Magnetic Nanocatalysis: Volume 2 Industrial Applications 9783110782165, 9783110782035

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Rajender S. Varma, Bubun Banerjee (Eds.) Magnetic Nanocatalysis

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Sustainable Polymers for Food Packaging. An Introduction Vimal Katiyar,  ISBN ----, e-ISBN ----

Nanomaterials for Water Remediation Ajay Kumar Mishra, Chaudhery M. Hussain and Shivani B. Mishra (Eds.),  ISBN ----, e-ISBN ----

Environmental Functional Nanomaterials Qiang Wang and Ziyi Zhong,  ISBN ----, e-ISBN ----

Solar Photovoltaic Power Generation Jinhuan Yang, Xiao Yuan and Liang Ji,  In cooperation with: Publishing House of Electronics Industry ISBN ----, e-ISBN ----

Magnetic Nanocatalysis Industrial Applications Edited by Rajender S. Varma and Bubun Banerjee

Editors Dr. Rajender S. Varma Regional Centre of Advanced Technologies and Materials Palacky University Šlechtitelů 27 783 71 OLOMOUC Czech Republic [email protected] Dr. Bubun Banerjee Department of Chemistry Akal University Talwandi Sabo, Bathinda 151302 Punjab India [email protected]

ISBN 978-3-11-078203-5 e-ISBN (PDF) 978-3-11-078216-5 e-ISBN (EPUB) 978-3-11-078224-0 Library of Congress Control Number: 2022931087 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2022 Walter de Gruyter GmbH, Berlin/Boston Cover image: Wittayayut/iStock/Getty Images Plus Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Dedicated to Sant Baba Iqbal Singh Ji, Founder Chancellor, Akal University

Shiromani Panth Rattan, Vidya Maartand, Padam Shri Sant Baba Iqbal Singh Ji, fondly known as ‘Baba Ji’, was born on May 1, 1926 in village Bharial Lahri, Tehsil Pathankot, District Gurdaspur (now Pathankot). Inspired by Sant Teja Singh Ji, the devout disciple of Sant Attar Singh Ji, he made a resolve to dedicate his life towards serving humanity and thus he started his journey of relentless service towards humanity following the footsteps of his Guru, Sant Attar Singh Ji Maharaj. He did B. Sc. in Agriculture and retired as the ‘Director of Agriculture’ from Himachal Pradesh Government in 1987. Realizing the poor condition, he felt to do something for the betterment of the society. With his own money he started a school called Akal Academy at Baru Sahib, Sirmaur, Himachal Pradesh, India (a prelude to Eternal University) with just five students in 1986. He tried to educate underprivileged children and treated thousands of patients at his charitable institution under The Kalgidhar Trust at Baru Sahib, Sirmaur, Himachal Pradesh, India. Baba Ji worked relentlessly in only one direction – imparting values-based education in rural India so that every rural child can have access to low-cost values-based education which is literacy embedded with moral, ethical and spiritual education. To carry forward this noble mission, he worked tirelessly and one by one, he established 129 Akal Academies in Punjab, Himachal Pradesh, Haryana, Uttar Pradesh and Rajasthan, wherein more than 70,000 students are being imparted the blend of modern scientific education. These students have not only excelled in academics but also imbibed spiritual ethos. Apart from making their life ideal and successful, they have also transformed the lives of their families and relatives who were previously addicted to consumption of various drugs. Far away from the urban milieu, these schools focus on valuesbased education to children from marginalized sections of society. As a social worker Baba Iqbal Singh ji didn’t restricted himself just to the education sector, he was involved in every facet of community life i.e. Schools, Hospital, Colleges, Women Care Center, De-addiction Centers. Baba Ji established Akal University in 2015 which is running successfully at Talwandi Sabo in Bathinda, Punjab. Baba ji sincerely believed that real contribution to society constitutes in working relentlessly for the poorest, oppressed and most backward sections of the society. https://doi.org/10.1515/9783110782165-202

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Dedicated to Sant Baba Iqbal Singh Ji, Founder Chancellor, Akal University

For his philanthropic and selfless services for social welfare, he was conferred various awards and honors: Dedicating his entire life to the service of humanity and social welfare, Baba Ji merged with the Divine Light on 29th January, 2022 at 2.30 p.m at the age of 96.

Foreword

Green chemistry, life cycle analysis/assessment and systems engineering approach can relate to each other in the practice of sustainable chemistry. Fundamental and applied knowledge of Green Chemistry and Engineering, skills and practices present major strategies by which environmental impact can be reduced significantly and potentially eliminated for a given industrial situation. Life cycle assessment or analysis (LCA) and sustainability allow green chemists and chemical engineers to evaluate their choices more holistically by considering the impacts of chemicals or processes. Thinking about life cycles and systems is complex and not taught in traditional chemistry courses. Catalysis is one of the most important principles of green chemistry and occupies the core of sustainable development. Catalysis by definition leads to waste minimization, avoids side reactions, improves conversion and selectivity, and above all increases process safety since reactions are conducted under milder conditions. Thus, it is recognized as important device to fight with the environmental challenges. Heterogeneous catalysis offers several configurations of multiphase reactors leading to greater control on reactions which can be conducted in a continuous mode: the so-called flow chemistry. Continuous catalytic reactors use less volume and inventory and are amenable to precise process control and process safety and profitability. Minimize, Substitute, Moderate and Simplify (MSMS) are at the heart of safer processes and products. Adding newer dimensions to solid catalysts such as magnetic property saves costs associated with separation and reuse. The past two decades have witnessed tremendous progress in the development of nanoscience and nanotechnology. Even otherwise, supported catalysts in traditional hydrogenation reactions have been used are nano. A large number of methods are reported for the synthesis of nanoparticles (NPs) with different size, shape, and composition. Comparative to bulk materials, high surface-to-volume ratio makes nanomaterials a viable alternative to conventional catalysts leading to process intensification. It has prompted investigators to synthesize and use different nanoparticles for diverse organic transformations. Constant endeavors have been directed to prepare either new heterogeneous nano catalysts or immobilize the active part of the homogeneous catalysts onto the interior pore surface of solid support to make them heterogeneous. However, on many occasions, heterogeneous nano catalysts cannot be recovered quantitatively. Furthermore, metal contamination in the product is https://doi.org/10.1515/9783110782165-203

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considered a major disadvantage for the large-scale industrial applicability of the metal-based heterogeneous nano catalysts. The use of magnetic nano catalysts permits to circumvent these demerits as the nanoparticles can be recovered easily after completion of the reaction by using a simple bar magnet. Thus, the recovered nano catalysts can be reused repeatedly for further reactions without any significant loss in catalytic activity. This book titled ‘Magnetic nanocatalysis: Industrial Applications’ co-edited by Rajender S. Varma and Bubun Banerjee will be a welcome addition to the scattered literature devoted to this area. The first chapter covers the applications of nanoscale zero valent iron (nZVI) as an efficient heterogeneous catalyst for environmental remediation. Chapter 2 deals with the use of ferrite nanoparticles in modern catalytic processes on small scale as well as for bulk production. Chapter 3 focuses on the recent advances and future perspectives of polymer grafted magnetic nanoparticles towards intelligent designing of drug delivery. The use of various magnetic nanocatalysts for wastewater treatment is discussed in Chapter 4. Whereas Chapter 5, the last chapter, describes the application of some of the green chemistry principles and magnetic nano catalyst towards the sustainable synthesis of value added materials. Overall, this book should find wide acceptance in industry and academia. Professor (Dr.) Ganapati D. Yadav D.Sc., D. Eng., USNAE, FTWAS, FNA, FASc, FNASc, FNAE, FRSC, FIE,FISTE, FIChemE, FIIChE, FICS, Padmashri Awardee (2016) Emeritus Professor of Eminence Former Vice Chancellor and R.T. Mody Distinguished Professor and Tata Chemicals Darbari Seth Distinguished Professor of Innovation and Leadership Institute of Chemical Technology, Mumbai, India President, India Chemical Society, Kolkata, India

About Prof. Ganapati D. Yadav Professor Ganapati D. Yadav is one of the topmost, highly prolific, and accomplished engineering-scientists in India. He is internationally recognized by many prestigious and rare awards as an academician, researcher and innovator, including his seminal contributions to education, research and innovation in Green Chemistry and Engineering, Catalysis, Chemical Engineering, Energy Engineering, Biotechnology, Nanotechnology, and Development of Clean and Green Technologies. For 10.5 years, he served as the Founding Vice Chancellor and R.T. Mody Distinguished Professor, and Tata Chemicals Darbari Seth Distinguished Professor of Leadership and Innovation at the Institute of Chemical Technology (ICT), Mumbai, which is a Deemed-to-be-University having Elite Status and Centre of Excellence given by the State Assembly on par with IITs/IISc/IISERs. He currently holds the titles of Emeritus Professor of Eminence and J.C. Bose National Fellow in ICT. He serves as the Adjunct Professor at University of Saskatchewan, Canada, RMIT University, Melbourne, Australia and Conjoint Professor, University of New Castle, Australia. He was conferred Padma Shri, the fourth highest civilian honour, by the President of India in 2016 for his outstanding contributions to Science and Engineering. He has been recipient of two honorary doctorates: D. Sc. (Hon. Causa, DYPU) and D. Eng. (Hon. Causa, NIT Agartala). As the Vice Chancellor he created many records. In the November 2020 and 2021 surveys of Stanford University, where Indian scientists in top 2% of those in the World are honoured, Professor Yadav is number one in India in Physical Chemistry which is within 0.2% of the world scientists and is ranked at 66, for both years which is remarkable. He is a chemical engineer, but his research is in the field of catalysis science and engineering which is counted as part of physical chemistry. His research productivity is phenomenal with supervision of 107 Doctoral and 135 Masters Theses, which is the first record in ICT and for any Engineering Professor in India. Besides, he has supervised 47 post-doctoral fellows, several summer fellows and research staff. He has published 503 original research papers, 115 granted national and PCT patents, 8 new patent applications; 3 books; h-index of 64, i10 index of 316; 15000+ citations in journals, patents, books, and monographs, and 850+ specials lectures/orations/seminars over the years. He is still actively involved in guiding 15 doctoral students, patenting, publishing, consulting, and transferring technologies to industry. Under his dynamic leadership, ICT made phenomenal progress having been declared as Category I institute, started 23 new academic programmes, 5 new Departments and several Centres of Excellence, and establishment of two off-campuses in Bhubaneswar with total support of IOCL and Marathwada with total support of Govt. of Maharashtra, and collected phenomenal funds. The ICT is listed in top 100 institutes in the Developing World by Times Higher Education Ranking in 2019. The Atal Innovation Ranking of MHRD has placed ICT as number 1 among Govt. funded Universities. He has personally won over 125 national and international honours, awards, fellowships, editorships, and several Life Time Achievement Awards by prestigious industrial organizations. He is an elected Fellow of Indian National Science Academy, Indian Academy of Sciences, National Academy of Sciences, India, Indian National Academy of Engineering as well as The World Academy of Sciences, Trieste (TWAS). He is a Fellow of Royal Society of Chemistry, UK, Institution of Chemical Engineers, UK, Indian Institute of Chemical Engineers, Indian Chemical Society, and Indian Society for Technical Education, among others. He was elected to the US National Academy of Engineering in 2022 and is among only 18 Indian nationals so far. He is currently the President of the Indian Chemical Society and Editor-in-Chief, Journal of the ICS being published by Elsevier.

https://doi.org/10.1515/9783110782165-204

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About Prof. Ganapati D. Yadav

The American Chemical Society (ACS) published a Festschrift (special issue) of Industrial and Engineering Chemistry Research (2014) in his honour with 65 original research papers from scientists from all over the world. He is the Founder President ACS India International Chapter. He has been or is on the editorial boards of prestigious journals like: ACS Sustainable Chemistry & Engineering, Green Chemistry, Applied Catalysis A: Gen, Journal of Molecular Catalysis A: Chem., Catalysis Communications, International Journal of Chemical Reactor Engineering, Clean Technologies and Environmental Policy, Current Catalysis, etc. He is the Founding Editor-in-Chief of Catalysis in Green Chemistry & Engineering (2017, Begell House, USA). He has been a member or chaired several national and international committees of MHRD, DST, DBT, UGC, AICTE, CSIR, the PSA’s on Green Chemistry, the Planning Commission’s Pan India S&T Committee, and the Government of Maharashtra’s Rajiv Gandhi S&T Commission Peers Group. He was Chairman, Research Council, CSIR-CSMCRI, member of RC of IICT Hyderabad and NIIST Trivandrum. He has served as a Chairman/member of Selection Committees of directors of many CSIR labs. He serves as Independent Director, on five renowned limited companies: Aarti Industries Ltd, Godrej Industries Ltd, Meghmani Organics Ltd, Bhageria Chemicals Ltd, and Clean Science and Technology Ltd. He is also a member of Apex Council of Indian Oil R&D; Expert Advisory Committee, ONGC Energy Centre (OEC); Glexcon India Advisory Board on Process Safety and the Governing Council DBT-IndianOil Energy Centre, and member of the DBT-Pan IIT Centre for Bioenergy. He is Chairman of DST’s National Expert Advisory Committee on Innovation, Incubation and Technology Enterprise, member of Advisory and Screening Committee of the Common Research and Technology Development Hubs of DSIR, Chairman, PAC of International Programmes in Chemical Sciences and Engineering, DST and Chairman, Expert Committee, Waste Management Technology, DST. He is a member of the Maharashtra Govt’s Expert Committee on implementation of the National Education Policy(NEP 2020). He had the honour of addressing 3 Convocations of renowned universities in India. He is fond of literature, etymology, and Sanskrit. The ICT’s University song is written by him. There are over 60 video clips covering his biography (both English &Marathi), lectures, panel discussions, interviews on TV on YouTube. https://www.youtube.com/playlist?list=PLclyJH91-TwvTScCVrcih3nrrPGgf8U8R

Contents Dedicated to Sant Baba Iqbal Singh Ji, Founder Chancellor, Akal University V Foreword

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About Prof. Ganapati D. Yadav

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Sandeep Kumar, Ravinderdeep Singh Brar, J. Nagendra Babu, Khadim Hussain Chapter 1 Nanoscale zerovalent iron (nZVI): an efficient heterogeneous catalyst for environment remediation 1 Cesar Maximo Oliva González, Oxana V. Kharissova, Lucy T. Gonzalez, Yolanda Peña Méndez, Boris I. Kharisov, Igor E. Uflyand Chapter 2 Ferrite nanoparticles in the modern catalytic processes 37 Pranab Ghosh, Sultana Yeasmin Chapter 3 Polymer-grafted magnetic nanoparticles toward intelligent designing of drug delivery: recent advances and future perspectives 73 Suresh Maddila, Nagaraju Kerru, Sreekantha B. Jonnalagadda Chapter 4 Magnetic nanocatalysts for wastewater treatment 97 Anshu Dandia, Sonam Parihar, Krishan Kumar, Surendra Saini, Vijay Parewa Chapter 5 Combination of green chemistry and magnetic nanocatalyst: a sustainable approach for the synthesis of value-added materials 131 Author list Index

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Sandeep Kumar*, Ravinderdeep Singh Brar, J. Nagendra Babu, Khadim Hussain

Chapter 1 Nanoscale zerovalent iron (nZVI): an efficient heterogeneous catalyst for environment remediation 1.1 Introduction Since the beginning of the Iron Age, the discovery of iron has proved a boon to the human race through the role it played in the evolution of various civilizations [1]. The twentieth century has witnessed the enormous applications of steel, an alloy of iron, as the hardest material used for the development of large infrastructures. Similarly, iron-based salts like FeSO4 and FeCl3 are being used in primary treatment like coagulation and flocculation of wastewater [2]. Iron is characterized by unique redox properties which could be exploited under ambient atmospheric conditions [3]. At the same time, the emergence of nanotechnology explored the various prospects of nanoscaled iron particles and rendered the nanoscale zerovalent iron (nZVI) the most effective properties such as high reactivity, better mobility than microscale zerovalent iron (mZVI) particles, intrinsic magnetic interactions, good adsorption capacities, low toxicity, and cost to act as a versatile engineered nanomaterial for environmental remediation [4]. The high reactivity of nZVI is attributed to inherent strong reducing tendencies of Fe(0) and is proficiently exploited for its reaction with a number of inorganic and organic substrates such as heavy metal ions, dyes, drugs, halogenated hydrocarbons, and reduction of organic compounds [5]. In recent years, nZVI has been progressively utilized in groundwater remediation and hazardous waste treatment. However, the applications of bare nZVI in catalytic processes are retarded by the surface passivation of nZVI on contact with air/moisture and/or by aggregation of nZVI [6]. The use of immobilizers as support and to act as stabilizing agents increases the catalytic efficiencies of nZVI [7, 8]. Thus, this chapter focuses on the mechanism and applications of nZVI in development of efficient nanocomposite materials as

*Corresponding author: Sandeep Kumar, Department of Chemistry, Akal University, Talwandi Sabo, Bathinda 151302, Punjab, India, e-mail: [email protected] Ravinderdeep Singh Brar, Department of Chemistry, Akal University, Talwandi Sabo, Bathinda 151302, Punjab, India J. Nagendra Babu, Khadim Hussain, Department of Chemistry, School of Basic and Applied Science, Central University of Punjab, Bathinda 151001, Punjab, India https://doi.org/10.1515/9783110782165-001

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heterogeneous catalysts to perform the Fenton process for the environmental remediation of wastewaters containing complex organic materials.

1.2 Synthesis of nZVI The reactivity and applicability of nZVI as an efficient environment remediating agent depends on its size, capping material, surface oxide layer, support material, and so on. Therefore, the process employed for manufacturing of nZVI plays a significant role in deciding the efficiency of the nanocatalyst formed [1]. Literature supports the higher reactivity of bare nZVI (10–103 times) than granular ZVI, owing to its high surface energy and magnetic properties [9]. A thin layer of oxide is formed on its surface when in contact with air and moisture. A mixed Fe(0)/Fe(II)/Fe(III) phase appeared on the surface when nZVI came in contact with water with major phase as lepidocrocite, that is, FeOOH [10, 11]. Core–shell particles, with protective oxide layer of appropriate thickness not prohibiting the transfer of electrons from the iron core, are more stable than the bare pyrophoric iron nanoparticles (FeNPs) and thus are found advantageous in practical applicability [1]. Prevention of agglomeration by using support or dispersing agents, capping of nZVI, and improving colloidal properties by using organic polymers may also result in enhanced efficiencies of nZVI [12]. Two general approaches are used for the synthesis of nZVI: top-down approach, that is, reducing the size of bulk iron to nanoscale; or bottom-up approach, that is, building nanoiron from atoms formed from ions or molecules [13].

1.2.1 Top-down synthesis In top-down approach, large-sized iron materials are converted to nZVI using mechanical or chemical processes such as milling [14], etching [15], pulsed laser ablation [16], and noble gas sputtering [17]. Milling is the most commonly employed process in which millimeter-sized iron fillings are milled to nanosized iron using vibrating mills and stirred ball mills. Being economical, this method is used for industrial-scale production of nZVI, as it does not require the use of expensive harmful chemicals. Capping agents are added as a grinding medium to prevent highly reactive pyrophoric iron particles from undergoing combustion and result in reduced reactivity of nanoparticles (NPs).

1.2.2 Bottom-up synthesis Bottom-up approaches are based on the “growth” of nZVI atom by atom starting from dissolved iron salts via chemical synthesis or self-assembly process.

Chapter 1 Nanoscale zerovalent iron (nZVI)

3

1.2.2.1 Solution synthesis The most commonly used process for nZVI synthesis involved the reduction and precipitation of ZVI under inert atmosphere from aqueous iron salts, usually chlorides or sulfates, using sodium borohydride as the reducing agent [18] as follows: 2 Fe2 + + BH4 − + 3 OH − ! 2 Fe0 + H3 BO3 + 2 H2 4 Fe2 + + 3 BH4 − + 9 OH − ! 4 Fe0 + 3 H3 BO3 + 12 H2

(1:1) (1:2)

Apart from sodium borohydride, other less frequently used reducing agents in solution methods are application of hydrazine [19] and sodium dithionite [20]. The solution-phase reduction method includes multiple steps for synthesis of nZVI, such as supersaturated solution preparation, nucleation, growth of nuclei, and agglomeration of nZVI, followed by washing, filtration, and dehydration of NPs. This step leads to the formation of a thin layer of oxide on the surface of nZVI. The nZVI are immobilized on inorganic/organic support or some capping materials are used to increase stability and increase mobility, to minimize aggregation, and reduce leaching of nZVI. Various inorganic materials used till date include aluminum hydroxide [21], SBA-15 silica [22], pumice [23], Mg-aminoclay [24], kaolin [25], zeolite [26], bentonite [27], montmorillonite (MMT) [28], marine clay [29], sepiolite [30], oyster shell [31], coral [32], carbon black [33], biochar (BC) [7], cation exchange membrane [34], silica fume [35], calcium-alginate bead [36], graphene oxide (GO) [37], and multiwalled carbon nanotubes [38]. Organic support and capping materials used for nZVI-organic composites can be monomers, polymers, or surfactants which may include pectin [39], long-chain carboxylic acids and amines [40], octa(cholinium)-polyhedral oligomeric silsesquioxane [41], rhamnolipid [42, 43], polyethylene glycol [44], polyvinylpyrrolidone, polyacrylic acid [45], carboxymethyl cellulose (CMC) [46], polystyrene resin [47], and polyvinyl alcohol-co-vinyl acetate-co-itaconic acid [48]. The sizes of nZVI particles depend on experimental conditions and the quantity and type of organic materials used as a support or capping agent (Figure 1.1). Due to safety and environmental concerns, use of expensive chemical reduction methods are being replaced by green synthetic methods that use extracts from natural products such as leaves, fruits, and bark containing high contents of alkaloids and polyphenols [49, 50]. These components react with iron ions in solution and reduce them to give nZVI particles. The extract used from natural products till date includes oak leaves extract, apricot, apple, avocado, eucalyptus, cherry, kiwi, mandarin, lemon, medlar, oak, mulberry, olive, passion fruit, orange, peach, pine, pear, pomegranate, quince, plum, raspberry, vine, strawberry, tea-black, tea-green, walnut leaf extracts, and yeast extract [51–53].

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Figure 1.1: Bottom-up approach for synthesis of nZVI using chemical reduction method.

1.2.2.2 Thermal synthesis High-temperature synthesis can be employed for supports that are thermally stable at higher temperature. In this approach, the supporting material is soaked in iron salt solution, dried, and iron salt is reduced on the surface of the supporting material using gaseous reducing agents such as H2 gas atmosphere or H2/Ar plasma [54]. Under these conditions, reduced GO (rGO) is obtained from GO and used as support to immobilize nZVI NPs [55, 56]. In another approach also called direct pyrolysis, the mixtures of organic materials and iron salts are prepared under an inert atmosphere and are projected to a hightemperature carbonization process, in which the organic materials turn into carbon and act as support for synthesized nZVI [57, 58]. Materials used for this purpose may include metal-organic framework [59], ion exchange resins [60], and BC derived from biowastes [61]. The chemical vapor deposition technique including gas-phase pyrolysis of thermally labile iron pentacarbonyl results in formation of nZVI, but toxicity of this compound is a major drawback of this application [62].

1.3 Structure of nZVI The typical structure of nZVI formed by a chemical reduction method using a bottomup approach consists of a core–shell structure [63]. The core contains zerovalent or metallic iron and is covered by an oxide shell with mixed Fe(II) and Fe(III) phase with a major phase as FeOOH [64]. The nZVI NPs exhibit excellent electron-donating tendencies, which renders it a high reactivity and thus acts as a versatile remediation

Chapter 1 Nanoscale zerovalent iron (nZVI)

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material [65]. The mixed-phase oxide shell is insoluble at neutral pH and thus prevents the oxidation of the inner nZVI core. The shell of nZVI is the site for chemical reaction onto which the substrates interact via chemisorption and electrostatic interactions [66]. The nZVI with defective and disordered oxide shells are potentially more reactive in comparison to a normal passive oxide layer [64]. The extremely small radii of NPs hindered the formation of crystals and thus made the oxide layer more amorphous and disordered. The amorphous nZVI NPs agglomerate and form a continuous oxide layer with less contrast in comparison to dense inner core. The interior nZVI core acts as the powerhouse of electron, and charge transfer is possible through the semiconducting outer oxide layer owing to its small thickness and defective sites present in its surface. This allows an effective reduction of contaminants on the surface of core–shell nZVI [67–69].

1.4 nZVI as a heterogeneous catalyst for the Fenton process The heterogeneous Fenton process utilizing solid catalyst has been widely accepted as an efficient method for the degradation of organic as well as inorganic pollutants in wastewater [70]. This process is carried out at ambient temperature and pressure, requires easy to use reagents, and also considered economical in terms of cost involvement [71]. Homogeneous Fenton process involves the reaction between H2O2 (HP) and aqueous ferrous ions (Fe2+) under acidic conditions and produces strong oxidant, that is, hydroxyl radicals (.OH), which causes degradation of toxic organic pollutants in water [72]. However, a homogeneous process has major disadvantages like consumption of catalyst and pH adjustments that cause iron precipitation and sludge disposal. Heterogeneous Fenton process overcomes the drawbacks of the homogeneous Fenton process by using solid iron oxides like Fe2O3, Fe3O4, FeO, and FeOOH as Fenton catalysts with HP [71, 73]. The nZVI has attracted a great attention from researchers to be used in heterogeneous Fenton and Fenton-like processes for water and wastewater treatment due to its low cost, nontoxicity, easy to synthesis, environmentally benign, and efficiency to degrade/transform a number of organic pollutants such as polycyclic aromatic hydrocarbons, halogenated compounds, nitrates, phosphates, phenols, dyes, and drugs [74, 75]. The pH has a significant effect on the performance of nZVI in the Fenton-like process for the removal of organic pollutants via controlling surface charge of catalyst, free radical generation, and amount of dissolved oxygen (DO) in the solution [76]. The removal of contaminants using nZVI involved complex interfacial pathways operating simultaneously or sequentially on the surface of nZVI, such as dissolution, adsorption, and redox reaction/precipitation. The nZVI produces Fe2+ ions on reaction with H2O or dissolved O2 or both [75, 77]. Similarly, on reaction with HP it is

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easily oxidized from Fe(0) to Fe(II) ions. The Fe2+ ions thus produced participate in the Fenton process to generate strongly oxidizing species such as .OH. These hydroxyl radicals cause oxidative degradation of organic/inorganic contaminants in wastewater and lead to their mineralization [78] (Figure 1.2):

Figure 1.2: Possible mechanism of Fenton catalytic oxidation process.

Feð0Þ + H2 O ! FeðIIÞ + H2 + 2 −OH Feð0Þ + O2 ðgÞ + 2 H + ! FeðIIÞ + H2 O2



(1:3) (1:4)

Feð0Þ + H2 O2 ! FeðIIÞ + 2 −OH

(1:5)

Feð0Þ + H2 O2 ! FeðIIIÞ + −OH +  OH

(1:6)

OH + Contaminants ! Mineralization

(1:7)

1.4.1 Degradation of organic compounds Synthetic organic compounds are active ingredients in various pharmaceuticals, cosmetics, textile products, and agricultural chemicals [79]. These compounds find their way into the environment via different anthropogenic activities [80]. Their presence in the environment may pose a serious threat to human and animal health. The elimination of these pollutants from the environment via sustainable ways has become a serious challenge for all researchers [81]. In this part of discussion, we will provide evidence in favor of nZVI as a heterogeneous Fenton catalyst to degrade various pollutants of environmental concern (Figure 1.3). The nZVI synthesized via solution phase reduction of ferrous ion using NaBH4 was used as a catalyst for the Fenton reaction employed for oxidative degradation of methyl tert-butyl ether 1 (MTBE) [82]. The ZVI acts as the source of catalytic ferrous

Chapter 1 Nanoscale zerovalent iron (nZVI)

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Figure 1.3: Organic compounds studied for nZVI-Fenton-like oxidation process.

iron, which along with HP generates .OH radical from the Fenton process, responsible for the overall degradation of MTBE and its by-product, that is, acetone. Further, the ratio of HP:MTBE played a significant role, as the rate of degradation increased linearly with increase in the ratio of HP:MTBE. The degradation reaction of MTBE was also found to be pH dependent. At pH 3, only 72% of degradation was observed, which was increased to maximum (99%) at pH 4, and decreased with further increase in pH. At pH 7, the observed reduction in MTBE concentration was nearly 96%. The reduced degradation rate at lower pH was ascribed to precipitation of ferrous ions resulting in decreased concentration of .OH radicals. The MTBE degradation followed second-order rate kinetics with rate constant values of 0.23 M−1 s−1 and 4.4 × 108 M−1 s−1, in the presence and absence of HP, respectively. Xu and Wang [83] investigated the use of nZVI as a catalyst in the Fenton process for removing 4-chloro-3-methylphenol2 (CMP) in the presence of HP. Conventional Fenton process (CFP) was found very effective in the degradation reaction of CMP. The enhancement in the rate of reaction was observed with the increase in the concentration of HP from 0.6 to 3.0 mM, which is responsible for more of .OH radicals produced in the reaction mixture. Further increase in the HP concentration (up to 6.0 mM) does not produce any significant change in the rate of reaction, which was ascribed to HPmediated inhibition of iron corrosion and scavenging effect of hydroxyl radicals. The optimum conditions for the CMP (0.7 mM) degradation were observed as nZVI dose of 0.5 g/L and HP concentration of 3.0 mM at pH 6.1. The CMP exhibited moderately increased oxidation with an incremental dose of nZVI (0.1–0.5 g/L). The increase in the number of active sites available on nZVI with increased catalytic dose produces more . OH from HP. However, further increase in nZVI dose (0.6 g/L) caused a reduction in degradation of CMP rather than enhancement, which was related to agglomeration of magnetic nZVI particles. The degradation process followed two-stage first-order kinetics, with the first stage composed of slow degradation ascribed to a heterogeneous

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reaction observed on the iron surface, and rapid degradation in the second stage involving Fenton reaction near the nZVI surface. The nZVI was also studied for the Fenton-like heterogeneous process for the treatment of contaminated soils [84]. Three different types of soil (Taikang, Chengchung, and Pianchen) were contaminated with pentachlorophenol 3 (1 g/kg of soil). Among the different catalytic doses of nZVI (0, 0.2, 0.5, and 1 wt%) used for the treatment of contaminated soil in the presence of 1% HP, the 1 wt% treatment was observed to cause maximum degradation of pentachlorophenol in the contaminated soils. Further, among all three soils, Pianchen was proven to be good as nZVI easily releases Fe2+ during oxidation. The addition of HP releases .OH in the reaction mixture, which further enhances the rate via oxidation–reduction reaction. This dual mechanism was proposed for enhanced phenol degradation, which are otherwise difficult to degrade. The effect of presence of CaCO3 on the degradative removal of pentachlorophenol from soil via the Fenton process was also evaluated. The addition of 5% CaCO3 for 40 h to the Fenton process increased the degradation rate of pentachlorophenol in Chengchung from 37% to 78% and in Pianchen from 43% to 76%. Sun et al. used MMT-supported nZVI (MMT-nZVI) [85] to induce a heterogeneous Fenton process for the degradation of 2,3′,4,5-tetrachlorobiphenyl 4 (PCB67) from soil. The PCB67 degradation process was highly affected by MMT-nZVI dose, HP concentration, and pH of the reaction mixture. The maximum oxidative removal of PCB67 (76.38%) was achieved within 80 min of reaction time, using MMT-nZVI dose of 2.98 wt% and HP dose of 4.59 wt% at initial pH 3.5. The degradation process was found to be endothermic with an activation energy requirement of 21.4 kJ/mol, and also followed pseudo-first-order kinetics. The aerobic oxidation-mediated formations of Fe2+ ions from MMT-nZVI were responsible for the activation of HP and formation of .OH for the oxidative degradation of PCB67. Two different degradation pathways were proposed with formation of different intermediates. Ethyl benzene and 3-hepten2-one as intermediates were proposed in the first degradation pathway, whereas dibutyl phthalate and butyl acetate were proposed as intermediates in the second degradation pathway. Iron-pillared clay (Fe-PILC) containing 6.1% (w/w) of Fe was synthesized by calcination (400 °C, 2 h) of exchange clay, which was obtained by mixing aqueous solution of iron complex [Fe3(OCOCH3)7OH.2H2O]NO3 with MMT clay [86]. Thus, prepared FePILC was evaluated for its catalytic activity in photo-Fenton process employed for the degradation of 2-chlorophenol 5 (2-CP). The leaching of iron suggests the presence of a homogeneous photo-Fenton process and results in enhancement of degradation rate of contaminants. Higher Fe-PILC catalytic loading achieves more conversions of 2-CP and 2.5-fold increase in the total organic content (TOC) removal with about a 2-fold consumption of HP. The complete oxidative removal of phenol 6 was achieved using nZVI as catalyst for heterogeneous photoelectro-Fenton (PEF) process under near-neutral pH within 30 min [87]. The degradation rate was found to increase with an increase in

Chapter 1 Nanoscale zerovalent iron (nZVI)

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nZVI dosage from 0.1 to 0.5 mg/L and HP concentration from 100 to 600 mg/L; and decreases with an increase in the initial phenol concentration from 100 to 400 mg/L and initial pH from 2 to 6.2. The optimum dose of nZVI and HP were 0.5 g/L and 500 mg/L, respectively. The complete removal was observed within 30 min at initial pH 6.2 and initial concentration of phenol 200 mg/L. Among the different current densities used for the heterogeneous PEF process, 12 mA/cm2 was found to be the optimum current density for the phenol removal. In another study, Babuponnusami and coworkers [88] used the nZVI immobilized on polyvinyl alcohol–alginate beads in the photoelectron-Fenton process for the oxidative removal of phenols and reduction of chemical oxygen demand (COD) from aqueous medium. The size of nZVI beads prepared via borohydride reduction method was in the range of 500–600 µm. Phenol degradation was achieved at a wide range of pH using 0.5 g/L nZVI and 400 mg/L. Further, the results showed that the degradation can also be performed at near-neutral pH (i.e., 6.2), which resolved the problem related to adjustment of pH of solution during the treatment process. The removal of phenol using nZVI in this heterogeneous process includes both adsorption and degradation. The adsorption of phenol on the nZVI surface increases with an increase in initial concentration of phenol, and thus blocks the nZVI surface to produce .OH radicals. Thus, a significant decrease in the activity of nZVI was observed at higher concentration of phenol. The kinetics of the removal process was observed to follow a pseudo-first-order rate. Xia and coworkers [89] prepared a hierarchical dendritic ZVI via high-efficient electrodeposition method with large specific surface area (SBET 41 m2/g). This was employed as a heterogeneous Fenton-like catalyst for the efficient removal of 35 ppm of phenol (90%) within 15 min of reaction time. The optimized conditions for the reaction were Fe(0) dose of 0.1 g/L and HP concentration of 6 mM at pH 4. In consecutive experiments, for the second cycle nearly 80% and for the third run 74% of phenol degradation was observed in 60 min. Ethanolamine 7 (ETA) is a commonly employed pH control agent to protect the plumbing system of power plants, and its discharge into water bodies is strictly prohibited because of its high refractory nature in biodegradability [151]. Effluent of nuclear power plants containing ETA and other dissolved organic materials was treated with nZVI (1 g/L) in the presence of HP (150 mL/L). It was observed that ETA concentration was decreased from 9.8 g/L to about