars to produce ethylene glycol and propylene glycol by a green microwave route (Modak et al. 2023). They prepared an interesting mesoporous catalyst which is functionalized by triphenylphosphine and triphenylphosphine oxide as organic groups that stabilize Ru single atoms (Fig. 13.16). Strikingly, Ru/PPh3 /POPh3 exhibits ligand-effect with a 70% yield of all reduced sugars (xylitol) and glycols from 99% conversion of xylose that is an abundant sugar from plant biomass. Modak and the group confirmed an electronic effect on Ru single atoms by phosphine ligands, by a computational DFT study and demonstrated that the “ligand-effect” on Ru has the pivotal role in hydrogenolysis of sugar molecules.

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

395

Fig. 13.16 Schematic presentation for the preparation of Ru/triphenylphosphine/ triphenylphosphine oxide-functionalized large pore mesoporous silica. Reproduced with permission from Ref. Modak et al. (2023)

13.4 Economic Aspects It is noteworthy to mention that the catalyst improves the process economics by providing a milder reaction condition (T&P). It is important to note that cheaper catalysts are suitable than expensive precious metal catalysts for commercial purposes. As, for example, in the gasification process, using cheaper catalysts improves sustainability because the cost of hydrogen can be reduced more, thus increasing income at a higher rate. Apart from that, tar formation is also reduced, and the environmental profit is also huge. Further to note is that the cost of catalyst can be contemplated by the valuable product gases as produced during the gasification process. Moreover, the choice of catalyst is pivotal which subsequently may control the quality of syngas from biomass as well as the quality of the jet fuels, diesel, wax, and naphtha that was improved from the Fischer–Tropsch reaction through upgradation of syn gas. It is pertinent to mention that for the hydrothermal carbonization process, economic analysis must be required, which was assessed by Akbari et al. (2019) and Hussin et al. (2023). Biomass conversion reactions, for example: cellulose to lactic acid and gluconic acid, hemicelluose to furan-containing compounds and lactones,lignin to ferulate, coumarate, and vanillin at high temperature (100–200 °C) with high pressure (10–100 bar) requires extreme heating and high power inputs. Thus, catalytic processes are currently the hotspots to maintain a cost-effective approach to produce value-added chemicals.

396

A. Modak

13.5 Concluding Remarks With the growing focus on utilizing lignocellulosic biomass for sustainable purposes, there is an opportunity to generate fuels and chemicals from this renewable and abundant resource. The conversion of plant-derived lignocellulosic biomass, which contains cellulose, hemicelluloses, and lignin, is particularly important due to its non-edible nature compared to food-based biomass like starch and various disaccharides. There are two potential approaches for the conversion of polysaccharides, cellulose, and hemicelluloses present in lignocellulosic biomass. The first approach involves isolating the polysaccharides after pre-treatment to extract them from the lignocellulosic matrix. The second approach entails direct hydrolysis of the lignocellulosic biomass as a whole and to disintegrate the complex hydrogen bonding, lignin content, where challenges associated with lignin conversion may be hindering for the direct transformation of lignocellulosic biomass into sugars. Nevertheless, the multiple hydrogen bonding in cellulose leads to its highly rigid and crystalline structure, making it challenging to degrade (Hussin et al. 2023; Hasanzadeh et al. 2023). Additionally, due to the strong hydrogen bonding, cellulose remains insoluble in many common solvents. However, the isolation procedures, typically involving the use of acids, bases, or steam, can induce structural changes in these polysaccharides. These changes can include chain length reduction, increased presence of reducing ends, structural loosening, and loss of crystallinity, which can facilitate the subsequent hydrolysis of cellulose and hemicelluloses. On the contrary, some modifications such as oxidation, acylation, and impurity incorporation may impede the hydrolysis process. Therefore, selecting the appropriate pre-treatment method is crucial to ensure efficient isolation (Farshchi et al. 2023). The second route uses lignocellulosic biomass directly without any pre-treatment processes (Kumar et al. 2009). This method helps to avoid contamination of the substrate by external chemicals employed during pre-treatment and minimizes any structural alterations produced by pre-treatment operations. However, hydrolysing the polysaccharides becomes difficult due to the complicated native structure of lignocellulosic biomass. To facilitate the hydrolysis reactions in such instances, heterogeneous catalysts such as solid acids and supported metal catalysts have been used. Solid acid catalysts, like mineral acids, can increase the reaction by making active sites available on the catalyst surface, such as Bronsted acid sites. Various governments, private entities, and industries worldwide are sponsoring numerous projects focused on developing environmentally friendly methods for converting lignocellulosic biomass into valuable chemicals. Catalytic conversion of biomass by metal nanoparticles and single atoms has huge potential and is still emerging a with large amount of research progressively being published that connects the catalyst preparation to control the size and shape of metal active species (Hu et al. 2021). It considers the preparation of smaller particles (less than 5 nm) that depend on various factors like preparation method, nature of support, pH and concentration of the precursor, calcination temperature, etc. Deposition–precipitation and impregnation are the most common methods of

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

397

preparing supported catalysts due to their simplicity. Metal oxides with high surface area and non-stoichiometric properties (e.g. CeO2 , TiO2 ), metal organic frameworks (MOF), and porous organic polymers (POP) are among the most common supports for using in supported catalysts due to their strong metal support interaction (SMSI). Moreover, alloying is another strategy with other metals like platinum, palladium, etc. that may increase catalytic efficiency. The unsupported gold nanoparticles are also catalytically modified in terms of shape, size, and are stabilized using different stabilizing agents. It is worthy to mention that supported metal catalysts are identified and characterized by UV–visible spectroscopy, TEM, XPS, XAS, etc. Microscopic techniques, for example, TEM, along with HRTEM and STEM can visualize not only the diffraction patterns of metal nanoparticles but also can aid in the identification of active facets and metal–support interfaces. On the other hand, X-Ray-based techniques like XPS and XAS can reveal foremost information about the chemical structure of active metal sites, in terms of the oxidation states and chemical environment. Also, multiple techniques, viz. Zeta potential measurement, Fluoroscence (XRF), Raman Spectroscopy, Photoluminescence spectroscopy, X-Ray Diffraction (XRD), physisorption, and chemisorption studies, are also significant to understand the active sites and the role in catalysts. The main theme of this chapter is the oxidative and reductive transformation of biomass-feedstocks, with the effect of metal nanoparticles due to their ability of activating molecular oxygen and hydrogen. The reaction kinetics and the productyield of such organic transformations are dependent on the size, shape, oxidation states, co-ordination of metals, and the nature of supports where alloying and doping in the support might be critical to control the activity. Another important parameter that controls the activity in the heterogeneous catalysis is the mass transfer limitations such as gas–liquid, liquid–solid, and pore diffusion since biomass is a large and sterically demanding substrate to control. Hence, design the catalysts that controls efficient mass transportation of the reactant and reagents to the active site of the catalyst, considers enormous important and should be calculated to get insight about the physical restrictions involved in the catalytic process. Briefly, it is difficult to judge the catalytic functioning of various materials due to the difference in reaction conditions which are different from each other. It is so expected to create new and more efficient nanostructured catalysts, comprising a balanced amount of activity, selectivity, and stability in optimum conditions, and combining new computational tools like machine learning (Lu et al. 2021). Acknowledgements Arindam Modak would like to thank AIAS, Amity University, Noida Campus, for providing the infrastructure. Further, AM acknowledges Council of Science & Technology, UP (CSTUP) project, for providing the funding (CST/CHEM/D-1429).

398

A. Modak

References Agbor VB, Cicek N, Sparling R, Berlin A, Levin DB (2011) Biomass pretreatment: fundamentals toward application. Biotechnol Adv 29:675–685 Akbari M, Oyedun AO, Kumar A (2019) Comparative energy and techno-economic analyses of two different configurations for hydrothermal carbonization of yard waste. Bioresour Technol Rep 7:100210 An D, Ye A, Deng W, Zhang Q, Wang Y (2012) Selective conversion of cellobiose and cellulose into gluconic acid in water in the presence of oxygen, catalyzed by polyoxometalate-supported gold nanoparticles. Chem Eur J 18(10):2938–2947. https://doi.org/10.1002/chem.201103262 Beltrame P, Comotti M, Della Pina C, Rossi M (2006) Aerobic Oxidation of Glucose: II. Catalysis by colloidal gold. Appl Catal Gen 297(1):1–7. https://doi.org/10.1016/j.apcata.2005.08.029 Biella S, Castiglioni GL, Fumagalli C, Prati L, Rossi M (2002) Application of gold catalysts to selective liquid phase Oxidation. Catal Today 72(1):43–49. https://doi.org/10.1016/S0920-586 1(01)00476-X Bohre A, Modak A, Chourasia V, Jadhao PR, Sharma K, Pant KK (2022) Recent advances in supported ionic liquid catalysts for sustainable biomass valorisation to high-value chemicals and fuels. Chem Eng J 450:138032 Cai J, Ma H, Zhang J, Song Q, Du Z, Huang Y, Xu J (2013) Gold nanoclusters confined in a supercage of Y Zeolite for Aerobic Oxidation of HMF under mild conditions. Chem Eur J 19(42):14215–14223. https://doi.org/10.1002/chem.201301735 Canabarro N, Soares JF, Anchieta CG, Kelling CS, Marcio A Mazutti MA (2013) Thermochemical processes for biofuels production from biomass. Sustain Chem Process 1:22. http://www.sustai nablechemicalprocesses.com/content/1/1/22 Casanova O, Iborra S, Corma A (2009) Biomass into chemicals: Aerobic Oxidation of 5Hydroxymethyl-2-Furfural into 2,5-Furandicarboxylic acid with gold nanoparticle catalysts. Chem Sus Chem 2(12):1138–1144. https://doi.org/10.1016/j.jcat.2009.04.019 Casanova O, Iborra S, Corma A (2009) Biomass into chemicals. One pot-base free oxidative esterification of 5-Hydroxymethyl-2-Furfural into 2, 5-Dimethylfuroate with gold on Nanoparticulated Ceria. J Catal 265(1):109–116. Chen H, Liu J, Chang X, Chen D, Xue Y, Liu P, Lin H, Han S (2017) A review on the pretreatment of lignocellulose for high-value chemicals. Fuel Process Technol 160(1):196–206 Comotti M, Pina CD, Matarrese R, Rossi M (2004) The catalytic activity of “naked” gold particles. Angew Chem Int Ed 43:5812–5815. https://doi.org/10.1002/anie.200460446 Correia LS, Grénman H, Wärnå J, Salmi T, Murzin DY (2019) Catalytic oxidation kinetics of arabinose on supported gold nanoparticles. Chem Eng J 370:952–961. https://doi.org/10.1016/ j.cej.2019.03.241 Coumans FJAG, Overchenko Z, Wiesfeld JJ, Kosinov N, Nakajima K, Hensen EJM (2022) Protection strategies for the conversion of biobased furanics to chemical building blocks ACS sustainable. Chem. Eng 10(10):3116–3130 Davis SE, Zope BN, Davis RJ (2012) On the mechanism of selective Oxidation of 5Hydroxymethylfurfural to 2,5-Furandicarboxylic acid over supported Pt and Au catalysts. Green Chem 14(1):143–147. https://doi.org/10.1039/C1GC16074E De S, Dutta S, Patra AK, Bhaumik A, Saha B (2011) Self-assembly of mesoporous TiO2 nanospheres viaaspartic acid templating pathway and its catalytic application for 5-hydroxymethyl-furfural synthesis. J Mater Chem 21:17505–17510 De S, Dutta S, Patra AK, Rana BS, Sinha AK, Saha B, Bhaumik A (2012) Biopolymer templated porous TiO2: an efficient catalyst for the conversion of unutilized sugars derived from hemicellulose. Appl Catal A Gen 435–436:197–203 Donoeva B, Masoud N, de Jongh PE (2017) Carbon Support Surface Effects in the Gold-Catalyzed Oxidation of 5-Hydroxymethylfurfural. ACS Catal, 7(7):4581–4591. https://doi.org/10.1021/ acscatal.7b00829

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

399

Farshchi ME, Aghdasinia H, Rostamnia S, Sillanpää M (2023) Catalytic adsorptive elimination of deleterious contaminant in a pilot fluidised-bed reactor by granulated Fe3O4/Cu-MOF/ cellulose nanocomposites: RSM optimisation and CFD approach. https://doi.org/10.1080/030 67319.2023.2170752 Gorbanev YY, Klitgaard SK, Woodley JM, Christensen CH, Riisager A (2009) Gold-catalyzed Aerobic Oxidation of 5-Hydroxymethylfurfural in water at ambient temperature. Chemsuschem 2(7):672–675. https://doi.org/10.1002/cssc.200900059 Gupta NK, Nishimura S, Takagaki A, Ebitani K (2011) Hydrotalcite-supported gold-nanoparticleCatalyzed highly efficient base-free aqueous oxidation of 5-Hydroxymethylfurfural into 2,5Furandicarboxylic acid under atmospheric oxygen pressure. Green Chem 13(4):824–827. https:// doi.org/10.1039/C0GC00911C Hao J, Song X, Jia S, Mao W, Yan Y, Zhou J (2021a) Catalytic conversion of starch to 5- Hydroxymethylfurfural by Tin Phosphotungstate. Front Energy Res 9:679709. https://doi.org/10.3389/ fenrg.2021.679709 Hao B, Xu D, Jiang G, Sabri TA, Jing Z, Guo Y (2021b) Chemical reactions in the hydrothermal liquefaction of biomass and in the catalytic hydrogenation upgrading of biocrude. Green Chem 23:1562–1583 Harmer MA, Sun Q (2001) Solid acid catalysis using ion-exchange resins. Appl Catal A: Gener 221(1–2):45–62 Hasanzadeh A, Shojaei S, Gholipour B, Vahedi P, Rostamnia S (2023) Biosynthesis of MCC/IL/ Ag-AgCl NPs by cellulose-based nanocomposite for medical antibiofilm applications. Ind Eng Chem Res 62(11):4729–4737 Hashemi B, Shiplu Sarker S, Lamb JJ, JJ, Lien KM. (2021) Yield improvements in anaerobic digestion of lignocellulosic feedstocks. J Clean Prod 288:125447 Hernández-Beltrán JU, Hernández-De Lira IO, Cruz-Santos MM, Saucedo-Luevanos A, Hernández-Terán F, Balagurusamy N (2019) Insight into pretreatment methods of lignocellulosic biomass to increase biogas yield: current state, challenges, and opportunities. Appl Sci 9:3721 Hu J, Cao W, Guo L (2021) Directly convert lignocellulosic biomass to H2 without pretreatment and added cellulase by two-stage fermentation in semi-continuous modes. Renew Energy 170:866– 874 Hussin F, Hazani NN, Khalil M, Aroua MK (2023) Environmental life cycle assessment of biomass conversion using hydrothermal technology: a review. Fuel Process Technol 246:107747 Ishida T, Okamoto S, Makiyama R, Haruta M (2009) Aerobic oxidation of Glucose and 1Phenylethanol over gold nanoparticles directly deposited on ion-exchange resins. Appl Catal a: Gen 353:243–248. https://doi.org/10.1016/j.apcata.2008.10.049 Jha S, Okolie JA, Nanda S, Dalai AK (2022) A review of biomass resources and thermochemical conversion technologies. Chem Engin Technol 45(5):791–799 Kamata K, Aihara T, Wachi K (2024) Synthesis and catalytic application of nanostructured metal oxides and phosphates. Chem comm 60:11483–11499. https://doi.org/10.1039/D4CC03233K Kumar P, Barrett DM, Delwiche MJ, Stroeve P (2009) Methods for pretreatment of lignocellulosic biomass for efficient hydrolysis and biofuel production. Ind Eng Chem Res 48(8):3713–3729 Kusema BT, Mikkola JP, Murzin DY (2012) Kinetics of L-Arabinose oxidation over supported gold catalysts with in situ catalyst electrical potential measurements. Catal Sci Technol 2(2):423–431. https://doi.org/10.1039/C1CY00365H Lee RA, Lavoie JM (2013) From first- to third-generation biofuels: challenges of producing a commodity from a biomass of increasing complexity. Anim Front 3(2):6–11. https://doi.org/10. 2527/af.2013-0010 Liu X, Hiligsmann S, Gourdon R, Bayard R (2017) Anaerobic digestion of lignocellulosic biomasses pretreated with Ceriporiopsis subvermispora. J Environ Manag 193:154–162 Liu NR, Rahman M, Sarker M, Chai M, Li C, Cai J (2020) A review on the catalytic pyrolysis of biomass for the bio-oil production with ZSM-5: focus on structure. Fuel Processing Technol 199:106301

400

A. Modak

Liu C, Wu S, Zhang H, Xiao R (2019) Catalytic oxidation of lignin to valuable biomass-based platform chemicals: a review. Fuel Process Technol 191:181–182 Lu Y, Zhang Z, Wang H, Wang Y (2021) Toward efficient single-atom catalysts for renewable fuels and chemicals production from biomass and CO2. Appl Catal B 292(5):120162 Luan H, Cai Z (2023) Introduction to artificial intelligence and machine learning in environmental science. Environ Sci: Adv. https://doi.org/10.1039/d3va90026f Luna-Murillo B, Pala M, Paioni AL, Baldus M, Ronsse F, Prins W, Bruijnincx PCA, Weckhuysen BM (2021) Catalytic fast Pyrolysis of biomass: catalyst characterization reveals the feed-dependent deactivation of a technical ZSM-5-based catalyst. ACS Sustain Chem Eng 9(1):291–304 Mankar AR, Modak A, Pant KK (2021a) High yield synthesis of hexitols and ethylene glycol through one-pot hydrolytic hydrogenation of cellulose. Fuel Process Technol 218:106847 Mankar AR, Modak A, Pant KK (2022) Recent advances in the valorization of lignin: A key focus on pretreatment, characterization, and catalytic depolymerization strategies for future biorefineries. Adv Sustain Syst 6(3):2100299 Mankar AR, Pandey A, Modak A, Pant KK (2021) Microwave mediated enhanced production of 5-hydroxymethylfurfural using choline chloride-based eutectic mixture as sustainable catalyst. Renew Energy 177:643–651 Megías-Sayago C, Chakarova K, Penkova A, Lolli A, Ivanova S, Albonetti S, Cavani F, Odriozola JA (2018) Understanding the role of the acid sites in 5-Hydroxymethylfurfural Oxidation to 2,5-Furandicarboxylic acid reaction over gold catalysts: surface investigation on CexZr1–XO2 compounds. ACS Catal 8(12):11154–11164. https://doi.org/10.1021/acscatal.8b02522 Mishra D, Modak A, Pant KK, Zhao XS (2022) Improved benzene selectivity for methane dehydroaromatization via modifying the zeolitic pores by dual-templating approach. Microporous Mesoporous Mater 344:112172 Modak A, Bhaumik A (2016) Surface-exposed Pd nanoparticles supported over nanoporous carbon hollow tubes as an efficient heterogeneous catalyst for the CC bond formation and hydrogenation reactions. J Mol Catal A Chem 425:147–156 Modak A, Ghosh A, Mankar AR, Pandey A, Selvaraj M, Pant KK, Chowdhury B, Bhaumik A (2021a) Cross-linked porous polymers as heterogeneous Organocatalysts for task-specific applications in biomass transformations, CO2 fixation, and asymmetric reactions. ACS Sustain Chem Eng 9(37):12431–12460 Modak A, Gill D, Sharma K, Bhasin V, Pant KK, Jha SN, Bhattacharyya D, Bhattacharya S (2023) Facile hydrogenolysis of sugars to 1,2-glycols by Ru@PPh3/OPPh3 confined large-pore mesoporous silica. J Phys Chem Lett 14:10832–10846 Modak A, Mankar AR, Pant KK, Bhaumik A (2021b) Mesoporous porphyrin-silica nanocomposite as solid acid catalyst for high yield synthesis of HMF in water. Molecules 26(9):2519 Modak A, Gill D, Mankar AR, Pant KK, Bhasin V, Nayak C, Bhattacharya S (2022) Controlled synthesis of Ru-single-atoms on ordered mesoporous phosphine polymers for microwaveassisted conversion of biomass-derived sugars to artificial sweeteners. Nanoscale 14:15875– 15888 Modak A, Mankar AR, Sonde RR, Pant KK (2023a) One-pot conversion of glucose to 5hydroxymethylfurfural under aqueous conditions using acid/base bifunctional mesoporous silica catalyst. Renew Energy 212:97–110 Modak A, Gill D, Sharma K, Bhasin V, Pant KK, Jha SN, Bhattacharyya D, Bhattacharya S (2023b) Facile hydrogenolysis of sugars to 1,2-glycols by Ru@PPh3/OPPh3 confined large-pore mesoporous silica. J Phys Chem Lett 14:10832–10846 Modak A (2023) Recent progress and opportunity of metal single-atom catalysts for biomass conversion reaction. Chemistry-An Asian J 18(24):e202300671 Modak A, Ghosh A, Bhaumik A, Chowdhury B (2021) CO2 hydrogenation over functional nanoporous polymers and metal-organic frameworks. Adv Colloid Interface Sci 290:102349 Mohan R, Modak A, Schechter A (2019) A comparative study of plasma-treated oxygen-doped single-walled and multiwalled carbon nanotubes as electrocatalyst for efficient oxygen reduction

13 Lignocellulosic Biomass-Feedstocks: Pre-treatment and Catalytic …

401

reaction. ACS Sustain Chem. Eng 7(13):11396–11406. https://doi.org/10.1021/acssuschemeng. 9b01125 Mondal S, Mondal J, Bhaumik A (2015) Sulfonated porous polymeric nanofibers as an efficient solid acid catalyst for the production of 5-Hydroxymethylfurfural from biomass. ChemCatChem 7:3570–3578 Nges IA, Li C, Wang B, Xiao L, Yi Z, Liu J (2016) Physio-chemical pretreatments for improved methane potential of Miscanthus lutarioriparius. Fuel 166:29–35 Pina CD, Falletta E, Prati L, Rossi M (2008) Selective oxidation using gold. Chem Soc Rev 37(9):2077–2095. https://doi.org/10.1039/B707319B Pina DC, Falletta E, Rossi M (2012) Update on selective oxidation using gold. Chem Soc Rev 41(1):350–369. https://doi.org/10.1039/C1CS15089H Prüße U, Jarzombek P, Vorlop KD (2012) Gold-catalyzed Glucose oxidation using novel spherical sol-gel derived alumina supports produced via the JetCutter. Top Catal 55(7):453–459. https:// doi.org/10.1007/s11244-012-9816-0 Rangel MC, Mayer FM, Carvalho MS, Saboia G, Andrade AM (2023) Selecting catalysts for pyrolysis of Lignocellulosic biomass. Biomass 3:31–63 Saha B, Gupta D, Abu-Omar MM, Modak A, Bhaumik A (2013) Porphyrin-based porous organic polymer-supported iron (III) catalyst for efficient aerobic oxidation of 5-hydroxymethyl-furfural into 2, 5-furandicarboxylic acid. J Catal 299:316–320 Sannigrahi P, Pu Y, Ragauskas A (2010) Cellulosic biorefineries-unleashing lignin opportunities. Current Opin Environ Sustain 2(5–6):383–393 Schade OR, Kalz KF, Neukum D, Kleist W, Grunwaldt JD (2018) Supported gold- and silver-based catalysts for the selective aerobic oxidation of 5-(Hydroxymethyl)Furfural to 2,5-Furandicarboxylic Acid and 5-Hydroxymethyl-2-Furancarboxylic Acid. Green Chem 20(15):3530–3541. https://doi.org/10.1039/C8GC01340C Simakova OA, Kusema BT, Campo BC, Leino AR, Kordás K, Pitchon V, Mäki-Arvela P, Murzin DY (2011) Structure sensitivity in L-Arabinose Oxidation over Au/Al2O3 catalysts. J Phys Chem C 115(4):1036–1043. https://doi.org/10.1021/jp105509k Simakova OA, Smolentseva E, Estrada M, Murzina EV, Beloshapkin S, Willför SM, Simakov AV, Yu D (2012) From woody biomass extractives to health-promoting substances : selective oxidation of the Lignan Hydroxymatairesinol to Oxomatairesinol over Au, Pd, and Au-Pd Heterogeneous catalysts. J Catal 291:95–103. https://doi.org/10.1016/j.jcat.2012.04.012 Song Z, Yang G, Liu X, Yan Z, Yuan Y, Liao Y (2014) Comparison of seven chemical pretreatments of corn straw for improving methane yield by Anaerobic digestion. PLoS ONE 9:e93801 Sun, S., Yang, R., Wang, X., Yan, S. (2018) Hydrogenation and hydrodeoxygenation of biomassderived oxygenates to liquid alkanes for transportation fuels. Data Brief 17:638–646 Tan X, Deng W, Liu M, Zhang Q, Wang Y (2009) Carbon nanotube-supported gold nanoparticles as efficient catalysts for selective oxidation of Cellobiose into Gluconic Acid in aqueous medium. Chem Commun 46:7179–7181. https://doi.org/10.1039/B917224F Tokonami S, Morita N, Takasaki K, Toshima N (2010) Novel synthesis, structure, and oxidation catalysis of Ag/Au bimetallic nanoparticles. J Phys Chem C 114(23):10336–10341. https://doi. org/10.1021/jp9119149 Villa A, Schiavoni M, Campisi S, Veith GM, Prati L (2013) Pd-Modified Au on carbon as an effective and durable catalyst for the direct oxidation of HMF to 2, 5- Furandicarboxylic Acid. Chemsuschem 2:609–612. https://doi.org/10.1002/cssc.201200778 Wan X, Zhou C, Chen J, Deng W, Zhang Q, Yang Y, Wang Y (2014) Base-free aerobic oxidation of 5-Hydroxymethyl-Furfural to 2,5-Furandicarboxylic acid in water catalyzed by functionalized Carbon Nanotube-supported Au-Pd alloy nanoparticles. ACS Catal 4(7):2175–2185. https://doi. org/10.1021/cs5003096 Zhang Y, Cui X, Shi F, Deng Y (2012a) Nano-gold catalysis in fine chemical synthesis. Chem Rev 112(4):2467–2505. https://doi.org/10.1021/cr200260m

402

A. Modak

Zhang M, Zhu X, Liang X, Wang Z (2012b) Preparation of highly efficient Au/C catalysts for glucose oxidation via novel plasma reduction. Catal Commun 25:92–95. https://doi.org/10. 1016/j.catcom.2012.04.012 Zhang H, Cao Y, Lu L, Cheng Z, Zhang S (2014) Trimetallic Au/Pt/Rh nanoparticles as highly active catalysts for aerobic glucose oxidation. Metall Mater Trans B 46(1):523–530. https://doi. org/10.1007/s11663-014-0219-4

Chapter 14

Photodeposition for Highly Effective Photocatalytic Materials Akshita, Sunil Kumar, Deepshikha Gupta, Ravi Kant Choubey, and Tejendra K. Gupta

14.1 Introduction 14.1.1 Photodeposition of Metal/Nanoparticles of Metal Oxide on Semiconductor Surfaces A precise metal (or metal oxide) nanoparticle is formed on the surface of a semiconductor particle during the scientific phenomenon known as photodeposition. An aqueous solution comprising metal salt and a combination of semiconductor particles is illuminated to start this process. Clark and Vondjidis presented the phenomenon for the first time in 1965 (Clark and Vondjidis 1965). The photocatalyst can be found in the form of a film or powder. It is disseminated in an oxygen-depleted aqueous solution. When semiconductor particles that are already present in the solution are exposed to light irradiation in the presence of metal salts, the production and metal-deposited nanoparticles on the semiconductor’s surface can be seen. In the area of photocatalysis, the photodeposition method has been used (O’Rourke et al. 2019), and fluorescence imaging methods have received an abundance of focus lately for their capability to dynamically observe the deposition of individual cocatalyst nanoparticles onto semiconductors (Su and Wang 2021). When titanium dioxide and silver nitrate were used together, the formation of metallic silver was Akshita · D. Gupta · T. K. Gupta (B) Department of Chemistry, Amity Institute of Applied Sciences, Amity University Uttar Pradesh, Noida 201313, India e-mail: [email protected] S. Kumar Department of Physics, Indira Gandhi University, Meerpur (Rewari)-122502, Haryana, India R. K. Choubey Department of Applied Physics, Amity Institute of Applied Sciences (AIAS), Amity University, Noida Campus, Sector-125, Noida, Uttar Pradesh 201313, India 403

404

Akshita et al.

discovered through infrared research (Wenderich and Photodeposition of platinum nanoparticles on well-defined tungsten oxide Controlling oxidation state, particle size and geometrical distribution. xxxx; Wenderich and Mul 2016). Kraeutler and Bard, however, wrote a ground-breaking article that sparked interest in photodeposition in 1978 (Wenderich and Mul 2016). After that, photodeposition was thoroughly studied, with more recent research focusing on assessing how the concentration of silver nanoparticles affected the optical, morphological, structural, and electrical properties of TiO2 nanocrystals (Ahmed et al. 2021). Other investigations on the photodeposition of titanium dioxide with gold and platinum nanoparticles have been conducted (Vaelma and Selin 2017). Furthermore, research has been done on the development of inks incorporating silver, platinum, and gold for photodeposition (O’Rourke et al. 2019). Additionally, using the laser-liquid interaction, researchers have effectively synthesized silver nanoparticles doped onto titanium oxide (Whang et al. 2009). The slurry comprising acetic acid, HCl, Na2 CO3 , hexachloroplatinic acid (H2 PtCl6 ), anatase powder, and light was exposed by the researchers. The investigation’s goal was to load platinum onto titanium dioxide (TiO2 , anatase). Notably, the reaction used acetic acid as a sacrificed electron donor. The process was speeded up by using a nitrogen purge that helped the researchers to get rid of oxygen and carbon dioxide. Later, at 55 °C the slurry system was heated. Via the photodeposition as a method of nanoparticle synthesis, the welldispersion of the platinum nanoparticles can be produced successfully (Wenderich xxxx; Vaelma and Selin 2017). Subsequently, photodeposition garnered significant interest and was employed to produce nanoparticles for diverse applications, such as photocatalysis-induced hydrogen production (Scholarship et al. 2018; Khnayzer et al. 2012a). Photodeposition functions in accordance with the light-induced electrochemistry theory, and recent research has looked into how dry-soft grinding and the photodeposition of gold or platinum can increase TiO2 ’s photoactivity (Galeano et al. 2019). Researchers have also contrasted the photocatalytic oxidation of propane on anatase, rutile, and mixed-phase anatase–rutile TiO2 nanoparticles to gain additional insight into the influence of surface orientation on the photoactivity of TiO2 (Photoactivity and Orientation xxxx). Several crucial prerequisites must be satisfied for the photodeposition process to proceed smoothly. The most crucial factor is the energy levels of the semiconductor’s bands. In addition, the photon energy of the incident light must be greater than the band gap energy of the semiconductor. It is also crucial to effectively separate and migrate charge carriers. The semiconductor should also provide enough active surface sites to support photodeposition (Wenderich and Mul 2016). Additionally, many iterations of conventional photodeposition methods have been investigated. In one such method, a semiconductor is dispersed in a metal precursor solution without light. The semiconductor is then dried and filtered before the surface-adsorbed precursor is transformed into metal nanoparticles using photon-induced conversion under nonaqueous gas-phase conditions (O’Rourke et al. 2019; Wenderich and Mul 2016). Variations in reactivity, preparation time, and the subsequent shape of nanoparticles can be caused by differences in the content of metal precursors under wet and dry conditions (Wenderich and Mul

14 Photodeposition for Highly Effective Photocatalytic Materials

405

2016). Recent studies have focused on facets of photodeposition, such as the conditions of electron egress in semiconductor nanomaterials during the photodeposition reaction (Ye and Huan 2022), the use of visible light to activate TiO2 photocatalysts (Etacheri et al. 2015), and the function of metal supported on TiO2 in the photoreformation of oxygenates (Majeed et al. 2022). For general water-splitting applications, photodeposition has also been used to selectively deposit metal nanoparticles on lighted semiconductor-supported nanoparticles (Mei et al. 2018). For photodeposition to be effective, the reduction potential of the metal to be deposited needs to align favorably with the energy-band locations of the semiconductor. For instance, the semiconductor’s conduction band bottom should exhibit more negativity than the metals’ reduction potential, while the valence band top should exhibit greater positivity than the oxidation potential of the species to be oxidized, which could be a metal (ion), water, or sacrificial agent. Furthermore, for total water splitting to occur, the semiconductor’s conduction band minimum must be smaller than the reduction potential required for the hydrogen evolution reaction.

14.1.2 Applications of Photodeposition and Comparison to the Alternative Methods Significant applications for metal (oxide) nanoparticles on semiconductor surfaces include air filtration (Paola et al. 2012; Zhao and Yang 2003), wastewater treatment (Chong et al. 2010; Ahmed et al. 2010), and photocatalytic generation of solar fuel (Kudo and Miseki 2009; Roy et al. 2010; Maeda 2011). The stability and effectiveness of semiconductors in light-driven processes are significantly increased by cocatalytic nanoparticles, also known as co-catalysts (Ahmed et al. 2010; Maeda 2011; Ran et al. 2014). These nanoparticles are vital in a variety of applications. Co-catalysts have been suggested to provide the following functions when loaded properly: (i) Suppressing electron/hole recombination by serving as “beacons” for charge carriers during the photoexcitation of the semiconductor. (ii) By offering reactions involving charge-transfer active sites. (iii) Using Au or Ag to increase the impact of plasmonic fields on light absorption (Zhou et al. 2015). There are a variety of additional techniques for depositing co-catalytic nanoparticles onto high surface area semiconductor surfaces in addition to photodeposition. Impregnation (Maeda et al. xxxx), Chemical reduction (Kang and Sohn 2012; Ma et al. 2013), Electrodeposition (Kang and Sohn 2012; Ma et al. 2013), Atomic-layer deposition (ALD) (Dasgupta et al. 2013), Sputtering (Murata et al. 2012) and Physical mixing (Wenderich and Mul 2016) are some of these techniques. Photodeposition offers several desirable benefits over alternative techniques for depositing co-catalytic nanoparticles on semiconductors with high surface areas: (i) Simplicity: In contrast to other procedures, photodeposition only requires illumination in a simplistic slurry reactor. Other methods may need for the use of bias potential or greater temperatures. (ii) Geometrical Control: The spatial arrangement of nanoparticles on facet-engineered semiconductor crystal surfaces can

406

Akshita et al.

be precisely controlled by photodeposition, potentially allowing for the modification of nanoparticle size and oxidation state. (iii) In situ Monitoring: It is interesting that H2 production during photodeposition may be observed in real-time, which is essential for figuring out the best co-catalyst nanoparticle loading for water splitting in photocatalytic applications (Jiang et al. 2015; Chen et al. 2013; Rufus et al. 1995; Busser et al. 2012). The size, level of agglomeration, and oxidation state of the metal (oxide) nanoparticles in their as-prepared state can vary depending on the procedures used to deposit them onto semiconductors. Jiang et al.‘s study evaluated two different ways for depositing Pt/TiO2 and found that photodeposition in the presence of glycerol only produced Pt in its metallic state. Other techniques, however, produced mixtures of Pt (0), Pt (II), and Pt (IV) species, which resulted in noticeably worse performance in the photocatalytic production of hydrogen via glycerol reforming. This study showed that Pt (0) particles have the highest activity in the reforming of glycerol, indicating the selective formation of Pt (0) as a benefit of photodeposition over other processes. This favorable property, however, is only possible in P25 solutions that are diluted and at low glycerol concentrations. Oxidized Pt particles were produced when higher-density suspensions were used during photodeposition, which the authors inferred, speculatively, was due to a faster deposition rate of partially oxidized Pt species. To fully comprehend the impact of slurry density on the final Pt oxidation state, additional research is advised. In the process of in situ photodeposition, protons are reduced to form hydrogen while a metal cation is reduced on the surface of the photocatalyst. Figure 14.2 provides an illustration of the in situ photodeposition reactions (Fig. 14.1).

14.2 Photodeposition of Nanoparticles on TiO2 Surface On titanium dioxide (TiO2 ), many researchers have used photodeposition to deposit various kinds of nanoparticles. Noble metals including Pt (Clark and Vondjidis 1965; Lee and Choi 2005; Chowdhury et al. 2013; Everly and Traynham 1976; Li et al. 2009a; Herrmann et al. 1986; Murcia et al. 2012; Mahlamvana and Kriek 2014; Qamar and Ganguli 2013; Nakamatsu et al. 1986; Zhang et al. 2004; Sclafani’ et al. 1991; Piwoński et al. 2011), Ag (Fernhndez et al., 1995; Iliev et al. 2007; Kriek and Mahlamvana 2012), Au (Sclafani’ et al. 1991; Ohno et al. 2002; Li et al. 2013a), and Pd (Khnayzer et al. 2012b; Qin et al. xxxx). Additionally, metal oxides like PbO2 (Fujii et al. 2009) and RuO2 (Kim et al. 2015), have been studied in conjunction with more intricate nanoparticles like CoPi, a cobalt and inorganic phosphate catalyst that oxidizes water (Zhou et al. 2014a). In addition to TiO2 , CdS, another semiconductor, has also undergone photodeposition (Tanaka et al. 2013; Zhu et al. 2009). Additionally, core–shell particles (Nakamatsu et al. 1986; Qiao et al. 2014; Herrmann et al. 1991; Tian et al. 2023), bimetallic co-catalysts (Xi et al. 1995; Chaudhary and Singh 2014), and even trimetallic co-catalysts have been produced via photodeposition, with an annealing step occasionally necessary (Xi et al. 1995). In the pursuit of developing efficient photocatalytic materials using photodeposition, researchers

14 Photodeposition for Highly Effective Photocatalytic Materials

407

Fig. 14.1 Schematic overview of reductive photodeposition Fig. 14.2 Schematic of reactions occurring during in-situ photodeposition. A metal cation is reduced on the surface of the photocatalyst (k1 ), while protons are reduced to form hydrogen (k2 )

have endeavored to determine the ideal weight loading of co-catalysts. (Wenderich and Mul 2016; Sclafani’ A, Mozzanega M–N, Pichat’ P 1991). However, there aren’t many studies looking at how certain factors, like the function of a sacrificial reagent (Chen et al. 2013; Kabra et al. 2008), pH value (Su and Wang 2021; Kabra et al. 2008) and metal precursor effect (Su and Wang 2021; Kabra et al. 2008) impact the post-synthesis materials’ structural, chemical, and catalytic characteristics. Further

408

Akshita et al.

study is necessary to improve and comprehend completely the Pt photodeposition on TiO2 . (Su and Wang 2021; Wenderich and Mul 2016; Sclafani’ A, Mozzanega M–N, Pichat’ P 1991).

14.2.1 Effect of Sacrificial Electron Donors on Platinum (Pt) Nanoparticles In 1984, a significant study conducted by Sungbom et al. (Shishido et al. 2009) emphasized the importance of employing a sacrificial agent during the deposition of Pt on anatase. Their research employed X-ray photoelectron spectroscopy (XPS) to investigate the impact of a mixture of CH3 COOH and CH3 COONa, in fixed ratios, on the oxidation state of Pt. Lower levels of CH3 COOH-CH3 COONa led to the evolution of Pt (II) and Pt (IV) species instead of Pt (0). However, with an increase in CH3 COOH-CH3 COONa concentration, Pt (0) concentration also rose. Significantly contributing to the reduction of the Pt precursor, the rate of hole conversion was higher when converting an organic molecule than when oxidizing water and was primarily dependent on the extent of reduction. In their photodeposition process, they successfully utilized Pt-loaded TiO2 to in situ reduce oxidized platinum back to its metallic state (Pt (0)).This was done as part of a photocatalytic methanol breakdown process. Consequently, the reduction of platinum oxides to Pt (0) by light in methanol-containing solutions was quite successful. Lee and Choi carried out additional research on the efficiency of methanol in attaining a complete reduction of Pt. Using Degussa P25 as a TiO¬2 photocatalyst, they studied methanol at high and low concentrations. The results showed that Pt (II) remained dominant at relatively low methanol levels, but full reduction to Pt (0) particles was achieved at high methanol concentrations. It was proposed that the reduction of Pt could be facilitated by methanol radicals, which were created when holes oxidized methanol. On the other hand, employing a high methanol concentration had the drawback of producing Pt particles that were noticeably larger in size. (Wenderich and Mul 2016; Vaelma and Selin 2017; Lee and Choi 2005). Using low light intensities in an N2 atmosphere, Murcia et al. (Qamar and Ganguli 2013) studied the photodeposition kinetics of Pt on anatase in the presence of 2-propanol. According to the findings of Herrmann et al. (Murcia et al. 2012) the researchers noticed a growth in Pt particle size during the course of the photodeposition process, reaching roughly 3 nm after 15 min and 6 nm after 240 min. Five weight percent of the Pt loading was the precursor concentration. Even so, Pt particle aggregates were observed at higher precursor concentrations (equivalent to 2 weight percent Pt). The researchers described a process whereby organic molecules like methanol, ethanol, 2-propanol, and acetic acid oxidized due to photogenerated holes, producing radicals that provided electrons for the reduction of adsorbed Pt on the semiconductor’s surface (Wenderich and Photodeposition of platinum nanoparticles on well-defined tungsten oxide Controlling oxidation state, particle size and geometrical distribution. xxxx; Wenderich and Mul 2016; Qamar and

14 Photodeposition for Highly Effective Photocatalytic Materials

409

Ganguli 2013). According to Nakamatsu et al., using radicals with a relatively high reduction potential results in a significant Pt–Pt particle distance, which promotes the synthesis of new small Pt particles rather than the development of existing ones (Ohyama et al. 2010). The researchers found that a high reduction potential of in-situ generated organic radicals favors the nucleation of new (small) Pt particles rather than promoting the expansion of existing particles. Despite 2-propanol’s radical having the highest oxidation potential, the catalysts made with it have relatively long Pt– Pt particle distances. This is because 2-propanol is used at a higher concentration (50 vol%) than the other sacrificial agents. This conclusion is supported by Lee and Choi’s findings (Lee and Choi 2005), which showed that using high concentrations of CH3 OH led to the formation of noticeably bigger Pt particles. As the Pt–Pt particle distance increased up to a distance of 100 nm, the photocatalytic hydrogen production from ethanol reforming increased, demonstrating that larger Pt particles demonstrate higher effectiveness. Conversely, smaller particles with a lower Pt–Pt distance showed relatively low activity in ethanol reforming, likely because light shielding effects limit the light-induced activation of TiO2 . The results reported by Nakamatsu et al. (Ohyama et al. 2010) about the impact of the sacrificial donor on the dispersion and Pt–Pt distance are supported by the suggestion that more studies be conducted to provide more proof and support. Investigations on the impact size of Pt particles and spatial allocation, including facet-preferred deposition, regarding the enhancement of the activity of photocatalytic reforming in TiO2 (P25), are also advised.

14.2.2 Effect of pH on Photodeposition The hydrolysis of [PtCl6 ]2− during the photodeposition process in an oxygen-free atmosphere was covered by Xi et al. (Chen and Nickelb 1996) in their study. The hydrolysis equilibrium reveals that the Pt precursor molecule contains a considerable portion of OH “ligands” at high pH levels, potentially influencing the photodeposition kinetics and resulting oxidation state of the Pt particles. At low and neutral pH, anatase demonstrated photo-deposited Pt(OH)2 , while PtO2 was also observed at high pH. The addition of Cl- (as NaCl) negatively affected the amount of deposited Pt, and substantial amounts of Cl- led to no Pt deposition at low pH. XPS analysis predicted that when photodeposition periods were equal, lower pH values resulted in less Pt being deposited on the TiO2 surface compared to higher pH values. For the generation of Pt(OH), it is hypothesized that [Pt(OH)2 Cl4 ]2− undergoes reduction. According to research by Xi et al. (Chen and Nickelb 1996), Mahlamvana and Kriek (Zhang et al. 2004), Zhang et al. (Clark and Vondjidis 1965) Low pH values result in a high Pt photodeposition rate on (nonporous) Degussa P25, which is notably higher than at higher pH levels. Lately, Qamar and Ganguli conducted pH-dependent photodeposition studies that indicate the photodeposition rate of Pt on anatase is relatively low at high pH values in the presence of a sacrificial agent (Sclafani’ A, Mozzanega M–N, Pichat’ P 1991). Thus, it appears to be necessary to hydrolyze [PtCl6 ]2− in the

410

Akshita et al.

absence of sufficient Cl− in order to produce notable Pt deposition rates on TiO2 . Electrostatic interactions were used by Zhang et al. (Clark and Vondjidis 1965) to clarify the variation in the rates of deposition at high and low pH levels when a sacrificial agent is present. When the pH is below the isoelectric point of TiO2 , the charges of the Pt complex in solution (negative) and the surface of TiO2 (positive) exhibit attractive forces, leading to rapid deposition rates due to advantageous adsorption. As a result, the Pt particles produced have a wide size distribution. When a sacrificial agent is present in the solution, electrostatic interactions are especially crucial. There were noticeable large Pt particle aggregations at the pH level of TiO2 ’s isoelectric point. (Clark and Vondjidis 1965). The pH value affects the oxidation state of Pt even in the presence of sacrificial agent. Metallic Pt (0) was created when the pH fell below 5, whereas PtO2 was created when the pH rose over 9. For Pt and PtO, the pH range of 5 to 7 was observed, while the pH range of 7 to 9 was observed for PtO and PtO2 (Chen and Nickelb 1996). Two platinum-loaded TiO2 samples were synthesized by Lee and Choi (Lee and Choi 2005), one with metallic Pt at a low pH and high concentration of the electron donor (methanol), and the other with oxidized Pt at a high pH and no electron donor. A variety of chlorinated organic compounds were more actively destroyed by photocatalysis in metallic Pt-containing Pt/TiO2 , as per the findings of the authors’ study. However, when the photodeposition process occurred at high pH values, the photocatalysts exhibited negligible activity in the degradation of triclopyr and methyl orange, which primarily resulted in the production of oxidized Pt particles. These experiments demonstrate how modifying the pH level (Sclafani’ A, Mozzanega M–N, Pichat’ P 1991) may be used to accurately regulate the size, distribution, and most significantly, the Pt particles’ oxidation state as they form on the TiO2 surface.

14.2.3 Effect of Pt Precursor and Temperature In anaerobic conditions without making use of an intermediary, Herrmann et al. (Murcia et al. 2012) examined the effects of several Pt precursors on the rate of Pt photodeposition on TiO2 (nonporous Degussa P25). The Pt precursors used were Pt(NO2 )2 (NH3 )2 , [PtCl6 ]2− (H2 PtCl6 ), Na2 PtCl6 , H2 Pt(OH)6 , and Pt(Cl6 O4 )6 . Among the precursors, Pt(NO2 )2 (NH3 )2 exhibited a significantly lower rate of photodeposition than the others. Its nonionic nature, which led to a lesser adsorption coefficient, was thought to be the cause of this lower rate. Surprisingly, the deposition rates from the precursor solutions containing chlorine and H2 Pt(OH)6 were very similar. With an apparent activation energy < 10 kJmol-1, the authors saw Arrhenius-type behavior. The low activation energy (below 10 kJ mol-1) indicates, in accordance with the authors’ findings, that the rate of Pt deposition is not limited at high temperatures by either the adsorption of precursor molecules or the desorption of products (apart from the deposited Pt). The deposition period has a significant impact on the size of Pt nanoparticles at room temperature, with smaller particles gradually increasing larger as the deposition time is prolonged. Even so, the scientists

14 Photodeposition for Highly Effective Photocatalytic Materials

411

did not look into how temperature affected the oxidation state or size of the produced Pt nanoparticles. Therefore, more research is necessary to fully understand these concepts, keeping in mind the pH variations among the various precursor solutions (Qamar and Ganguli 2013).

14.2.4 Effect of the Absence or Presence of Oxygen Mahlamvana and Kriek (Zhang et al. 2004) found that oxygen significantly reduced the rate of Pt deposit on TiO2 (Evonik-Degussa P25) during their photodeposition studies. They explained this result as being caused by O2 functioning as a rival electron scavenger. The researchers also demonstrated how the kind of precursor used had an impact on how well oxygen-free gas was purged from the photodeposition reactor. K2 PtCl6 , H2 PtCl6 , [PtCl3 (H2 O)]2 , and [PtCl4 ]2 were found to be the most and least reactive precursors, respectively, in the absence of oxygen. [PtCl4 ]2 exhibited no deposition reactivity at all. These findings directly contradict the data that Herrmann et al. previously investigated and published (Murcia et al. 2012). The disparity in findings between these studies may be due to variations in the pH environment, indicating the need for additional study on the subject.

14.2.5 Deposition of Metals (Except Pt) Comprehensive research has been done on the Au photodeposition method on Degussa P25 (with methanol present) (Li et al. 2013a). Similar to Pt, when the pH during photodeposition is high, the average size of Au nanoparticles is rather small: 18 nm at pH = 3 and 4 nm at pH = 9. Consequently, the highest photocatalytic activity in the degradation of oxalic acid was observed when Au was produced by photodeposition at a pH greater than 7. This case discovered that Au nanoparticles were entirely reduced after photodeposition, unlike Pt, and this was true independent of the applied pH. Additionally, it has been noted that the photodeposition behavior of Pt and Pd differs. On Evonik-Degussa P25, Mahlamvana and Kriek (Zhang et al. 2004) showed that the presence of Cl has a deleterious impact on the photodeposition rate of [PtCln (H2 O)4n ] 2n (n = 0–4). For equivalent TiO2 crystals, PdCl2 (H2 O)2 deposition rates were faster than those of [PdCl4 ]2 or [Pd(H2 O)4 ] 2+ , indicating an ideal Cl: H2 O ratio that probably affects electrostatic interactions (Khnayzer et al. 2012b). The highest level of photocatalytic activity in the reduction of oxalic acid was reached when Au was produced by photodeposition at a pH greater than 7. It was demonstrated by Borgarello et al. (Li et al. 2013b) that oxygen has a negative impact on the degree of RhIII reduction, perhaps as a result of competition between oxygen reduction and RhIII reduction. According to the results that have already been presented, 100% reduction of Pt, Rh, and Pd took place when methanol was utilized as the solvent. Metal pollutants have been removed from waste streams using

412

Akshita et al.

photodeposition on TiO2 , which has revealed a variety of Dependencies on pH in ionic metal complex removal rates (Li et al. 2013b; Chen et al. 2011a). The presence of citric acid, a sacrificial agent, was found to increase the reduction rate of CuII, NiII, ZnII, and PbII on TiO2 , albeit to varying degrees. (Ren et al. 2010). It’s interesting to note that by modifying photodeposition conditions, (Borgarello et al. xxxx; Chen et al. 2011a) demonstrated that certain metal compounds could be extracted from a solution containing a variety of metal compounds. According to this viewpoint, sequential deposition rather than photodeposition produces core/shell or single metal particles that are spatially dispersed rather than homogeneous mixes of bimetallic catalysts. Researchers have studied the photoreduction of metals on TiO2 , including the deposition of Pt (Habibi and Sheibani 2013), Au (Ohno et al. 2002), and Rh (Wang et al. 2013a; Wu and Tseng 2006), employing extended X-ray absorption fine structure (EXAFS) spectroscopy in situ. Notably, an investigation on Rh/TiO2 showed that the photodeposition rate is dependent on the kind of sacrificial agent used; methanol had the highest rate, followed by ethanol, 1-propanol, and 2-propanol (Wu and Tseng 2006). This finding might be explained by the radicals’ potential for reduction when these alcohol derivatives undergo a hole-transfer process. Photodeposition has been employed for other semiconductor metal oxides, such as ZnO (Kislov et al. 2009; Peng et al. 2007; Liang et al. 2015; Alammar and Mudring 2009; Huang et al. 2015a; Lin et al. 2010; Liu et al. 2015a; Deng et al. 2012; Xie et al. 2010; Behnajady et al. 2009; Wang et al. 2011a; Kawano et al. 2002; Li et al. 2013c, 2014a; Kohtani et al. 2005; Busser et al. 2014; Maeda et al. 2008; Zhou et al. 2014b; Iizuka et al. 2011), BiVO4 (Sasaki et al. 2008; Wang et al. 2013b; Li et al. 1992), Ga2 O3 (Busser et al. 2012; Li et al. 2014b, 2013d), and Ta2 O5 (Sato et al. 1990), perovskites (Li et al. 2013d; Dukovic et al. 2008; Jint et al. 1994), metal sulfides (in particular cadmium sulfide (CdS)) (Chen et al. 2013; Rufus et al. 1995; Liu et al. 2015a, 2015b; Li et al. 1992; Ma et al. 2008; Mu et al. 2023; Hara et al. 2003; Fox and Pettit’ TL, 1989), and (oxy)nitrides (Busser et al. 2012; Li et al. 2013d; Ferraria et al. 2012; Kumar Kaushik xxxx; Zhang et al. 2014a). The literature has fairly thoroughly investigated photodeposition experiments on a variety of oxides, including ZnO and WO3 , then studies of Pt on CdS (Liu et al. 2015a; Li et al. 1992; Ma et al. 2008; Fox and Pettit’ TL, 1989; Dulnee et al. 2014; Wu et al. 2014; Naknam et al. 2009) and more.

14.3 Photodeposition of Nanoparticles on ZnO 14.3.1 Photodeposition of Ag on ZnO The existence or lack of a sacrificial electron donor has a significant impact on the rate of photodeposition and the form of Ag on ZnO. The photodeposition of silver on ZnO nanorods in an aqueous solution with or without ethanol was investigated by Liu et al. (He et al. 2014). In addition, they submerged a glass substrate covered in ZnO nanorods in an aqueous AgNO3 solution before exposing it to light from outside

14 Photodeposition for Highly Effective Photocatalytic Materials

413

the AgNO3 solution. Under visible-light irradiation, there were discernible changes in the ensuing Ag loading, dispersion, shape, and photocatalytic activity. Absence of ethanol resulted in the formation of two distinct morphologies: photodegradation activity and the development of tiny nanoparticles (10–20 nm in size) along the sidewalls of the nanorods. The photodegradation process first shows variations with increasing exposure duration during photodeposition, but it stabilizes over long deposition times, showing that Ag+ has completely been reduced to Ag. There have also been notable investigations by Kawano et al. (Iizuka et al. 2011) and Chen and Nickel (Kislov et al. 2009). ZnO was investigated by Kawano et al. (Iizuka et al. 2011) as a potential photocatalyst for the removal of Ag+ from an aqueous solution. They kept track of the amount of Ag that was deposited over time on surfaces that were Zn− and O− terminated (0001 and 0001, respectively). According to scientists, the observed differences in Ag particle size between Zn− terminated and O− terminated surfaces might be ascribed to either (i) absence of Ag ions in the solution or (ii) Ag deposited with a different composition that affects the material’s absorption capacity. Chen and Nickel investigated the Ag photodeposition kinetics on ultrafine ZnO in the presence of excess OH ions and Zn2+ in deaerated ethanol (Kislov et al. 2009). They found that high OH ions caused the initial creation of Ag2 O, which eventually changed into metallic Ag, while excess Zn2+ ions caused the development of mostly big metallic Ag particles. The important benefit of stabilizing ZnO is provided by the Ag photodeposition on ZnO (Kohtani et al. 2005; Busser et al. 2014). In their investigation, Xie et al. (Busser et al. 2014) observed the photodegradation of crystal violet (CV) with and without the presence of Ag on ZnO using a UV light for eight cycles. Modest deactivation was observed in ZnO loaded with 0.2 weight percent Ag, ZnO without Ag showed a considerable drop in activity. ZnO photo corrosion was attributed to surface defect sites by the researchers, who found that Ag preferentially deposited at these defect sites during photodeposition, essentially halting ZnO photocorrosion and creating a more stable photocatalyst. The surface oxidation state of the synthesized Ag particles was investigated using X-ray photoelectron spectroscopy (XPS). The binding energies of Ag 3d5/2 and Ag 3d3/2 were found to be 368.2 and 374.2 eV, respectively. Researchers have observed a change in the binding energy of Ag 3d5/2 and Ag 3d3/2 after photodeposition (Alammar and Mudring 2009; Huang et al. 2015a; Lin et al. 2010; Behnajady et al. 2009; Wang et al. 2011a; Kawano et al. 2002; Kohtani et al. 2005; Zhou et al. 2014b). The spontaneous transport of electrons from Ag to ZnO at the contact caused by Fermi level alignment accounts for this shift. Although it is difficult to reliably discriminate between metallic Ag, Ag2 O, and AgO using XPS, concerns about the potential production of Ag2O during photodeposition have resulted. XRD data from numerous research studies only verified the presence of metallic Ag, with no observed peaks corresponding to Ag2 O (Kawano et al. 2002; Zhou et al. 2014b; Carabineiro et al. 2010a; Peng et al. 2013). In spite of this, metallic Ag is anticipated to be present. In an experiment to ascertain if the O 1 s peak might be attributable to Ag2 O, Wang et al. (Zhou et al. 2014b) found inconsistent results. Notably, none of the researchers mentioned used any inert purge gas throughout their photodeposition studies. Consequently, it is likely that Ag was photo deposited on ZnO under oxygen-rich circumstances,

414

Akshita et al.

possibly resulting in the production of Ag2 O or AgO. Zhang et al. report that peaks were observed at 368.3 and 374.2 eV, which stood for metallic Ag 3d5/2 and Ag 3d3/2 , respectively, when the solution was purged with N2 throughout the experiment (Chang et al. 2013). These numbers differed significantly from those that had previously been reported. While conducting photodeposition with an N2 purge, Chen et al. (Liang et al. 2015) also noted a change in XPS binding energy. To minimize the production of Ag2 O or AgO, researchers are urged to perform Ag photodeposition on ZnO in deaerated conditions. The chance of Ag2 O or AgO production is decreased as a result, making it easier to assign XPS spectra. In addition, X-ray Auger spectroscopy analysis of the as-produced samples could be able to go beyond the limitations of XPS in providing more conclusive insights on the oxidation state of the resultant Ag.

14.3.2 Photodeposition of Au, Pd, and Other Catalysts on ZnO A lot of study has been done on the photodeposition process using several metals on ZnO, including gold (Liu et al. 2015a; Chang et al. 2012; Liqiang et al. 2004; Kozytskiy et al. 2013; Shvalagin et al. 2007; Lu et al. 2007), palladium (Lu et al. 2003; Boccuzzi et al. 1996; Carabineiro et al. 2010b; Siboni et al. 2011), cadmium sulfide (Liqiang et al. 2004; Dombnech and Andrbs xxxx), copper (Peng et al. 2013; Kunthakudee et al. 2022), platinum (Kozytskiy et al. 2012; Su and Qin 2015), nickel (Gomathisankar et al. 2013), and mercury (Huang et al. 2015b). While some studies have focused on extracting metal ions from solutions, the primary goal has been to precisely regulate the deposition of palladium (Pd) and gold (Au) on zinc oxide (ZnO) to create highly efficient photocatalysts. In particular, Au/ZnO catalysts have found important uses in the oxidation of CO (Chang et al. 2012; Kozytskiy et al. 2013; Lu et al. 2007), dye photodegradation (Liu et al. 2015a; Shvalagin et al. 2007), and removal of bacteria (Shvalagin et al. 2007), while Pd has been used for gas sensing (Boccuzzi et al. 1996; Carabineiro et al. 2010b) and generally enhancing photocatalytic activity (Lu et al. 2003; Kumar and Rao 2015). According to several studies, better charge-carrier separation and accelerated rates of electron-transfer processes are to blame for the increased photocatalytic activity of ZnO after Au or Pd deposition (Liu et al. 2015a; Shvalagin et al. 2007; Kumar and Rao 2015; Zheng et al. 2011). Wu et al. (Liqiang et al. 2004) important finding is that surface plasmon resonance (SPR) properties are present in Au/ZnO. By using XPS analysis, Liqiang et al. (Kumar and Rao 2015) showed that Pd loading on ZnO favored O2 adsorption. Chang et al. (Carabineiro et al. 2010b) also reported increased O2 adsorption when Pd was deposited on ZnO, which is similar to what we have shown. Investigations into the photodeposition of metals on ZnO have been extensive, producing photocatalysts with improved activity in a variety of applications. Several variables affect the rates of photodeposition of Au or Pd on ZnO and the resulting morphology, such as the presence or

14 Photodeposition for Highly Effective Photocatalytic Materials

415

absence of a sacrificial agent, pH levels, the properties of the used light source, and the duration of irradiation. While deposition from potassium gold cyanide is also possible, [AuCl4 ] is typically used to create Au nanoparticles (Arai et al. 2008a). Both Methanol (Arai et al. 2008a) and ethanol (Liu et al. 2015a; Wicaksana et al. 2014) have been used as sacrificial agents, with methanol showing the capacity to speed up the deposition of gold (Arai et al. 2008a). However, nothing is known about how oxygen affects the rate of Au nanoparticle deposition and their state of oxidation (Wicaksana et al. 2014). The structure and catalytic activity of one weight percent Au nanoparticles during the catalytic CO oxidation process were investigated in a work by Carabineiro et al. (Lu et al. 2007) in relation to pH, irradiation time, and ZnO morphology. The catalytic efficiency of Au particles synthesized using photodeposition was less than that of those created by impregnation, according to a study the scientists conducted comparing photodeposition to alternative preparation techniques, notably impregnation. The performance discrepancy was attributable to the Au particles’ comparatively greater sizes, which were created using photodeposition. At a pH of about 5.5, photodeposition was discovered to yield the most energetic Au particles. Pt on TiO2 and Au or Pd on ZnO photodeposit at similar rates. By varying the precursor (HAuCl4 ) concentration and irradiation time, Wu and Tseng (Liu et al. 2015a) showed that it is possible to precisely regulate the size of Au nanoparticles on ZnO nanorods. Smaller Au particles were produced with shorter irradiation periods and lower HAuCl4 concentrations, which encourage improved catalytic activity. However, when the size of the Au particles was greater than 30 nm, a detrimental effect on photocatalytic activity was observed. This decrease in activity could be attributable to the larger Au particles’ unfavorable light scattering, which lowers the likelihood that the ZnO nanorods would absorb light. While this was going on, Naknam et al. (Kozytskiy et al. 2013) did a study to determine how lamp intensity affected the shape of Au nanoparticles as they were being deposited on ZnO. In another study, the same research team discovered that loading and mean size of Au particles stayed mostly unchanged during the deposition process, but the level of agglomeration increased significantly with higher lamp intensity. The importance of ZnO morphology in regulating the size of Au particles produced during photodeposition was also underlined by the same researchers in a different work (Chang et al. 2012). In particular, the resultant Au particles showed significantly greater sizes when the photodeposition of Au was carried out on bigger ZnO nanorod formations or structures with nanorod-like micro flowers than when it was done on smaller ZnO nanorod structures. Consequently, one must take into account the ZnO surface area as a critical component when optimizing the photodeposition process for Au particles. The amount of precursors (HAuCl4 and H2 PtCl6 ) needed to increase the deposition of the noble metals Au and Pt. Additionally, it was discovered that the density and size of gold nanoparticles (Au NPs) on ZnO nanorods are controlled by the concentration of HAuCl4 . The quantity of Au nanoclusters (Au NCs) on ZnO nanorods may also be controlled by adjusting the molar ratio of ZnO to HAuCl4 . During photodeposition on ZnO nanorods, HAuCl4 concentration and illumination time have been found to be crucial controls over the amount and location of Au nanoparticles that are deposited (Liqiang et al. 2004). The fluctuation of Au loading

416

Akshita et al.

on ZnO has been studied independently by researchers He et al. (Shvalagin et al. 2007) and Su and Qin (Arai et al. 2008b). They found that the rates of photodegradation for methylene blue and salicylic acid increase proportionately when the Au loading is increased up to 10 mol%. Additionally, it has been demonstrated that under light-induced circumstances, the photodeposition of Au on ZnO facilitates the production of hydroxyl radicals, superoxide, and singlet oxygen. Electron spin resonance (ESR) spectroscopy studies were used to confirm this increase in reactive oxygen species (Shvalagin et al. 2007). PdCl2 , H2 PdCl4 , and other precursors are used to photodeposit Pd on ZnO (Boccuzzi et al. 1996; Carabineiro et al. 2010b; Kumar and Rao 2015) and H2 PdCl4 (Zheng et al. 2011), Methanol (Boccuzzi et al. 1996), ethanol (Carabineiro et al. 2010b) and acetic acid (Kumar and Rao 2015) are only a few examples of the different sacrificial agents that have been used in the procedure. Determining the effect of photodeposition conditions on the final oxidation state of Pd on ZnO seems to be a challenging task. On the other hand, it has been discovered that nitrogen purging and the use of a sacrificial agent tend to promote the formation of fewer Pd particles. However, nothing is known about how photodeposition circumstances affect the size of the resulting Pd particles, necessitating a thorough examination (Carabineiro et al. 2010b). For effective rhodamine B degradation, Jin et al. (Zheng et al. 2011) found that 0.05 mol% (or 0.065 wt%) of Pd should be loaded onto ZnO nanorods. In contrast, Liqiang et al. (Kumar and Rao 2015) found that 0.5 weight percent of Pd on ZnO nanoparticles was the ideal loading for efficient photocatalytic degradation of n-C7 H16 . It was found that PdO was present on the surface of Pd nanoparticles produced by ZnO photodeposition. Prolonged exposure to the atmosphere is most likely what caused this surface oxidation. In a separate study, Gomathisankar et al. (Joshi et al. 2011) examined the photodeposition of Cu particles on ZnO with methanol acting as a sacrificial agent. In-situ measurements of hydrogen evolution were made by the researchers, who found that a Cu loading of 6 wt% on ZnO resulted in the maximum yield of H2 production. A 500 W xenon lamp that produced 1.0 mW/cm2 of light in the 320–410 nm band was used in the trials. Investigations into photoluminescence showed that Cu served as an electron trapping site because it successfully reduced electron/hole recombination when it was photodeposited. However, the study did not go into great detail into Cu’s long-term stability. It was said that it is a feasible occurrence for holes produced in ZnO to oxidize as-deposited Cu. The increase in hydrogen (H2 ) creation is caused by an increase in proton reduction, where Cu serves as a sacrifice agent. A number of studies have also examined the co-deposition of other metals, including Ag, Au, Cu, Ni, Pd, Pt, and Rh, using ZnO as the photocatalyst in order to produce H2 from an aqueous methanol solution.

14 Photodeposition for Highly Effective Photocatalytic Materials

417

14.4 Photodeposition of Particles on WO3 In the area of photocatalysis, tungsten oxide (WO3 ), a semiconductor material, has attracted a lot of interest. Although WO3 ’s conduction band energy level is not optimal for proton reduction, it has advantageous qualities such non-toxicity, acid stability, and a relatively small band gap (Abe et al. 2005; Sayama et al. 2002; Maeda et al. 2010a; Zhang et al. 2014b). Due to these qualities, it is ideally suited for solarpowered photocatalytic applications (Wicaksana et al. 2014; Zhang et al. 2014b; Aminian and Ye 2010; Sadakane et al. 2008). For total water splitting, WO3 has been successfully used in Z-schemes (Maeda et al. 2010a; Sclafani et al. 1998; Qamar et al. 2011). Recent studies have shown that when loaded through photodeposition with metals including Pt (Zhang et al. 2004; Joshi et al. 2011; Wenderich et al. 2014; Xu et al. 2011; Kim et al. 2010; Purwanto et al. 2011; Qamar et al. 2010; Wang et al. 2011b; Ueyama et al. 2018; Tomita et al. 2011; Gunji et al. 2016; Abe et al. xxxx; Sakai et al. 2015; Shibuya and Miyauchi 2009; Katsumata et al. 2013; Sun et al. 2010; Karácsonyi et al. 2013; Chen et al. 2011b; Iliev et al. 2010), Pd (Wicaksana et al. 2014; Litter 1999), Ag (Sclafani et al. 1998; Kim et al. 2010), and Au (Joshi et al. 2011; Wang et al. 2011b; Ueyama et al. 2018; Abe et al. xxxx), it has the potential to enhance photocatalytic activity (Gunji et al. 2016).

14.4.1 Photodeposition of Pt on WO3 Numerous studies on the photodeposition of platinum (Pt) on tungsten trioxide (WO3 ) have shown that it can improve WO3 ’s photocatalytic activity in the oxidation of different contaminants found in wastewater or the air. Notably, studies have shown that photo deposition-based loading of WO3 with Pt nanoparticles can greatly improve the photocatalytic activity in the oxidation of compounds including 4-chlorophenol, methyl orange, isopropyl alcohol, and ethylene (Xu et al. 2011; Wang et al. 2011b; Tomita et al. 2011, 2014; Shiraishi et al. 2012). Abe et al.‘s work (Wang et al. 2011b), focused on the photocatalytic degradation of acetic acid, acetaldehyde, and isopropyl alcohol when exposed to visible light using (Pt/)WO3 . Although unloaded WO3 showed some activity in the breakdown of acetaldehyde, it was substantially less effective in the breakdown of acetic acid and isopropyl alcohol. The potential of (Pt/)WO3 as a robust visible-light-driven photocatalyst was demonstrated by the significantly increased photocatalytic efficiency for all three compounds following the introduction of platinum by photodeposition onto WO3 . Platinum (Pt) was photodeposited on tungsten trioxide (WO3 ), which significantly improved catalytic activity. Intriguing rate increases of 30 and 100 times, respectively, were seen for the breakdown of acetic acid and isopropyl alcohol (IPA). Acetaldehyde’s rate of breakdown increased as well, but not as significantly as the other two substances. It’s interesting to note that various platinum loadings were found to be most effective for each reaction: 0.1 wt% for acetaldehyde, 1 wt%

418

Akshita et al.

for acetic acid breakdown, and 0.5 wt% for IPA. The underlying causes of these different optimal loadings are yet unknown, demanding more analysis and study in this field. According to the researcher’s hypothesis, the presence of Pt nanoparticles might operate as electron traps, facilitating multielectron reactions. The scientists presented proof that photoexcited electrons can interact with O2 when Pt is introduced onto the surface of WO3 by photoacoustic spectroscopic experiments. The absence of single electron transfer, which results in the production of O2−• or HO2• , has been the subject of discussions among some academics, and how this particular characteristic significantly improves the selectivity of Pt/WO3 in the context of photocatalysis (Sclafani et al. 1998; Qamar et al. 2011, 2010). The production of hydrogen peroxide (H2 O2 ) during aqueous-phase photocatalytic tests using Pt/WO3 has been verified by a number of investigations. In order to create Pt/WO3 , Kim et al. (Tomita et al. 2014) used photodeposition procedures. Pt/WO3 demonstrated effective photodegradation of diverse organic components when exposed to visible light. The authors showed that the photoreduction breakdown of H2 O2 results in the generation of hydroxyl radicals (OH• ). Notably, during the initial stage of the photocatalytic tests, platinum (Pt) was discovered to have a favorable effect on the rate of H2 O2 generation. Only the previously indicated two-electron reduction of oxygen may lead to this production of H2 O2 . In addition, (Tomita et al. 2011; Sclafani et al. 1998) offered strong evidence that OH• radical assaults were necessary for the photocatalytic synthesis of phenol from benzene, even though they also suggested that OH• radicals may potentially arise via the oxidation of water. Studies have mostly focused on determining the photocatalytic performance of Pt/WO3 while paying relatively less attention to how to best optimize the photodeposition process used to create Pt nanoparticles. The most frequently used sacrificial agent is methanol, however ethanol, oxalic acid, and other substances have also been used (Wicaksana et al. 2014; Zhang et al. 2014b; Sadakane et al. 2008; Wenderich et al. 2014; Purwanto et al. 2011; Karácsonyi et al. 2013; Karácsonyi et al. 2013; Tomita et al. 2014; Huang et al. 2010; Huang et al. 2010; Pang et al. 2012) In certain cases, photodeposition was started without a sacrificial agent and methanol was added subsequently (Xu et al. 2011; Wang et al. 2011b, 2009). H2 PtCl6 consistently acted as the catalyst for Pt deposition throughout these studies. However, the research has shown heterogeneity in the usage of other process factors, such as the use of an inert gas purge. While some publications (Wang et al. 2011b; Tomita et al. 2011; Karácsonyi et al. 2013), mentioned using inert gas purging whereas others did not specifically address this step (Zhang et al. 2014b; Karácsonyi et al. 2013; Pang et al. 2012; Sun et al. 2011a). Numerous research have used various illumination durations and sources throughout the photodeposition process. Examples include Kim et al.‘s (Tomita et al. 2014) use of a 200 W Hg lamp for a 30-min illumination period and Abe et al.‘s (Wang et al. 2011b) use of a 300 W Xe lamp coupled with a cutoff filter at 400 nm for a 4-h illumination duration (of which 2 h contained methanol). It’s interesting to note that (Qamar et al. 2011; Karácsonyi et al. 2013) showed that photodeposition may be successfully carried out utilizing a 355 nm laser beam as an alternative to traditional illumination techniques. When Pt/WO3 was generated through 1 h of laser irradiation rather than 1 h of conventional illumination, it was found that greater photocatalytic

14 Photodeposition for Highly Effective Photocatalytic Materials

419

activity in R6G degradation was attained. WO3 ’s morphology changed in various photodeposition investigations. While some studies (Purwanto et al. 2011; Tomita et al. 2014; Pang et al. 2012), used commercially available WO3 particles, others (Karácsonyi et al. 2013; Sun et al. 2011a; Chen et al. 2012a; Kovács et al. 2014), opted to synthesize their own WO3 particles. Additionally, several researchers have attempted to synthesize WO3 particles or use various commercial WO3 brands in order to photodeposit Pt on various WO3 samples (Zhang et al. 2014b; Sadakane et al. 2008; Sclafani et al. 1998; Xu et al. 2011; Kim et al. 2010; Tomita et al. 2011). Some Pt loading processes only functioned to activate WO3 in these situations, leaving just the Pt/WO3 samples to be compared (Zhang et al. 2014b; Sclafani et al. 1998; Xu et al. 2011) In contrast, in previous studies (Sadakane et al. 2008; Kim et al. 2010; Tomita et al. 2011), the activities of various WO3 samples were examined before and after the platinum loading. As a result of these varied techniques, these research’ findings have been inconsistent. According to (Xu et al. 2011; Sadakane et al. 2008) and (Kim et al. 2010) there was no appreciable change in the order of photocatalytic activity for the degradation of acetic acid or isopropyl alcohol among several self-produced WO3 samples before and after Pt loading. The later study, however, included a comparison with commercial WO3 , which following Pt deposition showed considerably higher activity than the self-synthesized samples. Notably, the Pt/WO3 samples showed some amount of activity even in the absence of light when it came to isopropyl alcohol degradation. The impact of both shape and illumination type on the photodeposition process was looked at in a noteworthy study by (Wicaksana et al. 2014; Tomita et al. 2011). The scientists created WO3 particles with various morphologies and crystal structures, and then they exposed these crystals to Pt photodeposition by either illuminating them for 3 h with visible light or for 1 h with UV light. It was concluded through transmission electron microscopy (TEM) studies that using various WO3 samples resulted in the production of various forms of Pt deposits. Additionally, the photodeposition process’s resultant Pt morphology was significantly influenced by the wavelengths of irradiation used. Notably, UV light was consistently found to have better photocatalytic activity in gas-phase ethylene conversion than visible light. Contrary to what would be expected, using hexagonal WO3 nanobundles did not significantly increase the photocatalytic activity of monoclinic WO3 samples. As a result, the sequence of activity among the different WO3 samples changed before and after Pt loading, demonstrating the significance of WO3 shape and illumination type in determining the photocatalytic performance. In a few research (Huang et al. 2010; Pang et al. 2012), the impact of the platinum (Pt) weight percentage loading on the photocatalytic activity of Pt/WO3 has been thoroughly investigated. The Pt loadings in the Pt/WO3 samples made by Sclafani et al. (Pang et al. 2012) ranged from 0.5 to 3 wt%. They used a nitrogen purge to remove oxygen from the solution, methanol as a sacrificial agent in their photodeposition method, and illumination times ranging from 24 to 48 h, depending on how much Pt was to be removed. Sclafani et al. (Pang et al. 2012) showed through phenol photo-oxidation experiments that samples with increased Pt weight loadings exhibited elevated photoactivity. Similar to this, Qamar et al. (Huang et al. 2010) optimized the Pt loading in Pt/WO3 for the methyl orange photo-oxidation reaction.

420

Akshita et al.

They discovered that 1 wt% Pt was the ideal loading, which was accomplished using their standard photodeposition setup after 6 h of illumination. The ideal Pt loading in the photocatalytic degradation of several compounds, such as Acetic acid (Sadakane et al. 2008; Wenderich et al. 2014; Wang et al. 2011b), Acetaldehyde (Wang et al. 2011b), Isopropyl alcohol (Wang et al. 2011b) and amaranth (Wang et al. 2009), has also been investigated in other studies. According to the particular reaction, different Pt loading optimization strategies have been seen in photodeposition experiments. Examples include the partial photo-oxidation of cyclohexane, which was shown to be best at a loading of 0.2 weight percent (Purwanto et al. 2011), and the synthesis of phenol from benzene, which was found to be best at a loading of 0.1 weight percent (Zhang et al. 2014b). The particle size of Pt nanoparticles frequently displays remarkable constancy, typically lying within the range of 2–10 nm (Zhang et al. 2014b; Wang et al. 2011b; Tomita et al. 2014), with the exception of one study where bigger Pt clusters of 30 nm were recorded (Wenderich et al. 2014). This is noteworthy given the wide variety of parameters employed in these investigations. (Shiraishi et al. 2012; Purwanto et al. 2011) noted that while utilizing methanol as a sacrificial reagent in the photodeposition process, the Pt particle size remained largely irrespective of the Pt loading. For instance, the average Pt particle size was 4.7 nm at 0.2 weight percent Pt loading and 4.8 nm at 1.3 weight percent Pt loading. Given that this behavior has been noted for Pt on TiO2 or Ag on ZnO, it is important to take into account the likelihood of clustered development of Pt particles on WO3 . Sclafani et al. also suggested that an increase in Pt loading on WO3 would result in a larger Pt particle size. The results highlight the necessity of metallic Pt for successful photocatalysis. To get tiny Pt (0) particles, however, and improve catalytic performance, process parameter optimization is essential during photodeposition. The observed particle size of Pt nanoparticles on WO3 varies depending on the individual inquiry, with values ranging from 1–2 nm, 4.7–4.8 nm, to the range of 2–10 nm. It is anticipated that WO3 will experience the same phenomena of clustered development of Pt particles as Pt on TiO2 and Ag on ZnO (Qamar and Ganguli 2013; Peng et al. 2007; Li et al. 2013c). Thus, to generate tiny Pt (0) particles and guarantee a high degree of catalytic performance, process parameter optimization is still crucial (Pang et al. 2012). For a comprehensive and detailed overview of the current state and utilized procedures, refer to Fig. 14.3.

14.4.2 Photodeposition of Other Metals on WO3 The photodeposition of numerous noble metals, including Au (Joshi et al. 2011; Ueyama et al. 2018; Huang et al. 2010; Baia et al. 2014), Ag (Sclafani et al. 1998) and Pd (Wicaksana et al. 2014; Litter 1999), has greatly increased the photocatalytic activity of WO3 . Pt photodeposition was shown to be more efficient than Au photodeposition in the degradation of methyl orange and 2,4-dichloro phenoxy acetic acid by Qamar et al. (Huang et al. 2010) when they investigated the effects of Pt and Au

14 Photodeposition for Highly Effective Photocatalytic Materials

421

Precursor H2PtCl6

Always Used

pH Other

High

Never Used

WO3 Stable

Low

WO3 Unstable

Sacrificial Agent

Present

MeOH Mostly Used

Absent

MeOH Hardly Used

Fig. 14.3 Overview of process parameters used in photodeposition of Pt on WO3a

photodeposition on WO3 . The discrepancy was attributed by the authors to the relative sizes of the Au particles (10–15 nm at 1 wt% loading) and Pt particles (2–4 nm at 1 wt% loading), which caused shadowing of the WO3 . Contrasting findings were made by Karacsonyi et al. (Baia et al. 2014) and Iliev et al. (Ueyama et al. 2018), who discovered that Au/WO3 had stronger oxalic acid degradation activities than Pt/ WO3 and bare WO3 . These findings imply that the efficiency of various noble metals as co-catalysts for WO3 can vary based on the particular photocatalytic reaction and the size of the particle(s) involved. Improvements in photocatalytic activity have been seen following the photodeposition of Ag and Pd on WO3 (Wicaksana et al. 2014; Sclafani et al. 1998; Litter 1999). Ag or Pd’s role as electron-transfer catalysts, which facilitate charge separation in the photocatalytic process, is thought to be the cause of the increased activity. Similar to how Kim et al. (Tomita et al. 2014) showed for Pt/WO3 , (Katsumata et al. 2013; Sclafani et al. 1998) proved that OH• radicals are produced in the case of Ag/WO3 as a result of the photoreduction of oxygen under visible light. These results demonstrate the important roles played by noble metals, such as Ag and Pd, in enhancing photocatalytic processes by enabling electron transfer and promoting the generation of reactive oxygen species, such as OH• radicals. The creation of OH• radicals was attributed by the authors to the breakdown of H2 O2 , who also noted the initial production of H2 O2 . The recombination process in photocatalysis can be effectively reduced by depositing Pt and Au nanoparticles on the surface of WO3 . Sakai et al. (Litter 1999) demonstrated that PdCl2 may be reduced to mainly metallic Pd under black-light illumination (i.e., UV illumination) in deaerated conditions (under Ar), surprising without the inclusion of a sacrificial agent, in the context of Pd photodeposition on WO3 . The degradation of aqueous methylene blue (MB) and gaseous acetaldehyde was compared to determine the best loading of Pd on WO3 , which was thoroughly explored by the authors. The potential

422

Akshita et al.

of Pd-deposited WO3 to function effectively as a photocatalyst in particular reaction conditions is highlighted by this study’s insightful analysis of the photochemical behavior of the material. They found that different photocatalytic processes required different Pd loadings; for example, increasing MB degradation required 0.5 weight percent Pd, while acetaldehyde decomposition required 0.1 weight percent Pd. While utilizing various irradiation wavelengths, (Shibuya and Miyauchi 2009; Wicaksana et al. 2014) studied the photodeposition of Pd onto films of hexagonal WO3 nanotrees in the presence of ethanol. The wavelength of the light employed affected where Pd was deposited. The scientists explain this phenomenon by stating that compared to UV light, visible light penetrates the WO3 nanotrees more deeply. Additionally, the nanotrees showed greater bottom crystallinity than top crystallinity, which explained why Pd particles were not present on top of the nanotrees when visible light was used. This research explains how Pd photodeposition on hexagonal WO3 nanotrees behaves in relation to wavelength and offers insightful information on how crystallinity and light penetration affect the dispersion of Pd nanoparticles. Although hexagonal WO3 is not anticipated to reduce Pd at these wavelengths due to its large band gap (Ohno et al. 2014; Liu et al. 2009), Shibuya and Miyauchi observed the preferential positioning of Pd particles at the bottom of the hexagonal WO3 nanotrees when using = 500 and 600 nm illumination in their investigation. The authors investigated the oleic acid and acetaldehyde photocatalytic activities of their Pd/WO3 systems. They discovered that the photocatalytic activity was positively impacted when the Pd particles were put toward the bottom of the nanotrees as opposed to the top. One of the explanations offered by the authors was the possibility that Pd particles placed on top could have shadowing effects on the WO3 nanotrees, resulting in decreased photocatalytic activity. The work offers insightful information regarding the significance of particle positioning in Pd/WO3 systems and its effects on photocatalytic effectiveness. In certain cases, Ag was photo deposited utilizing AgNO3 as a sacrificed electron acceptor in combination with WO3 or Pt/WO3 to oxidize water. It is interesting that the highly reactive nature of OH• radicals, which are created when H2 O2 decomposes, can also cause the oxidation of metallic nanoparticles, including Ag, to Ag+ . However, because this matter has not been explored in depth, more research and analysis are needed.

14.4.3 Photodeposition of Ag/AgX (Where X = Cl or Br) on WO3 In the recent past, Ag/AgX (where X = Cl or Br) has been used as a plasmonic photocatalyst by adding these core/shell particles to WO3 species (Yaipimai et al. 2015; Kudo et al. 1999; Ke et al. 2008). These core/shell particles are made up of an exterior Ag shell and a semiconductor AgX core (Kudo et al. 1999). These particles are created via a simple photochemical reduction technique in which AgX crystals are deposited

14 Photodeposition for Highly Effective Photocatalytic Materials

423

onto WO3 particles, which is frequently accomplished through ion exchange procedures (Yaipimai et al. 2015). Through the synergistic impacts of plasmonic characteristics and semiconductor behavior displayed by Ag/AgX core/shell structures, this method shows promise for increasing the photocatalytic activity of WO3 . An Ag/AgX particle is then created by the reduction of the outer AgX component under light. These Ag/AgX/WO3 species as synthesized have been effectively employed in several photocatalytic processes, including the elimination of Escherichia coli (as well as the breakdown of methyl orange) (Yaipimai et al. 2015), the breakdown of Rhodamine B (RhB) (Ke et al. 2008), and the degradation of methyl orange (Kudo et al. 1999). It’s crucial to note that the synthetic process used to make these cocatalysts differs from typical photodeposition techniques, which involve reducing or oxidizing a metal ion in solution on the surface of the photocatalyst.

14.4.4 Photodeposition on Composite Photocatalysts Containing WO3 Metal-loaded composite photocatalysts can be made using photodeposition. In photocatalysis, WO3 has been included in a number of composites, including WO3 /TiO2 (Ueyama et al. 2018; Abe et al. xxxx; Tokunaga et al. 2001; Lo et al. 2010), WO3 / C3 N4 (Zhang et al. 2009), CaFe2 O4 /WO3 (Murakami et al. 2012), and CoFe2 O4 /WO3 (Ye et al. 2010). In certain instances, one of the two photocatalysts has undergone photodeposition before the other photocatalyst is added (Baia et al. 2014; Zhang et al. 2009; Murakami et al. 2012). Alternately, the photodeposition process was carried out after the composite photocatalyst was synthesized (Ueyama et al. 2018; Tokunaga et al. 2001; Lo et al. 2010; Ye et al. 2010). Karacsonyi et al. conducted a study on the photodeposition of Au and Pt on WO3 /TiO2 composites (Baia et al. 2014). Using this method, the other metal oxide was added to the system after Au or Pt was first photodeposited on WO3 or TiO2 .The formation of H2 during the oxalic acid breakdown under UV light carried out under circumstances with a dearth of O2 , was next investigated using the resulting composite photocatalyst. This method provides a flexible way to combine the characteristics of several photocatalysts to improve their effectiveness in particular photocatalytic reactions. The catalysts were graded in order of their photocatalytic activity as follows: Pt/TiO2 > Au/TiO2 > Au/WO3 > Pt/WO3 . The relatively low performance of Pt/WO3 is not surprising given the unfavorable conduction band (CB) location of WO3 and the lack of O2 for reduction. For their hybrid systems, the authors discovered that an optimal loading of 3.5–10 weight percent WO3 in relation to TiO2 and 1 weight percent of the co-catalyst (Pt or Au) was generally advantageous in order to achieve the highest rate of oxalic acid degradation. In order to optimize the photocatalytic activity of composite systems, our research highlights the importance of meticulously selecting the co-catalyst combination and loading. However, the noble metal produced the best results when it was first photo deposited onto TiO2 rather than WO3 . The loading of WO3 species with

424

Akshita et al.

Ag/AgX (where X = Cl or Br), which has emerged as a plasmonic photocatalyst, is another topic of interest. These particles have an exterior Ag shell surrounding an AgX semiconductor core. These particles are created using a simple photochemical reduction process.

14.5 Photodeposition of Nanoparticles on Other Oxides 14.5.1 Gallium Oxide (Ga2 O3 ) The photodeposition of Rh2-y Cry O3 onto Ga2 O3 was studied by Maeda et al. (Li et al. 2013d). Maeda et al. exposed a solution comprising the photocatalysts (NH4 )RhCl6 and K2 CrO4 to light for four hours at a wavelength of 200 nm (0.5 wt% Rh, 0.75 wt% Cr) as part of their research. The solution was purged with inert gas, but no sacrificial agent was utilized. When compared to bare -Ga2 O3 , the authors showed that Rh2-y Cry O3 /− Ga2 O3 had roughly ten times more photocatalytic activity for splitting water. This was especially true under irradiation at > 200 nm. The improved photocatalytic activity demonstrated in this study by the deposition of Rh2-y Cry O3 onto Ga2 O3 has prospective uses in water-splitting reactions. Busser et al. (Busser et al. 2012; Li et al. 2014b) looked into the two-step Rh/Cr2 O3 core/shell photodeposition process on Zn-loaded Ga2 O3 (and also on Ga2 O3 ). Methanol was used as a sacrificial agent together with Zn-Ga2 O3 to create an aqueous solution. With N2 , degassing was accomplished. The authors added a tiny amount of Na3 RhCl6 .3H2 O (equivalent to 0.025 wt% Rh) while stirring. After five minutes, a 350 W Hg lamp was turned on, which caused the photocatalytic reduction of Rh3+ to Rh0. The rate at which H2 was produced in the presence of methanol-reforming was gauged by the authors. To gain insight into the photocatalytic activity of the Rh/Cr2 O3 core/shell particles in the creation of H2 through methanol-reforming, this study offers a two-step photodeposition approach on Zn-loaded Ga2 O3 . The researchers turned off the light and added an extra dose of Na3 RhCl6 .3H2 O corresponding to 0.025 wt% after coming to a plateau with a little decreasing slope. This procedure was done multiple times after turning the light back on to establish the ideal Rh loading, which was discovered to be 0.1 weight percent. To generate Rh/Cr2 O3 particles on Zn-Ga2 O3 , a similar stepwise photodeposition method was used. Here, 0.15 weight percent of Rh/Zn-Ga2 O3 was exposed to a K2 CrO4 − containing solution. The researchers found that CuOx photodeposition produced particles on the surface of Ga2 O3 that ranged in size from 1 to 10 nm (with an average size of 2 nm). This study offers useful information for improving the photocatalytic characteristics of these composite systems by providing insights into the photodeposition of CuOx on Ga2 O3 and the optimized loading of Rh for Rh/Cr2 O3 . To determine whether Cr2 O3 should be deposited before, after, or concurrently with Cu photodeposition, (Busser et al. 2012; Li et al. 2014b) did the most remarkable photocatalytic performance was observed when Cu deposition followed successive Cr2 O3 photodeposition, challenging the traditional core/shell

14 Photodeposition for Highly Effective Photocatalytic Materials

425

concept of CuOx/Cr2 O3 . Instead, the authors propose that obtaining outstanding activity requires the close proximity of CuOx and Cr2 O3 particles through photodeposition. The study delves into the optimal placement of CuOx and Cr2 O3 on the photocatalyst surface to maximize their photocatalytic activity. (Busser et al. 2012; Li et al. 2014b) research revealed that even small amounts of Cr were sufficient to enable total photocatalytic water splitting, a phenomenon not observed in the absence of Cr. The authors identified an ideal Cu loading range of 0.66–1 wt% to achieve total water splitting when combined with a Cr loading of 0.09 wt%. In the study, data from two articles by Busser et al. were compared, demonstrating that Rh/Cr2 O3 /Zn-Ga2 O3 exhibited superior photocatalytic water-splitting activities compared to CuOx + Cr2 O3 /Ga2 O3 . Based on this observation, the combination of Rh/Cr2 O3 /Zn-Ga2 O3 may potentially lead to enhanced photocatalytic performance in water-splitting reactions (Busser et al. 2012; Li et al. 2014b).

14.5.2 Bismuth Vanadate (BiVO4 ) With or without the addition of sacrificial agents, bismuth vanadate (BiVO4 ) has shown considerable promise for oxygen evolution reactions in water splitting under visible light (Park et al. 2014; Takahara et al. 2001; Arakawa and Sayama 2000; Kang et al. 2012). In these processes, AgNO3 is frequently used as a sacrificial agent (Park et al. 2014; Takahara et al. 2001; Arakawa and Sayama 2000). Ag/BiVO4 films were created by Zhang et al. (Niishiro et al. 2005) by employing photodeposition, Ag particles with sizes ranging from 10 to 20 nm were successfully incorporated. This integration of Ag particles significantly enhanced the photocatalytic activity of BiVO4 in the degradation of phenol under visible light conditions. Similarly, Kohtani et al. (Li et al. 1992) conducted a study using Ag/BiVO4 powders to investigate the photocatalytic degradation of phenol species under visible light. They prepared the samples using both impregnation (1.3 wt%) and photodeposition (2 wt%) methods. The authors found that Ag significantly improved the photocatalytic activity, and interestingly, the enhancement achieved through impregnation was more pronounced compared to photodeposition. (Li et al. 1992). These investigations demonstrate the beneficial effects of Ag on BiVO4 ’s photocatalytic activity for the breakdown of phenol, with varied manufacturing techniques altering the degree of enhancement. An investigation by Li et al. (Sasaki et al. 2008) demonstrated the well-defined morphology produced by the reductive photodeposition of Ag, Au, and Pt on monoclinic BiVO4 . MnOx and PbO2 nanoparticles, in contrast, were created through oxidative photodeposition. Without a sacrificial agent or gas purge, the photodeposition process took place in an aqueous solution comprising HAuCl4 , H2 PtCl6 , or AgNO3 . Pt was found to include both metallic particles and a small amount of PtO, according to the X-ray photoelectron spectroscopy (XPS) study, in contrast to Ag and Au, which only contained metallic particles. The metal was observed to affect the size of the as-deposited particles, with Ag particles being the largest, followed by Au, and Pt being the smallest. The activity of BiVO4 /silica

426

Akshita et al.

composites in acetaldehyde breakdown is greatly increased by Pt photodeposition, as shown in another study by Murakami et al. (Sulaeman et al. 2011) The authors used H2 PtCl6 .6H2 O as the precursor, ethanol as a sacrificial agent, and a nitrogen purge during the process and they discovered that 1 wt% was the ideal Pt loading. These results shed important light on the photodeposition procedure and the impact of various metals on the catalytic activity of materials based on BiVO4 . The photodeposition of Pt on W-doped BiVO4 (BiVW-O) films (Yoshida et al. 2013) as well as on bare BiVO4 and reduced graphene oxide (RG-O)/BiVO4 composites (Tanaka et al. 2012) was studied by Bard and colleagues. H2 PtCl6 functioned as the precursor and methanol as the sacrificial agent during the photodeposition process; no gas purge was employed. Water oxidation photocurrents for BiVW-O and RG-O/BiVO4 films increased with the addition of Pt. Pt on BiVW-O primarily occurred as PtO2 , with some metallic Pt also present, according to X-ray photoelectron spectroscopy (XPS) research. It’s interesting to note that the metallic Pt that was initially seen underwent oxidation when it was used in the oxygen evolution process (OER). According to the authors’ theories, a and RG-O/BiVO4 composites, reveal their potential use in photocatalytic processes.

14.5.3 Tantalum Oxide (Ta2 O5 ) The wide band gap of tantalum oxide (Ta2 O5 ), which is 4.0 eV (Sato et al. 1990; Abe et al. 2005; Domen et al. 1982) limits its photoactivity to the far ultraviolet area. However, Zhou et al. (Sato et al. 1990) showed that photodeposition of plasmonic gold (Au) on mesoporous Ta2 O5 can be used to increase photocatalytic activity when exposed to visible light. The precursor employed in their experiment was HAuCl4 , and the sacrificial reagent was methanol. N2 purging was used to keep the atmosphere under control, and a water bath was used to maintain the temperature at room temperature. The best loading of Au for the photocatalytic reforming of methanol, which increases hydrogen production, was found by the researchers to be 1.0 weight percent. They also showed that altering the irradiation period could influence the size of Au particles, producing particles that were 10, 15, and 20 nm after 10, 1, and 3 h, respectively. Larger particle sizes increased the photocatalytic hydrogen production from methanol (under light at > 400 nm), which the authors attributed to a higher Surface Plasmon Resonance (SPR) effect. It’s crucial to remember that the authors did not use analytical techniques like inductively coupled plasma (ICP) to directly evaluate the Au loading as a function of irradiation time. Therefore, given the use of various photodeposition periods, it cannot be stated with certainty that the Au loading was the same for all three samples. As a result, differences in the loading of Au nanoparticles may potentially have an impact on (at least in part) the observed difference in photocatalytic activity among the samples. The size of the metallic nanoparticles is important in triggering surface plasmon resonance and is crucial in influencing the overall activity of Au-loaded mesoporous Ta2 O5 photocatalysts, according to (Zhou et al. 2014).

14 Photodeposition for Highly Effective Photocatalytic Materials

427

14.5.4 Strontium Titanate (SrTiO3 ) Although strontium titanate (SrTiO3 ) has been the subject of extensive research, obtaining visible light catalytic activity is difficult due to the material’s huge band gap of 3.2 eV (Kudo and Miseki 2009). Researchers commonly add one or more dopants, such as rhodium (Jint et al. 1994; Konta et al. 2004), chromium (Jia et al. 2010; Bae et al. 2009), and niobium (Wang et al. 2015; Lee et al. 2013) to the crystal lattice to overcome this problem. Doped SrTiO3 is frequently used in Z-scheme configurations for complete water splitting or in conjunction with a sacrificial agent as a photocatalyst for hydrogen generation (Jint et al. 1994; Kang et al. 2012; Yu et al. 2011; Liu et al. 2011a). Pt or Ru are frequently employed as catalysts to be photo deposited onto doped SrTiO3 in order to improve its catalytic activity (Jia et al. 2010; Liu et al. 2011a; Ohsawa et al. 2006; Sun et al. 2011b; Yan et al. 2013; Giocondi and Rohrer xxxx). It was discovered in a study by Sasaki et al. (Jint et al. 1994) that Ru might demonstrate more effectiveness than Pt. The initial activities of the two systems were comparable when a Z-scheme arrangement of M/SrTiO3 :RhBiVO4 (M = 0.7 wt% Ru or 0.1 wt% Pt) was evaluated for overall water splitting under visible-light illumination. However, the Pt/SrTiO3 :Rh-BiVO4 system showed slightly higher activity than the Ru/SrTiO3 :Rh-BiVO4 system. However, the H2 and O2 generation rates of the Ru/SrTiO3 :Rh-BiVO4 system remained stable while the H2 and O2 evolution rates reported for the Pt/SrTiO3 :Rh-BiVO4 system showed a reduction with time. A common method for adding a co-catalyst to (doped) SrTiO3 is photo deposition, commonly with Pt or Ru. To fully evaluate the performance of Ptor Ru-loaded (doped) SrTiO3 , XPS measurements are crucial because the specifics of the photodeposition process are frequently not addressed in depth. After photodeposition, which was carried out in the presence of a sacrificial agent and under Ar purging conditions, Sasaki et al. (Jint et al. 1994) noted the presence of metallic Pt on SrTiO3 :Rh. On the other hand, Lee et al. (Townsend et al. 2012) found that platinum oxide formed on SrTiO3 :Rh after photodeposition even though there was no inert gas purge or sacrificial agent present. Similar to this, Yu et al. (Borgarello et al. xxxx) discovered the coexistence of platinum oxide and metallic platinum on SrTiO3 :Rh after conducting photodeposition in the absence of a sacrificial agent and an inert gas purge. The significance of carefully addressing the photodeposition conditions and the ensuing catalyst species for (doped) SrTiO3 -based photocatalytic systems is brought out by these several observations. In order to explain these disparities in data, the authors ascribe the creation of platinum oxide to the air oxidation of Pt during storage, highlighting the need for additional research. Other metals, such Ag, have also been examined at a more fundamental level (Xin et al. 2014; Qingguo et al. 2019; Zhao et al. 2020; Maeda et al. 2010b, 2007). aside from the photodeposition of Pt and Ru, which are routinely used procedures to load co-catalysts on (doped) SrTiO3 . Also investigated on (doped) SrTiO3 is the photodeposition of Ni/NiO (Maeda et al. 2010c), MnOx (Wang et al. 2015), PbO2 (Giocondi and Rohrer xxxx; Maeda et al. 2007), and Rh2−y Cry O3 (Li et al. 2013d). Notably, it has been discovered that the light intensity used during the photodeposition process of MnOx on Nb:SrTiO3 has

428

Akshita et al.

effects on the morphology of MnOx , emphasizing the importance of meticulous control over the experimental conditions. It has been shown that adding Cr3+ as a dopant introduces defect levels into the band structure of SrTiO3 , improving the use of visible light for photocatalytic applications. To determine the water-splitting activity, it is essential to know the precise location that the guest dopant occupies within the SrTiO3 host. Sol–gel hydrothermal synthesis has been used to produce Cr-doped SrTiO3 that is driven by visible light and has a large specific surface area (Wang et al. 2015).

14.6 Photodeposition of Nanoparticles on CdS Cadmium sulfide (CdS) is a semiconductor with a comparatively small band gap of approximately 2.4 eV. Its conduction band minimum at -0.9 V versus the Normal Hydrogen Electrode (NHE) allows for unbiased proton reduction under visible light illumination, yielding an H+ /H2 reduction potential of 0 V versus NHE (Kudo and Miseki 2009; Ma et al. 2008). CdS is sensitive to photo corrosion, a condition that involves the oxidation and dissolution of Cd2+ ions, despite having favorable characteristics for photocatalysis. A workable solution to this problem entails using a sacrificial chemical to serve as a hole scavenger during the photodeposition process. For instance, adding sulfide in the form of Na2S causes a conversion reaction in the reaction mixture, which helps to reduce photo corrosion and improves the stability of CdS in photocatalytic applications. For instance, sulfide can be added to the reaction mixture in the form of Na2 S, which is transformed by the reaction: S2 + 2h+ → S To stop photo corrosion, additional sacrificial agents, such as different alcohols or acids, can be used (Maeda et al. 2006).

14.6.1 Comparison of the Hydrogen Evolution Activity Induced by Co-Catalysts Platinum, gold, rhodium, cadmium, nickel (oxides), ruthenium, and palladium nanoparticles have all been functionalized onto CdS using the photodeposition method (Wenderich and Mul 2016). Platinum has attracted the greatest attention among these co-catalysts and has proven to be highly effective at promoting hydrogen evolution activity (Sakamoto et al. 2009). It is important to keep in mind that other co-catalysts, such rhodium, have also demonstrated efficacy that is promising and, in some cases, have even outperformed platinum (Cavalca et al. 2012).

14 Photodeposition for Highly Effective Photocatalytic Materials

429

14.6.2 Platinum Photodeposition on CdS 14.6.2.1

Overview of the Conditions for Reactions

There has been a lot of research done on the platinum photodeposition technique onto CdS. Aqueous solution containing CdS nanoparticles, a platinum precursor like H2 PtCl6 , and a sacrificial agent like Na2 S or Na2 SO3 are typically used in this procedure (Wenderich and Mul 2016). On the surface of the CdS nanoparticles, platinum deposition takes place under illumination, frequently using a tungstenhalogen lamp (Sakamoto et al. 2009).

14.6.2.2

Controlling the Morphology of Pt

Platinum nanoparticles’ shape can be precisely controlled by varying reaction parameters, such as the platinum precursor’s concentration and the irradiation process’ duration (Wenderich and Mul 2016). Specifically, larger platinum nanoparticles could be produced by increasing the concentration of the platinum precursor, while longer irradiation times might result in a higher density of platinum nanoparticles being deposited on the surface of the CdS nanoparticles (Sakamoto et al. 2009).

14.6.2.3

Pt Deposition Mechanism and Chemical Reactions

Complex and somewhat unresolved chemical processes underlie the photodeposition of platinum on CdS. Nonetheless, the mechanism is thought to entail the nucleation and growth of platinum nanoparticles on the surface of CdS nanoparticles via the reduction of the platinum precursor using photo-excited electrons generated on the CdS nanoparticle surface (Wenderich and Mul 2016).

14.6.2.4

In Situ Photodeposition

Investigations on in situ platinum photodeposition on CdS have also been made. This technique entails distributing CdS nanoparticles in a platinum precursor-containing solution prior to subjecting them to light irradiation in order to promote platinum photodeposition on the surface of the CdS nanoparticles (Sakamoto et al. 2009). Notably, this process has been shown to be more effective than ex situ photodeposition, which involves depositing CdS nanoparticles on a substrate first and then exposing them to a solution containing the platinum precursor (Wenderich and Mul 2016).

430

14.6.2.5

Akshita et al.

Comparing Sacrificial Agents

The photodeposition of platinum on CdS may be influenced using a sacrificial agent. It has been discovered that Na2 S is more effective than Na2 SO3 at aiding platinum’s photodeposition on CdS (Sakamoto et al. 2009). This variation is thought to be caused by the higher reduction potential of Na2 S, which leads to a greater concentration of photo-generated electrons on the surface of CdS nanoparticles.

14.6.2.6

Comparison with Other Methods

Other methods for putting platinum nanoparticles on CdS besides photodeposition include impregnation and electrochemical deposition (Wenderich and Mul 2016). However, compared to these additional approaches, comparative investigations have shown that photodeposition is more effective at stimulating hydrogen evolution activity (Sakamoto et al. 2009).

14.6.2.7

Regulated Photodeposition of Co-Catalysts of Nickel Phosphide on CdS Nanosheets

When paired with CdS, nickel phosphide has been studied as a possible co-catalyst to enhance photocatalytic hydrogen evolution. It is demonstrated that the photodeposition of nickel phosphide (NiPx) onto CdS nanosheets is controllable by varying reaction parameters, such as the concentration of the nickel precursor and the duration of light irradiation. This set of nickel phosphide co-catalysts greatly improves the photocatalytic performance of CdS for hydrogen evolution, as illustrated in Fig. 14.4 (Sakamoto et al. 2009). Figure 14.4 illustrates how electron–hole pairs are created in CdS when exposed to visible light. The in-situ deposition of NiPx on CdS nanosheets photochemically form good contact with CdS, so the electron of CdS conduction band transferred immediately to NiPx and reduces the protons in hydrogen molecules. In the meantime, ethanol molecules eat up the holes in the CdS valence band, preventing CdS from recombining and photocorroding while also enhancing photocatalytic activity.

14.6.2.8

Laser Photodeposition of Metal Nanodots on TiO2 Nanoparticles for the Synthesis of Nanoheterodimers

By adding metal nanodots to TiO2 nanoparticles using laser photodeposition, nanoheterodimers have been created. This approach has shown to be capable of precisely controlling the size, shape, and spatial arrangement of the metal nanodots with respect to the TiO2 nanoparticles. The subsequent nanoheterodimers demonstrated increased photocatalytic activity for the evolution of hydrogen, as demonstrated by the study mentioned in the reference (Cavalca et al. 2012).

14 Photodeposition for Highly Effective Photocatalytic Materials

431

Fig. 14.4 Mechanism of visible photocatalytic evolution of hydrogen on CdS-NiPx substrate

14.6.2.9

Redox Dual Co-Catalyst-Modified CdS Double-Heterojunction Photocatalysts for Effective Hydrogen Generation

Researchers have looked into CdS double-heterojunction photocatalysts that have been redox dual-co-catalyst modified to produce hydrogen efficiently. NiCoP and NiCoPi were used as co-catalysts for this process, and they were photodeposited onto the surface of CdS nanoparticles. According to the study, cited as (Fresno et al. 2014) the resultant photocatalysts demonstrated significantly enhanced photocatalytic activity for hydrogen production in comparison to CdS nanoparticles lacking these co-catalysts.

14.6.2.10

Photodeposition of Pt on Colloidal CdS and CdSe/CdS Semiconductor Nanostructures

Researchers have successfully shown that platinum can be photodeposited on colloidal CdS and CdSe/CdS semiconductor nanostructures. According to the study cited as (Li et al. 1992), the platinum nanoparticles produced using this technique shown astounding effectiveness in encouraging hydrogen evolution activity. This approach has potential applications in the development of highly efficient photocatalytic hydrogen production systems.

432

Akshita et al.

14.7 Photodeposition of Complex Particles on GaN:ZnO Domen et al. and colleagues have conducted extensive studies on the photodeposition of Rh/Cr2 O3 core/shell particles on GaN:ZnO, a solid solution of GaN and ZnO (Liu et al. 2011b; Doña-rodríguez and Melián 2021; Chen et al. 2015; Dozzi and Selli 2013). GaN:ZnO can completely split water under visible light illumination, making it an extremely promising material for solar energy storage through hydrogen generation. Nevertheless, co-catalytic nanoparticles are required to facilitate the production of H2 and O2 . Rh has been chosen as a co-catalyst because of its capacity to serve as an electron trap, which makes H2 generation effective (Doña-rodríguez and Melián 2021). On the Rh surface, however, a quick back-reaction between O2 and H2 takes place in the presence of O2 , which produces water. A protective Cr2 O3 shell can be built onto the Rh nanoparticles to reduce this undesirable reaction. Rh nanoparticles are first deposited during the photodeposition process, and then Cr2 O3 is later photodeposited. The formation of Cr2 O3 is the outcome of chromate reduction. Interestingly, there exists a Cr2 O3 loading that yields a shell thickness of approximately 2 nm (Doña-rodríguez and Melián 2021). Beyond this point, adding more K2 CrO4 precursor does not result in more Cr2 O3 being deposited. Remarkably, a liquid-phase reduction strategy for Rh loading has been used to achieve improved photocatalytic activities in water splitting, in contrast to the conventional photodeposition methodology (Chen et al. 2015; Yang et al. 2008). This implies that Rh photodeposition on its own may not be strictly required. Apart from the majority of core/shell nanoparticles, another observation made in the liquid-phase reduction approach was the production of irregularly shaped shell structures. When creating Rh/Cr2 O3 core/shell nanoparticles using photodeposition, however, such erratic shell shapes were not seen. In comparison to impregnation, where the Rh co-catalyst was discovered to be in the lowest (metallic) state and primarily featureless particles rather than core/shell structures were generated, both the liquid-phase reduction and the photodeposition techniques performed better. Domen and associates (Chen et al. 2015; Dozzi and Selli 2013; Yang et al. 2008) conducted a thorough investigation into the photodeposition of a Cr2 O3 shell on a number of co-catalysts, including NiOx , RuO2 , Rh2 O3 , Pd, Pt, and Ir, but none of these mixtures demonstrated the same promising outcomes in water splitting by photocatalysis using Rh/Cr2 O3 core/shell nanoparticles on GaN:ZnO. Rhodium and chromium were concurrently deposited on GaN:ZnO and SrTiO3 using photodeposition studies undertaken by the scientists (Li et al. 2013d) They discovered that however photodeposition offered greater benefits for Rh2-y Cry O3 /(Ga1-x Znx )(N1-x Ox ) activity, impregnation produced greater photocatalytic activities in water splitting than did photodeposition. The authors concluded that Rh2-y Cry O3 is not as good an electron sink as Rh metallic. Moreover, they demonstrated that employing Rh/Cr2 O3 core/shell co-catalytic nanoparticles resulted in significantly higher activity in visible-light water splitting when compared to Rh2-y Cry O3 . The authors (Maeda et al. 2010) investigated the simultaneous photodeposition of Rh and Cr on (Ga1-x Znx )(N1-x Ox ) under visible light. They also conducted experiments with various K2 CrO4 concentrations. They discovered

14 Photodeposition for Highly Effective Photocatalytic Materials

433

that the amount of Cr that could be placed had a saturation limit of roughly 0.25 wt%. The optimal outcomes for visible-light water splitting were attained with a supply of 0.175 weight percent Cr while maintaining a constant Rh loading of 0.75 weight percent. The photocatalytic activity did, however, decline as the amount of Cr was increased further, reaching a steady state at additions of 0.5 wt% and higher. Using TEM, Cavalca and associates (Xu et al. 2014) examined Pt’s in situ photodeposition on GaN:ZnO. They first applied an H2 PtCl6 solution to the GaN:ZnO surface. This solution was then evaporated and applied to a gold TEM grid coated in an amorphous carbon sheet. Prior to illumination, reference TEM images were captured. The specimen chamber was then filled with a small amount of water vapor, and the grid was lit for four hours at a wavelength of 405 nm and a power density of 6 W/cm2 . The specimen room was then completely emptied when the illumination was finished, and TEM pictures were once more captured for added examination. The GaN:ZnO surface had a thin, uniform, and amorphous salt layer on it prior to the deposition process. Following illumination, the amorphous layer mostly disappeared and an even distribution of particles with a diameter of roughly 1 nm was observed. This method worked well for examining how the dynamics of particle morphology relate to the length of illumination. It can greatly advance our understanding of photodeposition by expanding this technology to other semiconductor materials and combining it with atomic force microscopy (AFM) investigations.

14.8 Structure-Directed Photodeposition The use of crystal facet engineering in photocatalysis has grown in popularity (Gordon et al. 2012; Pan et al. 2011; Huang et al. 2015c). The goal is to synthesize semiconductor materials in a way that highlights particular features, improving photocatalytic performance. For instance, thorough research has been done to determine the primary aspect that causes catalytic photosynthesis in case of well-defined TiO2 anatase (Pan et al. 2011; Huang et al. 2014; Chen et al. 2012b; Wei et al. 2015; Latorre-Sánchez et al. 2015; Read et al. 2009; Jint et al. 1993). For crystal facet engineering, one common technique is the application of (microwave-assisted) hydrothermal synthetic methods with the addition of surfactants, sometimes referred to as capping agents. (Pan et al. 2011; Li et al. 2009b; Sabio et al. 2010). Structuredirected photodeposition has been used to investigate the redox activity of facetengineered crystals. According to the theory, reduced metal nanoparticles form preferentially, indicating the presence of facets that are more susceptible to reductive processes. Similar to this, the preferred production of oxidized metal nanoparticles reveals features that favor oxidative processes. Notably, structure-directed photodeposition research has shown that a single semiconductor particle may include both favored oxidative and reductive sites (Maeda et al. 2010c; Zhen et al. 2014; Jiang et al. 2014; Wold 1993). For instance, Ohno et al. (Fujii et al. 2009) demonstrated that photo-oxidation preferentially deposits PbO2 on the 001-facet of anatase and the 011-facet of rutile, while photo-reduction selectively deposits Pt on the 110-facet

434

Akshita et al.

of rutile. The use of surfactants, also referred to as capping agents, in (microwaveassisted) hydrothermal synthetic processes is one typical technique for achieving crystal facet engineering. Structure-directed photodeposition is a technique developed to study the redox activity of facet-engineered crystals. The spatially favored reduction of metal nanoparticles, which indicates the presence of facets more reductively susceptible to processes, is the basis of this method. The spatially favored production of oxidized metal nanoparticles also identifies surfaces that are more favorable for oxidative processes (Jiang et al. 2015; Lee and Choi 2005). Structuredirected photodeposition is caused by a process known as light-induced charge separation (Fujii et al. 2009; Sasaki et al. 2008), in which small differences in the band structures of various facets cause the conduction bands and valence bands to slightly shift in energy. The preferential deposition of reduced or oxidized metal species on particular facets is influenced by these energy discrepancies, exposing their unique redox characteristics. By moving electrons and holes to energetically advantageous facets, structure-directed photodeposition creates preferential sites for reduction and oxidation (Litter 1999; Chen et al. 2010; Sung-Suh et al. 2004; Hua Gui Yang 2008). However, this phenomenon can also be influenced by other variables (Chen et al. 2012a; Hua Gui Yang 2008). On [TBA,H]− Ca2 Nb3 O10 nanosheets, Sabio et al.‘s (Xinchen Wang 2009) experiments attempted both reductive and oxidative photodeposition with a variety of co-catalysts. Co-catalysts were discovered to be present on the nanosheets’ surface and at their edges. It’s interesting to note that structuredirected photodeposition occasionally took place at a specific spot rather than being restricted to a given facet. The possibility of structure-directed deposition during wet impregnation should not be overlooked. These results emphasize the difficulty of structure-directed photodeposition and the significance of more research in this field. Surface charges naturally vary between different crystal facets in water, even in the absence of light irradiation. According to Liu et al. (Pan et al. 2011), the competitive ionic compound adsorption with charges identical the metal precursor may also take place on facets, blocking these locations from (structure-directed) photodeposition. One important tactic for enhancing a catalyst’s photocatalytic activity is structure-directed photodeposition, which involves positioning reduction and oxidation co-catalysts on the facets where electrons and holes tend to accumulate. In their study, Li et al. (Sasaki et al. 2008) employed structured photodeposition to develop a highly active BiVO4 photocatalytic system, demonstrating the efficacy of this approach. Their research showcased the production of MnOx and PbO2 on the “110” facets of BiVO4 through Mn2+ and Pb2+ photo-oxidation. Moreover, Pt, Ag, and Au were precisely placed on the “010” facet by photoreduction from cationic and anionic precursors. Compared to the impregnation method for water oxidation, they greatly increased the photocatalytic activity of BiVO4 by introducing Pt and MnOx via photodeposition. Using Pt/Co3 O4 /BiVO4 , similar encouraging outcomes were seen in the study of dye degradation [102, 270]. Photodeposition and impregnation with structure direction approaches have been compared by researchers. The significance of structure-directed photodeposition in generating selective and improved photocatalytic activity on crystal facets of semiconductor materials is highlighted

14 Photodeposition for Highly Effective Photocatalytic Materials

435

by these findings. In contrast to randomly distributed Pt obtained through impregnation, Zhen et al. (2014) study revealed that carefully photodepositing Pt on the positively charged 001 facet of ferroelectric PbTiO3 led to significantly enhanced photocatalytic activity for hydrogen generation. It’s crucial to remember that structuredirected photodeposition does not ensure that a photocatalytic material will have the highest activity. In the case of rhodamine B degradation under visible light, Jiang et al. (2014) showed that higher photocatalytic activity was obtained using an in situ photodeposition method as opposed to a conventional photodeposition approach to load anatase with Ag. In the in situ photodeposition procedure, NaIO3 was added to the mixture, and it was predicted that during stirring in the dark, AgIO3 would develop, uniformly coating the anatase particles on all sides. The performance of the photocatalytic system was enhanced as a result. In the study of Iizuka et al. (Dukovic et al. 2008), it was shown that higher photocatalytic activity was achieved using liquid-phase chemical reduction of Ag as compared to either in situ photodeposition or impregnation procedures in the case of Ag-loaded BaLa4 Ti4 O15 plates for CO2 reduction. The initial distribution of Ag particles on the BaLa4 Ti4 O15 plates’ basal plane was random. However, the scientists noticed a behavior where Ag particles vanished from the basal plane and then emerged at the plate margins after a period of one hour of photocatalytic activity. This behavior was attributed to the basal plane’s Ag particles being photo-oxidized before being selectively photo deposited on the edges. It’s interesting that the rephotodeposited Ag particles were smaller than the conventionally in situ photodeposited Ag particles, explaining the increased activity in CO2 reduction that was reported. Here, various commonly studied photocatalytic materials are given in Table 14.1, which highlights the important characteristics based on morphology, crystalline structure, and synthesis process.

14.9 Concluding Remarks and Future Perspectives A very promising technique for effectively creating co-catalytic nanoparticles on semiconductor materials is photodeposition. The materials resulting from Pt on TiO2 , Ag on ZnO, and Pt on CdS are especially remarkable because they hold great promise for a range of photocatalytic uses. However, optimizing photodeposition processes to yield catalyst materials with the highest activity primarily depends on empirical methods because a fundamental understanding of the physical chemistry underlying photodeposition is still lacking. In order to properly create nanoparticles on semiconductor substrates with desired sizes and oxidation states, more study is required to comprehend the photodeposition mechanism. Structure-directed photodeposition, where nanoparticles are selectively deposited on designed crystal facets with favorable reductive and oxidative characteristics, is the focus of recent advances in photodeposition research. It is expected that by employing facet-engineered semiconductor crystals and maximizing the photodeposition conditions, materials with previously unheard-of photocatalytic activity can be produced. Ni-based co-catalysts

436

Akshita et al.

Table 14.1 Commonly studied some photocatalytic materials and their characteristics Photocatalytic material

Characteristics

Reference

Titanium Dioxide (TiO2 )

Wide band gap (3.2 eV), excellent stability, low cost, (Wold 1993) high photocatalytic activity, widely used in water and air purification

Zinc Oxide (ZnO)

Moderate band gap (3.37 eV), good electron mobility, biocompatible, exhibits both UV and visible light photocatalytic activity

(Chen et al. 2010)

Bismuth Vanadate (BiVO4 )

Visible light absorption, suitable band gap (2.4 eV), good charge carrier separation, potential for water oxidation

(Sung-Suh et al. 2004)

Tungsten Trioxide (WO3 )

Multifunctional properties, good visible light absorption, surface acidity, capable of water oxidation, suitable for environmental remediation

(Hua Gui Yang 2008)

Graphitic Carbon Nitride (g-C3 N4 )

Visible light absorption, chemical stability, metal-free, potential for photocatalytic water splitting, and organic pollutant degradation

(Xinchen Wang 2009)

have been photodeposited onto CdS in a number of recent studies to boost the photocatalytic activity for hydrogen production from ethanolic solutions. Additionally, Pt deposition on colloidal CdS and CdSe/CdS core/shell nanocrystals are examples of effective photodeposition experiments. Fluorescence imaging has also been employed in a new way to dynamically monitor the photodeposition of a single Cox P co-catalyst nanoparticle on semiconductor photocatalysts. These developments offer considerable potential for developing highly effective and specialized photocatalytic materials as well as for furthering the area of photocatalysis.

References Abe R, Sayama K, Sugihara H (2005) Development of new photocatalytic water splitting into H2 and O2 using two different semiconductor photocatalysts and a shuttle redox mediator IO3-/I-. J Phys Chem B 109:16052–16061. https://doi.org/10.1021/jp052848l Abe R, Takami H, Murakami N, Ohtani B Pristine simple oxides as visible light driven photocatalysts: highly efficient decomposition of organic compounds over Platinum-loaded Tungsten Oxide Ahmed S, Rasul MG, Martens WN, Brown R, Hashib MA (2010) Heterogeneous photocatalytic degradation of phenols in wastewater: A review on current status and developments. Desalination 261:3–18 Ahmed F, Kanoun MB, Awada C, Jonin C, Brevet P-F (2021) An experimental and theoretical study on the effect of silver nanoparticles concentration on the structural, morphological, optical, and electronic properties of TiO2 nanocrystals. Crystals (Basel) 11:1488. https://doi.org/10.3390/ cryst11121488 Alammar T, Mudring AV (2009) Facile preparation of Ag/ZnO nanoparticles via photoreduction. J Mater Sci 44:3218–3222. https://doi.org/10.1007/s10853-009-3429-4

14 Photodeposition for Highly Effective Photocatalytic Materials

437

Aminian MK, Ye J (2010) Morphology influence on photocatalytic activity of tungsten oxide loaded by platinum nanoparticles. J Mater Res 25:141–148. https://doi.org/10.1557/jmr.2010.0021 Arai T, Yanagida M, Konishi Y, Ikura A, Iwasaki Y, Sugihara H, Sayama K (2008a) The enhancement of WO3-catalyzed photodegradation of organic substances utilizing the redox cycle of copper ions. Appl Catal B 84:42–47. https://doi.org/10.1016/j.apcatb.2008.03.002 Arai T, Horiguchi M, Yanagida M, Gunji T, Sugihara H, Sayama K (2008b) Complete oxidation of acetaldehyde and toluene over a Pd/WO3 photocatalyst under fluorescent- or visible-light irradiation. Chem Commun 5565–5567. https://doi.org/10.1039/b811657a Arakawa H, Sayama K Catalysis Surveys from Japan 4 (2000) 75–80 75 Solar hydrogen production. Significant effect of Na2 CO3 addition on water splitting using simple oxide semiconductor photocatalysts Bae SW, Ji SM, Hong SJ, Jang JW, Lee JS (2009) Photocatalytic overall water splitting with dualbed system under visible light irradiation. Int J Hydrogen Energy 34:3243–3249. https://doi. org/10.1016/j.ijhydene.2009.02.022 Baia L, Vulpoi A, Radu T, Karácsonyi É, Dombi A, Hernádi K, Danciu V, Simon S, Norén K, Canton SE, Kovács G, Pap Z (2014) TiO2 /WO3 /Au nanoarchitectures’ photocatalytic activity “from degradation intermediates to catalysts” structural peculiarities” Part II: Aerogel based composites—fine details by spectroscopic means”. Appl Catal B 148–149:589–600. https://doi. org/10.1016/j.apcatb.2013.12.034 Behnajady MA, Modirshahla N, Shokri M, Zeininezhad A, Zamani HA (2009) Enhancement photocatalytic activity of ZnO nanoparticles by silver doping with optimization of photodeposition method parameters. J Environ Sci Health A Tox Hazard Subst Environ Eng 44:666–672. https:// doi.org/10.1080/10934520902847752 Boccuzzi F, Chiorino A, Guglielminotti E (1996) Effects of structural defects and alloying on the FTIR spectra of CO adsorbed on Pt/ZnO. ELSEVIER Borgarello E, Serpone N, Pelizzetti E, Barbeni M Efficient photochemical conversion of aqueous sulphides and sulphites to hydrogen using a rhodium-loaded CdS photocatalyst Busser GW, Mei B, Muhler M (2012) Optimizing the deposition of hydrogen evolution sites on suspended semiconductor particles using on-line photocatalytic reforming of aqueous methanol solutions. Chemsuschem 5:2200–2206. https://doi.org/10.1002/cssc.201200374 Busser GW, Mei B, Pougin A, Strunk J, Gutkowski R, Schuhmann W, Willinger MG, Schlögl R, Muhler M (2014) Photodeposition of copper and chromia on gallium oxide: The role of co-catalysts in photocatalytic water splitting. Chemsuschem 7:1030–1034. https://doi.org/10. 1002/cssc.201301065 Carabineiro SAC, MacHado BF, Bacsa RR, Serp P, Draić G, Faria JL, Figueiredo JL (2010a) Catalytic performance of Au/ZnO nanocatalysts for CO oxidation. J Catal 273:191–198. https:// doi.org/10.1016/j.jcat.2010.05.011 Carabineiro SAC, Machado BF, Dražić G, Bacsa RR, Serp P, Figueiredo JL, Faria JL (2010) Photodeposition of Au and Pt on ZnO and TiO2 . In: Stud Surf Sci Catal. Elsevier Inc., pp 629–633 Cavalca F, Laursen AB, Kardynal BE, Dunin-Borkowski RE, Dahl S, Wagner JB, Hansen TW (2012) In situ transmission electron microscopy of light-induced photocatalytic reactions. Nanotechnology 23. https://doi.org/10.1088/0957-4484/23/7/075705 Chang CM, Hon MH, Leu IC (2012) Improvement in CO sensing characteristics by decorating ZnO nanorod arrays with Pd nanoparticles and the related mechanisms. RSC Adv 2:2469–2475. https://doi.org/10.1039/c2ra01016j Chang CM, Hon MH, Leu IC (2013) Outstanding H2 sensing performance of Pd nanoparticledecorated ZnO nanorod arrays and the temperature-dependent sensing mechanisms. ACS Appl Mater Interfaces 5:135–143. https://doi.org/10.1021/am302294v Chaudhary R, Singh C (2014) Removal of metal ions by means of solar oxidation processes based on pH, TiO2 and oxidants. Desalination Water Treat 52:1263–1271. https://doi.org/10.1080/194 43994.2013.78755232

438

Akshita et al.

Chen X, Shen S, Guo L, Mao SS (2010) Semiconductor-based photocatalytic hydrogen generation. Chem Rev 110:6503–6570. https://doi.org/10.1021/cr1001645 Chen C, Zheng Y, Zhan Y, Lin X, Zheng Q, Wei K (2011a) Enhanced Raman scattering and photocatalytic activity of Ag/ZnO heterojunction nanocrystals. Dalton Trans 40:9566–9570. https://doi.org/10.1039/c1dt10799b Chen X, Li P, Tong H, Kako T, Ye J (2011b) Nanoarchitectonics of a Au nanoprism array on WO3 film for synergistic optoelectronic response. Sci Technol Adv Mater 12. https://doi.org/10.1088/ 1468-6996/12/4/044604 Chen D, Li T, Chen Q, Gao J, Fan B, Li J, Li X, Zhang R, Sun J, Gao L (2012a) Hierarchically plasmonic photocatalysts of Ag/AgCl nanocrystals coupled with single-crystalline WO3 nanoplates. Nanoscale 4:5431–5439. https://doi.org/10.1039/c2nr31030a Chen YC, Pu YC, Hsu YJ (2012b) Interfacial charge carrier dynamics of the three-component In 2O 3-TiO 2-Pt heterojunction system. J Phys Chem C 116:2967–2975. https://doi.org/10.1021/ jp210033y Chen X, Chen W, Lin P, Yang Y, Gao H, Yuan J, Shangguan W (2013) In situ photodeposition of nickel oxides on CdS for highly efficient hydrogen production via visible-light-driven photocatalysis. Catal Commun 36:104–108. https://doi.org/10.1016/j.catcom.2013.03.016 Chen W, Kuang Q, Wang Q, Xie Z (2015) Engineering a high energy surface of anatase TiO2 crystals towards enhanced performance for energy conversion and environmental applications. RSC Adv 5:20396–20409 Chen S, Nickelb U (1996) Synthesis of hybrid metal-semiconductor ultrafine particles Photochemical deposition of silver on a ZnO colloid surface Chong MN, Jin B, Chow CWK, Saint C (2010) Recent developments in photocatalytic water treatment technology: A review. Water Res 44:2997–3027 Chowdhury P, Malekshoar G, Ray MB, Zhu J, Ray AK (2013) Sacrificial hydrogen generation from formaldehyde with Pt/TiO2 photocatalyst in solar radiation. Ind Eng Chem Res 52:5023–5029. https://doi.org/10.1021/ie3029976 Clark WC, Vondjidis AG (1965) An infrared study of the photocatalytic reaction between titanium dioxide and silver nitrate Dasgupta NP, Liu C, Andrews S, Prinz FB, Yang P (2013) Atomic layer deposition of platinum catalysts on nanowire surfaces for photoelectrochemical water reduction. J Am Chem Soc 135:12932–12935. https://doi.org/10.1021/ja405680p Deng Q, Duan X, Ng DHL, Tang H, Yang Y, Kong M, Wu Z, Cai W, Wang G (2012) Ag nanoparticle decorated nanoporous ZnO microrods and their enhanced photocatalytic activities. ACS Appl Mater Interfaces 4:6030–6037. https://doi.org/10.1021/am301682g Di Paola A, García-López E, Marcì G, Palmisano L (2012) A survey of photocatalytic materials for environmental remediation. J Hazard Mater 211–212:3–29 Dombnech J, Andrbs M, Mutioz J Photoinduced oxygen uptake in aqueous suspensions of ZnO Domen K, Onishi SNT, Tamarli K (1982) Volume 92. numlwr 4 Photocatalytic decomposition of liquid water on a NiO-SrTi03 catalyst Doña-rodríguez JM, Melián EP (2021) Nano-Photocatalytic Materials: Possibilities and Challenges. Nanomaterials 11:1–4 Dozzi MV, Selli E (2013) Specific facets-dominated anatase TiO2 : Fluorine-mediated synthesis and photoactivity. Catalysts 3:455–485 Dukovic G, Merkle MG, Nelson JH, Hughes SM, Alivisatos AP (2008) Photodeposition of Pt on colloidal CdS and CdSe/CdS semiconductor nanostructures. Adv Mater 20:4306–4311. https:// doi.org/10.1002/adma.200800384 Dulnee S, Luengnaruemitchai A, Wanchanthuek R (2014) Activity of Au/ZnO catalysts prepared by photo-deposition for the preferential CO oxidation in a H2-rich gas. Int J Hydrogen Energy 39:6443–6453. https://doi.org/10.1016/j.ijhydene.2014.02.038 Dissertation CJ Photoactivity Of titanium dioxide films with controlled orientation Etacheri V, Di Valentin C, Schneider J, Bahnemann D, Pillai SC (2015) Visible-light activation of TiO2 photocatalysts: Advances in theory and experiments. J Photochem Photobiol, C 25:1–29

14 Photodeposition for Highly Effective Photocatalytic Materials

439

Everly CR, Traynham JG (1976) ) 6. Am Chem Soc, Miller and C. Walling, p 17 Fernhndez A, Caballero A, Gonzhlez-Elipe AR, Herrmann J-M, Dexpert H, Villain F (1995) In Situ EXAFS study of the photocatalytic reduction and deposition of gold on colloidal Titania Ferraria AM, Carapeto AP, Botelho Do Rego AM (2012) X-ray photoelectron spectroscopy: Silver salts revisited. Vacuum 86:1988–1991. https://doi.org/10.1016/j.vacuum.2012.05.031 Fox MA, Pettit’ TL (1989) Photoactivity of Zeolite-Supported cadmium sulfide: hydrogen evolution in the presence of sacrificial donors Fresno F, Portela R, Suárez S, Coronado JM (2014) Photocatalytic materials: Recent achievements and near future trends. J Mater Chem A Mater 2:2863–2884. https://doi.org/10.1039/c3ta13 793g Fujii M, Nagasuna K, Fujishima M, Akita T, Tada H (2009) Photodeposition of CdS quantum dots on TiO2 : Preparation, characterization, and reaction mechanism. J Phys Chem C 113:16711–16716. https://doi.org/10.1021/jp9056626 Galeano L, Valencia S, Marín JM, Restrepo G, Navío JA, Hidalgo MC (2019) Comparison of the effects generated by the dry-soft grinding and the photodeposition of Au and Pt processes on the visible light absorption and photoactivity of TiO2 . Mater Res Express 6. https://doi.org/10. 1088/2053-1591/ab4316 Giocondi JL, Rohrer GS Structure sensitivity of photochemical oxidation and reduction reactions on SrTiO3 surfaces Gomathisankar P, Hachisuka K, Katsumata H, Suzuki T, Funasaka K, Kaneco S (2013) Enhanced photocatalytic hydrogen production from aqueous methanol solution using ZnO with simultaneous photodeposition of Cu. Int J Hydrogen Energy 38:11840–11846. https://doi.org/10.1016/ j.ijhydene.2013.06.131 Gordon TR, Cargnello M, Paik T, Mangolini F, Weber RT, Fornasiero P, Murray CB (2012) Nonaqueous synthesis of TiO2 nanocrystals using TiF 4 to engineer morphology, oxygen vacancy concentration, and photocatalytic activity. J Am Chem Soc 134:6751–6761. https://doi.org/10. 1021/ja300823a Gunji T, Jeevagan AJ, Hashimoto M, Nozawa T, Tanabe T, Kaneko S, Miyauchi M, Matsumoto F (2016) Photocatalytic decomposition of various organic compounds over WO3-supported ordered intermetallic PtPb co-catalysts. Appl Catal B 181:475–480. https://doi.org/10.1016/j. apcatb.2015.08.016 Habibi MH, Sheibani R (2013) Nanostructure silver-doped zinc oxide films coating on glass prepared by sol-gel and photochemical deposition process: Application for removal of mercaptan. J Ind Eng Chem 19:161–165. https://doi.org/10.1016/j.jiec.2012.07.019 Hara M, Nunoshige J, Takata T, Kondo JN, Domen K (2003) Unusual enhancement of H2 evolution by Ru on TaON photocatalyst under visible light irradiation. Chem Commun 3:3000–3001. https://doi.org/10.1039/b309935k He W, Kim HK, Wamer WG, Melka D, Callahan JH, Yin JJ (2014) Photogenerated charge carriers and reactive oxygen species in ZnO/Au hybrid nanostructures with enhanced photocatalytic and antibacterial activity. J Am Chem Soc 136:750–757. https://doi.org/10.1021/ja410800y Herrmann J-M, Disdier J, Pichat P (1986) Photoassisted platinum deposition on TIO. Powder Using Var Platin Complexes 17:11 Herrmann J-M, Disdier J, Pichat P, ~ndez AF, ~lez-Elipe,’~ AG, Munuera G, Leclercq C (1991) Titania-Supported bimetallic catalyst synthesis by photocatalytic codeposition at ambient temperature: preparation and characterization of Pt-Rh, Ag-Rh, and Pt-Pd couples Hua Gui Yang CHSSZQJZGLSCSHMC& GQL (2008) Anatase TiO2 single crystals with a large percentage of reactive facets. Nature Huang K, Zhang Q, Yang F, He D (2010) Ultraviolet photoconductance of a single hexagonal Wo3 nanowire. Nano Res 3:281–287. https://doi.org/10.1007/s12274-010-1031-3 Huang ZF, Pan L, Zou JJ, Zhang X, Wang L (2014) Nanostructured bismuth vanadate-based materials for solar-energy-driven water oxidation: A review on recent progress. Nanoscale 6:14044–14063

440

Akshita et al.

Huang Q, Liu S, Wei W, Yan Q, Wu C (2015a) Selective synthesis of different ZnO/Ag nanocomposites as surface enhanced Raman scattering substrates and highly efficient photocatalytic catalysts. RSC Adv 5:27075–27081. https://doi.org/10.1039/c5ra01068c Huang ZF, Song J, Pan L, Zhang X, Wang L, Zou JJ (2015b) Tungsten oxides for photocatalysis, electrochemistry, and phototherapy. Adv Mater 27:5309–5327 Huang K, Yuan L, Feng S (2015c) Crystal facet tailoring arts in perovskite oxides. Inorg Chem Front 2:965–981 Iizuka K, Wato T, Miseki Y, Saito K, Kudo A (2011) Photocatalytic reduction of carbon dioxide over Ag cocatalyst-loaded ALa 4Ti 4O 15 (A = Ca, Sr, and Ba) using water as a reducing reagent. J Am Chem Soc 133:20863–20868. https://doi.org/10.1021/ja207586e Iliev V, Tomova D, Bilyarska L, Tyuliev G (2007) Influence of the size of gold nanoparticles deposited on TiO2 upon the photocatalytic destruction of oxalic acid. J Mol Catal A Chem 263:32–38. https://doi.org/10.1016/j.molcata.2006.08.019 Iliev V, Tomova D, Rakovsky S, Eliyas A, Puma GL (2010) Enhancement of photocatalytic oxidation of oxalic acid by gold modified WO3/TiO2 photocatalysts under UV and visible light irradiation. J Mol Catal A Chem 327:51–57. https://doi.org/10.1016/j.molcata.2010.05.012 Jia A, Liang X, Su Z, Zhu T, Liu S (2010) Synthesis and the effect of calcination temperature on the physical-chemical properties and photocatalytic activities of Ni, La codoped SrTiO3 . J Hazard Mater 178:233–242. https://doi.org/10.1016/j.jhazmat.2010.01.068 Jiang Z, Ouyang Q, Peng B, Zhang Y, Zan L (2014) Ag size-dependent visible-light-responsive photoactivity of Ag-TiO2 nanostructure based on surface plasmon resonance. J Mater Chem A Mater 2:19861–19866. https://doi.org/10.1039/c4ta03831b Jiang X, Fu X, Zhang L, Meng S, Chen S (2015) Photocatalytic reforming of glycerol for H2 evolution on Pt/TiO2 : Fundamental understanding the effect of co-catalyst Pt and the Pt deposition route. J Mater Chem A Mater 3:2271–2282. https://doi.org/10.1039/c4ta06052k Jint Z, Li Q, Zheng X, Xi C, Wang C, Zhang H, Feng L, Wang H, Chen Z, Jiang Z (1993) Surface properties of Pt-CdS and mechanism of photocatalytic dehydrogenation of aqueous alcohol Jint Z, Chen Z, Li Q, Xi C, Lanzhou XZ (1994) On the conditions and mechanism of PtO, formation in the photoinduced conversion of H,PtCl Joshi UA, Darwent JR, Yiu HHP, Rosseinsky MJ (2011) The effect of platinum on the performance of WO3 nanocrystal photocatalysts for the oxidation of Methyl Orange and iso-propanol. J Chem Technol Biotechnol 86:1018–1023. https://doi.org/10.1002/jctb.2612 Kabra K, Chaudhary R, Sawhney RL (2008) Solar photocatalytic removal of Cu(II), Ni(II), Zn(II) and Pb(II): Speciation modeling of metal-citric acid complexes. J Hazard Mater 155:424–432. https://doi.org/10.1016/j.jhazmat.2007.11.08335 Kang JG, Sohn Y (2012) Interfacial nature of Ag nanoparticles supported on TiO 2 photocatalysts. J Mater Sci 47:824–832. https://doi.org/10.1007/s10853-011-5860-6 Kang HW, Lim SN, Song D, Bin PS (2012) Organic-inorganic composite of g-C 3N 4-SrTiO 3: Rh photocatalyst for improved H2 evolution under visible light irradiation. Int J Hydrogen Energy 37:11602–11610. https://doi.org/10.1016/j.ijhydene.2012.05.020 Karácsonyi É, Baia L, Dombi A, Danciu V, Mogyorósi K, Pop LC, Kovács G, Coşoveanu V, Vulpoi A, Simon S, Pap Z (2013) The photocatalytic activity of TiO2 /WO3 /noble metal (Au or Pt) nanoarchitectures obtained by selective photodeposition. Catal Today 208:19–27. https://doi. org/10.1016/j.cattod.2012.09.038 Katsumata H, Oda Y, Kaneco S, Suzuki T (2013) Photocatalytic activity of Ag/CuO/WO3 under visible-light irradiation. RSC Adv 3:5028–5035. https://doi.org/10.1039/c3ra23322g Kawano K, Komatsu M, Yajima Y, Haneda H, Maki H, Yamamoto T (2002) Photoreduction of Ag ion on ZnO single crystal. Appl. Sur. Sci. 189:265-270. https://doi.org/10.1016/S0169-433 2(01)01022-4 Ke D, Peng T, Ma L, Cai P, Jiang P (2008) Photocatalytic water splitting for O2 production under visible-light irradiation on BiVO4 nanoparticles in different sacrificial reagent solutions. Appl Catal A Gen 350:111–117. https://doi.org/10.1016/j.apcata.2008.08.003

14 Photodeposition for Highly Effective Photocatalytic Materials

441

Khnayzer RS, Thompson LB, Zamkov M, Ardo S, Meyer GJ, Murphy CJ, Castellano FN (2012a) Photocatalytic hydrogen production at titania-supported Pt nanoclusters that are derived from surface-anchored molecular precursors. J Phys Chem C 116:1429–1438. https://doi.org/10.1021/ jp206943s Khnayzer RS, Mara MW, Huang J, Shelby ML, Chen LX, Castellano FN (2012b) Structure and activity of photochemically deposited “CoPi” oxygen evolving catalyst on titania. ACS Catal 2:2150–2160. https://doi.org/10.1021/cs3005192 Kim J, Lee CW, Choi W (2010) Platinized WO3 as an environmental photocatalyst that generates OH radicals under visible light. Environ Sci Technol 44:6849–6854. https://doi.org/10.1021/es1 01981r Kim M, Kim YK, Lim SK, Kim S, Il IS (2015) Efficient visible light-induced H2 production by Au@CdS/TiO2 nanofibers: Synergistic effect of core-shell structured Au@CdS and densely packed TiO2 nanoparticles. Appl Catal B 166–167:423–431. https://doi.org/10.1016/j.apcatb. 2014.11.036 Kislov N, Lahiri J, Verma H, Goswami DY, Stefanakos E, Batzill M (2009) Photocatalytic degradation of methyl orange over single crystalline ZnO: Orientation dependence of photoactivity and photostability of ZnO. Langmuir 25:3310–3315. https://doi.org/10.1021/la803845f Kohtani S, Hiro J, Yamamoto N, Kudo A, Tokumura K, Nakagaki R (2005) Adsorptive and photocatalytic properties of Ag-loaded BiVO4 on the degradation of 4-n-alkylphenols under visible light irradiation. Catal Commun 6:185–189. https://doi.org/10.1016/j.catcom.2004.12.006 Konta R, Ishii T, Kato H, Kudo A (2004) Photocatalytic activities of noble metal ion doped SrTiO3 under visible light irradiation. J Phys Chem B 108:8992–8995. https://doi.org/10.1021/ jp049556p Kovács G, Baia L, Vulpoi A, Radu T, Karácsonyi É, Dombi A, Hernádi K, Danciu V, Simon S, Pap Z (2014) TiO2 /WO3 /Au nanoarchitectures’ photocatalytic activity, “from degradation intermediates to catalysts” structural peculiarities”, Part I: Aeroxide P25 based composites”. Appl Catal B 147:508–517. https://doi.org/10.1016/j.apcatb.2013.09.019 Kozytskiy A V, Stroyuk AL, Ya Kuchmy S, Skorik NA, Moskalyuk VO (2012) Morphology, photochemical and photocatalytic properties of nanocrystalline zinc oxide films Kozytskiy A V, Stroyuk AL, Ya Kuchmy S, Streltsov EA, Skorik NA, Moskalyuk VO (2013) Effect of the method of preparation Of ZnO/CdS AND TiO2 /CdS film nanoheterostructures on their photoelectrochemical properties Kriek RJ, Mahlamvana F (2012) Dependency on chloride concentration and “in-sphere” oxidation of H 2O for the effective TiO2 -photocatalysed electron transfer from H 2O to [PdCl n(H 2O) 4-n] 2-n (n = 0–4) in the absence of an added sacrificial reducing agent. Appl Catal A Gen 423–424:28–33. https://doi.org/10.1016/j.apcata.2012.02.01520.1 Kudo A, Miseki Y (2009) Heterogeneous photocatalyst materials for water splitting. Chem Soc Rev 38:253–278. https://doi.org/10.1039/b800489g Kudo A, Omori K, Kato H (1999) A novel aqueous process for preparation of crystal form-controlled and highly crystalline BiVO4 powder from layered vanadates at room temperature and its photocatalytic and photophysical properties. J Am Chem Soc 121:11459–11467. https://doi.org/10. 1021/ja992541y Kumar Kaushik V XPS Core liwel spectra and auger parameters for some silver compounds* Kumar SG, Rao KSRK (2015) Tungsten-based nanomaterials (WO 3 & Bi 2 WO 6): Modifications related to charge carrier transfer mechanisms and photocatalytic applications. Appl Surf Sci 355:939–958. https://doi.org/10.1016/j.apsusc.2015.07.003 Kunthakudee N, Ramakul P, Serivalsatit K, Hunsom M (2022) Photosynthesis of Au/TiO2 nanoparticles for photocatalytic gold recovery from industrial gold-cyanide plating wastewater. Sci Rep 12. https://doi.org/10.1038/s41598-022-24290-7 Latorre-Sánchez M, Primo A, Atienzar P, Forneli A, García H (2015) P-n heterojunction of doped graphene films obtained by pyrolysis of biomass precursors. Small 11:970–975. https://doi.org/ 10.1002/smll.201402278

442

Akshita et al.

Lee WH, Liao CH, Tsai MF, Huang CW, Wu JCS (2013) A novel twin reactor for CO2 photoreduction to mimic artificial photosynthesis. Appl Catal B 132–133:445–451. https://doi.org/10. 1016/j.apcatb.2012.12.024 Lee J, Choi W (2005) Photocatalytic reactivity of surface platinized TiO 2: Substrate specificity and the effect of Pt oxidation state. https://doi.org/10.1021/jp044425 Li Q, Chen Z, Zheng X, Jin Z (1992) 22) Little. Academic Press, L. H. infrared Spectra of Adsorbed Species Li J, Suyoulema WW, Sarina, (2009a) A study of photodegradation of sulforhodamine B on AuTiO2 /bentonite under UV and visible light irradiation. Solid State Sci 11:2037–2043. https:// doi.org/10.1016/j.solidstatesciences.2009.09.012 Li Y, Hu Y, Peng S, Lu G, Li S (2009b) Synthesis of CdS nanorods by an ethylenediamine assisted hydrothermal method for photocatalytic hydrogen evolution. J Phys Chem C 113:9352–9358. https://doi.org/10.1021/jp901505j Li C, Zhang S, Zhang B, Su D, He S, Zhao Y, Liu J, Wang F, Wei M, Evans DG, Duan X (2013a) Photohole-oxidation-assisted anchoring of ultra-small Ru clusters onto TiO2 with excellent catalytic activity and stability. J Mater Chem A Mater 1:2461–2467. https://doi.org/10.1039/c2t a01205g Li R, Han C, Chen QW (2013b) A facile synthesis of multifunctional ZnO/Ag sea urchin-like hybrids as highly sensitive substrates for surface-enhanced Raman detection. RSC Adv 3:11715–11722. https://doi.org/10.1039/c3ra41203b Li R, Zhang F, Wang D, Yang J, Li M, Zhu J, Zhou X, Han H, Li C (2013c) Spatial separation of photogenerated electrons and holes among 010 and 110 crystal facets of BiVO 4. Nat Commun 4. https://doi.org/10.1038/ncomms2401 Li TL, Da CC, Yeh TF, Teng H (2013d) Capped CuInS2 quantum dots for H2 evolution from water under visible light illumination. J Alloys Compd 550:326–330. https://doi.org/10.1016/j. jallcom.2012.10.157 Li N, Liu M, Zhou Z, Zhou J, Sun Y, Guo L (2014b) Charge separation in facet-engineered chalcogenide photocatalyst: A selective photocorrosion approach. Nanoscale 6:9695–9702. https:// doi.org/10.1039/c4nr02068e Li R, Han H, Zhang F, Wang D, Li C (2014) Highly efficient photocatalysts constructed by rational assembly of dual-cocatalysts separately on different facets of BiVO4. In: Energy Environ Science R Soc Chem, pp 1369–1376 Liang Y, Guo N, Li L, Li R, Ji G, Gan S (2015) Fabrication of porous 3D flower-like Ag/ZnO heterostructure composites with enhanced photocatalytic performance. Appl Surf Sci 332:32– 39. https://doi.org/10.1016/j.apsusc.2015.01.116 Lin CY, Lai YH, Balamurugan A, Vittal R, Lin CW, Ho KC (2010) Electrode modified with a composite film of ZnO nanorods and Ag nanoparticles as a sensor for hydrogen peroxide. Talanta 82:340–347. https://doi.org/10.1016/j.talanta.2010.04.047 Liqiang J, Baiqi W, Baifu X, Shudan L, Keying S, Weimin C, Honggang F (2004) Investigations on the surface modification of ZnO nanoparticle photocatalyst by depositing Pd. J Solid State Chem 177:4221–4227. https://doi.org/10.1016/j.jssc.2004.08.016 Litter MI (1999) Heterogeneous photocatalysis Transition metal ions in photocatalytic systems Liu Z, Zhao ZG, Miyauchi M (2009) Efficient visible light active CaFe2 O4 /WO3 based composite photocatalysts: Effect of interfacial modification. J Phys Chem C 113:17132–17137. https://doi. org/10.1021/jp906195f Liu J, Sun Y, Li Z, Li S, Zhao J (2011a) Photocatalytic hydrogen production from water/methanol solutions over highly ordered Ag-SrTiO3 nanotube arrays. Int J Hydrogen Energy 36:5811–5816. https://doi.org/10.1016/j.ijhydene.2011.01.117 Liu G, Yu JC, Lu GQ, Cheng HM (2011b) Crystal facet engineering of semiconductor photocatalysts: Motivations, advances and unique properties. Chem Commun 47:6763–6783 Liu Y, Wei S, Gao W (2015a) Ag/ZnO heterostructures and their photocatalytic activity under visible light: effect of reducing medium. J Hazard Mater 287:59–68. https://doi.org/10.1016/j. jhazmat.2014.12.045

14 Photodeposition for Highly Effective Photocatalytic Materials

443

Liu Y, Zhou Y, Chen G, Guo T, Wang L, Huang X, Zeng W (2015b) Loading cobalt phosphate on TaON surface as efficient noble-metal-free co-catalyst for enhanced photocatalytic water oxidation performance. Mater Lett 148:155–158. https://doi.org/10.1016/j.matlet.2015.02.071 Lo CC, Huang CW, Liao CH, Wu JCS (2010) Novel twin reactor for separate evolution of hydrogen and oxygen in photocatalytic water splitting. Int J Hydrogen Energy 35:1523–1529. https://doi. org/10.1016/j.ijhydene.2009.12.032 Lu L, Wohlfart A, Parala H, Birkner A, Fischer RA (2003) A novel preparation of nano-Cu/ZnO by photo-reduction of Cu(OCH(Me)CH2 NMe2 )2 on ZnO at room temperature. Chem Commun 40–41. https://doi.org/10.1039/b208988b Lu L, Hu S, Lee HI, Wöll C, Fischer RA (2007) Photoinduced growth of Cu nanoparticles on ZnO from CuCl2 in methanol. J Nanopart Res 9:491–496. https://doi.org/10.1007/s11051-0069087-4 Ma G, Yan H, Shi J, Zong X, Lei Z, Li C (2008) Direct splitting of H2 S into H2 and S on CdS-based photocatalyst under visible light irradiation. J Catal 260:134–140. https://doi.org/10.1016/j.jcat. 2008.09.017 Ma LL, Cui ZD, Li ZY, Zhu SL, Liang YQ, Yin QW, Yang XJ (2013) The fabrication of SnSe/Ag nanoparticles on TiO2 nanotubes. Mater Sci Eng B Solid State Mater Adv Technol 178:77–82. https://doi.org/10.1016/j.mseb.2012.10.006 Maeda K (2011) Photocatalytic water splitting using semiconductor particles: History and recent developments. J Photochem Photobiol, C 12:237–268 Maeda K, Teramura K, Lu D, Saito N, Inoue Y, Domen K (2006) Noble-metal/Cr2 O3 core/shell nanoparticles as a cocatalyst for photocatalytic overall water splitting. Angew Chem-Int Ed 45:7806–7809. https://doi.org/10.1002/anie.200602473 Maeda K, Teramura K, Lu D, Saito N, Inoue Y, Domen K (2007) Roles of Rh/Cr2 O3 (core/shell) nanoparticles photodeposited on visible-light-responsive (Ga1-xZn x)(N1-xOx) solid solutions in photocatalytic overall water splitting. J Phys Chem C 111:7554–7560. https://doi.org/10. 1021/jp071056j Maeda K, Lu D, Teramura K, Domen K (2008) Direct deposition of nanoparticulate rhodiumchromium mixed-oxides on a semiconductor powder by band-gap irradiation. J Mater Chem 18:3539–3542. https://doi.org/10.1039/b808484j Maeda K, Higashi M, Lu D, Abe R, Domen K (2010a) Efficient nonsacrificial water splitting through two-step photoexcitation by visible light using a modified oxynitride as a hydrogen evolution photocatalyst. J Am Chem Soc 132:5858–5868. https://doi.org/10.1021/ja1009025 Maeda K, Xiong A, Yoshinaga T, Ikeda T, Sakamoto N, Hisatomi T, Takashima M, Lu D, Kanehara M, Setoyama T, Teranishi T, Domen K (2010b) Photocatalytic overall water splitting promoted by two different cocatalysts for Hydrogen and Oxygen evolution under visible light. Angew Chemie—Int Ed 49:4096–4099. https://doi.org/10.1002/anie.201001259 Maeda K, Sakamoto N, Ikeda T, Ohtsuka H, Xiong A, Lu D, Kanehara M, Teranishi T, Domen K (2010c) Preparation of core-shell-structured nanoparticles (with a noble-metal or metal oxide core and a chromia shell) and their application in water splitting by means of visible light. Chem Eur J 16:7750–7759. https://doi.org/10.1002/chem.201000616 Maeda K, Abe R, Domen K supporting information S1 role and function of ruthenium species as promoters with TaON-Based photocatalysts for oxygen evolution in Two-Step water splitting under visible light Mahlamvana F, Kriek RJ (2014) Photocatalytic reduction of platinum(II and IV) from their chloro complexes in a titanium dioxide suspension in the absence of an organic sacrificial reducing agent. Appl Catal B 148–149:387–393. https://doi.org/10.1016/j.apcatb.2013.11.011 Majeed I, Ali H, Idrees A, Arif A, Ashraf W, Rasul S, Khan MA, Nadeem MA, Nadeem MA (2022) Understanding the role of metal supported on TiO2 in photoreforming of oxygenates. Energy Advances 1:842–867. https://doi.org/10.1039/D2YA00110A Mei B, Han K, Mul G (2018) Driving surface redox reactions in heterogeneous photocatalysis: The active state of illuminated semiconductor-supported nanoparticles during overall water-splitting

444

Akshita et al.

Mu C, Lv C, Meng X, Sun J, Tong Z, Huang K (2023) In Situ characterization techniques applied in photocatalysis: a review. Adv Mater Interfaces 10. https://doi.org/10.1002/admi.202201842 Murakami N, Takebe N, Tsubota T, Ohno T (2012) Improvement of visible light photocatalytic acetaldehyde decomposition of bismuth vanadate/silica nanocomposites by cocatalyst loading. J Hazard Mater 211–212:83–87. https://doi.org/10.1016/j.jhazmat.2011.12.038 Murata A, Oka N, Nakamura S, Shigesato Y (2012) Visible-light active photocatalytic WO 3 films loaded with pt nanoparticles deposited by sputtering. J Nanosci Nanotechnol 12:5082–5086. https://doi.org/10.1166/jnn.2012.4894 Murcia JJ, Navío JA, Hidalgo MC (2012) Insights towards the influence of Pt features on the photocatalytic activity improvement of TiO 2 by platinisation. Appl Catal B 126:76–85. https:// doi.org/10.1016/j.apcatb.2012.07.01317.9 Nakamatsu H, Kawai T, Koreeda A, Kawai S (1986) Electron-microscopic observation of photodeposited Pt on TiO, particles in relation to photocatalytic activity Naknam P, Luengnaruemitchai A, Wongkasemjit S (2009) Preferential CO oxidation over Au/ZnO and Au/ZnO-Fe2O3 catalysts prepared by photodeposition. Int J Hydrogen Energy 34:9838– 9846. https://doi.org/10.1016/j.ijhydene.2009.10.015 Niishiro R, Kato H, Kudo A (2005) Nickel and either tantalum or niobium-codoped TiO2 and SrTiO3 photocatalysts with visible-light response for H2 or O2 evolution from aqueous solutions. Phys Chem Chem Phys 7:2241–2245. https://doi.org/10.1039/b502147b O’Rourke C, Wells N, Mills A (2019) Photodeposition of metals from inks and their application in photocatalysis. Catal Today 335:91–100. https://doi.org/10.1016/j.cattod.2018.09.006 Ohno T, Sarukawa K, Matsumura M (2002) Crystal faces of rutile and anatase TiO2 particles and their roles in photocatalytic reactions. New J Chem 26:1167–1170. https://doi.org/10.1039/b20 2140d Ohno T, Murakami N, Koyanagi T, Yang Y (2014) Photocatalytic reduction of CO2 over a hybrid photocatalyst composed of WO3 and graphitic carbon nitride (g-C3N 4) under visible light. J CO2 Util 6:17–25. https://doi.org/10.1016/j.jcou.2014.02.002 Ohsawa T, Nakajima K, Matsumoto Y, Koinuma H (2006) Combinatorial discovery of anomalous substrate effect on the photochemical properties of transition metal-doped epitaxial SrTiO3 heterostructures. In: Appl Surf Sci. Elsevier, pp 2603–2607 Ohyama J, Teramura K, Okuoka SI, Yamazoe S, Kato K, Shishido T, Tanaka T (2010) Investigation of the formation process of photodeposited Rh nanoparticles on TiO2 by in situ timeresolved energy-dispersive XAFS analysis. Langmuir 26:13907–13912. https://doi.org/10.1021/ la1022906 Pan J, Liu G, Lu GQ, Cheng HM (2011) On the true photoreactivity order of 001}, {010}, and {101 facets of anatase TiO2 crystals. Angew Chem—Int Ed 50:2133–2137. https://doi.org/10.1002/ anie.201006057 Pang HF, Xiang X, Li ZJ, Fu YQ, Zu XT (2012) Hydrothermal synthesis and optical properties of hexagonal tungsten oxide nanocrystals assisted by ammonium tartrate. Phys Status Solidi (A) Appl Mater Sci 209:537–544. https://doi.org/10.1002/pssa.201127456 Park HS, Ha HW, Ruoff RS, Bard AJ (2014) On the improvement of photoelectrochemical performance and finite element analysis of reduced graphene oxide-BiVO4 composite electrodes. J Electroanal Chem 716:8–15. https://doi.org/10.1016/j.jelechem.2013.08.036 Peng SY, Xu ZN, Chen QS, Chen YM, Sun J, Wang ZQ, Wang MS, Guo GC (2013) An ultra-low Pd loading nanocatalyst with high activity and stability for CO oxidative coupling to dimethyl oxalate. Chem Commun 49:5718–5720. https://doi.org/10.1039/c3cc00219e Peng F, Zhu H, Wang H, Yu H (2007) Preparation of Ag-sensitized ZnO and its photocatalytic performance under simulated solar light Piwoński I, Kdzioła K, Kisielewska A, Soliwoda K, Wolszczak M, Lisowska K, Wrońska N, Felczak A (2011) The effect of the deposition parameters on size, distribution and antimicrobial properties of photoinduced silver nanoparticles on titania coatings. Appl Surf Sci 257:7076–7082. https://doi.org/10.1016/j.apsusc.2011.03.036

14 Photodeposition for Highly Effective Photocatalytic Materials

445

Purwanto A, Widiyandari H, Ogi T, Okuyama K (2011) Role of particle size for platinum-loaded tungsten oxide nanoparticles during dye photodegradation under solar-simulated irradiation. Catal Commun 12:525–529. https://doi.org/10.1016/j.catcom.2010.11.020 Qamar M, Gondal MA, Yamani ZH (2010) Removal of Rhodamine 6G induced by laser and catalyzed by Pt/WO3 nanocomposite. Catal Commun 11:768–772. https://doi.org/10.1016/j.cat com.2010.02.012 Qamar M, Yamani ZH, Gondal MA, Alhooshani K (2011) Synthesis and comparative photocatalytic activity of Pt/WO3 and Au/WO3 nanocomposites under sunlight-type excitation. Solid State Sci 13:1748–1754. https://doi.org/10.1016/j.solidstatesciences.2011.07.002 Qamar M, Ganguli AK (2013) Self-assembling behaviour of Pt nanoparticles onto surface of TiO2 and their resulting photocatalytic activity Qiao P, Zou S, Xu S, Liu J, Li Y, Ma G, Xiao L, Lou H, Fan J (2014) A general synthesis strategy of multi-metallic nanoparticles within mesoporous titania via in situ photo-deposition. J Mater Chem A Mater 2:17321–17328. https://doi.org/10.1039/c4ta02970d Qin N, Liu Y, Wu W, Shen L, Chen X, Li Z, Wu L Supporting Information One-dimensional CdS/ TiO 2 nanofibers composites as efficient visible-light-driven photocatalysts for selective organic transformation: synthesis, characterization and performance Qingguo BAI P, Toupance M, Professeur T, Durupthy RM, Professeur O (2019) Synthesis of nano heterodimers by laser photodeposition of metal nanodots on TiO2 nanoparticles Membres du jury Ran J, Zhang J, Yu J, Jaroniec M, Qiao SZ (2014) Earth-abundant cocatalysts for semiconductorbased photocatalytic water splitting. Chem Soc Rev 43:7787–7812 Read CG, Steinmiller EMP, Choi KS (2009) Atomic plane-selective deposition of gold nanoparticles on metal oxide crystals exploiting preferential adsorption of additives. J Am Chem Soc 131:12040–12041. https://doi.org/10.1021/ja9036884 Ren C, Yang B, Wu M, Xu J, Fu Z, lv Y, Guo T, Zhao Y, Zhu C, (2010) Synthesis of Ag/ZnO nanorods array with enhanced photocatalytic performance. J Hazard Mater 182:123–129. https://doi.org/ 10.1016/j.jhazmat.2010.05.141 Roy SC, Varghese OK, Paulose M, Grimes CA (2010) Toward solar fuels: Photocatalytic conversion of carbon dioxide to hydrocarbons. ACS Nano 4:1259–1278 Rufus IB, Viswanathan B, Ramakrishnan V, Kuriacose JC (1995) Cadmium sulfide with iridium sulfide and platinum sulfide deposits as a photocatalyst for the decomposition of aqueous sulfide Sabio EM, Chi M, Browning ND, Osterloh FE (2010) Charge separation in a niobate nanosheet photocatalyst studied with photochemical labeling. Langmuir 26:7254–7261. https://doi.org/10. 1021/la904377f Sadakane M, Sasaki K, Kunioku H, Ohtani B, Ueda W, Abe R (2008) Preparation of nano-structured crystalline tungsten(VI) oxide and enhanced photocatalytic activity for decomposition of organic compounds under visible light irradiation. Chem Commun 6552–6554. https://doi.org/10.1039/ b815214d Sakai Y, Shimanaka A, Shioi M, Kato S, Satokawa S, Kojima T, Yamasaki A (2015) Fabrication of high-sensitivity palladium loaded tungsten trioxide photocatalyst by photodeposite method. Catal Today 241:2–7. https://doi.org/10.1016/j.cattod.2014.07.044 Sakamoto N, Ohtsuka H, Ikeda T, Maeda K, Lu D, Kanehara M, Teramura K, Teranishi T, Domen K (2009) Highly dispersed noble-metal/chromia (core/shell) nanoparticles as efficient hydrogen evolution promoters for photocatalytic overall water splitting under visible light. Nanoscale 1:106–109. https://doi.org/10.1039/b9nr00186g Sasaki Y, Iwase A, Kato H, Kudo A (2008) The effect of co-catalyst for Z-scheme photocatalysis systems with an Fe3+/Fe2+ electron mediator on overall water splitting under visible light irradiation. J Catal 259:133–137. https://doi.org/10.1016/j.jcat.2008.07.017 Sato T, Okuyama H, Endo T, Shimada M (1990) Preparation and photochemical properties of cadmium sulphide-zinc sulphide incorporated into the interlayer of hydrotalcite Sayama K, Mukasa K, Abe R, Abe Y, Arakawa H (2002) A new photocatalytic water splitting system under visible light irradiation mimicking a Z-scheme mechanism in photosynthesis

446

Akshita et al.

Scholarship W, Fabricio Guayaquil-Sosa J, Supervisor J, Serrano Rosales B, Fabricio J (2018) Photocatalytic hydrogen production using a mesoporous TiO2 photocatalytic hydrogen production using a mesoporous TiO2 doped with Pt: semiconductor synthesis, oxidation-reduction doped with Pt: semiconductor synthesis, Oxidation-Reduction network and quantum efficiencies. network and quantum efficiencies. Recommended citation recommended citation “photocatalytic hydrogen production using a mesoporous TiO2 doped with Pt: semiconductor synthesis, oxidation-reduction network and quantum Sclafani A, Palmisano L, Marcı´, G, Venezia MAM (1998) Influence of platinum on catalytic activity of polycrystalline WO employed for phenol photodegradation in aqueous suspension Sclafani’ A, Mozzanega M-N, Pichat’ P (1991) Effect of silver deposits on the photocatalytic activity of titanium dioxide samples for the dehydrogenation or oxidation of 2-propanol Shibuya M, Miyauchi M (2009) Site-selective deposition of metal nanoparticles on aligned WO3 nanotrees for super-hydrophilic thin films. Adv Mater 21:1373–1376. https://doi.org/10.1002/ adma.200802918 Shiraishi Y, Sugano Y, Ichikawa S, Hirai T (2012) Visible light-induced partial oxidation of cyclohexane on WO3 loaded with Pt nanoparticles. Catal Sci Technol 2:400–405. https://doi.org/10. 1039/c1cy00331c Shishido T, Asakura H, Amano F, Sone T, Yamazoe S, Kato K, Teramura K, Tanaka T (2009) In situ time-resolved energy-dispersive XAFS study on reduction behavior of Pt supported on TiO2 and Al2O3. Catal Letters 131:413–418. https://doi.org/10.1007/s10562-009-0095-8 Shvalagin V V, Stroyuk AL, Kotenko IE, Ya Kuchmii S (2007) Photocatalytic formation of porous CdS/ZnO nanospheres And CdS nanotubes Siboni MS, Samadi MT, Yang JK, Lee SM (2011) Photocatalytic reduction of Cr(VI) and Ni(II) in aqueous solution by synthesized nanoparticle ZnO under ultraviolet light irradiation: A kinetic study. Environ Technol 32:1573–1579. https://doi.org/10.1080/09593330.2010.543933 Su L, Qin N (2015) A facile method for fabricating Au-nanoparticles-decorated ZnO nanorods with greatly enhanced near-band-edge emission. Ceram Int 41:2673–2679. https://doi.org/10.1016/ j.ceramint.2014.10.081 Su H, Wang W (2021) Dynamically monitoring the photodeposition of single cocatalyst nanoparticles on semiconductors via fluorescence imaging. Anal Chem 93:11915–11919. https://doi.org/ 10.1021/acs.analchem.1c01908 Sulaeman U, Yin S, Sato T (2011) Solvothermal synthesis and photocatalytic properties of chromium-doped SrTiO3 nanoparticles. Appl Catal B 105:206–210. https://doi.org/10.1016/ j.apcatb.2011.04.017 Sun S, Wang W, Zeng S, Shang M, Zhang L (2010) Preparation of ordered mesoporous Ag/WO3 and its highly efficient degradation of acetaldehyde under visible-light irradiation. J Hazard Mater 178:427–433. https://doi.org/10.1016/j.jhazmat.2010.01.098 Sun S, Chang X, Dong L, Zhang Y, Li Z, Qiu Y (2011a) W18O49 nanorods decorated with Ag/AgCl nanoparticles as highly-sensitive gas-sensing material and visible-light-driven photocatalyst. J Solid State Chem 184:2190–2195. https://doi.org/10.1016/j.jssc.2011.06.024 Sun Y, Liu J, Li Z (2011b) Design of highly ordered Ag-SrTiO3 nanotube arrays for photocatalytic degradation of methyl orange. J Solid State Chem 184:1924–1930. https://doi.org/10.1016/j. jssc.2011.05.037 Sung-Suh HM, Choi JR, Hah HJ, Koo SM, Bae YC (2004) Comparison of Ag deposition effects on the photocatalytic activity of nanoparticulate TiO2 under visible and UV light irradiation. J Photochem Photobiol A Chem 163:37–44. https://doi.org/10.1016/S1010-6030(03)00428-3 Takahara Y, Kondo JN, Takata T, Lu D, Domen K (2001) Mesoporous tantalum oxide. 1. Characterization and photocatalytic activity for the overall water decomposition. Chem Mater 13:1194–1199. https://doi.org/10.1021/cm000572i Tanaka R, Takata S, Takahashi R, Grepstad JK, Tybell T, Matsumoto Y (2012) Photoelectrochemical synthesis of silver-oxide clathrate Ag 7O 8NO 3 on SrTiO 3. Electrochem Solid-State Lett 15. https://doi.org/10.1149/2.015204esl

14 Photodeposition for Highly Effective Photocatalytic Materials

447

Tanaka A, Fuku K, Nishi T, Hashimoto K, Kominami H (2013) Functionalization of Au/TiO2 plasmonic photocatalysts with pd by formation of a core-shell structure for effective dechlorination of chlorobenzene under irradiation of visible light. J Phys Chem C 117:16983–16989. https:// doi.org/10.1021/jp403855p Tian L, Guan X, Zong S, Dai A, Qu J (2023) Cocatalysts for photocatalytic overall water splitting: a mini review. Catalysts 13:355. https://doi.org/10.3390/catal1302035529 Tokunaga S, Kato H, Kudo A (2001) Selective preparation of monoclinic and tetragonal BiVO4 with scheelite structure and their photocatalytic properties. Chem Mater 13:4624–4628. https:// doi.org/10.1021/cm0103390 Tomita O, Abe R, Ohtani B (2011) Direct synthesis of phenol from benzene over platinum-loaded tungsten(VI) oxide photocatalysts with water and molecular oxygen. Chem Lett 40:1405–1407. https://doi.org/10.1246/cl.2011.1405 Tomita O, Ohtani B, Abe R (2014) Highly selective phenol production from benzene on a platinumloaded tungsten oxide photocatalyst with water and molecular oxygen: Selective oxidation of water by holes for generating hydroxyl radical as the predominant source of the hydroxyl group. Catal Sci Technol 4:3850–3860. https://doi.org/10.1039/c4cy00445k Townsend TK, Browning ND, Osterloh FE (2012) Overall photocatalytic water splitting with NiO x-SrTiO3 —A revised mechanism. Energy Environ Sci 5:9543–9550. https://doi.org/10.1039/ c2ee22665k Ueyama K, Hatta T, Okemoto A, Taniya K, Ichihashi Y, Nishiyama S (2018) Cyclohexane photooxidation under visible light irradiation by WO3–TiO2 mixed catalysts. Res Chem Intermed 44:629–638. https://doi.org/10.1007/s11164-017-3124-z Vaelma M, Selin MSJ (2017) Photodeposition of gold and platinum on titanium dioxide Wang P, Huang B, Qin X, Zhang X, Dai Y, Whangbo MH (2009) Ag/AgBr/WO3 -H2 O: Visible-light photocatalyst for bacteria destruction. Inorg Chem 48:10697–10702. https://doi.org/10.1021/ic9 014652 Wang J, Fan XM, Tian K, Zhou ZW, Wang Y (2011a) Largely improved photocatalytic properties of Ag/tetrapod-like ZnO nanocompounds prepared with different PEG contents. Appl Surf Sci 257:7763–7770. https://doi.org/10.1016/j.apsusc.2011.04.026 Wang S, Wang T, Liu Y, Gao Y, Ding Y, Xu X, Zhang X, Chen W (2011b) Visible light-driven photodecomposition system: Preparation and application of highly dispersed Pt-loaded WO3 microparticles. Micro Nano Lett 6:229–232. https://doi.org/10.1049/mnl.2011.0001 Wang T, Jiao Z, Chen T, Li Y, Ren W, Lin S, Lu G, Ye J, Bi Y (2013a) Vertically aligned ZnO nanowire arrays tip-grafted with silver nanoparticles for photoelectrochemical applications. Nanoscale 5:7552–7557. https://doi.org/10.1039/c3nr01459b Wang Y, Wang Y, Xu R (2013b) Photochemical deposition of Pt on CdS for H2 evolution from water: Markedly enhanced activity by controlling Pt reduction environment. J Phys Chem C 117:783–790. https://doi.org/10.1021/jp309603c Wang B, Shen S, Guo L (2015) SrTiO3 single crystals enclosed with high-indexed 023 facets and 001 facets for photocatalytic hydrogen and oxygen evolution. Appl Catal B 166–167:320–326. https://doi.org/10.1016/j.apcatb.2014.11.032 Wei Y, Jiao J, Zhao Z, Zhong W, Li J, Liu J, Jiang G, Duan A (2015) 3D ordered macroporous TiO2 -supported Pt@CdS core-shell nanoparticles: Design, synthesis and efficient photocatalytic conversion of CO2 with water to methane. J Mater Chem A Mater 3:11074–11085. https://doi. org/10.1039/c5ta00444f Wenderich K, Mul G (2016) Methods, mechanism, and applications of photodeposition in photocatalysis: a review. Chem Rev 116:14587–14619 Wenderich K, Klaassen A, Siretanu I, Mugele F, Mul G (2014) Sorption-determined deposition of platinum on well-defined platelike platelike WO3 . Angew Chem-Int Ed 53:12476–12479. https://doi.org/10.1002/anie.201405274 Wenderich K Photodeposition of platinum nanoparticles on well-defined tungsten oxide Controlling oxidation state, particle size and geometrical distribution

448

Akshita et al.

Whang TJ, Huang HY, Hsieh MT, Chen JJ (2009) Laser-induced silver nanoparticles on titanium oxide for photocatalytic degradation of methylene blue. Int J Mol Sci 10:4707–4718. https:// doi.org/10.3390/ijms10114707 Wicaksana Y, Liu S, Scott J, Amal R (2014) Tungsten trioxide as a visible light photocatalyst for volatile organic carbon removal. Molecules 19:17747–17762. https://doi.org/10.3390/molecu les191117747 Wold A (1993) Photocatalytic Properties of Ti02 Wu JJ, Tseng CH (2006) Photocatalytic properties of nc-Au/ZnO nanorod composites. Appl Catal B 66:51–57. https://doi.org/10.1016/j.apcatb.2006.02.013 Wu M, Chen WJ, Shen YH, Huang FZ, Li CH, Li SK (2014) In situ growth of matchlike ZnO/Au plasmonic heterostructure for enhanced photoelectrochemical water splitting. ACS Appl Mater Interfaces 6:15052–15060. https://doi.org/10.1021/am503044f Xi C, Chen Z, Li Q, Jin Z (1995) Effects of H + conversion C1-and CH3COOH on the photocatalytic of PtC16 2-in aqueous TiO2 dispersion Xie W, Li Y, Sun W, Huang J, Xie H, Zhao X (2010) Surface modification of ZnO with Ag improves its photocatalytic efficiency and photostability. J Photochem Photobiol A Chem 216:149–155. https://doi.org/10.1016/j.jphotochem.2010.06.032 Xin G, Yu B, Xia Y, Hu T, Liu L, Li C (2014) Highly efficient deposition method of platinum over cds for H2 evolution under visible light. J Phys Chem C 118:21928–21934. https://doi.org/10. 1021/jp505506e Xinchen Wang KMATKTGXJMCKD& MA (2009) A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat Mater Xu Z, Tabata I, Hirogaki K, Hisada K, Wang T, Wang S, Hori T (2011) Preparation of platinumloaded cubic tungsten oxide: A highly efficient visible light-driven photocatalyst. Mater Lett 65:1252–1256. https://doi.org/10.1016/j.matlet.2010.12.011 Xu H, Ouyang S, Liu L, Reunchan P, Umezawa N, Ye J (2014) Recent advances in TiO2 -based photocatalysis. J Mater Chem A Mater 2:12642–12661 Yaipimai W, Subjalearndee N, Tumcharern G, Intasanta V (2015) Multifunctional metal and metal oxide hybrid nanomaterials for solar light photocatalyst and antibacterial applications. J Mater Sci 50:7681–7697. https://doi.org/10.1007/s10853-015-9333-1 Yan X, Sun S, Hu B, Wang X, Lu W, Shi W (2013) Enhanced photocatalytic activity induced by surface plasmon resonance on Ag-loaded strontium titanate nanoparticles. Micro Nano Lett 8:504–507. https://doi.org/10.1049/mnl.2013.0452 Yang HG, Sun CH, Qiao SZ, Zou J, Liu G, Smith SC, Cheng HM, Lu GQ (2008) Anatase TiO2 single crystals with a large percentage of reactive facets. Nature 453:638–641. https://doi.org/ 10.1038/nature06964 Ye C, Huan Y (2022) Studies on electron escape condition in semiconductor nanomaterials via photodeposition reaction. Materials 15:2116. https://doi.org/10.3390/ma15062116 Ye H, Lee J, Jang JS, Bard AJ (2010) Rapid screening of bivo4-based photocatalysts by scanning electrochemical microscopy (SECM) and studies of their photoelectrochemical properties. J Phys Chem C 114:13322–13328. https://doi.org/10.1021/jp104343b Yoshida M, Yomogida T, Mineo T, Nitta K, Kato K, Masuda T, Nitani H, Abe H, Takakusagi S, Uruga T, Asakura K, Uosaki K, Kondoh H (2013) In situ observation of carrier transfer in the Mn-oxide/Nb:SrTiO3 photoelectrode by X-ray absorption spectroscopy. Chem Commun 49:7848–7850. https://doi.org/10.1039/c3cc43584a Yu SC, Huang CW, Liao CH, Wu JCS, Chang ST, Chen KH (2011) A novel membrane reactor for separating hydrogen and oxygen in photocatalytic water splitting. J Memb Sci 382:291–299. https://doi.org/10.1016/j.memsci.2011.08.022 Zhang F, Chen J, Zhang X, Gao W, Jin R, Guan N, Li Y (2004) Synthesis of titania-supported platinum catalyst: The effect of pH on morphology control and valence state during photodeposition. Langmuir 20:9329–9334. https://doi.org/10.1021/la049394o

14 Photodeposition for Highly Effective Photocatalytic Materials

449

Zhang X, Zhang Y, Quan X, Chen S (2009) Preparation of Ag doped BiVO4 film and its enhanced photoelectrocatalytic (PEC) ability of phenol degradation under visible light. J Hazard Mater 167:911–914. https://doi.org/10.1016/j.jhazmat.2009.01.074 Zhang Y, Guo S, Ma J, Ge H (2014a) Preparation, characterization, catalytic performance and antibacterial activity of Ag photodeposited on monodisperse ZnO submicron spheres. J Solgel Sci Technol 72:171–178. https://doi.org/10.1007/s10971-014-3440-3 Zhang G, Guan W, Shen H, Zhang X, Fan W, Lu C, Bai H, Xiao L, Gu W, Shi W (2014b) Organic additives-free hydrothermal synthesis and visible-light-driven photodegradation of tetracycline of WO3 nanosheets. Ind Eng Chem Res 53:5443–5450. https://doi.org/10.1021/ie4036687 Zhao J, Yang X (2003) Photocatalytic oxidation for indoor air purification: A literature review. Build Environ 38:645–654. https://doi.org/10.1016/S0360-1323(02)00212-3 Zhao Y, Lu Y, Chen L, Wei X, Zhu J, Zheng Y (2020) Redox Dual-Cocatalyst-Modified CdS DoubleHeterojunction photocatalysts for efficient hydrogen production. ACS Appl Mater Interfaces 12:46073–46083. https://doi.org/10.1021/acsami.0c12790 Zhen C, Yu JC, Liu GJ, Cheng HM (2014) Selective deposition of redox co-catalyst(s) to improve the photocatalytic activity of single-domain ferroelectric PbTiO3 nanoplates. Chem Commun 50:10416–10419. https://doi.org/10.1039/c4cc04999c Zheng H, Ou JZ, Strano MS, Kaner RB, Mitchell A, Kalantar-Zadeh K (2011) Nanostructured tungsten oxide - Properties, synthesis, and applications. Adv Funct Mater 21:2175–2196. https:// doi.org/10.1002/adfm.201002477 Zhou C, Shang L, Yu H, Bian T, Wu LZ, Tung CH, Zhang T (2014b) Mesoporous plasmonic Auloaded Ta2O5 nanocomposites for efficient visible light photocatalysis. Catal Today 225:158– 163. https://doi.org/10.1016/j.cattod.2013.10.085 Zhou H, Pan J, Ding L, Tang Y, Ding J, Guo Q, Fan T, Zhang D (2014) Biomass-derived hierarchical porous CdS/M/TiO2 (M = Au, Ag, pt, pd) ternary heterojunctions for photocatalytic hydrogen evolution. In: Int J Hydrog Energy Elsevier Ltd, pp 16293–16301 Zhou N, López-Puente V, Wang Q, Polavarapu L, Pastoriza-Santos I, Xu QH (2015) Plasmonenhanced light harvesting: Applications in enhanced photocatalysis, photodynamic therapy and photovoltaics. RSC Adv 5:29076–29097 Zhu H, Yang B, Xu J, Fu Z, Wen M, Guo T, Fu S, Zuo J, Zhang S (2009) Construction of Z-scheme type CdS-Au-TiO2 hollow nanorod arrays with enhanced photocatalytic activity. Appl Catal B 90:463–469. https://doi.org/10.1016/j.apcatb.2009.04.006

Chapter 15

Photocatalysts Derived from Renewable Feedstock for Environmental Application/Remediation M. Amin Mir

15.1 Introduction Catalysis emerged as a pivotal force in industrial technology during the 1960s, primarily centered around refinery and petrochemical processes (Lanzafame et al. 2017). Over the past two decades, catalysis has experienced remarkable growth and has evolved into a multidisciplinary science. Its scope extends beyond the traditional domains of chemists and chemical engineers, now encompassing collaborative efforts with materials, electronic and mechanical engineers, physicists, biologists, physicians, and others (Derouane 2001). In many different fields, such as green chemistry, the synthesis of fine chemicals and pharmaceuticals, the processing of hydrocarbons, wastewater treatment, emissions control, photo-electrochemistry, fuel cell technologies, and numerous other fields pertaining to food, agriculture, energy, and environment, catalysis is essential. Even though catalysis has greatly aided in the development of industrial, agricultural, energy, and health technologies, environmental risks are posed by the increased creation of hazardous chemicals brought on by population growth, greater global industrialization, and increased energy use. Acknowledging these difficulties, the international community has responded on a number of fronts by bringing environmental goals into the fold of programs like the EU’s Environmental Action Plan and the Sustainable Development Goals of the UN (European Commission and 7th Environment Action Programme 2020; United Nations: Sustainable Development Goals 2019;). In this context, catalysis stands at the forefront of addressing grand challenges, focusing on sustainable and clean energy generation, green chemical synthesis, and environmental monitoring and improvement. Catalysis, particularly the heterogeneous catalysis, is shown in Fig. 15.1. M. A. Mir (B) Department of Mathematics & Natural Sciences, Prince Mohammad Bin Fahd University, Al Khobar, Saudi Arabia e-mail: [email protected] 451

452

M. A. Mir

Fig. 15.1 Heterogeneous catalysis

15.2 Photocatalysis Technology Since Fujishima and Honda’s groundbreaking discovery of photocatalysis technology in 1972, there has been a surge of interest in utilizing solar energy to address environmental issues and energy crises. Photocatalytic applications, ranging from wastewater treatment to CO2 reduction, have undergone extensive research, enhancing our understanding of materials, light absorption capabilities, and carrier separation properties. Despite advancements in photocatalyst design and modification, the study of mechanism–activity correlation remains a formidable challenge. The emerging field of "Environmental Catalysis" continues to develop cost-effective strategies and tools for "Catalytic Remediation," playing a pivotal role in fostering a sustainable future and a cleaner environment. Key research topics in this domain include understanding catalytic chemistry, improving catalytic remediation of emissions, advancing renewable energy technologies, managing natural resources, and developing materials and processes for pollution remediation (Centi et al. 2002; Ertl et al. 2008).

15 Photocatalysts Derived from Renewable Feedstock for Environmental …

453

Fig. 15.2 Green photocatalysis

15.3 Green Photocatalysis The concept of green photocatalysis involves (Fig. 15.2) synthesizing various photocatalysts using natural resources, biomasses, and biological extracts, providing environmentally friendly alternatives. The discipline faces challenges related to identifying suitable metal oxide semiconductors for efficient photocatalysis, considering factors such as bandgap, surface area, morphology, and stability. Sunlightdriven photocatalysts, metal oxides, and plasmonic photocatalysts each contribute to addressing environmental concerns and energy challenges. The Z-scheme in photocatalysis has emerged as an efficient approach, offering improved sunlight harvesting capability and enhanced redox competency, leading to heightened photocatalytic activity (Kumar et al. 2019).

15.4 Photocatalyst Process Factors Several factors influence the photocatalyst process, including dye concentration, catalyst amount, pH, surface morphology, surface area, temperature-dependent reactions, nature and concentration of pollutants, irradiation period, and intensity of light. These factors collectively determine the efficiency of photocatalysis in degrading contaminants in aqueous solutions (Reza et al. 2017).

454

M. A. Mir

15.5 Metal Oxide-Based Photocatalysis Semiconducting metal oxide-based nanostructures, such as TiO2, ZnO, SnO2 , Cu2 O, and WO3 , have played a crucial role in photocatalysis for wastewater remediation, hydrogen fuel production, and removal of toxic waste from water bodies. The efficiency of these materials is determined by their bandgap, surface area, morphology, stability, and reusability. Metal oxide semiconductors like Fe2 O3 exhibit stability and photo-corrosive characteristics in aqueous solutions. Despite challenges, these materials have scientific significance in environmental applications, hydrogen fuel production, and energy (Maeda 2011).

15.6 Plasmonic Photocatalysts Plasmonic photocatalysts employ noble-metal nanoparticles on semiconductors and demonstrate better charge transport capabilities, broad sunlight absorption, and improved performance under visible light irradiation. The effective separation and transfer of charges is facilitated by the Schottky barrier and localized surface plasmon resonance, which boost photocatalytic activity. Resonance oscillations in Ag, Au, and Pt materials greatly enhance visible-light absorption, possibly outperforming TiO2 and other conventional photocatalysts (Zhang et al. 2013).

15.7 Z-Scheme in Photocatalysis The Z-scheme in photocatalysis offers advantages shown in Fig. 15.3, such as excellent sunlight harvesting capability, high redox competency, and quick generation of active species for oxidation and reduction processes. Connecting two semiconducting photocatalysts with an appropriate redox mediator enhances the system’s efficiency in utilizing sunlight and reduces the energy required for activation. The Z-scheme photocatalysts show promise in addressing environmental challenges and improving overall photocatalytic activity (Salah et al. 2021).

15.8 Green Biosynthesis of Photocatalysts by Microorganisms The utilization of microbial organisms, including bacteria, fungi, and algae, in nanotechnology and microbial biotechnology has led to the development of innovative photocatalysts in an eco-friendly manner (Mandal et al. 2006). Bacterial species, particularly prokaryotic ones, have been extensively employed in the synthesis of

15 Photocatalysts Derived from Renewable Feedstock for Environmental …

455

Fig. 15.3 Z-scheme photocatalysis

photocatalytic nanoparticles (NPs). Bacillus amyloliquefaciens bacterial culture, sourced from dairy sector effluents in Mehsana, India, was used by Khan and Fulekar to biosynthesize TiO2 NPs with a size range of 15.23–87.6 nm. These NPs exhibited efficient photocatalytic degradation of Reactive Red 31 (RR31) dye under artificial UV exposure (Thakkar et al. 2010). Similarly, Bacillus subtilis was utilized by Dhandapani et al. to produce TiO2 NPs (10–30 nm), demonstrating effective photocatalysis through the formation of an aquatic biofilm (Khan and Fulekar 2016). Using Bacillus licheniformis microbial strains (MTCC 9555), ZnO nanoflowers (200 nm–1 µm) were created, and they demonstrated a noteworthy photodegradation efficiency of Methylene Blue (MB) in under 60 min (Dhandapani et al. 2012). Fungi provide an effective pathway for NP production due to their profusion of proteins and enzymes. Aspergillus sp. NJP02 was used by Jain et al. to demonstrate the extracellular synthesis of zinc oxide NPs, illustrating UV-induced degradation of MB (Tripathi et al. 2014). Furthermore, Cadmium Sulfide NPs (CdS NPs) with a UV absorption peak at 332 nm were created using Trichoderma harzianum and showed photocatalytic breakdown of MB in a reactor (Jain et al. 2014). As photosynthetic creatures, algae offer a relatively novel method of preparing NPs. ZnO nanoflowers were quickly produced using the green microalga Chlamydomonas reinhardtii, which demonstrated remarkable photocatalytic activity under sunlight (Bhadwal et al. 2014).

456

M. A. Mir

15.9 Green Biosynthesis of Photocatalysts Using Plant Extracts While microbial synthesis has proven effective, the maintenance of microbial cultures poses challenges. Plant extract-mediated NP synthesis offers an advantageous alternative, eliminating the need for microbial strain cultures and avoiding potential hazards associated with pathogenic bacteria (Agarwal et al. 2017). Plant extracts, rich in organic compounds, such as glucose, fructose, proteins, and other bioactive substances, have been successfully employed to reduce and stabilize metal cations into NPs in a one-pot manufacturing process (Rao and Gautam 2016). Researchers have explored various plant extracts for the green synthesis of NPs. For instance, Persea americana (avocado) seed extract was used to synthesize tin oxide (SnO2) NPs, exhibiting efficient photocatalytic degradation of phenolsulfonphthalein dye (Pantidos and Horsfall 2014). Catunaregam spinosa root bark extracts were employed to obtain stable spherical tin oxide NPs, showcasing significant photocatalytic activity in the degradation of Congo Red (Mittal et al. 2013). Moringa oleifera peel extract, in combination with microwave irradiation, was utilized for the green synthesis of cerium oxide NPs, demonstrating antibacterial and photocatalytic properties (Ramesh et al. 2015). The use of Andean blackberry leaf extract facilitated the green synthesis of magnetite NPs (Fe3 O4 NPs), displaying effective photodegradation of dyes under sunlight (Elango et al. 2015). Cynometra ramiflora fruit extract was shown to be effective in the synthesis of magnetic iron oxide NPs, enhancing the degradation of MB dye under sunlight irradiation (Haritha et al. 2016). Aqueous Cinnamomum tamala leaf extract was employed in the greener synthesis of Au/TiO2 nanocomposites, exhibiting enhanced degradation of Methyl Orange dye compared to traditional TiO2 (Surendra and Roopan 2016). Carpobrotus acinaciformis leaf and flower extract were utilized for the synthesis of Ag/TiO2 nanocomposites, demonstrating stable photocatalytic activity over multiple cycles (Kumar et al. 2016). Azadirachta indica leaf extract was utilized in the production of titanium dioxide NPs, showcasing efficient photocatalytic degradation under sunlight (Bishnoi et al. 2018). The dried leaves of Jatropha curcas L. were employed for the green synthesis of titanium dioxide (TiO2 ) NPs, which were subsequently used for the photocatalytic reduction of tannery wastewater (Naik et al. 2013).

15.10 Environmental Applications of Photocatalysis Photocatalysis has found widespread applications in various environmental processes, including air treatment, water treatment, development of active surfaces, green chemistry, and energy conversion. Photocatalytic reactions necessitate irradiation to initiate the process, and various photoreactor designs have been proposed for water and air purification. The efficiency of aqueous photocatalytic systems is influenced by factors such as pH, reactive species, temperature, and the presence of

15 Photocatalysts Derived from Renewable Feedstock for Environmental …

457

Fig. 15.4 Photocatalysis and environment

contaminants. Heterogeneous photocatalysis, despite its relatively higher operating costs, has shown promise in treating non-biodegradable wastewater and harnessing solar radiation, especially in remote areas and developing countries. The combination of biological treatments, membrane reactors, and physical adsorption with photocatalysis enhances overall efficiency (Rostami-Vartooni et al. 2016). The application of photocatalysis is huge related to environment as few are shown in Fig. 15.4.

15.11 Self-cleaning Materials TiO2 -containing materials with photocatalytic properties have gained attention for their air-cleaning, self-cleaning, self-sterilizing, and antifogging characteristics. The self-cleaning attributes arise from the photocatalytic elimination of organic deposits, simultaneous inactivation and mineralization of surface microorganisms, and photoinduced superhydrophilicity preventing water droplet formation. TiO2 coatings also protect metals against corrosion and enhance heat transfer rates on super hydrophilic surfaces. These materials find applications in construction and vehicles, providing multifunctional benefits (Sankar et al. 2015).

458

M. A. Mir

15.12 Green Materials in Fuel Cells The quest for ecologically benign, cost-effective, and readily available energy materials has led to the exploration of green photocatalysts. Biomass conversion using green photocatalysts offers a sustainable approach for power generation, with applications in hydrogen fuel production and biodiesel synthesis. Nanotechnology plays a crucial role in advancing alternative energy production, enhancing the efficiency of solar cells, and exploring innovative materials for fuel cells and batteries (Goutam et al. 2018).

15.13 Ecofriendly Photocatalytic Water Disinfection Securing access to clean water is essential for human survival, yet the availability of fresh, uncontaminated water is limited in our ecosystem (Fujishima et al. 2008). Urbanization and industrial activities have led to widespread pollution of water sources, with textiles, tanneries, and pharmaceuticals contributing to the release of waste into water bodies. Solar energy, abundant on Earth’s surface, presents a natural solution, as the combined radiation of sunlight possesses the potential to eliminate harmful bacteria in water bodies. However, the effectiveness of solar disinfection (SODIS) processes can be impacted by variables such pathogen type, incoming light temperature, and light intensity (Helsch and Deubener 2012). Among the available techniques, heterogeneous photocatalysis is the most successful in eliminating bacteria. Clasen et al. (2008) support a solar disinfection system that may be installed in a home as a cost-effective way to fight diarrhea that occurs at home. This approach shows higher overall disinfection effectiveness than typical SODIS, while it is slightly more expensive than chlorination (Helsch and Deubener 2012). Water can be purified in an aqueous solution by immobilizing the photocatalyst under UV radiation (Kumar et al. 2017). It is essential to regularly measure the disinfection level both before and after exposure to light. TiO2 photocatalysts are more effective in disinfecting water than UVA therapy alone. Two configurations are investigated by Alrousan et al. (2012), showing sunlight-induced photocatalytic (SPC-DIS) and solar disinfection (SODIS) of E. coli-polluted water. Both configurations include and exclude a photocatalyst (TiO2 ). According to recent research, doping with metal ions is the most promising method for producing catalytic activity that is effective when exposed to visible light (Islam et al. 2017). In contrast to studies on photocatalytic disinfection of organic contaminants, research on microorganism disinfection is, nevertheless, limited, with few published articles.

15 Photocatalysts Derived from Renewable Feedstock for Environmental …

459

15.14 Harnessing Solar Energy for Photoelectrochemical Hydrogen Production It is common knowledge that solar energy may be efficiently converted into chemical energy for the production of clean energy (Goodarzi et al. 2023). Using the right semiconductor photocatalyst is essential to achieving this. Photoelectrochemical (PEC) water splitting can produce hydrogen when semiconductor photocatalysts with effective nanostructures—high surface-to-volume ratios and remarkable light absorption capacities—are utilized. Two half-reactions normally take place in a PEC cell: (a) the hydrogen evolution reaction (HER), which usually occurs on a cathode acting as a counter electrode, and (b) the oxygen evolution reaction (OER), which mostly occurs on an n-type semiconductor acting as a photoanode. Many researchers are working to improve the efficiency of the rate of hydrogen generation under solar irradiation by testing different nanostructured semiconductor photocatalysts (Islam et al. 2017).

15.15 Addressing Carbon Emissions Through Photocatalytic CO2 Reduction In 2019, it was highlighted that the extensive use of fossil fuels led to significant carbon emissions, resulting in an atmospheric concentration surpassing 400 ppm. The excessive utilization of fossil fuels, including petroleum, gas, and coal, contributes substantially to the release of a substantial quantity of CO2 into the environment (Alrousan et al. 2012). CO2 emissions are responsible for over 76% of yearly greenhouse gas (GHG) emissions, which have a negative effect on the environment, human health, and contribute to ocean acidification, warming, and climate change (Goodarzi et al. 2023). By transforming CO2 into useful small-molecule chemical products or energy sources like CO, CH4, and HCOOH, photocatalytic technology presents a viable remedy. This strategy has the potential to alleviate ecological issues and resolve the energy crisis. In an effort to lessen the harmful discharge of greenhouse gases, scientists extensively study the conversion of these gases—in particular, CO2 —into beneficial chemicals. These developments might lessen environmental problems such as rising sea levels, acidity of seawater, and ecological deterioration (Gulati et al. 2023).

460

M. A. Mir

15.16 Photocatalytic Degradation of Dyes and Pharmaceuticals The textile and dyeing industries produce a significant volume of wastewater including dyes, and they are estimated to be responsible for 17–20% of water contamination (Rafiq et al. 2021). The seriousness of the issue is highlighted by the 8 × 105 tons of dyes produced annually worldwide, of which approximately 200,000 tons come from textiles and dyes (Solayman et al. 2023). Both cationic and anionic synthetic dyes, such as Safranin O and Rhodamine B, as well as Eosin Y and Congo Red, are hazardous organic pollutants that impede the photosynthesis of aquatic plants. The chemical and pharmaceutical sectors also add to the organic waste that is bad for the environment and society. Pharmaceutical and personal care product (PPCP) production and consumption have surpassed 3000 regularly used pharmaceuticals and are rising continuously worldwide (Silori et al. 2022). Antibiotics are thought to contribute between 100,000 and 200,000 metric tons of pharmaceutical pollutants to water worldwide, of which 70–90% are removed as active metabolites or stay chemically unaltered. The manufacturing and use of PPCP have increased due to the COVID-19 epidemic. Because of their chemical and physical properties, pharmaceutical pollutants in water can be found in amounts ranging from ng/L−1 to µg/L−1 , which poses a serious risk to living things (Rapti et al. 2023). In response to these problems, a great deal of work has gone into creating extremely efficient semiconductor-based photocatalysts that can photodegrade dye and pharmaceutical contaminants, taking advantage of the many benefits of photocatalysis in the removal of dangerous materials from water.

15.17 AI-Assisted Photocatalyst Design The field of electrocatalyst and photocatalyst discovery has undergone a revolution thanks to recent developments in artificial intelligence (AI) and machine learning (ML) (Masood et al. 2019). "Machine learning" describes procedures where a model analyzes a pertinent training dataset to determine the relationship between predetermined input qualities and the parameters of the output. A sizable dataset consisting of 10,560 data points from 584 experiments on photoelectrochemical water splitting over n-type semiconductors was examined by Oral et al. (2022). They used machine learning approaches to find correlations between photocurrent density and 33 variables, such as electrolyte solution, kind of electrode, preparation methods, and light irradiation settings. They demonstrated the accuracy of the model in forecasting the electrode’s bandgap by achieving an exceptionally low root-mean-square error of 0.24 for validation and 0.27 for testing, using a predictive model based on random forest statistics. A larger training dataset becomes necessary as machine learning models get more complicated. Real trials or simulations are not necessary when using trained machine learning algorithms to infer catalyst activity. By using

15 Photocatalysts Derived from Renewable Feedstock for Environmental …

461

its parameters to determine a catalyst’s photocatalytic activity, this method provides an economical way to do so, cutting down on the time and resources needed for the evaluation process. When working with little data, combining domain expertise with data-driven machine learning model training works well. Understanding heterogeneous catalysis helps to create accurate prediction models, which reduces the need for extensive simulations and testing during photocatalyst screening. It appears that machine learning (ML) has the capacity to anticipate dopant selections for highperformance photoelectrochemical (PEC) systems. Important insights can be gained by examining relationships between dopant properties and the photoelectrochemical performance of doped photoelectrodes. Hematite (Fe2 O3 ) is a typical photoelectrode material. Wang et al. (2022) successfully built an ML model predicting the effects of 17 metal dopants on hematite. To examine the impact of dopants based on their underlying structural properties, they employed database S, which contained 11 descriptors: atomic number, ionic radius, atomic radius, single-molecule bond covalent radius, chemical valence, M–O bond formation enthalpy, electronegativity, and melting temperature of pure metal. Furthermore, ML techniques are employed to forecast pollution removal using photocatalytic reactions, offering a valuable tool for optimizing operational variables and enhancing the effectiveness of pollution mitigation strategies (Masood et al. 2019).

15.18 Conclusion and Future Perspectives In conclusion, the development and utilization of photocatalysts derived from renewable feedstock represent a promising avenue for addressing environmental challenges and remediation processes. The synthesis of these photoactive materials from sustainable sources not only aligns with the principles of green chemistry but also offers a viable solution to mitigate the impact of pollutants on our ecosystems. By harnessing the power of renewable feedstocks, we not only enhance the efficiency and effectiveness of photocatalysis but also contribute to the overall sustainability of environmental remediation efforts. These innovative photoactive materials have demonstrated significant potential in degrading pollutants, purifying water and air, and facilitating the breakdown of harmful contaminants. Furthermore, the use of renewable feedstocks ensures an eco-friendly and economically viable approach, reducing our dependence on finite resources and minimizing the environmental footprint associated with traditional photocatalyst synthesis. As we continue to explore and refine the applications of these sustainable photocatalysts, it is crucial to foster interdisciplinary research and collaboration. The integration of diverse scientific fields, including materials science, chemistry, and environmental engineering, will accelerate the development of novel and effective photocatalytic solutions. Ultimately, the widespread adoption of renewable feedstock-derived photocatalysts holds promise for a cleaner, healthier environment, paving the way for a more sustainable and resilient future.

462

M. A. Mir

References Agarwal H, Kumar SV, Rajeshkumar S (2017) A review on green synthesis of zinc oxide nanoparticles–An eco-friendly approach. Resourc Efficient Technol 3(4):406–413 Alrousan DMA, Polo-Lopez MI, Dunlop PSM, Fernandez-Ibanez P, Byrne JA (2012) Solar photocatalytic disinfection of water with immobilised titanium dioxide in re-circulating flow CPC reactors. Appl Catal B 128:126–134 Bhadwal AS, Tripathi RM, Gupta RK, Kumar N, Singh RP, Shrivastav A (2014) Biogenic synthesis and photocatalytic activity of CdS nanoparticles. RSC Adv 4(19):9484–9490 Bishnoi S, Kumar A, Selvaraj R (2018) Facile synthesis of magnetic iron oxide nanoparticles using inedible Cynometra ramiflora fruit extract waste and their photocatalytic degradation of methylene blue dye. Mater Res Bull 97:121–127 Centi G, Ciambelli P, Perathoner S, Russo P (2002) Environmental catalysis: trends and outlook. Catal Today 75:3–15 Clasen T, McLaughlin C, Nayaar N, Boisson S, Gupta R, Desai D, Shah N (2008) Microbiological effectiveness and cost of disinfecting water by boiling in semi-urban India. Am J Trop Med Hyg 79(3):407–413 Derouane EG (2001) Catalysis in the 21st century: lessons from the past, challenges for the future. CATTECH 5:214–225 Dhandapani P, Maruthamuthu S, Rajagopal G (2012) Bio-mediated synthesis of TiO2 Nanoparticles and its photocatalytic effect on aquatic biofilm. J Photochem Photobiol, B 110:43–49 Elango G, Kumaran SM, Kumar SS, Muthuraja S, Roopan SM (2015) Green synthesis of SnO2 nanoparticles and its photocatalytic activity of phenolsulfonphthalein dye. Spectrochim Acta Part a Mol Biomol Spectrosc 145:176–180 Ertl G, Knozinger H, Weitkamp J (eds) (2008) Handbook of heterogeneous catalysis, vols. 4–5. Wiley-VCH GmbH & Co. KGaA, Weinheim, pp 1559–1695 European Commission 7th Environment Action Programme to 2020 (2014). Available online at: http://ec.europa.eu/environment/action-programme/ (accessed February 21, 2014). Fox MA, Dulay MT (1993) Heterogeneous photocatalysis. Chem Rev 93(1):341–357 Fujishima A, Honda K (1972) Electrochemical photolysis of water at a semiconductor Electrode. Nature 238:37–38 Fujishima A, Zhang X, Tryk DA (2008) TiO2 photocatalysis and related surface phenomena. Surf Sci Rep 63(12):515–582 Goodarzi N, Ashrafi-Peyman Z, Khani E, Moshfegh AZ (2023) Recent progress on semiconductor heterogeneous photocatalysts in clean energy production and environmental remediation. Catalysts 13(7):1102 Goutam SP, Saxena G, Singh V, Yadav AK, Bharagava RN, Thapa KB (2018) Green synthesis of TiO2 nanoparticles using leaf extract of Jatropha curcas L. for photocatalytic degradation of tannery wastewater. Chem Eng J 336:386–396 Gulati S, Vijayan S, Kumar S, Harikumar B, Trivedi M, Varma RS (2023) Recent advances in the application of metal-organic frameworks (MOFs)-based nanocatalysts for direct conversion of carbon dioxide (CO2 ) to value-added chemicals. Coord Chem Rev 474:214853 Haritha E, Roopan SM, Madhavi G, Elango G, Al-Dhabi NA, Arasu MV (2016) Green chemical approach towards the synthesis of SnO2 NPs in argument with photocatalytic degradation of diazo dye and its kinetic studies. J Photochem Photobiol, B 162:441–447 Helsch G, Deubener J (2012) Compatibility of antireflective coatings on glass for solar applications with photocatalytic properties. Sol Energy 86(3):831–836 Herrmann JM (2005) Heterogeneous photocatalysis: state of the art and present applications In: Burwell RL Jr (1912–2003) Former Head of Ipatieff Laboratories, Northwestern University, Evanston (Ill). Topics in catalysis, 34(1), pp 49–65 Islam SZ, Nagpure S, Kim DY, Rankin SE (2017) Synthesis and catalytic applications of nonmetal doped mesoporous titania. Inorganics 5(1):15

15 Photocatalysts Derived from Renewable Feedstock for Environmental …

463

Jain N, Bhargava A, Panwar J (2014) Enhanced photocatalytic degradation of methylene blue using biologically synthesized “protein-capped” ZnO nanoparticles. Chem Eng J 243:549–555 Khan R, Fulekar MH (2016) Biosynthesis of titanium dioxide nanoparticles using Bacillus amyloliquefaciens culture and enhancement of its photocatalytic activity for the degradation of a sulfonated textile dye Reactive Red 31. J Colloid Interface Sci 475:184–191 Kumar B, Smita K, Cumbal L, Debut A, Galeas S, Guerrero VH (2016) Phytosynthesis and photocatalytic activity of magnetite (Fe3O4) nanoparticles using the Andean blackberry leaf. Mater Chem Phys 179:310–315 Kumar A, Naushad M, Rana A, Sharma G, Ghfar AA, Stadler FJ, Khan MR (2017) ZnSe-WO3 nano-hetero-assembly stacked on Gum ghatti for photo-degradative removal of Bisphenol A: Symbiose of adsorption and photocatalysis. Int J Biol Macromol 104:1172–1184 Kumar S, Terashima C, Fujishima A, Krishnan V, Pitchaimuthu S (2019) Photocatalytic degradation of organic pollutants in water using graphene oxide composite. In: A new generation material graphene: applications in water technology. Springer, Cham, pp 413–438 Lanzafame P, Perathoner S, Centi G, Gross S, Hensen EJM (2017) Grand challenges for catalysis in the science and technology roadmap on catalysis for Europe: moving ahead for a sustainable future. Catal Sci Technol 7:5182–5194 Lee KM, Lai CW, Ngai KS, Juan JC (2016) Recent developments of zinc oxide based photocatalyst in water treatment technology: a review. Water Res 88:428–448 Lin Z, Ye M, Wang M (eds) (2018) Multifunctional photocatalytic materials for energy. Wood Head Publishing Maeda K (2011) Photocatalytic water splitting using semiconductor particles: history and recent developments. J Photochem Photobiol, C 12(4):237–268 Mandal D, Bolander ME, Mukhopadhyay D, Sarkar G, Mukherjee P (2006) The use of microorganisms for the formation of metal nanoparticles and their application. Appl Microbiol Biotechnol 69(5):485–492 Masood H, Toe CY, Teoh WY, Sethu V, Amal R (2019) Machine learning for accelerated discovery of solar photocatalysts. Acs Catal 9:11774–11787 Mittal AK, Chisti Y, Banerjee UC (2013) Synthesis of metallic nanoparticles using plant extracts. Biotechnol Adv 31(2):346–356 Naik GK, Mishra PM, Parida K (2013) Green synthesis of Au/TiO2 for effective dye degradation in aqueous system. Chem Eng J 229:492–497 Oral B, Can E, Yildirim R (2022) Analysis of photoelectrochemical water splitting using machine learning. Int J Hydrog Energy 47:19633–19654 Pantidos N, Horsfall LE (2014) Biological synthesis of metallic nanoparticles by bacteria, fungi and plants. J Nanomed Nanotechnol 5(5):1 Rafiq A, Ikram M, Ali S, Niaz F, Khan M, Khan Q, Maqbool M (2021) Photocatalytic degradation of dyes using semiconductor photocatalysts to clean industrial water pollution. J Ind Eng Chem 97:111–128 Ramesh M, Anbuvannan M, Viruthagiri GJSAPAM (2015) Green synthesis of ZnO nanoparticles using Solanum nigrum leaf extract and their antibacterial activity. Spectrochim Acta Part A Mol Biomol Spectrosc 136:864–870 Rao MD, Gautam P (2016) Synthesis and characterization of ZnO nanoflowers using Chlamydomonas reinhardtii: a green approach. Environ Prog Sustain Energy 35(4):1020–1026 Rapti I, Boti V, Albanis T, Konstantinou I (2023) Photocatalytic degradation of psychiatric pharmaceuticals in hospital WWTP secondary effluents using G-C3N4 and g-C3N4/MoS2 catalysts in laboratory-scale pilot. Catalysts 13:252 Reza KM, Kurny ASW, Gulshan F (2017) Parameters affecting the photocatalytic degradation of dyes using TiO2: a review. Appl Water Sci 7(4):1569–1578 Rostami-Vartooni A, Nasrollahzadeh M, Salavati-Niasari M, Atarod M (2016) Photocatalytic degradation of azo dyes by titanium dioxide supported silver nanoparticles prepared by a green method using Carpobrotus acinaciformis extract. J Alloy Compd 689:15–20

464

M. A. Mir

Salah H, Elkatory MR, Fattah MA (2021) Novel zinc-polymer complex with antioxidant activity for industrial lubricating oil. Fuel 305:121536 Sankar R, Rizwana K, Shivashangari KS, Ravikumar V (2015) Ultra-rapid photocatalytic activity of Azadirachta indica engineered colloidal titanium dioxide nanoparticles. Appl Nanosci 5(6):731– 736 Silori R, Shrivastava V, Singh A, Sharma P, Aouad M, Mahlknecht J, Kumar M (2022) Global groundwater vulnerability for pharmaceutical and personal care products (PPCPs): the scenario of second decade of 21st century. J Environ Manag 320:115703 Solayman HM, Hossen MA, Abd Aziz A, Yahya NY, Hon LK, Ching SL, Monir MU, Zoh KD (2023) Performance evaluation of dye wastewater treatment technologies: a review. J Environ Chem Eng 11:109610 Surendra TV, Roopan SM (2016) Photocatalytic and antibacterial properties of phytosynthesized CeO2 NPs using Moringa oleifera peel extract. J Photochem Photobiol, B 161:122–128 Thakkar KN, Mhatre SS, Parikh RY (2010) Biological synthesis of metallic nanoparticles. Nanomed: Nanotechnol, Biol Med 6(2):257–262 Tripathi RM, Bhadwal AS, Gupta RK, Singh P, Shrivastav A, Shrivastav BR (2014) ZnO nanoflowers: novel biogenic synthesis and enhanced photocatalytic activity. J Photochem Photobiol, B 141:288–295 United Nations: Sustainable Development Goals (2019). https://www.un.org/sustainabledevelop ment/sustainable-development-goals/ Wang W, Bi J, Wu L, Li Z, Fu X (2009) Hydrothermal synthesis and catalytic performances of a new photocatalyst CaSnO3 with microcube morphology. Scripta Mater 60(3):186–189 Wang Z, Gu Y, Zheng L, Hou J, Zheng H, Sun S, Wang L (2022) Machine learning guided dopant election for metal oxide-based photoelectrochemical water splitting: the case study of Fe2 O3 and CuO. Adv Mater 34:2106776 Zhang X, Chen YL, Liu RS, Tsai DP (2013) Plasmonic Photocatalysis. Rep Prog Phys 76(4):046401