Nanocomposite and Nanohybrid Materials: Processing and Applications 9783111137902, 9783111137896

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Rajesh Kumar Verma, Devendra Kumar Singh, J. Paulo Davim (Eds.) Nanocomposite and Nanohybrid Materials

Advanced Composites

Edited by J. Paulo Davim

Volume 17

Nanocomposite and Nanohybrid Materials Edited by Rajesh Kumar Verma, Devendra Kumar Singh and J. Paulo Davim

Editors Prof. Rajesh Kumar Verma School of Engineering Harcourt Butler Technical University (HBTU) Department of Mechanical Engineering Kanpur 208002, Uttar Pradesh India [email protected] Devendra Kumar Singh Madan Mohan Malaviya University of Technology Department of Mechanical Engineering Materials and Morphology Laboratory Gorakhpur 273010, Uttar Pradesh India [email protected] Prof. Dr. J. Paulo Davim University of Aveiro Department of Mechanical Engineering Campus Santiago 3810-193 Aveiro Portugal [email protected]

ISBN 978-3-11-113789-6 e-ISBN (PDF) 978-3-11-113790-2 e-ISBN (EPUB) 978-3-11-113925-8 ISSN 2192-8983 Library of Congress Control Number: 2023943549 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. © 2023 Walter de Gruyter GmbH, Berlin/Boston Cover image: gettyimages/thinkstockphotos, Abalone Shell Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Preface Nanocomposites and nanohybrids are the novel class of the advanced composite materials required for specific applications having excellent physio-mechanical properties. Sometimes, microfibers or macro-size reinforcing materials-based composites unable to provide the desired mechanical and chemical properties. Due to this limitation, the matrix properties could be improved by the supplement of nanomaterials. Nanocomposites are extensively employed in multifunctional applications of structure components such as aircraft, aviation, biomedical, sports goods, routine life products, optical components, sensors, etc. owing to their enhanced synergistic effect and aspect ratio. The costeffectiveness, ease of manufacturing, and durability are also the prime elements for its distinctiveness. Using carbons nanoparticles (CNPs) is an effective way to attain high strengthened smart materials. This gives them better mechanical, chemical, thermal, and optical as well as biological properties. Through nanotechnology and molecular tailoring, nanohybrids can identify sick tissue in a noninvasive and improved manner. Various exciting nanoparticles (NPs) such as graphene derivatives, nanohydroxyapatite (n-Hap), zirconium oxide, aluminum oxide, carbon nano tube (CNT, SWCNTS, MWCNTS), carbon nano onion (CNO), carbon nano sheet (CNS), carbon nano rod (CNR), zirconium oxide, and several organic and inorganic nanomaterials (OI-NM). Implants made of polymer and augmented with nanoparticles have already been effectively proven in previous cutting-edge research studies. Among these, polymeric nanocomposites (PNCs) show promising properties (light weight, flexibility, low cost, large surface area to volume ratio, good strength, etc.), which can bring resolution to the healthcare system. Among other applications, the healthcare system has emerged as an outstanding research area due to the high requirements of novel material with required characteristics. The studies on nanocomposites and hybrids require more attention to explore their highest benefits in society and trade interests. Limitations of the conventional production methods have persuaded scholars to delve into alternate nanocomposite and nanohybrids development. For the consideration of manufacturing aspects, advancements in additive manufacturing (AM) technologies and rapid tooling are widely used. The component production in the mode of 3D printing technology has ensured the manufacturing of several complex structures and designs with the help of computer-aided design tools. Because of pressing environmental issues and innately inadequate physical-mechanical characteristics with low performance, polymer-based 3D printing materials are currently in use. The development of a sustainable high-performing polymer composite material is needed in the current scenario. Fused deposition modeling (FDM), one of the mainly used 3D printing methods, is the most widely used method for manufacturing thermoplastic components. While evaluating the physical, chemical, thermal, and mechanical performance of the polymer nanocomposites, the proposed book focuses on the unified aim to evaluate conflicting manufacturing performances related to quality and productivity indexes. Research disciplines such as Hybrid nanomaterials, alloy nanomaterials, and composites https://doi.org/10.1515/9783111137902-202

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Preface

might benefit from the capabilities of nanotechnology in the future. The role of catalysis and the nanotechnology phenomenon for the fabrication of nanomaterials and composites will be discussed in depth. The optical, electrical, and magnetic characteristics, surfaces and interfaces at the nano- and micrometer scales, single-molecule biological nanotechnology and nanobiology will be targeted for the development of efficient products. The biomedical imaging at the nanoscale and composites issues required for costeffective and environmentally friendly materials shall be explored. Through the use of analytical evaluations, this book provides readers with a contemporary understanding of a variety of different nanohybrid polymeric nanocomposite materials and technologies. Each chapter is written by a leading expert in the subject, ensuring that readers receive a comprehensive picture of the breakthroughs and advancements that have been made in a variety of nanomaterials, polymeric materials, and polymer nanocomposites for high-performance applications, biopolymers, biodegradable composites, biomaterials, and methods. Thus, in this book, the prime highlight is to overview of the advances in various hybrid polymer nanocomposites and their diverse application in structural, aeronautical, automotive industries, and healthcare fields (e.g., drug delivery, food processing, 3D prosthesis and implants development, dental restorative materials, bioimaging applications, and other miscellaneous biomedical and manufacturing components). The synthesis, production, and characterization of nanoparticles will be the starting points for the proposed book. It will then move on to discuss the manufacturing aspect of hybrid polymer-based nanocomposites and their final product applications. The difficulties associated with the phase of producing polymers will be expanded by utilizing a variety of control approaches, statistical tools, and modules that were recently developed by distinguished academics. The most interesting topic that will be covered in this book is polymer matrix bio-nanocomposites and nanohybrid composites, namely, their potential applications in the engineering field.

Acknowledgments This book Nanocomposite and Nanohybrid Materials: Processing and Applications owes its existence to the pretentious assistance, support, and guidance of numerous distinguished individuals and scholars. First and foremost, we would want to offer my most sincere gratitude to the Almighty for blessing me with good health, grace, wisdom, patience, and the essential guidance to finish this job. Our most profound appreciation goes to Prof. Samsher, Hon'ble Vice Chancellor, Harcourt Butler Technical University (HBTU) Kanpur, India, for his continuous support, stimulating environment toward research, and constant direction for the timely completion of this book. We are incredibly grateful to him for motivating us to think independently, good-naturedly, and solve numerous problems with perseverance. We are fortunate to have his advice and support to express our thankfulness for their support and belief. We are very grateful to the University Chancellor and H.E. Hon’ble Governor of Uttar Pradesh and Government of Uttar Pradesh State for providing us with good infrastructure and technical support, which helped to finalize this task. Their contributions played a crucial role in bringing this endeavor to fruition. The authors would like to express their gratitude to all the contributors and eminent scholars who supported us continuously through their technical expertise and findings in the finalization of this task. We sincerely appreciate our global research collaborators from the University of Aveiro, Portugal; Kansas State University, United States; and the University of Western Macedonia, Greece. Their assistance and collaboration were invaluable in the creation of this book. In addition, we are highly obliged to all the contributing authors for their continuous support and help in completing this task in a time-bound manner. We are also deeply thankful to the research scholars, namely, Dr. Prakhar Kumar Kharwar, Dr. Jogendra Kumar, Mr. Shivi Kesarwani, Mr. Kuldeep Kumar, Mr. Kaushlendra Kumar, Mr. Balram Jaiswal, Mr. Rahul Vishwakarma, Mr. Virat Mani Vidhyasagar, and Mr. Shailesh Kumar Gupta. Their diligent work and valuable findings in the field of Nanocomposite and Nanohybrid Materials have contributed significantly to this project. The role of students at the Madan Mohan Malaviya University of Technology, Gorakhpur, India is also significant in this work. The authors would like to express their utmost gratitude to the reviewers, editorial members, and the team at DE GRUYTER publication for their precious time and effort devoted to this book. Their exceptional contributions were instrumental in shaping this book into its present form. This milestone could not have been achieved without their unwavering guidance, support, and collaboration. Finally, but most importantly, I thank ALMIGHTY GOD, my Lord, for giving me the will, power, and strength to complete this valuable research book. Prof. Dr. Rajesh Kumar Verma Dr. Devendra Kumar Singh Prof. Dr. J. Paulo Davim https://doi.org/10.1515/9783111137902-203

Contents Preface

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Acknowledgments

VII

Rachna Dixit, Kumari Arpita, Vishal Chand 1 The current scenario in nanocomposite and nanohybrid materials

1

Akshay C. Jadhav, Bhagyashri N. Annaldewar, Nilesh C. Jadhav 2 A current perspective on nanocomposite and nanohybrid material: developments and trends 29 Ravi Shankar Rai, Harsh Arora 3 Synthetic nanomaterials: fabrication, development, and characterization 55 Niraj Kumari, Dipti Bharti, Rahul Singh, Amit Kumar, Minakshi Awasthi, Brij Kishore Tiwari 4 Advances in fabrication, development, and characterization of synthetic nanomaterials 85 Shashank Sharma, Sanjay Kumar Dubey 5 Structural, morphological, thermal, and long persistent properties of synthesized nanostructured phosphor 99 Dr. N. Muthukumaran, Dr. G. Prince Arulraj 6 Mechanical characteristics and surface roughness testing of nanomaterials in enhancing the discharge over spillways

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Minakshi Awasthi, Vanya Arun, Ankita Awasthi, Amit Kumar, Niraj Kumari, Dipti Bharti 7 Biomedical considerations of nanomaterials based on biological aspects in biomedical field 139 Siddhartha Ghanty, Abhratanu Ganguly, Sayantani Nanda, Kanchana Das, Moutushi Mandi, Saurabh Sarkar, Prem Rajak 8 Nanomaterial-based molecular imaging and targeted cancer therapy: current progress and limitations 161

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Prem Rajak, Abhratanu Ganguly, Manas Paramanik, Sudip Paramanik, Moutushi Mandi, Anik Dutta, Sukhendu Dey 9 Emerging perspectives of nanoparticles to treat neurodegenerative diseases 179 Alaa Kamo, Ali Ozcan, Ozlem Ates Sonmezoglu, Savas Sonmezoglu 10 Understanding antibacterial disinfection mechanisms of oxide-based photocatalytic materials 195 A. T. Erturk, G. Özer 11 Nanocomposites and nanohybrids in additive manufacturing

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Virat Mani Vidyasagar, Umang Dubey, Devendra Kumar Singh, Rajesh Kumar Verma, Panagiotis Kyratsis 12 Characterization and mechanical properties analysis of carbon nanotube and hydroxyapatite-modified polymethyl methacrylate bone cement for bio-nanocomposite 237 Kuldeep Kumar, Shivam Kumar Dubey, Shivi Kesarwani, Prakhar Kumar Kharwar, Arpan Kumar Mondal, Rajesh Kumar Verma, Mark J. Jackson 13 Role of nanomaterials in enhancing the performance of polymer composite materials 259 Sudip Paramanik, Abhratanu Ganguly, Koushik Jana, Prem Rajak, Manas Paramanik 14 Nanotechnology: a novel weapon for insect pest and vector management 277 M. Thirukumaran, K. Senthilkumar, R. Selvabharathi 15 Effect of carbon nanotubes, aluminum hydroxide, and zinc borate on the mechanical and fire properties of epoxy nanocomposite 297 Anjali Awasthi, Ashish Kapoor, Soma Banerjee 16 Recent advancements in polymer nanocomposites-based adsorbents for chromium removal 315 About the editors List of contributors Index

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337 339

Rachna Dixit, Kumari Arpita, Vishal Chand✶

1 The current scenario in nanocomposite and nanohybrid materials Abstract: Nanocomposites and nanohybrid materials have emerged as a revolutionary class of cutting-edge advanced materials that have gained wide popularity because of their multifunctionalities and offer a set of unique and outstanding properties like biodegradability, biocompatible, processibility, mechanical properties, flexibility, and magnetic and optical properties. The global market for nanohybrid composites is expected to increase from US$2.2 billion in 2021 to US$3.6 billion by 2026, at a CAGR of 10.4%. The international market for nanocomposites was originally anticipated to be worth US$6 billion in 2020 but is now expected to increase to US$16.7 billion by 2027 at a CAGR of 15.7% during the study period of 2020–2027, reflecting the altered post-COVID-19 business scenario. Due to increased demand from packaging, defense, aerospace, drug delivery, electronics, automobile, and semiconductor applications, the market is expanding. This chapter discusses some of the recent innovations in nanocomposites and nanohybrids and provides an overview of future applications. Keywords: Nanocomposites, nanohybrids, packaging, aerospace, drug delivery, automobile

1.1 Introduction According to legend, Richard P. Feynman, recipient of the 1965 Nobel Prize in Physics, first proposed the idea of nanotechnology approximately 50 years ago. On December 26, 1959, he delivered an outstanding talk titled “There’s Plenty of Room at the Bottom” at the American Physical Society’s annual meeting held at the California Institute of Technology. In this presentation, he discussed miniaturizing computers and writing 24 volumes of the Encyclopedia Britannica on the tip of a pin. Additionally, he implied that we may arrange the atoms anyhow we please. A physicist should thus be able to create any chemical compound by placing the atoms where the chemist directs. Nanotechnology studies materials with smaller particle sizes, with diameters ranging from 1 to 100 nanometers, giving materials unique features employed in certain applications. The biological, physical, and chemical characteristics of materials at the nanoscale are distinct from those of discrete atoms and molecules or bulk matter. The outstanding qualities of emerging materials allow for novel applications [1]. ✶

Corresponding author: Vishal Chand, Department of Biotechnology, CSJM University Kanpur, Uttar Pradesh, India Rachna Dixit, Kumari Arpita, Department of Biotechnology, CSJM University Kanpur, Uttar Pradesh, India

https://doi.org/10.1515/9783111137902-001

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Rachna Dixit, Kumari Arpita, Vishal Chand

Nanoscale engineering, technology, and science that are focused on managing, availing use of, and comprehending the special qualities of matter that can develop at nanoscales are collectively referred to as nanotechnology. These features are believed to give significant societal and economic benefits [2, 3]. In this era, innovative nanostructures, especially nanocomposites, and nanohybrids, are showing emerging potential through the orientation and arrangement of atoms according to demands.

1.1.1 Nanocomposite Nanocomposites are composites that have a bulk phase and other nanoscale particles dispersed throughout that bulk phase to enhance the properties of the bulk phase. The characteristics of the bulk material or phase are modified using these nanoscale particles, which may be of a single kind or several different types. In comparison to individual atoms and molecules or bulk materials, nanocomposites have different characteristics. According to their matrix, there are different forms of nanocomposites: Metal matrix nanocomposites (MMNC), polymer matrix nanocomposites (PMNC), and ceramic matrix nanocomposites (CMNC). Nanocomposites have attracted interest recently owing to its superior thermal, mechanical, and solvent-resistant qualities in contrast to pure or conventional composite materials [4]. The distribution of particle size, surface qualities, geometric form, and dispersion state, among other factors, may all significantly affect the composite’s properties, as is widely acknowledged. Polymer nanocomposites (PNCs) are becoming progressively prevalent as a consequence of the commercial availability of nanoparticles nowadays. The mechanical characteristics of these composites including modulus, strength, water, gas, and hydrocarbon permeability, dimensional and thermal stability, flame retardancy, chemical resistance, and optical characteristics are greatly enhanced [5]. Nanocomposites perform better than traditional composites in terms of thermal, mechanical, electrical, and barrier qualities. They can also substantially lower flammability while preserving the transparency of the polymer matrix.

1.1.2 Nanohybrids Nanohybrids refer to materials or structures that combine two or more different nanoscale components. These components can be different forms of nanoparticles, such as metal oxides, metal, carbon-based materials, or polymers, or a combination of nanoparticles and larger structures, such as nanotubes or nanowires. The combination of different components in a nanohybrid can result in unique properties, which are different from any of the individual components alone. For example, metallic nanoparticle incorporation into a polymer matrix can result in improved electrical conductivity, while the combination of carbon nanotubes and metal nanoparticles can lead to enhanced catalytic activity [109]. Nanohybrids have a broad range of potential applications, including

1 The current scenario in nanocomposite and nanohybrid materials

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biomedical engineering, energy storage, and conversion, electronics, and catalysis. However, the nanohybrid formation requires careful consideration of the interactions between the different components and the synthesis methods used to produce them, as well as potential toxicity and environmental impact [6–8]. In comparison to traditional composites, hybrid materials offer a variety of noteworthy benefits.

1.2 Classification and application of nanocomposites Based on their matrix components, nanocomposite materials can be categorized into three classes, much like micro composites (Fig. 1.1): MMNC, (PMNC), and (CMNC).

Nanocomposite Materials

Metal Matrix Composite (MMNC)

Polymer Matrix Composite (PMNC)

Ceramic Matrix Composite (CMNC)

Fig. 1.1: Types of matrix-based nanocomposites.

1.2.1 Polymer matrix nanocomposites (PMNC) The most prevalent type is PMNC, which would have isolated nanoscale particles equally dispersed throughout a polymer. PMNCs are a type of composite material in which nanoscale particles are dispersed throughout a polymer matrix. The goal is to achieve uniform distribution of the nanoparticles within the polymer matrix, which can improve the material’s mechanical, thermal, electrical, and other properties. In an ideal PMNC, the nanoparticles are isolated and equally dispersed throughout the polymer, which enhances the material’s strength, stiffness, and toughness while also reducing weight and increasing resistance to wear and corrosion. However, achieving perfect dispersion of nanoparticles in a polymer matrix can be challenging, and the degree of dispersion can affect the material’s performance. New opportunities in micro-optics, energy conversion, electronics, and storage are made possible by functional nanocomposites with improved physical characteristics. Most of the time, the change in the desired feature and the filler load are correlated. PNCs have indeed garnered a lot of interest and attention over the past decade. This is mainly due to their potential to improve the properties of traditional polymer composites by incorporating nanoscale particles into the polymer matrix. The sol-gel technique is indeed a promising method for synthesizing polymer nanocomposites with well-dispersed nanoparticles. In this technique, a sol

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(a stable colloidal suspension of nanoparticles) is prepared from metal alkoxides, metal salts, or other precursors, which are then hydrolyzed and condensed to form a gel. The resulting gel contains a three-dimensional network of nanoparticles, which can be subsequently incorporated into a polymer matrix. One of the advantages of the sol-gel technique is that it allows for precise control over the size, shape, and distribution of the nanoparticles, as well as the ability to tailor the chemical composition of the resulting PNC. By controlling the conditions of the sol-gel process, such as the pH, temperature, and concentration of the precursors, it is possible to achieve a high degree of dispersion of the nanoparticles in the polymer matrix. The sol-gel technique can be used to prepare nanoparticles with surface functionalities that can interact with the polymer matrix, leading to improved interfacial adhesion and mechanical properties. This can be achieved by modifying the surface of the nanoparticles with functional groups that can react with the polymer matrix during the gelation process. PMNCs offer aerospace, construction, electronics, and biomedical applications [17]. However, the packaging and automotive sectors remain the largest consumers of PMNCs, accounting for around 80% of the total demand. These nanocomposite materials allow engineers and designers to optimize a product’s performance in strength, stiffness, thermal conductivity heat resistance, chemical resistance, electrical conductivity, and many other properties. These nanocomposites were first used in the automotive sector for their propensity to substitute metals with rigidity, thermal and mechanical resistance, and lower power consumption. Its use is also made possible by the fact that it can be painted with other automotive components and put through the same processes as metallic materials when manufacturing vehicles. The first company to deploy nanocomposites in automobiles was General Motors, which resulted in a mass decrease of approximately one kilogram. In the past, auto components were manufactured from polypropylene and glass fillers, which had the drawback of being out of harmony with other auto parts. The nanoseals TM, which is used in footboards, friezes, dashboards, and station wagon floors is an example of higher quality materials that can be produced by using less filler, as in the nanocomposites. They are used in the footboards of General Motors’ Astro and safari cars, Basell, Blackhawk, Automotive Plastics, Gitto Glob, and other companies, and are manufactured polyolefin nanocomposites containing, for example, polyethylene and polypropylene. Car parts, including handles, rearview mirrors, timing belts, engine covers, gas tank parts, bumpers, etc., also make use of nanocomposites, particularly nylon (polyamide)-based ones made by Honeywell, Bayer, RTP Company, UBE, Unitika, and Toyota Motors. In particular, nylon nanocomposites have been used to create films for food products and beverage packaging, as well as multilayer bottles made from polyethylene terephthalate (PET). The improved oxygen and carbon dioxide barrier properties of these materials help to extend the shelf life of food and beverages, prevent spoilage, and maintain freshness. Additionally, nylon nanocomposites can also provide better resistance to moisture, chemicals, and other environmental factors [4]. Nanocomposites are used in alcoholic beverage and soft drink bottles and the packaging of cheese and meat in Europe and the USA because they enhance packaging flexibility and

1 The current scenario in nanocomposite and nanohybrid materials

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rip resistance while also controlling humidity. Due to their desirable qualities like effective barrier function, mechanical strength, and thermal stability, bio nanocomposites have demonstrated enormous potential as a packaging material. A possible biofiller that has good UV shielding and thermal stability qualities in green bio nanocomposites is cellulose nanocrystals from sugarcane bagasse fiber [5]. Imperm is a nylon MDXD6/ clay nanocomposite made by Nanocor that is used as a barrier in carbonated drink and beer bottles, in the packaging of cheese and meat, and as an interior layer in the packaging of milk by-products and juice. PET bottles with 5% Imperm added have a shelf life extension of six months and a reduction in carbon dioxide loss of under 10%. M9TM has been developed by Mitsubishi Gas Chemical Company for use in the packaging industry. It is specifically designed for use in juice bottles, beer bottles, and multilayer films due to its excellent gas barrier properties. M9TM is a type of polyester material that contains an organic-inorganic hybrid layer, which gives it enhanced gas barrier properties compared to traditional PET materials. It has been shown to provide superior barrier performance against oxygen, carbon dioxide, and water vapor, which can help extend the shelf life of packaged products and maintain their freshness. Other examples include a polyamide 6 nanocomposite – Durethan KU2-2601 – coating juice bottles with barrier films made by Bayer and polyamide 6/polyamide nanocomposites- AEGISTM NC – developed by Honeywell Polymer –used as barriers in bottles and films. PNCs have the potential to play a significant role in the development of sustainable energy sources in the energy sector. By providing novel techniques for energy extraction from safe and affordable resources, PNCs can help improve the efficiency and sustainability of energy production. Examples are fuel cell membranes, solar panels, nuclear reactors, and capacitors. The adaptability of nanocomposites is significant in the biomedical sector, making them useful for a variety of biomedical applications. Nanocomposites can satisfy various prerequisites for implementation in medically utilized materials, including, biodegradability, biocompatibility, and mechanical attributes – specifically, tissue engineering applications in the form of a hydrogel, dental implications, control release of medicine, bone substitution, and repair because of this and the fact that they can be carefully adjusted by adding different clay concentrations. Furthermore, Novamont AS (Novara, Italy) manufactures a starch/Polyvinyl alcohol (PVA) nanocomposite that, due to its excellent mechanical qualities, potentially replaces the use of lowdensity PE films in water-soluble washing bags. Other commercial applications include cables due to low released heat rate and slow burning; the substitution of PE tubes with Foster Corporation’s polyamide 12 nanocomposites (marketed as SETTM) and Noble Polymer’s ForteTM nanocomposite for furniture and home appliances (Tab. 1.1). Bayer AG and Exaltec are both companies that produce PNC materials for various applications, including automotive. Bayer’s polypropylene (PP) nanocomposites are expected to replace pure PP in vehicle components, such as interior and exterior trim, due to their improved mechanical properties, such as increased stiffness, strength, and impact resistance. These materials are made by incorporating small amounts of nanoscale particles, such as clay or silica, into the PP matrix, which helps reinforce

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Tab. 1.1: Polymer matrix nanocomposites applications. Supplier

Base resin

Reinforcement

Applications

Citation

Southern clay product, Basell Polyolefins, and General Motors (GM) (R&D)facility in Warren, Mich.

Thermoplastic Polyolefin

Organo-clay hybrids

For the  General Motors Safari and Astro vans, auto body-side claddings are lightweight, durable, and resistant to impact and UV Radiation, and step assist (lightweight)

Japan’s Ube Industries

Nylon/ copolymer and Nylon  (NCH)

Organo-clay hybrids

Toyota Motors’ timing belt cover, barrier films, and structural Applications

[]

Bayer AG, a German multinational and Life sciences company (Durethan LDPU- and LPDU -)

Nylon or polycaprolactam

Organo-clay hybrids

Transparent barrier film packaging

[]

Clariant Technologies

Polypropylene

Organo-clay hybrids

Packaging materials

[]

Honeywell (Aegis)

Nylon or polycaprolactam

Organo-clay hybrids

Bottles and film

[]

Kabelwerk Eupenof Belgium

Copolymer of ethylene vinyl acetate

Organo-clay hybrids

Cable and wear

[]

Imperm Nanocor

Nylon or polycaprolactam

Organo-clay hybrids

PET beer bottles, molding

[]

RTP Imagineering plastics

Nylon or polycaprolactam

Organo-clay hybrids

For many purposes

[]

[]

the material and improve its overall performance. Exaltec’s PC (polycarbonate) nanocomposites, on the other hand, are projected to be used in automobile glasses due to their improved abrasion resistance without compromising optical clarity. These materials are made by incorporating nanoscale particles, such as silicon dioxide, into the PC matrix, which helps improve its hardness and scratch resistance. The application of PNCs in the automotive industry has become increasingly popular in recent years

1 The current scenario in nanocomposite and nanohybrid materials

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due to their ability to improve performance, reduce weight, and increase efficiency. By incorporating nanoscale particles into polymer matrices, companies like Bayer and Exaltec are able to create materials with superior mechanical, thermal, and optical properties, which can help meet the demanding requirements of the automotive industry. Barrier applications, which can also be used to maintain film transparency and extend food shelf life, are another burgeoning industry. As an illustration, beer can have a shelf life of 28.5 weeks when an Imperm nanocomposite is used in a pet bottle. In addition, another potential use for nanopigments is as a low-toxicity substitute for palladium and cadmium pigments. Polymer/clay nanocomposite applications in the distant future will be determined by research findings, industry, existing markets, and the degree of nanocomposite property advancement. Additionally, the necessity of their large-scale use, the required investment capital, manufacturing costs, and profitability should be considered [9].

1.2.2 Metal matrix nanocomposites (MMNC) MMNCs are a type of composite materials that is similar to metal matrix composites (MMCs) but with the addition of nanoscale particles as the reinforcement phase. The nanoscale particles are typically ceramic or metallic and are dispersed throughout the metal matrix in a controlled manner. A fibrous or particle phase is one of two phases that often coexist in a metallic matrix. Cutting tools and oil drilling inserts are composed of cobalt (Co) particulate and tungsten carbide (WC), and composites formed by reinforcing an A1 matrix with SiC particles are used in automotive, aerospace applications, thermal management, and other fields. These nanocomposite MMNCs are constructed from nanoscale reinforcing materials and a ductile alloy or metal matrix. The ductility and toughness, as well as high modulus and strength applications, of these materials are only a few of their ceramic and metal qualities [9, 10]. Due to this, these nanocomposites are ideal for producing materials with high service temperatures and shear/compression strengths. They have enormous potential for use in many sectors, such as the production of structural materials and the automotive and aerospace sectors (Tab. 1.2) [9]. The compound annual growth rate (CAGR) of the global metal matrix composite market was 6.34% from 2015 to 2020, with the market reaching a size of approximately US$455.34 million in 2020. The market is expected to continue growing, with a projected CAGR of 7.38% from 2020 to 2025, reaching a size of US$649.33 million. From 2025 to 2030, the market is projected to grow at a CAGR of 6.87%, reaching a size of US$905.15 million. This growth is attributed to several factors, including the increasing demand for lightweight and high-performance materials in various industries, such as aerospace, automotive, and electronics [20]. The superior mechanical properties and other performance characteristics of MMCs make them an attractive alternative to traditional materials in these applications. Additionally, ongoing research and de-

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Tab. 1.2: Metal matrix nanocomposites applications. Metal nanocomposites

Applications

Citation

Ni/TiO

Superior anticorrosion performance, and high photo electrochemical activity

[]

Al/AlO

Microelectronic industry

[]

Al/AlN

Microelectronic industry

[]

Fe/FeC/FeB

Structural materials

[]

Au/Ag

Microelectronics, optical devices, light energy conversion

[]

Fe/TiN, Fe/MgO

Catalysts, magnetic devices

[]

velopment efforts are focused on improving the manufacturing processes and performance of MMCs, which is expected to further increase their adoption and expand their range of applications [19].

1.2.3 Ceramic matrix nanocomposites (CMNC) The aluminum oxide (Al2O3)/silicon carbide (SiC) combination in particular has several potential applications for ceramic matrix nanocomposites (CMNC). All of the research has shown that the characteristics of the Al2O3 matrix are significantly improved by the inclusion of a small volume fraction (10%) of SiC with a certain size. In certain studies, the crack-bridging function of nanoscale reinforcements has been employed to explain this toughening phenomenon. Incorporating high-strength nanofibers, such as carbon nanotubes or graphene, into ceramic matrices can create novel nanocomposites with improved mechanical properties, including increased strength, toughness, and resistance to failure compared to traditional ceramic materials. Ceramics are inherently brittle and prone to failure under mechanical stress, which limits their use in many applications. By incorporating nanofibers into the ceramic matrix, the resulting nanocomposite can withstand greater forces and stresses without fracturing, making it a more attractive material for various applications. The high surface area of the nanofibers also provides increased contact area between the reinforcement phase and the ceramic matrix, resulting in enhanced load transfer and improved mechanical properties. Additionally, the nanofibers can act as crack arresters, slowing the propagation of cracks within the ceramic material and preventing

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catastrophic failure. Applications for CMNCs include aerospace components, ballistic armor, cutting tools, and biomedical implants, among others. Ongoing research and development efforts are focused on improving the manufacturing processes and performance of these materials for various applications. Several methods have been documented for creating CMNCs –spray pyrolysis, the traditional powder approach, CVD and PVD vapor methods, and the polymer precursor pathway. Chemical methods are commonly used to produce CMNCs, and the sol-gel process, template synthesis, and colloidal and precipitation techniques are among the most frequently used methods. The sol-gel process involves the synthesis of a sol, which is a stable colloidal suspension of nanoparticles, followed by the gelation of the sol to form a solid matrix. The sol is typically prepared by hydrolyzing metal alkoxides in a suitable solvent, followed by condensation to form a three-dimensional network of metaloxygen bonds. The resulting gel can be dried and sintered to produce a CMNC. Template synthesis involves the use of a sacrificial template, such as a polymer or biological material, to create a porous ceramic matrix. The template is first coated with a ceramic precursor, which is then pyrolyzed to form the ceramic matrix. The template is subsequently removed, leaving behind a porous ceramic matrix that can be filled with nanofibers or other reinforcing materials. Colloidal and precipitation techniques involve the synthesis of nanoparticles in a solution, followed by their incorporation into a ceramic matrix. Colloidal techniques involve the stabilization of nanoparticles in a solution through the use of surfactants or other stabilizing agents, while precipitation techniques involve the precipitation of nanoparticles from a solution by changing its chemical composition or temperature. Controlling the various parameters of these chemical methods, such as solvent type, time, water/metal ratio, pH, and precursor, can allow for precise control of the final material’s structure and chemical characteristics, including the distribution of nanofibers within the ceramic matrix. This control is essential for optimizing the mechanical, thermal, and electrical properties of the resulting nanocomposite material for specific applications [11]. Dr. Koichi Niihara is widely regarded as the pioneer of CMNCs, having first demonstrated their potential in the early 1980s. In particular, his work on the Al2O3/SiC complex was groundbreaking and demonstrated the significant improvements in mechanical properties that could be achieved through the incorporation of nanofibers into a ceramic matrix [18]. Niihara’s work showed that the addition of SiC nanofibers to an Al2O3 matrix could significantly improve the toughness and strength of the resulting ceramic matrix nanocomposite. The SiC nanofibers acted as reinforcing elements within the ceramic matrix, effectively bridging the cracks and preventing their propagation. This resulted in a material with much higher fracture toughness than conventional ceramic materials [10, 11]. Many subsequent studies have confirmed these findings, showing that the addition of small volume fractions of suitable-sized SiC particles (i.e. 10%) can significantly enhance the strength and toughness of ceramic matrix nanocomposites. The crack-bridging function of the nano-sized reinforcements has been

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proposed as a mechanism for this toughening effect [12]. Ceramic materials are known for their excellent hardness and high temperature stability, but they are also brittle and prone to rapid failure under stress. Incorporating high-strength nanofibers, such as SiC, carbon nanotubes, or alumina fibers, into the ceramic matrix can improve its mechanical properties, such as toughness, strength, and wear resistance. These nanofibers act as reinforcing elements within the ceramic matrix, effectively bridging the cracks and preventing their propagation, resulting in a material with much higher fracture toughness than conventional ceramic materials [13]. According to a report by Markets and Markets, the global ceramic matrix composites market was valued at US$8.7 billion in 2020 and is projected to reach US$23.3 billion by 2030, at a CAGR of 10.6% from 2020 to 2030 [14]. Table 1.3 represents the various types of ceramic nanocomposites along with its application. Tab. 1.3: Ceramic matrix nanocomposite applications. Ceramic nanocomposite

Applications

Citation

FeO/SiO/C

It acts as a high-performance Fentonlike catalyst for the discoloration of methylene blue, wastewater treatment, and removal of organic pollutants from water systems

[, ]

SiO /Co

Sensors, optics, and catalysis

[]

ZnO/Co

Study of interparticle interactions (optical femtosecond), a field effect transistor is used

[]

SiN (silicon nitride)/SiC

Materials for structures

[]

PbTiO(perovskite tetragonal)/PbZrO

Micro-electromechanical, microelectronic systems

[]

TiO /FeO

Magnetic-based recording media with high density, catalysts, and ferrofluids

[]

AlO/LnAlO, AlO/NdAlO

Optical amplifiers, phosphors, solidstate laser media

[]

AlO /Ni

For engineering parts

[]

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1.2.4 Future prospects of nanocomposites 1.2.4.1 Agricultural applications Polyvinyl alcohol-modified PEDOT-PSS{poly(3,4-ethylene-dioxythiophene)-poly(styrene sulfonate)}sensors are advantageous due to their low cost, straightforward construction method, outstanding sensitivity, good repeatability, and reproducibility (titanium dioxide). High- performance sensors made of TiO2 nanocomposites may be advantageous for agricultural applications in quantifying soil moisture content and relative humidity [130]. As a plant growth stimulant, carbon nanofibers (CNF) are used because they increase a plant’s capacity to absorb water, expedite germination, and are harmless even at high dosages. Acylated-homoserine lactones (AHLs) are signaling molecules used by many gram-negative bacteria for quorum sensing, which is a mechanism of intercellular communication that regulates gene expression in response to changes in cell density. In their study, Gupta et al. demonstrated that CNFs can be used as a carrier to transport AHLs to chickpea plants, which resulted in the upregulation of genes related to defense mechanisms and increased resistance to fungal infections. The CNFs acted as physical support for the AHLs, protecting them from degradation and facilitating their uptake by the plant cells [131]. The polymer-bi-metal-carbon (PBMC) composite developed by Kumar et al. consists of bimetallic (Cu/Zn) nanoparticles dispersed within CNFs, which are then embedded within polyvinyl alcohol (PVA)-starch composite. The incorporation of the bimetallic nanoparticles enhances the electrocatalytic activity of the composite, making it suitable for use in fuel cells and other electrochemical applications. The PVA-starch composite serves as a binder for the CNFs, providing mechanical stability to the overall structure. The resulting PBMC composite exhibits good electrical conductivity, mechanical strength, and electrocatalytic activity, making it a promising material for various applications in energy storage and conversion [133]. Using the created cationic polymeric composite as fertilizer to accelerate plant development is an efficient application for it. Micronutrient (Cu/Zn) releases from CNFs and regulated polymeric composite releases: The study also revealed that the encapsulation of polymers in PBMC results in a comparatively sluggish release of micronutrients when compared to CNFs. Furthermore, The PBMC-based formulation developed by Kumar et al. using bimetallic (Cu/Zn) nanoparticle-dispersed CNFs enclosed in a PVA-starch composite can be used as a micronutrient in agriculture. The Cu/Zn-CNFs can be effectively delivered to plants from the roots to the shoots and leaves, thus providing an alternative and sustainable method for plant nutrient delivery (Fig. 1.2). The biodegradable nature of the PBMC-based formulation also makes it environmentally friendly [132]. Nanocomposites can be used to develop animal feed that is more easily digestible and provides better nutrition. For example, nanocellulose can be used as a binder in animal feed pellets, improving their digestibility and reducing waste.

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Fig. 1.2: A conceptual illustration of the fabrication of the Cu/Zn-CNF-dispersed polymeric composite and its use in agriculture. Reprinted (Kumar et al.) with permission; copyright 2018 Springer Science Business Media, LLC, a division of Springer Nature [132].

1.2.4.2 Smart fertilizers Research is focusing more on safe and effective fertilizers made from bio-based resources (also known as organic or greener fertilizers) that offer a comparable or higher crop yield than inorganic fertilizers, improve the mitigation of environmental stressors, and advance sustainable development and ethical agricultural practices. These fertilizers are considered to be more environmentally friendly and sustainable than traditional inorganic fertilizers, which have been associated with various negative impacts on the environment, such as eutrophication, soil degradation, and water pollution. To address these issues, researchers are exploring the use of intelligent agrochemical systems, such as slow and controlled-release fertilizer systems (CRFs), which can provide a more precise and targeted delivery of nutrients to crops, reducing the potential for runoff and waste.

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CRFs can release nutrients gradually over an extended period, based on the needs of the plant, and are designed to reduce the leaching of nutrients into the environment, improving the efficiency of nutrient uptake by crops while minimizing environmental impacts. Additionally, CRFs can enhance soil fertility, improve soil structure, and reduce the need for frequent fertilization. The development of safe and effective bio-based fertilizers and intelligent agrochemical systems holds enormous potential in advancing sustainable agriculture and mitigating environmental stressors associated with traditional fertilizers. However, it is important to conduct rigorous research to evaluate the safety, efficacy, and environmental impact of these systems before their widespread adoption [139].

1.2.4.3 Medical applications NiMoO4/chitosan nanocomposites have been investigated for various biomedical applications, including electrochemical sensing, drug delivery, and antibacterial activity. In the case of electrochemical sensing, a study reported by Saber et al. showed that the NiMoO4/chitosan nanocomposite exhibited high sensitivity and selectivity in the detection of the antihypertensive drug amlodipine in both pharmaceutical and serum samples. In drug delivery applications, NiMoO4/chitosan nanocomposites have been explored as potential carriers for cancer drugs, such as doxorubicin. Studies have shown that nanocomposites can improve the drug’s bioavailability, enhance its therapeutic efficacy, and reduce its toxicity to healthy cells. Furthermore, the antibacterial activity of NiMoO4/chitosan nanocomposites has been investigated for potential wound-healing applications. The nanocomposites exhibited strong antibacterial activity against both gram-positive and gram-negative bacteria, making them promising candidates for use in wound dressings and other medical applications [133]. In recent years, electrochemical immunosensors based on nanocomposites have shown promising results for the early detection of prostate cancer. These sensors typically involve the immobilization of specific antibodies onto a surface, such as gold nanoparticles, that have been functionalized with a chitosan biopolymer nanocomposite film [23]. The detection of prostate cancer biomarkers is then achieved by measuring changes in the electrical properties of the nanocomposite film due to the binding of the target biomolecule. This approach has the potential to improve the sensitivity and specificity of prostate cancer diagnostics while also reducing the cost and time required for testing [134].

1.2.4.4 Food packaging and bioactive systems Bio-based materials have also been used as nanocomposites in food packaging and bioactive systems. Nanocomposites are materials that consist of a matrix material (such as starch, cellulose, or chitosan) and nanoparticles (such as clay minerals or metal oxides) that are added to improve the material’s mechanical, barrier, or antimi-

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crobial properties. In food packaging, nanocomposites can be used to improve the barrier properties of the packaging, which can help to extend the shelf life of the product. For example, nanoclay particles can be added to starch-based films to improve their water vapor barrier properties, while metal oxide nanoparticles can be added to chitosan films to enhance their antimicrobial properties. In addition to their use in food packaging, bio-based nanocomposites can also be used in bioactive systems. Bioactive systems are materials that have the ability to interact with biological systems in a specific way, such as by releasing active compounds or by promoting cellular responses. In the context of food, bioactive systems can be used to deliver nutrients or functional compounds (such as antioxidants or antimicrobial agents) to enhance the nutritional value or safety of the product. Bio-based nanocomposites can be used to create bioactive systems by incorporating bioactive compounds (such as plant extracts or essential oils) into the matrix material, which can then be released in a controlled manner over time. For example, chitosan-based nanocomposites can be used to deliver antimicrobial compounds to food products to inhibit the growth of bacteria or fungi. The use of bio-based nanocomposites in food packaging and bioactive systems offers many potential benefits, including improved food safety, enhanced shelf life, and increased nutritional value. Moreover, In the case of gum arabic nanocomposites, the nanoparticles are typically derived from materials such as clay minerals, titanium dioxide, or silver nanoparticles. When incorporated into the gum arabic matrix, these nanoparticles can help improve the mechanical strength and barrier properties of the coating, as well as provide additional functionality such as antimicrobial activity. Several studies have demonstrated the potential of gum arabic nanocomposite coatings for improving the postharvest quality of fruits and vegetables. For example, a study on strawberries found that a gum arabic-titanium dioxide nanocomposite coating significantly reduced weight loss and maintained the overall quality of the fruit during storage. Another study on apples found that a gum arabic-silver nanoparticle coating was effective in reducing microbial growth and maintaining fruit quality during storage. There have been several studies that have demonstrated the potential of aloe vera gel (AVG) as an edible coating for fruit preservation. One of the key advantages of using AVG as a coating material is its excellent antioxidative and antibacterial properties, which can help to extend the shelf life of fruits and prevent spoilage. AVG is a bio-based nanocomposite system that is derived from the inner leaf gel of the aloe vera plant. It contains a wide range of bioactive compounds, including vitamins, minerals, enzymes, and polysaccharides, which have been shown to have potent antioxidant and antibacterial effects. When applied as a coating on fruits, AVG can help to prevent the growth of spoilage-causing microorganisms and reduce the oxidation of fruits, which can lead to discoloration and loss of texture. Additionally, AVG coatings can help maintain the moisture content of fruits, which can help prevent shrinkage and maintain their overall quality. It was demonstrated that AVG retains the color of

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the coat for any significant period, keeps the vegetable firm, and retains essential vitamins, and enhances the ripening delay [140–143].

1.3 Classification and applications of nanohybrids 1.3.1 Carbon-carbon nanohybrids (CCNHs) The three key carbon nanostructures – 0-D(zero-dimensional) fullerenes, 1-D Carbon nanotubes (SWNTs and MWNTs), 2-D graphene, and carbon nanohorns – can be combined to produce carbon-based NHs (CNHs). CNHs and fullerenes (cage-like structures) with open ends provide special benefits for the synthesis of endohedral nanohybrids in addition to enabling the fabrication of their exohedral forms [24]. Nano-peapods are a class of nanocomposite materials consisting of carbon nanotubes (CNTs) or CNHs filled with pure or functionalized graphene or fullerene through various techniques such as cavity-filling, heat annealing, or in situ growth from vapor-based deposition procedures. The term “nano-peapods” comes from the structure of the composite material, which resembles a peapod with the CNT or CNH serving as the outer shell and the graphene or fullerene filling the interior cavity. Nano-peapods have attracted significant attention due to their unique structural and electronic properties, as well as their potential applications in various fields such as electronics, energy storage, and biomedicine. For example, the graphene or fullerene filling in the CNT or CNH can improve the mechanical strength and conductivity of the material, while also providing additional functionality such as catalytic activity or drug delivery capabilities [25]. The carbon nano-onion is a multilayered hybrid fullerene structure that can be synthesized using similar techniques as the water-assisted electric arc method. This method involves the use of a high-power electric arc to vaporize graphite electrodes in the presence of water vapor or other gases, resulting in the formation of carbon nanomaterials such as carbon nanotubes, graphene, and fullerenes [118]. The carbon nano-onion is a unique structure that consists of concentric layers of fullerenes or fullerene-like structures, with each layer separated by a thin graphitic layer. These layers can be thought of as “onion shells,” hence the name carbon nano-onion [26–28]. In contrast to the synthesis of carbon nano-onions, the exohedral conjugation of CNTs, graphene, and fullerenes [29] involves the functionalization of the outer surface of these materials with polymers, conjugating molecules, or covalent functionalities [30]. This functionalization can alter the electronic and structural properties of the carbon nanomaterials and regulate the ensemble process, which can be useful for applications such as sensing, catalysis, and drug delivery. Examples of this derivatization include the attachment of chemically active molecules [32], polymeric assemblies [29, 31], CNTs, and graphene oxidation to attach polar hydroxyl or carboxyl surface groups (-OH or -COOH) [33]. For example, Fullerene-CNT NHs are created by refluxing fullerenes functionalized with porphyrin derivatives with acid-treated CNT-

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COOH solutions as a consequence of an interaction between the amine group of the porphyrin molecule and the carboxyl functionality of the CNT. Most often, efficient exohedral bonding between fullerene and CNT [21] (nanobuds) or graphene and CNTs [30] is achieved using catalytic reaction procedures using vapor-phase reactant molecules. These graphitic nanomaterials may also produce NH-based thin film multilayer assemblies through non-covalent and electrostatic interactions with the aid of spin-casting, drop-casting, and dipping processes [33, 35, 36]. The multifunctional and enhanced qualities originating from individual species have provided the carbonaceous nanomaterials (CNMs) with the utility of hybridization. CNTs have distinctive optical, electrical, chargecarrying, and mechanical capabilities, compared to graphene, which has high electrical conductivity, mechanical stability, and a substantial reactive surface area. Fullerenes exhibit high photoactivity and electron density [34]. It can therefore improve organic photovoltaics [37] and optical limiting and switching, optoelectronic devices [38], singlet excited state quenching [32], charge transfer electron-hole shuttling [39], field effect transistors [39], bandgap tenability [24], nonlinear optical properties [38], etc. by improving photoinduced electricity production. Hybridized graphene, which has a significantly high surface area, conductivity, transmittance, and low physical thickness due to its conjugation with CNTs or fullerenes, can serve as a leading candidate for photovoltaic and optoelectronic device’s transparent conducting films [40, 41]. These alterations also allow for a variety of applications, including structural health monitoring, biomolecular sensing, electrochemical, and many more applications [42, 43].

1.3.2 Carbon-metal nanohybrids (CMNHs) CNTs, fullerenes, and graphene are incorporated with various metal oxide or metallic nanomaterials in the carbon-metal nanohybrid (CMNH) production procedures [44]. CMNHs comprise assemblies with a range of metallic nanomaterials, including semiconducting quantum dots (CdTe, CdSe, etc.), metal oxide nanomaterials (ZnO, SiO2, TiO2, CuO, Fe3O4, etc.), lanthanide series metals, noble metals, and ligand-based metallic (ferrocene). Four major mechanisms can be used to manufacture CMNHs: (i) Metallic nanomaterials (MNMs) are deposited through vapor deposition, arc discharge, wet chemical, and thermal annealing methods into the interior cavities of CNTs and fullerenes [45–48]. (ii) Embedding MNMs on CNT surfaces that have been functionalized with porphyrin derivatives, pyrene, and other coupling molecules [49, 50]. Applying aerosol, solgel, hydrothermal, and hydrothermal processes to decorate CNM surfaces with MNMs [51–53]. (iii) Electrochemical, electroless deposition, and redox processes were implemented to grow MNMs in situ on CNM surfaces. By integrating metallic and graphitic nanostructures, distinctive and synergistic electrical, mechanical, sensing ability, optical, catalytic, and magnetic properties are produced with potential applica-

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tions in many fields; for example solar cells and organic photovoltaics and, proton exchange fuel cells, optoelectronics, supercapacitors and batteries, gas, and chemical sensing, environmental pollution monitoring, biomedical imaging, mitigation, etc. [54–67]. CNTs and graphene with large active surface areas show mechanical and thermal stability, which leads to the formation of Li-ion storage devices with high capacity, efficiency, and durability [52]. Similarly, when TiO2, Ag, or ZnO are conjugated with CNMs, their antibacterial activity is improved, facilitating them to be used in the treatment of water and purifying applications [67]. Utilizing the improved sorption and electrical sensitivity of CMNHs, better protein sensors, gas, or chemicals (trinitrotoluene, H2O2, etc.) are being developed [64]. The cornerstone of MRI contrast agent research is endohedral metallofullerenes, which have the potential to be used as MRI contrast agents with incredibly high water relativities [68, 69].

1.3.3 Metal-metal nanohybrids (MMNHs) Metal-metal nanohybrids (MMNHs) are synthesized when metal oxides and metals are conjugated to produce multi-metallic ensembles. Metals can be classified according to their functions, such as magnetic (Fe2O3, Fe3O4), plasmonic (Pt, Au, Ag), quantum dots (ZnO, CdSe, CdTe, PbS, ZnS,), semiconducting oxides (TiO2), etc. [70–72]. Conjugated metallic NMs are constructed using several synthesis techniques, which are determined by the desired hybrid structures, properties, and applications. Among them, wet chemical reactions are the most common synthesis strategy involving the thermal breakdown or reduction of metal salts. Wet chemical processes come in a variety of forms, such as polyol techniques, ion implantation, photochemical deposition, hydrothermal, solvothermal, electroless plating, epitaxial growth sol-gel, etc. [22, 73–80]. Processes involving vapor-gas phases, such as plasma-assisted deposition [82] and flame aerosol [81], are also often used. Co-reduction [83] or sequential reduction [74] can produce core-shell-based nanostructures, in which MNMs that have already been produced can act as a “seed” for later production of a different kind of nanomaterial with a different chemical composition. To achieve patterned growth, optical lithography is also used in combination with conventional techniques [84]. Hollow spherical [85], porous [86], or tubular [87] forms can be produced via template-based growth techniques. However, the oil-water interface, inorganic silica, polymer, or block-co-polymer matrices are used in matrix-bound procedures, where NHs are formed using coprecipitation, emulsification, ion implantation, and reverse micellization processes [79, 88–90]. Occasionally, inorganic [91] or organic [92] linkers or spacers can be used to separate core-shell metallic layers from one another. Furthermore, in “green” or “biogenic” synthesis techniques, natural extracts act as reducing agents, capping agents, or solvents [93]. MMNHs can be used in industries, including photovoltaics, catalysis, solar cells, biomedical engineering, nanotherapeutics,

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and bactericidal applications. This is because of their synergistic qualities [77, 94–97]. Coaxial Ag-TiO2 core-shell nanowire arrays with high specific surface area and effective electron transport can boost the efficiency of collecting the electron to be used in dyesensitized solar cells [77]. Plasmonic, magnetic, and semiconducting metal NM-based MMNHs have emerged being implemented in bio-applications [94], These innovations include the improvement of contrast in MRI for identifying pathogens and diseases, photothermal ablation of these cells by near-IR irradiation, and separation of cancer cells from cell mixtures [98, 99]. The plasmonic characteristics of Ag and Au are coupled to provide very effective surface-enhanced Raman scattering (SERS) and localized surface plasmon resonance for the detection of disease- specific proteins (SPR) [73]. The photoluminescent properties of semiconducting quantum dots are reported to be enhanced when combined with plasmonic or magnetic particles used in fluorescence microscopy or bio-imaging, such as Au-CdSe-ZnS or Fe3O4 CdS [100, 101]. Due to their bandgap modulation, superior charged separation, and charge transfer processes, they are excellent candidates for the degradation of organic pollutants [86] and the inactivation of bacteria when exposed to UV or visible light. It has also been demonstrated that combining TiO2, ZnO and Ag with other MNMs can improve their photocatalytic activities [97]. The environmental importance of MMNHs is increased by these numerous applications, especially in biomedicine.

1.3.4 Coated nanohybrids with organic molecules (OMCNHs) A substantial volume of literature classifies nanomaterials covered with biomolecules, organic molecules, biomolecules, or polymers as nanohybrids, whether they are metallic, carbonaceous, or polymeric. The term “nanohybrids” can refer to a wide range of materials that combine different types of nanomaterials or nanoscale structures to create new composite materials with unique properties. In addition to the carbonbased nanohybrids we previously discussed, layer-by-layer hierarchical thin films are another type of nanohybrid that has been extensively studied. OMCNH synthesis techniques discussed in the literature include the organic molecules physisorption, [102] electrochemical immobilization of DNA molecules, protein, or enzyme, polymer grafting from or grafting to NM surfaces, [103] emulsification, and ion exchange [104]. These coated NMs are being studied for use in nanoelectronics, photovoltaics, chemical and biological sensing, controlled drug delivery, bio-imaging, and cancer treatment [102, 105–108]. Porphyrin surface functionalization is applied to CNMs [102]. Enhanced efficiency of charge transfer in photovoltaic and dye-sensitized solar cells by employing phthalocyanine and various other substances. Similar to this, organic polymers like poly (vinyl pyrrolidone) (PVP) and polyethylene glycol (PEG) [110] are grafted onto or coated on plasmonic or magnetic particles to increase their solubility for improved bio-imaging, drug administration, or sensing. Additionally, metallic NMs are conjugated with organic fluorophores to improve contrast and tagging [106]. The

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majority of these compounds appear to be simply coated-NMs for environmental reasons, therefore proper risk estimation may not necessitate a thorough and independent environmental review. Physiosorbed coatings have received attention in established environmental fate and toxicological literature. To improve the NMs’ dispersion in a chosen solvent, substances like PVP, citrate, gum arabic, PEG, copolymers, etc. are frequently adsorbed onto them. The effects of these substances on the environment have also been researched [111–114]. However, more sophisticated supramolecules or heterocyclic structures, such as porphyrins, that are covalently attached to the NM surfaces are being used to modify the surfaces of NMs recently [115–117]. Furthermore, organic molecules or polymers on the NM surface have different conformations, which are known to have an impact on their destiny, transformation, and toxicity [119]. It is crucial to systematically evaluate the nano-EHS behavior of these intricate chemically coated NHs.

1.4 Conclusion and future prospects of nanohybrids A recent study focused on evaluating the potential use of Fe-Au composite NHs as contrast agents for Magnetomotive Optical Coherence Tomography (MMOCT) in an animal model. While the study may have reported on the efficacy of the contrast agents, it did not provide any information on adverse effects on the animal model used. It is important to note that the use of nanoparticles in biomedical applications, including contrast agents, is a rapidly developing field, and the potential risks and adverse effects of these materials are still being studied. Some nanoparticles have been shown to be toxic to cells and organisms, while others have been found to be biocompatible and safe for use. To ensure the safety and efficacy of nanoparticles in biomedical applications, it is essential to conduct rigorous studies on their potential adverse effects, including their impact on cellular and organ function, immune response, and long-term toxicity. It is also important to follow appropriate guidelines and regulations for the use of nanoparticles in animal studies and clinical trials to ensure their safe and ethical use [135]. On the other hand, studies are highlighting the negative impacts of nanohybrid materials as well. Chen et al. (2020) evaluated the toxicity of mesoporous silica/Ag NHs on the eye using a rat animal model. The results of this study showed that even at safe dosages, the NH material caused adverse effects such as dry eye and corneal damage. It is important to note that the toxicity of NH materials can be influenced by various factors, such as the size, shape, surface chemistry, and concentration of the nanoparticles. Additionally, the toxicity of these materials can vary depending on the route of administration, exposure time, and the target organ or tissue. Therefore, it is essential to conduct rigorous toxicity studies on NH materials, including in vitro and in vivo evaluations, to understand their potential adverse effects and develop appropriate safety guidelines and regulations for their use in biomedical applications. It is also important to consider the

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potential risks and benefits of NH materials and weigh them carefully before their use in clinical applications. They advised that these negative impacts could be reduced by fetal bovine serum (FBS) treatment [136]. Magnevist (Gd-DTPA) and Dotarem (Gd-DOTA) are examples of T1 contrast agents [137, 138].

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[128] Wang R, Liu X, Wu R, Yu B, Li H, Zhang X, Xie J, Yang ST. Fe3O4/SiO2/C nanocomposite as a highperformance Fenton-like catalyst in a neutral environment. RSC Adv 2016, 6(11), 8594–8600. https://doi.org/10.1039/c5ra22890e. [129] Sales L, Robles-Dutenhefner P, Nunes D, Mohallem N, Gusevskaya E, Sousa E. Characterization and catalytic activity studies of sol–gel Co–SiO2 nanocomposites. Mater Charact Mar. 2003, 50(2–3), 95–99. https://doi.org/10.1016/s1044-5803(03)00073-1. [130] Beecroft LL, Ober CK. Nanocomposite materials for optical applications. Chem Mater 1997, 9, 1302–1317. [131] Khasim S, Pasha A, Badi N, et al. PVA treated PEDOT-PSS: TiO2 nanocomposite based highperformance sensors towards detection of relative humidity and soil moisture content for agricultural applications. J Polym Environ 2021, 29, 612–623. https://doi.org/10.1007/s10924-020-01905-6. [132] Gupta GS, Kumar A, Verma N. Bacterial homoserine lactones as a nanocomposite fertilizer and defense regulator for chickpeas. Nanotechnol Environ Sci 2019, 6, 1246–1258. [133] Kumar R, Ashfaq M, Verma N. Synthesis of novel PVA–starch formulation-supported Cu–Zn nanoparticle carrying carbon nanofibers as a nano fertilizer: Controlled release of micronutrients. J Mater Sci 2018, 53(10), 7150–7164. [134] Lou BS, Rajaji U, Chen SM, Chen TW. A simple sonochemical- assisted synthesis of NiMoO4/chitosan nanocomposite for electrochemical sensing of amlodipine in pharmaceutical and serum samples. Ultrason Sonochem Jun. 2020, 64, 104827. https://doi.org/10.1016/j.ultsonch.2019.104827. [135] Suresh L, Brahman PK, Reddy KR, B JS. Development of an electrochemical immunosensor based on gold nanoparticles incorporated chitosan biopolymer nanocomposite film for the detection of prostate cancer using PSA as a biomarker. Enzyme Microb Technol May 2018, 112, 43–51. https://doi.org/10.1016/j.enzmictec.2017.10.009. [136] Indoliya A, Dhar D, Mohan M, Poddar R. J Magn Magn Mater 2020, 514, 167211. [137] Chen X, Zhu S, Hu X, Sun D, Yang J, Yang C, Wu W, Li Y, Gu X, Li M, Liu B, Ge L, Gu Z, Xu H. Nanoscale 2020, 12, 13637–13653. [138] Affram K, Smith T, Helsper S, Rosenberg JT, Han B, Trevino J, Agyare E. Cancer Nanotechnol 2020, 11, 5. [139] Dai Y, Wu C, Wang S, Li Q, Zhang M, Li J, Xu K. Nanomedicine 2018, 14, 547–555. [140] Wang C, Song S, Yang Z, Liu Y, He Z, Zhou C, et al. Hydrophobic modification of castor oil-based polyurethane coated fertilizer to improve the controlled release of nutrients with polysiloxane and halloysite. Prog Org Coat 2022, 165, 106756. 10.1016/j.porgcoat.2022.106756. [141] Ates B, Koytepe S, Ulu A, Gurses C, Thakur VK. Chemistry, structures, and advanced applications of nanocomposites from biorenewable resources. Chem Rev 2020, 120(17), 9304–9362. 10.1021/acs. chemrev.9b00553. [142] Salehi F. Edible coating of fruits and vegetables using natural gums: A review. Int J Fruit Sci 2020, 20 (S2), S570–89. 10.1080/15538362.2020.1746730. [143] Saleem MS, Ejaz S, Anjum MA, Nawaz A, Naz S, Hussain S, et al. Postharvest application of gum arabic edible coating delays ripening and maintains the quality of persimmon fruits during storage. J Food Process Preserv 2020, 44(8), 14583. 10.1111/jfpp.14583.

Akshay C. Jadhav✶, Bhagyashri N. Annaldewar, Nilesh C. Jadhav

2 A current perspective on nanocomposite and nanohybrid material: developments and trends Abstract: The increasing demand for nanostructured materials with original chemicalphysical and morphological properties has given rise to nanocomposites and nanohybrid materials. These materials consist of organic and inorganic components interfaced at the nanoscale. This structure allows its recognition in materials science due to its extraordinary mechanical and chemical properties and multifunctional nature. Hybrid nanomaterials and nanocomposites are both able to synergistically combine the peculiar physicochemical properties of their components and give rise to collective properties due to their interaction at the nanoscale. Several parameters, including composition, concentration, morphology, etc., can be suitably modified to control the properties of nanohybrids and nanocomposites and the different applications for which they can be designed. The distinctive properties of nanocomposite materials involve significantly improved mechanical properties, barrier properties, weight reduction, and improved, long-lasting performance in terms of heat, wear, and scratchresistance. Developing nanocomposite and nanohybrid materials attracts keen interest in various industrial applications. The nanocomposites generally exhibit a 45% increase in hardness and a 70% increase in Young’s modulus compared to pure polymer matrix. Similarly, research shows that the tensile strength and strain at break of the composites shows increase by 35% and 40%, respectively. In addition, nanoscale components improved the thermal stability of the composites, with an increase in the onset degradation temperature, compared to the pure polymer matrix. This chapter aims to provide an overview and the current scenario of hybrid nanocomposites and nanohybrids, focusing on various potential applications of this fascinating class of materials. Keywords: Nanocomposites, nanohybrid, nanomaterials, polymers, matrix

✶

Corresponding author: Akshay C. Jadhav, Department of Fibres and Textile Processing Technology, Institute of Chemical Technology, University Under Section-3 of UGC Act 1956, Mumbai 400019, Maharashtra, India, e-mail: [email protected] Bhagyashri N. Annaldewar, Nilesh C. Jadhav, Department of Fibres and Textile Processing Technology, Institute of Chemical Technology, University Under Section-3 of UGC Act 1956, Mumbai 400019, Maharashtra, India

https://doi.org/10.1515/9783111137902-002

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2.1 Introduction A few decades ago humongous research has been carried out on composite materials. Nanocomposite has an extensive involvement in this area where strength-to-weight ratio, cheaper technologies, and simplicity in fabrication are required. Nanomaterials provide various properties to the material where the conventional method has yet to show promising results; their applications are expanding very fast due to their superior performance in making structures. Hybrid composites are a mix of different fibers done to carry out the manufacturing process, replacing the traditional method, without harming its properties. Suppose nanotubes are used along with the conventional fibers, they are called hybrid nanocomposites. Nanotechnology has revolutionized materials science, leading to the development of nanocomposites and nanohybrid materials with exceptional properties. These materials consist of two or more constituents, one of which is in the nanoscale range, and exhibit unique physical and chemical properties, including high strength, durability, and improved functionality. With the increasing demand for advanced materials in various industries, there is a growing interest in the research and development of nanocomposite and nanohybrid materials. This has resulted in a significant surge in scientific publications and commercial products, based on these materials. Nanocomposites and nanohybrid materials have attracted significant attention in recent years due to their unique and improved properties over conventional materials. These materials are the result of combining two or more different types of materials at the nanoscale level, resulting in improved physical, chemical, mechanical, and electrical properties. In this context, this topic aims to provide an overview of the current scenario of nanocomposite and nanohybrid materials, highlighting the recent advances, challenges, and the potential applications of these materials in various fields, including energy, electronics, biomedical, and environmental sciences. The current scenario in nanocomposite and nanohybrid materials is highly promising, with ongoing research and development aimed at improving their properties and expanding their range of applications. Scientists and engineers are constantly exploring new methods and techniques to synthesize and characterize these materials, with a focus on developing more efficient and sustainable production processes. Furthermore, the market for nanocomposite and nanohybrid materials is also growing at a rapid pace, driven by the increasing demand for high-performance materials with unique properties. The market is highly competitive, with many companies investing in research and development to stay ahead of the curve. Nanocomposite materials can overcome the drawbacks of conventional materials and are currently receiving more attention in both basic and practical areas of materials science. A nanocomposite is created when a polymeric framework is strengthened with additives made of nanomaterials to improve certain characteristics of the materials. It is recognized that the combination of nanoparticles with various matrices causes significant alterations in the mechanical, physical, artificial, and electronic

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characteristics of nanocomposites due to their remarkable thermal, mechanical, and electric characteristics. These characteristics make them ideal for a variety of applications in addition to a testing ground for critical basic science theories. Even though the properties of polymers are not particularly superior when compared to other materials such as most metals, their use in the production of products and structures is limited. When a polymer system (matrix) and a reinforcing material (filler) are coupled to create a composite, their qualities can be improved. As regards the properties of the matrix, the filler’s characteristics, particularly the size of the filler – strongly influence the overall attributes of the composite. Polymer nanocomposites (PNC), often known as nanotechnology, are made from polymer composites with filler sizes in the nanoscale domain. The topic of nanotechnology in composite materials has received a lot of attention and it has the potential to improve our quality of life – it does have the possibility to make this world a better place to live in [1]. PNCs are one of the most well-known areas in nanotechnology for current research and advancements, and the examination field encompasses a broad variety of subjects that may be researched. Nanoelectronics, polymeric bio-nanomaterials, reinforced PNCs, nanocomposite-based drug delivery devices, etc. would all be included in this area [2]. The current scenario in nanocomposites and nanohybrid composites is provided in this chapter. It covers their characteristics, synthesis techniques, and applications in many industries. Overall, the current scenario in nanocomposite and nanohybrid materials is highly promising, with significant potential for further growth and development in the future.

2.2 Nanotechnology Nanotechnology has revolutionized the way we understand and manipulate materials, as it enables scientists and engineers to design and synthesize materials at the nanoscale with specific properties and functions. This has opened up new opportunities to create innovative products and applications with enhanced performance, such as stronger, lighter, and more durable materials, advanced sensors and electronics, targeted drug delivery systems, and more efficient energy storage and conversion devices. Moreover, nanotechnology has also enabled the development of multifunctional materials and composites, which combine different materials and structures at the nanoscale to achieve synergistic effects and optimize their properties. For instance, by incorporating nanoparticles or nanofibers into a polymer matrix, it is possible to enhance its mechanical, thermal, electrical, or optical properties, as well as its dimensional stability. Overall, nanotechnology has enormous potential to address many of the current and future challenges facing our society, including climate change, health, energy, and sustainability. However, it also raises some ethical, environmental, and safety

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concerns that need to be carefully addressed and regulated to ensure its responsible and beneficial use. The dimensional stability of a material plays a crucial role in determining its properties. The nanostructure of composite materials has always been instrumental in enhancing their characteristics and monitoring their structure at the nanoscale. Nanotechnology is a highly promising field that has the potential to revolutionize technological applications across various industries such as semiconductors, biotechnology, energy storage, and organic and inorganic materials [3]. Nanotechnology encompasses the study and development of devices and materials with sizes in the nanometer range, typically ranging between 1 and 100 nm [4]. It offers a plethora of opportunities to create innovative products with unique properties in several fields, including chemistry, polymers, textiles, food, and pharmaceuticals.

2.3 Classification of nanomaterials Nanostructures are generally grouped based on their dimensions. Figure 2.1 shows different nanomaterials based on their dimensions [5]. – Zero-dimensional (0-D) nanomaterial Nanomaterials are materials with at least one dimension in the nanoscale range, typically between 1 and 100 nanometers. However, when all three dimensions of a material are in the nanoscale range, it is considered a nanostructure. Metallic nanoparticles and quantum dots are two examples of such nanostructures. They both have dimensions in the range of 1 to 100 nanometers in all three directions. These materials often exhibit unique physical and chemical properties that differ from their bulk counterparts, making them appealing for a variety of applications in fields such as electronics, catalysis, and biomedicine. – One-dimensional (Quasi 1-D) nanomaterial Some nanomaterials have one dimension outside the nanoscale range, while the other two dimensions are within the nanoscale range. Nanotubes and nanorods are examples of such nanomaterials. They typically have two dimensions in the range of 1 to 100 nanometers and a third dimension outside this range. These materials often exhibit unique physical and chemical properties that are different from their bulk counterparts, which make them attractive for various applications in fields such as electronics, optics, and energy. – Two-dimensional (2-D) nanomaterial Some nanomaterials have two dimensions outside the nanoscale range, while one dimension is within this range. Nanocoatings and nanosheets belong to this category of nanomaterials. They typically have one dimension between 1 and 100 nanometers and two dimensions outside of this range. These materials exhibit unique physical and

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NMs classification based on dimensionality 0D

1D

2D

3D

Nanospheres, clusters

Nanotubes, wires, rods

Thin films, plates, layered structures

Bulk NMs, polycrystals

Quantum dots

Metal nanorods, Ceramic crystals

Carbon coated nanoplates

Liposome

Fullerenes

Carbon nanotubes, Metallic nanotubes

Polycrystalline Graphene sheets

Au

Gold nanoparticles

Gold nanowires, Polymeric nanofibers, Self assembled structures

Layered nanomaterials

Dendrimer

Fig. 2.1: Classification of nanomaterials. Reproduced with permission from Alkaç et al. [6].

chemical properties that are different from their bulk counterparts, which make them attractive for various applications such as coatings, energy storage, and catalysis – Three-dimensional (3-D) nanomaterial If materials have an overall size in the millimeter or micrometer range, but exhibit nanoscale features or are fabricated using nanoscale building blocks, they can be referred to as “3D nanomaterials.” These materials often possess unique properties that arise from the nanoscale features, such as high surface area-to-volume ratio, enhanced mechanical properties, and improved catalytic activity. 3D nanomaterials have numerous potential applications in various fields, including energy storage, biomedical engineering, and environmental remediation [5].

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2.3.1 Synthesis of nanoparticles Nanoparticles can be synthesized using three main methods: physical, chemical, and biological. Each method has its own advantages and limitations. Physical methods involve the use of physical principles such as evaporation, condensation, and milling to produce nanoparticles. For example, physical vapor deposition (PVD) and laser ablation are common physical methods used to synthesize nanoparticles. These methods typically require expensive equipment and can be time-consuming. Chemical methods involve the use of chemical reactions to produce nanoparticles. These methods include precipitation, sol-gel, and hydrothermal synthesis. Chemical methods are relatively simple, cost low, and can be easily scaled up for industrial production. Biological methods use living organisms or their by-products to produce nanoparticles. This method includes the use of microorganisms, plants, and biological molecules such as enzymes to synthesize nanoparticles. Biological methods are eco-friendly, costeffective, and offer precise control over nanoparticle size and shape. Overall, each method has its own advantages and disadvantages, and the choice of the method depends on the specific application requirements.

2.3.1.1 Physical synthesis – Evaporation-condensation This is a physical method for synthesizing nanoparticles. This technique uses a tube boiler operating at atmospheric pressure to create nanoparticles. The process involves vaporizing a precursor material into a carrier gas and then condensing the gas in a furnace. Nanoparticles are produced as a result of the condensation process. This method is relatively simple and can be used to synthesize a variety of nanoparticles with different properties. However, the size and shape of the nanoparticles produced using this method may not be uniform. Additionally, the equipment required for this technique can be expensive, which may limit its scalability for large-scale production [7]. – Mechanical milling Mechanical milling is a process that involves the use of a ball milling device to produce nanoparticles in a solid state. The primary goal of this technique is to reduce the particle size while simultaneously blending the particles in multiple phases. It is a widely used method for the production of nanomaterials, with tailored properties for various applications such as electronics, energy storage, and biomedical engineering. This process technique aims to reduce particle size while blending the particles in several phases. – Mechanochemical synthesis Mechanochemical synthesis involves the use of mechanical energy to drive a chemical reaction and produce nanoparticles. Chemical precursors such as mixtures of chlor-

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ides, metals, or oxides react with one another during the synthesis process, either through ball milling or heat treatment, resulting in nanoparticles scattered in a matrix. Subsequently, solvent washing is used to extract the matrix and obtain pure nanoparticles. This method is widely used in the production of tailored nanomaterials for various applications in fields such as electronics, catalysis, and energy storage [7]. – Laser ablation Laser ablation is a widely used method for producing nanoparticles with a narrow size distribution. It involves using a laser pulse to raise the temperature of the precursor material to its boiling point, which produces a plasma plume of the precursor material. The plasma plume then undergoes condensation, resulting in the formation of nanoparticles. This method is particularly useful for producing nanoparticles with high purity and controlled size, and it has various applications in fields such as electronics, biomedicine, and energy storage [7].

2.3.1.2 Chemical synthesis Chemical synthesis methods rely on the reduction of metal ions under favorable conditions to form nanoparticles. Here are some examples of chemical methods: – Chemical reduction Chemical reduction is a commonly used and straightforward technique for producing metal nanoparticles. The process involves the reduction of metal precursor salts using a suitable reducing agent, either at room temperature or higher temperatures, to synthesize nanoparticles. Examples of reducing agents include sodium borohydride, hexamethylenetetramine, and sodium citrate. To prevent the nanoparticles from aggregating in the solution, stabilizers like polyvinyl pyrrolidone and sodium dodecyl sulphate are used [8]. – Microemulsion process The microemulsion process involves a clear solution made up of water, oil, surfactant, and co-surfactant. This technique is used during nanoparticle synthesis to facilitate the reaction between a water-soluble precursor and an oil-soluble reducing agent by keeping them together. The microemulsion serves as a medium where the reactants can interact to produce nanoparticles [8]. – Hydrothermal/Solvothermal The hydrothermal method is a process by which nanoparticles can be synthesized. In this method, a water-insoluble precursor is subjected to high temperatures and pressures using water as the medium. An alternative method, called the solvothermal process, is similar to the hydrothermal method but uses a solvent instead of water. The reaction takes place under supercritical conditions [9].

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– Sonochemical method The synthesis of metal nanoparticles can be achieved through a method that involves exposing the metal precursor solution to solid ultrasonic radiations, typically with frequencies ranging from 20 kHz to 10 MHz. This process induces cavitation, which results in the formation of nanoparticles. This method is known for its simplicity, and is widely used in the preparation of nanoparticles [10]. – Sol-gel process The sol-gel method is a process for creating inorganic systems by generating a colloidal suspension, known as a sol, and then allowing the sol to gel and form a diphasic system consisting of both solid and liquid phases. This method is widely used for synthesizing nanocoatings on fabrics, and it typically involves using metal alkoxides as a precursor for the sol-gel synthesis of nanoparticles. Silicon alkoxides, or Si(OR)4, are among the most commonly used metal alkoxides in the sol-gel process. During the solgel process, the precursor undergoes hydrolysis and condensation by reacting with water in the presence of a catalyst such as a mineral acid or base [11, 12]. – Biological methods Chemical methods for preparing nanoparticles have been found to be both non-ecofriendly and costly, prompting many researchers to explore alternative, more sustainable approaches. In recent years, a number of eco-friendly and cost-effective methods have been proposed for synthesizing nanoparticles. These methods often involve the use of plant extracts and microorganisms as substitutes for synthetic reducing agents and stabilizers. By utilizing these natural sources, researchers are able to reduce the environmental impact of nanoparticle synthesis and minimize costs, while still producing high-quality nanoparticles [13].

2.4 Nanohybrids Multicomponent composites or hierarchical structures, where more than two presynthesized nanomaterials (NMs) are bonded together to extract multifunctionality, have replaced single particle synthesis in producing materials at the nanoscale. These assemblages are known as nanohybrids. Nanohybrids are generally synthesized or formed by in situ chemical reduction, direct mixing, microwave irradiation, hydrothermal process, sol-gel process, thermal degradation, deposition of atomic layers, and other methods. These nanohybrids are nanoscale/hierarchical assemblies of different types of NMs coupled by non-covalent bonds (e.g., van der Waals forces, hydrogen bonding, and electrostatic forces) or covalent bonds (molecular bonds). These nanohybrids have all of their constituents in nanoscale dimensions unlike nanocomposites, which contain matrix materials in macroscopic or bulk length scale dimensions. The prime objective of synthesizing nanohybrids is to produce composite

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materials with enhanced component characteristics. The majority of nanohybrids are made up of nanomaterials with distinctive physical or chemical properties. The inherent attributes of the ensembles should differ when they are conjugated [14, 15]. Table 2.1, summarizes some key information about nanohybrid materials. It is also conceivable that throughout hybridization, more than one component trait would become dominant, which could be due to the function of conjugation or the synthesis process. These modifications may manifest in the final product’s size, structure, surface chemistry, dissolving characteristics, absorption characteristics, oxidation resistance, band-gap energetics, etc. Also, it is feasible that novel and distinctive properties may arise; for instance, exceptional mechanical and physical performance, increased reactivity, and localized alterations in chemical or electrical properties [16]. Tab. 2.1: Summarizing some key information about nanohybrid materials. Characteristics

Description

Composition

Two or more different types of nanoscale components combined together

Synthesis methods Sol-gel, co-precipitation, electrospinning, etc. Nanoscale components

Nanoparticles, nanotubes, nanofibers, etc.

Properties

Enhanced mechanical, electrical, optical, and/or biological properties due to synergistic effects between components

Applications

Electronics, energy storage, catalysis, sensing, drug delivery, etc.

Examples

Carbon nanotube/metal nanoparticle composites, inorganic nanoparticle/organic polymer hybrids, etc.

Advantages

Improved properties over individual components, wide range of potential applications

Challenges

Difficulties in controlling properties and interactions between components, challenges in large-scale synthesis and production

2.4.1 Nanohybrid composites Nanohybrid composites are comprised of various nanocomponents in a single matrix. The overall behavior of the nanohybrid composites depends upon the addition of the individual nanocomponents that have distinct properties. This results in a further satisfactory equilibrium amongst the advantages and disadvantages. The importance of utilizing a nanohybrid composite is that it consists of multiple components, as this helps the components to complement each other, complementing the one that lacks essential properties. As a result, equilibrium between price and performance via appropriate material design could be achieved. The overall properties of the nanohybrid

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composites mainly depend on the material content, type of material, amount of material combined, nanomaterial to matrix bonding, and the kind of matrix used. Also, in a nanohybrid composite, the overall strength is reliant on the failure strain of the individual nanocomponents. Utmost hybrid properties are attained when the individual nanocomponents are in a highly stressed state. A positive or a negative hybrid effect is defined as a deviation of a certain property, such as structural or mechanical, from the rule of hybrid mixture [17]. The hybrid effect was utilized to depict the phenomenon of an obvious synergistic enhancement in the physio-chemical properties of a composite comprising at least two kinds of nanoelements. The process of selecting the type of nanomaterials for the manufacturing of nanohybrid composite is not determined by the purpose of hybridization, requirements placed on the material, or the plan being developed and set up for the specific application. The issue of picking the sort of feasible nanocomponents and their properties is of major significance while planning, designing, and creating nanohybrid composites. The fruitful utilization of nanohybrid composites is not at all entirely by the mechanical, physical and chemical stability properties of the nanomaterial/matrix system [18].

2.4.2 Classification of nanohybrid materials Class I hybrids: These hybrids are based on Van der Waals forces, hydrogen bonds, or weak electrostatic interactions characterized by weak interactions between the phases. Class II hybrids: These hybrids exhibit strong interactions of the first order amongst the phases consisting of covalent bonds and ionic bonds. If the chemical interactions between both the organic and inorganic phases are weak (Class I hybrids), it is possible to have, as described below in Fig. 2.2(a), a continuous phase that “traps” one dispersed phase, (b) or two continuous interpenetrated phases.

Fig. 2.2: Class I hybrid materials. Reproduced with permission from Rando et al. [19].

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If the chemical interactions amongst the organic and inorganic phases are strong (Class II hybrids), it is possible to have discrete inorganic units as described below in Fig. 2.3 (a’) clusters, covalently linked to a continuous organic phase or vice versa, (b’) or two continuous steps linked covalently [20].

Fig. 2.3: Class II hybrid materials. Reproduced with permission from Rando et al. [19].

2.4.3 Examples of nanohybrids NHs can be divided into four main categories: carbon-carbon NHs (CCNH), carbonmetal NHs (CMNH), metal-metal NHs (MMNH), and organo-metal-carbon NHs (OMCNH). While this classification system is beneficial for identifying important characteristics related to the safety of these nanoensembles, it should not be considered the sole basis for categorizing them. Carbon-based nanomaterials (CNMs) have been always at the forefront of materials science and these include carbon nanotubes (CNTs), graphene family-based nanomaterials (GFNs) such as graphene, graphene oxide, and reduced graphene oxide, and most recently, emerging materials such as carbon dots (CDs) and graphitic carbon nitride (g-C3N4). CNMs offer intriguing catalytic, redox, fluorescence, and luminescence capabilities in addition to being chemically stable and structurally varied. They also exhibit strong light absorption and electron-transfer properties. Even with these potential benefits, metal/metal oxide nanoparticles (MNPs) such as TiO2 and ZnO semiconductors perform some of the key functions more effectively than CNMs, including providing wide bandgaps, maintaining high electron-hole pairs dissociation and transfer efficiency, having outstanding heat transfer and electron transfer properties, and being able to donate metal ions (such as Ag +) for biocidal applications. Hence, synthesizing nanohybrids with at least two different NMs (such CNMs & MNPs) that have different characteristics and complementary capabilities offers enormous potential for solving problems. A summary of various applications is shown in Tab. 2.2, covering processes and devices used in electronic and energy industries, biomedical fields, environmental remediation, catalytic processes, construction materials, lubrication, heat transfer, and more [21].

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Tab. 2.2: Various types and the present applications of nanohybrids [21, 36]. Wide applications fields

Definite applications

Nano hybrid class

Specific types

Biomedical

MRI agents

CMNH

Gadofullerene

Bioimaging and cancer therapy

CMNH

Quantum dots-iron oxide – carbon nanotubes

MMNH

Gold-ferrous shell-core

CCNH

Fullerene – carbon nanotubes

MMNH

Gold-iron oxide

CMNH

Quantum dots-iron oxide – carbon nanotubes

CMNH

Manganese dioxide/carbon nanotubes hybrid

Drug delivery

Energy and Electronics

Energy storage/ supercapacitors

Carbon nanotubes/ruthenium dioxide hybrid Graphene-manganese oxide

Field effect transistors

CCNH

Graphene oxide-carbon nanotubes peapods

CMNH

Graphene-zinc oxide hybrid Graphene nanosheet/metal nitride

CCNH

Fullerene-carbon nanotubes peapods Graphene/carbon nanotubes hybrid

OMCNH

Poly(-hexylthiophene)-fullerene hybrid Graphene/organic molecule hybrid

Photovoltaics

CCNH

Graphene/fullerene hybrid

Transparent conductive films

CCNH

Carbon nanotubes/graphene exohedral hybrid

MMNH

Silver/titanium dioxide nanowire

CCNH

Graphene/carbon nanotubes exohedral hybrid

CMNH

Platinum-reduced graphene oxide

MMNH

Palladium-copper

Fuel cell

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Tab. 2.2 (continued) Wide applications fields

Definite applications

Nano hybrid class

Specific types

Environmental monitoring and remediation

Biosensors

CCNH

Reduced graphene oxide-multiwalled carbon nanotubes

Contaminant degradation

CMNH

Carbon nanotubes-titanium dioxide

Antimicrobial

CMNH

Zinc oxide-reduced graphene oxide Silver-graphene oxide Graphene-zinc oxide

Bio-imaging

CCNH

Carbon nano-anions

Gas-sensors

CCNH

Graphene-carbon nanotubes hybrid

Construction industry

Structural health monitoring

CCNH

Carbon nanotubes-graphene nanoplatelet hybrids

Catalysis

Catalyst

CMNH

Carbon nanotubes/palladium Gold-graphene

CCNH

N-doped carbon nanotubes-graphene peapods

OMCNH

Carbon nanotubes-enzyme

MMNH

Gold-palladium shell structure

2.4.3.1 Silica nanohybrids The numerous distinctive qualities of silica nanoparticles give them a special matrix for integrating functional components. In the beginning, the high porosity of amorphous silica nanoparticles offers the three-dimensional space necessary for the doping of functional components, also known as the dopants. Since the porosity is adequately customizable, small molecules or macro-size materials can be held. The dopants can be conveniently incorporated into a silica shell or adhered to the surface of a silica nanoparticle by chemical bonding or physical adsorption. Secondly, silica nanoparticles can be described as transparent. Because they cannot interact with magnetic fields or absorb light within near-infrared, visible regions, or ultraviolet regions, the dopants inside the silica matrix can maintain their unique magnetic and optical properties. And lastly, the silica matrices are safe and suitable for biomedical research. Silica nanohybrids may be generated in several ways. Whenever silica matrix is synthesized, multifunctional elements, including fluorophores, pharmacological molecules, and photosensitizers, are frequently trapped inside the silica. Functional mole-

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Akshay C. Jadhav, Bhagyashri N. Annaldewar, Nilesh C. Jadhav

cules are sometimes adsorbed on the surface of silica nanoparticles, but this is less often. Following the production of the pure silica nanoparticles, active molecules are immobilized during the decoration process. Before decoration, the surfaces of silica nanoparticles are generally designed and synthesized with amino or carboxyl groups. Adding functionalized components to silica nanoparticles gives additional functionalities, including fluorescence, magnetism, medicinal potentiality, and catalytic functionality. In addition, silica nanoparticles provide more than just shielding for dopants; they also strengthen or enhance their physical characteristics. For instance, those trapped demonstrate a larger quantum yield and improved photostability, compared to free fluorophores. Once incorporated into the silica matrix, the drug molecules’ release rate may be modulated. Silica shells act as a barrier, reducing the toxicity of metal nanoparticles and quantum dots. A good substrate for creating multifunctional nanomaterials that can do several functions at once is provided by silica nanoparticles [22].

2.4.3.2 Clay nanohybrids Due to the multifunctional characteristics displayed, the outcome of the synergistic effects originating from the two possibilities multifunctional nanohybrid materials based on layered clays have lately been extensively utilized for diverse purposes. In particular, clay minerals have been used for therapeutic and protecting purposes for as long as humankind has been in existence. As part of pelotherapy, thermal muds known as peloids have been utilized locally or more broadly to treat rheumatism, arthritis, and traumatic injury caused to the bones and muscles. There is constant interest in the creation of clay minerals for biological purposes, such as pharmaceuticals, cosmetics, or even medical ones, due to their great features, such as relatively low toxicity, biocompatibility, and the promise of controlled release. So, their advancement for biological applications, such as pharmacological, aesthetic, and even medical ones, has attracted endless attention. Nanohybrids made of clay are frequently employed in pharmaceuticals. Recently, there has been a lot of interest in a novel technique that involves the hybridization of drugs with clay minerals for pharmaceutical applications. Controlled delivery, controlled release, improved water solubility, improved dispersion ability, and the possibility of target delivery are just a few of the exciting attributes that hybridization may provide [23].

2.4.3.3 Metal nanohybrids (MNHs) Metallic nanohybrids are tiny metal nanoparticles encapsulated in a dielectric substance. MNHs have a more significant synergistic impact than single metallic nanoparticles and are synthesized utilizing two or three distinct metals (bimetallic and trimetallic NPs).

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MNHs and quantum emitters (QEs) offer a variety of utilization in the medical field for quantum-emitter-based luminescence biomarkers. The extensive usage of nanometals has recently been discovered in removing organic pollutants, insecticides, heavy metals, and microorganisms like viruses, bacteria, etc., from an aquatic environment. The application of metal ions in MNHs plays a crucial role in chemical reactions, ecological systems, and environmental systems. Metal ion coordination opens a new window for developing self-assembled functional proteins [24].

2.4.3.4 Metal oxide nanohybrids (MONHs) Researchers are particularly interested in metal oxide NPs in their pure, doped, or nanohybrid forms because they may be used in the development of electronic applications such as electrical appliances and electrochemical sensors. They are more user-friendly, less expensive, and faster, and offer real-time detection and online data analysis. In general, mono and coupled semiconductors that are heterostructures or composites are often used. Together, organic moieties carbon materials are also doped with metal ion NPs, in which, molybdenum oxide (MoOx), manganese oxide (MnO2), tin oxide (SnO2), titanium oxide (TiO2), and tungsten oxide (WO3) are also incorporated to generate MONHs. Tungsten oxide stands out among these for its outstanding mechanical, structural, and electrical characteristics. Therefore, it has many applications in electrocatalysis, gas sensors, and electrochromic and photochromic displays [25].

2.4.4 Application of nanohybrids Many natural essential oils (EOs) are extracted from natural plant sources used in medicinal pharmaceuticals, agricultural, food industry, and cosmetic industries due to their vital unique properties and enormous advantages. The chemical compositions of these essential oils are very complex. These highly volatile natural EOs contain complex chemical compounds such as phenols, ketones, aldehydes, terpenes, alcohols, flavonoids, esters, and phenylpropanoids. Due to these flexible bioactive molecules, EOs find multiple usages in treating various diseases such as nutritional, gastronomic, antiulcer, organoleptic, anticancer, antiaging, antidepressant, antipyretic, antitussive, analgesic, insecticidal, larvicidal, etc. [26]. Therefore, nano-encapsulation technology has been highly suggested as a groundbreaking method that helps in overcoming the limitations caused due to EOs usage by further enhancing their bio-efficacy and bio-availability, and, further, shielding them from extreme circumstances due to the nanoclay’s abundant availability, unique layered structure, bio-inert nature, intercalation, high retention capacities, and excellent swelling properties. Encapsulating EOs into nanoclays has been proven to be most ef-

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ficient for the protection and preservation of the EOs in storage, which helps retain its efficiency and thus provides controlled and measured release of EOs in the polymer matrix. Developing drug carriers capable of transporting drugs has been generating considerable interest lately. A versatile method for the conveyance of many anticancer and diagnostic chemicals has been made possible using inorganic nanohybrids. Additionally, scientists have been working to create inorganic nanohybrids to create drug delivery systems (DDSs) that have a variety of benefits compared to traditional carriers, including better drug retention, better pharmacokinetics, well-controlled releasing properties, and more specialized therapeutic intervention. Drug delivery systems include inorganic nanohybrids like mesoporous silica nanoparticles (MSNs), layered double hydroxides (LDHs), metal-organic frameworks (MOFs), metal nanoparticles (e.g., Gold (Au)-NPs, Silver (Ag)-NPs), and metal oxide nanoparticles (e.g., cerium oxide (CeO2), iron oxide (Fe3O4), or manganese oxide) [26]. The primary pollutant sources that are harming the atmosphere are cars, residential activities, rapid industrial expansion, and improper garbage management. For the protection of the environment as well as people, these contaminants must be regularly monitored. Standard monitoring systems for hazardous gases are costly, larger, and time consuming. Inorganic and organic hybrid materials are promising prospects for a wide range of applications, including gas sensors. Signals are generated from the analytical data provided by gas sensors. For the detection of harmful gases, several polymeric/inorganic nanohybrids have already been utilized [27]. Since their conductivity varies when exposed to gas molecules, conducting polymers such as polyacetylene (PA), poly (3,4-ethylene dioxythiophene) (PEDOT), poly (phenylene vinylene) (PPV), polythiophene (PT), polyaniline (PANI), and polypyrrole (PPy) have shown good potential in gas sensing applications. These polymers offer advantages such as cost efficiency, high functionality, outstanding stability, faster response time, rapid recovery, accessible synthesis, and a substantial surface area. Its gas-sensing capability is also constrained by several drawbacks, including weak sensitivity, delayed response, poor selectivity, and poor recovery. Polymer nanohybrids and inorganic nanomaterials improve stability, sensitivity, and responsiveness, while overcoming flaws in polymers and metal oxides. Polymer composites, along with inorganic nanomaterials, such as metal oxides, metal oxide semiconductors, and other substances, are a well-known class of sensing materials that have improved properties such as enhanced sensitivity, large area of surface, reduced sensor working environment, and identification of a diverse variety of gases. Several strategies, including physical, chemical, and electrochemical ones, have been used in the past to create polymeric/inorganic nanohybrids for gas sensing [28].

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2.4.5 Application of nanohybrid nanocomposites 2.4.5.1 Biomedical applications Hybrid nanocomposites have also been investigated as potential materials for biosensors, which are healthcare devices that detect and analyze biological compounds. For example, nanoparticles of gold, silver, or other metals can be integrated into a polymer matrix to create a plasmonic nanocomposite that can detect small concentrations of certain biomolecules, such as glucose or cholesterol. Similarly, magnetic nanocomposites can be designed to detect pathogens or biomarkers in biological fluids. In regenerative medicine, hybrid nanocomposites have shown promise as tissue engineering and repair materials. Combining biodegradable polymers with nanoparticles of ceramic, metal, or carbon makes it possible to create composites with enhanced structural, mechanical, and biological properties. For example, nanocomposites of poly (lactic-co-glycolic acid) (PLGA) with hydroxyapatite or bio-glass nanoparticles have been used for bone tissue engineering. Similarly, nanocomposites of chitosan with silver or gold nanoparticles have been studied for wound healing and antibacterial coatings. Overall, the biomedical applications of hybrid nanocomposites are diverse and growing, with potential benefits for diagnostics, drug delivery, tissue engineering, and other healthcare fields. However, further research is needed to optimize the design, synthesis, and characterization of these materials and evaluate their safety and efficacy in preclinical and clinical studies [29].

2.4.5.2 Textile applications This technology can be used as an alternative option over the conventional method of fabric treatment. The use of nanocomposites in textile production can reduce harmful chemicals and conserve resources. Nanocomposite can impart certain properties to the textile material without harming its original properties like breathability, aesthetics, and intrinsic flexibility. Additionally, research is underway to develop nanocomposites that are biodegradable and eco-friendly. These materials can be used for effective shielding from harmful UV radiation. Many nanoparticles like ZnO (Zinc oxide), TiO2 (Titanium Dioxide) and SiO2 (Silicon dioxide) are considered the best inorganic UV blockers and have displayed remarkable ability in UV protective function. Some other multifunctional properties like self-cleanability, water repellence, UV protection, and antimicrobial function can be produced as a green treatment of textiles. In conclusion, the application of nanocomposites in textiles has the potential to revolutionize the industry by providing multifunctional structures with enhanced properties. As technology advances, nanocomposites will continue to be an exciting area of research and development for a more sustainable and efficient textile industry [30].

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2.4.5.3 Civil engineering applications The most attractive prospect for structural construction uses as yet has to be composite structures. Today’s advantages of hybrid nanoalloys encourage their use in recent construction and development projects. Over the past 20 years, some full-scale building constructions of these materials have been developed. These structures have complex shapes, and these materials have been used to renovate and replace old, deteriorating traditional structures as well as to build new facilities. These nanocomposites are significantly lighter than traditional structures. Due to their lightweight, low maintenance needs, resistance to environmental effects, and ability to be framed, nanocomposite materials are becoming increasingly popular globally [31].

2.4.5.4 Food packaging applications Nanofillers’ use in food packaging can potentially improve the mechanical, thermal, and barrier properties of biopolymers. These biopolymers can perform significantly better using even small amounts of nanofillers, such as clay. The filler improves the overall mechanical, thermal, and barrier properties. However, as with any new technology, it is essential to carefully consider the potential impact on human health and the environment. Research is needed to fully understand the effect of hybrid nanocomposites on human health, including the identification, characterization, and quantification of the nanoparticles used in these materials. The migration of nanoparticles from the packaging to the food products is also an important consideration that must be addressed. To ensure the safety of nano-packaged foods, it is essential to have strict safety controls in place and to regularly monitor the migration of nanoparticles from the packaging to the food products. Additionally, communication and transparency with consumers about the use of nanocomposite materials in food packaging are crucial to maintaining trust and confidence in the food industry [32].

2.4.5.5 Telecommunication applications The requirement for both power and data transmission in the telecommunication industry is increasing, leading to the need for innovative solutions such as hybrid cables. This cable is a flexible cabling solution that includes power transmission capabilities for network equipment, along with optical fiber cables for data transmission. The hybrid composite cable is essential for uninterrupted power transmission in the telecom fields, ensuring that the components and terminations of the network remain powered and connected. Copper wirings are used to regulate the telecom terminations and components. Copper pair is also used for fiber optic components in telecom applications and for basic tagging needs in railway line signaling. In the railway industry, quad cables

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have traditionally been used for communication and signaling. However, with the increasing demand for data transmission, optical fiber cables have become the backbone of communication. Customers now expect to have access to communication services while travelling, putting pressure on railway companies to provide these services with lower investments. The limitations of each medium mean that railway companies have had to choose between them when implementing communication solutions. However, the new hybrid composite cable design provides a more efficient solution for communication while travelling, incorporating both power and data transmission capabilities in a single cable. This innovative cabling solution allows railway companies to provide uninterrupted communication services to their customers, improving their overall experience [33].

2.4.5.6 Aerospace applications The aircraft industry continues to benefit from advancements in polymer nanocomposites as they converge with other emerging technologies. Some potential uses, including those for structural applications, electronic appliances, and vehicle health systems, are highlighted, in particular, by the preparation of nanocomposites – future benefits of cutting-edge polymer materials in preparing ultra-lightweight structures and macromolecules with shape memory. Hybrid nanocomposites are widely used in the aerospace industry for several reasons, including their low costs, high availability, low environmental impact, and ease of use and maintenance. These nanocomposites are energy-efficient lightweight materials that will reduce airplane weight by 40% while increasing electrical and thermal conductivity. Additionally, lighter CNTs hybrids are used to substitute the wiring in commercial airplanes [34].

2.4.5.7 Automotive applications The car manufacturing industry is paying close attention to nanocomposite technology and its suppliers. They have a well-developed automotive application due to the considerable weight reduction, better integration of parts into other automotive components, and lower production and tooling costs. In the automotive industry, hybrid nanocomposites are frequently used for aerodynamic design, lightweight product design, styling and part consolidation enhancement, and to increase safety and crashworthiness. Current global demands for fuel efficiency and greenhouse gas emissions reductions for manufacturing and transportation are creating interest in high-quality, lightweight materials with minimal failure costs to replace metals [35].

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2.4.5.8 Defense applications For a broad range of military applications, nanocomposites hold the potential for significant technological advancements. The possibilities offered by nanocomposites for enhancing propellers in the defense industry are astounding. Although these technological developments will probably only be recognized in a few years, many exciting areas are currently being researched, particularly for military applications. Aerodynamics, mobility, stealth, sensing, power production and management, intelligent structures and materials, resilience and robustness, among other innovations, are to be used inside the stages and are directly applicable to the military field. Nanocomposites also affect systems in the battle space that deal with information and signal processing, autonomy, and intelligence. Particularly, in the context of data innovation, generous focus points are expected to be identified. Nanocomposites will also affect systems in the battle space that deal with information and signal processing, autonomy, and intelligence. The development of miniature uncrewed autonomous vehicles, robotics technology, and data technology, in general, are all expected to benefit significantly from these new, empowering skills, including danger recognition, and novel electronic features and interface frameworks [36].

2.4.5.9 Miscellaneous applications Indeed, hybrid nanocomposites have a wide range of potential applications across various industries due to their unique properties and versatility. In the transportation industry, for example, they can be used to create lightweight and robust materials for automobiles, airplanes, and other vehicles. In naval and space crafts, they can provide improved durability and resistance to corrosion. Wind power generation can be used to create more efficient wind turbine blades. Hybrid nanocomposites can also be used in the oil and gas industry to develop durable and corrosion-resistant equipment, and in portable electronics, for improved energy storage and longer battery life. In sporting goods, they can be used to create lightweight and durable equipment, such as tennis rackets and golf clubs. Other potential applications include the use of hybrid nanocomposites in sensors and actuators for improved precision and responsiveness, as well as in agricultural machinery for improved durability and resistance to wear and tear. In the field of solar cells, they can be used to improve energy efficiency and reduce costs. Overall, the potential applications of hybrid nanocomposites are vast and diverse, and as research continues to develop, we can expect to see even more exciting and innovative uses of these materials [34].

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2.5 Current challenges of nanocomposites and nanohybrids The current challenge is to produce nanocomposites and nanohybrids at a competitive cost and with superior performance, than replacement materials. Every polymer nanocomposite must begin by selecting the correct nanomaterial from an available variety. Achieving accurate permutations and combinations along with the accurate weight percentages are beyond the reach for many scientists since the expense of certain nanomaterials frequently outweighs the benefit from the property enhancement. The advancement of all polymer nanocomposites depends heavily on finding costeffective methods to mass-produce viable nanohybrid composites. Although the current approaches are effective and consistently supply the market with a range of nanomaterials, additional approaches have the potential to reduce costs and boost nanomaterial production volumes. While current methods such as arc discharge, laser ablation, and chemical vapor deposition have successfully provided the industry with a steady supply of various nanomaterials, other potential methods exist to decrease cost and increase the volume of nanomaterial production. For example, using waste materials, such as food waste, to create activated nanohybrid composites is a promising new method that can potentially reduce cost and waste. Overall, continued research and development in this area will be crucial for advancing the field of nanohybrid composites and expanding their use in various industries [35, 36].

2.6 Future scope of work Nanocomposites and nanohybrid materials are innovative materials that have attracted significant attention in recent years due to their unique properties and potential applications in various fields. The current scenario in nanocomposites and nanohybrid materials is characterized by the ongoing research and development efforts aimed at improving the performance, durability, and functionality of these materials. The future scope of nanocomposite and nanohybrid materials is vast and promising, with several potential applications in various fields. Some of the future trends in this field are: 1. Biomedical applications: Nanocomposite and nanohybrid materials have immense potential for use in biomedical applications such as drug delivery, tissue engineering, and medical implants. With ongoing research and development in this field, it is expected that these materials will be used more extensively in the future for medical purposes. 2. Environmental applications: With increasing concerns about environmental pollution, nanocomposites and nanohybrid materials have the potential to play a

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crucial role in environmental remediation. These materials can be used in water treatment, air purification, and waste management, among other applications. Energy applications: Nanocomposites and nanohybrid materials have significant potential for use in energy-related applications such as solar cells, fuel cells, and batteries. These materials can enhance the efficiency and performance of these devices and contribute to the development of sustainable energy sources. Aerospace applications: The aerospace industry is another area where nanocomposites and nanohybrid materials are expected to have significant impact. These materials can be used in aircraft components, such as wings and fuselage, to improve their strength, durability, and resistance to environmental factors. 3D printing: The development of new nanocomposites and nanohybrids with improved properties has the potential to revolutionize the field of 3D printing. The use of these materials in 3D printing can enhance the quality and accuracy of printed parts, allowing for the production of complex and intricate designs.

The future scope of nanocomposites and nanohybrid materials is vast, and ongoing research and development efforts are expected to contribute to the development of innovative and useful applications in various fields. These materials have the potential to revolutionize several industries and contribute to the development of sustainable technologies [36].

2.7 Conclusion Nanohybrids and nanocomposites, which combine two or more different types of materials at the nanoscale level, have attracted much attention from researchers and scientists in recent decades. These materials offer a range of advantages, such as enhanced performance, reduced weight and volume, and lower costs, making them ideal for a variety of industries. One industry that can benefit greatly from using nanohybrid nanocomposites is transportation. By incorporating these materials into vehicles, it is possible to reduce weight, improve fuel efficiency, and enhance overall performance. This can lead to significant cost savings for the transportation industry. Similarly, the aerospace and defense industries can also benefit from the use of hybrid nanocomposites. These materials can be used to produce stronger, lighter, and more durable aircraft and spacecraft components, which can help to improve safety and performance while reducing costs. In the automobile industry, hybrid nanocomposites can be used to produce lightweight components that can help to reduce fuel consumption and emissions while also improving the overall performance of vehicles. The biomedical industry can also benefit from these materials, as they can be used to produce implants and other medical devices that are more durable and effective than traditional materials. The electronic industry is another sector that can benefit from using hybrid nanocom-

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posites. These materials can produce smaller, more efficient electronic components used in various applications, from smartphones to computers and other high-tech devices. Overall, the use of hybrid nanocomposites holds great promise for a wide range of industries. As researchers continue to explore the potential applications of these materials, we can expect to see even more impressive advancements in the field of cuttingedge technology. The future scope of nanocomposites and nanohybrid materials is extensive and holds tremendous potential for numerous applications in various fields. These advanced materials have exceptional mechanical, thermal, and electrical properties, making them ideal for a wide range of applications in fields such as electronics, aerospace, automotive, biomedical, and energy storage. Nanocomposite materials are already being used to develop stronger and lighter materials for building aircraft and automobiles, while nanohybrid materials are contributing to advancements in drug delivery systems, tissue engineering, and medical implants. Furthermore, the development of sustainable and eco-friendly technologies is an increasingly significant focus, and nanocomposite and nanohybrid materials can contribute to this effort. For instance, they can be used to create advanced energy storage systems for renewable energy sources such as solar and wind power. As research and development in this field continue to progress, the future scope of nanocomposite and nanohybrid materials is likely to expand further, offering exciting opportunities for innovation and discovery.

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Ravi Shankar Rai✶, Harsh Arora

3 Synthetic nanomaterials: fabrication, development, and characterization Abstract: The present era is considered as the nanotech age and over the last two decades considerable growth in the field of synthetic nanomaterials has happened. The demand for nanomaterials has improved extensively in a variety of industries, including electronics, pharmaceuticals, energy, defense, agriculture, food, and sanitation because of their tunable, physical, chemical, and biological properties compared to their bulk counterparts. Synthetic nanomaterials are classified based on their size, shape, composition, origin, and toxicity. Due to the increasing utility and industrial applications of nanomaterials, it has become important to study their fabrication, recent developments, advanced characterization techniques, and sustainability. Therefore, researchers and technocrats must collaborate to fabricate better and nontoxic nanomaterials that can diminish negative impacts of nanotechnology. In the present chapter, detailed discussions on the fabrication and characterization techniques along with recent developments in the field of synthetic nanomaterials has been explored. Further, categorization of synthetic nanomaterials and their current scenario have been discussed to provide a basis to researchers for developing new combinations of synthetic nanomaterials. The chapter concludes with a summary, future perspectives of synthetic nanomaterials, current issues and their potential solutions, and future outlook. Keywords: Nanotechnology, nanomaterials, fabrication, nanostructures, nanocomposites

3.1 Introduction Nanomaterials (NMs) offer a competitive environment among atomic and bulk materials. Nanoscience investigates the compelling and unique characteristics that are neither found in atomic and molecular level nor at the macro level. It does this by emphasizing on the fundamental variations of material’s conduct in the range of 1–100 nanometers. As a material is reduced in size towards the nanoscale, its characteristics have undergone significant modification. Nanotechnology (NT) involves the use of entities and systems having dimensions between 1 and 100 nm [1]. The word “size” comes to mind ✶ Corresponding author: Ravi Shankar Rai, Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, India; Department of Mechanical Engineering, Sandip Institute of Technology and Research Center, Nashik, Maharashtra, India, e-mails: [email protected]; [email protected] Harsh Arora, Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand, India

https://doi.org/10.1515/9783111137902-003

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when the word “NMs” is mentioned, but NT is more than just dimensions; this further involves structural characteristics and the alteration in those characteristics at minute levels to create NMs that are better suited for intended use [2]. These distinctive qualities indicate the potential for the development of new nanomaterials with applications in energy, defense, farming, and medicine. They have already enhanced common commercial products like sunscreen and stain-resistant clothes. Materials can be divided into three groups: semiconductors, insulators, and conductors. Small changes in a material’s size, which impact how its electrons behave, can modify its properties at nanometer-length scales. For instance, as a metal gets smaller, its electrons are confined to specific energy band rather than being free to roam throughout the energy levels. The final factor determining a material’s properties is the quantization of energy, often known as quantum confinement. Additionally, in insulating materials like transition metal oxides, imperfections govern a material’s behavior; this effect is accentuated in nanoscale structures due to their large surface and/or interfacial areas. Exciton size in NMs is regulated by the crystalline structure and orientation of materials in relation to additional nanostructures (NSs) in place of electron-hole association, whereas exciton size in semiconductors is essential for activities like light emission [3]. Ideal NMs combine beneficial aspects of bulk and molecular materials into substances that are easily developed, produced, and included in useful technologies. The dimensions or shapes of the material are stated to show that the structure and shape significantly affect the performance of NMs in their advanced use [4]. As an illustration, NMs are described as nanowires, nanorods, nanotubes, nanospheres, nanoleaves, hierarchical NSs, nanoribbons, nanoshells, nanoplates, nanocages, nanoflowers, nanobuds, nanochains, nanosheets, nanorings, and nanoparticles in a number of examples [5–7]. This makes it evident that in order to improve performance across a range of fields, greater attention is being paid to the composition and shape of NMs rather than only their dimensions. These NMs are categorized as zero-dimensional, one-dimensional, two-dimensional, and there dimensional nanostructured materials (NSMs) based on dimensions. From environmental safety to renewable power generation, regeneration, and energy storing materials, more attention has been given to development or construction of synthetic NMs to overcome the barriers of conventional materials for advanced applications [8–10]. It is clear that the present fabrication techniques of the microelectronics industry cannot be directly adapted to the nanoscale. Therefore, what we refer to as nanofabrication – the development and production of substances at nanoscale sizes – demands advances in material amalgamation, chemical alteration, analysis techniques, advanced characterization techniques, and approaches based on different fields of science and technology. As a result, researchers from all around the world are working to develop “top-down” and “bottomup” methods for designing NSs that can interact with macro systems and have potential to scale up for production of nanodevices of practical use [11]. “Top-down” methods directly imprint a design into a substrate using sophisticated lithography, electron-beam printing, and nanoimprinting methods. Due to their historical roots, these techniques are particularly successful in creating NSs based on metal and semiconductors. This chapter

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deals with the synthetic NMs and their classifications based on different attributes. Further the NMs fabrication techniques along with synthesis approaches are discussed in detail and their developments for different fields of applications are illustrated with examples. The properties of synthesized NMs must be analyzed based on their intended applications using various advanced characterization techniques as discussed in the work. The current chapter also discusses the challenges of synthetic NMs; their future outlook is discussed at the end of this chapter, which provides the basis for further research.

3.2 Current scenario and research directions of NMs The current status of NMs based on economy states that the size of the global market for NMs should grow significantly between 2021 and 2027 as a result of NT’s progressive involvement in a broader industrial divisions, including food industry, cosmetics, hospitals, pharmaceuticals, opto-electronic industries, etc. [12]. The net worth of NMs globally in 2020 had been estimated as US$7.1 billion during the COVID-19 outbreak and will grow by 9.7% annually to US$12.1 billion in 2026. According to the US National NT Initiative, the federal government permits for NT proposals increased steadily from US$0.464 billion (during 2001) to approximately US$6.2 billion (during 2019). The NMs market in the US reached US$2.1 billion in 2021. The expenditure of Japan and European Union in NT also grew from US$1.8 billion and US$1.5 billion, respectively, in the years 2005–2010, to US$3–4 billion in the years 2019–2020 [13, 14]. For NT projects between 2010 and 2020, China, Taiwan, and South Korea each allocated US$250, 110, and 300 million [15]. Nanotools, NSMs, and nanodevices are three main areas into which current NT research can be categorized. Figure 3.1 provides a schematic representation of the numerous elements that make up these categories. NSMs and nanodevices are produced and tested using a variety of technologies and procedures called nanotools. The invention of novel synthetic techniques and significant developments in supramolecular (SM) chemistry has driven the production of NSMs. NSMs with perfect control over size, shape, and functioning have been made possible by improvements in synthetic processes. A remarkable advancement in SM chemistry has made it possible to design molecular parts so that they interact positively with one another and self-assemble on the nanoscale into larger, well-defined entities with specific features through noncovalent interactions. In particular at the nanoscale, quantum effects may begin to dominate the material’s actions, influencing its characteristics such as optical, electrical, and magnetic. Along with its small dimensions, NSMs have superior chemical features including improved or novel reactivity or the ability to cross biological barriers that larger materials cannot [16]. Nanodevices are NSM-based systems that execute particular tasks more effectively or with novel characteristics. New device paradigms based on NSMs have emerged recently,

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Synthetic Nanomaterials

NANODEVICES

Nanoelectronics Spintronics Nanosensors Drug delivery system Nanooptoelectronics

NANOMATERIALS

Nanoparticles Nanowires Fullerene, CNTs Graphene Nanocomposites

NANOTOOLS

Synthetic methods Surface science Nanolithography Analytic tools Computer simulation

Fig. 3.1: Role of synthetic nanomaterials for different elements of nanotechnology.

including nanoelectronic, nanooptoelectronic, spintronic, and nanosensor devices, as well as drug and gene delivery systems. Integrated circuits with nanoscale transistors that fill up sufficient capabilities into small devices have already altered the semiconductor device business [17, 18]. The developed synthetic NMs-based devices and systems are providing basis to the different sectors and affecting the technologies all over the world as depicted in Fig. 3.2.

Impact of Synthetic NMs on world

Fig. 3.2: Illustrative depictions of potential sectors affected by synthetic NMs.

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3.3 Categorization of NMs The major categorization of NMs is basically one depending on their origin, dimensionality, morphology, state and chemical compositions. The five characteristics of nanoparticle geometry, morphology, composition, homogeneity, and aggregation have been used by numerous writers to categorize NMs [19]. The different classes of NMs and their suitable examples with potential applications are discussed in this section.

3.3.1 Classification of NMs as per their origin Initially, NMs are divided into two categories namely natural and anthropogenic, depending on their origin. Regardless of whether or not they were intentionally created, this final classification is further categorized into incidental and engineered NMs. In general, ultrafine particles are NMs that are naturally occurring and accidental in nature. As unintended by-products of human activities, NMs are also present. IC-engine, power plants, furnaces, jets, metal and polymer gases or fumes, food processing techniques, and electric motors are a few examples of what this means. If exposure from car emissions began to be reported at the end of the 1990s, evidence of the widespread production of nanoparticles by kitchen appliances and printing machines has just lately been available. Recently, it was shown that cigarette smoke contains potentially harmful NMs. Materials processing such as smelting and arc welding are found to be reasons for exposing workers to high levels of airborne NMs. Last but not least, NMs are currently produced using diversified range of precursors, including metals and its oxides, carbon, semiconductors, and resins. They can have their surfaces treated or coated and are created for certain purposes. They can be found in diversified range of morphologies, including spherical, fibrous, wires, rods, tubes, grasses, pallets, films, and more unusual flower-like patterns [20]. Manufactured NMs are distinguished from natural and accidental NMs by their regulated size, proportion, form, and elemental ratio.

3.3.2 Classification of NMs based on dimension NMs are categorized into four groups based on their dimensionality: 0D, 1D, 2D, and 3D. All outside NM dimensions must be at the nanoscale, or between 1 and 100 nm, to be considered zero-dimensional (0D). In electronics, quantum dots which are semiconductor nanocrystals with diameters of roughly 10 nm, act as a potential well to confine electrons and holes effectively. A variety of NM types are also included in the 0D NMs, such as TiO2, dendrimers, carbon spheres, palladium cubes, ZnO rings, SiC, MgO, and V2O5 [21]. The third exterior dimension of one-dimensional (1D) NMs is typically at the microscale, giving them remaining dimensions at nanolevel. Nanorods, nanowires, nanofibers, and nanotubes fall under this category. Inorganic substances

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like carbon, oxides of Ti, Si, Al, nylon, polyvinyl alcohol, polyurethane, polylactic acid, polycarbonate, etc. have all been used to create nanofibers. They can be spun into yarn or shaped into a web for use in filtration applications. Although copper or tungsten sulfides, boron nitride, molybdenum, and different halides including NiCl2, CdCl2, and CdI2 can also be used to create nanotubes, carbon nanotubes (CNTs) are the most well-known [22]. Nanowires possess highest aspect ratio and their ability to confine electrons laterally as a result is extremely valuable for electrical applications. Thin films, nanocoatings, and nanoplates are considered as 2D NMs, because they have dimension along only one axis in nm. The majority of their applications are in physics and electronics, such as when producing electronic parts with insulating or conductive facets or when modifying optical characteristics. The final subcategory of 2D NMs is made up of nanoplates, which can be produced using materials like Ag, Au, graphene, or can be of natural origin like smectic clay [23]. Three-dimensional (3D) NMs are the last dimensional category of NMs, and they lack outward nanoscale dimensions, yet exhibit internal nanoscale properties such as NSMs and nanocomposites (NCs). In general, nanofillers that are spread throughout a bulk matrix are referred to as NC materials. These nanofillers come in 0D, 1D, and 2D NM varieties. Matrix materials can be made of metals, ceramics, or polymers. The finished product can be a fiber, film, or volume that is 1D, 2D, or 3D [24].

3.3.3 Classification of NMs based on morphologies Long CNTs used to span an electrical circuit are only one example of how the morphologies of NMs aid in their diverse functions. Anisotropic microcrystalline whiskers on amorphous NMs typically take on the shape of nanospheres or spheres, depending on the crystal structure. In general, small NMs group together. These may come in a variety of shapes, including cups, rods, and threads. The discipline of micromeritics focuses on small particles. The key to utilizing the features of NMs for applications in a variety of developing technologies is controlling their morphology. Among the various uses, Au-based NMs are suited for filters and biosensors due to better optical characteristics. Regardless of the fact that NM morphology is extremely important, it is rarely understood and almost never controlled. This, however, is of utmost significance. The important morphological aspects such as degree of flatness, aspect ratio, and sphericity must be investigated effectively for intended uses [25]. The morphologies with small aspect ratios can be round, oval, cubic, prismatic, helical, or pillar-shaped. Colloids, suspensions, and powders are all different types of particle collections.

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3.3.4 Classification of NMs based on chemical composition Based on the chemical makeup of the components, NMs could also be divided into different categories. Silver, which is used in bioengineering, antimicrobial, optical and conductive devices, is an example of a metal and metal alloy NM. Catalysts, conductors, furnaces, antimicrobials and lubrication additives are among uses of copper. Gold has been used in fuel cells, electronics, heat dissipation, specialty alloys, medication delivery, medical testing, and cancer diagnosis [26]. Iron is used for its reactivity in the treatment of contaminated water because of its bactericide capabilities, paramagnetic characteristics in drug carriers, the storage of data, and magnetic detection. Palladium and platinum are used as catalysts. Due to their great strength and light weight, materials including Al, Mg, Ti, Al-Mg alloys, and Ti-Al alloys are employed in aerospace and high-temperature applications. The excellent magnetic characteristics of the Fe-Si-B-based alloys are used in electronics [27]. Metal oxides make up the second chemical class of NMs. As an antibacterial agent for filtration devices, UV filtersbased sunscreens, catalyst, and solar cells, titanium dioxide has a variety of uses. ZnO is employed for treatment of materials and has excellent UV, catalytic, and antibacterial characteristics [6, 28]. Another group of NMs includes semiconductors. Quantum mechanics controls the optical and electrical characteristics of semiconductors at the nanoscale. Electronics, solid-state lighting, solar cells, rechargeable batteries, photovoltaics, and biological applications all make use of nanosilicon. One of the most wellknown types of NMs is carbon nano-objects. They consist of carbon black, fullerenes, CNTs, carbon nanofibers, and graphene [29]. The last group of NMs is polymers. Their uses include flexible electrical components, fire-resistant and antibacterial textiles, fuel cells, filtration, and reinforcement for structural composite parts.

3.3.5 Classification of NMs based on state The states of additional NMs are categorized into five major modes, namely: isometric, scattered, inhomogeneous, agglomeration, and suspension. NMs occur in different phases such as suspension, discrete, colloidal, and agglomeration stages according to electromagnetic characteristics and chemistry. Magnetic nanoparticles (NPs), for instance, are grouped in the agglomeration stage until they are processed or surfacefunctionalized. Based on the aforementioned standards, Fig. 3.3 depicts the many types of NMs and their categorization.

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Categorization of nanomaterials (NMs)

Based on dimension

Based on origin

• •

Natural NMs Synthetic NMs

0D

1D

Based on chemical composition

Based on state

Single constituent, Composites, Inorganic, Organic {Ceramic NMs, metallic NMs, polymeric NMs…..}

Isometric, Dispersed, Inhomogeneous, Agglomerate, Suspension

Based on morphology

2D

3D

• • • • • •

Flatness Sphericity Aspect ratio

High aspect ratio Nanowires Nanotubes Nanohelics Nanotubes Nanobelts

• • • •

Low aspect ratio Nanospheres Nanocubes Nanopyramide Nanoflowers

Fig. 3.3: Categorization of broad range of NMs.

3.4 Fabrication techniques of NMs It is obvious that the microelectronics industry’s present fabrication techniques will not work on the nanoscale. Therefore, the creation of structures at the nm scale, or what we refer to as nanofabrication, necessitates advances in amalgamation of materials, advanced characterization and their physical significances, basic principles, incorporating fields like applied sciences, bioengineering, and technology [30]. As shown in Fig. 3.4, there are three distinct ways to synthesize NMs: physically, chemically, and biologically.

3.4.1 Physical method Various techniques such as mechanical milling, lithography, evaporation-condensation method, plasma method, gas condensation, vapor deposition and laser-based synthesis are included in the physical approach or technique. In laser ablation synthesis, NMs are produced through projection of high intensity laser rays into the specimen surface. The high intensity rays produced from laser strikes on the surface cause ablation of specimen and the specimen materials start vaporizing into fine particles that are further collected as nanoparticles. A wide variety of NMs, including metal, ceramic, and oxide composite NMs, can be produced using this method [31]. Lithography, which uses a concentrated beam of light or electrons, can be considered as a prominent procedure for development of nanoarchitectures. The two most popular types of lithography are masked and maskless lithography. Masked nanolithography transfers nanopatterns on a broad area of specimen applying a predetermined template [32]. A cost-effective

3 Synthetic nanomaterials: fabrication, development, and characterization

Physical method • • • •

Chemical method

Synthesis of nanomaterials •

Gas phase deposition Mechanical milling Electron beam lithography Aerosol

• • •

Biological method • • • • •

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Thermal decomposition Micro emulsion Hydrothermal Electrochemical decomposition

Plant Fungi Algae Bacteria Yeast

Fig. 3.4: Illustration of broad techniques for synthesis of NMs.

method for converting bigger particles into nanoscale goods is mechanical milling. When making NCs, mechanical milling is a useful tool for efficiently combining different phases. A special type of NMs called ball-milled carbon NMs have been employed in various energy and environment fields for storage, conversion, and remediation [33].

3.4.2 Biological method The biological pathway uses a variety of techniques, such as those mediated by fungi, algae, bacteria, yeast, etc. In many ways, NMs produced using a biogenic enzymatic approach are superior to those produced using chemical processes. Even while the latter techniques can quickly and in huge quantities make NPs of a specific size and shape, they are difficult, out-of-date, expensive, and ineffective, and they produce hazardous toxic wastes that are bad for both the environment and human health [28]. The following physiological constituents can be used to produce NMs using varied biochemical techniques [26]: – Microbes – Plants – Algae – Fungi – Yeast – Actinomycetes – Bacteria

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3.4.3 Chemical method The chemical approach uses a variety of techniques, including thermal breakdown, electrochemical deposition, coprecipitation, microemulsion, hydrothermal, and sonochemical deposition. Magnetic NMs are made via a variety of chemical processes, including flow injection syntheses, hydrothermal techniques, sol-gel methods, microwave-based methods and chemical hydrolysis and spray pyrolysis. Chemical vapor deposition (CVD) processes are essential for the fabrication of NMs made of carbon. Precursors are rated perfect for CVD if they have acceptable costing, stability, purity, and volatility and no hazards. Their disintegration should also not produce any pollutants. CVD methods are well-known techniques of production of two-dimensional NMs and are generally a successful strategy for creating high-quality NMs [34]. The cost-effective sol-gel method also has a number of additional benefits, such as the homogeneity, low temperature, and suitability with which complex NSs and composites can be created. Engineering NMs have recently shown a lot of interest in the microwave-aided methods that are based on solution phase synthesis and they have benefits of both solvothermal and microwave heating. It is intriguing and beneficial for development of distinguished morphologies of synthetic NMs [35, 36].

3.4.4 Approaches for nanofabrication According to a variety of researches, there are two fundamental classes in which to generally classify engineered NM productions: namely “top-down” strategy and “bottom-up” strategy. The “top-down” strategy involves chemical, mechanical, and physical processes to convert larger-scale bulk matter to nanoscale things. In the “bottom-up” approach, nanoscale structures are created by clustering atomic or molecule parts through physical or chemical processes. Additionally, researchers are looking at the idea of mechanosynthetic chemistry, or molecular synthesis, which would enable particles to combine themselves to form NSs via a technique known as the “bottom-to-bottom” method. Of late, the highest used nanofabrication method for the large scale manufacturing of NMs is the bottom-up method [37]. Figure 3.5 summarizes both the approaches to nanofabrication along with their examples. As a result, researchers from all over the world are working diligently to develop “top-down” and “bottom-up” methods for designing surface NSs, which may interact with macroscale materials and also have suitability for scaling up the process for the production of nanodevices for advanced systems and coveted uses [37, 38]. i. “Top-down” approach “Top-down” methods directly imprint a design into a substrate using sophisticated lithography, electron-beam writing, and nanoimprinting methods. Due to their historical roots, these techniques are particularly successful in creating NSs based on metal

Arc discharge

Top down

Sonication

Exfoliation

Laser ablation

Fig. 3.5: Common techniques to synthesize NMs.

sputtering

Mechanical milling

Lithography

Synthesis techniques of NMs Hydrother mal method

Physical vapor transport

Sol-gel method

Bottom up

Solvothermal methods

Templateassisted method

Molecular beam epitaxy

Chemical vapor deposition

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and semiconductors. The top-down approach is widely applied to the synthesis of ultrathin NMs. In top-down methods, fabrication is initiated from size reduction of bulk material though crushing, peeling, and diffusing in a variety of routes to obtain the nanoparticles or NSs. The peeling of graphite layers with the use of scotch tape to create the incredibly thin monoatomic layer known as graphene is one of the best example for synthetic NMs. Several top-down techniques are used to create NMs. One of the well-known top-down techniques involves mechanical milling, which involves reduction of materials into nanoscale particles or NSs by ball milling (mechanical crushing) as illustrated in Fig. 3.6(a). One well-known top-down method for creating NMs is lithography, which includes photolithography, ion beam, and electron beam. Covalent organic monolayer objects are also made using lithographic polymerization. In general, nanoarchitecture has been produced using masked and maskless lithography. In addition to these techniques, NMs can also be created using a number of additional methods like laser ablation, arc discharge, and sputtering [39]. To obtain defect-free sheets, though, so that the top-down synthesis procedure may fully realize the potential of the NMs, a number of restrictions must be overcome. ii. “Bottom-up” approach Atoms are typically sewn together to create atomically thin particles or sheets of NMs in bottom-up techniques. Bottom-up techniques take advantage of atoms or molecules that impulsively coalesce to form well-arranged NSs or NMs as illustrated in Fig. 3.6(b). This method is highly helpful for building precise systems at the nanoscale, especially for biological, organic, and other soft materials, especially NSs within optical diffraction range. CVD, solvothermal, molecular beam epitaxy, and hydrothermal techniques are some of the bottom-up strategies. The bottom-up methods are often renowned for producing 2D sheets of materials of excellent quality. Almost all 2D NMs are synthesized using bottom-up methods; however, bottom-up methods are routinely used to create 2D metal-organic NSs, coordination polymers, and covalent-organic NSs [40]. Nonlayered nanosheets, or NMs, are frequently created using solution-based chemical processes, and are typically synthesized using the wet chemical approach. The earlier approaches faced significant obstacles when scaling up or producing high-quality NMs. For instance, it was challenging to manage the coprecipitation method’s chemical homogeneity and particle size. Along with the product, impurities also precipitated. Similar to this, the sol-gel method takes long and post-processing is necessary to obtain excellent purity of synthetic NMs. Several good-quality synthetic NMs or NSs were created through this strong technology of CVD, which may be used to create a variety of NMs. Nevertheless, because of the strict requirements for the high vacuum, high temperature, and particular substrate, its use for commercial purposes is restricted. However, the wet chemical processes are better known for producing NMs without a layer structure. These procedures still need a lot of work to be established for the synthesis of NMs because they are in their initial phases. This study has made it abundantly evident that there are a variety of bottom-up methods

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Ball milling

High speed Capping agent

Reactants

Bulk precursor

Activated precursor High speed

High speed

Ball milling

Ball milling

(a)

(b)

Fig. 3.6: Development of synthetic NMs via (a) “top-down” and (b) “bottom-up” approach using high speed ball milling technique.

for creating NMs, and that major efforts are needed to uncover more durable methods that will enable the creation of NMs of the highest caliber and devoid of any undesirable flaws [41]. To effectively utilize the special characteristics of the NMs, a clean method must be developed to transfer the NMs onto the necessary substrate. Hybrid approaches must be developed by integrating both the techniques to develop highperformance synthetic NMs for advanced applications in different environments.

3.5 Development of NMs for varied applications Due to the fact that they have different physicochemical properties from their counterparts, NMs have potential in varied sectors of biotechnology, opto-electronics, agriculture, and food industries. These characteristics of nanoparticles compared to bulk material are because of their tiny size, huge surface area, and high surface energy. As the first nanoceramics were being developed in the 1980s, numerous applications in several sectors were investigated. Compared to their metallic counterparts, nanoceramics are more reliable and cost-effective. Numerous home products, including sunscreen, socks, sports equipment, clothing, bedding, detergents, mobile phones, and electronic devices, use NMs and their different forms [42]. Due to the distinguished features of synthetic NMs, they can be employed for specific applications based on demands of the industries or customers. By changing their atoms, NMs can primarily have their color, strength, conductivity, and reactivity significantly altered to suit the

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user’s preferences. Most importantly, NMs are completely safe for everyday use in solid form. Additionally, because NMs have some antibacterial qualities, they have been used to disinfect water. NT offers a chance to improve treatment methodologies of wastewater for more effective environmental remediation and its sustainability concerns [14]. As shown in Fig. 3.7, NMs exhibit varied spans of specific utilities to make industrial advancement and life becomes efficient and effortless by employing NMs based technologies. This section has covered the specifics of varied applications of synthetic NMs.

Electronics Bioengineering

Biogas production

Medicine

Applications of NMs

Food & cosmetics

Energy& Environment

Construction Agriculture

Fig. 3.7: Development in NMs for different field of applications.

3.5.1 Electronics Over the past few years, the rising demand for display panels of bigger size and with better display characteristics has led to NMs becoming more common in display technology. Computer monitors and televisions commonly have these displays. Current displays use light-emitting diodes (LEDs) made from a variety of materials; including cadmium sulfide, lead telluride, zinc selenide, and sulfide. The popularity of portable consumer electronics like laptops and mobile phones has led to an increase in compact and wispy energy storage systems with large storage capabilities. When choosing a material to be used as a separator plate in batteries, NMs are the better choice [25]. Aerogel batteries have a much better energy storage capacity than traditional batteries because of their structure, which is similar to foam. Metal hydride and nanocrystalline nickel batteries have a higher surface area than conventional batteries, requiring less charge during their lifetime.

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3.5.2 Water treatment To produce safe water, treatments of wastewater techniques have been created. Production of safe drinking water free from microbial contamination operates on the premise of inactivating and eliminating pathogens. Numerous techniques, including the use of UV rays, ozone, chlorination, sterilization, and filtration using the separation based on size approach, have been developed for disinfecting water. In comparison to conventional water treatment technologies, photocatalysis is receiving increasing attention for its ability to inactivate waterborne biohazards. Graphene, metal-free conjugated polymer polymers, ZnO, and metallates have all been employed as primary components for wastewater treatment using photocatalysts. The photocatalytic pathogen inactivation mechanism has been enhanced by the introduction of metaloxyhalides and transition metal dichalcogenides. In comparison to zero- and one- dimensional synthetic NMs, the two-dimensional NMs excel in energy production, structural advancement, tenability, and charge separation, offering appropriate locations adsorption and surface reactivity of contaminants [33]. This is because they have distinct structural traits. Recently, variants of graphene-based NMs have been presented as promising antibacterial disinfectants. Broad-spectrum antimicrobial agents and graphene-based materials have the ability to destroy and minimize a variety of live organisms. Due to certain structural and associated properties, they have qualities and superior structures that can defeat harmful germs and function as effective disinfectants [8].

3.5.3 Biogas production The production of biogas and methane from organic substances including animal manure, agricultural wastes, industrial waste food, and sewage sludge is accomplished by the complicated microbial process known as anaerobic digestion. It comprises four sequential microbiological processes carried out by a group of microorganisms: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The final result, called biogas, is mostly composed of methane, which makes up 60–70% of it, carbon dioxide, which makes up 30–40%, and a few other gases, including ammonia, hydrogen sulfide, hydrogen, nitrogen, oxygen, and a small quantity of water vapor. Using NMs is advantageous because of their accurate ion dosing, which enables improvement of the anaerobic digestion process and increased methane generation [43]. On the other hand, there may be certain toxicological and environmental risks with the widespread application of synthetic NMs.

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3.5.4 Agriculture Synthetic NMs have notable role in the processing of food, corps and agriculture. NT has the potential to substantially modify current farming practices. Due to several reasons such leaching, photolysis, drifting, hydrolysis, and microbial degradation, the majority of agrochemicals applied to crops are lost and do not reach the desired area. A low-cost, site-specific method of applying fertilizers and insecticides that minimizes collateral harm is provided by NMs and nanocapsules. Due to its ability to precisely manage and release fertilizers, insecticides, and herbicides, NT is becoming more and more popular in agriculture. High sensitivity, low detection limits, excellent selectivity, rapid responses, and compact dimensions are all characteristics of nanosensors used to detect pesticide residue [44]. They can also establish the amount of moisture and nutrients in the soil.

3.5.5 Nanobioremediation The effective abolition of contaminants present in the polluted environment can be done using synthetic NMs. These synthetic NMs have shown to be effective at manipulating and detoxifying a variety of pollutants, the process being known as nanobioremediation. Nanobioremediation is a cost-effective, nontoxic way to create a sustainable environment. As they are less harmful to microorganisms than other materials, NMs are possible candidates for the bioremediation process. Additionally, they have stronger microbial activity against hazardous and particle waste, which speeds up the cleanup process and lowers costs. Examples of NMs employed in nanobioremediation include CNTs, iron and its compounds at nanoscale, nanoscale dendrimers, customized NMs, and single enzyme NMs [45]. During the removal of pollutants having high hydrophobicity and soil treatment, some of the synthetic polymeric NMs have been used. Biogenic uranite-based NMs have been used in uranium bioremediation. Additionally, several naturally occurring NMs were produced by organisms like Noaea mucronata, Centaurea virgata, Scariola orientalis, Reseda lutea, Eleagnum angustifolia, Bacillus sp., and Gundelia tournefortii to eradicate the heavy metals and their ions such as lead, copper, zinc, and nickel.

3.5.6 Extraction and exploration of oil The large surface area-to-volume ratio of synthetic NMs and their chemical receptiveness have attracted the attention of researchers in the upstream petroleum sector. NMs have been studied as potential water flooding additives since the first day of their manufacturing. As an effective additive for flooded water and affected flooding region, NMs have also been researched (secondary and tertiary recoveries). For en-

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hanced oil recovery (EOR) applications, NMs were studied on a lab scale as wettability modifiers, emulsion stabilizers, and performance enhancers for polymer, and surfactant flooding processes [46]. Of all the several types of NMs, silica NMs have drawn the greatest attention for use in EOR applications.

3.5.7 Drug delivery The biomedical use of mesoporous silica NMs (MSNs) has attracted attention. Mesoporous features and huge surface area made MSNs a more viable alternative f than traditional methods for drug delivery. In the field of biomedical research, MSN applications have grown exponentially. The use of MSNs as nanocarriers, with their distinctive mesoporous architectures, has been studied for a number of therapeutic purposes, including the engineering of bone and tendon tissue, the treatment of diabetes, the treatment of cancer, and the delivery of drugs to treat inflammation. Due to various anatomical obstacles and the presence of the eye’s clearance processes, an ophthalmic medication supply carrier requires effective transfer of drug into the aperture of the patient. However, NMs-based medicine delivery will be more beneficial than traditional techniques. To increase the bio-accumulation of an ophthalmic medication precursor in ocular drug supply carriers, researchers have used various agents such as hydrogel, liposomes, polymeric micelles, and dendrimers [26]. The most effective tool recently developed to meet requirements for the optimum drug supply is nanocarrier-based ocular medication delivery systems. Due to their tiny size, they are highly suited to the large diffusivity inside membranes of the corneal epithelium. Numerous investigations were shown that the topical injection of these NMs increased the drug permeability in the cornea [16]. Additionally, the developments in their demands or utilities of synthetic NMs have been used as ophthalmic medication supply carriers that likely use several NSs agents as drug delivery.

3.5.8 Food Food NT has been expanding quickly over the few years as a result of the unique properties that nanoscale structures have demonstrated, which enhance material characteristics such as sensing, bioengineering properties, physical attributes, chemical behavior, antimicrobial, and healthful concerns of the eatables. Food scientists in particular are modifying conceptual frameworks from other disciplines. Several disciplines have the potential to offer solutions for the food business, including materials science and engineering, pharmaceutics, colloidal and polymer sciences, and condensed matter physics [47]. The use of NT improves the food sector by improving the processes of gathering, processing, preserving, and packing. The coated films of synthetic NMs have the ability to effectively interact with antimicrobial compounds when they are used to package food and allow them to sustain their nutritional values for long durations.

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3.5.9 Cosmetics and sunscreens Usually conventional sunscreen that shields against ultraviolet (UV) rays does not maintain its stability over time. Synthetic NMs such as TiO2- and ZnO-based sunscreen have a number of advantages, out of which the effective protection of skin from UV rays is the most desirable feature. Therefore certain sunscreens use ZnO and TiO2 NPs for better sun protection factor. Both zinc oxide and titanium oxide NMs absorb and reflect UV radiation in addition to being transparent to visible light [48]. Iron oxide NMs are used in some lipsticks as a pigment.

3.5.10 Vaccine development Vaccines are frequently regarded as essential immunological weapons in the fight against infectious illnesses because they give recipients strong, long-lasting immune protection. Due to their distinct physicochemical characteristics in comparison to other bulk compounds, NMs are highly in demand for bio-engineering and medicinal applications. NPs have the ability to enter tissues deeply, enhance cellular uptake, and escape from lysosomal compartments. The Covid-19 epidemic, which is currently affecting large populations because of their wide prevalence, protracted maturation timespan, unavailability of suitable medicines or vaccines, and lack of any obvious signs of abatement, only makes the situation worse. NMs possess the potential to be used as complementary, viral mimics, and vehicles for antigen delivery. So an mRNA vaccine that was administered via lipid NMs was the first vaccine to be created and put into clinical trials. By activating antigen-representing cells, the adjuvant’s primary function is to improve specific feedback of immune structure to the least amount of antigen administered [49]. Al NPs are used as adjuvants in vaccines against several diseases such as tetanus and influenza virus. The main purpose of these adjuvants in vaccines is to stimulate potent antigen-specific immune responses. Another potential possibility for a NMs vaccine is hyaluronic acid (HA), which is both biodegradable and naturally occurring in humans. In addition, HA has shown promise in clinical trials for the cancer therapy [50].

3.5.11 Gas sensor In the course of normal production and existence, gases which are flammable, volatile, toxic, and hazardous cause serious threat to the health and safety of both people and the environment. There is consequently an acute need for high-performance machinery that can identify these toxic gases. Gas sensors play a crucial part in the identification of several gases because of their capacity to transform a specified volume of gas percentage into electrical signals. They are useful since they are affordable, fast to

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respond, sensitive, and picky. Additionally, the gas sensor gadget does not require any additional wiring or calibration to be employed for optoelectronic devices. These sensing devices are highly demanding in a wide range of fields, such as monitoring and diagnostics. The procedure of developing NM-based gas sensors has been mastered by scientists during the last few decades. The core operating concept of several gas sensor types, including semiconductors, polymers, and electrolytes, allows for differentiation [42]. The sensors based on semiconductor devices act as the most significant and highly demanding sensor across the globe because of their versatility, high response, cost economics, and ease of fabrication.

3.5.12 Construction NT has resulted in quicker, less expensive, and safer practices in the construction industry. Incorporating nanosilica into traditional concrete has the effect of enhancing its mechanical properties and durability. Hematite NMs are added to concrete to strengthen it. Steel is incomparable as a building material due to its availability and adaptability. High-strength construction cables fabricated from steel for bridges are made possible by the introduction of NMs for the steel industry to produce nano-sized steel. Glass is an essential part of building supplies. Due to the potential advantages of adding NT, glass for construction purposes is a popular research area. Due to their antimicrobial, sterilizing, and catalyzing properties as well as their capacity to catalyze a powerful chemical process, which disassociates organic compounds and contaminants, titanium dioxide NMs are used to cover glazing. NT-based window coverings are better at blocking heat and light from the outside. Self-healing qualities, corrosion resistance, and insulation can all be accomplished by adding NMs to paints. The NMs-induced paints are most suitable for the protection of metallic pipe and fittings from oxidation and rusting brought on through sea or river due to their hydrophobic qualities [51]. The inclusion of NMs benefits paints because they are lighter and have superior qualities. Large things, like airplanes, can benefit from this technique because it makes them lighter overall and requires less paint, benefiting both the environment and the bottom line of the business.

3.6 Characterization of NMs The advancements in the broad range of characterization approaches have also been prioritized in light of the extraordinary and novel features discovered in NSMs. This is because it is necessary to look into and identify the properties that are created in terms of microstructure, physical attributes, chemical behaviors, mechanical strength, optical, and electrical nature. The evaluation of the discovered attributes and their relationship to the functionality of the examined materials determines the signifi-

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cance of a thorough and correct characterization [21]. The efficiency and failure of NMs can then be predicted using this knowledge. Numerous systems were adopted to investigate physicochemical characteristics of NMs [42]. These procedures include methods from the categories of thermal analysis, electrophoresis, chromatography, and so on, as well as techniques from the fields of optics, microscopy, scattering, and spectroscopy. The available characterization techniques that are frequently used to characterize the NMs are listed in Tab. 3.1. An overview of the characterization procedures is shown in Fig. 3.8. To understand how NMs behave in intended applications, the following main properties of NMs must be researched and analyzed.

Emission spectroscopy PL

Surface morphology

SEM

FTIR

Functional group analysis

Internal morphology

TEM

Fig. 3.8: Different characterization techniques used for analysis of synthetic NMs.

3.6.1 Size One of the most fundamental and important metrics for the characterization of NMs is particle size. This element affects whether a particle is micro or nanoscale, as well

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as its size, distribution, and scale. Most frequently, the method used to measure particle size and distribution is electron microscopy. For the examination of solid-phase bulk samples, laser diffraction methods are used, while images acquired through scanning electron microscope (SEM) and transmission electron microscope (TEM) are employed for investigation of size of fabricated NMs. The two major methodologies that are employed to measure the NPs dispersed in the solution are photon correlation spectroscopy and centrifugation. It is challenging and maybe even irresponsible to employ imaging techniques when working on gaseous phase NPs. A scanning mobility particle sizer (SMPS) was employed as a result because it is quicker and more accurate than other measurement methods.

3.6.2 Surface area and surface energy Another crucial aspect to take into account when describing synthesized NMs is their surface area. The effectiveness and response of NMs are greatly impacted by the proportion of surface area to volume. The most desirable process for the analysis of surface area of NMs is Brunauer-Emmett-Teller (BET) technique. The surface area of NPs discovered in solution can be determined by a simple titration, although this method is tedious and time-consuming. Nuclear magnetic resonance (NMR) spectroscopy is found to be an effective technique and as a result widely employed further. A differential mobility analyzer (DMA) and a modified SMPS are used to calculate surface area of gaseous phase NMs. The surface charge and total surface energy of synthetic NMs determines the interactions it has with a target. One of the most popular uses for a zeta potentiometer is to measure the surface charge and stability of NMs dispersed in liquid phase. The gaseous phase NMs can be analyzed though a dynamic mechanical analyzer.

3.6.3 Composition and concentration The compositional analysis of elements and their compounds in the synthetic NMs are closely related to their purity and functionality. In spite of secondary reactions and contaminations during the process, it is feasible that the NPs’ increased secondary or undesirable element content will reduce its effectiveness. The technique known as X-ray photoelectron spectroscopy (XPS) is frequently employed to measure percentage elements available in the synthetic NMs. Few characterizations involve chemically digesting NPs first, and then processing through solution phase synthesis that may involve spectroscopic techniques for mass and atomic percentage and ion chromatography. Solution-phase chemical methods are employed to investigate NPs in the gaseous phase that have been collected by filtering. To examine the concentration of air or gas for the specific chemical operation, it is important to compute amount of particles available in

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the NMs, which spread in the gas. By taking into account elements including the concentration, size, and dispersion of NMs in a defined volume of air or gas, response may be assessed in terms of its efficacy. The measurements of concentration are often performed using a condensation particle counter.

3.6.4 Morphology and crystallography These two features, which are crucial for making use of NMs’ capabilities, may be found in a large span of forms and surface patterns. There are numerous shapes, including irregular, spherical, flat, cylindrical, tubular, and cylindrical. The surfaces of these structures might be uniform or have imperfections, and they can be crystalline or amorphous. The surface is often identified using imaging techniques that employ SEM and TEM analysis. When using electron microscopy for imaging, the NPs disperse in the solution extracted though filtration; whereas the gaseous phase NPs are surface depositions for further investigation. The analysis of configuration of atoms, molecules, and their compounds available in the crystals formed in the NMs is known as crystallography. Powder X-ray, electron, or neutron diffraction crystallography are best suited to determine the structural organization of NMs. The description of the characterization procedures that are frequently employed in NM analysis and property evaluation are listed in Tab. 3.1. Reliable and trustworthy measuring techniques for NMs will have a big impact on the use of these materials in Tab. 3.1: Summary of characterization techniques employed to investigate characteristics of synthetic NMs. Specific attributes of NMs

Required method of characterizations

References

Size, shape, dispersion, and aspect ratio

SEM, TEM, atomic force microscopy, Scanning tunneling microscopy

Mass, thermal degradation

Thermo gravimetric analyzer

[]

Bonding structure, surface composition, ligand binding

Fourier transform infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance

[]

Structure, crystal orientation, phase, microstructures, texture, defects, grain morphology, deformation

Electron backscatter diffraction

[]

Optoelectronic characteristics

UV spectroscopy, PL spectroscopy, Fluorescence spectroscopy

Realistic D particle visualization, quantitative information

Electron tomography

[, ]

[]

[]

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Tab. 3.1 (continued) Specific attributes of NMs

Required method of characterizations

References

Magnetic characteristics

Vibrating sample magnetometer

[]

Dielectric characteristics

Broadband dielectric spectroscopy

[]

Thermal characteristics

Thermal gravimetric analysis, differential scanning calorimetry

Compositional analysis

X-ray fluorescence spectroscopy, mass spectroscopy

[]

Elemental surface analysis

Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy

[]

Polymorph crystallinity, and crystallite size

X-ray powder diffraction, Wide angle X-ray scattering

[]

Surface area and porosity

Brunauer-Emmett-Teller surface area, Mercury intrusion porosimetry

[]

Wettability and surface energy

Contact angle measurements

[]

[, ]

commercial applications and the industry’s capacity to follow regulations. However, there are significant challenges in the study of NMs because of the interdisciplinary nature of the topic, the lack of suitable reference materials for the calibration of analytical equipment, the difficulties associated with sample preparation for analysis, and the interpretation of the data [18]. Additional open issues in NP characterization include the in situ and online measurements of NP concentration, particularly in scaled-up manufacturing, as well as their analysis in intricate matrices. It is also important to monitor the waste and effluents from industrial processes [23]. As the production of nanoparticles increases, more accurate measurement techniques will be required. This makes it crucial to clearly specify the NMs that have been created via a number of different techniques.

3.7 Summary and future outlook The last two decades have seen considerable growth in the field of synthetic NMs. As current technology quickly became obsolete in favor of new ones, business expanded. The demands for NMs have improved extensively in a variety of industries, including electronics, pharmaceuticals, energy, defense, agriculture, food, and sanitation. However, the widespread and careless use of NMs raises some issues for public safety, health, and the environment. Therefore, researchers and technocrats must collaborate to fabricate better and nontoxic NMs that can diminish negative impacts of NT

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and cause sustainable development. There are now plenty of theoretical and experimental literature investigations on NMs and NT. The efficiency of fabrication of NMs defines the advancement in the future technologies and in materials engineering. The creation and efficient application of NMs, however, present numerous difficulties. In this part, some of the most pressing issues are discussed, along with potential solutions and future outlook. – The performance of NMs may be impacted due to defects, and their inborn qualities. Currently CNTs are well-known strongest nanomaterials for varied applications. The tensile strength of CNTs, however, is significantly reduced by impurities, discontinuous tube lengths, flaws, and random orientations. – Another significant problem is the synthesis of NMs by efficient, affordable methods. High-quality NMs are typically created in challenging conditions with complex apparatus, which restricts their large-scale manufacture. The synthesis of 2D NMs is more dependent on this problem. The majority of low-cost production techniques are used on a big scale; however they typically result in low-quality, defective items. Controlled NM synthesis is still a difficult task. More concentrated efforts are needed to create novel synthesis techniques that overcome the drawbacks of existing ones. – Performance in pertinent sectors is significantly harmed by the intrinsic problem of particle aggregation at the nanoscale level. When NMs collide, the majority of them begin to group together. Agglomeration may occur as a result of electrostatic interactions, physical entanglement, or high surface energy. The high surface areas and other distinctive characteristics of NMs are damaged as a result of excessive agglomeration. These make it difficult to use composite materials or high-throughput electrode materials in practical applications. – The creation of 3D designs allows for the tuning of NMs’ efficiency. To enhance the intrinsic properties of numerous NMs, including graphene, 3D designs have been tested. Large specific surface area and rapid electron or mass carrier mechanics have been made possible by 3D designs of 2D graphene. The excellent intrinsic characteristics of graphene combined with 3D porous architectures have made this possible. The area of nanotechnology research that has received the most attention is the integration of graphene and CNT assemblies into 3D designs. By making the interior of other NMs available, porous designs of other NMs can be built to improve their catalytic performance. – The two-dimensional ultrathin NMs are a remarkable family of NMs having significant physical characteristics; yet, with the exception of graphene, few experimental findings and examination of such NMs have been performed. Two of the biggest problems with two-dimensional ultrathin NMs is their stability and production. It is projected that their synthesis and practical application will receive more attention in the future. – Industry is using NMs more frequently, and demand for the manufacturing of nanoscale materials is rising. Furthermore, the field of nanotechnology study has

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–

–

–

–

a very broad scope; when new NMs with intriguing properties are explored, new regions will be found in the future. Out of all the concerns, the most controlling factor for the fabrication of NMs is its toxicity or human hazards that cannot be disregarded. However the fullfledged investigations and findings of toxic behavior of synthetic NMs are not yet studied. This is a huge issue given their use in the home, workplace, and environment. Uncertainty exists over the potential contribution of compounds containing nanoparticles to cellular toxicity. The scientific community must work to close the information gap between the quick growth of NMs and their potential toxicity in vivo. For the safe design and marketing of nanotechnology, a thorough understanding of how NMs interact with organisms, tissues, and proteins is essential. Developments of NT-based domains are related to advancements and future of synthetic NMs and modern technologies. The development of NMs-based engineering techniques is targeting the development of sustainable and clean production of energies. They have produced novel categories of devices such as solar and hydrogen fuel cells, that can act as an efficient catalysts for advanced applications like water splitting and hydrogen storage. These materials have showed promising outcomes. The future of NMs in the realm of nanomedicine is very bright. The dedicated biological compounds and drugs can effectively transfer to the human body though synthetic NMs-based nanocarriers. Research on the negative effects of synthetic NMs must be done in-depth before NMs-based technology and items are made available for purchase. Additionally, it is necessary to identify the risk, assess the dangers, and develop safety measures. The creation of safe items and technology is required. When creating new technology, the most significant factor that must be taken into consideration is thorough investigation of toxicity and human hazards. This is a much needed aspect for the scenarios when prolonged exposure of NMs with human body will occur. Further researchers should create an accurate database of drug dose and its impacts, which includes overall exposure duration, maximum limit, and allowable limits for work safety and health monitoring. The dangers associated with NMs exposure could be reduced to acceptable levels with the use of effective risk assessment and analysis methods.

Nomenclature ZnO TiO2 MgO SiC V2O5

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Zinc oxide Titanium oxide Magnesium oxide Silicon carbide Vanadium oxide

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NiCl2 CdCl2 CdI2 CNTs NMs NCs CVD LEDs NT UV EOR HA MSMs NSs NPs SEM TEM SMPS NMR DMA BET XPS

Nickel chloride Cadmium chloride Cadmium iodide Carbon nanotubes Nanomaterials Nanocomposites Chemical vapor deposition Light emitting diodes Nanotechnology Ultraviolet Enhanced oil recovery Hyaluronic acid Mesoporous silica nanomaterials Nanomaterials Nanoparticles Scanning electron microscope Transmission electron microscope Scanning mobility particle sizer Nuclear magnetic resonance Differential mobility analyzer Brunauer-Emmett-Teller X-ray photoelectron spectroscopy

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Niraj Kumari, Dipti Bharti✶, Rahul Singh, Amit Kumar, Minakshi Awasthi, Brij Kishore Tiwari

4 Advances in fabrication, development, and characterization of synthetic nanomaterials Abstract: Synthetic nanomaterials have developed into an incredible class of materials science, which consists of broad spectrum of materials in the range of 1–100 nm with at least one-dimensional structure. Nanomaterials can be fabricated by a bottom-up approach or a top-down approach with marvelous properties that are different from their counterparts. Their properties can be modulated by controlling the shape, size, structure, synthesis methods, monodispersity, and functionalization. They can be used in several research fields such as engineering, medical, environmental and agriculture because of their unique bio-physio-chemical properties. Analysis of synthetic nanomaterials have been characterized by X-ray diffraction analysis, scanning electron microscopic (SEM) technique, transmission electron microscopy (TEM) methods and UV-vis to determine their lattice pattern, morphology, dispersion, surface plasmon resonance. Further, the Fourier transform infrared (FTIR) spectroscopy analysis confirmed the binding of functional groups and the magnetic properties, which has been illustrated by the vibrating sample magnetometer (VSM) analysis that indicates synthesized materials have a saturation magnetization and coactivity. This chapter aims to illustrate the advancement in fabrication, development, and numerous characterizations of synthetic nanomaterials, which determine the features, functionalization, and their sector-specific applications in different fields of nanotechnology. Keywords: Nanotechnology, bottom-up approach, top-down approach, functionalization, monodispersity

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Corresponding author: Dipti Bharti, Department of Applied Science and Humanities, Darbhanga College of Engineering, Darbhanga, Bihar, India, e-mail: [email protected] Niraj Kumari, Rahul Singh, Department of Applied Science and Humanities, Darbhanga College of Engineering, Darbhanga, Bihar, India Amit Kumar, Department of Mechanical Engineering, Invertis University Bareilly, Uttar Pradesh, India Minakshi Awasthi, Department of Applied Science, Greater Noida Institute of Engineering & Technology, Greater Noida, Uttar Pradesh, India Brij Kishore Tiwari, Department of Applied Science & Humanities, G.L. Bajaj Institutes of Technology and Management, Greater Noida, India https://doi.org/10.1515/9783111137902-004

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4.1 Introduction Globally, the nanotechnology is considered as the most rapidly growing branch of science in modern research, which connects various disciplines of science and engineering, including the agricultural sector, significant areas in medical and pharmaceuticals industries, biotechnology, chemical sciences, physics, and many more. The study of the fabrication, development and utilization of materials that have dimensions in the range of 1 to 100 nm (approximately) is carried out under the nanotechnology branch [1–3]. The various properties including all the physical, chemical, and biological methods are changes in molecules or atoms and their corresponding bulk within this range [4]. Nanomaterials are the core particles of nanotechnology. The famous scientist, Richard Feynman, was the first introduce the concept of nanotechnology and nanoscience during the delivery of his lecture on the topic, “There is plenty of room at the bottom” at the American institute of Technology (AIT) America. The word “nano” implies the value 10−9 derived from the Greek word nanos, meaning “dwarf,” and used as a prefix [5, 6]. So, the nanostructured materials is defined as the smallest molecule having a dimension lesser than 100 nm. Let us understand with few examples, the dimension of the human hair is around ~10,000 nm wide, in the structure of DNA, a strand is around 2.5 nm wide, and the size of hydrogen atom is ~0.1 nm. For the growth, development, and synthesis of nanoparticles, as a surface analytical tool for the fabrication of nanomaterials as well as to change its different properties, photonics is a branch of science that plays a major role globally, nowadays [7]. Nanomaterial components with at least one dimension in the range of 10 – 100 nm are defined as particulate dispersal of solid particles. The synthesis fabrication of nanomolecules provides important methods for nanotechnology and nanosciences. Preparation of nanoparticles into bulk shapes, converting them to nano size is a different challenge in the field of nanoscience as far engineering applications are concerned [8, 9]. The ratio of surface and volume of nanoparticles is the most significant characteristic of nanoparticles, allowing them to associate with other particles easily [10]. By manipulating the composition and dimensions of the nanomaterials in a controlled manner, various physical, chemical, biological, photo-electrochemical, mechanical, thermal, electrical, optical, magnetic, and catalytic properties can possibly be modulated [11, 12]. There is a different type of artificial process for nanomaterials under development to increase their properties and retard the fabricating costs. Method-specific nanomaterials are generated by modifying their optical, electrical, mechanical, physical, chemical and biological properties. Now, scientists are able to identify nanomaterials from different characterizing tools and techniques to find useful applications [13, 14]. Therefore, nanomaterials are found everywhere, from viruses to cellular organization in the living world, from kitchenware to electronics, from renewable energy to aerospace, etc. [15, 16]. For the synthesis and fabrication of nanomaterials, various chemical and synthetic methods have evolved with time. Two such methods reported for the synthesis of different nanocomponents are: bottom-up (self-assembly) and top-down approach. The bottom-up approach is the

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Gibbs free energy-based method, which includes the synthesis of structure in molecule at molecule, atom at atom, or by its self-arrangement mechanism. Therefore, the synthesized materials are closure to a thermodynamic equilibrium state [17, 18]. In the case of the top-down approach, the bulk material breaks down into fine particles through size reduction up to nanoparticles by conventional techniques such as lithographic techniques [19]. Few physical methods are reported for the synthesis of nanomaterials; they have been employed in mechanical grinding, ball milling, ultrasonication, radiolysis, spray-pyrolysis, electrospinning, light irradiation, ablation with laser, etc. Chemicalbased methods includes, chemical reduction, sol-gel method, coprecipitation, salvothermal, spray pyrolysis, micellar medium, template-based methods, etc. [20]. The nanocomponent contains well-defined chemical, physical, and medicinal properties compared to their bulk size. These prepared nanomolecules also enhanced the mechanical strength because of their increased chemical reactivity or stability, stiffness, size, etc. – all these properties are enhanced in nanoparticles. Various uses of nanoparticles are reported in literature because of their specific and significant properties [21–23]. It is impossible to search for the different physical and chemical properties of nanomolecules after the synthesis, such as their shape, size, morphology, surface area, solubility and stability, because their physical, chemical, and biological identities are altered [24, 25]. Therefore, investigation of their properties is carried out by X-ray diffractometry (XRD) for crystal structure study; Ultraviolet–Visible spectroscopy (UV–Vis) for authentication of synthesized nanomaterials; Fourier-transform infrared spectroscopy (FTIR) for the recognition of functional groups; scanning electron microscopy (SEM) for the morphology of nanomaterials; atomic force microscopy (AFM) for surface interaction forces mapping; shape, size, and structure visualization by transmission electron microscopy (TEM); and energy-dispersive X-ray spectroscopy (EDX) for purity determination and for mapping elemental composition determination. In this chapter, we describe, how applied machinery can effectively work to adopt the different methods of microparticles synthesis for a enlarged circumference of its characterizations [26, 27].

4.2 Fabrication of nanomaterials This study has been found to explore the material and methods used in the preparation of microparticles. Microparticles are majorly prepared by using two ways depicted in Fig. 4.1. a) Bottom-up method The process of creating nanomaterials from the bottom-up method, also known as self-assembly, needs the application of physical or chemical forces to join component parts into useful nanostructures. Through atom to atom cluster, materials are created using this technique at the nanoscale [17, 60]. Examples of bottom-up approaches by applying chemical forces and other mechanical force to build everything for existence

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Fig. 4.1: Fabricating techniques for the formation of nanoparticles.

include biological and soft chemical systems [18]. By creating atomic clusters that may come together form increasingly complex structures, scientists are attempting to mimic nature. The most abundantly adopted bottom-up techniques for creating nanomaterials include sol-gel, co-precipitation, chemical vapor deposition (CVD), spinning, laser pyrolysis, and biosynthesis [19, 27, 61]. b) Sol-gel method Metal oxides, ceramics, and glasses are frequently made using the sol-gel process, a soft chemical method that is very pliable. Usually, in this method, metal alkoxides or organic metalloid inorganic salts are used. Suspension in colloidal form or a sol from the precursor components is formed; a sequence of hydrolysis and reactions of polycondensation take place [28]. During the reaction period at room temperature and pressure, the molecules found in the sol-gel system transition from homogenous sol liquid to a solidifying gel state. Following gel formation, metal oxide nanoparticles are created by calcining and drying at various temperatures. Compared to high-temperature techniques, which produce pure, homogeneous, and meta-stable nanomaterials at lower operating temperatures, it has significant advantages. The main disadvantages of this metal alkoxide-based sol-gel method, particularly for mixed metal oxide, include sensitive moisture and a lack of precursor availability [29]. c) Spinning method A device called a spinning disc reactor was utilized for the spinning method of synthesizing nanomaterials (SDR). Inside an SDR chamber or reactor, a rotating disc revolves while being subjected to controlled physical conditions, including temperature and humidity. By pulling out oxygen from the reaction tank and replacing it with nitrogen

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or another inert gas, an inert atmosphere is generated in order to stop the chemical reactions. It is crucial to annihilate oxygen gas from the vessel to avoid reactions that may reduce their effectiveness during the production of nanomaterials. This method involves spinning and precipitation to combine the smaller molecules [22, 29]. The SDR’s characteristics, such as temperature, rotation speed, humidity, disc surface area, precursor to liquid ratio, and many more have an effect on the properties of the microparticles [30]. d) Chemical vapor deposition (CVD) method Chemical vapor accumulation is a type of chemical procedure that calls for a reaction to turn volatile precursors into solid molecules that are then deposited on surfaces at the right temperature. In this process, the powder or film is deposited when gaseous particles come into contact with a heated, heterogeneous surface. In the CVD process, the majority of reactions are endothermic, in which energy is expended to the reacting body in the form of mass energy [31]. In this method, temperature has a significant impact on the synthesis of nanomaterials. The creation of homogenous, pure, and rigid nanomaterials is one of the key benefits of this technique. Formation of the explosive, dangerous, and corrosive precursor gases that are formed as toxic gaseous as a byproduct is the major disadvantage of this process. Based on the input energy to initiate the process, the CVD method is subcategorized as plasma-enhanced CVD, thermal-activated CVD, and photo-initiated CVD [32, 33]. e) Pyrolysis method This is the typical technique for synthesizing nanomaterials on an industrial scale in large quantities. The foundation of pyrolysis is the burning of precursor materials under intense pressure and heat. Pyrolysis is a heat-aided chemical process in which a substance is heated at elevated temperatures in the boiler without oxygen to break it down into smaller components. The precursor ingredients are introduced into the boiler through a small aperture in either liquid or gaseous form. When compared to alternative methods of nanomaterial production, pyrolysis offers several benefits, including a continuous process, high yield, ease of use, and cost-effectiveness [33, 34]. f) Biosynthesis method The biosynthetic approach for producing nanomaterials is economical, nontoxic, of high yield, quick, biodegradable, and environmentally benign. Many studies have looked at the biosynthesis of nanomaterials using a variety of biological components, including viruses, bacteria, fungi, yeast, microalgae, plants, domestic waste, and outdated medications [34]. As a result, this special technique has improved the properties of nanomaterials, which have several uses in the fields of engineering, agriculture, and medicine. Microorganisms may naturally adapt to a variety of conditions and multiply quickly with little upkeep. These microbes have the capacity to manufacture a small number of distinctive nanomaterials, including nanocellulose, nanowires, and exo-polysaccharides. In comparison to chemical and physical procedures, biosynthe-

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sis is a safer way to create nanomaterials. Microorganisms can produce nanomaterials either through extracellular or intracellular processes [35]. g) Top-down methods Breaking down a material to its atomic level is necessary for the top-down method. In this technique, at the microscopic level, the long-range ordered linkage of structures is used to synthesize the nanomaterials. It is also known as a destructive technique. It is based on the disintegration of large-scale materials at the nanoscale [11–14]. When bottom-up methods fail and there is a need to generate materials with complex shapes or sizes, top-down methods are more readily available. Mechanical ball milling, laserassisted ablation, sputtering, nanolithography, and thermal breakdown are few of the most frequently used techniques within this process for making nanomaterials [36]. h) Mechanical milling method The majority of economical and high-yield processes for the production of nanomaterials use mechanical milling methods. In this milling procedure, the materials are ground at the nanoscale using balls and a milling chamber. A ball mill is a vessel made of stainless steel that contains a lot of tiny, rotating tungsten carbide, silicon carbide, iron, and steel balls. By using this method, materials are ground and put into a metal container where they are reduced to the nanoscale. In a ball mill, the grinding medium has the kinetic energy, which is transferred to reduce the size of the material. This method is most frequently used, showing various advantages as compared to other top-down procedures [36]. The milling vial is filled with a quantity of the grinding materials, which is compressed. The vial-balls interaction and friction evolve pressure and heat, which leads to dramatic phase transition at elevated temperatures. Particle fracture, plastic deformation, and cold welding, which preserve the nanomaterials’ shape and size, are some significant aspects that have an impact on the fabrication process and maintain the quality of nanomaterials [37]. i) Nanolithography method Nanolithography is used to develop materials at the nanoscale from bulk materials. It is an extremely useful and powerful technique for the synthesis of 2D metal array at nanoscale on surfaces through a multistep procedure, with defined size, shape, and spacing. Lithography is the process of nanomaterials synthesis from light-sensitive bulk materials to nanoscale of the required shape and size, which selectively reshuffles a section of the bulk materials to develop the required shape [12–17]. It exists as optical, multi-photon, electron-beam, nano-imprint and scanning probe lithography. The primary benefit of nanolithography is high-yield, uniformly sized and shaped nanoparticles. The expensive setup and complexity of the equipment are a few limitations in this method [38]. j) Laser ablation method Using several solvent precursors and laser-assisted ablation procedures, nanomaterials can be produced. The simplest and fastest way for producing several nanomateri-

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als from metallic solutions dissolved in liquid solutions uses laser irradiation [19, 20]. These nanomaterials include metals, polymers, semiconductors, and complex semiconductor alloys. This method does not require a prolonged chemical reaction period, high temperature, or pressure. Water-based ultrapure colloidal solutions are made while nanomaterials are being generated. Instead of using the traditional chemical reduction method to make metals, this top-down approach can be used to make metal nanoparticles [25]. This method is perfect for environmentally friendly research since it allows the synthesis of stable nanomaterials in organic solvents or with the help of nontoxic solvents such as water. Therefore, this method costs less, is eco-friendly, and nonhazardous [39]. k) Sputtering method Sputtering is the method of creating nanomaterials in which intense plasma particles are used to attack the surface of the target material, ejecting minute particles of a solid material or atoms. Atoms are expelled from the target when they are accelerated by the result of attack of ions, which results in a momentum transfer. In reaction to collisions with ions expelled from the surface of the targeted substances, sputtering deposits nanomaterials on the surface [38]. So, a tiny layer of nanomaterials is applied, and it is subsequently annealed. Nanomaterials’ size and shape are affected by several variables, which includes annealing temperature, time, substrate, layer thickness, etc. With this technique, a broad range of nanocomponents, including pure metals, semiconductors, alloys, oxides, carbides, sulphides, and nitrides can be excited and sputtered [31]. The limitation of the sputtering of inert gas composition is that the surface morphology, composition, texture, and optical properties of the nanomaterial coating are affected [40]. l) Thermal decomposition method This technique is a novel one for the thermal breakdown-based production of stable mono-dispersed nanomaterials. This process turns endothermic because the main reaction takes place in the presence of heat. With heat, the chemical bond breaking and depositing inside compounds is essential for the synthesis of nanomaterials. The size and shape of nanomaterials are controlled by temperature, pressure, reactant concentrations, stabilizer concentrations, synthesis time, and surfactant type. Researchers have noted that unlike biological approaches, solvent-free thermal decomposition leads to the simultaneous production of nanomaterials in large amounts [36]. They also claim that the process is simple to moderate and with limit in requirement of raw materials. The main drawback of this strategy is the challenge to deposit pure nanomaterials from a wide range of combinations of metal compositions [41].

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4.3 Characterization The properties that characterize diverse aspects of nanoparticles govern their potential use in various fields. Nanomaterials are used in a wide industrial domain, including in engineering, agriculture, and medicine. To ascertain the chemical, physical, and biological properties of nanomaterials prior to their use, characterization is crucial. Nanomaterials’ physical characteristics, such as their optical, mechanical, magnetic, electrical, and thermal capabilities, are crucial in understanding how best to use them for sustainable energy. The stability of the nanomaterials with regard to the targeted molecules and their sensitivity to environmental factors viz. heat, moisture, and light are both influenced by the chemical reactivity. The biological features of nanoparticles include toxicity, flammability, oxidative potential, reduction potential, anticorrosion, antibacterial, antifungal, and disinfectant capabilities [11, 12, 42]. The biological characteristics of the nanomaterials, including their anticorrosiveness, antibacterial, antifungal, disinfection, toxicity, flammability, oxidative potential, and reduction potential, all influence the specific uses to which they are put. In order to characterize the surface of nanomaterials, numerous approaches are used to explain the features of nanomaterials Tab. 4.1. An overview of the characterization procedures is shown in Fig. 4.2. Scanning electron microscopy (SEM), extended X-ray absorption fine structure (EXAFS), Transmission electron microscopy (TEM), and low-energy electron diffraction (LEED) are common techniques for characterizing nanomaterials. These techniques are used to detect surface topography, while secondary ion mass spectroscopy (SIMS), auger electron spectra (AES), electron probe microanalysis (EPMA), and other techniques are used to identify surface complexes of nanomaterials [43]. Tab. 4.1: Characterization of nanomaterials in different phases. Characteristics of nanomaterials

Solid phase

Liquid phase

Gaseous phase

1.

Size

Laser diffraction and Electron microscope (SEM, TEM)

Photon correlation spectroscopy (dynamic light scattering) and centrifugation

Optimal particles counter (OPC) method

2.

Surface area

BrunauerChemical Emmett-Teller titration and NMR (BET) theory spectroscopy

Scanning mobility particle sizer (SMPS) and differential mobility particle sizer (DMPS)

References [, ]

[, , ]

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Tab. 4.1 (continued) Characteristics of nanomaterials

Solid phase

Liquid phase

Gaseous phase

References

3.

Composition

Chemical digestion method and X-ray photoelectron spectroscopy (XPS)

Ion chromatography and mass spectrometry

Wet chemical methods or spectrometric

4.

Surface morphology

SEM and TEM

SEM, TEM, and particles deposition

SEM and TEM

[–]

5.

Surface charge

Point zero charge (PZC)

Zeta potential

Differential mobility particle sizer (DMPS) analyzer

[–]

6.

Crystallography

X-ray X-ray diffractometer diffractometer

X-ray diffractometer

[, ]

[, ]

a) Size of nanomaterials One of the most fundamental and significant metrics of nanomaterials is their particle size. This measurement is used to find the size and dispersal of the materials. Basis the size, they are on the micro- or nanoscale. The size ranges from 1 nm to 100 nm. The determination of the particle size and its distribution is by the electron microscopy technique. However, in the solid phase, the sample is used to identify by the technique of laser diffraction and for the analysis of size and cluster, Scanning electron microscope (SEM) and transmission electron microscope (TEM) are used. In liquid phase, the techniques adopted to gauge the particle size and distribution are photon correlation spectroscopy and centrifugation. It is particularly difficult to find the dimension and distribution of nanomaterials when they are present in the gaseous phase. When nanomaterials are present in a gaseous phase, it can be particularly challenging to measure their size and distribution; as a consequence, scanning mobility particle size (SMPS) is used to assess the particle size; it is faster and more accurate than other measuring techniques [43–45]. b) Surface area of nanomaterials Another crucial characteristic to describe is the surface area of materials. It is quantified in terms of the impact ratio of surface area-to-volume ratio to know the characteristics of nanomaterials. The performance and properties of nanomaterials are significantly affected by their surface area-to-volume ratio. The most popular charac-

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terizing method for figuring out surface areas and pore size distribution in solid phases is BET analysis [39–44]. For the determination of particle surface area in the liquid phase, the titration method is adopted. The advance and quick method to find out the surface area of nano particles is the nuclear magnetic resonance spectroscopy (NMR). With the help of differential mobility analyzer (DMA) and a modified SMPS, the surface area of nanomaterials present in the gaseous phase is measured [46]. c) Composition of nanomaterials Purity and effectiveness are closely tied to the chemical or elemental makeup of nanomaterials, which determines their effectiveness and activity. If undesirable components in nanomaterials diminish their activity and effectiveness, this could lead to unintended/harmful side effects. As a result, the purity of nanomaterials is determined by composition [1, 18]. X-ray photoelectron spectroscopy (XPS) has been adopted for the determination of nanomaterials’ composition. In addition to spectrometric or wet chemical methods, several methods have been employed to study nanomaterials in liquid and gaseous phases, including mass spectrometry, ion chromatography, and atomic emission spectroscopy (AES) [47]. d) Surface morphology of nanomaterials Nanomaterials have a wide size-spectral and form, which is vital for harnessing their features. Nanomaterials can be flat, asymmetrical, cylindrical, hexagonal, cubic, spherical, tubular, or conical in shape. These shapes have two different surface morphologies, crystalline and amorphous, both of which can have a smooth or uneven surface. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) use imaging techniques for surface morphology analysis of nanomaterials. By imaging techniques, a layer is formed on the surface and the nanomaterials in liquid medium are also examined by SEM and TEM [21–25]. Particles collected by filtration and electrostatic force are used to study surface morphology in gaseous phase nanomaterials, and the collected particles are studied by SEM and TEM [48–50]. e) Surface charge of nanomaterials The interactions of nanomaterials with targeted substances are analyzed by either the overall charges or their surface charges. The fixed charges present on the surface of nanomaterials made with different metallic and non-metallic substances plays crucial role in defining the properties of nanoparticles [51–55]. By using the zeta potentiometer, the determination of dispersion and the surface charges stability of materials in liquid phase are determined. In another way, the surface charge of nanomaterials present in the gaseous phase is also determined by using differential mobility analyzer (DMA) [56–58]. f) Crystallography of nanomaterials Crystallography comprises the technique of systematic arrangement of atoms or molecules within the material itself. Atoms or molecules are arranged in a unique plane, which negotiate the structural arrangement and cause nanomaterials’ properties.

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Fig. 4.2: Overview of characterizing technique.

Powder X-ray, electron and diffraction of neutrons are used to find the structural organization of nanomaterials [59].

4.4 Conclusion Nanotechnology was initially described by their functional properties, which stated that these nanoparticles may interact with other significant disciplines connected to humans and the environment. This book chapter provides important information about the synthesis and characterization of nanoparticles. With the help of this investigation, a suitable method may be chosen for the synthesis of nanomaterials with the desired properties. Nowadays, various molecular nanocomponents, their synthesis, characterization, and applications in various disciplines are of interest to various industries. In summary, the study of nanomaterials is responsible for the revolution in various sectors such as building frameworks, gas and oil industries, catering industries, pharma industries etc. Finally, ensure the growing nanomaterial-based manufacture and characterisation, including its impact on human beings’ animals, environment, and the overall humanization process.

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[5] [6] [7]

[8] [9] [10] [11] [12] [13]

[14] [15] [16] [17] [18] [19] [20] [21] [22]

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Shashank Sharma✶, Sanjay Kumar Dubey

5 Structural, morphological, thermal, and long persistent properties of synthesized nanostructured phosphor Abstract: By using a chemical combustion synthesis (CCS) approach, an akermanitestructured (Ca2MgSi2O7) composite nanophosphor with varying amounts of doped Eu2+ and co-doped Dy3+ ions were successfully synthesized. In this present investigation, the structural, morphological, elemental composition, and thermal characteristics have been studied as an outcome of XRD, FESEM, EDX, and TL characterizations. XRD patterns have shown that the as-synthesized powder samples have single-phase tetragonal crystal structure. Thermoluminescence (TL) properties have been evaluated, including with kinetic or trapping parameters. At 110.78 °C, single TL glow curve peak of the synthesized sample UV exposed for 15 min gives optimum intensity. In this sequence, it was confirmed that the doping concentration effect of rare earth ions is more responsible for the enhancement of TL intensity. The extensive variety of TL materials discovered so far and their different physical appearances allow the determination of different radiation features. Based on the result of TL characteristics and evaluated trapping parameters, it was found that as-synthesized nano-sized material is an excellent TL material that exhibits long persistent property. TL materials with deeper traps can be used in high temperature radiation dosimetry applications. In this sequence, the present article describes the significant roles of dopant and co-dopant rare earth ions in enhancing the long persistent properties of as-synthesized nano-sized Ca2MgSi2O7: Eu2+, Dy3+ phosphor. Keywords: Chemical combustion synthesis (CCS), akermanite, Ca2MgSi2O7:Eu2+, Dy3+, thermoluminescence, radiation dosimetry

Acknowledgments: The authors express their heartfelt gratitude to all research institutions that helped the experimental facility to complete this entire research work. Muffle furnace and other experimental research equipment facility have been provided by the department of physics, Dr. Radha Bai Govt. Navin Girls College, Raipur, Chhattisgarh, India. XRD, FESEM, and EDX characterization facilities have been provided by the National Institute of Technology (NIT) Raipur, Chhattisgarh, India and the TL equipment facility has been provided by the Pt. Ravishankar Shukla University, Raipur, Chhattisgarh, India. ✶ Corresponding author: Shashank Sharma, Department of Applied Physics, Dr. C. V. Raman University, Kota, Bilaspur 495113, Chhattisgarh, India, e-mail: [email protected], Orcid ID: https://orcid.org/0000-0002-1316-6021 Sanjay Kumar Dubey, Department of Physics, Dr. Radha Bai, Govt. Navin Girls College, Mathpara, Raipur, 492001, Chhattisgarh, India, e-mail: [email protected] Orcid ID: https://orcid.org/0000-0002-8729-7163

https://doi.org/10.1515/9783111137902-005

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5.1 Introduction Chemical combustion synthesis (CCS) technique has developed into a more significant and well-established procedure for the formation of homogenous, unagglomerated, superfine crystalline, nanostructured, composite oxide ceramic powder materials, which is possible in the absence of the requirement for intermediate breakdown and/or calcining stages [1, 2]. Akermanite structure exists in Ca2MgSi2O7: Eu2+, Dy3+ phosphor. The CCS technique using NH2CONH2 (as a fuel) and H3BO3 (as a flux) is a simple, efficient, and affordable approach for the synthesis process. Ca2MgSi2O7: Eu2+, Dy3+ is a well-known efficient phosphor that exhibits green emission with excellent stability and persistency [3]. A vast variety of chemical compounds known as mellite, are identified by their usual structure composition ½A2 T1 T22 O7 ], [where A = Ba, Sr, Ca; T1 = Mg, Zn, Cu, Mn, Co; T2 = Ge, Si] and have been extensively investigated in the form of optical materials [4, 5]. The numerous advantages of White Light Emitting Diodes (WLEDs), such as in lighting fixtures, safety-indicating road signs, luminous paints, graphical arts, and other potential industries, are being given more and more attention [6]. According to a “hole transfer model”, put forward by Matsuzawa et al., it was stated that Eu2+ ions served as electron traps (Eu2+ + e → Eu+) while Dy3+ ions served as hole traps (Dy3+ + hole → Dy4+). Between the lower energy state (ground) and higher energy state (excited) state of Eu2+ ions, Dy3+ ions serve as deep hole trap levels [7]. TL measurements can provide considerable information about the traps in the long-lasting phosphors, including their nature. In order to understand more about trapping energy and detrapping procedures, temperaturedependent glow intensity is recorded using TL spectra [8, 9]. Nowadays, the CCS approach is widely used for the synthesis of nano-sized materials, because it allows for control of the size of the particles, shape, morphology and its chemical composition, and phase structure of the as-prepared powder materials [10]. That is, the crystallite grain size of the formed powder sample is achieved in the nanometer range (1–100 nm). One of the liquid-phase methods for the synthesis, the CCS approach, is a more efficient and energy-saving way to produce phosphor with smaller particle sizes and regular morphologies. Creating oxides, aluminates, and silicate phosphor powders using the CCS approach is a simple and quick procedure that has lately been employed successfully for large-scale manufacturing. The europium (Eu) and dysprosium (Dy) ions have drawn a lot of interest among other rare-earth-doped phosphors. Many varieties of Eu-doped and Dy-co-doped phosphors have been created recently. Previous literature: the work done on this synthesized material highlights its applications, advantages, and drawbacks. Our result shows a remarkable and novel work that is different from previous literature. That is, higher TL intensity and the proper combination between oxidizer, fuel, and flux. Previous studies used ammonium nitrate (NH4NO3) as an oxidizer and urea employed as a fuel to synthesize this material. But currently, we have used all metal nitrates as oxidizers and boric acid employed as flux, along with urea employed as a fuel. Using flux further accelerated the prepara-

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tion process of the material sample. Due to this, the perfect combination of fuel and material gave the appearance of superfine nanocrystalline structure. As a result, the doping process became simpler. The rare earth ions must have well occupied the host crystal lattice sites without affecting the crystal structure of Ca2MgSi2O7. The main advantages of this unique TL material are that it is more suited to a variety of important applications such as in radiation oncology, medicine, energy storage devices, high radiation dosimetry, and in vivo dosimetry on patients during radiotherapy treatments in medical fields due to its higher TL intensity.

5.2 Experimental section 5.2.1 Phosphor synthesis process The exothermic exchange between fuel and oxidizer is the foundation of the CCS approach. Regarding ease of use, cost-effectiveness, energy efficiency, purity, and uniformity, this technique offers a number of benefits over the other approaches [10–12]. The CCS process necessitates the use of fuel and oxidizers. Boric acid is employed as flux, along with urea employed as a fuel, while all metal nitrates are utilized as oxidizers. The stoichiometric proportions of all metal nitrates and fuel are estimated using propellant chemistry. Consequently, when the ratio of oxidizer to fuel is equal to 1, the heat of combustion is at its optimum. Ca2MgSi2O7:Eu2+, Dy3+ (CMSED) phosphor was synthesized well using a low-temperature CCS approach. The precursor chemical ingredients such as Ca (NO3)2✶6H2O, Mg(NO3)2✶6H2O, SiO2✶H2O, Eu(NO3)3✶5H2O, Dy(NO3)3✶5H2O, and NH2CONH2, as well as H3BO3 were employed in the present experiment. The chemical reagents employed for this experiment were all of analytical reagent grade and purity (99.99%). A schematic diagram of the synthetization process of CMSED composite material is shown in Fig. 5.1. The fuel and oxidizers were combined with all of the components in the appropriate ratios. The next step involved adding a very small amount of double-distilled ionized water. A large-capacity cylindrical silica crucible was employed to preserve the mixture after it had been converted into a well-homogenized paste, and it was placed in a muffle furnace that had already been preheated and calibrated at 650 °C for 5 min. The combination evaporates and ignites when heated quickly, producing a white substance. In a matter of minutes, the entire combustion process is complete. The resultant powder samples were stored in a 30-mL sealed silica crucible with a weak reducing environment provided by burning charcoal, and then they were post-annealed at 950 °C for one hour. Finally, the finished goods were eventually produced once the programmable muffle furnace cooled down. The resulting phosphor was then stored in water-and air-tight container for additional characterization analysis like XRD, FESEM, EDX, and TL. This is the process sequence of a chemical reaction mechanism:

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CaðNO3 Þ2 + MgðNO3 Þ2 + SiO2 ✶ H2 O + NH2 CONH2 + H3 BO3 ! Ca2 MgSi2 O7 + H2 Oð"Þ + CO2 ð"Þ + N2 ð"Þ

(5:1)

CaðNO3 Þ2 + MgðNO3 Þ2 + SiO2 ✶ H2 O + EuðNO3 Þ3 + DyðNO3 Þ3 + NH2 CONH2 + H3 BO3 ! Ca2 MgSi2 O7 :Eu2 + , Dy3 + + H2 Oð"Þ + CO2 ð"Þ + N2 ð"Þ

Fig. 5.1: Schematic diagram showing synthesis of Ca2MgSi2O7: Eu2+, Dy3+ Phosphor.

(5:2)

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5.2.2 Phosphor characterization techniques Using a D8 Advanced Bruker XRD diffractometer, the structural characterization and phase purity of Ca2MgSi2O7: (RE: Eu2+, Dy3+) nanocrystalline powder sample were measured within the range of Bragg’s angle 2θ (10 °C ≤ 2θ ≤ 80 °C) with target Cu-Kα radiation (λ = 1.54056 Å). The elemental composition and surface morphological analysis of the as-synthesized powder material were measured with the help of a ZEISS EVO Series EVO 18 field emission scanning electron microscope fitted with an EDX (Energy Dispersive X-ray Spectrum). Using an integral personal computer-based TL reader (Nucleonix TL-10091), the TL data were recorded.

5.3 Results and discussion 5.3.1 Analysis of powder X-ray diffraction (XRD) With the use of powder XRD patterns, the crystal structure and phase purity of obtained powder samples are examined. The powder XRD pattern of as-synthesized Ca2MgSi2O7: Eu2+, Dy3+ sample are displayed in Fig. 5.2. The synthesized CMSED crystal structure was single-phased and well-indexed with the JCPDS file #77-1149 [13], as indicated by the XRD pattern and Data Base Code AMCSD file 0008032 [14]. Akermanite-type structure describes the crystalline structures of synthesized phosphor, which is a member of the tetragonal crystal system with the cell parameters a = b = 7.8071 Å, c = 4.9821 Å; and α = 90°, β = 90°, γ = 90°, and space group is P¯421 m (113 space number & D32d space group) while point group is −42 m. Ca2MgSi2O7 crystal structure has a cell volume of 303.663 Å3 and a molar density of 2.944 gm/cm3 [15]. Minimal effects of the doped Eu and Dy ions on host lattice crystal structures. The doping ions are present since there are no further impurity diffraction peaks and their contents have been integrated into the host crystal lattice site (Ca2MgSi2O7).

5.3.1.1 Confirmation of the existence of doping ions occupying the host crystal lattice sites According to Jiang et al. [16], Ca2+ sites, Mg2+ sites, or Si4+ sites may be used to incorporate Eu2+ into the host (CMS) lattice site. Mg2+ (0.58 Å) and Si4+ (0.26 Å) sites are small, whereas Ca2+ (1.12 Å) is exactly the same size as Eu2+ (1.12 Å). Hence, Eu2+ ions primarily occupy into [CaO8] anion complexes in host Ca2MgSi2O7 phosphor and barely ever into tetrahedral [MgO4] and [SiO4] sites [16]. As a result, it is indeed preferable for Eu2+ doping ions to incorporate the Ca2+ lattice sites. The doping ion [Eu2+] has the ability to incorporate two varied lattice sites from the inside of the undoped structure (Ca2MgSi2O7). The eightcoordinated Ca2+ site (Ca1 site) and the six-coordinated Ca2+ site (Ca2 site) are two alternative crystal lattice sites that Ca2+ can incorporate. When Eu2+ cation enters the undoped

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Fig. 5.2: Powder XRD patterns of synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor.

crystal lattice site, it incorporates nearly all of the original Ca2+ sites. In the forms of (Eu1) EuO6 & (Eu2) EuO8 with 6 & 8 coordination, Eu2+ cations are positioned in two different crystallographic lattice sites. A long decay time of the phosphor is very essential because the co-dopant [Dy3+] ion enhances electron trapping and provides additional trap levels [17]. Figure 5.2 displays that the crystalline nano-sized material has been synthesized at 950 °C. Compared to the high-temperature conventional solid-state synthesis approach, the sample preparation temperature is reduced to at least 200–300 °C.

5.3.1.2 Estimation of crystallite size (D) The XRD measurement displays a slight shift towards the larger angle in contrast to the standard reference data. From the XRD diffraction peaks, the crystallite size was determined with the help of the Debye-Scherrer empirical formula [15]. Debye-Scherrer empirical expression is as follows: D=

kλ βCosθ

(5:3)

where k (0.94) stands for the Debye-Scherrer constant, D stands for the crystallite size for respective (hkl) plane, θ stands for the corresponding Braggs diffraction angle, λ stands for the wavelength of the incident X-ray radiation, and β stands for the FWHM (full width at half maxima) in radiations. Table 5.1 presents that the average crystallite size (D) of as-synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor was determined with the

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Tab. 5.1: Determination of average crystallite size (D) of synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor. Braggs angle (θ)

Respective (hkl) planes

. . . . . . . Average Crystallite Size (D)

      

Calculated crystallite size (D)  nm  nm  nm  nm  nm  nm  nm ~. nm

help of more intense and isolated powder XRD peaks with respective Braggs angle (2θ) and their respective (hkl) planes.

5.3.2 Analysis of surface morphology (FESEM) FESEM analyses were performed to determine the size, shape, and surface morphology of the synthesized materials. Figure 5.3 represents a general overview of the surface morphology of the combustion-synthesized Ca2MgSi2O7: Eu2+, Dy3+ powder sample calcined at 950 °C with a magnification of 30.00 K X. The finding suggests that grain morphology is not the cause of the increase in luminescence efficiency. The precursor powders were micron-sized and spherical in appearance. Moreover, it exhibits aggregated grains that may be the result of the powder’s residence time within a combustion furnace. Throughout the combustion reaction process, the particles cluster and get larger. It is apparent that the synthesized powder sample contains particles with a variety of size distributions. It is shown clearly that the as-prepared powder samples were comprised of a complex distribution of particles of varied size and shape. The sample appears to have small particles with a diameter of 1 μm, indicating that the synthesized crystal is in nano form.

5.3.3 Analysis of energy dispersive x-ray spectrum (EDX) Both organic analysis and quantifiable data analysis describing the chemical composition and elemental structure of the powder material samples are provided with the help of EDX spectrum analysis. EDX spectrum may be extensively used to predict with certainty whether powder samples contain additional elements such as contaminants or adducts. These impurities are either provided with the basic materials to be modified or they happen accidentally with the reagent molecules. The number of components in

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Fig. 5.3: FESEM image of Ca2MgSi2O7: Eu2+, Dy3+ phosphor with 30.00 K X magnification.

Fig. 5.4: EDX spectrum of synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor.

a spectrum is inversely proportional to its intensity. EDS is an effective method for determining the chemical makeup of as-synthesized powder samples. It has been figured out that the sample material’s chemical composition was determined using EDX spectroscopy. A conventional technique is used to determine and mea-

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sure the chemical compositions of sample areas with superfine crystal structures from as small as feasible nanometer range. The EDX spectrum reveals that the actual chemical composition and existence of elements in as-synthesized Ca2MgSi2O7: Eu2+, Dy3+ sample in Fig. 5.4 comprises the examination of the elements Ca, Mg, Si, O, Dy, and Eu in detail. Furthermore, the relevant EDX spectrum for the doping ions (Eu and Dy) clearly shows their presence. On observing the EDX spectrum of the as-synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor, it is clear that there was no observable additional emission except Ca (calcium), Si (silicon), and O (oxygen). Table 5.2 presents the chemical composition of elements determined in weight percent and atomic percent. Tab. 5.2: Chemical composition of synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor. Elements OK Mg K Si K Ca L Eu L Dy L Total

Atomic (%)

Weight (%)

. . . . . . .

. . . . . . .

5.3.4 Analysis of thermoluminescence (TL) spectra High-temperature radiation dosimetry seems to be the major application in which TL phosphors are often used. If a mechanism is established, novel luminescent materials can be used in a variety of ways. TL dosimetry has implications for radiation protection, health physics, and personal monitoring. TL materials have exceptional thermal, chemical, and mechanical properties, as well as a low reliance on radiation energy, a high degree of sensitivity, minimal fading, and a very low threshold dosage [18], indicating that they are an ideal thermoluminescent material.

5.3.4.1 Determination of thermoluminescence (TL) trapping or kinetic parameters TL trapping or kinetic parameters are known to be an excellent and systematic technique for determining the trap positions of any kind of powder material sample. Almost any phosphor’s TL analysis is primarily determined by its own trapping or kinetic parameters. The peak-shape approach is an excellent option for figuring relevant kinetic parameters. Basically, three types of kinetic parameters are determined by this method, which are as follows: First is the order of kinetics (b), under which

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1st, 2nd & 3rd order of kinetics are determined. Second is the frequency factor (s), and third is the trap-depth, which is also called as activation energy (E) [19–21]. Chen has proposed the empirical framework known as the peak-shape method. Usually, this eminent method is identified to as Chen’s empirical method [22]. This technique is additionally applicable to assessing the defect centers and band-gaps of prohibited energy in which the energy levels are located. As a consequence, this technique is frequently applied as a practical and effective way to examine the entirety of the obtained TL glow peak curve. As shown in Fig. 5.5., Tm denotes the optimum temperature of the obtained TL glow peak curve; and T1 denotes the temperature at halfminima intensity (i.e. ascending order part of the obtained TL glow peak curve), while T2 denotes the temperature at half-maxima intensity (i.e. descending order part of the obtained TL glow peak curve). These temperature differences have been used to derive the other significant general order parameters (τ, δ, ω); where τ is determined by Tm−T1, and δ is determined by T2−Tm, and ω is determined by T2−T1. All trapping parameters are determined using these general order parameters (τ, δ, ω) [27]. Peak Shape of TL Glow Curve

TL Intensity (a.u.)

Im

ω lm/2

τ

δ

Tm

T1

T2

Temperature (in K) Fig. 5.5: Peak shape of TL glow curve.

5.3.4.1.1 Determination of order of kinetics (b) This trapping or kinetic parameter is a very essential parameter for any TL glow peak curve that may be evaluated by applying geometric shape factor [µg] from the preceding numerical expression as follows: μg =

δ T2 − Tm = T2 − T1 ω

(5:4)

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In order to distinguish between 1st, 2nd, and mixed order of kinetics, the geometric shape factor (µg) is an important factor for the evaluation of any TL) glow peak curve. A precalculated standard numerical value of the geometric shape factor (µg) helps in determining the different order of kinetics. Case 1: If the value of µg is in the range of (0.39–0.42), then the 1st-order of kinetics is determined. Case 2: If the value of µg is in the range of (0.49–0.52), then the 2nd-order of kinetics is determined. Case 3: If the value of µg is in the range of (0.43–0.48), then the mixed order of kinetics is determined [23–26]. 5.3.4.1.2 Determination of activation energy or trap depth (E) The trapped electron requires considerable energy to liberate itself. It is referred to as activation energy, which is also called as “trap depth,” and it is responsible for forcibly releasing an electron from the defect-center and afterwards it is transported to the conduction band [27]. The following numerical expression, which is applicable to any order of kinetics (such as 1stt, 2nd, and mixed order of kinetics), can be utilized to determine the value of trap depth. ! kT2m Eα = Cα (5:5) − bα ð2kTm Þ α With the assistance of the aforementioned numerical expression, which probably applies for any kinetics-related general order, Cα and bα (where the value of α is τ, δ, & ω) are evaluated [47]:   (5:6) Cτ = ½1.51 + 3 μg − 0.42 , bτ = ½1.58 + 4.2ðμ g − 0.42Þ Cδ = ½0.976 + 7.3ðμg − 0.42Þ, bδ = 0

(5:7)

Cω = ½2.52 + 10.2ðμg − 0.42Þ, bω = 1.0

(5:8)

5.3.4.1.3 Determination of frequency factor (s−1) Among the most important trapping or kinetic parameters is frequency factor, which is extensively used for the characterization of any material sample [27]. The preceding numerical expression (as described earlier) is used to substitute the predefined variables, namely order of kinetics [b] and trap depth or activation energy [E] in order to compute this trapping parameter, which is called the frequency factor (s−1).   βE 2kTm expð− E=kTm Þ = s 1 + ð b − 1Þ (5:9) E kT2m

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where k stands for the “Boltzmann constant,” which has a value of 1.380649 × 10−23 m2kgs−2 K−1; E stands for the “trap depth or activation energy,” which has a unit of electron volt (eV); and b determines the “1st, 2nd, and mixed order of kinetics”. The value of b = 1 for 1st order of kinetics, and the value of b = 2 for 2nd order of kinetics. In addition, Tm stands for the “optimum temperature” peak position of TL glow curve, and β stands the “heating rate” of the any synthesized powder sample, which was taken as its value 50Cs−1 at current research work [23–26].

5.3.4.2 Doping concentration effect of Eu2+ and Dy3+ ions To examine the trap centers and trap level in a solid substance – whether inorganic, insulator, or semiconductor – stimulated after ultraviolet exposure to any source of radiation, TL is considered as one of the most effective techniques [27]. In such situations, the charge carriers (holes or electrons) are liberated with a 5 °C/s constant heating rate, the TL glow curve peak of the Eu2+-doped and Dy3+-co-doped UV-irradiated sample material is depicted in Fig. 5.6. It is noticeable that the TL intensity increases with rising concentrations of Dy3+ ions, attains its maximum intensity, and then declines with decreasing concentrations of Dy3+ ions. As the concentration of activator ions increases, very little separation exists between the activator ions. As the ions interact more, the transferred energy increases. On the contrary, as the activator concentration increases, the energy that the ions store decreases. As a result, the activator ion concentration is at its optimum [27]. Both Matsuzawa et al. and Lin et al. proposed that the co-doped Dy3+ ions in many long-lasting phosphors (i.e. MAl2O4: [RE: Eu2+, Dy3+] & M2MgSi2O7: [RE: Eu2+, Dy3+], where M = Sr) acted as a hole trap level, enhancing the long afterglow process [30, 31]. The determined values (0.59–0.76 eV) of activation energy of the as-synthesized phosphor confirm their existence with respect to the long persistent phosphors if the determined values of trap depth or activation energy (E) lies in the range of 0.65–0.75 eV. It is ideally suited for long persistent or long afterglow characteristics, according to Sakai and Mashangva’s research reports [28, 29]. On the basis of our determined values of trap depth, the as-synthesized Ca2MgSi2O7: 2+ Eu , Dy3+ phosphor is an excellent thermoluminescent material and an efficient longpersistent phosphor. The long afterglow properties observed may also be as a result of the co-dopant [Dy3+] ion-created traps existing, which can liberate the trapped holes and then recombine with the electrons that preceded the luminescence intensity. It is quite clear that the dysprosium ion is more responsible for the hole trap level, which is due to its natural behavior. That is, as soon as the dysprosium ion enters the host crystal lattice, its natural properties cause it to generate a hole trap level. These hole trap levels are trapped very deeply in a host lattice site. It is because of these deeper traps that the material exhibits long-persisting properties. The TL glow curve clarifies that an increase in UV radiation exposure time is precisely correlated with an initial increase in TL intensity. The TL intensity of as-

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5 Structural, morphological, thermal, and long persistent properties

Thermoluminescence Intensity (a.u.)

80000

110.78°C

5 min UV Exposure Time

70000

10 min UV Exposure Time 15 min UV Exposure Time

60000

20 min UV Exposure Time 25 min UV Exposure Time

50000 40000 30000 20000 10000 0

25

50

75

100

125 150 175 200 Temperature (°C)

225

250

275

300

Fig. 5.6: TL glow curve of synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor. Tab. 5.3: The evaluated trapping parameters of synthesized Ca2MgSi2O7: Eu2+, Dy3+ phosphor. UV exposure time (s)

HTR (K/s)

T (°C) (K)

Tm (°C) (K)

T (°C) (K)

τ

δ

ω

 min  min  min  min  min

 °Cs−  °Cs−  °Cs−  °Cs−  °Cs−

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

. . . . .

Shape Activation Frequency factor (µg) energy (E) factor (S) (eV) (s−) . . . . .

. . . . .

. ×  . ×  . ×  . ×  . × 

synthesized phosphor was measured during experimental evaluation at different UV radiation exposure times such as 5 min, 10 min, 15 min, 20 min, and 25 min. It was eventually determined that 15 min of UV radiation exposure is the maximum amount of time for the TL intensity to occur. After that, it starts to fall down. It is estimated that a considerable number of charge carriers are liberated as the UV irradiation rises over time based on their experimental observations and findings of the TL glow curves. Hence, a rise in TL intensity is caused by the trap density (the trap density of charge carriers may be increasing). The effect caused during such a reduction in TL, meanwhile, begins to be destroyed after 15 min (a specific UV exposure time) because of the decline in TL caused by traps density. Thus, a reasonable explanation for the reduced TL intensity for longer irradiation times may be the declining charge carrier density (i.e. 20-min and 25-min UV irradiation exposure times).

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The optimum TL-intensity level for 15 min of UV radiation exposure time is shown in Tab. 5.3. The activation energy or trap depth (E) and frequency factor (s) of assynthesized phosphor have been found to be in the range of (0.59–0.76 eV) and (1.2 × 107 to 8.55 × 107 s−1), respectively. For the determination of order of kinetics, the geometric shape factor (μg) was found to be in the range of 0.52–0.55, indicating second order of kinetics. In comparison to the recombination mechanism process, it offers a superior possibility of re-trapping discharged charge carriers (i.e. electrons or holes) and is mainly responsible for the depths of deeper traps. The study of TL characteristics of the synthesized Ca2MgSi2O7:Eu2+, Dy3+ phosphor revealed that the phosphor obtained a very strong glow peak curve at 110 °C. The outcomes of the experimental investigation clearly reveal that the precise role of dopant [Eu2+] ions is to serve as both a luminescence center as well as a trap center [32], because the co-dopant [Dy3+] rare earth ions enhance the persistent luminescence during the doping process with the singly dopant [Eu2+] ions. On the other hand, the precise role of co-dopant [Dy3+] ion is to serve as both a trap center, as well as a luminescence center [32]. This is mainly because the precise roles of co-dopant [Dy3+] ions and other lattice defects are uncertain. Basically, the co-dopant [Dy3+] ion acts to capture electrons or holes or simply to generate or alter imperfections. This is possible because of charge compensation.

5.4 Conclusion Eu2+-doped & Dy3+-co-doped M2MgSi2O7 (where M = Ca) nanocrystalline and composite powder sample have successfully formed with the help of CCS technique, and various characterization techniques for understanding their luminescence and spectroscopic properties were thoroughly discussed. The standard JCPDS file #77-1149 was a good match with the powder XRD pattern of the synthesized phosphor. According to the FESEM micrographs, the as-synthesized phosphor was obtained in the nano-range with much better homogeneity and displays nanocrystalline behavior and a strong connection with crystal grain, which indicates that powder size and shape are tightly controlled. This may be mainly due to the material being synthesized at 950 °C. The powder XRD patterns and FESEM micrographs have revealed no discernible change; as a result, as-synthesized powder samples are effectively crystallized into tetragonal crystal structures. The EDX spectrum has confirmed the existence of the Ca, Mg, Si, O, Eu, and Dy elements in as-synthesized powder sample. A very strong single TL glow curve peak was assigned at 110.78 °C. The behavior of the TL glow curve represents that the optimum UV radiation exposure time has been found to be 15 min for the TL intensity to occur. The determined values of geometric shape factor (µg), indicating second order kinetics, are mainly responsible for depths of deeper traps. The TL intensity rises as the concentration of Dy3+ ions rises, reaches its maximum value, and then declines when Dy3+ concentrations rise after-

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wards due to the concentration quenching mechanism. The precise role of co-dopant [Dy3+] ion is to serve as both a trap center, as well as a luminescence center. The codopant ions enhance the persistent luminescence during the doping process with the single dopant [Eu2+] ions. According to the calculated values of trap depth or activation energy (E), the as-synthesized phosphor is an excellent long-persistent phosphor and efficient thermoluminescent material.

5.5 Future scope of this research work Composite materials are an ideal ecofriendly and nontoxic material, which attract attention towards better options to develop applications in various emerging research fields without affecting the environment. This as-synthesized material is extensively applicable for high-temperature TL radiation dosimetry, long-persistent process, archaeological-dating, and forensic science, as well as mineral-prospering areas. Materials have excellent thermal, chemical, and mechanical stabilities, as well as high levels of sensitivity, minimal dependence on UV radiation energy, a low threshold for exposure, and slight-fading. The uses of innovative luminous materials depend on our understanding of the mechanism. Medical dosimetry, environmental radiation, oncology radiation, biological science, radiation physics, high amounts of radiation beams are highly utilized in radiation therapy or radio-therapy for cancer treatment to kill cancer cells, medicine, neutron-dosimetry, UV radiation monitoring, thermoluminescent materials for highlevel photon dosimetry radiation, TL radiation dosimeters used in personnel monitoring should be standardized and well examined, as well as archaeological dating, mineral prospering, forensic science, reactor engineering and radiation dosimetry, are all areas where high-temperature TL radiation dosimetry is important. The luminescent features of biomaterials have prospective applications in different areas such as DNA transplantation of tumor in the field of biological science, signal processing or image recognition in the field of computer science and information technology, drug delivery in the field of pharmaceutical science, and in the field of nutrition therapy, chemotherapy, as well as in the fields of tissue engineering and bone-tissue engineering. Competing interest of research work: In our current research investigations, there are no competing financial interests or any other conflicts of interest.

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References [1] [2] [3] [4] [5] [6]

[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

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Kingsley JJ, Patil KC. A novel combustion process for the synthesis of fine particle α-alumina and related oxide materials. Mater Lett 1988, 6, 427–432. Kingsley JJ, Manickam N, Patil KC. Combustion synthesis and properties of fine particle fluorescent aluminous oxides. Bull Mater Sci 1990, 13, 179–189. Yen WM, Weber MJ. Inorganic Phosphors: Compositions, Preparation and Optical Properties. CRC press, 2004. Sharma S, Dubey SK, Diwakar AK, Pandey S. Structural characterization and luminescence properties of Ca2MgSi2O7 (CMS) phosphor. Int J Sci Res Phys Appl Sci 2022, 9, 49–53. Talwar GJ, Joshi CP, Moharil SV, Dhopte SM, Muthal PL, Kondawar VK. Combustion synthesis of Sr3MgSi2O8:Eu2+ and Sr2MgSi2O7:Eu2+ phosphors. J Lumin 2009, 129, 1239–1241. Lin L, Zhonghua ZH, Zhang W, Zheng Z, Min YI. Photo-luminescence properties and thermoluminescence curve analysis of a new white long-lasting phosphor: Ca2MgSi2O7: Dy3+. J Rare Earths 2009, 27, 749–752. Sharma S, Dubey SK, Diwakar AK. Luminescence investigation on Ca2MgSi2O7:Eu2+, Dy3+ phosphor. Int J Mater Sci 2021, 2, 8–15. Jia D, Wang XJ, Yen WM. Delocalization, thermal ionization, and energy transfer in singly doped and codoped CaAl4O7 and Y2O3. Phys Rev B 2004, 69, 235113. McKeever SW. Thermoluminescence of Solids. Cambridge University Press, 1988. Bhatkar VB, Bhatkar NV. Combustion synthesis and photoluminescence study of silicate biomaterials. Bull Mater Sci 2011, 34, 1281–1284. Ekambaram S, Patil KC. Synthesis and properties of rare earth doped lamp phosphors. Bull Mater Sci 1995, 18, 921–930. Ekambaram S, Patil KC. Synthesis and properties of Eu2+ activated blue phosphors. J Alloys Compd 1997, 248, 7–12. JCPDS (Joint Committee on Powder Diffraction Standard) PDF File No. 77-1149. Data Base Code AMCSD (American Mineralogist Crystal Structure Database) 0008032. Sharma S, Dubey SK, Diwakar AK, Pandey S. Novel white light emitting (Ca2MgSi2O7: Dy3+) Phosphor. J Mater Sci Res 2021, 8, 164–171. Jiang L, Chang C, Mao D, Feng C. Concentration quenching of Eu2+ in Ca2MgSi2O7: Eu2+ phosphor. Mater Sci Eng B 2003, 103, 271–275. Aitasalo T, Hölsä J, Jungner H, Lastusaari M, Niittykoski J. Thermoluminescence study of persistent luminescence materials: Eu2+-and R3+-doped calcium aluminates, CaAl2O4: Eu2+, R3+. J Phys Chem B 2006, 110, 4589–4598. Sharma S, Dubey SK. Significant contribution of deeper traps for long afterglow process in synthesized thermoluminescence material. J Miner Sci Mater 2022, 3, 1–6. Chen R, Mckeever S. Theory of Thermoluminescence and Related Phenomena. World Sci. Publishers, 1997. Yuan ZX, Chang CK, Mao DL, Ying W. Effect of composition on the luminescent properties of Sr4Al14O25: Eu2+, Dy3+ phosphors. J Alloys Compd 2004, 377, 268–271. Gökçe M, Oğuz KF, Karalı T, Prokic M. Influence of heating rate on thermoluminescence of Mg2SiO4: Tb dosimeter. J Phys D Appl Phys 2009, 42, 105412. Chen R. Thermally stimulated current curves with non-constant recombination lifetime. J Phys D Appl Phys 1969, 2, 371. Pagonis V, Kitis G, Furetta C. Numerical and Practical Exercises in Thermoluminescence. Springer Science & Business Media, 2006. Ege AT, Ekdal E, Karali T, Can N. Determination of thermoluminescence kinetic parameters of Li2B4O7: Cu, Ag, P. Radiat Meas 2007, 42, 1280–1284.

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[25] Jose MT, Anishia SR, Annalakshmi O, Ramasamy V. Determination of thermoluminescence kinetic parameters of thulium doped lithium calcium borate. Radiat Meas 2011, 46, 1026–1032. [26] Deshpande A, Dhoble NS, Gedam SC, Dhoble SJ. Photo and thermoluminescence in K2Mg(SO4)2:Dy phosphor and evaluation of trapping parameters. J Lumin 2016, 180, 58–63. [27] Sharma S, Dubey SK. Specific role of Novel TL material in various favorable applications. Insights Min Sci Technol 2022, 3, 1–9. [28] Mashangva M, Singh MN, Singh TB. Estimation of optimal trapping parameters relevant to persistent luminescence. Indian J Pure Appl Phys 2011, 49, 583–589. [29] Sakai R, Katsumata T, Komuro S, Morikawa T. Effect of composition on the phosphorescence from BaAl2O4: Eu2+, Dy3+ crystals. J Lumin 1999, 85, 149–154. [30] Matsuzawa T, Aoki Y, Takeuchi N, Murayama Y. A new long phosphorescent phosphor with high brightness, SrAl2O4: Eu2+, Dy3+. J Electrochem Soc 1996, 143(8), 2670–2676. [31] Lin Y, Nan CW, Zhou X, Wu J, Wang H, Chen D, Xu S. Preparation and characterization of long afterglow M2MgSi2O7-based (M: Ca, Sr, Ba) photoluminescent phosphors. Mater Chem Phys 2003, 82, 860–863. [32] Dubey SK, Sharma S, Diwakar AK, Pandey S. Synthesization of monoclinic (Ba2MgSi2O7:Dy3+) structure by combustion route. J Mater Sci Res 2021, 8, 172–179.

Dr. N. Muthukumaran✶, Dr. G. Prince Arulraj

6 Mechanical characteristics and surface roughness testing of nanomaterials in enhancing the discharge over spillways Abstract: Nanomaterials have many emerging applications. An attempt is made in this work to use the nanomaterials constructed in the flume 10 × 0.55 × 0.60 m3 size. The first spillway is plastered with cement mortar in a ratio of 1:3, the second spillway model is plastered with cement mortar wherein 40% of the cement is substituted with nanosilica fume, the third spillway model with 30% of the cement being substituted with nanocement, and the fourth spillway model with 40% of the cement being substituted with nano-fly ash. Experiments are carried out to assess the discharge over these spillways. For all the selected models, three slopes, 0.003333, 0.007778, and 0.012222 are used to calculate the discharges. The mechanical characteristics of the selected nanomaterials in enhancing the discharge are evaluated as a result. The optimal replacement levels of nanomaterials are obtained. The mechanical characteristics and surface roughness of the plaster materials containing nanoparticles are studied accordingly. The experiments related to porosity, roughness height, SEM analysis, and abrasion resistance are likewise carried out. It is found from the experimental studies that the use of nanomaterials increased the discharge over spillways in the range of 13–191%. Keywords: Nanomaterials, porosity, spillway, roughness height, SEM analysis, mechanical characteristics

6.1 Introduction Recently, because of drastic climate changes, there is greater uncertainty about the changes in seasons. High-intensity rainfall, floods, and droughts in many areas may happen because of climate change. The impact of these occurrences on the reservoir is that the water surface increases faster. This condition endangers the safety of the dams. Spillways represent the hydraulic structures used for discharging the floodwater from upstream to downstream of the reservoirs. The ogee profile spillway is hydraulically effective, structurally reliable, and sufficient to dispose of the excessive flood efficiently to downstream of dams. This spill✶

Corresponding author: Dr. N. Muthukumaran, Department of Civil Engineering, V.S.B College of Engineering Technical Campus, Coimbatore, Tamilnadu, India Dr. G. Prince Arulraj, Karunya Institute of Technology and Sciences, Karunya Nagar, Coimbatore, Tamil Nadu, India https://doi.org/10.1515/9783111137902-006

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way is responsible for regulating erosion if an appropriate energy dissipater is attached at the tail end of the structure. Generally, water flow occurs over these spillways during floods whenever the water level goes beyond the permissible bound. Likewise, the external portions of the spillways will be eroded when the water flows with extremely higher velocities. Cavitation will occur at the outer part of these spillways whenever the pressure drops below the vapor pressure. Cavitation is avoided by decreasing the flow velocity and by increasing the boundary pressure [1]. The capacities of the available spillways shall be improved by expanding the spillway crest, by enlarging the discharge coefficients or operating heads, or by the integration of these above two methods. The spillway is typically regarded as a critical structural element of the dams. Spillways are often used as redirecting mechanisms for excess water, which is redirected to different canals, ensuring the dams’ safety. The three primary units of a spillway are: the control unit allowing water to flow to the spillway, the discharge unit directing the stream from the control unit to the stream bed from the lower side of the dam, and the terminal unit restoring the flow to the river with minimal erosions at the dam’s toe. The ogee spillway is typically referred to as an S-shaped control weir, indicating the downstream-structure portion of the spillway. The ogee spillway is an improved variant of the straight drop spillway. Its shape is defined by the geometry of the bottom nappe of the free-falling jet, which is regulated by the projectile standard. The jet rises considerably above the surface of the spillway, and the jet-to-face portion is ventilated. The water falls over the curved surface of the ogee spillway. They play an important function in safely directing floodwaters downstream. Although the water drains from the higher-lower heads, it creates a greater amount of kinetic energy in the spillway foot; thus, it is critical to dissipate energy efficiently or it may cause erosion at the chute surface [2]. The ogee shape has been primarily examined by Bazin [3] and also few other researchers evaluated the physical model information from the USACE and the USBR [4]. The USACE was more concerned with the water released from the spillways in the late 1950s [5]. The ogee spillway offers a safe path for water, reducing floods. In technical terms, the ogee spillway is analogous to the functioning of the boiler’s safety valves. Typically, ogee spillways are used to release floodwaters from dams [6]. Modernizing the important principles for hydraulic structure safeness is needed for preserving the speed of climate change, lowering the possibly hazardous aftereffects on structural integrity, trying to balance the requirement for continued expansion and enhancing spillway capacities for increased discharge [7].

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6.2 Review of literature Nanoforum is a European Union-supported thematic network that provides a wideranging information source regarding every area of nanotechnology such as business, technical, and social working groups. Nanotechnology is one of the emerging technologies that permit the development of materials with enhanced or innovative properties; therefore, the utility of nanotechnology is enormous. A critical effort is made by this study, and the future is predicted to signify a clear summary of where nanotechnology stands currently concerning the effects it may possess on industries. The interpretations from twenty researchers as well as industry professionals have been offered typically from Europe in descriptive and numerical forms. Radu [8] considered the use of nanomaterials in the cement composition that may considerably lower carbon dioxide (CO2) emissions. It was noticed that nanomaterials used on the surfaces of structural elements of the buildings may result in higher environmental cleaning owing to photolytic reactions. Nanosensors used in concrete structures measure the concrete-sensitivity, viscosity, shrinkage, temperature, moisture, potential of hydrogen (PH), CO2, stress, reinforcement corrosion, and vibration. Carbon nanotubes increase the compressive strengths of cement mortar (CM) specimens and alter the electrical properties that are used in structural health monitoring and damage prevention. It was seen that the use of nanomaterials in the construction fields is appropriate for structural concretes, real-time structural monitoring, coating, and thermal insulation, etc. The final report of the Mid-America Transportation Center (MATC) describes the mechanical properties of different additives and mixtures with cementitious materials, and assessments were made with standard concrete and concrete with nanosilica fumes. It was seen that the nanosilica enhanced the compressive strength as well as elastic modulus. Mamok [9] conducted experiments in a flume setting at the Sebelas Maret University’s Hydro laboratory, where Labyrinth sharp crest spillways (LSCS) have been employed to enhance capacity without reducing the spillway peak. Six different varieties of LSCS have been utilized in this study, including the wooden Ogee prototype and acrylic LSCS. Water with varying discharges was directed to flow into the flume for testing purposes. The discharge is computed using different heads above the spillway. Both the Ogee and the LSCS were evaluated. It was determined that LSCS had a greater capacity for water discharge than the other. The water draining through the LSCS was mostly trapezoid type-1 and approximately 170% higher than that flowing via the Ogee spillways. Ali Akbar Firoozi et al. [10] examined the capability of nanotechnology in construction engineering-based applications. They studied the roles of nanotechnology in civil engineering-based applications. Also, it was observed that nanotechnology is a quickly growing research domain where the distinct properties of the materials attained on the nanoscale may be largely used in infrastructure construction. Many promising indications of improvement are expected, which may change the operational life and life cycle construction costs.

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Amir Abbas Kamanbedast et al. [11] investigated the surface roughness of the ogee spillway using a working prototype. The hydraulic performance graph and discharge coefficients were calculated. They studied a physical hydraulic model to calculate these characteristics. The measuring test was carried out by the Supreme Complex Khuzestan Water and Power Industry. In the ogee spillway model, they measured the hydraulic parameters and studied the surface roughness. There were six forms of surface roughness and five flow speeds to consider. As a response, they determined that the spillway’s relative roughness improves surface roughness while decreasing the cavitation index. Mainak Ghosal and Arun Kumar [12] conducted experiments on different types of cement (OPC, PPC, PSC) with nanosilica and nanotubes. They discovered that the addition of nanoparticles improved the mechanical characteristics of CM. Dhaktode Asaram et al. [13] conducted a field experiment to investigate the influence of ogee spillway surface slopes on the dissipation of energy. The slopes of the three modeled ogee spillway models are 1:1, 0.85:1, and 0.75:1, respectively. Alpaslan [14] developed an artificial neural network (ANN)-based model for calculating discharge levels from the ogee spillways, and the results were examined. A spillway with a width of 7.5 cm, a depth of 15 cm, and a length of 5 m was used. For dissimilar heads, discharge rates above the spillway were calculated. Discharge values have also been estimated using the measured heads’ expressions. Here, it was intended to examine the performance of the ANN-based model in calculating the discharges through ogee spillways; for this objective, both mathematical and methodical evaluations have been carried out. The ANN-based model yielded better and more precise results. The results revealed that the ANN-based model may be an alternate methodology for determining the discharge values over the spillways.

6.3 Background of the study Nanoscience corresponds to the study of manipulations of the materials in their atomic and macromolecular scales; thereby the characteristics vary considerably from those on larger scales. It refers to the design, representation, production, and applications of materials by regulating the sizes at nanometer scales. The term nanotechnology has been recommended by Taniguchi in 1974, and it was principally disseminated in 1980s by Drexler [15]. Nanotechnology signifies the formation and use of materials, devices, and systems by controlling matter at a nanometer scale. It considers taking the benefit of enhanced properties that rise exclusively from the nanoscale and generating beneficial or functional constituents possessing novel or superior properties.

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6.3.1 Nanotechnology in engineering Nanotechnology represents an active research area that includes numerous domains such as civil engineering, construction materials, etc. [16] Moreover, nanotechnology finds its application in several domains such as microbiology, medicine, electronic, chemical, materials science, etc. On the other hand, the prospective applications of several developments in nanotechnology in the construction domain are ever-growing. Construction is not a fresh science or technology; however it experienced abundant modifications starting from its origin, and the sizes of the particles are considered the most serious factor. At the nanoscale, (whatever from 100 or less than a few nanometers or 10−9 meters) material properties are changed from that of larger scales [17]. Since the particles become nano-sized, the quantity of atoms at the surface rises relatively with those of the inner-side, and this results in enhanced properties.

6.3.2 Nanotechnology in cement-based materials Here, nanotechnology can be signified as the recognition, controlling, and restructuring of the matter at nanometers for creating materials with enhanced fundamental properties. Recently, applications and advancements in nanotechnology concerning construction domains are unbalanced [18]. The exploitation of nanotechnology in concrete on a profitable scale remains restricted; nonetheless, limited results are effectively transformed into commercial products. The faster advancements in the nanoscience of cementitious materials are because of the increased primary knowledge regarding the types of cement at the nanoscale level. Nanoscience and nano-engineering represent the nano-modified concrete expressions that came into regular use. These are the two foremost possibilities concerning the applications of nanotechnology in concrete-based research [19]. Exploration and manipulation of inner properties at the nanometer scales of matters for obtaining excellent properties and performances of materials are the most lively research domains in recent times. The possibilities for the real-world applications of nanotechnology in cement-based materials are considerably large. Materials at the nanoscale act very much contrary to what they are in larger form. It corresponds to the creation, and applications of designs from engineering led to the understanding and production of enhanced materials possessing improved capabilities. There is not much information available when dealing with the production of nanocements. When the cement with nano-sized particles can be synthesized and processed, this may open up a larger volume of applications in all cement-based composite domains. Nanotechnology can increase the ability of concrete and then leads towards the formation of enhanced, sustainable, advanced cement-based composites with exceptional mechanical, thermal, and electrical properties that will promote numerous fresh prospects to arise in the upcoming days.

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6.4 Materials and methods 6.4.1 Analysis using ordinary Portland cement Portland cement is the major constituent in concrete and mortars and it is made from limestone. Portland cement is made out of finer particles that are generated by burning limestone and clay minerals together in a kiln to produce clinker, which is then crushed and mixed with 2–3% gypsum. After that, it is classified as Ordinary Portland Cement (OPC) – 43 grade and 53 grade, with only the second grade being used in this experiment to produce normal CM (1:3). Table 6.1 lists the main components of the Portland cement. Figure 6.1 is the scanning electron microscope (SEM) image of a typical CM Tab. 6.1: Basic constituents of Portland cement. Portland cement constituents Cement

Mass (%)

Calcium oxide (CaO) Silicon dioxide (SiO) Aluminum oxide (AlO) Ferric oxide (FeO) Sulphur (VI) oxide (SO)

% to % % to % .% to % % to % .% to .%

It is understood evidently from the SEM results of the normal CM that the CH particles are dispersed throughout and the C-S-H formation can be identified. When compared

Fig. 6.1: SEM image of normal cement mortar.

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with the other SEM images containing nanoparticles, the porosity value is high for the normal CM.

6.4.2 Analysis using nanocement Normal cement particles range in size from 50 to 90 μm. Nanocement particles range in size from a few nanometers to roughly 100 nanometers. These nanocement particles increase the bulk characteristics and the compressive strength of the cement, reduce the environmental pollution and the end-product thickness, and also increase the overall cost-effectiveness. The nanoparticles in the mortar provide a poreless, long-lasting surface. Nanocement for laboratory experiments is produced by grinding the OPC into nanocement. The nanoparticles are ground in a high-energy ball-grinding mill (Alaa et al.) [20]. The use of nanocement in CM improves the smoothness and reduces the surface roughness, thus boosting the flow rate. These nanoparticles additionally occupy the mortar pores, resulting in a smooth surface. Figure 6.2 depicts the SEM image of a CM containing 30% nanocement. The calcium hydroxide crystals (CH) and the C-S-H are scattered throughout the SEM image of CM containing 30% nanocement. The nanoparticles considerably enhanced the calcium silicate hydration (C-S-H) development stage. The nano-sized particles contained in the mortar rendered the surface smooth, based on the SEM image of the CM containing 30% nanocement. Since the nanoparticles occupied the pore spaces, the porosity decreased.

Fig. 6.2: SEM image of cement mortar (CM) containing 30% nanocement.

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6.4.3 Analysis using nano-fly ash The fly ash not only improves strength and durability but also reduces the requirement for cement. The fineness, particle shape, hardness, and freeze-thaw resistance are the unique properties of fly ash. However, the main disadvantage of fly ash is the problem of initial strength reduction. This drawback of fly ash can be overcome by using nano-fly ash. The transformation of micro-size to nano-structured fly ash results in a rougher and more reactive product with a smooth, glassy, and inert surface. Hence, nano-fly ash is used for partial replacements of cement.

Fig. 6.3: SEM image of cement mortar containing 40% nano-fly ash.

Fly ash (FA) is considered a cementitious constituent in concretes as per British standards from the 1980s [21]. It is used for replacing portions of cement for producing concretes of high durability [22] and with reduced cost. Nonetheless, many researchers [23] observed that the hydration process of concrete gets retarded and the initial strength will be lesser than that in ordinary concrete with the addition of fly ash. High-intensity ball milling machines are used to produce nano-fly ash. High-impact collisions are used to reduce microcrystalline materials to nanocrystalline structures without causing chemical changes [24]. In this study, SEM analysis is used to determine the particle size of nano-fly ash [25]. Figure 6.3 shows the equivalent SEM image of the CM containing 40% nano-fly ash. Ettringite (CS) and Portlandite (CH) formation can be realized from the SEM image. Ettringite is the mineral term for calcium sulfoaluminate (3CaO•Al2O3•3CaSO4•32H2O) and this can gradually soften and re-form in any of the existing voids. The CH deposits on the C-S-H are also identified. The nano-fly ash as a partial replacement in CM caused increased pozzolanic interactions that resulted in decreased surface roughness.

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6.4.4 Analysis using nanosilica fume The dimension of the silica fume is typically a hundred times lesser than normal cement particles. When the silica nanoparticles are added to the concrete, silicon dioxide mixes with the free calcium hydroxide existing at the micro holes and will form calcium silicate, also making the concrete to be dense, less penetrable, and highly resistant. With the use of silica nanoparticles, a smooth and homogenous surface can be obtained, which increases the velocity and the flow rate of the fluid in the channels. The silica fume on being mixed with the concrete will remain inert originally. When Portland cement and the water in the mixing interact, the primary chemical interactions create two chemical components: (a) calcium silicate hydrate (CSH) – a resilience crystallization compound, and (b) calcium hydroxide (CH) – responsible for enclosing pores inside the concrete as filler or leaching out from inferior concrete. The pozzolanic reaction occurs at the silica fumes with the CH, causing additional CSH in practically all of the empty spaces around the hydrated cement particles. This additional CSH provides the concrete with highly compressive, comparatively flexural, and enhanced bond strength; yet, it provides a thicker matrix often in locations with smaller voids prone to the toxic material entrance. The silica fume size is 100 times lesser than the normal cement particle. With the use of silica nanoparticles, smooth and homogeneous surface can be obtained that increases the flow rate in channels. Silica fume is a reactive pozzolanic material because of its maximum fineness with a surface area of 20,000 m2/kg. Nanosilica fume is produced by grinding the silica fume; the nanoparticles are prepared by a high-energy ball grinding mill. The equivalent SEM image of the cement mortar containing 40% nanosilica fume is depicted in Fig. 6.4.

Fig. 6.4: SEM image of the cement mortar containing 40% nanosilica fume.

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The C-S-H formation is clearly observed from the SEM image of CM with 40% nanosilica fume. It can also be seen that the Ettringite and CH formation occurred; likewise, the porosity is less when compared with the normal cement mortar.

6.5 Experimental results and discussions 6.5.1 Experimental flume The tests are carried out in a tilting flume measuring 10 × 0.55 × 0.60 m3. The flume is made up of three parts: an inflow chamber, a flume section, and a collection tank. Water is enabled to flow through the inflow chamber through three centrifugal pumps with capacities of 5hp, 3hp, and 2hp, consecutively. To decrease turbulence and regulate the flow, water from the inflow chamber is passed through two vertical layers of weld mesh. The water in the flume is regulated by two gates, one at the entry and another at the exit. A 4.2 × 0.7 × 0.6 m3 collection tank is installed at the flume’s edge to record the discharge. The time necessary for a 15-cm increase in the collection tank is determined using a piezometer installed in the collection tank. The channel’s bed slope can be varied. A transparent Perspex sheet is installed in the center of the flume to monitor the flow. The flow depth is determined using a hook gauge mounted on a trolley.

6.5.2 Design of ogee spillway Ogee spillways are widely used for concrete, brickwork, as well as other earthen dams. These ogee spillways were previously constructed using Bazin’s Profile. Numerous enhanced profiles were suggested to overcome negative pressure that may create cavitation problems, as well as other characteristics such as hydraulic efficiency, stability, and economy. Numerous customary ogee shapes are represented as the Waterways experimental station (WES) standard spillway shapes. The downstream section (d/s) profiles are signified using equation (6.1) below [26]: X n = K × Hd n−1 ×Y

(6:1)

where (X, Y) indicates the coordinates of the points in the ogee profile whose origin is the highest crest point known as the apex. Hd is the design head that contains the velocity head. K and n are constants determined by the slope of the upstream face. Therefore, for a spillway possessing a vertical u/s face, accordingly, the d/s crest can be expressed mathematically as per equation (6.2) below:

6 Mechanical characteristics and surface roughness testing

X 1.85 = K × Hd 0.85 × y

127

(6:2)

In this present study, the K is fixed as 2, and then equation (6.2) can be represented as, X 1.85 = 19.98 × y

(6:3)

The coordinates are found using equation (6.3) and the spillway coordinates are listed in Tab. 6.2. Tab. 6.2: Coordinates (in cm) of the ogee spillway. X

Y

 .  .  .  .  .  .  .  .  . 

         

The adopted downstream spillway profile is displayed in Fig. 6.5. (0,0) (12.04,5) (17.56,10) (21.87,15) (25.55,20) (28.83,25) (31.82,30) (34.59,35) (37.18,40) (39.63,45) Fig. 6.5: Adopted downstream spillway profile.

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6.5.3 Fabrication of ogee spillway The ogee spillway is constructed in the following stages. The ogee spillway is built within the tilting flume using 1:6 cement mortar bricks and is hardened for seven days. Four spillways are built to perform the tests.

Fig. 6.6: Articulation of the fabricated ogee spillway.

Cement mortar (CM) 1:6 is used to plaster the first spillway. In the second spillway, CM with 30% nanocement is used to plaster the surface of the spillway. In the third spillway, CM with 40% of nano-fly ash is used to plaster the spillway surface. The fourth spillway is plastered using mortar containing 40% of nanosilica fume. The fabricated ogee spillway is displayed in Fig. 6.6.

6.5.4 Experimental investigations Several rounds of experiments are carried out for determining the effectiveness of the nanomaterials in raising the discharge capacities of the spillways. The examination is done using a tilting flume. The impacts of nanocement, nano-fly ash, and nanosilica fume on enhancing the spillway’s discharge capacity are examined appropriately. This study employs three slopes: 0.003333, 0.007778, and 0.012222. These slopes are classified as mild slopes. Since most natural channels and rivers have just a mild slope, the mild slope was selected for this investigation. Figure 6.7 depicts the spillway stagedischarge graph with nanomaterials when the channel slope is 0.003333. Figure 6.8 depicts the spillway stage-discharge graph with nanomaterials when the channel slope is

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0.007778. Figure 6.9 depicts the stage-discharge graph of the spillways containing nanomaterials, with a channel slope of 0.012222.

Slope 0.003333 6 5

40% nano fly ash

Depth (cm)

4 3

30% nano cement

2

OPC 1

40 % nano silica fume

0 0.0000 0.0050 0.0100 0.0150 0.0200 0.0250 0.0300

Discharge (m³/ℎ) Fig. 6.7: Stage-discharge graph in spillways with nanomaterials (slope = 0.003333).

Slope 0.007778 6 5

Depth (cm)

4

40% nano fly ash

3

30% nano cement 2

OPC

1

40 % nano silica fume

0 0.0000 0.0050 0.0100 0.0150 0.0200 0.0250 0.0300

Discharge (m³/ℎ) Fig. 6.8: Stage-discharge graph in spillways with nanomaterials (slope = 0.007778).

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Slope 0.012222 6 5

Depth (cm)

4

40% nano fly ash

3

30% nano cement 2

OPC

1

40 % nano silica fume

0 0.0000

0.0100

0.0200

0.0300

0.0400

Discharge (m³/ℎ) Fig. 6.9: Stage-discharge graph for spillways with nanomaterials (slope = 0.012222).

It can be seen from Figs. 6.7–6.9 that the nanosilica fume is more effective in increasing the discharge over the spillways when compared with nanocement and nano-fly ash. The respective percentage rises in discharge values of these spillways with nanomaterials are given in Tabs. 6.3–6.5. Tab. 6.3: Percentage increase in discharges plastered with 30% of nanocement. Percentage increase in discharge (m/h) with nanocement S.No. Depth (cm) Slope  (.) Slope  (.) Slope  (.) . . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

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Tab. 6.4: Percentage increase in discharges plastered with 40% of nano-fly ash. Percentage increase in discharge (m/h) with nano-fly ash S.No. Depth (cm) Slope  (.) Slope  (.) Slope  (.) . . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

Tab. 6.5: Percentage increase in discharges plastered with 40% of nanosilica fume. Percentage increase in discharge (m/h) with nanosilica fume S.No. Depth (cm) Slope  (.) Slope  (.) Slope  (.) . . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

. . . . . . . . . .

It is understood from Figs. 6.7–6.9 and Tabs. 6.3–6.5 that the discharge of the spillway rises considerably for spillways that use the nanomaterials. The percentage increase fluctuates between 13.41 and 71.96 for those spillways using 30% nanocement with a slope of 0.003333. The percentage growth fluctuates between 7.41 and 90.96 for those spillways using 30% nanocement with a slope of 0.007778. Similarly, the percentage rise fluctuates between 15.38 and 88.05 in the case of the spillway using 30% nanocement with a slope of 0.012222. The percentage rise shows a discrepancy between 25.0 and 191.20 in the case of spillways with 40% nano-fly ash possessing a slope of 0.003333. The percentage rise shows a variation around 20.01 and 200.65 concerning the spillway formed using 40% nano-fly ash with a slope of 0.007778. Likewise, the percentage increase fluctuates around 16.23 and 150.97 concerning the spillway using 40% nano-fly ash with a slope of 0.012222.

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The percentage growth shows a discrepancy between 24.99 and 100.54 in spillways using 40% nanosilica fume with a slope of 0.003333. The percentage growth fluctuates around 19.84 and 63.72 in the case of the spillways with 40% nanosilica fume when the slope is 0.007778. The percentage growth fluctuates between 29.31 and 92.05 in spillways using 40% nanosilica fume for a slope of 0.012222. The discharge over the spillways is considerably greater when considering the spillways using 40% nano-fly ash when compared with the spillways using 30% of nanocement and 40% nanosilica fumes. The major causes of increased discharge include smooth surfaces as well as reduced surface porosity while nanomaterials are being used.

6.6 Testing surface roughness, porosity, and abrasion resistance 6.6.1 Surface roughness test Surface roughness, often known as roughness, is a constituent of surface texture that is assessed using the nonconformances of the normal vector in the ideal form of a real surface [27, 28]. When the nonconformities are larger then the surface will be rougher, and when the nonconformities are smaller then the surface will be smoother. Rougher surfaces typically will be wearing out more rapidly and also possess a greater friction coefficient when compared with smoother surfaces. The portable surface roughness tester (Mitutoyo`SJ-210 model) [29] is used in this experimentation for determining the surface roughness parameters such as Ra, Rq, and Rz. A 2.4-inch liquid-crystal display (LCD) delivers exceptional visibility as its digital visual display. In the internal memory, 10 measurement situations, as well as a measured profile can be put in storage. An additional memory card may be used as the extended memory for storing a larger quantity of the measured surface profiles. This device displays the measurements on the micrometer scale. Table 6.6 displays the comparison analysis of the roughness height values of mortar while using dissimilar nanomaterials. Tab. 6.6: Roughness height values for plastering materials with different nanomaterials. Roughness height

Cement mortar tiles

Cement mortar with % nanocement

Ra Rq Rz

. µm . µm . µm . µm . µm . µm

Cement mortar with % nanofly ash

Cement mortar with % nanosilica fume

. µm . µm . µm

. µm . µm . µm

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From Tab. 6.6, it can be seen that the surface with nano-fly ash has a smooth surface followed by nanocement and nanosilica fume.

6.6.2 Porosity test Table 6.7 gives a comparative analysis of the porosity values of tiles with dissimilar nanomaterials. Tab. 6.7: Porosity values of tiles with dissimilar nanomaterials. S.No.

Type of mortar

. . . .

Cement mortar Cement mortar with % nanosilica fume Cement mortar with % nanocement Cement mortar with % nano-fly ash

Porosity . . . .

From Tab. 6.7, it can be clearly inferred that the tiles with 40% of nano-fly ash possess the lowest value with respect to porosity.

6.6.3 Abrasion resistance test Abrasion, as signified by the American Society for Testing and Materials (ASTM), is the physical wear caused by harder particles. Abrasion resistance represents the capability of a surface to resist wearing away by friction [30]. This parameter is critically significant in the construction of floorings, highways, or pavements. Abrasion resistance will be predominantly reliant on better curing; it however relies on additional aspects like materials, proportion, etc. Table 6.8 shows the abrasion resistance of ordinary cement mortar and cement mortar containing 30% nanocement, 40% nano-fly ash, and 40% nanosilica fumes. From Tab. 6.8, it is evident that when the replacement percentages of cement with nanomaterials increase, then the percentage rise in abrasion resistance also rises correspondingly. The maximum percentage of increase in abrasion resistance is seen while the substitution level of cement with nano-fly ash is 40%. The value of the percentage increase in abrasion resistance is 31.41% for a 30% replacement of cement with nanocement. The value of the percentage increase in abrasion resistance is 44.50% for a 40% replacement of cement with nano-fly ash. The value of the percentage increase in abrasion resistance is 36.64% for a 40% replacement of cement with nanosilica fumes. Hence, it can be concluded that, as nanomaterials improve the abra-

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Tab. 6.8: Abrasion resistance of cement mortar and that with nanomaterials. Sl. Mortar No.

Abrasion Percentage increase resistance in abrasion resistance

.

Cement mortar



–

.

Cement mortar with % of nanocement



.

.

Cement mortar with % of nano-fly ash



.

.

Cement mortar with % of nanosilica



.

sion resistance significantly, they will increase the life of spillways and reduce the maintenance cost to a significant level.

6.7 Conclusions and future recommendations In this chapter, the surface roughness testing and the influence of nanomaterials in enhancing the discharge over spillways are examined using experiments, and the following conclusions are drawn: – It is noticed from the SEM image of the normal cement mortar that the CH particles are dispersed throughout and C-S-H formation is identified. When compared with other SEM images containing nanoparticles, the porosity value is higher for the normal cement mortar tiles. – It is observed from the SEM image of CM with 30% nanocement that the calcium hydroxide crystals (CH) and C-S-H are dispersed throughout. The nanoparticles considerably enhanced the calcium silicate hydration (C-S-H) development stage. The nano-sized particles contained in the mortar rendered the surface extremely smooth, according to the SEM image of the CM with 30% nanocement. As the nanoparticles filled the pore spaces, the porosity decreased. – It is perceived from the SEM image of CM with 40% nanosilica fumes that the C-SH formation is noticed. Ettringite and CH formation also occurred. The porosity is lesser when compared with normal cement. – It is seen that the discharges over spillways increase vastly concerning the spillways formed using nanomaterials. – It is understood that the percentage increase varies between 13.41 and 71.96 in spillways using 30% of nanocement with a slope of 0.003333. The percentage rise varies between 7.41 and 90.96 in spillways using 30% nanocement with a slope of

6 Mechanical characteristics and surface roughness testing

–

–

–

– –

–

135

0.007778. Also, the percentage rise shows a discrepancy between 15.38 and 88.05 for spillways with 30% nanocement with a slope of 0.012222. It is perceived that the percentage rise varies from 25.0 to 191.20 for the spillway of 40% nano-fly ash with a slope of 0.003333. The percentage rise varies from 20.01 to 200.65 in spillway using 40% nano-fly ash with a slope of 0.007778. The percentage rise shows a discrepancy from 16.23 to 150.97 in the spillway utilizing 40% nano-fly ash with a slope of 0.012222. For the spillway containing 40% nanosilica fume and a slope of 0.003333, the percentage increase ranges between 24.99 and 100.54. For the spillway containing 40% nanosilica fume and a slope of 0.007778, the percentage increase ranges between 19.84 and 63.72. For the spillway containing 40% nanosilica fume and a slope of 0.012222, the percentage increase ranges between 29.31 and 92.05. The discharge in the spillways is very high concerning the spillways using 40% nano-fly ash with respect to 30% of nanocement and 40% nanosilica fumes. The causes for this rise in discharges are due to smooth surfaces as well as lower porosity of the surfaces while nanomaterials are utilized. It is observed that the surface having nano-fly ash possessed the highest smooth surface followed by nanocement and nanosilica fume. It is seen that when the replacement percentages of cement substituted by nanomaterials increase, the percentage rise in abrasion resistance also increases correspondingly. It is observed that the nanomaterials largely enhance the abrasion resistance, and also increase the life of spillways while reducing the maintenance cost to a higher extent.

Ultimately, it can be concluded from the results that the employment of nanomaterials improved the discharge over spillways ranging between 13% and 191%, and thus, will offer a better solution for improving the discharge over spillways with improved mechanical properties. In future work, surface roughness testing and the effects of nanomaterials in enhancing the discharge over spillways will be carried out with a few other nanomaterials in order to further validate the effectiveness in selecting the best nanomaterials to meet the required objectives.

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Parsaie A, Shareef SJS, Haghiabi AH. Numerical simulation of flow on circular crested stepped spillway. Appl Water Sci 2022, 12, 215. Ashiq M, Sattar A. Optimization of energy dissipation works for Nai Gaj dam project. World Environ Water Res Cong 2010. Bazin HE. Recent experiments on the flow of water over weirs. Proc EngiMel ‘8’ Club Phila 1888, 16(6), 393–148.

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Minakshi Awasthi, Vanya Arun, Ankita Awasthi, Amit Kumar, Niraj Kumari, Dipti Bharti✶

7 Biomedical considerations of nanomaterials based on biological aspects in biomedical field Abstract: The requirements for highly functionalized biomaterials have evolved as the domain of biomedical engineering has grown to be more precise and comprehensive. Specifically, novel natural hybrid biomaterials comprising several or even more biochemical, morphological, and optical characteristics are being produced and employed in a diverse range of biological applications. In this study, we categorize new advanced enhanced organic/inorganic hybrid biomaterials into nanoparticles and nanocomposites and characterize their functionalities. We also highlight the latest development in bulk materials, known as nanocomposites and smart organic/inorganic hybrid nanocomposites, for biomedical applications. Furthermore, we explore how the suggested technique and its limitations may affect the creation of nanoparticles and composite materials in the future. Functional organic/inorganic hybrid nanoparticles-based nanohybrids containing physico-chemical properties of both inorganic and organic materials have the possibilities to be used as highly advanced biomaterials in a variety of biomedical sectors, with the ultimate objective of effectively detecting and treating a variety of human illnesses. There are several hybrid nanomaterials that are used in carrying out complex biological functions such as Metal Organ Framework, carbon-based hybrids, polymer-ceramic, lipid polymer, and protein polymer – they can be used in tissue engineering, cancer treatment, and drug delivery. Hybrid nanoparticles can be easily made with the help of co-precipitation, followed by curing the material at 100 °C in an oven. Keywords: Biomaterials, nanocomposites, nanohybrids, biomedical applications, organic hybrid composites, inorganic hybrid composites

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Corresponding author: Dipti Bharti, Department of Applied Science and Humanities, Darbhanga College of Engineering, Darbhanga, Bihar, India, e-mail: [email protected] Minakshi Awasthi, Department of Applied Science, Greater Noida Institute of Engineering and Technology, Greater Noida, Uttar Pradesh, India Vanya Arun, Department of Electronics and Communication Engineering, IILM University, Greater Noida, Uttar Pradesh, India Ankita Awasthi, Department of Mechatronics Engineering, IILM University, Greater Noida, Uttar Pradesh, India Amit Kumar, Department of Mechanical Engineering, Indian Institute of Technology, Ropar, Punjab, India Niraj Kumari, Department of Applied Science and Humanities, Darbhanga College of Engineering, Darbhanga, Bihar, India https://doi.org/10.1515/9783111137902-007

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7.1 Introduction In medical applications, for the detection and treatment of a number of disorders, nanomaterials composed of polymers, ceramics, metallic, and nanocomposites have a long history of usage. Polymers serve as the foundation for typical biomaterials. Due to their properties of being both biocompatible and biodegradable, polymers have remained intact. The utilization of polymer biomaterials for drug delivery has been especially impressive, and a number of polymer-based drug delivery devices have already received clinical use approval. Biological applications also make use of inorganic materials such as minerals, glasses, and ceramics. Compared to organic materials, inorganic materials have a number of benefits, such as mechanical, thermal, optical, and magnetic characteristics, as well as a linked porous structure [1]. The biomedical field requires factors founded on biological principles because they help us comprehend how biological systems work and how medicines, technology, and other treatments engage with them. The most recent studies in the area of biomedical concerns based on biological elements will be covered in this literature survey. The creation of polymers for surgical devices is one of the most important factors in the biological industry. These substances need to communicate with the nearby tissue, be nontoxic, and be safe. In a new research by the writers looked into the biological compatibility of graphene oxide (GO) with healthy bone marrow mesenchymal stem cells. (hBMSCs). They discovered that GO could facilitate the transformation of hBMSCs into bone cells and had no deleterious effects on them. In uses involving bone tissue engineering; the writers speculate that GO may be a viable substance. The creation of medication transport methods that can target particular cells or organs is a crucial component of scientific concerns, based on biological factors. The use of nanoparticles in medication administration was covered in a recent study emphasized how crucial it is to comprehend the cellular obstacles that medications must get past in order to reach their intended cells or tissues. The benefits and drawbacks of various nanocarriers, including dendrimers, polymeric nanoparticles, and liposomes, were also covered by the writers. The investigation of the immunological system and its relationships with illnesses and treatments is another field of study in scientific concerns, based on biological elements. The immune system’s function in COVID-19 was examined in a new research. They discovered that individuals with COVID-19 had an immunological response that was dysregulated, marked by elevated pro-inflammatory markers and decreased T cell counts. According to the writers, discovering how the immune system reacts to COVID-19 may help in the creation of fresh treatments. Studying hereditary variables that may affect the onset of illnesses and patients’ responses to treatments is yet another crucial component in the biological field. Li et al. (2021) recently explored the function of genomic variations in the emergence of

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breast cancer. They discovered that there was a higher chance of breast cancer due to a mutation in the BRCA1 gene. According to the writers, DNA testing may be used to identify people who are at a high risk of getting breast cancer, allowing for early action. Biomedical research and development is a field that is growing quickly and has the potential to change how we diagnose, treat, and prevent a wide range of diseases. However, as with any field, there are certain considerations that must be taken into account in order to ensure that the work being done is both safe and effective. In this article, we’ll talk about some of the most important biomedical factors that are based on biological factors. One of the most important considerations in the biomedical field is understanding the underlying physiology and pathophysiology of a disease. This includes understanding how the disease develops and progresses, as well as the mechanisms that contribute to its development. By better understanding these underlying processes, researchers and clinicians are better able to develop targeted treatments and interventions that can slow or even halt the progression of the disease. Another key consideration in the biomedical field is the analysis of genetic and environmental factors that contribute to the development and progression of a disease. This includes identifying genetic mutations or variations that increase the risk of developing a disease, as well as identifying environmental factors such as exposure to toxins or pollutants that may also contribute to the development of a disease. By understanding these risk factors, researchers and clinicians are better able to identify individuals who are at a higher risk of developing a disease and can take steps to prevent or delay its onset [2–4]. Not only is it important to know what causes a disease, but it is also important to figure out which treatments are safe and effective. This includes evaluating the potential side effects of a treatment, as well as its effectiveness in treating the disease. By carefully evaluating the safety and efficacy of a treatment, researchers and clinicians can ensure that the treatment is both safe and effective, and can make informed decisions about which treatment options are best for a particular patient. Finally, it is also important to consider ethical and cultural factors in the biomedical field. This includes taking into account the cultural and social factors that may influence a patient’s willingness to participate in a study or accept a particular treatment, as well as ensuring that the rights and autonomy of patients are respected throughout the research and treatment process. The biomedical considerations that are based on biological aspects in the biomedical field are crucial aspects in ensuring that the work being done in this field is safe, effective, and ethical. Researchers and clinicians can work to improve the health and well-being of people all over the world by understanding the underlying causes of diseases, evaluating the safety and efficacy of treatment options, and considering ethical and cultural factors [5]. Although many biomaterials use organic and inorganic materials separately, the need for structurally diverse biomaterials has risen, necessitating the creation of organic/inorganic hybrid materials [6–8]. Organic/inorganic hybrid nanocomposites are

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often used to describe a mix of organic and inorganic materials, with sizes on the submicron scale. The surfaces of inorganic nanoparticles that are not water soluble, such as gold nanoparticles (Au-NP), ferric oxide (Fe3O4) nanoparticles, microelectronics quantum dots (QDs), carbon dots, etc. can be modified with biopolymers, eventually resulting hybrid composites that can be used as therapeutic or diagnostic tools. By utilizing the optical or physical properties of inorganic nanoparticles, it is therefore possible to create new functional therapeutic agents that can deliver drugs via a surface polymer while also being used for biomedical imaging. Additionally, the superior mechanical characteristics of polymer composites that incorporate inorganic ceramic nanoparticles make them acceptable for use as bone transplant materials. The creation of several medicines and medical devices, such as drug delivery vehicles, scaffolding in tissue-engineered devices, cardiovascular stents, and prosthetics, has placed a significant amount of attention on organic/inorganic hybrid materials, which depend on their unique physicochemical capabilities [9]. According to publication trends from the last decade, development involving sustainably grown composite materials has grown significantly in the area of biomedical engineering. Until recently, most research on organic/inorganic nanocomposites was concentrated in materials science and traditional engineering. However, more lately, the field of biomedical has been an important area of study for hybrid materials. The usage of hybrid nanomaterials in various biomedical applications, including theranostics, immunotherapy for cancer, photo medicine, photo thermal treatment, gene editing, and signal transduction, in response to physical stimuli, is then described. We examine specifically how organic/inorganic hybrid materials are used in CRISPR/Cas9 gene editing and cancer treatment. Furthermore, we go through the most current uses of organic/inorganic hybrid materials in medical supplies, such as tissue engineering scaffolds, vascular stents, and dental implants. In terms of biological applications, we conclude with a summary of the challenges and opportunities presented by organic/inorganic hybrid materials [10, 11]. According to the binding force causing the interaction between an organic/inorganic hybrid material’s organic and inorganic components, there are two categories. In between the organic and inorganic components of Class 1 hybrid materials, the van der Waals, electrostatic, or hydrogen bonds play a minor role in the interaction. The strong interactions seen in covalent or ionic-covalent bonds, on the other hand, keep Class 2 hybrid materials bound together. In recent years, there has been advancement in the creation of Class 2 nanocomposites with strong and stable binding. Phase separation is minimized, organic-inorganic interfaces are easily defined, and Class 2 hybrid materials with covalent bonds may be exploited to create whole new technologies from functionalized alkoxides. In this review (bulk materials), organic/inorganic hybrid materials will be thought of in terms of hybrid nanoparticles and nanocomposites. Nanomaterials are hybrid matrices made of inorganic and organic materials bigger than the micron scale, as opposed to hybrid nanoparticles, which are made of natural and inorganic materials at the

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Tab. 7.1: Classification of Class-1 and Class-2 hybrid nanomaterials (organic component and inorganic component with their binding force). Type of hybrid material

Organic component

Inorganic component

Binding force

Sol-gel Organosilicates Organometallics Organosilicates Organometallics

Organic precursors Organic silanes Organic molecules Organic silanes Organic molecules

Inorganic precursors Inorganic silicates Metal ions or clusters Inorganic silicates Metal ions or clusters

Covalent bonds Covalent bonds Covalent bonds Covalent bonds Covalent bonds

nanoscale. Table 7.1 shows the hybrid nanoparticles and nanocomposites, two different forms of organic/inorganic hybrids that can be further divided into classes 1 and 2, based on the strength of their bonds, which is in turn influenced by the method used to create them. a) Organosilicates: These materials are formed through the condensation of organic silanes and inorganic silicates. Organic silanes contain alkoxy or halogen groups that can react with the silanol groups in the inorganic silicates to form a network of covalent bonds. Organosilicates are known for their high thermal stability and resistance to chemical attack. b) Organometallics: These materials are formed through the coordination of organic molecules with metal ions or clusters. Organic molecules contain ligands that can form covalent bonds with metal ions or clusters. Organometallics are known for their unique optical, electronic, and magnetic properties. Examples of organometallics include metal carbonyls, metal phosphines, and metal complex compounds. Organic or inorganic compounds that are 1–100 nm in size are generally considered to be nanoparticles. Evaluating variations in material characteristics as a result of particle size is made possible by the use of nanoparticles. According to their size, Au, Ag, and Cu nanomaterials, in the metal category, each have distinctive electrical, optical, and catalytic features. Particle size, shape, interparticle spacing, and the kind of organic shell, if any, all have a key role in how these nanoparticles behave and differ greatly from bulk metals or molecule compounds. It is essential that inorganic nanoparticles be distributed in the aqueous phase if they are to be employed in biomedical applications. Additionally, nanoparticles should be chemically inert and free of deteriorating processes such as partial oxidation or compaction. Metallic nanoparticles are frequently combined with polymer stabilizers to increase their chemical stability, while allowing the particles to spread in solution. These organic/inorganic nanocrystals can also make the original material more processible and biocompatible, and the surface polymer can change the nanoparticles’ characteristics. Hybrid nanoparticles can possess special qualities that go above and beyond those of the original components, in addition to sharing traits with both inorganic and organic nanomaterials. In

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light of this, a number of biological applications, such as medication administration, phototherapy, and image-guided therapy, can benefit from the use of hybrid nanoparticles [12, 13].

7.2 Hybrid nanocomposites Hybrid nanocomposites are a type of material that combines the properties of two or more different materials at the nanoscale. In the biomedical field, these materials are getting more and more attention because they have unique properties and could be used in a wide range of medical and biotechnological applications. In the biomedical field, one of the most promising ways to use hybrid nanocomposites is to make new biomaterials for use in medical implants and devices. These materials can be made to have the same properties as natural tissues, like bone and cartilage, and can be used to fix or replace damaged or diseased tissues. For example, hybrid nanocomposites made of ceramics and polymers have been developed for use in bone repair and replacement, while hybrid nanocomposites made of metals and polymers have been developed for use in joint replacements. Another potential application of hybrid nanocomposites in the biomedical field is in the development of new drug delivery systems. These materials can be made to release drugs in a controlled way; so they can be sent to specific tissues or cells and stay there for a long time. Hybrid nanocomposites made of lipids and polymers have been developed for use in targeted drug delivery, while hybrid nanocomposites made of metals and polymers have been developed for use in imagingguided drug delivery [13, 14]. Hybrid nanocomposites can also be used in diagnostic tools, like biosensors and imaging probes, to find out what is wrong. For example, hybrid nanocomposites made of metals and polymers can be designed to detect specific biomolecules, such as proteins or nucleic acids, and can be used in diagnostic assays. Similarly, hybrid nanocomposites can be designed to be used as imaging probes, allowing for in vivo visualization of specific tissues or cells. A blend of organic and inorganic materials with nanoscale dimensions is often referred to as organic/inorganic hybrid nanocomposites. Both heterogeneous and homogeneous combinations of organic and inorganic materials are possible in hybrid nanocomposites. Each organic or inorganic constituent has domains with sizes ranging from a few angstroms to a few 10 nm. Here are a few examples of hybrid nanocomposites, which are materials that combine the properties of both inorganic and organic components; they are shown in Fig. 7.1: a) Polymer/clay nanocomposites: These materials are formed by incorporating clay nanoparticles into a polymer matrix. The clay nanoparticles provide mechanical reinforcement and improved thermal stability to the polymer, while the polymer matrix provides flexibility and improved processibility to the clay.

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b) Metal oxide/polymer nanocomposites: Metal oxide nanoparticles, like silica, titanium dioxide, or zinc oxide, are mixed into a polymer matrix to make these materials. The metal oxide nanoparticles give the polymer better optical and electronic properties, like UV absorption or photocatalytic activity, while the polymer matrix gives the polymer better ability to be processed and better mechanical properties. c) Carbon nanotube/polymer nanocomposites: These materials are formed by incorporating carbon nanotubes into a polymer matrix. The carbon nanotube provides high electrical conductivity and mechanical strength to the polymer, while the polymer matrix provides improved processibility and flexibility [15]. d) Protein/inorganic nanoparticles nanocomposites: Inorganic nanoparticles, like gold or silver nanoparticles, are mixed with a protein matrix to make these materials. The inorganic nanoparticles, like surface-enhanced Raman scattering, give the protein better optical properties, while the protein matrix makes the protein biocompatible and stable. e) Hybrid organic-inorganic perovskite solar cells: These materials are formed by incorporating inorganic perovskite compounds into an organic-inorganic hybrid material. The perovskite compounds provide efficient light absorption and charge transport properties, while the organic-inorganic hybrid materials provide stability and flexibility.

Fig. 7.1: Different types of hybrid nanomaterials.

As with the hybrid nanoparticles we have already talked about, the materials in organic/inorganic hybrid nanocomposites should be stronger than the sum of the two phases. The composition and type of organic and inorganic components of hybrid nanocomposites dictate its characteristics. Hybrid nanocomposites have superior physicochemical properties compared to their constituent parts, particularly in terms of thermal and mechanical stability [16, 17].

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In order to create hybrid nanoparticles, at least two distinct elements must be at the nanoscale. By combining these substances, it is possible to produce brand new qualities and capabilities that are not found in the parts alone. Hybrid nanoparticles have received a great deal of attention from the scientific community due to their possible use in tissue engineering, imaging, and medication transport. As far as biological concerns go, some kinds of composite nanoparticles include: nanoparticles made of a polymer-based center and an exterior coating made of lipids, known as lipid-polymer hybrids. They are ideal for drug transport uses due to their biocompatibility, stability, and great drug-loading capability. Hybrid nanoparticles made of silica and gold nanoparticles have a silica exterior and a gold center. Their visual characteristics and biocompatibility have been used for medicinal and diagnostic purposes. Carbon-based composite nanoparticles have been researched for their possible applications in tissue engineering, imaging, and medication transport. Examples of these materials include graphene oxide and carbon nanotubes. Their tensile toughness, biocompatibility, and surface area are all high. Hybrid materials made of proteins and nanoparticles have a protein-based outer layer and a nanoparticle interior. Their biocompatibility and capacity to target particular cells and organs have allowed them to be used in medication transport uses. Hybrid magnetic nanoparticles have a lipid- or polymer-based coating around a magnetic center. They have enduring uses for MRI and medication administration because they can be directed to particular locations using an additional magnetic field. Hybrid materials made of a polymer-based framework and nanoparticles are known as polymer-nanoparticle hybrid materials. Because of their capacity to regulate drug release and imitate the interstitial matrix of tissues, they can been used for tissue engineering and drug transport. In addition, the interior inorganic components of hybrid composites can influence their linked porosity networks as well as their magnetic, electrical, redox, and chemical characteristics. Hybrid nanocomposites’ interior porosity makes them appropriate for usage as medication delivery systems. Hybrid nanocomposites are also used for tissue regeneration as they may serve as scaffolds for cell treatment. For tissue regeneration, porous hybrid nanocomposites containing osteoinductive chemicals, which encourage cell differentiation into bone, have been used. Functional hydrogels with various types of organic and inorganic components are also used for a variety of bio applications, including tissue engineering and drug delivery.

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Tab. 7.2: Tabulated representation of application of hybrid nanocomposites with respect to their utilization in biomedical field [18, 19]. S. Hybrid Properties No. nanocomposites

Biomedical field



Polymer-ceramic hybrid composites

These materials combine the properties of ceramics, such Bone repair and as high strength and biocompatibility, with the replacement, as well properties of polymers, such as flexibility and as for dental implants biodegradability.



Lipid-polymer hybrid composites

These materials are used in targeted drug delivery systems. Lipids are used as carriers to transport drugs to specific tissues or cells, while polymers are used to control the release of drugs.

Cancer drugs



Metal-polymer hybrid composites

These materials are used in imaging-guided drug delivery and in diagnostic applications, such as biosensors and imaging probes. These materials can be designed to detect specific biomolecules, such as proteins or nucleic acids.

Diagnostic assays, such as, in cancer diagnosis



Carbon-based hybrid composites

Carbon-based hybrid composites, such as graphene oxide and carbon nanotubes, can be functionalized with bio molecules such as peptides and antibodies for specific targeting.

Biosensors, bio imaging, and drug delivery



Chitosan-based hybrid composites

Chitosan is a biodegradable, biocompatible, and nonWound healing, toxic natural polymer that is derived from crustacean tissue engineering, shells. Examples of chitosan-based hybrid composites are and drug delivery chitosan-silica and chitosan-clay.

7.3 Creation of sophisticated hybrid nanomaterials In recent years, a lot of research has been carried out to use the good things about of inorganic and organic nanoparticles from a biological point of view. The distance and alignments of nanoparticles must be managed to fully use their beneficial features in order to increase the applicability of nanoparticles in a variety of disciplines. As a result, numerous synthetic techniques have been created, such as surface treatment, identity, metal-organic frameworks (MOFs), physical blending, and in situ deposition, to modify the surface characteristics of nanoparticles and regulate their arrangement in order to achieve the desired physicochemical properties. The incorporation of small molecules or synthetic polymers onto the nanoparticles’ surface is a straightforward way for reducing the interfacial incompatibility between nanoparticles and polar/non-polar solvents or matrix materials. Hybrid nanomaterials are a diverse class of materials that can be broadly categorized into several different types, based on the types of components that are com-

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bined to form the hybrid material. Some examples of the different types of hybrid nanomaterials include: a) Metal-organic frameworks (MOFs): These materials are composed of metal ions or clusters that are connected by organic linkers. They have large surface areas and high porosity, making them useful for gas storage and separation, catalysis, and sensing applications. The formation of metal organic framework is shown in Fig. 7.2.

Fig. 7.2: Representation of metal organic framework (MOF).

b) Carbon-based hybrids: These materials are composed of carbon-based materials such as graphene and carbon nanotube that are combined with other materials such as metals, polymers, and ceramics. They are known for their high electrical conductivity and mechanical strength, making them useful for various applications such as biosensors, bio imaging, and drug delivery. Carbon nanotube contains Sp2 carbon molecular bonding. Its cylindrical shaped graphene structure is represented in Fig. 7.3.

Fig. 7.3: Graphical representation of carbon nanotube in the nanometer scale.

c) Polymer-inorganic hybrids: These materials are composed of inorganic materials such as ceramics and metals, which are combined with polymers. They are

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known for their enhanced mechanical, thermal, and electrical properties, compared to pure polymers, making them useful in various biomedical and electronic applications. d) Lipid-polymer hybrids: These materials are composed of lipids and polymers. They are widely used in drug delivery systems because of their ability to encapsulate drugs and target specific cells. e) Inorganic-organic hybrids: These materials are composed of inorganic and organic materials that are combined together. They have unique optical and electronic properties, making them useful in various applications such as solar cells, LED, and sensors. f) Biopolymer-inorganic hybrids: These materials are composed of inorganic materials such as ceramics and metals that are combined with biopolymers, such as chitosan, cellulose, and starch. They are known for their biocompatibility and biodegradability, making them useful in various biomedical applications such as tissue engineering and wound healing With the help of this straightforward technique, the nanoparticles’ ability to disperse in polymer matrices is improved, and they may also be further modified, broadening the scope of their potential uses. Additionally, a number of techniques have been developed to enhance the physicochemical features of nanoparticles by manipulating their alignment. In contrast to their initial shapes, assembled nanoparticles might exhibit fascinating traits or qualities. As a result of controlling the nanoparticle configurations with techniques such as self-assembly and MOFs, several hybrid nanostructures have been created. Similar to this, a technique for creating nanocomposites with polymer matrices has been created to enhance their biomechanical and other features. Nanoparticles need to be steadily disseminated inside polymer matrices to produce well-defined nanocomposites with the desired characteristics. Physical and chemical techniques may be divided into two main groups for synthesizing hybrid nanocomposites with great homogeneity. As opposed to chemical methods, which use in situ deposition techniques, physical methods use solution and melt mixing. Table 7.2 lists the elements needed to produce hybrid nanomaterials, as well as the synthetic processes and types of hybrid nanomaterials that they are classified into. Even though certain inorganic nanoparticles exhibit distinct physical and chemical bulk properties, their surface characteristics – particularly their biocompatibility and colloidal stability – often make them unsuitable for biomedical applications. The reticuloendothelial system (RES) clears nanoparticles quickly because they are likely to form agglomerates or aggregates. By coating inorganic nanoparticles with organic polymers, their physicochemical characteristics may be changed, enhancing their biocompatibility and extending the duration that they spend in the bloodstream. This enables inorganic nanoparticles to be used in a wider range of applications.

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7.4 System-composed nanoparticles A system composed of nanoparticles refers to a combination of multiple nanoparticles in a larger system or structure. These systems can be made by putting together nanoparticles or by making nanoparticles right where they are needed in a larger system. The size, shape, composition, and functionalization of the nanoparticles’ surfaces can be changed to change their properties and how they behave in these systems. One example of a system composed of nanoparticles is a nanoparticles aggregate, which is created by assembling individual nanoparticles together. These aggregates can be formed by the physical or chemical interactions between the nanoparticles, and their properties such as size and shape, can be controlled by adjusting the conditions under which they are formed. A dendrimer is another example. It is a highly branched, monodispersed, nanoscale polymer with a defined structure that can be synthesized with precise control over its size, shape, and chemical functionality. Dendrimers have been used in drug delivery, imaging, and as scaffolds for tissue engineering. Nanocomposites are also systems composed of nanoparticles, which are created by incorporating nanoparticles in a larger matrix or host material. These composites can be made by blending nanoparticles with a polymer, for instance, to create a material with enhanced mechanical or electrical properties. The systems composed of nanoparticles are a diverse class of materials that can be created by assembling individual nanoparticles together, or by synthesizing nanoparticles in situ within a larger system, or by incorporating nanoparticles into a larger matrix or host material. These systems have unique properties and potential applications in various fields such as biomedical, electronics, and materials science [20–22].

7.5 Hybrid nanocomposite materials’ fabrication techniques Hybrid nanocomposites are manufactured by combining two or more different types of nanoparticles or materials at the nanoscale. There are several methods for manufacturing hybrid nanocomposites, including: a) Co-precipitation: This method involves the simultaneous precipitation of two or more types of nanoparticles from a solution. The nanoparticles can be precipitated by adding a chemical reagent or by changing the pH or temperature of the solution. Hybrid nanoparticles made by co-precipitation are particles created by combining two or more materials using a chemical process known as co-precipitation. In this process, the different materials’ solutions are mixed together, which makes the materials come out of solution and form particles. The resulting particles are typically very small, on the order of nanometers, and can have unique properties due to the combination of materi-

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als. These particles are widely used in various fields like catalysts, sensors, drug delivery, etc. Fig. 7.4 shows the procedure for the formation of nanoparticles through the coprecipitation method.

Addition of following solution (FeCl2, FeCl3, NiCl2.6H2O, NaOH)

Addition of Distilled Water in freshly prepared solution

Stirring the solution continuously

Again addition of NaOH dropwise

Stirring the solution continuously

Black Precipitation

Measuring pH and washing

Drying in oven at 100 °C

Formation of Nanoparticles composites

Fig. 7.4: Flowchart representation of the co-precipitation process to prepare nanomaterials [23].

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b) Sol-gel: In this method, a precursor solution is formed by mixing a metal or metal oxide precursor with a polymer or organic solvent. Then, the precursor solution goes through a series of chemical reactions that make a gel. The gel is then dried and calcined to form the desired hybrid nanocomposite. Hybrid nanoparticles fabricated through sol-gel are particles that are made by combining two or more materials through a chemical process called sol-gel. A schematic diagram of the procedure of sol-gel preparation has been discussed in Fig. 7.5. These processes involve the formation of a precursor solution, called “sol,” which is then allowed to gel, or solidify, forming a solid network of the materials. The resulting particles are typically very small, on the order of nanometers, and can have unique properties due to the combination of materials. These particles are widely used in various fields like catalysts, sensors, drug delivery, and optical materials.

Fig. 7.5: Schematic representation of the procedure used in sol-gel formation.

c) Layer-by-layer assembly: This method involves the sequential adsorption of layers of nanoparticles onto a substrate. The nanoparticles can be absorbed by either an electrostatic or a covalent interaction. This method allows for precise control over the thickness and composition of the hybrid nanocomposites. Hybrid nanoparticles fabricated through layer-by-layer assembly are particles that are made by combining two or more different materials through a process called layer-by-layer assembly, as shown in Fig. 7.6. This process involves the sequential adsorption of positively and negatively charged materials onto a substrate, forming a multilayer film. The resulting particles are typically very small, on the order of nanometers, and can have unique properties due to the combination of materials. These particles are widely used in various fields like catalysts, sensors, drug delivery, and energy storage.

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Fig. 7.6: Layer by layer architectural representation of nanoparticles.

d) In situ synthesis: This method involves synthesizing one type of nanoparticle within another type of nanoparticle or matrix. For example, metal nanoparticles can be synthesized within a polymer matrix, or a polymer can be synthesized within a metal matrix, as shown in Fig. 7.7. Hybrid nanoparticles fabricated through in situ synthesis are particles that are made by combining two or more different materials through a process called in situ synthesis. This process involves the simultaneous chemical reaction of the materials in a single reaction vessel or reaction environment, rather than adding the materials together after they have been synthesized separately. In situ synthesis can be performed under various conditions, like high temperature, pressure, and vacuum, or under a specific chemical environment. These particles are typically very small, on the order of nanometers, and can have unique properties due to the combination of materials. These particles are widely used in a wide range of applications, including catalysts, sensors, drug delivery, and advanced material science.

Fig. 7.7: In situ synthesis of polymeric-based nanocomposites.

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e) Mixing: This method involves mixing two or more types of nanoparticles. The nanoparticles can be mixed in a solution, on a surface, or in the gas phase. Hybrid nanoparticles fabricated through mixing are particles that are made by combining two or more different materials through a process called mixing. This process involves physically mixing the materials, usually in liquid or powder form, to form a homogenous mixture. The resulting particles are typically very small, on the order of nanometers, and can have unique properties due to the combination of materials. These particles are widely used in various fields like catalysts, sensors, drug delivery, and advanced material science. The mixing process can be performed with different techniques like mechanical mixing, ultrasonication, ball milling, or high-energy mixing. Figure 7.8 shows the schematic representation of the formation of nanoparticles with the help of the extrusion process.

Fig. 7.8: Formation of inorganic nanoparticles with the help of mechanical mixing (extrusion process).

f) Polymer blending: This method involves blending two or more types of polymers to form hybrid nanocomposites. The polymers can be blended in a solution, on a surface, or in the gas phase. Hybrid nanoparticles fabricated through polymer blending are particles that are made by combining two or more polymers through a process called polymer blending. This process involves physically mixing the polymers, usually in a liquid or powder form, to form a homogenous mixture. The resulting particles are typically very small, on the order of nanometers, and can have unique properties due to the combination of polymers. These particles are widely used in various fields like catalysts, sensors, drug delivery, and advanced material science, and also in the production of polymer composites. The blending process can be performed with different techniques like mechanical mixing, ultrasonication, and high-energy mixing. The properties of the blended polymers can be tailored by adjusting the composition, molecular weight, and chemical structure of the polymers used. Each method has its own advantages and disadvantages, and the choice of method depends on the specific application and the desired properties of the hybrid nanocomposites [24–26].

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7.6 Advantages and disadvantages of hybrid nanocomposites Hybrid nanocomposites have several advantages over traditional single-component materials. Some of these advantages include: a) Enhanced properties: The combination of different materials in hybrid nanocomposites can result in improved properties, such as increased strength, stiffness, thermal stability, and electrical conductivity. b) Multifunctionality: Hybrid nanocomposites can have multiple functions due to the presence of multiple components. For example, a hybrid nanocomposite may have both electrical and thermal conductivity. c) Tailored properties: The properties of a hybrid nanocomposites can be tailored by adjusting the composition, size, shape, and distribution of the different components. d) Improved stability: Hybrid nanocomposites can have improved stability due to the interaction between the different components. e) Cost-effectiveness: Hybrid nanocomposites can be cost-effective as they can make use of low-cost fillers or reinforcements to improve the properties of a material. f) Biocompatibility: Hybrid nanocomposites can be biocompatible, and therefore can be used in biomedical applications. g) High specific surface area: Hybrid nanocomposites have a high specific surface area, which leads to enhanced chemical reactivity and catalytic activity. h) Low toxicity: Hybrid nanocomposites can be made of biodegradable and nontoxic materials, which make them suitable for environmental and biological applications. Hybrid nanocomposites, while having many advantages, also have some disadvantages. Some of these disadvantages include: a) Complex synthesis: Synthesis of hybrid nanocomposites can be complex and difficult, requiring specialized techniques and equipment. b) Limited compatibility: Not all materials are compatible with each other, and some materials may not be able to be blended together to form a stable hybrid nanocomposite. c) High cost: The synthesis process of hybrid nanocomposites can be expensive, and the materials used may also be costly. d) Limited scalability: The synthesis of hybrid nanocomposites may not be easily scalable, making it difficult to produce large quantities of the material. e) Low dispersion: The distribution of the different components in a hybrid nanocomposite may not be uniform, leading to low dispersion and poor performance.

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f)

Difficult characterization: Characterizing hybrid nanocomposites can be difficult, as it requires advanced techniques and equipment to study the different components and their interactions. g) Environmental concerns: Some of the materials used to make hybrid nanocomposites may be toxic or harmful to the environment, and proper disposal of these materials must be considered. h) Lack of standards: There are currently few standards for the production and characterization of hybrid nanocomposites, which can make it difficult to compare different materials and ensure consistency.

7.7 Biological properties of hybrid nanocomposites Hybrid nanocomposites have gained attention in the biomedical field due to their unique properties and potential applications [27–29]. Some biomedical considerations for hybrid nanocomposites, based on their biological aspects, are: a) Biocompatibility: The biocompatibility of hybrid nanocomposites is an important consideration in biomedical applications. The inorganic and organic components of the nanocomposites should not be toxic or cause an immune response, when introduced into the body. Some hybrid nanocomposites, such as those based on biodegradable polymers, can be designed to degrade or be eliminated from the body after use. b) Targeted delivery: Hybrid nanocomposites can be designed to target specific cells or tissues within the body. For example, some hybrid nanocomposites can be coated with biomolecules such as antibodies or peptides that bind to specific cell surface receptors. This allows the nanocomposites to be directed to the desired location within the body. c) Imaging: Hybrid nanocomposites can be designed to improve imaging sensitivity and specificity. For example, some hybrid nanocomposites can be functionalized with contrast agents such as gold or iron oxide nanoparticles that can be detected by imaging techniques such as magnetic resonance imaging (MRI) or computed tomography (CT). d) Therapeutic: Hybrid nanocomposites can be designed to deliver therapeutic agents to cells or tissues. For example, some hybrid nanocomposites can be loaded with drugs or genetic materials that can be released in a controlled manner to treat diseases or conditions. e) Biodegradable: Some hybrid nanocomposites are made from biodegradable materials that can break down and be eliminated from the body over time, reducing the risk of long-term toxicity.

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Here are a few examples of biomedical applications of hybrid nanocomposites: a) Drug delivery: Hybrid nanocomposites can be used to deliver drugs to specific cells or tissues within the body. For example, liposomes, which are spherical vesicles made from a lipid bilayer, can be loaded with drugs and functionalized with biomolecules that target specific cells. Liposomes can be made hybrid by incorporating inorganic nanoparticles like gold nanoparticles that can be used for imaging or hyperthermia treatment. b) Tissue engineering: Hybrid nanocomposites can be used to create scaffolds for tissue engineering. For example, electrospun nanofibers made from a polymer and clay hybrid can be used to create scaffolds that mimic the extracellular matrix of a tissue. These scaffolds can be used to guide the growth of cells and create new tissue [30]. c) Cancer therapy: Hybrid nanocomposites can be used for cancer therapy. For example, gold nanoparticles can be functionalized with biomolecules that target cancer cells, and loaded with drugs that can be delivered directly to the cancer cells. This can improve the effectiveness of the therapy while minimizing side effects [31, 32]. d) Diagnostics: Hybrid nanocomposites can be used to improve the sensitivity and specificity of diagnostic techniques. For example, gold nanoparticles can be functionalized with biomolecules that bind to specific biomarkers of a disease, such as cancer cells, and used in diagnostic techniques such as surface-enhanced Raman spectroscopy (SERS) for early detection of diseases. e) Implant: Hybrid nanocomposites can be used to create implantable medical devices. For example, hybrid nanocomposites made from biodegradable polymers and inorganic nanoparticles can be used to create implantable devices such as stents and neural probes that degrade over time and reduce the need for additional surgeries to remove the device [33]. These are just a few examples of the many potential biomedical applications of hybrid nanocomposites. Further research is needed to fully understand the properties and potential of these materials as well as to develop new methods for their production, characterization, and use in biomedical applications. Based on the biological aspects discussed in this manuscript, it is clear that the field of biomedical research is rapidly advancing. By understanding the complex interactions between biological systems and medical treatments, researchers are able to develop more effective and personalized therapies for a wide range of diseases. However, it is also important to note that there are many challenges that remain in the field. For example, there is still much to learn about the genetic and environmental factors that contribute to disease, and how these factors can be targeted to improve patient outcomes. Additionally, the development of new therapies must be balanced with considerations of safety and ethical concerns. Looking to the future, it is clear that there is a great deal of work to be done in order to continue advancing biomedi-

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cal research. One promising avenue for future research is the use of machine learning and other advanced computational tools to analyze large datasets and identify new targets for therapy. Additionally, researchers will need to continue working collaboratively across disciplines in order to fully understand the complex interactions between biological systems and medical treatments.

7.8 Conclusion In conclusion, hybrid nanomaterials have shown great promise in the biomedical field due to their unique properties and versatility. However, their biological aspects must be considered to ensure their safe and effective use in biomedical applications. This includes understanding their toxicity, biocompatibility, and interactions with biological systems. Further research is necessary to fully understand the biological impact of these materials and to develop new and improved hybrid nanomaterials for use in biomedical applications. – Drug delivery that is under control: Hybrid nanocomposites are perfect for drug delivery uses because they can be made to discharge medications gradually. – Hybrid nanocomposites can be used to build substrates for tissue engineering, giving cells a safe and recyclable surface to develop on. – Hybrid nanocomposites can be used as imaging or biosensors in diagnostic applications. – Hybrid nanocomposites with nanoparticles incorporated into a polymer matrix can have better mechanical properties, making them suitable for embedded devices. – Composite nanocomposites can be created to lessen the toxicity of specific substances, like metals or plastics, making them better for medicinal uses. – Due to their distinctive qualities and adaptability, hybrid nanocomposites show a great deal of promise in biological uses. – To make mixed nanocomposites that are best suited for particular biological uses, additional study is required. The healthcare field’s use of hybrid nanocomposites has the ability to completely transform uses such as tissue engineering, medication transport, and diagnostics.

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Siddhartha Ghanty, Abhratanu Ganguly, Sayantani Nanda, Kanchana Das, Moutushi Mandi, Saurabh Sarkar, Prem Rajak✶

8 Nanomaterial-based molecular imaging and targeted cancer therapy: current progress and limitations Abstract: Nanotechnology is an emerging field in medicine that has perspectives to diagnose and treat several ailments. Among the leading cause of mortality, cancer is the major one that requires early diagnosis, intensive care, and treatment for better survival rates. Current imaging techniques and treatment strategies have multiple limitations, such as side effects, and lack of specificity and sensitivity. Hence, new reliable approaches are warranted to counter the limitations of the current treatment methods. Nanomaterial-based diagnostic methods and treatment procedures may enable healthcare professionals to better diagnose and treat cancer. They bear several advantages such as minimal toxicity, biocompatibility, higher stability, improved cellular permeability, more retention time, and accurate targeting ability. However, most research using nanomaterials in cancer therapy is restricted to experimentalmodel animals. Hence, there is a need to extend the applications of nanomaterials in clinical trials. This chapter reviews in detail the prospects of nanomaterials in molecular imaging and targeted therapy of malignant tumors. In addition, challenges for nanomaterial-based therapies will also be discussed. Keywords: Nanomaterials, cancer, targeted-drug delivery, metastasis, biocompatibility

8.1 Introduction Nanotechnology is a burgeoning field in medical science and engineering that enhances innovative research in molecular imaging and therapy of various diseases. Development of nanomedicines has great perspective in treatment of diseases that are not treatable at present. Cancer is among the most fatal diseases worldwide [1]. The uncontrolled development and cell proliferation are hallmark features of cancer. Cancer may result from changes in genetic components caused by exposure to pollutants and other environmen✶

Corresponding author: Prem Rajak, Department of Animal Science, Kazi Nazrul University, Asansol, West Bengal, India, e-mail: [email protected], ORCID ID: https://orcid.org/0000-0002-1693-8090 Siddhartha Ghanty, Abhratanu Ganguly, Sayantani Nanda, Department of Animal Science, Kazi Nazrul University, Asansol, West Bengal, India Kanchana Das, Moutushi Mandi, Toxicology Research Unit, Department of Zoology, The University of Burdwan, West Bengal, India Saurabh Sarkar, Department of Zoology, Gushkara Mahavidyalaya, Gushkara, West Bengal, India

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tal factors. Pollutants like pesticides and heavy metals are detrimental to living organisms [2–8]. They fuel oxidative stress and impose adverse impacts on physiological processes [9–11]. Environmental pollutants can lead to compromised immunity, reproductive fitness, and cardiovascular systems [12–19]. Phytochemicals have multiple antioxidant, antidiabetic, anti-inflammatory, and anticancer properties that can improve human health [20]. Metastasis may invade the circulatory system and other tissues. Cancer is primarily treated through chemotherapy, surgery, and radiation exposure. Chemotherapy is the process of treating cancer with chemical drugs. Chemical drugs are systematically allowed to reach the metastatic cells to selectively target uncontrolled proliferation of cells. These medications have serious side effects due to their high level of toxicity and potential to harm healthy cells. Radiation therapy includes the use of gamma rays, high energy electrons, and X rays to irradiate and induce apoptosis of cancer cells. In the vicinity of cancer cells or along the radiation pathway, radiation can also harm healthy tissues [21]. PTT, or photothermal treatment is another measure to remove cancer cells. In this method, photon energy is converted into intense heat energy to kill metastatic cells. Using nanostructures in photothermal therapy can help to some extent, to resolve this issue. Because nanoparticles (NPs) can specifically and precisely enter tumor tissues and cancer cells, they have the ability to target only cancer cells. Nanoparticles (NPs) are tiny but solid structures, usually 1 to 100 nm in diameter. They are classified as a subgroup of colloidal particles [22]. The presence of NPs in nature has long been known and is not exclusively limited to contemporary laboratories [23]. With a focus on malignant tumors, the current study examines the potential use of NPs in molecular imaging and cancer therapy. A wide variety of nanocarriers, primarily polymeric micelles, polymeric NPs, nanoemulsions, liposomes, and dendrimers are employed as precision cancer nanomedicines, following significant advancements in material science and nanotechnology. NPs have special physical and mechanical properties that favor their application in medical science. NPs are of nano-scale size with high surface area-to-volume ratio and stability. Moreover, the surface of NPs could easily be conjugated with various biomolecules like antibodies, proteins etc. that can specifically diagnose particular diseases. When NPs enter any biological system like blood circulation, they are rapidly surrounded by various biomolecules, mainly proteins, to form corona [24]. Binding of NPs with proteins in corona modulates the surface properties, size, and stability of NPs, providing them a biological identity. Such NPs conjugated with biomolecules trigger physiological responses like intracellular uptake, trafficking, bio distribution, and toxicity. In some cases, binding of NPs with opsonins can fuel clearance through mononuclear phagocyte system [25]. Apolipoproteins and albumin, conjugated with corona, could contribute to stealth effects of NPs [26]. It is interesting to note that the surface of NPs, when conjugated with serum proteins, improves targeted delivery to specific organs. Preparation of NP-protein conjugant is generally determined by physico-chemical structure, protein source, and exposure time. Various contaminants elicit detrimental impacts on health and NPs could protect from such health hazards [27,28]. These facts and finding from various experiments lead to the rapid understanding of opportunities in

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nanotechnology for imaging and targeted drug delivery to treat various diseases, including the metastatic cancer. Therefore, the present chapter aims to overview our current grasp of tumor biology and NP-based cancer diagnosis and therapies. Moreover, the literature also presents the limitations of NPs in disease diagnosis and future scopes to improve the use of nanotechnology in cancer theranostics.

8.2 NPs types and application in cancer therapy Unique features of NPs like nano-scale size, shape, and high surface-area enhance their efficacy for drug delivery and therapeutics [29]. Due to the higher retention time and enhanced permeability, NPs have great perspectives in cancer therapy. Larger particles, with diameter greater than 100 nm, are most frequently targeted by circulating phagocytes, compared to the smaller particles [30]. On the other hand, smaller particles (less than 10 nm) can be more easily removed from circulation by phagocytes [31]. NPs have unique surface properties that enhance their bioavailability and half-life for better treatment of metastatic cells. Polyethylene glycol (PEG) and other hydrophilic coatings on nanoparticles (NPs) reduce opsonization and, subsequently, immune system clearance [32]. As a result, hydrophilic NPs are frequently developed, enabling medications to persist longer in the bloodstream and to target tumors more efficiently [33]. The numerous characteristics of NPs have a significant impact on cancer treatment, when taken collectively [34]. NPs can be used as the delivery system for radiosensitizers and anticancer medications to reach cancer cells. NPs can have various properties, including semiconducting, metallic, and magnetic properties. Therapeutic medicines are now being delivered to tumor cells via NPs. Such advantage of using NPs has assisted in the development of several therapeutic agents and molecular markers to specifically diagnose and target metastatic cells in patients.

8.2.1 Liposomes The overall liposome structure is vascular, with the water compartment in the liposome’s inner layer being hydrophilic in nature and the lipid layer bordered by one or more hydrophobic layers – uni or multilayered in nature. They are of multiples sizes, ranging from nanometers to few microns. A large number of pharmacological agents can be integrated into lipid bilayers or the aqueous compartments of liposomes (lipophilic compounds). The reticuloendothelial system might eliminate conventional liposomes from circulation. By utilizing tiny liposomes (10 nm), which are composed of neutral, saturated phospholipids, and cholesterol, the duration of circulation can be prolonged. Several recent investigations have used liposomes that are structurally

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modulated using polyethylene glycol [35]. Liposomes can be employed as a great delivery mechanism for drugs like doxorubicin, paclitaxel, and nucleic acid due to their increased antitumor activity and bioavailability [36].

8.2.2 Polymeric nanoparticles (PNPs) PNPs are unique structures with specific colloidal properties [37]. The nanosphere or nanocapsule that is utilized to deliver regulated medicine delivery inside the region of the target side, either has the drug encapsulated in it or is bound to the outer surface of the NPs [38]. However, because it is difficult to remove them from the system, they build up and turn poisonous. Studies on the toxicity of biodisposable polymers such as polylactic acid, alginate, chitosan, and poly (amino acids) as well as albumin have shown that these materials can improve targeted delivery and biocompatibility of drugs, with reduced detrimental impacts on patients [39]. Studies have established the use of polysorbates as a coating for PNPs and as a surfactant. The blood-brain barrier (BBB) endothelial cell membrane interacts more favorably with NPs with an exterior coating [40]. In a rat model of xenografted glioma, indomethacin nanocapsules decreased tumor development and increased survival. The fact that numerous anti-cancer medications are currently undergoing clinical trials shows how quickly this field of study is developing. HPMA copolymer-DACH-platinate, altered HPMA copolymer-platinate, dextran-camptothecin, PEG-camptothecin, HPMA copolymer-doxorubicin galactosamine (PK2), and HPMA copolymer-paclitaxel are a few examples of these substances [41].

8.2.3 Polymeric micelles (PMs) PMs, also known as “micellar nanocontainers,” are used to create drug carriers and diagnostic imaging agents [42]. Polymeric micelles with lengths of 10–100 nanometers are frequently observed. PMs prevent inappropriate drug release and breakdown of hydrophobic medications. The shell of stabilized micelles protects drugs from serum proteins and other immune cells. Therefore, the PMs can increase bioavailability and better transportation of drugs to targeted sites in patients. Moreover, PMs might have less toxicity with increased surface area that enhances their efficacy against metastatic cells and other diseased tissues. The drug is released from the micelle via diffusion once it has reached the target cells. Some clinical trials for the use of PMs as anti-cancer drugdelivery agents have either already been completed or are underway [43, 44].

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8.2.4 Dendrimers Dendrimers are spiral polymeric macromolecules having hyperbranched structures. Dendrimers are distinct from other species due to their branching structures. The synthesis process of dendrimers employs usage of acrylic acid solution and an ammonia core. The synthesis process yields tri-acid and ethylenediamine, which can react with acrylic acid to generate hexa-acid. Hexa-acid in turn combines with “hexa-amine” (Generation 1) to synthesize “hexa-amine” (Generation 2), and so forth. Dendrimers typically range in size from 1 to 10 nanometers. Colapicchioni et al. [45] state that the size of dendrimers varies between 15 nm and a few micrometers. They target nucleic acids due to their unique architecture. Dendrimers possess a definite molecular weight, tunable bioavailability, branching, and surface charge. There are also dendrimers other than those made of triethanolamine (TEA), polypropylene glycol, and polyethylene glycol. Initially, dendrimers were created to help manage Medical Device Regulation (MDR). The dendrimers produced considerably retarded the growth of epithelial carcinoma xenografts when compared to mice that received a single type of chemotherapeutic medication [46].

8.2.5 Nanoemulsions Colloidal NPs are heterogeneous mixtures having diameter of 10 to 1,000 nm and are also known as oil droplets in the aqueous medium [47]. Three different types of nanoemulsions can be produced, such as water-in-oil nanoemulsions, bi-continuous nanoemulsions, and oil-in-water nanoemulsions. There has been a lot of study done on nanoemulsions with modified membranes. For instance, nanoemulsions like spirulina and paclitaxel nanoemulsions have been reported with increased antitumor efficacy by modulating TLR4/NF-kB signaling cascades [48, 49]. In another study, nanoemulsions conjugated with bevacizumab, rapamycin, and temozolomide were effective in treating melanoma [50]. Nanoemulsions are advantageous compared to liposomes because of their optical properties, biodegradability, and stability [51]. However, it is important to note that nanoemulsions require high pressure, temperature, as well as costly equipment like homogenizers and microfluidizers. Hence, the practical applicability of nanoemulsions faces challenges.

8.2.6 Quantum dots Quantum dots are specialized nanostructures with several important features that have strong relevance in medical science, pharmaceuticals, and engineering. Quantum dots are of most importance for the imaging of metastatic cells in patients. Quantum dots tagged with various markers are injected into the circulation of patients for

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better and more precise visualization of tumors throughput the body. Moreover, quantum dots show higher bioavailability-stabilized structural architecture, increased surface-to-volume ratio as well as reduced cytotoxicity. They are specialized in targeted drug release to minimize irrational drug waste and better targeted delivery. Interestingly, microscopic fluorescent imaging analysis using quantum dots are helpful in exploring the pattern of differentiation of various cell lineages during the course of normal embryo development. Notably, in some studies, several injections of quantum dots did not show any evidence of toxicity in experimental setups [52] (Fig. 8.1).

Fig. 8.1: Various NPs having potential scope in cancer treatment.

8.3 NPs used in oncology Several nanoparticles have been developed and used in experiments for their efficacy against cancer. These include -

8.3.1 Silica nanoparticles (SiNPs) Although SiNPs have great scope for targeted drug delivery and disease therapy, they have also been found as hazardous to the reproductive system through an unknown mechanism [53]. In the absence of serum, the produced amorphous monodisperse SiNPs can arrest the various stages of the cell cycles. [54]. According to a study, SiNPs

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can cause G2/M arrest by upregulating Chk1and, and downregulating Cdc25C and cyclin B1/Cdc2 [55]. Other studies have demonstrated the efficacy of SiNPs to induce apoptosis through DNA damage; signaling pathways involving nitric oxide and tumor necrosis factors, and other mechanisms [56].

8.3.2 Selenium nanoparticles (SeNPs) Selenium is an essential micronutrient that is required to maintain basic physiology of cells and tissues. In addition, it is a strong antioxidant that protects cells from oxidative stress [57]. In addition, it has been established that inadequate selenium intake is linked to several other illnesses, including diabetes, infertility, cardiovascular issues, and various cancers [58]. Numerous studies have investigated the impacts of SeNPs on cell cycle of metastatic cells. [59, 60]. SeNPs have been shown by Lou et al. [60] to suppress the development of breast cancer cells (MDA-MB-231) and cervical cancer cells (Hela). Suppression of these cell lines were achieved via the induction of cell cycle arrest at the S phase. Such impacts of SeNPs support the anticancer properties of these molecules against a variety of malignant cells.

8.3.3 Zinc dioxide nanoparticles (ZnONPs) ZnONPs have been investigated for their potential health promoting effects. They are known to exert strong cytotoxic impacts on tumor cells. They also reduce the uncontrolled proliferation of breast cancer cells. Using ZnO nanostructures as anticancer therapeutic agents is suggested due to apoptosis-inducing feature of Zn that forwards optimism to speed up the production of anticancer medicines [61]. Interestingly, ZnONPs are observed to specifically target only the malignant cells without disturbing the health ones [62]. Patel et al. [63] have investigated the cell-cycle-dependent uptake of ZnONPs by malignant cells and healthier cells. Results indicated that. malignant cells uptake the ZnONPs more rapidly than the healthier cells. Moreover, ZnONPs induce the production of free radicals inside malignant cells, thereby inducing apoptosis and cellular demise at either the S or the G2/M phases.

8.3.4 Silver nanoparticles (AgNPs) The most scientifically investigated agents among the zero-dimensional nanoparticles are AgNPs that promoted their novel application in drug synthesis, cancer treatment, drug delivery system, and food packaging as well as cosmetic industries [64]. AgNPs can modulate the NF-kβ and nuclear factor E2-related factor 2-mediated signaling cascades at the subcellular levels. Moreover, AgNPs can activate p38 mitogen-activated

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protein kinase to induce DNA damage, cell cycle arrest, and cellular demise of cancerous cells [65]. Stable AgNPs were developed using the green synthesis approach by Panzarini and colleagues, who discovered that the spherical, evenly scattered AgNPs prevent Hela cell proliferation in the cell cycle phases while boosting up the population of subG1 cells [66]. Moreover, AgNPs can arrest the cell cycle of metastatic cells at the G0-G1 phase.

8.3.5 Gold nanoparticles (AuNPs) Due to their excellent plasmonic capabilities, simplicity in synthesis, adaptability, low cytotoxicity, increased bioavailability, and biocompatibility, AuNPs have attracted increased attention of the scientific communities around the globe. Gold nanocages for drugs do not usually disintegrate in biological systems when combined with AuNPs, for therapeutic approaches. Instead, they raise the local temperature, which has therapeutic benefits on cancer cells [67]. AuNPs can be conjugated with the various antibodies that can selectively bind with proteins expressed in high quantity in cancerous cells. This has potential to detect and image the cancer cells more precisely at an early stage throughput the body. Development of new techniques for the quick treatment of cancer has been made possible by employing AuNPs, which has unique physico-chemical features. Therefore the development of modified AuNPs and the subsequent usage in cancer diagnosis and treatment could provide healthcare practitioners with an alternative for cancer treatment.

8.3.6 Magnetic nanoparticles (MNPs) Inorganic materials are combined with other materials that provide active functional groups to produce MNPs. The use of nanotechnology in cancer diagnosis and therapy has always attracted a lot of scientists [68]. A new, personalized therapy approach for cancer patients has been made possible by discovering MNPs [69, 70]. The goal of MNP-based tumor treatment involves the specific molecular imaging and diagnosis of metastatic cells as well as their uncontrolled proliferation at various parts of the body in patients [71, 72]. MNPs offer high magnetic moments and better surface-to-volume ratio for enhanced hyperthermia-based cancer treatment and targeted drug delivery vehicle. Interestingly, MNPs can be used in combination with the Magnetic Resonance Imaging for better contrast of metastatic cells inside the body. Most recent developments in nanotechnology further open the scopes of MNPs in drug delivery science and other medical applications.

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8.3.7 Flavonoid nanoparticles (FNPs) Plants include a variety of flavonoids having a 15-Carbon skeleton. In addition, the molecular structure of flavonoids is constituted with the two benzene rings connected by a ridge of 3-Caron atoms. FNPs, due to their natural architecture, are highly biocompatible, with less toxicity. Bioavailability of FNPs is higher with greater intestinal absorption. Moreover, they prevent the proliferation of metastatic cells and have chemoprotective impacts during the cancer treatment [73]. Since pharmacokinetic qualities of flavonoids present a substantial obstacle, it is essential to develop nanoengineered systems that could significantly increase their therapeutic potential as anti-metastatic drugs [74]. Numerous cancer models have been tested using FNPs in both in vitro and in vivo studies. Among the several studies, flavonoids of green tea were found to inhibit several cancers like lung cancer, skin cancer, breast cancer, and others (Fig. 8.2). However, it is important to note that most of the studies demonstrating anticancer efficacy of FNPs are in the preclinical stage (Tab. 8.1).

Fig. 8.2: Several ways of nanoparticles targeting cancerous cells.

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Tab. 8.1: Advantages and disadvantages of various NPs in cancer diagnosis and therapy. NPs

Advantages

Disadvantages

AuNPs

Enhanced contrast in imaging; not photo bleaching; less invasive

Toxicity of metallic core; less affinity for tumor cells; less biocompatibility and low optical signal

AgNPs

Improved biocompatibility; enhanced anticancer activity

Exerts cytotoxicity; off-target effects with less sensitivity

Quantum dots

High quality fluorescence for imaging; multiple molecular targets

Cytotoxicity; less biocompatibility

Lyposomes Better biocompatibility; less cytotoxic; improved drug delivery

Stability issues; thermo-labile; prone to disintegration

ZnONPs

Induces ROS; stimulates chemokine and cytokine release; triggers apoptosis of cancer cells

Off-target effects; Less accumulation in target cells

SiNPs

Antioxidant property; apoptotic impacts on metastatic cells

Fuels cytotoxic impacts; less target sensitivity

SeNPs

Target cancer cells by arresting cell cycle; triggers apoptotic pathways

Less stable; cytotoxic; less target specificity for metastatic cells

MNPs

Improves disease imaging; enhances hyperthermia-based cancer treatment

Toxicity concerns; less biocompatibility

FNPs

Enhances antitumor effects; reduces systemic toxicity. improved biocompatibility

Limited encapsulation rate; low bioavailability

8.4 Challenges to nanomedicine There is very little data on the field of nanomedicine, which is a still a burgeoning one. The practical application of nanomedicine is far away and at present, it is at experimental stage. We cannot clearly state the health risks of nanotechnology. The health risks of nanotechnology are due to complete lack of evidence about their safety. Nanotechnology has shown its efficacy against metastatic cells. However, all issues of oncology are not solved by nanomedicine. We cannot clearly state the health issues of nanotechnology due to a lack of knowledge regarding the drawbacks of nanomedicine. Nevertheless, NPs can enter body through various routes that might harm the physiological systems. NPs can reach the targeted site for a localized increase in drug concentration to treat cancer. NPs are employed to treat cancer by acting as drug delivery systems, contrasting agents, and radio- and drug-sensitizing agents [75]. However, NPs show various shortcomings in clinical trials. First, biological obstacles exist within the body, making it difficult for NPs administered by intravenous injection to reach the

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tumor location [76]. Secondly, the model animals sometimes do not accurately reflect the features of the tumor microenvironment of the humanoid system [77]. Additionally, a low number of accessible receptors, uneven expression of cell surface receptors, and less affinity prevent NPs from binding to target cells [78], whereas NPs that extravasate into a portion of the tumor’s microenvironment and do not effectively diffuse to the entire tumor mass can further limit the efficacy of NPs [79]. Moreover, the impact of NPs on tumor cells is limited by the interaction of NPs with serum proteins [80]. The therapeutic efficacy of NPs is decreased when physicochemical properties are directly modified. This is because changing one parameter may have an impact on other factors. Notably, larger NPs can accumulate in extracellular matrix rather than in tumor cells, whereas smaller NPs are prone to be removed by kidneys. More significantly, large NPs (>200 nm) accumulate in extracellular spaces and do not reach the tumor mass, while small NPs (10 nm) are removed by the kidney [81]. Because nanoparticles have a larger surface area, they are more chemically reactive, which makes it difficult to predict how they will perform under various conditions and if they will breach the plasma membrane and enter cells. One of the primary elements influencing MNPs’ toxicity is their surface modification. ROS are produced when the chemical reactivity of NPs is increased. ROS results in oxidative stress, DNA damage, and lipid peroxidation that can result in undesirable consequences. A number of studies have shown that green synthesized AgNPs fuel free radical production, which has the negative effects of cytotoxicity and genotoxicity [82]. AgNP overdose was discovered to be hazardous and caused several health problems in both animals and humans [83]. Certain demerits have imposed restrictions on the application of NPs; however, some potential alternatives are available to get over these limits. Furthermore, NPs can induce physical damage while usage, leading to improper functioning of the corresponding structures. These nanoparticles are transformed into their most attractive forms to maximize efficiency, but at this small diameter, they are practically impossible to process further, and if they invade undesirable cells or tissues or accumulate over time, they can have hazardous effects. There needs to be more nanomedicine-based medical trials conducted for clear confirmation. Risk management, communication, and assessment are significant ethical issues in clinical studies. However, a comprehensive and thorough evaluation of chemical properties is needed for translational success in the nanomedicine development process [84]. It is also essential to educate people about the benefits and associated risks to avoid public criticism. Though there are certain findings that demonstrate the anticancer properties of NPs, more experiments are still required for long-term validation of results. Further experiments with respect to safety, endocytosis, transportation, degradation, and mitigation of adverse impacts are required in order to escalate clinical trials (Fig. 8.3).

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Fig. 8.3: Issues with nanoparticles in drug delivery and cancer therapy.

8.5 Future scopes Cancer is a complicated disease, characterized by a uncontrolled cell proliferation, metastasis, and combination of several physiological dysfunctions. Targeting metastatic cells with multifunctional NPs could be advantageous when compared with singlefunction NPs. Therefore, more focus on the development of NPs with multifunction ability is required for better diagnosis and treatment of metastasis. AuNPs and AgNPs have been tested against various cancers using in vitro and in vivo studies and they have shown positive results. However, studies involving clinical trials should be conducted to explore their anticancer efficacy in human population. Further, the mode of action and toxicity potentials of NPs are to be explored in human samples in the near future. There is massive demand for studies that aim to unravel the detrimental impacts of these nanoscale materials on inflammation, genetic architecture, organs, tissues, and cells. Quantum dots are reported to exhibit undesirable impacts on brain and germ cells, thus indicating their potency to fuel neurotoxicity and reproductive toxicity. Notably, the development of reliable and innovative preclinical models to improve clinical prediction should also be the focus of future research. In addition, adequate techniques are to be developed in the near future to assess and explore in detail the environmental impacts of NPs and the subsequent exposure status (Fig. 8.4).

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Fig. 8.4: Types, implications, and limitations of NPs in cancer imaging and treatment.

8.6 Conclusion Cancer is one of the major fatal diseases around the world. Due to the various challenges in the treatment of cancer cells, new technologies are required for better diagnosis and treatment. Hence, application of nanotechnology-based therapeutic strategies is gaining popularity as new alternatives for molecular imaging and treatments for metastatic cells. Several NPs have been synthesized with varied structural features that have potential scope for targeted drug delivery, therapy, and molecular imaging. They have nanoscale size, high surface area-to-volume size, and enhanced biocompatibility that make them potent candidates as drug vehicles and as nanomedicine. However, certain drawbacks like allergic reactions, risk of chemical reactions, and rapid removal through excretion exist with NPs. Further experiments are needed to investigate the impacts of various NPs on the metabolism and physiology of healthier cells. Moreover, toxic consequences of NP administration require further investigations. Thence, considering the advantageous facts and resolving the issues related to NPs, nanotechnology could lead to a revolution in clinical translation for NP-based cancer therapy. Conflict of interests: Authors declare that there is no known conflict of interests.

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Prem Rajak✶, Abhratanu Ganguly, Manas Paramanik, Sudip Paramanik, Moutushi Mandi, Anik Dutta, Sukhendu Dey

9 Emerging perspectives of nanoparticles to treat neurodegenerative diseases Abstract: The application of nanoparticles (NPs) in medicine is an emerging field to advance the therapy of diseases that are difficult to treat. NPs are favored as therapeutic drugs because of their nanoscale size, high surface area, amenability to surface modifications, and better effectiveness. Moreover, they can deeply penetrate tissues like the central nervous system (CNS), which are not easily accessible to other drugs. Neurodegenerative diseases (NDDs) are prevalent in many parts of the world. They are characterized by neuronal death and subsequent blockage in optimum neuronal activities. Most prevalent NDDs are Alzheimer’s disease (AD) and Parkinson’s disease (PD). AD is characterized by the abnormal deposition of amyloid proteins, forming plaques around brain cells. PD is caused by the deposition of Lewy bodies. All these toxic buildups of proteins lead to neuronal death. Several metal NPs, nanocomposites, and quantum dots have been tested using human cell lines and animal models to explore their efficacy against the causative factors of NDDs. These NPs showed a positive response in the majority of such experiments. However, most of these experiments are in infancy. Certain concerns regarding toxicity, half-life, and biocompatibility of drugs also persist that need to be addressed in the near future. Keywords: Nanoparticles, neurodegenerative disease, central nervous system, therapy

9.1 Introduction The world is witness to several technological advancements and artificial intelligence that have escalated research in life sciences and engineering. Some technologies have contributed to the diagnosis and treatment of fatal diseases that were not easily detectable and curable at an early stage. In addition, the implication of new technologies in medical science has the potential to combat various disorders and ailments in patients [1]. Among the several emerging technologies, nanotechnology is foremost in ✶ Corresponding author: Prem Rajak, Department of Animal Science, Kazi Nazrul University, Asansol, West Bengal, India, e-mail: [email protected], ORCID: 0000-0002-1693-8090 Abhratanu Ganguly, Manas Paramanik, Sudip Paramanik, Department of Animal Science, Kazi Nazrul University, Asansol, West Bengal, India Moutushi Mandi, Sukhendu Dey, The University of Burdwan, Purba Bardhaman, West Bengal, India Anik Dutta, Post Graduate Department of Zoology, Darjeeling Government College, Darjeeling, West Bengal, India

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the present era. It is an approach that facilitates target-specific diagnostics and therapeutics of various diseases [2]. The implication of nanotechnology in medical science is popularly referred to as nanotheranostics [3]. Nanotheranostics involves the integration of several platforms of nanotechnology, which mainly diagnose a particular physical and physiological condition, resulting in targeted detection and therapeutics of a specific disease. Nanoparticles (NPs) have attracted global attention for investigations in biomedical research for the theranostics of various ailments. NPs are important components of nanomedicine that are gaining popularity worldwide. They are known to have high molecular specificity. NPs have a diameter of less than 100 nm and a higher surface-tovolume ratio, enabling them to adsorb more drugs and have wide circulation through blood vessels [4]. The large area of NPs provides unique properties that enhance their mechanical, magnetic, catalytic, and optical characteristics [3]. They have unique surface properties due to their specific electronic structures. Notably, properties of NPs are modulated by their shape and size, and such properties could promote personalized treatment of diseases. To produce monodispersed NPs and facilitate their intracellular movements, it is essential to control their shape and size to prevent their aggregation and erroneous distribution in the body. In addition, the properties of NPs can be modulated by tagging with other agents to increase their therapeutic efficacy against a range of physiological ailments. Unique physicochemical properties of NPs can also be used as vehicles for the transportation of medicines to the targeted site. This reduces the wastage of medicines, and the drugs can be effective even at a verily low dose. Moreover, nanocarriers are also more stable and provide long-lasting impacts. Such special features of NPs enhance their effectiveness as potential therapeutic agents against a wide spectrum of diseases. Many polymeric NPs are known for their biocompatibility and enhanced stability [5]. These nanopolymers are synthesized from natural polymers like chitosan. They exhibit superior advantages for their surface modification and controlled solubility that favors a great pharmacokinetic profile [4]. Metallic NPs are also being studied for their pharmacokinetic potential. They are flexible, biocompatible, and have unique electronic and optical properties. Metal NPs can also be conjugated with ligands like proteins, antibodies, and oligonucleotides to diagnose specific biomarkers of the diseases. NPs are being investigated for their potential free radical scavenging activities. NPs, alone or in combination with other agents, can successfully scavenge free radicals and subvert oxidative stress. Oxidative stress is key to several physiological ailments and fatal diseases [6–9]. Hence, targeting free radicals with NPs could help mitigate various diseases in patients [10]. Moreover, the antioxidative property of NPs and nanocomposites could also help boost natural health. One of the promising applications of nanotechnology is the early diagnosis and prevention of emerging neurodegenerative diseases (NDDs), which are determined by hereditary or sporadic factors. NDDs are characterized by neural dysfunction and a failure in proper nervous system-body coordination [11].

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The present book chapter provides an overview of NDDs and the potential therapeutic implications of nanotechnology in it.

9.2 Neurodegeneration Neurodegeneration is the basis of all NDDs. Neurodegeneration results from toxic proteins or metabolites that build up in neural tissues as a response to mitochondrial dysfunction [12]. This promotes premature neuronal death and promotes neurodegeneration. This outcome promotes impaired nervous system functioning, and leads to subverted memory and reduced neural-muscle coordination. Several theories assume that neurodegeneration may be promoted by genetic mutations, exposure to pollutants, and several stressful conditions. Pollutants like pesticides, heavy metals, and toxic gases affect normal physiology and fuel oxidative stress (OS) [13–17]. Moreover, these detrimental compounds are also associated with compromised immunity, developmental anomalies, and mortality [18, 19]. Studies have claimed that pollutants could affect reproductive fitness and promote pulmonary as well as cardiovascular ailments [20–28]. In addition, they could escalate the formation and deposition of toxic metabolites in neurons, leading to neurodegeneration and the onset of NDDs. Neurodegeneration is responsible for emerging old-age diseases like PD, AD, and Huntington’s disease.

9.2.1 Alzheimer’s disease AD is the most prevalent NDD across the globe. Most cases are reported in developed countries. However, AD is spreading quickly in many developing countries, including India. AD causes dementia with cognitive loss and is mainly common in people with old age. However, signs of the disease are now being detected even at a lower age. AD may result in the mass death of patients in developed countries. Vos et al. [29] have claimed that the disease impacts more than 25 million patients worldwide and might affect 42.3 million people by 2020 [30, 31]. The primary reason for the onset of the disease is the deposition of toxic proteins in neurons, leading to synaptic injuries. This results in neurodegeneration, reduced cognition, dementia, and behavioral alterations in the patients [31]. The molecular mechanism of the disease revolves around the catalytic role of cyclin-dependent kinase 5 (CDK5). Typical functions of the protein are essential for neuronal growth and development [32]. However, hyperactivation of CDK5 results in hyperphosphorylation of tau protein. Tau, in normal conditions, helps to maintain neuronal morphology and plasticity. Hyperactivation generates neurofibrillary tangles of tau protein, impairing neuronal plasticity and physiology [33]. Accumulating toxic neurofibrillary tangles lead to the premature demise of neuronal cells and the

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subsequent onset of neurodegeneration. In addition, defective processing of amyloid precursor proteins because of genetic issues may also result in neural degeneration. Lloret et al. [34] have reported that a reduction in p25 levels increases amyloidinduced neurotoxicity. This has been associated with impaired calcium signaling and enhances neural degeneration. Therefore, abnormal accumulation of amyloid beta leads to toxic consequences and the onset of AD in patients [35].

9.2.2 Parkinson’s disease PD is the second most prevalent NDD in the world. It disturbs the central nervous system (CNS) of the patient. PD is diagnosed by stiffness of limbs, tremors in hands and joints, slow movement, and reduced coordination between the different parts of the body [36]. The ailment mainly results from the premature death of vital neuronal cells in specific parts, especially in the substantia nigra region in CNS. Dopamine is an important neurotransmitter that is crucial for controlling body movement and maintaining coordination between the different body parts. Neuronal death in the substantia nigra leads to a decline in dopamine levels in the brain that disrupts normal functioning and neural-muscle coordination [37]. Another important cause of PD is the formation of filamentous structures in the brain. These filamentous structures are formed of alpha-synuclein, a vital protein of the CNS. It plays a pivotal function in recycling and compartmentalizing neurotransmitters in the brain. Excessive accumulation of alpha-synuclein in the brain imposes toxic consequences, leading to neurodegeneration [38]. This protein, when it aggregates in large amounts, forms Lewy bodies in the brain and develops alpha synucleinopathy [39]. Excessive aggregation of Lewy bodies leads to reduced dopamine production, promoting the disease’s onset. Therefore, AD and PD are the two most prevalent NDDs across the globe that need intervention of nanotechnology for early theranostics of the disease. Several advancements have been made in this field using NPs and nanocomposites for the targeted therapy of these NDDs. For nanotechnology and its implication in the context of neurodegeneration, see Fig. 9.1.

9.3 Site-specific drug delivery by NPs Nanoengineered NPs have potential scope for their use as a vehicle for the transport of medicines to the targeted area. Their small size and enlarged surface area are advantageous in medical science as they reach the deep tissues that are tough to access by other medicines. Therefore, NPs directly target the affected area of the patient [40]. Interestingly, NPs and nanocomposites can be tailed in a specific way and as per the

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Fig. 9.1: Characteristics of NDDs. Mitochondrial dysfunction, amyloid beta plaques, cortical shrinkage, and dementia characterize AD. PD is characterized by α-synuclein aggregation, oxidative stress, injuries of dopaminergic neurons, motor dysfunction, and lack of coordination.

need of the individual patient, thereby enhancing their practical applicability for personalized treatment with higher success rates [41]. The implication of different metal NPs to produce electromagnetic waves for targeted disease therapy has potential scope in NDD treatment. This technology can also be combined with lesser technology to enhance the effectiveness of the nanoparticle-mediated deep tissue therapy of neurological disorders. One of the significant issues during the theranostics of CNS ailments is crossing the blood-brain barrier (BBB). BBB reduces the circulation of conventional medicines to the CNS and, therefore, reduces their effectiveness. It is important to note that lipid solubility enhances drug delivery to the brain as they can cross BBB. Passive transportation of lipid-soluble molecules occurs through transcellular passive transport. The properties of NPs can be modified, which may increase liposolubility and enhance drug delivery to the targeted site of the CNS. NPs can be engineered to carry anticoagulation agents to dissolve blot clots in the brain to facilitate the treatment of NDDs. Moreover, small size, large surface area, and hydrophobicity could help to carry drugs that can dissolve neurofibriilar tangles and toxic metabolites from various brain parts to combat neurodegeneration. Numerous studies have been performed to understand the potential implications of NPs in the treatment of NDDs. Multiple studies using cell cultures and animal models have been used across the world that support the possible medical implications of NPs and nanocomposites in theranostics of AD and PD at molecular levels.

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9.4 Targeting neurodegeneration Multiple studies have been performed across the globe that claims the beneficial impacts of nanotechnology on neurodegeneration. Such studies have been performed either using animal models or cell lines.

9.4.1 Studies using animal models Animal models provide an excellent platform to study the implications of NPs and nanocomposites in NDDs and other ailments in the body. Interestingly, results of several studies on animal models are extremely positive. Results obtained using animal models are now scaled up in humans. The major NP that has been extensively used in medical research is the gold nanoparticle (AuNPs). AuNPs have certain features like nanoscale size, increased flexibility, various shapes, and high surface area that make them extremely suitable for clinicians [42]. AuNPs tagged with gastric-releasing peptide receptor were investigated for their impacts on mouse tumor treatment [43]. The results thus obtained were positive and opened the scope for the treatment and prevention of NDDs. In another investigation, mice administered with AuNPs tagged medicine have successfully removed tumor and did not impose any adverse impact on the overall health of the treated individuals [44]. This finding suggests that NPs could also be used to selectively destroy the neurofibrillary tangles and toxic proteins in the brain to mitigate NDDs. Notably, the implication of nanotechnology in synchrotron radiation X-ray computerized topography, which is a high-speed advanced imaging process for diagnosis. In a study, silica NPs were widely circulated and distributed throughout the mice body; they assisted in treating neuron-related defects [45].

9.4.2 Studies using cell lines Cell culture is another platform to investigate the implications of NPs in many diseases, including AD and PD. Cells are designed as per various cell types of the body such as neural cells, macrophages etc. for better experiments of targeted therapies. Researchers have designed and cultured several cell lines of the brain to study different factors and treatment methods for a number of neurological diseases [46]. Researchers have employed cell-based approaches to study the impacts of NPs on AD and PD [47]. NPs help in the ablation of macrophages, which results in an overall reduction of the inflammation of cells, thus providing scope for the theranostics of NDDs. Nanotechnology has also been implicated in the diagnosis of neuronal diseases. NPs and nanocomposites are used in diagnostic approaches like computed tomography and cellular imaging [48]. The application of NPs in magnetic resonance spectroscopy provides better imaging and diagnostics for diseases like AD and PD by selective

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detection of overexpressed CDK5 proteins and other toxic proteins. Interestingly, nanoparticle-mediated therapies have helped to enhance the level of dopamine to enhance motor activities [49]. Therefore, results using cell lines have indicated that NPs could work at cellular levels to mitigate factors responsible for neurodegenerative diseases. Moreover, the findings are interesting and suggest trials in human samples.

9.4.3 Studies in human subjects Limited investigations have been documented exploring the impacts of NPs in diagnosing and treating NDDs. Nanotheranostics have been employed in voluntary patients. In a study, personalized treatment using a nanotheranostic approach was carried out where metallothionine was used as a biomarker of the NDDs [50]. Patients suffering from NDDs were injected with metallothionine drug discovery biomarker that helped in targeting specific cells to remove malignancy and neural dysfunction that usually leads to neurological disorders. However, in another study, AuNPs injected in a voluntary patient were not able to completely treat AD, though it was effective in the early diagnosis of neurodegenerative disorders [51]. Therefore, NPs could be used to target specific areas in the CNS for better diagnosis and treatment of neurodegeneration. Notably, NPs with dual functions have been found to target amyloid plaques in the CNS of animal models with AD [52]. It is worth mentioning that despite having lots of research done in animal and cell line models, direct studies employing human subjects is still in its infancy and needs extensive studies to reach any definite conclusion regarding the effectiveness of NPs and nanocomposites on theranostics of NDDs, on clinical grounds.

9.5 Crossing BBB One of the major challenges for neuromedicine is crossing the BBB. BBB is mostly selective to macromolecules and does not allow them to reach the neuronal tissues. NPs could be advantageous for the targeted therapy of neurological diseases because of their tiny size, flexibility, high surface area, hydrophobicity, and charge. Nonetheless, an ideal nanoparticle considered for drug delivery should be biocompatible, less toxic, and show effective binding with therapeutic medicines. All these features are crucial to cross the BBB and to exert targeted therapy. NPs can access CNS via noninvasive approaches like intranasal delivery or invasive approaches that imply direct intraventricular or intracerebral implantation [53]. In some instances, temporary disruption of BBB is also helpful for an effective drug delivery. Notably, NPs have unique features that provide additional advantages of adequate transportation and adsorp-

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tion across the blood-brain barrier [48]. Additionally, NPs modulated with other ligands can also deliver drugs with high effectiveness. NPs and nanocomposites can help open the right junctions to reach the neural cells. Nanoconjugates can also follow the transcytosis process to cross the endothelial cells [54]. Moreover, NPs can be used with receptor-mediated transcytosis to effectively distribute to the brain tissues to treat NDDs. Therefore, NPs and nanocomposites with special features could be potential alternatives with higher effectiveness in place of existing drug delivery vehicles to treat NDDs like AD, PD, and multiple sclerosis.

9.5.1 Nanocomposites Aggregation of amyloid beta is responsible for the onset of AD. Thence, most of the therapeutic approaches include amyloid beta-targeted therapies. Tau also contributes to AD. In a study, methylene blue-loaded multifunctional nanocomposite was prepared and allowed to bind hyperphosphorylated tau protein. The surface-decorated CeNC helped to subvert mitochondrial stress and tau hyperphosphorylation. In addition, methylene blue blocked the aggregation of hyperphosphorylated tau protein [55]. Therefore, synergistic effects of CeNC and methylene blue were effective against AD. Oxidative stress is responsible for several physiological ailments. Exposure to pollutants may be responsible for oxidative stress and the subsequent physiological ailments, including NDDs. Certain plant products could be beneficial in mitigating several diseases and pathogenic infections. In a study, the effect of alginate nanocomposite (BANC) on PD model of Drosophila melanogaster was investigated [56]. Nanocomposites reduced lipid peroxidation and oxidative stress (OS), and increased total glutathione contents in flies. However, the brain of flies with PD did not show any significant change. OS is fueled by reactive oxygen species (ROS) and therefore, ROS could be a factor in the onset of NDDs. In a study, selenium nanocomposites with enhanced biocompatibility were detected to neutralize ROS and therefore, OS [57]. Hence, various nanocomposites can target the causative factors like reactive oxygen species and OS to mitigate NDDs in patients.

9.5.2 Metal NPs Nerve growth factors orchestrate a vital role in neural growth and differentiation. However, its role in preventing neurodegeneration is limited due to its reduced efficiency in crossing the BBB and slow diffusion with a short half-life. Metal NPs can be used as an effective carrier of nerve growth factors. However, NPs show instability in the neuronal environment, cellular toxicity, and subcellular aggregation. Notably, these limitations can be minimized by coating the NPs with metals, alloys, and polymers. Gold-coated nanocarriers are more effective due to their higher biocompatibility, stability, and tum-

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ble-surface properties. Such features of gold-coated nanocarriers allow the drugs to be released in a controlled manner to treat the neurodegeneration more precisely and effectively. In another study, paramagnetic iron oxide NPs were used to express MICRORNA141, which resulted in the synthesis of brain-derived neurotrophic factor (BDNF), DAT, and 5-TH [58]. BDNF prevents neurodegeneration. Detection of aggregated amyloid proteins is important in the diagnosis of NDDs. Gold NPs can be used in the detection of amyloid proteins. Noncovalent interactions between gold NPs and amyloid fibrils produce an intense choral response that can be detected to diagnose neurodegeneration. Detection and quantification of DA are essential to diagnose neurodegeneration. Gold NPs could play a pivotal role in it. DA DNA aptamer-AuNP conjugate enhances the signal of surface plasmon resonance [59]. This facilitates the quantification of DA from femtomolar concentration to picomolar concentration. The lowest concentration range can be measured through the surface plasmon resonance technique. Therefore, metal NPs have the potential to be used as an effective drug vehicle for the treatment of neural diseases. In addition, various metal nanoparticle conjugates could also be implicated in the selective treatment of NDDs.

9.5.3 Quantum dots PD is caused by the excess accumulation of amyloid fibrils. Alpha-synuclein aggregates massively to fuel neurodegeneration. Therefore, targeting the aggregation of amyloid fibrils could be helpful in the prevention of NDDs. In a study, graphene quantum dots were found to prevent abnormal accumulation of alpha-synuclein [60]. Interestingly, graphene quantum dots led to the disintegration of mature amyloid fibrils. They also prevented premature neuronal death. Notably, graphene quantum dots were able to reduce Lewy body and Lewy neurite formation, and assisted in mitigating mitochondrial dysfunction. Graphene dots also prevent aggregated alphasynuclein from spreading from one neuron to another. Therefore, graphene quantum dots have the potential to act as an anti-aggregating agent against alpha-synuclein. It also provides a novel approach to treat PD by the disintegration of mature amyloid fibrils and Lewy bodies from neuronal cells. Therefore, quantum dots could be effective in the treatment of NDD. However, their impacts on the immune system and other toxicities have not been investigated. Moreover, the effectiveness of quantum dots to cross the BBB is still a matter of detailed investigation. However, preliminary studies claimed the potential implication of quantum dots in the treatment of both early-stage and late-stage NDDs, such as lateral sclerosis, AD, and PD (Fig. 9.2).

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Fig. 9.2: Transportation of NPs through the central nervous system. NPs employ both active and passive routes. Active route is facilitated by transcellular and paracellular diffusion. Passive transport is promoted by adsorptive transcytosis and receptor-mediated transcytosis.

9.6 Biomarkers and biosensors Alteration in neural connectivity and neural architecture is the main feature of neurodegeneration. The occurrence of dendritic spines and micron size protrusion in the shaft of dendrites are the characteristic features of neuronal connectivity. Specially resolved nanoparticle-enhanced photoporation can help to detect such alterations in synaptic connections that could be indicative of neurodegeneration. Spatially resolved NPenhanced Photoporation (SNAP) could be helpful in screening neuronal connectivity with respect to neurodevelopmental and neurodegenerative disorders [61]. In the case of AD, several proteins such as amyloid beta 1–40 and tau are considered as markers for the diagnosis of the disease. Antibodies of these proteins loaded on gold NPs could be used as biosensors to monitor the abnormal fibrillation and aggregation of these proteins in neurons for the early detection and treatment of the disease. Graphene quantum dots are helpful in diagnosing and inhibiting dopamine neuron loss [59] (Fig. 9.3).

9.7 Limitations and potential solutions Though NPs have several scopes in diagnosing and treating NDDs, they have their own limitations. The first limitation is that most of the research works demonstrating the potential use of NPs in the treatment of NDDs are in infancy. Most of the works

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Fig. 9.3: Potential NPs in medicine and diagnosis of NDDs.

are done either in vivo or in vitro. Till date, human trials are limited without any conclusive data. Thence, more investigations are essential to achieve a definite conclusion. Moreover, certain NPs have shown toxicities in some animal models. Therefore, detailed toxicity profiles of NPs, nanocomposites, and nanoparticle-based quantum dots are still pending or under investigation. Many practitioners around the globe are unaware of the properties and their usage in patients. Therefore, practitioners need to be trained well before the application at a growing level. One of the important criteria in pharmaceuticals is the concentration of any medicine. Lots of work still needs to be done to establish particular concentrations of NPs that could work for the effective treatment of NDDs. Half-life is also crucial for the activity of any drug. Studies on the half-life of NPs for treatment purposes are lacking. Therefore, NPs could be a promising approach to diagnosing and treating NDDs. However, more research work is still needed to become a ground reality. Toxicity and biocompatibility are the two major factors that limit the efficacy of NPs for the theranostic purpose of neurodegenerative disease. Therefore, modulating existing NPs with biologically derived conjugates could be beneficial in reducing toxicity and enhancing biocompatibility. NPs formulated using plant extracts, protein-

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based materials, exosomes, microorganisms, etc. might improve the efficacy of NPs against NDDs. Such bioNPs could be cost-effective, environmental-friendly, biologically compatible as well as renewable, which reduces the limitations of NPs in the theranostics of NDDs.

9.8 Conclusion Nanotechnology is an emerging medical field with strong potential to treat several diseases that are still untreatable at present. NP-mediated therapies have greater specificity and deep tissue accessibility for the effective treatment of diseases. NDDs like AD and PD have become common diseases in both developed and developing countries. These diseases are marked by the toxic buildup of protein aggregates that promote neuronal death and the subsequent loss in cognition and motor functions. Several animal and cell line studies have suggested that nanocomposites and NPs can block aggregation of amyloid fibrils and alpha-synuclein in neurons to prevent neurodegeneration. NPs can also be employed for effective diagnosis and treatment across the blood-brain barrier. They can also be developed as biosensors tagged with specific antibodies to bind and detect various markers of neurodegeneration. However, more studies are needed to reach a conclusive decision and make the therapy a reality for patients. The development of green-NPs could be the future scope of nanotechnology in the theranostics of NDD. NPs developed from plant extract, microorganisms, exosomes, etc. could reduce the toxicity and enhance the biocompatibility of these nanomedicines. More experimental results involving green NPs should be conducted to achieve a definite conclusion. Conflict of interest: The authors declare that there is no known competing interest.

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Alaa Kamo, Ali Ozcan, Ozlem Ates Sonmezoglu, Savas Sonmezoglu✶

10 Understanding antibacterial disinfection mechanisms of oxide-based photocatalytic materials Abstract: Despite the fast-developing technological advances, the world of science and industry is still far from controlling environmental and health issues. Today, the COVID19 pandemic has demonstrated that it is essential to focus on the development of novel technologies, materials, and medical innovations to control these issues. In particular, microbial pathogens that directly or indirectly affect human health can sometimes threaten human health and cause dangerous infectious diseases. Recent developments show that engineered photocatalytic nanomaterials possessing antibacterial properties are attracting scientists as an alternative bacterial infection treatment method to overcome such bacterial/viral epidemics that have posed a serious problem and increased disquiet in recent years. Various oxide-based photocatalytic nanomaterials have been designed to work efficiently in outdoor and indoor environments for the photocatalytic disinfection of different pathogens. In this chapter, we throw light on the antibacterial mechanisms proposed on the most studied oxide-based photocatalysts, such as TiO2, ZnO, SnO2, CuO, and Zn2SnO4, and their relationship to the types of interactions triggering antibacterial activity. Finally, we discuss in detail the effect of intrinsic properties of nanomaterials, such as particle size, shape, zeta potential, and roughness on antibacterial activity, and the ways to improve the antibacterial activity of oxide-based nano-photocatalyst. Keywords: Oxide-based photocatalytic materials, Antibacterial disinfection mechanisms; Engineered nanomaterials (ENMs), Antibacterial agents, Oxidative stress by ROS generation, Release of metal ions

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Corresponding author: Savas Sonmezoglu, Nanotechnology R&D Laboratory, Karamanoglu Mehmetbey University, Karaman 70100, Türkiye; Department of Metallurgical and Materials Engineering, Karamanoglu Mehmetbey University, Karaman, Türkiye Alaa Kamo, Nanotechnology R&D Laboratory, Karamanoglu Mehmetbey University, Karaman 70100, Türkiye; Department of Bioengineering, Karamanoglu Mehmetbey University, Karaman 70100, Türkiye Ozlem Ates Sonmezoglu, Department of Bioengineering, Karamanoglu Mehmetbey University, Karaman 70100, Türkiye Ali Ozcan, Department of Chemistry and Chemical Processing Technologies, Vocational School of Technical Sciences, Karaman, 70100, Türkiye https://doi.org/10.1515/9783111137902-010

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10.1 Introduction Antibiotics are a class of synthetic or natural compounds used to fight bacterial infections. These compounds are used with the aim of completely killing the bacteria or preventing the growth and multiplication of the bacteria. Based on their efficacy, they can be classified as narrow- or broad-spectrum. Due to their reasonable price and strong efficacy, these compounds have become the most common treatment method in treating bacteria-related infections. Apart from this, biologically relevant antibiotics have been widely used in agricultural practices for multiple purposes such as increasing crop yield, animal husbandry, treating infected animals, and growth promoters in animal feeds [1]. According to the Center for Disease Dynamics, Economics, & Policy’s 2021 report, which evaluates the status of antibiotics worldwide, there has been a 65% rise in the usage of antibiotics among humans between 2000 and 2015. The report was published on February 3, 2021 [2], while consumption of antibiotics in animals is expected to increase by 11.5% between 2017 and 2030. If current habits of antibiotic consumption persist, it is foreseen that worldwide antibiotic consumption is expected to increase by 200% between 2015 and 2030 [2]. In the plant agricultural industry, antibiotics have been used to control certain diseases that affect fruits, vegetables, or ornament plants. Among those antibiotics, streptomycin and oxytetracycline are broad-spectrum antibiotics that have been commonly used [3]. Currently, streptomycin is the only chemical method approved for foliar use by US Environmental Protection Agency (EPA) to fight citrus greening (phloemrestricted diseases caused by CLas) in Florida. The effectiveness of the treatment is still an ongoing debate, since most applied treatments are found not to reach target sites. Due to the widespread use of antibiotics for disease management in humans and animals, unused antibiotics going into the drainage, contamination of soil and water in the plant agriculture industry, and bacteria developing resistance to treatments are becoming a huge problem. Bacterial infections-induced illnesses have become a major cause of death worldwide [4]. Already, more than 70% of bacterial infections are resistant to antibiotics at some level [5]. Antimicrobial-resistant (AMR) bacteria are likely to be transmitted to the soil or directly to humans. Studies reported in the literature show that these bacteria carry the NDM-1 gene, which is a super-resistant gene [6]. According to the study, published in The Lancet on January 19, 2022, it is estimated that 1.27 million deaths were directly related to antimicrobial-resistant infections in 2019 [7]. With the increase in the use of antibiotics, the resistance to them in bacteria will increase and cause more deaths worldwide. A report published in 2016 estimates that as many as 10 million people can die each year by 2050 due to AMR [8]. There are many alternatives to antibiotics to cure bacterial infections such as predatory bacteria [9], bacteriophage therapy [10], competitive exclusion of pathogens [11], and bacteriocins [12]. However, none of them has shown as much efficiency as antibiotic treatment. Hence, it is necessary to explore new strategies to develop a new generation of antibacterial agents that can eradicate bacterial infections.

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Nanotechnology has led to advances in many fields of technology and science. Nanotechnology applied in the pharmaceutical industry attracts the attention of many researchers because of the offered advantages [13]. In general, the term engineered nanomaterials (ENMs) can be used to describe compounds with at least one dimension in the range of 1–100 nm in size. Compounds sizes above 100 nm are considered bulk materials. The properties of ENMs are affected by their particle size, which is not the case for bulk materials. As the size of the material decreases, the percentage of atoms on the surface increases proportionally compared to the total number of bulk material atoms. This higher surface-to-volume ratio provides drastically different properties for ENMs making electronic energy states unique. In most cases, smaller ENMs exhibit higher antibacterial activity than their larger counterparts [14, 15]. The increased surface-to-volume ratio of the ENMs increases the antibacterial activity by providing greater contact of the ENMs with the bacteria [16]. Various ENMs have taken great attention because of their bactericidal properties. ENMs like titanium dioxide (TiO2), zinc oxide (ZnO), silver oxide (Ag2O), copper (II) oxide (CuO), magnesium oxide (MgO), and calcium oxide (CaO) exhibit antibacterial activity. It is hoped that these ENMs will be less prone to increasing resistance in bacteria compared to antibiotics. Contrary to antibiotics that target a specific protein in bacteria, ENMs do not contribute to bacterial resistance [17]. Therefore, they offer a great advantage in treating bacterial infections with resistance to antibiotics. At the same time, ENMs can have more than one antibacterial mode of action (such as reactive oxygen species (ROS) generation and antimicrobial ion release), which prolongs bacterial resistance also to ENMs. Although mechanisms such as the release of metal ions and ROS production are suggested, the exact mechanisms of the antibacterial effect of ENMs are still unknown [18].

10.2 Proposed antibacterial mechanisms of ENMs The use of ENMs in healthcare has risen, leading to more research focused on exploring how ENMs combat bacterial infections [19]. For ENMs to display their antibacterial properties, they need to interact with bacterial cells. The recommended contact patterns are: i) electrostatic attraction, [20], ii) receptor-ligand, [21], iii) van der Waals forces [22], and iv) hydrophobic interactions [21]. Once the interaction occurs, ENMs can typically adhere to the bacterial membrane and cause damage to it. ENMs can also infiltrate the cell and interact with vital components necessary for the bacteria to survive, such as DNA, proteins, and ribosomes, ultimately resulting in the death of the bacteria. The exact mechanism of how oxide-based ENMs exhibit antibacterial activity is not entirely clear, but there are two suggested possibilities: 1) inducing oxidative stress and producing ROS (reactive oxygen species), and 2) releasing metal ions from oxide particles [18] (Fig. 10.1).

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Fig. 10.1: Various antibacterial activity mechanisms of ENMs [23]. Reproduced with permission from Dizaj et al., Materials Science and Engineering: C, published by Elsevier, 2014.

10.2.1 Oxidative stress by ROS production ROS refers to reactive substances that are generated during certain metabolic processes involving oxygen. ENMs can create various types of ROS by reducing oxygen molecules. There are four types of ROS: superoxide radical (O2.-), singlet oxygen (O2.), hydroxyl radical (OH.), and hydrogen peroxide (H2O2). ENMs can generate ROS through several mechanisms, but the primary method is believed to be photocatalytic activity. When oxide materials are stimulated by the light energy that is equal to or greater than their band gap, an electron is encouraged to move from the valence band to the conduction band, creating a positive charge hole in the valence band (as shown in Fig. 10.2). Positively charged valence band holes function as oxidizing agents, while conduction band electrons function as reducing agents. The electrons produced react with O2 that is absorbed on the semiconductor surface, resulting in the generation of ROS, such as O2.–, O2., and H2O2, while the holes react with H2O to produce OH radicals [24]. In general, the presence of ROS can cause harm to cells by breaking down DNA and oxidizing amino acids and polyunsaturated fatty acids (Fig. 10.3). Hydroxyl radicals and superoxide are generated by photocatalytic activity and carry a negative charge. These reactive species may remain on the surface of the bacterial cell because they cannot easily penetrate the positively charged cell membrane. However, hydrogen peroxide (H2O2) can enter the cell membrane and cause damage to the bacteria, leading to its destruction [26]. Some studies have reported that ROS reactive oxygen species can induce cell membrane damage [27] and cause peroxidation of lipids that disrupt the cell membrane and inhibit the growth of bacteria [28]. The general mecha-

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Fig. 10.2: Photocatalytic mechanism of TiO2 [25]. Reproduced with permission from Sujatha et al., Environments, published by MDPI, 2020.

Fig. 10.3: Lipid peroxidation mechanism [31]. Reproduced with permission from Medina-Meza et al., Innovative Food Science & Emerging Technologies, published by Elsevier, 2014.

nism is that polyunsaturated fatty acids are attacked by free radicals causing lipid peroxidation. Peroxidation causes a change in membrane fluidity, a decrease in membrane potential, and an increase in the permeability of membranes to H+ and other ions. Thus, it causes cell death by causing the membranes to rupture and the organelle content to be released into the cytoplasm [29]. Huang et al. investigated oxidative damage in the cell membrane using TiO2 photocatalysis. The result of the study suggested that lipid peroxidation initiates the release of intracellular components and eventually the bacteria’s death [30]. Furthermore, ROS can target proteins and impede the function of specific periplasmic enzymes that are vital for the survival of bacterial cells [32]. ROS, such as

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hydroxyl radical, cause reversible or irreversible oxidative modification on intracellular proteins and ultimately oxidative damage [33]. When intracellular protein structures are oxidized, carbonyl groups are formed on their side chains (proline, arginine, lysine, and threonine). The cytoskeleton, which comprises various proteins and enzymes, can undergo structural and functional alterations due to oxidative stress-induced modifications in protein structures. Changes in structure and function in proteins can prevent the vital activities and proliferation of bacteria. ROS can also significantly reduce many crucial cellular metabolic processes dependent on proteins, such as energy, carbohydrate, nucleotide, and amino acid metabolisms [34], and surprisingly ROS can damage DNA without a clear visible disturbance to the cell membrane of bacteria [35] Li et al. have shown in their study that the hydroxyl radical (OH•) is a strong and nonselective oxidant that can destroy organic biomolecules such as DNA, lipids, carbohydrates, proteins, nucleic acids, and amino acids [36].

10.2.2 Release of metal ions Metal ions interact with functional protein and nucleic acid groups such as carboxyl (– COOH), amino (–NH), and mercapto (–SH) [37]. Besides damaging enzyme activity, metal ions affect normal physiological processes, change cell structure, and inhibit bacteria. Interactions between metal ions and membrane proteins lead to a significant variation in membrane permeability through the denaturation of proteins and lipopolysaccharide degradation [38]. When cell membrane lipids are damaged, internal components are released, which results in the death of the bacteria. In addition, metal ions can inhibit many proteins and kill bacteria by preventing translation and replication processes. In addition, the oxidation of the side chains of amino acids can catalyze the formation of carbonyls attached to proteins by the release of metal ions by photocatalytic activity. When it comes to enzymes, protein carboxylation causes them to lose their catalytic activity, which subsequently encourages the breakdown of proteins. Enzymes and proteins are essential for the life of the bacteria [39]. The degradation of proteins and enzymes adversely affects DNA replication and translation processes. This prevents the proliferation of bacteria, causing the death of the bacterial cell.

10.3 ENM properties related to antibacterial efficacy 10.3.1 The effect of size The electrical and optical properties of materials typically change significantly when their sizes shrink at the atomic and molecular levels, giving rise to various electronic, optical, magnetic, and mechanical properties of nanomaterials [40]. Due to the quan-

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tum size effect of small particles, ROS production increases by providing better light absorption, thus increasing antibacterial activity. In addition, the confining dimensions energy levels become distinct and the material’s band gap widens as the particle size shrinks [41]. At the same time, small ENMs can enter the cell easier than large ENMs, and that can be done by forming pores in the cell membrane of the bacteria. ENMs can thus inactivate and damage essential molecules such as DNA, lipid, and protein [42].

10.3.2 The effect of surface-related defects There is also a link between the presence of edges, defects, or corners in the nanostructure of ENMs and the production of ROS [43, 44]. Many studies reported that defects affect the photocatalytic activities of metal oxides. The most important defect is oxygen vacancies. With the formation of oxygen vacancies – a vacancy is formed at the position of the original oxygen atom – so that the surrounding atoms are rearranged [45, 46]. Between the valence band and the conduction band, they simultaneously generate the donor level [47]. This increases the photocatalytic activity of metal oxides under both UV and visible light [48, 49]. Apart from this, separation and migration of photogenerated electron-hole pairs are affected by oxygen vacancies [50]. As a result, it promotes the generation of ROS, which in turn improves photocatalytic activity. ZnO whiskers (t-ZnO), nano-sized ZnO particles (n-ZnO), and micro-sized ZnO particles (m-ZnO) were tested for their antibacterial efficacy against Escherichia coli by Xu et al. [51]. These particles had 29%, 19%, and 17% oxygen vacancies, respectively. The results showed that t-ZnO particles had greater antibacterial activity. According to the authors, t-ZnO increases H2O2 generation. The increased antimicrobial activity followed this.

10.3.3 The effect of shape Another factor that can affect antibacterial activity of ENMs is their shape. ENMs can take various shapes, which can be controlled by the synthesis processes. Common nanomaterial shapes include spheres, nanotubes, nanospheres, nanoneedles, nanorods, truncated triangles, nanorings, nanowires, nanocubes, and more [52]. By interacting with periplasmic enzymes, variously shaped nanoparticles (NPs) can harm bacterial cells to varying degrees [53]. For instance, Laha et al. showed that sheetshaped ENMs and spherical CuO NPs both increased the likelihood of membrane damage in Bacillus subtilis and Escherichia coli, respectively [54]. Another study found that compared to cubes with tiny spaces, cubes with wide voids, and octopod-shaped silver oxide, cubes-shaped silver oxide NPs had the highest antibacterial activity [55]. The direct mechanism is still not completely understood, though.

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10.3.4 The effect of surface coating Another significant factor affecting antibacterial activity is the surface charge (zeta potential) of the ENMs. The zeta potential is measured to understand binding of organic molecules to the surface, solution dispersion behavior, and long-term stability of ENMs. Cells in nature are negatively charged cell walls; therefore, they electrostatically attract positively charged ENMs, and many studies have shown that having positive zeta potential increases their antibacterial activity [56, 57]. Haldorai and Shim looked into the antibacterial properties of a composite made of chitosan and zinc oxide against an Escherichia coli bacteria strain [58]. In this study, it was reported that the zeta potential was increased to + 23.7 mV by forming composites with chitosan. According to the authors, the interaction of the negatively charged bacterial membranes with the positively charged composite impeded cellular growth by preventing nutrient uptake by the cells.

10.3.5 The effect of roughness Roughness is another element that affects antibacterial activity. The surface area/volume ratio, bacterial protein adsorption, and bacterial adhesion all decrease as ENM roughness rises [59, 60]. According to Padmavathy and Vijayaraghavan, the roughness of zinc oxide’s surface boosts the antibacterial activity via mechanically damaging Escherichia coli’s cell membrane [26]. However, to date, there is no comprehensive study investigating the role of the roughness of ENMs in their antibacterial activity.

10.3.6 The effect of bacteria type The sensitivity of the species can also have an impact on the antibacterial activity of ENMs. For instance, Pseudomonas desmolyticum and Staphylococcus aureus were shown to be less sensitive to CuO NPs than Escherichia coli and Klebsiella aerogenes bacterial strains [61], according to Naika et al. Additionally, a great deal of research has demonstrated that MgO ENMs are more effective against gram-negative bacteria than gram-positive bacteria. The discrepancy in the cell membrane’s structure is likely the root of the problem. While gram-positive bacteria like Staphylococcus aureus only have one peptidoglycan layer in their cell walls, gram-negative bacteria like Escherichia coli primarily consist of thin lipid A, peptidoglycan, and lipopolysaccharide layers [62].

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10.4 Oxide-based semiconductor photocatalysts used as antibacterial agents There are two types of antibacterial substances: organic and inorganic. The low heat resistance, high decomposability, and short half-lives of organic compounds prevent them from being widely used as antibacterial agents. Therefore, it has become more attractive to use inorganic compounds as antibacterial agents. In recent years, inorganic ENMs such as oxide-based semiconductor photocatalysts have been reported to show high antibacterial activity. Oxide-based semiconductor photocatalysts ENMs such as TiO2, ZnO, SnO2, CuO, Zn2SnO4, MgO, CaO, and α-Fe2O3 have many attractive properties such as low cost, readily synthesizable, and biocompatible. Therefore, it is thought that oxide-based semiconductor ENMs can replace conventional antibiotics in the eradication of bacterial infections.

10.4.1 Titanium dioxide Among the semiconductor oxides, TiO2 is one of the most appealing materials due to its favorable valence band and conduction band positions, low cost, chemical stability, photostability, and nontoxicity, dioxide is one of the most promising photocatalysts [63]. TiO2 ENMs are used to degrade a variety of pollutants, including polycyclic aromatic hydrocarbons, dyes, chlorinated organic compounds, phenols, pesticides, cyanide, phenols, and heavy metals because of their low selectivity [64]. In nature, TiO2 has three different phases mainly anatase, rutile, and brookite as shown in Fig. 10.4. Anatase and brookite are metastable under environmental conditions and can be easily converted to a stable rutile form by raising the temperature.

Fig. 10.4: Crystal structure of titanium dioxide phases of anatase, rutile, and brookite [65]. Reproduced with permission from Pelaez et al., Applied Catalysis B: Environmental, published by Elsevier, 2012.

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Although the TiO2 anatase form has a lower absorbance ability against sunlight than rutile owing to its wider band gap than the rutile form, many studies have reported that the photocatalytic activity of anatase is higher than that of rutile [66, 67]. This is because the anatase phase has a higher ability to bind hydroxyl groups and a lower e–/h+ recombination rate compared to rutile [68]. In addition, rutile has disadvantages such as large grain size, lower specific surface areas, and worse surface adsorption capacity, which limit its photocatalytic activity [69, 70]. Fujishima and Zhang reported that anatase and rutile forms of TiO2 exhibited higher photocatalytic activity than brookite [71]. Zhang et al. reported that the anatase form of TiO2 showed higher photocatalytic activity than the rutile form [72]. In this study, it was reported that rutile and brookite have a direct band gap, while the anatase form has an indirect band gap. In the same study, it was suggested that indirect band gap anatase has a longer photoexcited electron and hole lifetime compared to direct band gap rutile and brookite. At the same time, it was reported that the anatase form of TiO2 has the lightest average effective mass of photogenerated electrons and holes than the rutile and brookite forms. The lightest effective mass accelerates the migration of photogenerated electrons and holes from the inner surface of the anatase TiO2 ENM to its surface, resulting in increased photocatalytic activity by reducing the recombination of charge carriers of anatase form. Furthermore, Li et al. reported that TiO2 nanotubes showed higher antibacterial activity in the anatase form than in the rutile form [70]. The main reason for this is that the rutile phase is prone to fast electron-hole pair recombination. This, in turn, limits the photocatalytic antibacterial activity by reducing the production of ROS. TiO2 ENMs are more cost-effective than other ENMs and have adequate chemical and thermal stability and low toxicity [73]. The most significant benefits of TiO2 ENMs are their unlimited lifetime and immunity to the effects of microbial and organic chemical degradation [74]. The biggest drawback of TiO2 is that it requires ultraviolet light to activate the substance and begin inhibiting germs. Due to the genetic harm that TiO2 causes in human cells and tissues, its use is restricted. Only about 5% of solar energy can be absorbed due to the wide band gap (3.2 eV) of TiO2, which also causes a high level of electron and hole recombination. Therefore, modifications are made to increase the photocatalytic efficiency of TiO2. The efficiency of TiO2 can be increased by modifying the surface of photocatalysts with metals, doping with metal or nonmetal ions, and forming composites [75]. Numerous studies have demonstrated that doping TiO2 ENMs with metal ions greatly improves their antibacterial and photocatalytic properties [5, 76]. Also, doping TiO2 with metal ions can shift the light absorption range of TiO2 ENMs towards visible light, thus increasing photocatalytic activity under both visible light and UV. ENMs can produce ROS by photocatalytic activity. When TiO2 is excited by light energy equal to or greater than its band gap, e-/h+ pairs are formed. Afterwards, these e-/h+ pairs are transferred to water molecules on the ENM surface promoting the generation of ROS. The steps for ROS generation are illustrated in Fig. 10.2.

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When activated by UV light, TiO2 produces photocatalytic oxidizing power, which accounts for its inhibitory activity [77]. The photocatalytic nature of TiO2 ENMs enables efficient bacteria destruction, as they generate reactive oxygen species (ROS) when exposed to UV light. Among all produced ROS, OH• radical is the most significant oxidant species used in bacterial inactivation [78]. There are many studies investigating the effect of ROS generated on the surfaces of the stimulated TiO2 ENMs on bacterial cell morphology [79, 80]. Jalvo et al. showed that the morphology of Pseudomonas putida cells and Staphylococcus aureus was preserved on the surface of the non-UV irradiated TiO2 coating [80]. However, it was shown that all bacterial cells were damaged after 2 h of UV radiation exposure. In addition, high amounts of ROS were detected in the cell samples exposed to UV. Carré et al. suggested that antibacterial photocatalytic activity causes lipid peroxidation, which increases membrane permeability and disrupts cell integrity [81]. Besides ROS production, TiO2 can cause mechanical damage to bacteria. PigeotRe´maya et al. reported that the interaction between TiO2 NPs and Escherichia coli in the dark damaged the outer membrane integrity of the bacteria [79]. In 1985, the first study on the antimicrobial activity of TiO2 was reported by Matsunaga et al. [82]. In this study, the antimicrobial activity of TiO2/Pt catalyst against various microorganisms such as Saccharomyces cerevisiae, Escherichia coli, and Lactobacillus acidophilus was investigated. The viability of microorganisms when treated under metal halide lamp irradiation for 60 min was 54%, 20%, and, 0%, respectively. However, when the irradiation time was increased to 120 min, no viable cells for all bacteria were observed. The authors reported that when microorganisms were treated with TiO2/Pt catalyst, coenzyme A in cells is photo-electrochemically oxidized and causes cell death by inhibiting the respiration of cells [82]. Aminedi et al. evaluated the antibacterial activity of P25– TiO2 ENMs, nanorods, and nanotubes against Agrobacterium Tumefaciense [83]. In this study, it was reported that the antibacterial activity of photo-irradiated TiO2 with different shapes follows the order of P25– TiO2 > nanorod > nanotube. The band gap of synthesized P25– TiO2 ENMs, nanorods, and nanotubes was 3.2 eV, 3.4 eV, and 3.5 eV, respectively. The authors reported that the increased antibacterial activity was owing to the difference in the band gap. TiO2 NPs with narrower band gaps absorb more UV light and increase ROS production, which has an important role in the antibacterial activity of semiconductor materials.

10.4.2 Zinc oxide Zinc oxide (ZnO) is one of the materials considered as an alternative to TiO2 in photocatalytic studies due to its chemical and physical properties such as its low toxicity, superoxidative rate, and high electrochemical stability. Zinc oxide ENMs have many application areas such as targeted drug delivery, biosensors, smart UV sensors, antioxidant activity, environmental remediation, drought-enhancing agent, and crop nutrient source [84]. In addition, ZnO NPs have a 3.3 eV band gap and are n-type semiconductors. Three different crystal types of ZnO can be found: hexagonal wurtzite, cubic rock salt,

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and cubic zinc blend. Compared to wurtzite, the other two crystal formations are less reliable. The antibacterial action mechanism of ZnO ENMs is yet not completely understood. However, there are several suggested mechanisms, including the generation of ROS, the buildup of NPs on bacterial cell surfaces as a result of electrostatic interactions, and the release of antimicrobial zinc ions [36, 85]. Many studies have shown the formation of ROS as the first probable mechanism responsible for the antibacterial activity of ZnO ENMs [26, 86]. Li et al. investigated the potential of seven different metal oxide types (TiO2, ZnO, CeO2, SiO2, CuO, Fe2O3, and Al2O3) to generate ROS for antibacterial activity. According to their results, they have shown that ZnO is the material with the highest ROS production next to TiO2. The authors reported that this is because ZnO is an n-type semiconductor and the position of its valence and conduction bands [36]. Rawal et al. reported theoretically the size effect on ZnO nanoparticles’ ability to generate ROS [87]. The authors simulated water binding and catalytic activity of ZnO 9 Å to 15 Å and translated it to splitting in water molecules. They found out that 9 Å had 10% reactive oxygens on the surface while 15 Å had 3%, which is the main mechanism for ROS generation on ZnO nanoparticle surface. Other studies reported were also consistent with strong ROS production capacity for ZnO ENMs. Raghupathi et al. reported that the ZnO antibacterial activity is due to an increment in ROS production from ZnO NPs under UV light [88]. In Sawai’s study, it was reported that H2O2 produced as a result of ZnO photocatalytic activity prevents cell growth by penetrating the cell membrane of Escherichia coli [89]. The production of Zn2+ ions, which can damage the bacterial cell membrane and interact with intracellular components, is the second likely mechanism of ZnO’s antibacterial effect [85]. Zn+2 ions that are released from ZnO NPs can affect the cell membrane permeability of bacteria and can lead to bacterial cell death by inactivating many biomolecules such as enzymes [36, 90]. Released Zn+2 ions have an important effect on amino acid metabolism, enzyme system degradation, and ion and active transport inhibition [91]. According to Li et al., antibacterial action of ZnO NPs is caused by the release of Zn+2 ions [92]. The electrostatic contact between the bacterial cell membrane and ENMs is the third potential antibacterial activity mechanism of ZnO ENMs. By rupturing the bacterial cell wall, the electrostatic force that develops between the negatively charged bacterial cells and the positively charged ZnO kills the bacteria. According to Zhang’s research, ZnO nanofluids have a zeta potential of roughly + 24 mV at a pH of 7. Additionally, it has been noted that the lipopolysaccharide’s polysaccharides cause the Escherichia coli surface to be negatively charged at pH 7. Because of this, it was hypothesized in this study that ZnO’s antibacterial activity may result in electrostatic contact with the surface of Escherichia coli [93]. Using conventional bio-TEM technologies, Wahab et al. detected damage to cell membranes caused by the interaction of bacteria with ZnO ENMs. According to the process outlined in Fig. 10.5, the binding of ZnO ENMs to the bacterial cell membrane and the breakdown of the cell’s outer membrane can be seen in the bio-TEM pictures [94].

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Fig. 10.5: TEM images of (a) E. coli, (b and inset) ZnO-MSs treated E. coli, c) S. aureus, (d and inset) ZnO-MSs treated S. aureus [94]. Reproduced with permission from Wahab et al., Biomass and Bioenergy, published by Elsevier, 2012.

The shape, size, and concentration of ZnO NPs, among other things, can have an impact on their antibacterial activity. For instance, Hasanzadeh et al. examined the antibacterial efficacy of ZnO ENMs with three distinct forms in a recently published study – nanoplates, spheres, and pyramids [95]. In comparison to nanospheres and nanoplates, nanopyramids demonstrated greater antibacterial activity. The researchers hypothesized that higher antibacterial activity of nanopyramids is caused by their bigger surface area and tetrahedral shape compared to nanospheres and nanoplates. Many studies have reported that the antibacterial activity of ZnO NPs depends on the size of the NPs [96]. Smaller size ZnO NPs can easily penetrate the bacterial cell membrane due to their higher specific surface area, thus increasing their antibacterial activity [86, 97]. Padmavathy and Vijayaraghavan evaluated the antibacterial activity of 12 nm-, 45 nm-, and 2 µm-sized ZnO ENMs. According to reported results, 12-nm size NPs showed higher antibacterial activity than the other two sizes of ZnO ENMs. They suggested that smaller NPs increase H2O2 formation due to their high surface area, leading to higher antibacterial activity [26]. Similar to this, Yamamoto assessed the impact of ZnO ENM particle size on antibacterial activity in the 100–800 nm range. According to one study, antibacterial effectiveness of ZnO ENMs rises as particle size decreases [86]. In a different investigation, Naqvi et al. looked into the antibacterial activity of ZnO ENMs of various diameters (8, 15, 46, and 59 nm) against a strain of Staphylococcus aureus bacterium [98]. In this study, it was reported that as the size of

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the ENMs decreased, the antibacterial activity increased. The authors suggested that the antibacterial activity of ZnO NPs is due to the released Zn ions. According to the study, as the particle size decreased, the released Zn ion concentration increased. This may be due to the large surface-to-volume ratio of small ENMs. Smaller sizes of ENMs were also reported to better inhibit bio-film formation. In a microfluidic chamber study simulating plant phloem channels, Naranjo et al. tested bio-film eradication (Liberibacter crescent) of nano-ZnO (4 nm) compared to bulk ZnO (800 nm)[99]. The authors found out that nano ZnO was more effective than bulk ZnO due to higher release of Zn, generation of intracellular ROS, lipid peroxidation, and cell membrane damage. The concentration of ZnO ENMs is another factor that affects their antibacterial activity. As the concentration of ENMs increases, so does the amount of ROS produced from the ZnO surface, leading to a higher antibacterial activity. Jalal et al. observed that increasing the concentration of ZnO NPs improved the antibacterial activity against Escherichia coli due to an increase in the production of hydrogen peroxide from the ZnO surface [100]. Similarly, Bhuyan et al. investigated the inhibitory effect of ZnO NPs at different concentrations against bacterial strains including Staphylococcus aureus, Escherichia coli, and Streptococcus pyogenes [101]. Their findings revealed that the antibacterial activity increased with the concentration of ZnO NPs, and grampositive bacteria (Staphylococcus aureus) were more susceptible than gram-negative bacteria. In another study, Wahab et al. assessed the antibacterial activity of ZnO ENMs and found that the inhibition of bacterial growth increased with the concentration of ZnO NPs within the range of 5–45 μg/ml [94]. The use of ZnO NPs is limited due to disadvantages such as low solubility, wide band gap, photocatalytic activity only in the ultraviolet region, and high recombination rate. By creating heterojunction/composites with other metal oxides or by doping other ions as impurities, these issues are resolved [102–104]. Dhandapani et al. evaluated the antibacterial activity of RGO-ZnO against Escherichia coli and Staphylococcus aureus bacterial strains under sunlight [105]. Their findings showed that the RGO-ZnO composite has greater antibacterial activity than ZRGO-ZnO’s surface area contributes to improved antibacterial activity. By increasing the amount of light absorbed, this increased the creation of OH.

10.4.3 Tin oxide Oxide of tin has a band gap of 3.6 eV at room temperature and it is characterized by its rutile-type crystal with a tetragonal shape. However, SnO2 has various polymorphs similar to silica, such as α-PbO2 type (Pbcn), ZrO2 type orthorhombic phase I (Pbca), CaCl2 type (Pnnm), pyrite type (Pb3), and fluorite type (Fm3m) [106]. Tin oxide has many features such as wide band gap, high carrier concentration, chemical inertness, mechanical hardness, thermal resistance, and high and excellent selectivity to gases [107].

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Therefore, tin oxide (SnO2) has many applications such as lithium-ion batteries, antireflective coatings, transparent conductive electrodes in ionic devices, solar cells, catalytic support materials, gas sensors, and energy storage [108]. Many studies have reported that SnO2 shows antibacterial activity [106, 109]. There are three proposed mechanisms for the antibacterial activity of SnO2. The first is ROS production, the second is the interaction between bacteria and SnO2 ENMs, and finally the third is the release of Sn+4 metal. To comprehend the generation of ROS triggered by SnO2, researchers Vidhu and Philip examined its antibacterial properties on Escherichia coli. They proposed that the ROS produced by SnO2 ENMs react with the cell membrane, facilitating their entry into the bacterial cell. The study also concluded that the antibacterial activity increased with an increase in ENM concentration [107]. Similarly, Rehman et al. conducted a study on the antibacterial activity of SnO2 NPs against Escherichia coli. The SEM results indicated that the SnO2 NPs damaged the cell membrane by interacting with it. It was suggested that this interaction between SnO2 NPs and bacteria produced ROS, such as O2.–, O2., H2O2, and OH., on the cell wall, leading to oxidative stress on the cell wall and cell damage [110]. The size and concentration of the SnO2 NPs have an impact on their antibacterial activity. Al-Hada et al. evaluated the effect of calcination temperature on SnO2 NPs. They observed that the particle size increased as the calcination temperature increased. Antibacterial activities of SnO2 NPs with different sizes obtained from this study toward Escherichia coli and Bacillus subtilis were investigated. It was reported that SnO2 ENMs with smaller sizes showed higher antibacterial activity [111]. The main reason for this is that as the size of the ENMs gets smaller, the surface area increases. Thus, it absorbs more light and leads to more ROS production. Therefore, it leads to an increase in antibacterial activity.

10.4.4 Copper oxide Copper oxide (CuO) is a p-type semiconductor material with a band gap of about that of a monoclinic crystal structure [112]. Copper oxide exists in two disparate forms, which are cupric oxide (CuO) and cuprous oxide (Cu2O). Cu2O and CuO ENMs have a band gap of 2.2–2.5 eV and 1.21–1.55 eV, respectively. CuO is thermodynamically more stable than Cu2O [113]. CuO ENMs have various uses in energy storage devices, photocatalysis, batteries, and biosensors because of their special qualities as high-temperature superconductors, including superconductivity, electron correlation effects, and rotation dynamics [114]. In addition, CuO ENMs are more robust and stable and have a longer shelf life than organic antibacterial agents [115]. Therefore, their use as an antibacterial agent is increasing. Although the band gap of CuO NPs is narrowing compared to many oxidebased semiconductors, the potentials of valence and conduction bands negatively affect their photocatalytic antibacterial activity. Since the conduction band (EC) value of CuO NPs (0.69) is greater than the redox potential (EH) (−0.2) of O2/O2.-, it does not generate

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O2.- radicals [36]. At the same time, as the potential of the valence band (EV) (2.39) of CuO is very close to the redox potential of the OH. radical, the formation of the OH. radical becomes difficult [36]. Thus, the photocatalytic antibacterial activity of CuO NPs is limited. Therefore, in order to increase the photocatalytic antibacterial activity of CuO NPs, modifications such as doping or composite formation that will increase ROS production are required. Despite the fact that the antibacterial mechanism of copper oxide ENMs is not entirely known, there are several hypothesized processes, including the release of antimicrobial copper ions, contact killing of CuO ENMs with contacting the bacterial cell membrane, and ROS formation. The thiol groups are thought to decrease the Cu2+ ions from the protein’s cysteine amino acid to Cu1+ (equation (10.1)). Then, in a process akin to the Fenton reaction, Cu1+ ions combine with adsorbed O2 or H2O2 to produce singlet oxygen and hydroxyl radicals (equations (10.2)–(10.4)) [113]. Cu+ 2 + Protein‐CysðSÞ ! Cu+ 1 + Protein‐CysðS+Þ

(10:1)

Cu+ 1 + O2 ! Cu2 + + O2 .−

(10:2)

Cu+ + O2 .− + 2H + ! Cu+2 + H2 O2

(10:3)

Cu+2 + H2 O2 ! OH. + H2 O2

(10:4)

The O2.– level decreases rapidly because O2.– reacts with Cu+2 to form Cu+1 (equation 10.5) [113] Cu+ 2 + O2. − ! Cu+ 1 + O2

(10:5)

Applerot et al. investigated the antibacterial activity of CuO ENMs toward Escherichia coli and Staphylococcus aureus. It is clearly shown that in the SEM images, CuO NPs accumulate on the surface of both bacteria strains. At the same time, TEM images show that CuO NPs enter the bacteria by disrupting the bacterial cell membrane. According to the results of the same study, smaller size ENMs produced more ROS, and the amount of intracellular ATP decreased in both bacteria strains, and it was suggested that the produced ROS inhibit both bacteria by promoting ATP oxidation [116]. Another mechanism proposed for CuO ENMs is the release of Cu ions. Cu2O ENMs exhibit higher antibacterial activity than CuO ENMs due to their ability to release more harmful Cu1+ ions than CuO ENMs, even though numerous studies have indicated that CuO ENMs are more effective as antibacterial agents [117]. Naika et al. investigated the antibacterial activity of CuO ENMs against Klebsiella aerogenes, Escherichia coli, Staphylococcus aureus, and Pseudomonas desmolyticum. According to this study, cross-linking between the strands of nucleic acids caused by free copper ions can bond with DNA molecules and damage the helical helix [61]. Various factors such as size, shape, and concentration can affect the antibacterial activity of CuO ENMs. Černík and Thekkae Padil investigated the antibacterial activity

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of two different sizes of CuO NPs (4.8 ± 1.6 nm and 7.8 ± 2.3 nm) against Staphylococcus aureus and Escherichia coli. According to their results, smaller-size ENMs showed higher antibacterial activity [118]. The increase in antibacterial activity was suggested due to the surface area/volume ratio provided by smaller ENMs. Another study investigated the effect of CuO nanoparticle size on antibacterial efficacy, Azam et al., evaluated the antibacterial activity of CuO nanoparticles synthesized in different sizes (20, 21, 25, and 27 nm) against gram-negative bacteria (E. coli and P. aeruginosa) and gram-positive bacteria (B. subtilis and S. aureus)[119]. The authors indicated that antibacterial activity is highest when the particle size is minimal (20 ± 1.24 nm). Ozcan et al. developed a formulation that contains nano-Cu (2.5 nm to 5 nm) in the formulation fixed in a silica core-shell carrier [120]. The study aimed to control the overall size of carrier particles (silica) to engineer the sustained release of Cu to have the best efficacy against Curesistant X. perforans bacteria strains. The authors found that 50-nm particles had the best efficacy as against 180- nm and 600-nm particles due to higher Cu release after each simulated wash, and all formulations were superior compared to CuO and Cu2O controls. The controlled release of Cu is critical for agricultural applications since higher release causes phytotoxicity to plant tissue while the strong antibacterial efficacy is dependent on free Cu concentration. Therefore, engineering Cu release is critical. The form of the ENMs is the second element influencing CuO’s antibacterial activity. The antibacterial effects of spherical and plate-shaped CuO NPs against B. subtilis, M. luteous, Escherichia coli, and P. vulgaris were studied by Laha et al. [54] The SEM pictures they collected showed that the sheet-shaped ENMs and the spherical ENMs both caused higher membrane damage to B. subtilis and Escherichia coli, respectively. The scientists underlined that the explanation for this sensitivity may be because small spherical-shaped CuO NPs may easily enter bacterial cells while large sheetshaped CuO NPs cannot pass through the outer membrane of gram-negative (E. coli) bacteria. On the other hand, gram-positive bacteria were more seriously harmed by sheet-shaped CuO NPs with a larger surface charge.

10.4.5 Zinc stannate Zinc stannate which is generally called Zinc tix oxide (Zn2SnO4) is a semiconductor with an inverse spinel structure, similar to SnO2 and ZnO [121], which has high electrical conductivity, chemical sensitivity, and low apparent absorption [122]. It has a band gap between 3.3 and 3.6 eV, which allows for its use in optoelectronic devices and chemical sensors [123]. Recent studies have investigated the antibacterial activity of Zn2SnO4, which is still in its preliminary stages [124]. Zn2SnO4 NPs release Sn4+ and Zn2+ ions that bind to electron-donating groups in molecules containing oxygen, sulfur, or nitrogen, causing oxidative stress through the formation of ROS [123]. The mechanisms of ROS production in Zn2SnO4 are similar to those of TiO2 ENM.

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Pandimurugan and Sankaranarayanan conducted a study to investigate the antibacterial properties of ZnO, SnO2, and Zn2SnO4 nanoparticles against various bacterial strains, including Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, and S. Dysenteriae [123]. They found that Zn2SnO4 NPs had the highest antibacterial activity among the three types of NPs, and this was attributed to the greater amount of oxygen vacancies and ROS production. The release of Zn+2 and Sn+4 ions was also suggested as a mechanism of antibacterial activity, as these ions bound to the bacterial cell membrane and prevented bacterial proliferation. Jeronsia et al. reported similar findings, where Zn2SnO4 NPs increased the permeability of the cell membrane by electrostatic interaction and exhibited antibacterial activity against various bacterial strains [125]. Dinesh et al. also reported that the antibacterial activity of Zn2SnO4 NPs increased with increasing concentration, and electrostatic interaction between the ENMs and the cell membrane led to bacterial death [126]. However, due to the limited number of studies on Zn2SnO4 ENMs’ antibacterial activity, further research is needed to better understand the factors that affect their efficacy.

10.4.6 Other oxide-based ENMs Apart from the oxide-based ENMs mentioned above, many oxide ENMs such as MgO, CaO, Ag2O, and Fe2O3 show antibacterial activity. MgO, also known as periclase, is a metal oxide that occurs naturally in nature as a mineral [39]. It can function as both a catalyst and catalyst support in various organic processes [127]. Recently, Di et al. demonstrated that MgO ENMs have potential applications in tumor treatment [128]. MgO ENMs are cost-effective, widely available, and biocompatible, making them promising antibacterial agents [34]. Studies have shown that MgO ENMs can damage bacterial cell membranes, resulting in the release of internal components and ultimately bacterial cell death [129]. The antibacterial activity of MgO NPs is attributed to the production of superoxide radicals by reacting with oxygen on the cell surface [130]. This reaction damages the phospholipid structure and proteins of the bacterial cell membrane. Numerous studies have indicated the antibacterial potential of MgO NPs [130–132]. Jin and He examined the impact of MgO ENMs on Escherichia coli and Salmonella Stanley bacteria and found that the antibacterial activity increased with the concentration of MgO NPs. These NPs had a significant effect on membrane integrity, and the authors suggested that membrane disruption caused the bacteria’s death [129]. Huang et al. studied the antibacterial activity of MgO NPs within a particle size range of 45–70 nm and reported that antibacterial activity increased as the particle size decreased [133]. Makhluf et al. also found similar results [134]. These studies showed that the rise in antibacterial activity could be attributed to the increased specific surface area due to the reduction in ENM size. Calcium oxide (CaO) is a metal oxide that is considered safe for both humans and animals. It has many potential applications, such as serving as a catalyst, a water treatment agent, an adsorbent, and an antibacterial agent [135]. Tang et al. reported

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that CaO NPs)exhibit antibacterial activity against L. Plantarum bacterial strain. The authors suggested that the antibacterial activity of CaO NPs is due to an increase in the concentration of O2, which results from a decrease in particle size [136]. Bhatti et al. investigated the antibacterial properties of CaO NPs against Escherichia coli. They found that CaO NPs create superoxide and hydroxyl radicals, which in turn lead to antibacterial activity [137]. However, there are few studies in the literature on the antibacterial activity of CaO NPs, so further research is needed to better understand this property. Silver oxide (Ag2O) ENMs are particles with an oxide magnetic nanostructure. Ag2O NPs generally have a particle size between 20nm and 80 nm and a surface area between 10m2.g−1 and 50 m2.g−1 [64]. Silver oxide ENMs are used in various fields such as plasmon photonic devices, photovoltaic devices, batteries, and optical storage devices [138]. At the same time, Ag2O ENMs have been reported to exhibit antibacterial activity [139]. The antibacterial activity of Ag2O NPs is due to the released Ag1+ ions, the interaction between the cell membrane and ENMs, and ROS production [113]. Dharmaraj et al. showed that Ag2O NPs have antibacterial activity against Salmonella spp., Vibrio parahaemolyticus, Enterobacter sp, and Micrococcus sp bacterial strains. In this study, it was reported that the antibacterial activity of Ag2O NPs increased with increasing concentration. In addition, in the protein leakage analysis, it was shown that the protein amounts of V. parahaemolyticus, Salmonella sp, Enterobacter sp, and Micrococcus sp bacteria strains after treatment with Ag2O NP were 2.8, 3.5, 3, and 4.3 times higher, respectively, than the control. The authors suggested that Ag2O ENMs cause protein leakage by increasing membrane permeability resulting in cell death [138]. In another study, Wang et al. evaluated the antibacterial activity of Ag2O NPs in the form of octahedral and cubic at concentrations of 1, 5, and 10 μg / mL against Escherichia coli bacteria. According to their results, as the concentration of NPs increased, antibacterial activity also increased. It was also reported in this study that the crystal form of Ag2O particles affected the antibacterial activity. Ag2O NPs in octahedral and cubic forms at a concentration of 10 μg.mL−1 showed the same antibacterial activity, but cubic Ag2O NPs at concentrations of 1 μg.mL−1 and 5 μg.mL−1 showed higher antibacterial activity [140]. Iron oxide (III) is a metal oxide commonly used in various biotechnological and biomedical applications [113] due to its stability and abundance in nature as the mineral hematite α- Fe2O3 [39]. Hematite ENMs are also widely used in catalytic reactions, batteries, paint production, gas sensors, and magnetic storage devices due to their low cost, excellent chemical stability, low toxicity, and adjustable optical and magnetic properties [141]. Many studies have reported that hematite (α-Fe2O3) NPs also have antibacterial activity, which is due to the effect of oxidative stress created by the formation of reactive oxygen species and the direct interaction of the ENMs with bacterial cell walls via electrostatic force. Several studies have evaluated the antibacterial activity of hematite ENMs against various bacterial strains, including E. coli, K. pneumonia, B. subtilis, and S. aureus, and found that increasing the concentration of ENMs in-

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creases antibacterial activity. The disruption of cellular membranes is likely due to different interactions, such as electrostatic, dipole-dipole, hydrogen bonding, hydrophobic, and van der Waals forces [142]. Despite some contradictory results regarding the production of O2.– radicals, more studies are needed to fully understand the antibacterial activity of hematite ENMs.

10.5 Conclusion and future directions Antibiotic resistance in bacteria reduces the effectiveness of antibiotics. Therefore, it is necessary to develop new antibacterial agents. With nanotechnological developments, the use of ENMs as antibacterial agents is increasing. Oxide-based semiconductor photocatalyst ENMs appear to be the most promising materials with antibacterial activity. Although the antibacterial mechanism of these ENMs is not fully understood, it has been reported in many studies that they successfully inhibit bacteria as an antibacterial agent. The antibacterial activity of oxide-based semiconductor photocatalyst ENMs is due to ROS and ion release that damage the cell structure and intracellular components. The antibacterial activity of these ENMs is affected by the size, shape, zeta potential, and concentration of the ENMs. For example, as the size of ENMs decreases, their antibacterial activity increases. At the same time, as the concentration of ENMs increases, the inhibition ability of ENMs increases. Many studies have reported that oxide-based semiconductor photocatalysts nanoparticles such as TiO2, ZnO, SnO2, CuO, Zn2SnO4, MgO, Ag2O, CaO, and α-Fe2O3 exhibit antibacterial activity. Nowadays, studies are carried out to understand the antibacterial activity of these ENMs. In addition, researches have been carried out to increase the antibacterial activity of ENMs. The most researched method to increase the antibacterial activity of ENMs is doping. In many studies, it has been reported that ROS production is increased by doping. However, due to the wide band gap of semiconductors, they need UV to generate ROS. The doping improves the antibacterial activity of the ENMs by activating the material without the need for harmful UV light. We believe that oxidebased semiconductor photocatalyst ENMs can be used as an antibacterial agent that can replace conventional antibiotics in many areas due to their low cost, easy synthesis, and biocompatible properties. However, further investigation is needed to fully understand the antibacterial activity of oxide-based semiconductors. The effects of the produced reactive oxygen species on lipids, proteins, enzymes, and DNA, which have a vital role in bacteria, should be investigated in more detail. Apart from this, more comprehensive studies are needed to understand how properties such as size, shape, and zeta potential of ENMs affect antibacterial activity.

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A. T. Erturk✶, G. Özer

11 Nanocomposites and nanohybrids in additive manufacturing Abstract: Additive manufacturing (AM) has undergone significant technological development since its emergence in the 1970s. This development is expected to continue and take an important place in the manufacturing sector. Developing new materials for AM processes is among today’s essential issues. This chapter gives general insight into the application of nanocomposites and nanohybrids in the AM. AM has become very common in the last few years, with its benefits to high-tech products and its superior features such as enabling the production of end products. Additive manufacturing is used in many areas such as defense industry, automotive, medicine, biomedical, biomedical engineering, and medical/pharmaceutical industries. In particular, it is not possible to produce some specific products by traditional methods. On this point, AM technologies have become quite advantageous. The content presents recent advances and classification of 3D printing processes for nanocomposites. These include high-performance polymer, and metal and ceramic nanocomposites, which are expected to expand into applications requiring highly durable materials suitable against extreme conditions. Input material properties, as well as the processing parameters for AM processes of nanocomposites and nanohybrids, are explained. General information for the mechanical properties of the AM components made of nanocomposites and nanohybrids is presented. Keywords: Additive manufacturing (AM), nanocomposites (NCs), nanohybrids (NHs), polymer nanoparticles (PNPs), metal nanoparticles (MNPs), ceramic nanoparticles (CNPs)

11.1 Classification of 3D printing processes for nanocomposites The additive manufacturing (AM) technology can offer unrivaled advantages compared to other traditional processes, both in terms of reduced material usage, costeffectiveness and on-time production, and the ability to modify products depending on their design features [1–4]. While there are many AM technologies developed ✶

Corresponding author: A. T. Erturk, Department of Mechanical Engineering, Kocaeli University, Izmit 41001, Turkiye, e-mail: [email protected] G. Özer, Fatih Sultan Mehmet Vakif University, Aluminum Test Training, and Research Center (ALUTEAM), TR 34445, Halic Campus, Istanbul, Turkey https://doi.org/10.1515/9783111137902-011

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Fig. 11.1: Classification of AM technologies.

today, the American Society for Testing and Materials (ASTM) group formulated the “ASTM F42 – Additive Manufacturing” standard in 2010, which classifies AM operations into seven categories (Fig. 11.1) [5, 6].

11.1.1 Metal-based additive manufacturing (M-AM) Metal AM systems are based on the deposition of metal raw material on a substrate. A solid wire feed or metal powder is often used as feedstock in commercial methods. Among the many different metal AM technologies, directed energy deposition (DED) and powder bed fusion (PBF) technologies are the most widely used ones. Each individual method has its advantages and disadvantages. However, the most commonly used systems in the commercial market include laser powder bed fusion (LPBF) technology due to its superior solutions favoring layer thicknesses typically between 10 µm and 50 μm. The newer systems for PBF are able to achieve powder coating deposits down to 20 μm and minimum specification features between 100 µm and 150 μm. On the other hand, powder-fed DED printers have layer thicknesses up to about 250 μm [7, 8].

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11.1.2 Polymer-based additive manufacturing (P-AM) Polymers are materials classified into thermoplastics and thermosets according to their thermomechanical behavior. The use of polymers and polymer composites is widespread in AM because they are lightweight and corrosion-resistant and have mechanical, thermal, electrical, fire resistance, and biocompatible properties [9]. Sheet Lamination (SHL), Material Jetting (MJT), Fused Filament Fabrication (FFF), Powder Bed Fusion (PBF), and VAT Polymerization (VPP) are commonly used Polymer Additive Manufacturing (P-AM) methods [8].

11.1.3 Ceramic-based additive manufacturing (C-AM) Soon Ceramic Additive Manufacturing (C-AM) technology will evolve in use by overcoming the technical limitations of slow production speed, defects, and limited print materials. Research in modeling, formula-based printing process control, and fusion technology to overcome these limitations are promising [10].

11.2 Advances in nanocomposite materials for use in AM An influential group of materials that has emerged in AM technologies in recent years is nanomaterials, which is capable of lowering sintering temperatures and improving mechanical and electrical properties. Nanomaterials and AM offer numerous advantages, but homogeneity needs to be improved. Nanocomposites (NCs), a nanomaterial, are of interest to related industries because of their many properties, like as improved fire performance, good thermal conductivity, durability, and lightweight. There is considerable potential for the production of NCs when integrating and blending nanomaterials into base materials via 3D printing. Therefore, improving manufacturing of NCs from the perspective of cost, thermal properties, and reliability will open up new opportunities [11]. Considering the problems experienced due to the production of composites, which are seen as an essential alternative material to meet industrial needs, it is observed that the search for production techniques other than traditional methods is increasing. At this point, AM methods are undoubtedly leading the way in producing metals and alloys. In particular, the production of composites by laser-assisted AM has aroused great interest over the last few years because of advantages of near-zero waste generation, high dimensional accuracy, short production time, and high flexibility in terms of product shape [12]. NCs in AM are the cornerstone of rapid develop-

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ment processes for innovative and advanced materials, bioengineering, defense, and transportation sectors [13]. Commercially produced polymer materials for AM technologies do not have the desired advanced performance. Therefore, it is a necessity to develop polymers with superior properties compatible with AM technologies. Polymers generally do not perform as well as expected in, thermal, mechanical, and electrical properties due to their poor properties, such as heat-transfer, conductivity, and strength. Because of this reason, they are strengthened by adding filler particles or reinforcement to fulfil required features for industrial utilization in functional applications. Therefore, polymer nanocomposites (PNCs) have become very important for AM technologies. PNCs are obtained by the addition of homogeneously scattered nanofillers into the polymer matrix. These nanoparticles are usually nanometer-sized and act as reinforcement to impart functional characteristics. PNCs are attracting attention due to the superior improvement in electrical, mechanical, chemical, and thermal properties even at shallow reinforcement content. Many nanoparticles in composites have been synthesized especially for the AM processes, mainly focusing on enhanced mechanical and electrical behaviors [14]. Two ways of obtaining nanomaterials in AM technologies have been described: (1) automatic or manual production of nanomaterials by the periodic standing of the processing of 3D printing of the main matrix material and (2) premixing nanomaterials into the host matrix. The main characteristics of the PNCs operating in AM can be given briefly as follows: The mechanical behavior of 3D-printed items seems to be highly dependent on the fabrication direction. In particular, the anisotropy effect is prominent in mechanical properties. However, AM/PNCs materials do not exhibit an anisotropy effect. Filament homogeneity is a crucial factor in determining part quality. Factors such as feed rate, temperature, specific heat, thermal expansion coefficient, and heat transfer coefficient affect filament output. Incorporating a small nanofiller can significantly change the rheological behavior, and that is very important in the process of filament extrusion. Existence of nanoparticles can significantly affect the printability of the filament. In addition, an inhomogeneous dispersion (agglomeration) will also affect the printability of the filament [15, 16].

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11.2.1 Some critical/high-performance 3D-printed polymer nanocomposites 11.2.1.1 Multiwalled carbon nanotube (MWNT) This material is produced using existing commercially standard resin epoxy-based mixture blended with a little amount of multiwalled carbon nanotube (MWCNT) dispersion. Dispersing techniques – both mechanical mixing and ultrasonic dispersion – must be used to disperse the MWCNT into the resin and prevent agglomeration homogeneously. With no preprocessing, MWCNTs tend to agglomerate [18]. In a study, disperse MWCNTs into a polymer matrix were used to improve toughness and thermomechanical properties of nanocomposites. Not filled, 0.5 wt% and one wt% carbon nanotube (CNT) added epoxy samples were studied. In this study, the effects of sonication time and energy were investigated, and 1 h was the most effective time for both specimens. In addition, sonication energy was found to affect toughness significantly. It was suggested that 2 h of sonication and 50% amplitude allowed proper dispersion of CNTs into epoxy matrices without disrupting the structure of CNTs [16]. In addition, the impacts of the MWNT aspect ratio on electrical and mechanical properties of epoxy/MWNT NCs was detected. NCs with higher aspect ratios show better conductivity. According to the results of the state of dispersion study conducted in this study, it was observed that MWNTs were generally well spread out and merely sporadic aggregation occurred [19].

11.2.1.2 Polyamide 12/carbon nanotubes nanocomposites Polyamide 12 (PA12) and CNTs nanocomposite is made from PA12 powder added CNTcoated PA12 powder. PA12 is a vital material widely used in the Selective Laser Sintering (SLS) method [18]. Polymer parts produced by the FFF method often display poor and anisotropic mechanical properties compared to their injection-molded (IM) opposing pieces. Parts created by conventional injection molding (IM) show higher anisotropic mechanical properties than those produced by FFF. Therefore, improvement is required for FFF 3D printing parts. For this purpose, NCs have gained importance. The production of CNT-reinforced PA12 filament is an area open for improvement. PA12/CNT parts were found to show significant mechanical strengthening, including impact and tensile strength increases of 125% and 18%, respectively, compared to conventional PA12 samples. In addition, PA12/CNT components display enhanced tensile strength, i.e. interface bond strength, as CNTs enable fast thermal energy transfer from the newly deposited filament to the weld interface [20].

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11.2.1.3 Carbon black-filled nylon 12 nanocomposite This material is made of nylon12 strengthened with 4 wt% carbon black [18]. In previous studies, SLS was attempted to produce an electrically conducting PNC made of nylon12/carbon black. The results show that SLS can successfully fabricate carbon black-filled nylon12 NCs. Moreover, the NC’s electrical conductivity was five times greater than that of the pure polymer rendered by SLS, proving that 3D-printed NCs show superior electrical conductivity [21].

11.2.1.4 Polyamide 12/graphene nanoplatelets nanocomposite Graphene and its derivatives are of immense interest in academic and industrial researches because of their valuable properties and unique applications. High production costs limit the use of graphene. Therefore, graphene nanoplatelets (GNPs) have been defined as a replacement for graphene. GNPs produce multifunctional and lowcost NCs with superior features such as mechanical strength, high aspect ratio, and high electrical conductivity [22]. In previous studies, the hot compression technique fabricated paraffin oil and GNP nanocomposite-doped polyamide 12 matrices. It was found that the microhardness and elastic modulus of PA 12 enhanced in direct proportion to the ascending content of paraffin oil and GNPs. It was also found that the composites produced in the wear studies played a crucial role on improvement the wear resistance and minimizing friction coefficient. Therefore, these results are significant for designing and using self-lubricating NCs in applications for light weight bearing [23]. In another study, NC filaments suitable for fused deposition modeling (FDM) were produced and printed seamlessly via a commercial FDM printer. The elastic modulus and thermal conductivity of FDM-produced PA 12/GNP components were 7% and 51.4% higher than those of compression-molded (CM) components, which were simultaneously kept in good Ultimate Tensile Strenght (UTS) [24].

11.2.1.5 Advances in additive technology for polymer-based nanocomposites In a study, nanosilica was used to strengthen parts of nylon12 produced by the SLS method. A dissolution-precipitation process produced nanosilica 3 wt% and nylon12 composite powder for the SLS operation. The results show that nanosilica is uniformly dispersed in the structure at the nanoscale level. The impact strength, tensile strength, and modulus of SLS samples made from the composite powder are 9.54%, 20.9%, and 39.4% higher than those of pure nylon12 SLS samples, respectively; the elongation at break is reduced by around 3.65% [25]. Metal-based nanoparticles increase mechanical strength in polymer matrix composite structures. Microbial control is possible using Ag and Cu nanoparticles for medical purposes [26, 27]. Lee et al. fabricated featuring po-

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rous scaffolds using 3D SLS printing. The researchers found that cold atmospheric plasma (CAP) therapy and NPs can potentially improve hMSC growth and favorable performance in comparison to bare scaffolds. The results of their research shows the possibility of potential integration CAP and pharma-loaded NPs embedded inside a scaffold to promote restoring a cartilage [28]. Gnanasekaran et al. studied the desktop 3D printing of nontraditional PNCs (CNT and graphene-based PBT) by FDM. Their results indicated that Polybutylene Terephthalate (PBT)/CNT components have better conductivity and mechanical properties than PBT/graphene structures [29]. Gu et al. investigated calcium and antibiotic releasing inkjet printing micropatterns (∼50 μm) as a new way to prevent forming of biofilm colonies and facilitate osteogenic-cell growth on surfaces of orthopedic implants. The composition of micropattern nanocomposites superficially printed on a TiAl6V4 alloy was determined by formulating inks containing ∼10–100 nmsized rifampicin (rifampin) and poly(lactic-co-glycolic acid) (PLGA) disintegrated in organic fluidic solution and suspending an ∼100-nm mixture of HA and β-tricalcium phosphate (β-TCP) nanoparticles in solution, which precipitated together to form an NC structure. Adding Biphasic Calcium Phosphate (BCP) nanoparticles into inks caused blockage of some printer nozzles and resulted in less homogeneous micropattern properties. The addition of BCP nanoparticles accelerated rifampicin (RFP) release [30]. Aktitiz et al. performed the in situ synthesis of 3D printable monometallic and bimetallic CuAg 27–53 nm diameter photocurable polymeric resin containing nanoparticles with electromechanical properties by stereolithography (SLA) method. They found that elasticity modulus, tensile strength, tensile elongation, and glass transition temperature of printable polymers with nanoparticles decreased progressively compared to pure polymer. The results show that the nanoparticles are well scattered in the polymer matrix without agglomeration, and the values of resistance are significantly reduced from 456,620 to 1,500 MΩ with increasing quantity of added Ag, thus enabling the production of PNCs for capacitors and electronic applications [31]. Leon et al. studied materials with improved adhesive properties depending on blends of Acrylonitrile Butadiene Styrene (ABS) thermoplastic copolymer matrix and thermoplastic polyurethane as an additive for FFF process. It was reported to lead to better fusion among the layers avoiding any loss of yield strength, probably due to uniform distribution of the polymer blend resulting from hydrogen bond interaction of supramolecular polymers (thermoplastic polyurethane polar groups and ABS acrylonitrile & aromatic segments) [32]. Joyes et al. reported that 3D-printed spherical heterogeneous polymer particle composites are mechanically light, robust, and exhibit noticeable fracture toughness behavior. The effect of 3D-printed layer thickness on Young modulus was reported to be negligible. With a 300-nm particle diameter and a 5-μm particle chain width, a 3D-printed layer thickness of smaller than 80 μm was reported to present smooth and uniform fracture edges. When the layer thickness exceeds a critical value, it is reported to become irregular with asymmetric fractures. How to specify this threshold layer thickness value for composites still remains an open question and could be a subject for future research. They confirmed the applicability of Young modulus predicted by the Cox-Krenchel approach

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with Carman-Reifsnider modification to the mechanical analysis of heterogeneous polymer particle composites, as it deviates by 5.5% from experimental results. They reported upper modulus when the particle chains are in parallel orientation to the direction of the force and a modulus as small as modulus of the pure polymer when aligned perpendicularly [33]. Bernasconi et al. fabricated magnetically steerable microrobotic prototype devices for water purifying by merging stereolithography 3D printing and wet-metallization. They used an initial electroless metallization step followed by electrolytic deposition to provide conductibility to the surface. Different metallic layers applied functional films on 3D-printed components by electrolysis and electrolytic deposition to acquire the necessary functions. For photodegradation of pollutants and bacterial killing, they created a nanocoating composite consisting titania NPs in a silver matrix. The resulting microdevice showed significant function of semiconductor nanoparticles against water pollutants and antimicrobial efficacy against gram-negative bacteria [34]. Table 11.1 summarizes a few essential 3D-printed PNC-related technologies [14]. Tab. 11.1: A few crucial 3D-printed polymer nanocomposites-related technologies. [14], [44]. Materials

Reinforcement

Additive Fields of use/properties manufacturing technique

PLA

HA

FFF

Biomedical, medical applications, enhanced mechanical and thermomechanical properties.

PLA

CNT

FFF

Conductive, shape memory apps, enhanced recovery force, and memoryshape.

ABS

Metal particles, OMMT, MWCNT, Graphene

FFF

Aerospace, low electrical conductivity applications, enhanced electrical, thermal, and mechanical properties.

Epoxy

CNF

VP

Mechanical engineering, enhanced mechanical properties (tensile strength and hardness).

Photopolymer TO, CCT, nanosilica, MMT

VP

Electromagnetic, shape memory, mechanical applications. Improved tensile and elastic properties and viscosity.

PA

MJF, SLS

Electrical and electronics applications, mechanical engineering, and thermal applications. Enhanced electrical, mechanical, thermal, impact properties, flame retardancy, and reduced flammability.

Glass beads, carbon black, MWCNT, carbon nanofibers, nanosilica

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11.2.2 Advances in additive technology for metal-based nanocomposites Metal-based NCs have gained a place in AM technology with their superior thermal and mechanical properties. Cr-Co, Ti, Ni, W alloys, and maraging steel can exhibit strengths exceeding 1,000 MPa. Their excellent mechanical characteristics are preferable for load-carrying and wear applications. The preferred applications of metalbased nanocomposites are biomedical, aerospace, space, and defense industries. The weight reduction and mechanical performance enhancement of structural components that result from high strength improve fuel consumption in all vehicle types: aerospace, air, sea, and land. Although aluminum exhibits lower mechanical strength than the mentioned metal alloys, it is indispensable in terms of cost, especially in highly competitive industries such as automotive. AM technologies such as WAAM, DED, and PBF provide metallurgical defect elimination and reduction of grain size in aluminum-based NCs [35]. Ko et al. performed an empirical research on improving a slurry-based layered casting system capable of producing 1–3 nm-sized self-assembled monolayer (SAM)-protected Au nanoparticles-doped metal composites. Compared to the powder-based AM process, the slurry-based process has been reported to improve the step effect by providing components with better green density by casting thinner layers. They presented a slurry-slab casting system that offers a simple design, low cost, and easy cleaning for slurry of different formations used in composite production [36]. Martin et al. studied grain refinement mechanisms in AM nanofunctionalized aluminum alloy composites induced by thermal conditions occurring in AM. They found that Al3Ta intermetallic compounds have significant grain refinement capacity, and when 1vol% Ta (50–80 nm) is used in the composite, the grain size is decreased by a factor of 1,000 against pure aluminum. During AM, they applied the nanofunctionalization approach with Al3Ta and Al3Zr intermetallic systems in the aluminum composite structure. They stated that similar work might apply other prevalent alloys including nickel, iron, and titanium [37].

11.2.3 Advances in additive technology for ceramic-based nanocomposites Ceramics are a group of chemically and dimensionally stable, low-density materials. Their applications are where these properties and electrical resistivity are in demand. The high cost and long processing time are disadvantages to their use [35]. A nanophase in a ceramic matrix is characterized as ceramic nanocomposites. The most well-known outstanding properties in the application of ceramics are hardness, wear resistance, and thermal resistance. In obtaining ceramic nanocomposites, homogenous dispersion with reinforcement and matrix interface adhesion is critical [38]. Friedel et al. have carried out one of the pioneering studies in the fabrication of composite parts containing

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complex-shaped pyrolysis of preceramic polymers microparticles by selective laser curing (SLC). They locally generated the polymer-phase curing reaction of layers of SiCloaded polysiloxane powder with carbon dioxide laser at around 400 °C. In a following pyrolysis process at 1,200 °C in Ar atmosphere, they converted the Si-O-C/SiC into ceramic samples. They performed post-infiltration with liquid silicone to produce dense parts. Minimal linear shrinkage of 3.3% existed during pyrolysis, while roughly invariant dimensional stability to the ultimate Si infiltration was reported. Stress was 2.0 MPa when the specimen fails after laser hardening, 17 MPa after pyrolysis, and 220 MPa after infiltrating the porous component in liquid silicon [39]. Ceramic part production is the processing of slurry or powder particulate raw material according to the design form. Binder Jetting (BJ), Inkjet Printing (IJP), Direct Ink Writing (DIW), Digital Light Processing (DLP), Selective Laser (SL), and Two-photon Polymerization (TPP) using slurry form feedstock are AM technologies used for ceramic part manufacturing. The methods that use powder particles as raw materials are SLS and SLM, which is a process by laser energyinduced fusion or fluid binder [40]. Scaffolds with a 3D architecture produced by AM technology used for bone regeneration require a mechanically stable and interconnected porous structure. 3D printing of ceramic SiOC(N) porous scaffolds has been tested for their biocompatibility in terms of osteointegration potential (cell proliferation and metabolism) using mesenchymal stem cells (MSCs) to settle whether an economical 3D printing method can regenerate bone. The results of this research offer promising and workable bioactivity opportunities for bone regeneration applications [41]. Du et al. reported latest progress in the 3D printing of scaffolds based on ceramics with osteogenic property and mechanical properties for bone tissue engineering. Nanoparticles used in past applications include hydroxyapatite (HA), Ca-P, silica, tricalcium silicate, beta-TCP/Fe3O4, CuFeSe2 nanocrystals, and bioactive glass (BG). Given the limited number of materials currently available on the market, it has been reported that it is difficult to restrain surface characteristics, mechanical properties, degradation, and pore size of bone tissue engineering. This topic is open for development and research [42]. Kim et al. studied the effect of FDM in AM on the dielectric behavior of three-phase nanocomposites applying polyvinylidene fluoride, barium titanate (BaTiO3), and MWCNTs. They reported that the printing process serves homogeneous dispersion of nanoparticles, alleviates cluster forms of nanoparticles, and can improve the dielectric properties over conventional solvent-cast Poly(vinylidene) Fluoride (PVDF) by reducing microcracks/gaps in the matrix [43].

11.3 Mechanical properties NC polymers produced by AM exhibit superior mechanical properties compared to those produced by conventional methods. The improved mechanical properties of a few important 3D-printed NC polymers are given in Tab. 11.2.

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Tab. 11.2: Improvement of mechanical properties of a few important 3D-printed polymer NCs [14]. Materials Additive manufacturing technique

Reinforcement (wt%) Improved mechanical properties

PLA

FFF

HA (–%)

Impact strength: % Compressive strength: %

PLA

FFF

HA (–%)

Thermomechanical: %

PLA

FFF

CNF (–%)

Tensile strength: % Elastic modulus: % Strain at break: % Toughness: %

ABS

FFF

ZnFeO (–%)

Tensile strength: % Hardness: % Thermal conductivity: %

Epoxy

VP

CNF–PEG treated (–%)

Tensile strength:  Hardness: %

PA

MJF

Glass beads (%)

Tensile modulus: % Flexural modulus: %

PA

SLS

MWCNT

Tensile strength: %

PLA

SLS

CC (%)

Strength up to  MPa

11.4 Conclusion and future perspective Nanocomposites (NCs) will have a more important commercial future than traditional composites. Smaller (nano) size additives in the matrix phase give modulus and improved strength compared to conventional composites. This has led to a significant improvement in cross-layered composites, especially compared to unidirectional composites. NCs, especially used in sports equipment (hockey, tennis equipment), will gain importance in future aerospace and wind energy structures. Additive manufacturing (AM) has undergone significant technological development since its emergence in the 1970s. This development is expected to continue and take an important place in the manufacturing sector in the course of time. In particular, the improvement of new materials for AM processes is among the important issues of today. These include production of polymer NCs, which are expected to be used widely in practices that require highly durable materials for supreme conditions. Although there are numerous studies on NCs in the literature, information on AM applications of NCs is still limited. This will vary as AM technology continues to develop and more industries realize the importance of AM/nanocomposites.

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The progression of polymer NCs for AM allows the production of many multifunctional parts with design flexibility, enabling performance improvement for materials. AM does not completely replace the role of traditional manufacturing processes; it adds to them and helps improve them. This can benefit many industries, including but not limited to the aerospace, aviation, medical, automotive, oil, and gas industries. However, for AM/nanocomposites to become commercially widespread, some points still need to be developed: New materials for AM need to be developed, and their compatibility with different AM methods needs to be investigated. There is still a standardization problem in AM technology, and testing standards explicitly tailored for NCs need to be established. The lack of speed in AM processes also needs to be improved. AM raw material costs should be reduced [17].

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Virat Mani Vidyasagar, Umang Dubey, Devendra Kumar Singh, Rajesh Kumar Verma✶, Panagiotis Kyratsis

12 Characterization and mechanical properties analysis of carbon nanotube and hydroxyapatite-modified polymethyl methacrylate bone cement for bio-nanocomposite Abstract: This article focuses on the significant increase in the mechanical strength of PMMA (polymethyl methacrylate) that was achieved through the incorporation of multiwall carbon nanotube (MWCNT) and nano-size hydroxyapatite (HA) powders at varied loadings ranging from 0.25 to 0.75 wt%. This study aimed to validate the potential applications of this modified bio-nanocomposite through mechanical investigation and characterization. According to the findings, the incorporation of 0.5 wt% of both HA and MWCNT nanoparticles into the PMMA bone cement powder resulted in increase in the flexural strength of 26.67%, the flexural modulus of 24.32%, the compression strength of 14.58%, and the compression modulus of 50.8%. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD) are used to investigate the distribution and interaction of reinforced nanoparticles within the PMMA polymer matrix further. Due to this compatibility between fillers and matrix, improvement in mechanical properties is observed in the developed bio-nanocomposite. Overall, the FTIR analysis provided valuable insights into the functional group composition and molecular interactions within the produced nanocomposites, confirming the presence of specific vibrational modes and demonstrating the compatibility between the filler materials and the polymeric matrix. Keywords: PMMA, bone cement, hydroxyapatite, multiwall carbon nanotube

✶ Corresponding author: Rajesh Kumar Verma, Department of Mechanical Engineering, School of Engineering, Harcourt Butler Technical University, Kanpur 208002, Uttar Pradesh, India, e-mail: [email protected] Virat Mani Vidyasagar, Devendra Kumar Singh, Materials and Morphology Laboratory, Department of Mechanical Engineering, Madan Mohan Malaviya University of Technology, Gorakhpur 273010, Uttar Pradesh, India Umang Dubey, Department of Production Engineering, National Institute of Technology Tiruchirappalli, Tiruchirappalli 620015, Tamil Nadu, India Panagiotis Kyratsis, Department of Product and Systems Design, Engineering University of Western, Macedonia

https://doi.org/10.1515/9783111137902-012

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12.1 Introduction Bone cement that is based on polymethyl methacrylate (PMMA) has maintained its position as a prominent biological substance ever since it was first developed in the year 1960 [1]. It is most commonly used to attach the bone joint and replaces the function of being employed as gap filler in implants. This is done so that mechanical anti-bone interlocking can be maintained. The contribution of the biomechanical variables to the enhancement of the biocompatibility feature is extremely important for the features of bone cement [2]. PMMA bone cement is produced by combining two different components, a powder, and a liquid. Benzoyl peroxide (BPO), often known as the initiator, and PMMA powder make up the powder component. Methyl methacrylate monomer is used as the liquid component, while N, N-dimethyl-P-toluidine serves as a reaction promoter. When these two components are combined, cement that is similar to paste is produced. After a few minutes, this paste-like cement transforms into bone cement [3]. During the course of the past three decades, there has been an increase in the use of PMMA bone cement as a biomaterial for use in bonerelated surgical applications [4, 5]. Experiments conducted in healthcare facilities have demonstrated that the product possesses good levels of biocompatibility, bioactivity, biodegradation potential, and mechanical characteristics [6, 7]. The most current biomaterials, bio-ceramics, and metallic compounds guarantee biocompatibility and mechanical qualities that are comparable to bone and tooth [8]. When joints need to be replaced, PMMA bone cement is typically used as a form of grouting [9]. PMMA bone cement continues to be used as the supporting material for fully and partially detachable prostheses. Due to the physical and aesthetic features it possesses, it is used extensively in the production of polymer-based prostheses. PMMA resins have high flexural fatigue and good performances when compared to other polymers that are used as biomaterial [10–12]. PMMA can be made stronger with different fillers, such as glass fibers, carbon fibers, barium, zirconium, and ceramics [13, 14]. According to previous research, adding hydroxyapatite (HA) to PMMA makes its mechanical, thermal, and rheological qualities better. HA is a naturally occurring calcium apatite (Ca10(PO4)6(OH)2), and because it is stiff, dense, and bioactive [15, 16], it is suggested for use as a reinforcement in biomaterials. One of the best things about using nano-sized materials is that they have a high surface area-to-volume ratio, which opens up interesting possibilities and gives them better dynamic properties in a narrow range of uses. Carbon nanotubes (CNT), graphene (G), graphene oxide (GO), carbon fibers, and carbon black have all been examined recently to improve the mechanical qualities of polymeric matrices [17–20]. With the addition of 15 wt% HA, the flexibility and compressive qualities of PMMA-based cement stayed the same, but the flexural modulus went up by 25%, from 2 to 2.5 GPa [21]. Studies show that G and GO are two types of carbon-based nanomaterials (CBNs) that can be used to improve the mechanical qualities of polymer matrix composites [22, 23]. In a study that was carried out by Wang et al. [24], the researchers introduced MWCNT)

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into PMMA bone cement. They found that the cement had increased compatibility with cells and a better ability to integrate with bone tissue. According to the results, MWCNTmodified PMMA bone cement offers a significant potential for use in orthopedic applications. Ormsby et al. [25] investigated and characterized the mechanical characteristics of a nanocomposite composed of PMMA bone cement and MWCNT in concentrations ranging from 0.1 to 1.0 wt%. They discovered that adding GO particles and carbon nanotubes to the PMMA/hydroxyapatite mixture improved the results. To be more specific, the inclusion of GO particles significantly increased the elastic modulus and bending resistance of the cement, but the addition of carbon nanotubes had very little impact [26, 27]. To evaluate various commercial PMMA bone cement properties, a GO composite powder was used. As a result, the compressive strength of the bone cement increased by 12.6%, and the biological and physical aspects of the bone cement were improved [28]. Further research showed that using a clinically normal mixing method to mix MWCNT with PMMA bone cement could improve its static mechanical performance [29]. These research findings show the potential of employing nanomaterials such as MWCNT and GO to improve the mechanical properties and performance of PMMA bone cement, making it more appropriate for orthopedic applications. In comparison to PMMA, the research on the biocompatibility behaviour of CNT has received a significantly lower amount of attention in the prior state of the art [30, 31]. According to Webster et al. [32], CNT could be used in orthopedic bone cement to support cell proliferation at the bone-cement interface. This would minimize the risk of aseptic loosening caused by the cement. The results of the preliminary research on CNT-modified biomaterials show that cytotoxic reactions can occur and that the materials could be used for orthopedic applications [31]. Nanocomposite coatings for biomedical implants and bone cement were produced by Singh et al. [33] using a nanocomposite modified by MWCNT. This work uses the freeze granulation technique for PMMA-modified hydroxyapatite. The proposed method may result in higher material homogeneity and improved MWCNT dispersion. X-ray diffractometry, field emission scanning electron microscopy, and micro-Raman spectroscopies were used in order to investigate the nanocomposite phase composition and surface morphology. An MWCNT-reinforced nanocomposite with a concentration of 0.1 wt% MWCNTs in a PMMA/HA nanocomposite material was found to display the best mechanical qualities when tested using a nanoindentation method. This was revealed after the material was subjected to the testing procedure. This study limited in-depth mechanical examination at the macroscale of a modified PMMA-based nanocomposite. Previous work [32] has not studied the influence of mechanical strength on the addition of MWCNT and HA in equal amounts. Also, MWCNT was added directly to PMMA powder and hand-mixed, which has only been partially investigated in prior work. The presence of MWCNT was confirmed with the assistance of XRD and FTIR data. The presented paper illustrates a cost-effective, time-consuming, and efficient fabrication methodology contrary to the previous work. The finding of the present work illustrated an efficient method for incorporating MWCNT/HA@PMMA bone cement.

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According to the findings of a comprehensive literature review, it has been determined that a significant amount of work has been done on the traditional PMMA bone cement. However, research into the use of HA and MWCNT) combined in PMMA bone cement has not been carried up to its full potential yet. For its optimal utilization, both society and the biomedical sector need to pay more attention to it in the academic world and in the biomedical sector. The focus of this study is on the development of a PMMA bone cement modified with HA and MWCNT nanofillers. To make three different types of composites, three different weight ratios of HA and MWCNT were used: 0.5 wt%, 1.5 wt%, and 2.5 wt%. In order to evaluate the application potential, the mechanical properties of the material, such as its compression strength and flexural strength, were investigated. Following that, FTIR and XRD investigations were carried out on these nanocomposites in order to investigate the crystal structure behaviour and the presence of functional groups, respectively. In addition, a scanning electron microscope (SEM) examination of fractured surfaces was carried out after the mechanical testing was completed in order to investigate the root cause of the shift in the material’s mechanical properties. It is possible that the current study will make a substantial contribution to the synthesis, development, and characterization of biomaterials. The suggested PMMA-based biopolymer has the potential to be very cost-effective when it is manufactured in big quantities. The research indicates that it possesses exceptional compressive and flexural strength performance. The chemical characterization of the developed material expresses the compatibility of the nanomaterials that have been infused with the material, which serves as the fundamental matrix.

12.2 Materials selection and fabrication PMMA bone cement served as a base for the fabrication of the nanocomposite samples that were used in this investigation. M/s. Global Corporation in Ahmedabad, India, was the source of the PMMA bone cement that was used in this procedure. PMMA bone cement is made up of three components, i.e. 75 wt% methyl methacrylate styrene copolymer, 15 wt% PMMA, and 10 wt% barium sulfate United States Pharmacopeia (USF) and European Pharmacopoeia (EP). In order to improve the characteristics of the polymer, two distinct kinds of nanoparticles were included. MWCNTs were one of the nanoparticles that were used. These MWCNTs were supplied by Ad-nano technologies, located in Bangalore, India. They had a purity of 99%, an average particle diameter of 10–15 nm, and an average length of 5 µm. HA was the other kind of nanoparticle that was used in the process of fabricating the nanocomposite. The HA nanoparticles came from a company called M/s. Nano Research Lab, which is based in the Indian state of Jharkhand. The average particle size of the HA nanoparticles was between 20 nm and 80 nm, and the HA nanoparticles had a molecular weight of 1004.6 g/mol. The purity of the HA nanoparticles was 99.5%. The morphology of the

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HA nanoparticles could be described as spherical. For the purpose of fabricating the nanocomposite samples, these nanoparticles, specifically MWCNT and HA, were mixed into the PMMA bone cement. In this study, we made biopolymer nanocomposites by using different amounts of MWCNT) and HA in PMMA bone cement. Initially, an effort is made to mix HA powder with a highly concentrated NH4OH solution. The HA and MWCNT fillers replaced 0.25,0.5 and 0.75 wt.% of PMMA Powder respectively. PMMA, HA, and MWCNT particles were blended into the powder, which had an M/P ratio of 0.5 (M stands for liquid monomer and P for powder). To make the samples, MMA monomer and PMMAMWCNT-HA (PMH) powder were combined. After an hour of sitting at room temperature, the mixture began to harden. P-NEAT, PMH-1, PMH-2, and PMH-3 were the four types of samples developed. (PMMA bone cement with no reinforcement (P-NEAT) and PMMA bone cement reinforced with MWCNT and HA (P-NEAT)). Fig. 12.1 depicts a simplified flowchart of the operations that must be followed for creating PMMAMWCNT-HA nanocomposites. The percentages of HA and MWCNT nanofillers employed in PMMA bone cement are shown in Tab. 12.1. Tab. 12.1: Classification of specimens. Sample

PMMA

HA

MWCNT

Weight percentage

P-(pristine)

 gm

. gm

. gm

.%

PGH-A

. gm

. gm

. gm

.%

PGH-B

. gm

. gm

. gm

.%

PGH-C

. gm

. gm

. gm

.%

12.3 Characterization techniques 12.3.1 X-ray diffraction (XRD) X-ray diffraction (XRD) was employed in this investigation to examine the phase composition and crystal structure of the nanocomposite samples, as well as the HA and MWCNT nanoparticles and the PMMA bone cement. The equal dispersion of these nanoparticles is critical for efficiently exploiting their capabilities. The chemical composition of the composites was confirmed by XRD, and the nanoparticles were uniformly scattered within the material. We used a Raguku Model Ultima IV 0.3 KW sealed X-Ray tube and a D/teX Ultra silicon strip detector operating at 200 V and 30A for the XRD analysis. We were able to evaluate the diffraction patterns and acquire significant information about the arrangement and structure of the materials under study using this XRD diffractometer.

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Fig. 12.1: The PMMA-HA-MWCNT nanocomposite manufacturing technique.

12.3.2 Infrared spectroscopy (FTIR) Fourier Transform Infrared Spectroscopy (FTIR) was used to investigate the effect of functional groups and elemental composition in the produced nanocomposite [34]. We can use FTIR spectroscopy to examine the characteristic absorption bands of the various functional groups present in the nanocomposite. The BOMEM DA8 FTIR spectrometer is used for this study. The transmittance of the nanocomposite samples was measured using FTIR spectroscopy in this work. The transmittance measurements offered useful information for analysis. We concentrated on specific infrared spectrum regions ranging from 2,000 to 1,800 cm, 1,550 to 1,400 cm, and 750 to 500 cm. These spectrum areas were chosen because they convey significant information about the nanocomposite’s functional groups and elemental composition. This investigation aided us in understanding the chemical structure and properties of the produced nanocomposite.

12.3.3 Mechanical testing 12.3.3.1 Compression testing The compressive strength of bone cement is critical for treatments such as dental implant implantation and prosthesis repair [35]. Therefore, testing the compressive strength and compressive modulus of the nanocomposites is crucial. The results were compared to

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commercially available PMMA bone cement to establish the optimal amount of the nanoparticles for strengthening. The ISO5833-2002 [36] compression standard was used for the evaluation. Measurements of 12 ± 0.1 mm in length and 6 ± 0.1 mm in diameter were taken of the study samples. Three separate tests were performed on each sample of PMMA nanocomposite bone cement.

12.3.3.2 Flexural testing Flexural strength is crucial for procedures such as total hip replacement and spinal bolt fixation [37]. Therefore, it is crucial to analyze the flexural strength and flexural modulus of the manufactured nanocomposites in order to establish the optimum reinforcing quantity. Bone cement that included HA, MWCNTs, and pure PMMA was tested for its flexural strength. ISO5833-2002 [38] was followed in order to carry out the flexural test. The dimensions of the specimens employed in this research were 75 ± 0.1 mm in length, 10 ± 0.1 mm in width, and 3.3 ± 0.1 mm in thickness. At a rate of 5 mm/min, the samples were pushed and pulled. Equation (12.1) can be used to estimate the flexural strength using data from a three-point bend test. Three separate tests were performed on each sample of PMMA nanocomposite bone cement. s=

3 × Fmax × L 3 × Fmax × L s = 2 × w × t2 2 × w × t2

(12:1)

where Fmax is the maximum force w = width in mm t = thickness in mm

12.3.4 Morphology study 12.3.4.1 Scanning electron microscope (SEM) analysis Using a scanning electron microscope (SEM), one is able to investigate the fracture property of bone and other related composites, such as PMMA bone cement [39]. In order to establish what led to the mechanical failure of the nanocomposite, it is important to analyze the surface that has been broken/fractured. The results of the mechanical test were determined by analyzing the fracture surface morphology of the generated nanocomposite with an XL-30 SEM. Ten thousand volts was the level of the electron beams voltage. To analyze the fracture surface, we cut the specimens into sections and sputtered them with gold coating.

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12.4 Results 12.4.1 Flexural strength and modulus The stress-strain performance of MWCNT and HA-reinforced PMMA bone cement comprising 0.25, 0.5, and 0.75 wt% of MWCNT-HA reinforcements were investigated with respect to the stress-strain performance of pure PMMA bone cement, which served as a standard reference. Fig. 12.2 depicts the stress-strain performance of pure PMMA bone cement and MWCNT-HA reinforced cement respectively. According to the data presented in Figs. 12.3 and 12.4, the unmodified PMMA bone cement had a flexural strength of 64.33 ± 0.3 MPa and a flexural modulus of 3086.21 ± 126 MPa. The addition of 0.25 wt% of MWCNT-HA led to a rise of 12.15% in flexural strength (72.03 ± 0.2 MPa) and a 3.85% increase in flexural modulus (3204.23 ± 172 MPa). The incorporation of 0.5 wt% of MWCNT-HA resulted in an improvement of 26.67% in flexural strength (81.49 ± 0.4 MPa) and a 24.32% increase in flexural modulus (3835.70 ± 144 MPa). However, the flexural strength reduced to 77.45 ± 0.3 MPa with additional inclusion of MWCNT-HA, and the flexural modulus decreased to 3609.74 ± 166 MPa at 0.75 wt% MWCNT-HA. In contrast, this study found that hybrid reinforcement increased the flexural strength of PMMA bone cement by 26.67%, while in previous studies MWCNT inclusion alone increased the flexural strength by just 12.8% [40]. The flexural strength was improved by 24.0% at a concentration of 25 wt% hybrid reinforcement of GO and chitosan (CS) nanoparticles, which is still lower than the improvement observed in the current study [41]. An excessive amount of reinforcement might cause brittleness because of the agglomeration of the filler. According to findings from different investigations, the agglomeration of HA nanoparticles may be the reason for the loss in flexural strength that occurs with increased stress [42]. Due to the elongated shape of CNTs, they act in a direction that is perpendicular to the formation of the initial breakage. This prevents the crack from spreading and improves the mechanical performance. Due to their high aspect ratio, CNTs dispersed in PMMA strengthen the interface bonding, leading to an increase in the tensile modulus of the modified biomaterial [40]. However, higher concentrations of CNTs have been shown to change the crystalline phase, which may lead to the formation of intersecting surfaces in the presence of higher nanomaterial concentrations. The material’s flexural strength may be diminished as a result of this effect caused by overlapping surfaces [43, 44]. According to the findings, the incorporation of 0.5 wt% MWCNT-HA appears to provide the most desirable mechanical properties. The measured values of flexural strength and modulus are presented in a simplified form in Tab. 12.2, which may be found below.

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Tab. 12.2: Flexural test results. Sample

Uniform reinforcement (HA + MWCNT) (wt%)

Flexural strength (MPa)

Flexural modulus (MPa)

P-NEAT



. ± .

. ± 

PMH-

.

. ± .

. ± 

PMH-

.

. ± .

. ± 

PMH-

.

. ± .

. ± 

Fig. 12.2: Stress-strain behavior of PMMA-MWCNT-HA nanocomposites in flexural strength.

Fig. 12.3: Flexural strength of PMMA-MWCNT-HA nanocomposites.

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Fig. 12.4: Flexural modulus of PMMA-MWCNT-HA nanocomposites.

12.4.2 Compression strength and modulus The stress-strain behaviour of PMMA bone cement with and without the inclusion of MWCNT-HA reinforcement was assessed in this study. Figs. 12.5–12.7 show the results of reinforced polymer matrix with respect to pristine polymer. The pristine PMMA bone cement’s stress-strain performance (without any additions) is shown in Fig. 12.5. It had a compression modulus of about 728.33 ± 152 MPa and a compression strength of approximately 86.34 ± 0.3 MPa. The addition of 0.25 wt% of MWCNT-HA raises the compression strength by 6.7% (which is equivalent to 92.13 MPa ± 0.3 MPa) and raises the compression modulus by 22.1% (which is equivalent to 889.302 MPa ± 173 MPa). The performance of PMMA bone cement improved significantly when 0.5 wt% MWCNT-HA reinforcements were added. The compression modulus increased by 50.8% to around 1098.34 ± 122 MPa, while the compression strength increased by 14.58% to approximately 98.93 ± 0.4 MPa. Adding a higher concentration of MWCNT-HA such as 0.75 wt% resulted in a minor decrease in compression strength to around 94.83 ± 0.2 MPa and compression modulus to around 1,009.74 ± 188 MPa. Previous study has shown that adding HA to PMMA bone cement increased its compression strength by 13% [44]. But the current study shows that adding hybrid reinforcement, especially MWCNT-HA, increases compression strength by 14.58%. When compared to another study in which 0.5% by weight of GO was added to PMMA bone cement to make it more effective the gain was only 8.4%. When the same amount of HA and MWCNT-HA were added together in a 0.5 wt% reinforcement range, the compression strength went up 4.58% more than when GO was added alone [45]. Since fillers have a tendency to agglomerate, an overabundance of reinforcement makes the material fragile. Compression strength shows decline under higher loading as HA nanoparticles accumulate [46]. Mechanical performance of the new material can be

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enhanced by using CNT-modified PMMA bone cement interfaces, which may also serve as an efficient stress transfer mechanism [47]. Tab. 12.3 summarizes the measured compression strength and modulus. Tab. 12.3: Compression test results. Sample

Uniform reinforcement (HA + MWCNT) (wt%)

Compression strength (MPa)

Compression modulus (MPa)

P-ONLY



. ± .

. ± 

PMH-A

.

. ± .

. ± 

PMH-B

.

. ± .

. ± 

PMH-C

.

. ± .

. ± 

Fig. 12.5: Stress-strain behavior of PMMA-MWCNT-HA nanocomposites in compression strength.

12.4.3 X-ray diffraction peaks The diffraction peaks of the PMMA bone cement, MWCNT, HA, and PMH-2 sample are all visible in the X-ray diffraction image. A similar pattern was also seen with PMMA bone cement in the earlier work [48]. Test results demonstrated the presence of HA in an amorphous polymeric matrix (see Fig. 12.8). Certain findings suggest that HA’s

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Fig. 12.6: Compression strength of PMMA-MWCNT-HA nanocomposites.

Fig. 12.7: Compression modulus of PMMA-MWCNT-HA nanocomposites.

structural integrity is maintained upon contact with certain acidic or critical functions, allowing it to continue to promote bone formation as before. Previous research [41, 49] confirmed that the HA predictor had three peaks at inclinations of 28.3°, 31.6°, and 49.2°. The presence of the graphitic plane is confirmed by the occurrence of high peaks at 2θ = 26.2° and low peaks at 2θ = 36° [50, 51]. By comparing the obtained diffraction peaks to previous studies, we can ensure that the nanoparticles in the generated nanocomposite have the required crystal structure. Fig. 12.8 shows PMMA bone cement with HA and MWCNT added, as seen by XRD analysis.

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Fig. 12.8: X-ray diffraction pattern of PMMA-MWCNT-HA nanocomposites.

12.4.4 Fourier transformation infrared spectroscopy plot The graph of the FTIR analysis depicts the functional groups that are present in the samples of PMMA bone cement, MWCNT, HA, and PMH-2 (Fig. 12.9). Previous research [52] found that the PMMA bone cement exhibited transmission maxima at 1,065 cm−1 and 837 cm−1. These values were found to be the most significant. Band shift to 1,730 cm−1 and broadening in the curve of the PMH-2 sample represent interactions in the mixture and are seen in the spectra of PMMA bone cement, where the distinctive band of the C = O group peaks at 1,720 cm−1. At 1,048 cm−1, there is a significant peak that corresponds to the phosphate group (PO43-), which is in agreement with earlier studies [8]. Fig. 12.9 further reveals the presence of infrared bands at 1,097 cm−1 and 962 cm−1, both of which are characteristic of phosphate. At 810 cm−1 and 757 cm−1, one may see additional bands that are associated with phosphate. Carboxylic (-CO2H) and hydroxyl (-OH) surface groups are responsible for the two transmittance bands that occur at 3,424 and 1,043 cm−1, respectively [53]. The validation of the nanocomposite by comparing the data on the acquired functional groups with the results of earlier tests verifies that the nanoparticles and polymer shows the appropriate functional groups. The FTIR spectrum elucidates the chemical composition, bonding characteristics, and interaction of hydroxyapatite (HA) with polymethyl methacrylate (PMMA) bone cement.

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Fig. 12.9: FTIR plot of PMMA-MWCNT-HA nanocomposites.

12.4.5 Scanning electron microscopy The SEM study of the broken surfaces obtained following mechanical testing reveals variations in the mechanical characteristics of the produced nanocomposite. Fig. 12.11 depicts the features of all four samples using SEM images with a resolution of 200 m. The P-NEAT SEM micrographs demonstrate that the PMMA bone cement appears in the sample as a white substance. The rough surface of the PMH-1 sample implies that nanoparticles are dispersed evenly. Previous research [54, 55] has also found finely dispersed nanoparticles in the fracture surface analysis of composite bone cement. Earlier research [25, 40, 45] highlighted agglomerates as a crucial element impacting the mechanical characteristics of carbon/PMMA bone cement nanocomposites. The existence of voids in the PGH-3 sample is depicted in Fig. 12.10. Due to graphene’s structural properties, its high concentration causes agglomeration and poor diffusion within the polymer matrix, resulting in void formation [56]. At high reinforcement loading, similar void formation has been reported in other HA hybrid nanocomposites. The existence of voids causes stress concentrations inside the sample, resulting in sample fracture. SEM Images of the PMH-1 and PMH-2 samples show that when only a small amount of MWCNT was employed, there were no agglomerates visible. This finding is in line with the findings of prior research on polymer matrix nanocomposites [57–59]. The PMH-3 sample, which had the highest concentration of MWCNTs and HA of all the sam-

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Fig. 12.10: SEM micrograph of PMMA-MWCNT-HA nanocomposites.

Fig. 12.11: SEM micrograph of PMH-3 sample with voids.

ples, demonstrated poor dispersion and the existence of voids within the PMMA matrix. This was despite the fact that it contained the highest concentration of MWCNTs and HA of all the samples. As the concentration of HA increased, the uneven distribution of HA inside the PMMA-MWCNT-HA cement cross section grew more evident. The PMH-2 sample, on the other hand, displayed a homogeneous distribution, which resulted in exceptional mechanical strength [60]. According to the findings, in order to attain an optimal degree of mechanical strength in the PMMA bone cement matrix, a hybrid rein-

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forcement that consists of HA and MWCNT in concentrations of up to 0.5 wt% is necessary. These hybrid reinforced polymers can be used in a variety of distinct applications.

12.5 Discussion As a biomaterial, PMMA bone cement has a lot of untapped potential in the area of orthopedics. On the other hand, its mechanical qualities have shown to be a significant disadvantage. The current work focuses on nanoparticle reinforcement as a way to improve these qualities. The current study reveals that the mechanical characteristics of PMMA bone cement can be significantly enhanced by the chemical attachment of HA and MWCNT). In spite of the large addition of nanoparticles, earlier experiments carried out in this field showed only a marginal change in the material’s flexural strength [25, 40, 61]. In contrast, the results of this work show that the inclusion of a trace quantity of HA coupled with MWCNT leads to a significant improvement in the material’s mechanical properties. The flexural strength of the material is significantly improved with the addition of just 0.5 wt% of HA and MWCNT, going from 64.33 MPa to 81.49 MPa. However, as the MWCNT loading is increased beyond 0.75 wt%, the mechanical properties begin to deteriorate, which ultimately results in the creation of voids and pores, as shown by the analysis of SEM images [45].When compared to other types of reinforcement, hybrid reinforcement leads to an increase in flexural strength that is 26.67% higher and an increase in compressive strength that is 14.58% higher [21]. Previous research found that using HA powder at a weight percentage of 8% resulted in a 10.9% increase in compressive strength [42]. The mechanical analysis reveals the dependency of HA and MWCNT in improving the mechanical characteristics of PMMA bone cement. Improving the mechanical behaviour of the material requires, first and foremost, reinforcing the connection that exists between these nanoparticles and the PMMA matrix. The FTIR analysis turns out to be the most successful method when it comes to identifying individual functional groups included within the nanocomposite. The peaks detected by FTIR provide evidence that both HA and MWCNT are present and are distributed consistently across the sample. It is important to note that there were no observable shifts in the relative positions of the functional groupings that were observed. C = O peaks in PMMA can be seen at 1,725 cm−1 [2]. Pure PMMA bone cement underwent XRD examination to determine its crystal structure, and the results showed three prominent peaks at 2 Ø = 14.1, 2 Ø = 29.0, and 2 Ø = 42.5. These variations are consistent with the amorphous nature of PMMA, as shown in prior studies [59, 62, 63]. In line with the findings of other investigations, XRD examination of pure PMMA bone cement showed that it is of an amorphous character. The combination of FTIR and XRD data confirms the uniform dispersion of both reinforcements throughout the PMMA bone cement matrix. Nanocomposite bone cement made of PMMA, MWCNT, and HA shows immense

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promise as a potential application for the repair of bone microfractures and the filling of bone gaps caused by injury or damage. Producing this nanocomposite in large quantities is entirely possible, and only requires a small amount of time and effort. In addition, it exhibits promise for use as a bone screw for the support of implants, despite the fact that it would require extra production methods. These new findings have major therapeutic implications because they shed light on how the addition of MWCNT and HA can affect the activity of bone cement. Additionally, they help us understand the mechanical and physicochemical features of these designed bio composites, which is a contribution to our overall knowledge. To ease the process of reinforcing, it is vital to understand the biological reactions of MWCNT and HA-filled materials and investigate the microstructure of the PMMA-MWCNT-HA bone cement nanocomposite. Overall, this research takes us closer to developing sophisticated biomaterials with greater mechanical qualities. This opens up possibilities for improved orthopedic applications and the potential for further developments in the sector.

12.6 Conclusion The results of this research have the potential to bring about a major shift in the manufacture of PMMA bone cement by leading to the development of an innovative commercial strategy that improves the material’s mechanical properties. The purpose of this study is to evaluate the effect that varying the weight percentage of MWCNT and HA as well as the reinforcing limit has on the properties of the nanocomposite. In order to successfully construct PMMA-MWCNT-HA nanocomposite bone cement, a procedure that was both straightforward and cost-effective was used. The mechanical characteristics of PMMA bone cement were significantly improved with the addition of merely 0.5 wt% of both HA and MWCNT. The compression strength and compression modulus of the pristine PMMA bone cement jumped by 14.58% and 50.8%, respectively, when 0.25 wt% of HA and MWCNT, which is equivalent to 0.5 wt% of hybrid reinforcement, were added into the material. In addition, the incorporation of 0.5 wt% of hybrid reinforcement composed of HA and MWCNT resulted in an increase of 26.67% and 24.32% in the flexural strength and flexural modulus, respectively. The findings of the XRD and FTIR analyses indicated an appropriate dispersion of HA and MWCNTs as reinforcements in the PMMA bone cement matrix. This was demonstrated by a comparison of the obtained pattern peaks with those from the previous studies. The proper distribution of HA and MWCNT within the PMMA bone cement matrix could be seen clearly in the SEM pictures of the cracked area of the material. However, the PMH-3 sample, which had the highest reinforcement level, displayed decreased mechanical performance due to voids formed by nonuniform distribution of HA and MWCNT.

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The PMMA-based nanocomposites that were described in this work have showed potential uses in a variety of other fields, including tissue engineering, gene therapy, and food preservation, in addition to their prospective application in orthopedics. It is essential to attain better attributes such as strong compressive and flexural strength in order to make sure that prostheses and implants last for a long time. The addition of filler materials like MWCNT and HA results in a significant improvement in these desirable qualities. It is recommended that more studies, including testing and analysis of a more complex kind, be carried out as part as a future scope. It is necessary to conduct mechanical tests, such as fracture strength and tensile strength, in order to carry out an all-encompassing analysis of the overall increase in the mechanical properties of nanocomposites. In further research, other weight percentages can be investigated to locate the most effective level of reinforcement. Declaration of competing interest: The authors declared no potential conflicts of interest.

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Kuldeep Kumar, Shivam Kumar Dubey, Shivi Kesarwani, Prakhar Kumar Kharwar, Arpan Kumar Mondal, Rajesh Kumar Verma✶, Mark J. Jackson

13 Role of nanomaterials in enhancing the performance of polymer composite materials Abstract: Lightweight polymer matrix composites are widely used in various engineering applications due to their unique virtue of being lightweight with higher strength. After discovering nanomaterials, it is observed that the nanomaterials play a significant role in enhancing the property of existing polymer composites by many folds. The effects of nanomaterials are mainly governed by the uniform dispersion and aspect ratio of the nanomaterial. The main challenge in adding nanomaterials in a polymer matrix is the complex interfacial regions between the nanoparticles and the polymer matrices. The amazing features of nanoparticles are tuned by their incorporation into the matrix. Very tiny scales produce a huge specific surface area, highlighting the significance of interactions between the polymers and nanoparticles. Analysis of the intercalation process between the nanoparticles and the polymer bases is therefore necessary to achieve the desired characteristics (e.g., mechanical, thermal, optical, and electric). This chapter mainly focuses on the effect of GO particles in CFRP composite. The result shows that a nominal amount (0.5 wt% of GO) enhances the mechanical properties of a conventional composite. Keywords: Nanomaterials, polymer, CNT, CFRP, GO

13.1 Introduction Fiber-reinforced polymers (FRPs) are widely used in the manufacturing sector due to their improved mechanical performance. Sometimes, they become limited due to the anisotropic behavior and require high-performance characteristics [1]. The study

✶

Corresponding author: Rajesh Kumar Verma, Department of Mechanical Engineering, Harcourt Butler Technical University, Kanpur 208002, Uttar Pradesh, India, e-mail: [email protected] Kuldeep Kumar, Shivam Kumar Dubey, Shivi Kesarwani, Department of Mechanical Engineering, Madan Mohan Malaviya University of Technology, Gorakhpur 273010, Uttar Pradesh, India Prakhar Kumar Kharwar, Bhartiya Skill Development University, Jaipur, Rajasthan, India Arpan Kumar Mondal, Department of Mechanical Engineering, National Institute of Technical Teachers Training and Research, Kolkata 700106, West Bengal, India Mark J. Jackson, Collage of Technology and Aviation Kansas State University, Aerospace Campus, Salina, KS 67401, USA https://doi.org/10.1515/9783111137902-013

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shows that supplementation by nanomaterials could overcome such limitations in the matrix. This chapter highlights the improvement of polymers’ physio-mechanical characteristics by adding carbon-based nanomaterials (CBNs). Polymer composites generally consist of natural or synthetic high-strength fiber in a resin matrix. Carbon and glass fiber is are the most used in polymer composites. It offers excellent corrosion resistivity and mechanical features for multifunctional components. CBNs play a significant role in advanced composite materials and are broadly used in aerospace applications, drug delivery, or modern electronic components [2, 3]. It improve the composite’s interfacial properties, which results in excellent physio-mechanical properties. It is one of the most preferred nanofillers used widely at present, for example in single-walled carbon nanotubes (SWCNT), multiwall carbon nanotubes (MWCNT), graphene and its derivative (GO), and carbon nano onion (CNO) [3–5]. This paper summarizes an extensive prior state of work to identify the exceptional features of carbon derivatives, i.e. graphene oxide in the polymer matrix. An attempt has been made to study the effect of GO in CFRP composites. The addition of varying weight percentages in the polymer matrix shows the desired improvements in the matrix phase, which leads to an overall improvement in the mechanical performances of the modified composites [6]. The findings of prior works are proposed for feasible modification and application of polymer composites for different emerging needs of manufacturing industries. Due to the carbon-based nanomaterials’ superior weight-to-strength ratio and better mechanical qualities compared to traditional materials, composite materials play an important role in the current mechanical sector as a substitute to conventional materials [7]. As a consequence, there is a lot of potential in the area of composite materials. Nowadays, the mechanical industries are working on lowering the weight of components without compromising their strength. A composite material comprises two or more materials of different properties, which results in the material having different properties than the parent material, such as improved thermal conductivity, increased fatigue life, and better temperature-conditional behavior [8]. The matrix is the composite’s base material, while the reinforcing material is the ingredient that is added to the matrix. Now, in addition to the matrix and the reinforcement, fillers are added to the composites. The fiber and the matrix can be used to classify composite materials. Particulate composites, fiber composites, and laminate composites are all fiber-based composites. Metal matrix composites, ceramic matrix composites, and polymer matrix composites are all based on a matrix [9]. By adding a tiny amount of nanomaterial or nanofillers to the matrix material during composite manufacture, the mechanical characteristics of the composite materials can be improved. Epoxy and polyester resins are utilized as matrix materials in composite production. In comparison to other matrix materials, epoxy is one of the most often used matrix materials in the fabrication of composites because it has strong mechanical qualities, good adhesive strength, good chemical and solvent resistance, minimal shrinkage, and moisture resistance [10].

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13.1.1 Nanocomposites Nanocomposites are currently driving research in the field of composite materials. A nanocomposite is a two-material composite in which one of the components is in the nanoscale. Filler materials are commonly used to enhance the properties of conventional composites. They also enhance abrasion resistance, toughness, and provide dimensional and thermal stability [11]. Researchers are performing additional study work by adding nanomaterials to the matrix material to improve the traditional composite materials’ mechanical and other qualities [12]. The most difficult aspects of adding nanomaterial to the matrix material are uniform mixing of the nanomaterial with the matrix and raising the viscosity of the matrix when the nanomaterial is added.

13.1.2 Nanomaterials Nanomaterials are materials with nanoscale particle sizes ranging from 1 to 100 nanometers [13]. As shown in Fig. 13.1, nanoparticles are mostly zero-dimensional nanomaterials, whereas nanorods, nanotubes, and nanowires are one-dimensional nanomaterials, and nanofilms, nanolayers, and nano coatings are two-dimensional nanomaterials. Carbon, metal, dendrimers, and composites are all types of nanomaterials. The mechanical and thermal characteristics of zero-dimensional nanomaterials with polymer matrix are excellent. Nanotubes or nanorods with composites are utilized to strengthen the polymer or impart electric conductivity. Nanosilica, aluminum oxide, titanium oxide, silicon carbide, graphene, carbon nanofibers, and multiwall carbon nanotubes are several commercially available nanomaterials. Graphene is a carbon-based substance made up of carbon atoms linked together in a hexagonal arrangement. Because graphene is extremely thin, it is classified as a two-dimensional material. Graphene offers a plethora of possible uses in practically every sector (like electronics, automobile, medicine, aviation, and much more) [3, 14]. Nanomaterials based on dimensionality are shown in Fig. 13.2.

13.1.3 Application of nanomaterials Today, nanomaterials have become a more popular research area due to their great potential. They provide high conductivity, good chemical and electrochemical stability, and excellent mechanical strength to enhance the properties of conventional composite materials. The specific properties of advanced nanomaterials offer a new opportunity in advanced engineering, automobile, electronics aerospace, and biomedical applications [15]. Nanomaterials play a significant role in the field of advanced material science; Nanomaterials are very versatile materials used almost everywhere, such as in aerospace applications, drug delivery, or in modern display applications. The introduction of

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Fig. 13.1: Classification of nanomaterials.

NMs Based on Dimensionally

1-D Nanotubes, wires, rods

2-D Thin films, plates

3-D Bulk, NMs, polycrystal

Carbon coated nanoplates

Liposome

Quantum dots

Metal nanoroads, Ceramic crystal

Fullerenes

Carbon nanotubes, Metallic nanotubes

Graphene sheet

Polycrystalline

Gold nanoparticles

Gold nanowires, Polymeric nanofibers

Layered nanomaterials

Dendrimer

0-D Nanospheres clusters

Fig. 13.2: Nanomaterials based on dimensionally.

nanomaterials in polymer composites has improved the mechanical and electrical properties and optical properties. It improves the interfacial properties of the composite, which is the backbone of the mechanical properties, thus improving the mechanical properties [16]. The application of nanomaterials in various fields is shown in Fig. 13.3. After going through various literature surveys, it has been found that various works have been performed on graphene oxide-reinforced CFRP composite characterization but does not include much work regarding characterization at some other wt% of GO. In the chapter I have gone through, there is still a gap in the findings of the opti-

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Fig. 13.3: Application of nanomaterials.

mum wt% of GO to attain maximum mechanical properties. There are several works done on carbon fiber composite, but very little work has been done on reinforcement with GO as a nanofiller and 400 GSM plain weaves carbon fiber. After doing numerous literature surveys and research gaps, the objective of this experimental research work has been decided. The objective of this experimental research is given below. – To understand and study graphene oxide-reinforced CFRP composite. – To fabricate graphene oxide-reinforced CFRP composite material. – Comparative study of mechanical properties of Pristine Carbon Fiber-Reinforced Polymer (CFRP) and CFRP-reinforced with different wt% of GO. – It enhances the property of a material by selecting the appropriate reinforcement.

13.2 Materials and method For the development of nanocomposites, the Carbon fiber-reinforced polymer (CFRP) is a bi-directional sheet reinforcing material (400 GSM, plain weave) used to make laminated polymer composites. Epoxy resin (LapoxL12) is employed as the matrix component, and the binder substance is used as a hardener. Graphene oxide (GO) is used as a secondary reinforcement material with varying wt% (0%, 0.5%, 1.5%, and 2%) to enhance the conventional composite. The properties of the materials used in CFRP, GO, and Epoxy resin is shown in Tabs. 13.1–13.3.

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Tab. 13.1: Properties of CFRP. Filament type

 K

Woven pattern

Unidirectional

Tensile strength (MPa)

≥,

Size (mm)

Width  Thickness . 

Area weight (g/m )



Tab. 13.2: Physical properties of graphene oxide. Graphene oxide

Description

Purity

%

Thickness

.– nm

Number of layers

– layer

Carbon content

–%

Surface area

– m/g

Bulk density

. g/cm

Physical form

Fluffy, Very light powder

Tab. 13.3: Properties of epoxy resin. Tensile strength

 MPa

Specific gravity ( °C)

.–.

Density

. g/cm

Hardener

K-

Tensile modulus

. GPa

Mixing ratio

:

13.2.1 Development of CFRP/epoxy modified by GO nanocomposite The fabrication of CFRP/epoxy modified by GO nanocomposite was done by the hand layout method, which is shown in Fig. 13.4. The epoxy and hardener were mixed in 10:1 ratio and utilized for the fabrication process of the proposed composite. GO with weight percentages such as 0%, 0.5%, 1.5%, and 2% was mixed with acetone and soni-

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Fig. 13.4: Schematic diagram of the fabrication process of GO/CFRP composite.

cated 45 min by ultrasonic clearer. The mixture of weight percentage of GO and epoxy resin was by magnetic stirrer with a hot plate for 60 min. After that, the mixture of epoxy resin and GO was cooled to room temperature. After that, the prepared resin material is lapped in CFRP material layer by layer using a manual layout technique, and a hydraulic compress machine was used for 24 h to cure the material at room temperature. STEPS INVOLVED IN THE FABRICATION OF THE COMPOSITE I. Weighing of epoxy and the nanomaterial. II. Sonication of nanomaterial for its dispersion in acetone. III. Mixing of nanomaterial in epoxy by a mechanical stirrer. IV. Pouring hardener in the GO/Epoxy solution. V. Hand lay up for uniform distribution of epoxy in the carbon fiber. VI. Hot press curing. VII. Finally, the composites are cut into different dimensions according to the ASTM standard.

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13.3 Characterization of the developed nanocomposite 13.3.1 FTIR spectroscopy Fourier transform infrared (FTIR) spectroscopy was performed on the developed nanocomposite, and the spectra revealed the composition of solids, liquids, and gases. FTIR is basically a quality verification tool that determines the presence of different functional groups. The most common use is identifying unknown materials and confirming the production material (incoming or outgoing). Usually, a little amount of material in powder form is required for testing. In FTIR, x-axis represents the infrared spectrum and the y-axis represents the absorbance or frequency [17]. For midrange IR, the wave number is plotted between 4,000 and 400 cm¯1. Carbon fiber has phenolic/hydroxyl, carbonyl, and carboxylic functional groups on the surface fibers, as well as certain nitrogen-containing functional groups, according to previous research. As shown in Fig. 13.5, a result of the strong contact, elongation was reduced as compared to standard carbon fiber epoxy composites. The spectra demonstrate that adding GO to a composite raises its modulus. The FTIR spectra of a CFRP/epoxy modified with 0.5 wt% reinforcement were collected to examine the bonding between GO and the epoxy resin. Both the asymmetric mode of stretching at 1242.45 cm−1 and the symmetric mode of stretching at 826.6 cm−1 of the vinyl ether bond are seen. The surface roughness of carbon fibers plays a vital role in improving the mechanical characteristics of hybrid composites like GO/CF/EP. The O-H groups of carbon fiber attacked the epoxy carbon of GO, causing the strain ring to expand. As the number of peaks of the amine group in 0.5 wt% of GO in CF/EP composite is more as compared to the pristine sample, we can say that the better mechanical property will hold the composite.

13.3.2 Mechanical characterization Mechanical characterization is very important to study the properties of the developed nanocomposites. Four types of testing were performed on the developed nanocomposite, such as Tensile, 3-point Flexural, and Impact. For the mechanical characterization, the developed sample is cut according to the ASTM standard, the results of which are shown in Tab. 13.4 and Fig. 13.6.

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Fig. 13.5: FTIR Spectra of, (a) 0.5 wt% of GO CFRP Composite, (b) Pristine composite.

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Tab. 13.4: ASTM standard and dimension. S.No

Test

ASTM standard

Dimension (mm)



-point flexural test

ASTM D

 ×  × 



Impact Test

ASTM D

 ×  × 



Tensile Test

ASTM D

 ×  × 

Fig. 13.6: Prepared specimens of mechanical testing.

13.4 Results and discussion 13.4.1 Tensile test Tensile testing is a method employed to evaluate the material’s tensile strength, yield strength, and ductility. It specifies the force required to fracture a composite or plastic specimen as well as how much the sample must extend or stretch before it breaks. These tests result in stress-strain diagrams, which are used to determine the tensile modulus [18]. The tensile test was performed according ASTM D3039 standard, which is shown in Fig. 13.7. Tensile tests were performed at room temperature using a Universal Testing Machine (Instron model 3382) with a constant crosshead speed of 5 mm/min. For each treatment, three replicate tests were performed in order to get a credible mean and standard deviation. Figure 13.8 shows the results of a tensile test performed on neat CFRP/epoxy composites and the incorporated weight percentages of GO. The effects of GO concentrations on the CFRP/epoxy-based nanocomposite performance are quiet good. The 0.5 wt% of GO-reinforced CFRP composite sample has the maximum tensile

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Fig. 13.7: Universal Testing Machine (INSTRON 3382).

Tensile Strength (MPa)

Tensile Strength

Tensile Strength (MPa) 800 700 600 500 400 300 200 100 0

726.39

687.47 569.45

530.36

0

0.5

1.5 Weight % of GO

Fig. 13.8: Tensile strength of GO-reinforced CFRP composite.

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strength. Young’s Modulus appears to improve up to 0.5 wt% GO concentrations, after which it begins to decline. Figure 13.9 explores the sress-strain behavior of neat, and CFRP/epoxy modified by 0.5, 1.5.and 2.5 wt% of GO nanoparticle. The tested results revealed that incorporation of nominal 0.5 wt% of GO in CFRP/epoxy increases the tensile strength, and when further incorporated by 1.5 and 2.5 wt%, it decreases the strength, which may be an agglomeration effect that acts as crack propagation.

Fig. 13.9: Tensile load vs extension graph of GO-reinforced CFRP composite of (a) Neat/CFRP/epoxy sample, (b) 0.5 wt% of GO, (c) 1.5 wt% of GO and (d) 2.5 wt% of GO.

13.4.2 Flexural test The flexural test was performed on the developed specimens. The specimen was cut according to the ASTM D7264 standard [19]. There are three nanocomposite specimens tested with different wt% and the average value of each GO wt% was taken. The flexural test is used to determine the mechanical characteristics of materials when they are bent. Five layers were chosen to maintain a 0.45 mm average ply thickness across systems while keeping the total thickness at 3 mm. A three-point bending test was performed on a standard-sized specimen in accordance with ASTM D7264, as shown in Fig. 13.10. Flexural testing was performed at room temperature using an Instron model 3382 Universal Testing Machine with a constant crosshead speed of 5 mm/min. For each sample, the data presented is a mean of the repeated trials. It was observed that the maximum flexural load is found to be at 0.5 wt% of GO-reinforced CFRP nanocomposite and similar variation in flexural modulus is also achieved at the same wt% of GO

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Fig. 13.10: Flexural test setup (3-point bending test).

and at the same concentration, Flexural strength is 528.21 MPa, which is 21.25% more as compared to the neat sample. It can be concluded that the fraction amount of GO nanoparticles enhances the conventional composite. However, the experiment also revealed that when the amount of wt% of GO in the CFRP/epoxy composite increased, the flexural strength started to follow a decreasing trend. It can be revealed that as per the increase in the amount of GO particle in CFRP/epoxy above the nominal wt%, it formed the agglomeration effect, which occurred with crack propagation and decreased the flexural strength. The flexural load, stress, and flexural modulus are shown in Figs. 13.11–13.13. The flexural stress vs strain graph is shown in Fig. 13.14.

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Flexural Load

Maximum Flexural Load (N) 1000 900 800 700 600 500 400 300 200 100 0

858.33 797.47 707.9

0

669

0.5

1.5

2.5

Weight % of GO Fig. 13.11: Flexural Load of neat sample and CFRP modified by GO wt%.

Flexural stress at Maximum Flexural Load (MPa) Flexural stress at Maximum Flexural Load (MPa) Flexural stress (MPa)

600 500

528.21

490.75

435.63

412.25

400 300 200 100 0 0

0.5

1.5

2.5

Weight % of GO Fig. 13.12: Flexural stress of neat sample and CFRP modified by GO wt%.

Flexural Modulus (MPa)

Flexural Modulus (MPa) 25 19.91 20 15

16.15

14.75

13.15

10 5 0 0

0.5

1.5 Weight % of GO

Flexural Modulus (MPa) Fig. 13.13: Flexural modulus of GO-reinforced CFRP composite with different wt% of GO.

2.5

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Fig. 13.14: Flexural stress vs Flexural strain graph of nanocomposite (a) Neat sample (b) 0.5 wt% of GO, (C) 1.5 wt% of GO and (d) 2.5 wt% of GO.

13.4.3 Impact test The composite’s resistance to impacts is investigated during the Izod impact strength testing method. In this approach, a swinging arm swings up to a certain height, releases, swings down, breaks the specimen, and repeats the process. The impact strength is recorded after that. The Izod test has been performed on the standard size of the specimen according to the ASTM D256 [20]. The impact test was performed at CIPET Lucknow India. The impact test setup is shown in Fig. 13.15. As shown in Fig. 13.16, the CFRP modified by 0.5 wt% sample attained the maximum impact strength (276.19 kJ/m2) as compared to the neat sample and CFRP modified by 1.5 wt% and 2.5 wt% nanocomposite sample. It is revealed that beyond 0.5 wt% of GO, the impact strength of the GO nanoparticle in CFRP/epoxy decreases, possibly due to the agglomeration effect.

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Fig. 13.15: Impact test setup.

Impact Strength(kJ/m2) 300

276.19

260.32

Impact Strength

250 200

180.95 142.86

150 100 50 0

0

0.5

1.5

2.5

Weight % of GO Fig. 13.16: Impact strength of neat sample and CFRP modified by varying the wt% of GO nanocomposite.

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13.5 Conclusion –

–

–

–

In this study, four composites were fabricated by the hand-layup technique with different weight percentages of GO used as a nanofiller – 0, 0.5,1.5, and 2.5 wt%. Mechanical characterization has been performed in this work and flexural test, impact test, as well as tensile Test were conducted. The preliminary data from this study demonstrate that reinforcing GO into a CFRP conventional composite increases the mechanical properties. With the addition of the GO to the CFRP/epoxy sample, Young’s modulus and flexural strength improved. When comparing the different GO concentrations, the increase in GO concentration did have an influence on tensile and flexural strength. The best Graphene Oxide reinforcement percentage was at 0.5 wt%; the composite with this % of reinforcement leads to 21.25% and 36.96% improvement in flexural strength and tensile strength, respectively, when compared to the neat composite sample. Similarly, tensile strength is also improved by 36.96% by adding GO as a nanofiller, compared to the without reinforcement of GO in CFRP/epoxy. Improvements in epoxy resin characteristics and interfacial contact between the reinforcement and the matrix via hydrogen bonding and mechanical interlocking of graphene oxide increased the mechanical properties. The graphene oxide filler appears to have a threshold at 0.5 wt%; therefore, any more than this amount may cause the particles to amalgamate, resulting in poor graphene dispersion and hence a detrimental impact on the mechanical qualities.

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Sudip Paramanik, Abhratanu Ganguly, Koushik Jana, Prem Rajak, Manas Paramanik ✶

14 Nanotechnology: a novel weapon for insect pest and vector management Abstract: Nearly three-fourths of the global fauna are insects and about 1% of them are regarded as major pests or vectors. Sustainable agricultural practices vastly depend on the mitigation of insect pests, the devastators of human food. Some members transmit life-threatening vector-borne diseases. After the 1950s, synthetic insecticides gained popularity in pest and vector control strategies but their detrimental nature on the environment forced the management program’s switch to an eco-friendly approach. Nanoscience offers one such efficacious green alternative to suppress the furious action of pests and vector insects on food and health of humans. Nanotechnology can be useful for controlling insect pest and vector populations through the lipid, polymer, clay, metal, and other formulations of nanomaterial-based insecticides, nano-mediated genes or DNA transfer to plants, and encapsulated nanoparticles show great stability, permeability, and specificity. The big advantage is that because of their miniature feature, they are able to spread easily on the body of the target insects and are rather harmless to non-target organisms. This chapter discusses the various formulation techniques of nanomaterials, bio-nanoinsecticides, their modes of action on the different target insect groups, their relevance to pest and vector insect management, and the future challenges and prospects. Keywords: Nanotechnology, bio-nanoinsecticides, insect pest management, insect vector management

14.1 Introduction Insects delineate the largest and most miscellaneous faunal group in the world’s known organisms. Some of these interfere directly or indirectly with human property and health – acting as pests or vectors. Agricultural productivity is greatly reduced due to insect pests and the estimated global loss of total crop production is about 15.7% [1]. Vector insects like mosquitoes, flies, ticks, etc. are spreaders of dreadful diseases like dengue, chikungunya, yellow fever, Zika, trypanosomiasis, leishmaniasis, malaria, etc.,

✶

Corresponding author: Manas Paramanik, Department of Animal Science, Kazi Nazrul University, Asansol, Paschim Bardhaman 713340, West Bengal, India, e-mail: [email protected] Sudip Paramanik, Abhratanu Ganguly, Koushik Jana, Prem Rajak, Department of Animal Science, Kazi Nazrul University, Asansol, Paschim Bardhaman 713340, West Bengal, India https://doi.org/10.1515/9783111137902-014

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which comprise 17% of the commonly occurring infectious diseases and annually cause the death of over 7 lac people [2]. Pest control was revolutionized when dichlorodiphenyl trichloroacetic acid (DDT) was revealed to have remarkable pesticidal qualities during World War II. Eventually, DDT became less expensive, was found efficacious even at low concentrations practically against most insects, and was thought to be secure for the environment [3]. After the popularity of DDT, more synthetic insecticides like organophosphates and pyrethroids were formulated and gained traction. But within a few decades, they led to the emergence of resistant pests and vector strains. Chemical methods to control these culprits also impose negative effects on public health as well as on non-target or beneficial organisms that are present in the application sites along with target insects. Thus, environmentally amiable and sustainable control of insect pests and vector populations becomes a need of the hour. Infusion of nanotechnology in pest and vector management strategies somehow tries to fulfill this growing demand and becomes an emerging benison to nature. The term nano, which means dwarf, is believed to originate from Greek. The British Standards Institution described nanotechnology as the delineation, characterization, identification, production, and the use of system and structures with the implementation of materials that are usually of size less than 1,000 nm [4]. When particles are shrunk to the nanorange, the surface area-to-volume ratio rises, increasing the magnitude of their reactivity by many folds, with changes in their mechanical, electrical, and optical characteristics. These properties have a wide range of alluring and cutting-edge applications [5]. Despite all of their benefits and potentials, the great majority of studies on insect-nanoparticle interactions focused on their production and insecticidal activity. Nanotechnology has been used to create either the main working component or the carrier element in nanoinsecticides. Minute size and greater surface area of nanoparticles enable the insect pests to come in contact with a greater volume of insecticides [6]. The amount of nanopesticides needed to effectively manage pests is very little; thus, the application of nanoinsecticides instead of chemical pesticides can turn down the harmful pesticide load on the environment [7].

14.2 Nanoformulation techniques and their applications in entomotoxicity In order to vanquish the limitations of conventional insecticides, including their restricted water solubility, early degradation, and increased resistance, insecticide nanoformulations have gained a lot of attention. For better insect pest and vector management, several nanoformulations that are gaining prominence in making nanopesticides include nanoencapsulations, nanoemulsions, nanogels, nanomicelles, nanoparticles, etc. (Fig. 14.1).

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Fig. 14.1: Some common nanomaterials formulated to combat insect pests and vectors. (a) nanocapsule, (b) nanoemulsion, (c) nanogel, (d) nanomicelles [90].

14.2.1 Nanoencapsulation Encapsulation is an evolving technology with plentiful potential in various fields, including in insect pest and vector management. Nanoencapsulation is the process of casing the desired materials with different nanoscale compounds, and allowing the chemical to be released slowly but effectively. A membrane is used in the nanoencapsulation for a controlled delivery process containing tiny particles or droplets of a liquid or solid substance of an active ingredient in the core with the aim of preventing the destruction of core material from infelicitous impacts of light, moisture, oxygen, and other ecological factors [8]. This guarantees that the pesticide will only be released in the desired environment, as at a specified pH, temperature, moisture level, external ultrasonic frequency, or when specific components are present [9]. Many fumigant insecticides have the ability to combat insect pests at a greater scale but their rapid release confines their efficacy. Nanoencapsulation can be an answer to this problem. Nanoencapsulation of essential oils from Rosmarinus officinalis with 2hydroxypropyl-beta-cyclodextrin reduces the delivery rate of the potential compound, and induces toxicity [10]. Controlled delivery technologies have become a method that promises to use resources as efficiently as possible while also lowering the pollution (Fig. 14.2). The distribution of bioactive materials to various locations throughout the target body is directly influenced by the molecular size. So, nanoencapsulation has better effectiveness than microencapsulation in promoting the controlled release and facilitating the specific targeting of the bioactive core material. The encapsulation materials like polymer-based materials, inorganic porous nanomaterials, solid lipid nanoparticles, and layered double hydroxides (LDHs) encapsulate the bioactive pesticidal particles to form various types of nanomaterials such as nanocapsules, nanospheres, micelles, nanogels, liposomes, inorganic nanocages, etc. [11].

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Fig. 14.2: Controlled release nanoformulation for sustainable agricultural practices [91].

14.2.2 Nanoemulsions Nanoemulsions are isotropic, catalytically steady, colloidal dispersions with 20–200 nm particle sizes, prepared through oil, water, a surfactant, and a co-surfactant. Nanoemulsions often exhibit more resilience to gravity separation and droplet accumulation than some other emulsions because of the smaller size of the droplets they contain [12]. Additionally, nanoemulsions are crucial formulations for improving the solubility and dissolution qualities of compounds that are weakly water-soluble. A nanoemulsion can dramatically increase the bioavailability and effectiveness of water-insoluble pesticides by dissolving them into tiny oil droplets [13]. Nanoemulsion significantly minimizes the consumption of organic solvents, relative to conventional insecticide formulations. An eco-friendly nanoemulsion system that contains environmentally acceptable surfactants, 41% (w/w) glyphosate isopropylamine, and esterified vegetable oils was made [14]. The nanoemulsion had a number of benefits over emulsions and microemulsions, including a shorter contact angle, stronger insecticidal action, and decreased cytotoxicity. A nanoemulsion of insecticides with amazing stability may be easily created but the emulsifiers may be harmful. Green nanoemulsions and lowenergy techniques (such as self-emulsification, phase transition, phase inversion temperature approaches, etc.) provide promising solutions to these problems [15, 16]. Methyl laurate and alkyl polyglycoside (APG), and polyoxyethylene 3-lauryl ether (C12E3) as the oil phase and the mixed surfactant are used respectively for formulating a beneficial oil-in-water green nanoemulsion. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements revealed that this optimized nanoemulsion possesses excellent spreading properties and monodispersed droplet size distribution (PDI < 0.2). The inclusion of water-insoluble pesticide β-cypermethrin had no discernible impact on the dimension and stability of the nanoemulsions [17].

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Encapsulation of unstable nanogel, having pesticidal properties through the nanoemulsion of lambda-cyhalothrin, increases the stability of the nanogel even at a higher temperature [18].

14.2.3 Nanogels Nanogels are hydrogel materials formed by physical or chemical crosslinking of the polymer through covalent or van der Waals interactions with high water holding capacity. The encapsulation of nanogel materials protects them from degradation by environmental factors like light, water, etc. Researchers’ interest in nanogels as nanoscopic drug carriers has increased and numerous investigations have been done on nanogels as pheromones and essential oil carriers. It has been demonstrated that nanogel systems have the ability to administer active components continuously, precisely, and stably. Pheromones are extremely specific and ecologically benign potential biocontrol tools need to be protected from deterioration. The rate of pheromone evaporation reduced significantly and extends its potency up to 33 weeks in nanogel carriers as compared to that of the pure form of the active compound, whose potency is about 3 weeks [19]. The flexibility and viscosity of nanogel boost the pesticide’s retention rate and washing resistance by about 80 times [20]. Encapsulation of the nanogel increases the protection of λ-cyhalothrin by 9.33 times and is also responsible for the reduction of foliar ultraviolet (UV) degradation and implementation of pesticides in water bodies. A Permethrin nanogel formulation was recently introduced by The Institute of Pesticide Formulation Technology (Gurgaon) to withstand the impregnation of this pesticide in clothing. While working in forests, this concoction can shield people from mosquito bites [21]. Kala et al. [22] created a chitosan-gel-structured nanocapsule with lemongrass oil that shows abiding anti-mosquito properties.

14.2.4 Nanomicelles The core of micelles is hydrophobic and acts as a reservoir of bioactive chemicals. The outer shells are hydrophilic, assisting the steric stability, water solubility, and inactivating bioactive core ingredients throughout the delivery process. The micelles formed by the conjugation of camptothecin with polyethylene glycol, displayed a synchronous and rapid-release profile due to the formation of amphiphilic copolymer [23]. Tian et al. [24] showed that the self-assembled nanomicelle of the prodrug Fipronil (FP) and coupler cinnamic acid possessed toxicity against the larval stages of the pest Plutella xylostella.

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14.2.5 Nanoparticles A nanoparticle (NP) is an ultrafine particle of size between 1 and 100 nm that possesses properties distinct from those of non-nano-sized particles with a comparable chemical component [25]. NPs can be used alone as pesticides if they have insecticidal properties or can be used as nanocarriers to deliver insecticides. The employment of NPs as nanocarriers is encouraged by their unique properties, including enlarged relative surface area, efficient bearing strength, expeditious bulk transfer to the target, and simple attaching capability with diverse chemical insecticides [26]. One of the most promising NP having insecticidal features is amorphous nanosilica, which is obtained from diatoms, the epidermal layer of vegetables, straw, rice husk, and volcanic soil [27–29]. NPs can be classified into 3 groups according to their origins – (i) Synthetic, (ii) Plant-based, and (iii) Microbial origin. Silica NPs, nickel NPs, and titanium dioxide NPs have all been described in various articles to have insecticidal properties. Numerous nonmetal NPs, such as sulphur, chitosan, and reduced graphene oxide, can be used as nanoinsecticides. Metalloids, including copper, silver, gold, platinum, and metal oxides NPs, including copper oxide, zinc oxide, silver oxide, and titanium dioxide, have also been demonstrated as insecticidal agents. Consequently, NPs can be employed to create novel formulations of insecticides and insect repellents. According to Torney [30], nanotechnology offers potential uses in NP-mediated gene (DNA) transfer. Transferring DNA and other beneficial substances into the host plant tissues can be utilized to shield beneficial plants from insect pests.

14.2.5.1 Green synthesis of nanoparticles The production of nanomaterials becomes reliable, long-lasting, and ecofriendly through the invention of ‘green synthesis’ in the field of materials science. It is a secure and sustainable way to create NPs for a variety of functions, including nanoinsecticidal and biomedical applications. Green synthesis is accomplished using fungi, algae, bacteria, and plants. Phytochemicals from seeds, fruits, flowers, leaves, roots, stems, and barks of plants have been tried in the formulations of a variety of NPs. Phytochemicals may act as organic stabilizing and/or reducing agents during the construction process of NPs (Fig. 14.3). The general consensus is that plant-derived NPs have higher biological properties and can be used in a variety of fields, including the protection of human health, bioengineering, agriculture, food science and technology, and biocontrol. [31]. Green synthesis of silver nanoparticles (AgNPs) is relatively easy. Silver metal ion solution and a reducing biological agent are required for the environmentally friendly synthesis of AgNPs. Reducing and stabilizing Ag ions with biomolecules obtained from plants is the simplest as well as least expensive way to produce AgNPs. The biomolecules may be carbohydrates, amino acids, vitamins, phenolics, saponins, alkaloids, ter-

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Fig. 14.3: Green synthesis of nanoparticles using plant extract [92].

penes, etc. Because of the simple synthesis process, surface functionalization, distinctive properties, low toxicity, and extremely biocompatible nature, gold nanoparticles (AuNPs) have also drawn attention. Like AgNPs, various biogenic chemical components can act as reducing agents of gold metal ions in the generation of AuNPs. In addition, other metals like platinum (Pt), titanium (Ti), copper (Cu), nickel (Ni), manganese (Mn), palladium (Pd), cerium (Ce), etc., and metal oxides like CuO, ZnO, SnO2, Al2O3, MgO, TiO2, etc., some of which are low-cost, have recently been used to generate plant-based NPs for the control of a variety of harmful insects.

14.2.5.2 Efficacy of nanoparticles against insect pests Sahayaraj et al. [32] formulated pungam oil-based silver nanoparticles (PO-AgNPs) and pungam oil-based gold nanoparticles (PO-AuNPs), which caused more mortality than commercial neem insecticides in the pest Pericallia ricini. PO-AgNPs and PO-AuNPs treatments distinctly affected the development of all the life stages as well as fecundity and hatchability. Goswami et al. [33] investigated the effectiveness of NPs made from metal oxides to restrict the rice weevil population. This study reveals that seven days of exposure to hydrophilic AgNPs brings maximum mortality (95%), followed by hydrophobic AgNPs (86%) and lipophilic AgNPs (70%) at 1 g kg−1 dose. Aluminum oxide nanoparticles (Al2O3NP) exhibited almost cent percent mortality at 0.1 g kg−1 dose. A significant pesticidal action of nanostructured alumina was observed by Teodoro et al. [34] on stored food pest models Sitophilus oryzae and Rhyzopertha dominica. In pesticidal assessment, the synthesized nickel nanoparticles (NiNPs) of methanolic extract from Cocos nucifera

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showed 97.31% mortality against the agricultural pest Callasobruchus maculates [35]. Kalpana and Rajeswari [36] evaluated synthesized palladium nanoparticles (PdNPs) of the aqueous extract of Lagenaria siceraria peel against S. oryzae and found significant insecticidal activity. Zinc oxide nanoparticles (ZnONP), and titanium dioxide nanoparticles (TiO2NP), individually and also in combination, showed suitable insecticidal efficacy against tomato-potato psyllid Bactericera cockerelli [37].

14.2.5.3 Efficacy of nanoparticles against insect vectors Green-synthesized NPs are also effective against insect vectors. Silver and gold NPs synthesized from the aqueous extract of bark of the Indian spice Cinnamomum zeylanicum have mosquito larvicidal potential against Anopheles stephensi and Culex quinquefasciatus [38]. Mondal et al. [39] evaluated the efficiency of AgNPs made from the aqueous root extract of Parthenium hysterophorus against Cx. quinquefasciatus larvae. Nanocrystalline silver particles made from the extracts of leaves and berries of Solanum nigrum showed effectiveness against the Cx. quinquefasciatus and An. stephensi larvae [40]. Nickel Nanoparticles (NiNPs) of methanolic extract of Cocos nucifera showed Aedes ageypti larvicidal activity [41]. Nanoparticles synthesized from leaf extract of Swietenia mahagoni exhibited great larvicidal efficacy against three common mosquito vectors, An. stephensi, Cx. quinquefasciatus, and Cx. vishnui [42]. AuNPs phytofabricated with Euphorbia peplus leaves extract were screened for larvicidal activity against Culex pipiens by Ghramh [43]. According to Narayanan et al. [44], titanium dioxide nanoparticles (TiO2NP) fabricated through the leaf extract of Pouteria campechiana have magnificent fatal puissance against larval and pupal Aedes aegypti. Copper nanoparticles (CuNPs) synthesized from the bacteria Morganella morganii show great potentiality against the larvae of An. stephensi, Cx. quinquefasciatus and Ae. aegypti [45]. The green synthesized magnesium oxide nanoparticles (MgONPs) of brown algae Cystoseira crinita significantly affect the larvae and pupae of Musca domestica [46]. When non-target organisms like larvae of Chironomus circumdatus (chironomid, important in the aquatic food chain), Toxorhynchites (predators of mosquito larvae), and Diplonychus annulatum (aquatic predator) that share common habitats with mosquitoes are exposed to synthesized NPs, no abnormalities were observed [40, 47, 48].

14.3 Mode of action of different nanomaterials Recently, a lot of scientific attention has progressed in the formulation of novel insecticides using NPs created by diverse synthesis processes. Although numerous works of study have been done to evaluate their toxicity against a variety of insects, it is still not very clear exactly how they work against insects. Some research has addressed

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the toxicokinetics and toxicodynamics of nanoinsecticides. Toxicokinetics relates to the motion and modification of an insecticide within a body and Toxicodynamics relates to the physiological, biochemical, and molecular impacts and the pathways by which they act [49]. During insect-nanoproduct interaction, the disservice occurring in the insect body may be external or internal.

14.3.1 External toxic effects Stadler et al. [50] depicted that due to triboelectric forces, charged nanostructured alumina (NSA) particles adhered to the insect’s cuticle and caused the wax layer to be absorbed by surface area phenomena, which stimulates the insect to become dehydrated. Nanoalumina dust synthesized by the glycine-nitrate combustion process showed greater effectiveness and factors like size, surface area, and morphology of the particles impact the insecticidal’s efficacy [51]. When nanoemulsion of Pimpinella anisum was applied to Tribolium castaneum, the cuticle displayed severe damage, including changes in pigmentation, muscular degeneration, thickness change, and epidermal necrosis, as well as cellular debris and a loss of the ability to distinguish between the endocuticle and exocuticle [52]. Carbon-silver nanohybrid blackened the heads and guts of An. stephensi and Cx. quinquefasciatus and damaged the cuticle membrane and cell organization [53]. AgNPs made from Pedalium murex seed extract showed cuticular damage and hair loss on the antenna, head, and abdomen in Ae. aegypti larvae [54].

14.3.2 Internal toxicity After the entry of bioactive NPs into the insect’s body, they interfere with various biological pathways by reducing protein synthesis, altering the activity of some receptors, producing reactive oxygen species (ROS), and regulating some gene activity. Various types of nanoparticles and their activity in the insect’s body are depicted in Tab. 14.1.

14.4 Imminent hurdles on field application of nanoinsecticides and future challenges Nanotechnology is a developing field with significant implications for the economy, society, and the environment. As a result, it elicits both favorable and negative responses. One of the biggest problems for NP application in agriculture is phytotoxicity. The phytotoxicity of NPs to plants is determined by the properties of the NP, exposure

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Tab. 14.1: Action mechanism of nanoparticles in the insect’s body. Name of nanoparticle

Type of Target species nanoparticle

Mechanism of action

Gold nanoparticles

Synthetic

Drosophila melanogaster

Inactivation of copper-dependent enzymes, tyrosinase, and Cu-Zn superoxide dismutase, cuticular demelanization

[]

Drosophila melanogaster

Inappropriate pigmentation and reduction in locomotor ability in the larval stage

[]

Drosophila melanogaster

Reduced survival, longevity, impaired development of ovary, and egg-laying capability

[]

Drosophila melanogaster

Decrease in the viability and delay in development, decrease in the number of germline stem cells (GSCs), and increase in ROS’ species level in testes

[]

Drosophila melanogaster

Shortening of life span, accumulation of reactive oxygen species (ROS), and activation of Nrf-dependent antioxidant pathway

[]

Chironomus riparius

Downregulation of the ribosomal protein gene (CrL), Upregulation of the Balbiani ring protein gene (CrBR.), and gonadotrophinreleasing hormone gene (CrGnRH)mediated signal transduction pathway in the larval stage

[]

Chironomus riparius

Up or downregulation of the ecdysteroid receptor (EcR) expression, impairment in development, growth, moulting of larva

[]

Blattella germanica

Decrease in ootheca viability, hatching of nymphs, effect on postembryonic development

[]

Drosophila melanogaster

Reduction in life span and fertility, presence of DNA fragmentation, overexpression of the stress proteins

[]

Blaberus discoidalis

Affects the nervous system, neural communication, and locomotion

[]

Silver nanoparticles

Reference

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Tab. 14.1 (continued) Name of nanoparticle

Type of Target species nanoparticle

Mechanism of action

Silver nanoparticles synthesized from aqueous extract of Cassia fistula fruit pulp

Plant-derived Aedes albopictus and Culex pipiens pallens

Reduction of the activity of two important marker enzymes: Acetylcholinesterase and α- and βcarboxylesterase

Reference []

Silver nanoparticles synthesized from leaf extract of Ficus religiosa

Helicoverpa armigera Inhibition of gut protease activity

[]

Hedychium coronariumsynthesized silver nanoparticles

Aedes aegypti

Damage of midgut epithelial cells

[]

Silver nanoparticles synthesized using Aquilaria sinensis and Pogostemon cablin essential oils

Aedes albopictus

Effected the midgut epithelial cells and brush border

[]

Polyethylene glycol nanoparticles of Citrus peel essential oil

Tuta absoluta

Reduced larval mortality and induced egg hatching

[]

Lobelia leschenaultiana encapsulated ZnO nanoparticles

Aedes aegypti

Rupture of the midgut, accumulation of nanoparticles in thorax and abdomen, loss of antenna lateral hairs, and anal gills

[]

Fabricated gold nanoparticles using latex of Jatropha curcas

Aedes aegypti

Inhibition of catalytic potential of trypsin

[]

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period, concentrations, and the plant species and their ages. Copper nanoparticles were found to be poisonous to two crop species, mung bean (Phaseolus radiatus) and wheat (Triticum aestivum), as evidenced by the lower growth rate of seedlings [55]. Yang and Watts [56] evaluated the phytotoxicity of nanoscale alumina (nano-Al2O3) and reported that uncoated alumina particles hindered root elongation of corn, cucumber, soybean, cabbage, and carrot. Lin and Xing [57] revealed that seed germination and root growth of radish, rape, ryegrass, lettuce, corn, and cucumber were greatly affected by nanomaterials of multi-walled carbon nanotube (MWCNT), Al, Al2O3, Zn, and ZnO. A study found TiO2 NPs inhibit leaf development and transpiration in Zea mays seedlings, mostly because of reduced hydraulic conductivities [58]. These works drew the attention of scientists who argue that NPs can harm plants. Studies also demonstrated that some NPs of fullerene, carbon nanotubes, and metal oxides are harmful to non-target organisms. The microcalorimetric analysis of carboxymethyl-β-cyclodextrin-Fe3O4 magnetic nanoparticles-Diuron (CM-β-CD-MNPsDiuron), a nanopesticide, confirmed toxicity against microorganisms in the soil [59]. After ingesting soil, AgNPs connected to soil colloids appeared to be absorbed by earthworms and moved to the gut epithelium, where they impose significant consequences and biological complexities, when used in large quantities [60]. Nanomaterials are applied to the aquatic environment to eradicate immature stages of terrestrial insect vectors (such as mosquitoes), which may pose a serious hazard to aquatic life that is not the intended target. Oxidative damage in the neural tissue of fish as a result of uncoated fullerene exposure indicates a potential deleterious influence of nanomaterials on the health of aquatic organisms [61]. Emulsion-based formulations are also dangerous because surfactants, a crucial component, are hazardous to aquatic ecosystems [62]. Although nanoformulations have many advantages, the aforementioned issues suggest that sometimes these may be ecotoxic too. Coordinated measures, supported by scientific evidence, are necessary to guarantee their safety, prior to field application. Even, though there are intermittent findings of efficient nanopesticides and assessments of their toxicity on non-target species, yet, a more thorough investigation of the ecosystem’s trophic levels is necessary.

14.5 Conclusion Insect pests and vectors have become a threatening issue almost throughout the world and require instantaneous and utmost attention [1, 2, 63, 64]. Formulation of an effective management strategy with area-wise systematic information on those insects is essential [65, 66]. Phytochemicals from different parts of plants are already preferred over conventional synthetic insecticides in vector and pest control strategies

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because of several advantages [67, 68]. But the use of these phytochemicals is not up to the mark as it should be, probably because of their early degradable nature and scanty information in field trials [69]. In these scenarios, nanotechnology can become a problem-solving tool. Bio-nanomaterials have a significant function to perform in the insect vector and pest management in many countries as they transform from chemical-based agriculture to green agriculture. Nano-based insecticides have the potential to outperform traditional insecticides, simultaneously lowering the burden of pesticides in the environment. Though some reports are threatening the application of nanopesticides, there is little evidence that green-fabricated nanoparticles are highly hazardous. Most of them are target-specific and safe for non-target beneficial organisms. Firdaus et al. [70] showed that nanotreatment prevents the movement of pesticides in earthworms after ingestion. Majority of the pesticide residues were detected in the earthworm tissue in non-nano treatments, but it was primarily found in the gut in nano-treatments. AgNPs made from Pergularia daemia, Catharanthus roseus, and Plumeria rubra did not express any toxicity to fish Poecilia reticulata [71, 72].

14.6 Future scope Different nanoformulation techniques involved in the formation and delivery of pesticides are effective and creative pest control technologies that address the existing challenges of pollution, protection of the environment, and unsustainable land reuse practices. The development of nanoencapsulation can improve the targeted administration of pesticides through controlled-release systems while decreasing undesirable problems like an early breakdown of active ingredients, poor water solubility, etc. The creation of new insect-resistance strains could be assisted by gene transfer via nanoparticles. So far, nanotechnologies are not applied against a large number of pests and vectors, including non-mosquito vectors. It can provide green, sustainable, environmentfriendly, and target-specific tools for insect pest and vector management.

List of abbreviations and nomenclature DDT LDH APG C12E3 DLS TEM NP AgNP

Dichloro-diphenyl trichloroacetic acid Layered double hydroxide Alkyl polyglycoside Polyoxyethylene 3-lauryl ether Dynamic light scattering Transmission electron microscopy Nanoparticle Silver nanoparticle

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AuNP PO-AgNP PO-AuNP Al2O3NP PdNP ZnONP TiO2NP NiNP CuNP MgONP NSA ROS MWCNT CM-β-CD-MNP

Gold nanoparticle Pungam oil-based silver nanoparticle Pungam oil-based gold nanoparticle Aluminum oxide nanoparticle Palladium nanoparticle Zinc oxide nanoparticle Titanium dioxide nanoparticle Nickel nanoparticle Copper nanoparticle Magnesium oxide nanoparticle Nanostructured alumina Reactive oxygen species Multi-walled carbon nanotube Carboxymethyl-β-cyclodextrin-Fe3O4 magnetic nanoparticle

Conflict of interests: None.

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Patil CD, Borase HP, Patil SV, Salunkhe RB, Salunke BK. Larvicidal activity of silver nanoparticles synthesized using Pergularia daemia plant latex against Aedes aegypti and Anopheles stephensi and nontarget fish Poecillia reticulata. Parasitol Res 2012, 111(2), 555–562. Patil CD, Patil SV, Borase HP, Salunke BK, Salunkhe RB. Larvicidal activity of silver nanoparticles synthesized using Plumeria rubra plant latex against Aedes aegypti and Anopheles stephensi. Parasitol Res 2012, 110(5), 1815–1822. Armstrong N, Ramamoorthy M, Lyon D, Jones K, Duttaroy A. Mechanism of silver nanoparticles action on insect pigmentation reveals intervention of copper homeostasis. PLoS One 2013, 8(1), e53186. Ávalos A, Haza AI, Drosopoulou E, Mavragani-Tsipidou P, Morales P. In vivo genotoxicity assessment of silver nanoparticles of different sizes by the Somatic Mutation and Recombination Test (SMART) on Drosophila. Food Chem Toxicol 2015, 85, 114–119. Raj A, Shah P, Agrawal N. Dose-dependent effect of silver nanoparticles (AgNPs) on fertility and survival of Drosophila: An in-vivo study. PLoS One 2017, 12(5), e0178051. Ong C, Lee QY, Cai Y, et al. Silver nanoparticles disrupt germline stem cell maintenance in the Drosophila testis. Sci Rep 2016, 6(1), 1–10. Mao BH, Chen ZY, Wang YJ, Yan SJ. Silver nanoparticles have lethal and sublethal adverse effects on development and longevity by inducing ROS-mediated stress responses. Sci Rep 2018, 8(1), 1–16. Nair PM, Park SY, Lee SW, Choi J. Differential expression of ribosomal protein gene, gonadotrophin releasing hormone gene and Balbiani ring protein gene in silver nanoparticles exposed Chironomus riparius. Aquat Toxicol 2011, 101(1), 31–37. Nair PM, Choi J. Modulation in the mRNA expression of ecdysone receptor gene in aquatic midge, Chironomus riparius upon exposure to nonylphenol and silver nanoparticles. Environ Toxicol Pharmacol 2012, 33(1), 98–106. Small T, Ochoa-Zapater MA, Gallello G, et al. Gold-nanoparticles ingestion disrupts reproduction and development in the German cockroach. Sci Total Environ 2016, 565, 882–888. Pompa PP, Vecchio G, Galeone A, et al. In vivo toxicity assessment of gold nanoparticles in Drosophila melanogaster. Nano Res 2011, 4(4), 405–413. Rocha A, Zhou Y, Kundu S, González JM, Bradleigh Vinson S, Liang H. In vivo observation of gold nanoparticles in the central nervous system of Blaberus discoidalis. J Nanobiotechnol 2011, 9(1), 1–9. Fouad H, Hongjie L, Hosni D, et al. Controlling Aedes albopictus and Culex pipiens pallens using silver nanoparticles synthesized from aqueous extract of Cassia fistula fruit pulp and its mode of action. Artif Cells Nanomed Biotechnol 2018, 46(3), 558–567. Kantrao S, Ravindra MA, Akbar SM, Jayanthi PK, Venkataraman A. Effect of biosynthesized Silver nanoparticles on growth and development of Helicoverpa armigera (Lepidoptera: Noctuidae): Interaction with midgut protease. J Asia Pac Entomol 2017, 20(2), 583–589. Kalimuthu K, Panneerselvam C, Chou C, et al. Control of dengue and Zika virus vector Aedes aegypti using the predatory copepod Megacyclops formosanus: Synergy with Hedychium coronariumsynthesized silver nanoparticles and related histological changes in targeted mosquitoes. Process Saf Environ Prot 2017, 109, 82–96. Ga’al H, Fouad H, Mao G, Tian J, Jianchu M. Larvicidal and pupicidal evaluation of silver nanoparticles synthesized using Aquilaria sinensis and Pogostemon cablin essential oils against dengue and zika viruses vector Aedes albopictus mosquito and its histopathological analysis. Artif Cells Nanomed Biotechnol 2018, 46(6), 1171–1179. Campolo O, Cherif A, Ricupero M, et al. Citrus peel essential oil nanoformulations to control the tomato borer, Tuta absoluta: Chemical properties and biological activity. Sci Rep 2017, 7(1), 13036. Banumathi B, Vaseeharan B, Ishwarya R, et al. Toxicity of herbal extracts used in ethno-veterinary medicine and green-encapsulated ZnO nanoparticles against Aedes aegypti and microbial pathogens. Parasitol Res 2017, 116, 1637–1651.

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M. Thirukumaran✶, K. Senthilkumar, R. Selvabharathi

15 Effect of carbon nanotubes, aluminum hydroxide, and zinc borate on the mechanical and fire properties of epoxy nanocomposite Abstract: This chapter discusses the fabrication of nanocomposites composed of carbon nanotubes (CNT), aluminum hydroxide (Al(OH)2), and zinc borate (2ZnO.3B2O3.3.5H2O) with enhanced mechanical and fire characteristics. Using the melt condensation process, 2.5%, 5%, and 7.5% carbon nanotubes, aluminum hydroxide, and zinc borate were added to the 95% to 85% epoxy resin matrix. To understand the produced nanocomposite’s flammability property, a JIS UL-94 test is conducted. The yield point of 36.5 MPa was reached by the carbon nanotubes/epoxy samples; they showed increased tensile strength; and the carbon nanotubes composite also produced ductility cracks. Carbon nanotubes with a concentration of 7.5% and epoxy with 90% achieved a higher Shore-D hardness value of 119. The results of the three-point bending tests made it clearly evident that carbon nanotubes made of composite materials had the highest flexural strength and modulus. In addition, it was discovered that the burning property increased with the concentration of nanofillers. For epoxy with 10% zinc borate, flame retardant property was shown to be effective. Keywords: Nanocomposite, mechanical properties, flame retardant, SEM

15.1 Introduction Nanocomposite materials outperformed traditional materials in terms of strength-toweight ratio. In order to create a nanocomposite material with better mechanical characteristics, the matrix and nanofillers must have a high surface-to-volume ratio. Thermosetting polymer matrices are employed as matrix materials for polymeric composites because they are more stiff and durable than thermoplastic polymers [1–3]. Nanocompo-

✶ Corresponding author: M. Thirukumaran, Department of Mechanical Engineering, P.S.R. Engineering College, Sivakasi 626140, Tamil Nadu, India, e-mail: [email protected]@gmail.com K. Senthilkumar, Department of Mechanical Engineering, PSG Institute of Technology and Applied Research, Coimbatore 641062, Tamil Nadu, India R. Selvabharathi, Department of Mechanical Engineering, AAA College of Engineering and Technology, Sivakasi 626123, Tamil Nadu, India

https://doi.org/10.1515/9783111137902-015

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sites are made from cellulose, starch, chitin, and chitosan as fillers, and epoxy and polyester as resins [4]. Epoxy resins are used to create high-performance fiber-reinforced composite materials, such as lightweight structural panels and parts, but they are flammable when used in flame-resistant applications. Epoxy is used in electrical devices, adhesives, and structural laminates. Increasing its flame resistance is essential for many industries. Over the last ten years, the desired properties of the epoxy matrix have been achieved by combining it with carbon nanotubes, mineral silicates, hard oxides, carbides, graphene, and ceramics [5]. Halogen-based flame retardants remain harmful to the environment despite improvements in the flame resistance ability of epoxy composites [6]. High concentrations of flame retardants can lower the mechanical properties and heat release rate of epoxy composites, leading to thermo-oxidative and structural degradation, which can have serious consequences for vehicle/building occupants/fire fighters [7]. Polymer composites, which are used as structural load-bearing components, are expected to decrease in strength at temperatures close to the glass transition temperature, causing them to deform and collapse, which can lead to fire and burns. Polymer composites must improve their thermo-mechanical characteristics and flammability resistance to withstand fire exposure [8]. Halogen-free technologies focus on flame retardants containing phosphorus, nitrogen, silicone, boron, zinc, iron, and aluminum [9]. Polymer composites can be improved with nanofillers by increasing their flame propagation speed, thermal stability, and smoke release amounts as well as their fire resistance. The structure and chemical composition of the nanofillers have an impact on the fire retardant capability of nanocomposites, which can change how they respond to flame [10]. Fire-retardant metallic nanoparticles are used in polymer matrices that explore various fire-retardant properties. Nanocomposites can self-extinguish by releasing water molecules in the presence of fire, creating an endothermic process [11]. Magnesium hydroxide and aluminum trihydroxide are non-halogen fire retardants that can be added to polymer composites to reduce the limiting oxygen index. Polymer surfaces generate a barrier to reduce heat flow and increase fire retardance, which can delay ignition and spread fire through char formation. Metal hydroxide FRs decompose at high temperatures, leading to the production of water, which dilutes flammable gases, lessens oxygen influence, and slows flame propagation. Antimony oxide alternatives have been identified due to the need for less tinting strength, smoke, and cost/performance balance, as well as potential toxicity [12, 13]. Study by Riyazuddin et al. [14] on the additive effects of alumina trihydride, zinc borate, and melamine on epoxy resin. He developed the two flame-retardant systems, 20% alumina trihydride/ zinc borate and 20% alumina trihydride /melamine mixtures, to produce the epoxy resins. Using the combined effect of alumina trihydride and melamine, he discovered outstanding flame retardance. He also discovered that despite having great thermal stability at 600 °C, this composite had an alumina trihydride that manifested as a higher limiting oxygen index and a reduction in the peak heat release rate. According to Iqbal et al. [15], alumina trihydride has better thermal stability and flameretardant properties. He reported that during the condensation phase, the weight loss

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of the composite decreased from 62% to 15% while the 15%, alumina trihydride maintained the glass transition temperature. Moreover, the composite’s Young’s modulus and ultimate tensile strength showed enhanced values. In comparison to 175 s for pure epoxy resin and 180 s for modified epoxy resins including phosphorus, 15% alumina trihydride-reinforced modified epoxy resin reaches 283 s in UL-94 testing (V-1 grade). As a result of alumina trihydride’s ability to suppress smoke, an aluminum oxide layer was created on the surface of the remaining carbon. ATH was intended to enhance the epoxy’s activation energy and increase flame retardancy through degradation. However, as alumina trihydride increases, mechanical properties deteriorate [16]. Zinc borate (2ZnO.3B2O3.3.5H2O) is suitable for polymers with high processing temperatures. Zinc borate retains translucency due to its low specific gravity, toxicity, and refractive index. Zinc borate is a low-cost substitute for antimony oxide in polyvinyl chloride goods and an afterglow suppressor in mining belts [17]. Carbon nanotubes are a promising substitute for flame retardants in polymers, such as polypropylene, polyester, polylactic acid, lignocellulose, and epoxy resin. Carbon nanotubes can be used to alter the fire behavior of polymer composites. Carbon nanotubes have a long and large aspect ratio, enabling them to build a shielding network to reduce heat release and weight loss during combustion. Carbon nanotubes add a low flame spread rate, smoke suppression, and anti-dripping capabilities to polymer composites, improving their fire resistance [18, 19]. Rahatekar et al. [20] found that epoxy/multiwall carbon nanotubes composites had a 50% lower MLR than plain epoxy. Zhang et al. [21] synthesized flame retardant carbon nanotubes to make epoxy more flammable. Also, he experimented with adding silicon and 9,10-Dihydro-9,10-Oxa-10-Phosphaphenanthrene-10-Oxide (DOPO) additives at a constant loading rate of 8%. After burning, the transmission electron microscopy revealed well-dispersed carbon nanotubes in addition to high 31% limiting oxygen index value and consistent char-layer surfaces. A flame-retardant mechanism based on carbon nanotubes, silicon particles, and 9,10-Dihydro-9,10-Oxa-10-Phosphaphenanthrene-10Oxide structures is thought to be responsible for these effects. This chapter discusses the fabrication of nanocomposites composed of carbon nanotubes (CNT), aluminum hydroxide (Al(OH)2), and zinc borate (2ZnO.3B2O3.3.5H2O) with enhanced mechanical and fire characteristics. From the literature survey, the nanofiller content (2.5–7.5 wt%) leads the augment of mechanical and physical properties of the composite [22, 23]. So, using the melt condensation process, 2.5%, 5%, and 7.5% carbon nanotubes [24], aluminum hydroxide [25], and zinc borate [26] were added to the 97.5% to 92.5% epoxy resin matrix. To comprehend the produced nanocomposite’s flammability property, a JIS UL-94 test is conducted.

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15.2 Materials and methods For the current research, epoxy resin was acquired from Araldite in Chennai, India, while single-walled carbon nanotubes (diameter of 20–30 nm and a purity of more than 97%), aluminum hydroxide (diameter of 20–30 nm and a purity of more than 93%), and 2ZnO.3B2O3.3.5H2O (average particle size of 20–30 nm and a purity of more than 93%) were purchased from Sigma Aldrich in Chennai, India. Figure 15.1 illustrates the setup of an experiment to develop a nanocomposite. In order to improve the nanocomposite’s microstructure, mechanical, and thermal properties, many flame retardant fillers were added to the epoxy resin. The improved bonding structure was created using epoxy resin and a blended hardener in the ratio of 90:10 (As per manufacturer), employing the nanoparticles used for the manufacture of nanocomposites. Then, the 97.5% to 92.5% epoxy, 7.5% to 2.5% carbon nanotubes content, 7.5% to 2.5% aluminum hydroxide content, and 7.5% to 2.5% 2ZnO.3B2O3.3.5H2O content were prepared in a separate plate that was stirred for 3 to 4 min at a rotation speed of 500 rpm using stirred machinery, whereas hand lay-up methods used three different ratios as shown in Tab. 15.1. At a temperature of 25 °C, the composite plate with dimensions of 200 × 100 × 3 mm was created.

Fig. 15.1: Setup of experiment to develop a nanocomposite.

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Tab. 15.1: Nanocomposite composition. Specimen code

Composition description

1.

.% epoxy and .% carbon nanotubes

2.

% epoxy and % carbon nanotubes

3.

.% epoxy and .% carbon nanotubes

4.

.% epoxy and .% aluminum hydroxide

5.

% epoxy and % aluminum hydroxide

6.

.% epoxy and .% aluminum hydroxide

7.

.% epoxy and .% zinc borate

8.

% epoxy and % zinc borate

9.

.% epoxy and .% zinc borate

15.3 Characterization 15.3.1 Mechanical properties According to the ASTM D638 standard, the tensile tests were performed using a Universal Testing Machine (UTM) from Instron Instrument at a crosshead speed of 50 mm/min and gauge length of 50 mm. The same UTM was used for flexural testing in accordance with the ASTM D 790 standard. The test was conducted using a crosshead speed of 10 mm/min and a span length of 50 mm. Using an impact tester (Deepak Polyplast, India), the composite specimen’s charpy impact strength was assessed in accordance with ASTM D256. A Shore’D hardness tester was used to determine the composite’s hardness in accordance with the ASTM D2240 standard.

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15.3.2 Flammability properties The UL-94 horizontal burning test evaluates flammability properties such as burning rate, dripping characteristics, and combustion of the nanocomposite in accordance with the ASTM D635. A 20 mm blue flame was applied to one end of the horizontally clamped specimen for 30 s during the horizontal burning test, and it was then removed when fire started. Next, the length of time it took for the flame to travel 25 mm from the front end to the second mark from the first mark was noted.

15.3.3 Thermal properties According to the ASTM D 6370–99 standard, the thermal stability of the nanocomposites was investigated using TGA (Pyris 7, Perkin Elmer, USA). To investigate the thermal stability of the composite materials, samples of 10 mg in powder form were heated at a rate of 10 °C/min from 30 °C to 600 °C. With the increase in temperature, it helps to assess the sample mass loss rate.

15.3.4 Morphological analysis We examined the microstructure of carbon nanotubes, aluminum hydroxide, and zinc borate /epoxy composites using a scanning electron microscope (SEM, JEOL model JSM6400). Three different types of composite materials were created of dimensions 10 × 10 × 3 mm thickness for the microstructure investigations. After the UL-94 flammability test, this was also used to observe the char shape of the burned sample surface.

15.4 Result and discussion 15.4.1 Microstructure analysis By using electron microscopy, the morphology of carbon nanotubes, aluminum hydroxide, and zinc borate fillers with epoxy was examined. Figure 15.2 (a–c) clearly indicates that the outer surface layers of these flame retardants were devoid of small holes and cracks, and they had good boundary layer separation and noticeably improved interior surfaces. In contrast, carbon nanotubes particles had strong boundary layer separation [27]. Compared to aluminum hydroxide and zinc borate nanoparticles, carbon nanotubes nanoparticles are smaller and more homogeneous. Along with creating the microstructure’s secondary phase and stable grain boundaries, the

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carbon nanotubes also prevented the outer surface layer’s delamination and tiny fracture. After being combined with aluminum hydroxide and zinc borate, the epoxy nanocomposite materials have been produced in a variety of structures. With epoxy, nanoparticles, in the case of zinc borate, exhibit improved separation and a welldefined shape. The bonding strengths of zinc borate structures have remained constant; however, in contrast to other composition strengths, the outer surface strength of the 2.5% zinc borate 97.5% epoxy composite structure rapidly decreased. In the microstructure regions, the elongation ratio abruptly started to decrease [17]. Epoxy and aluminum hydroxide particles with polar surfaces interact well. The variations in these particles’ surface properties may provide an explanation for these events. As the inner surface layers of the recrystallization structure gradually decreased and the outer surface layer developed micro cracks, the bonding strength of the aluminum hydroxide was strengthened by employing 5% aluminum hydroxide 95%epoxy. Consequently, to create epoxy composites, carbon nanotubes, aluminum hydroxide, and zinc borate nanoparticles were employed. Furthermore, 2.5% of the carbon nanotubes, aluminum hydroxide, and zinc borate with epoxy composites formed fine boundary structures. The epoxy resin quickly disintegrated due to its higher binding strength of 5% to 7.5% compared to 2.5% [28].

Fig. 15.2: Microstructure image of (a) carbon nanotubes, (b) aluminum hydroxide, and (c) zinc borate nanocomposite.

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15.4.2 Mechanical properties The mechanical characteristics of carbon nanotubes, aluminum hydroxide, and zinc borate, as well as epoxy nanocomposites, are examined in this section. Tensile testing samples were made using epoxy resin at the dimensionally prescribed thickness of 125 × 3 mm to increase the elongation ratio. Tensile strength of 97.5% epoxy and 7.5% carbon nanotubes nanocomposite was 28.5 MPa, while that of 97.5% epoxy and 7.5% zinc borate was 17.4 MPa as shown in Fig. 15.3a, because, in comparison to aluminum hydroxide and zinc borate, the carbon nanotubes were combining with the epoxy resin to boost the bonding strength of the composite. In comparison to 2.5% and 5% carbon nanotubes samples, the bonding strength and yield point of 7.5% carbon nanotubes samples were 6.64% and 11.32%, respectively. This finding suggests that as the carbon nanotubes’ loading content was raised, the tensile strength increased as well. When the 2.5% aluminum hydroxide materials were compared to the 5% and 7.5% aluminum hydroxide composites, it was clear that the 2.5% aluminum hydroxide materials had a low aluminum hydroxide (97.5% epoxy, 2.5% aluminum hydroxide) material elongation ratio. At 23.5 MPa, the 97.5% epoxy and 2.5% aluminum hydroxide sample was obtained. The material’s tensile strength was dramatically reduced by 2.5% to 7.5% aluminum hydroxide. This finding showed that when the aluminum hydroxide’s loading content rose, the tensile strength declined. Agglomeration occurred at higher loading conditions, which affected the nanocomposite’s ability to elongate. Similar findings were seen with zinc borate nanocomposite [28]. This discovery demonstrated that tensile strength decreased as zinc borate’s loading concentration increased. A 92.5% epoxy 7.5% zinc borate sample’s tensile strength was 20.5 MPa, which is the critical strength at which zinc borate powder has been shown to maintain the integrity of a composite structure. The necessary bonding strength between aluminum hydroxide and zinc borate was not being formed, and this resulted in a dramatic drop in the nanocomposite’s elongation ratio. Figure 15.3b shows that the elongation of the nanocomposite was greatest when the carbon nanotubes were better reacted in epoxy. Three-point tests on a composite material with dimensions of 125 × 12.7 × 3 were performed to determine the flexural strength. While the flexural result of 95% epoxy 5% carbon nanotubes composite rose at 45.7 MPa, the flexural result of 97.5% epoxy 2.5% carbon nanotubes composite stretched at 40.3 MPa. However, at 50.5 MPa, the 15% carbon nanotubes components produced superior performance. Because the composite layers created a high crystallization structure, the bonding characteristics of the carbon nanotubes were adequately included. As a result of the carbon nanotube’s better load-bearing capacity when compared to aluminum hydroxide and zinc borate, the composite’s elongation was at its greatest. The 97.5% epoxy 2.5% aluminum hydroxide composition of the aluminum hydroxide nanocomposite was increased to 37 MPa. While epoxy only significantly improved the elongation ratio of the composite materials, aluminum hydroxide exhibited strong flexural characteristics. At 36.7 MPa, the zinc borate nanocomposite obtained a 97.5% epoxy 2.5%

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zinc borate flexural strength. A blinded structure was created in the composite while the 2.5% to 7.5% zinc borate powder was combined with the epoxy. Due to the agglomeration that occurred in the structure, the flexural strength of the aluminum hydroxide and zinc borate nanocomposite was somewhat reduced to about 5% to 7.5% of nanoparticles compared to the 2.5% of nanoparticles.

Fig. 15.3: Tensile strength (a) and flexural strength (b) of nanocomposite.

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Impact strength tests were performed on carbon nanotubes, aluminum hydroxide, and zinc borate and epoxy nanocomposites with dimensions of 65 × 13 × 3 mm in accordance with ASTM D256. Figure 15.4a clearly indicates that when the amount of nanofiller is increased, the impact strength of every filled nanocomposite increases. Similar results were obtained for carbon nanotubes composite, though tensile and bending strength results for aluminum hydroxide and zinc borate nanocomposite were slightly different. Impact strength measurements clearly showed an increase in the impact strength of 7.5% for carbon nanotubes at 66 J/m2 when compared to aluminum hydroxide and zinc borate nanomaterials. Impact strength was greatly boosted as a result of the carbon nanotubes composition’s higher hardness value. Figure 15.4b shows that 111D was the hardness value for 92.5% epoxy 7.5% carbon nanotubes nanocomposite materials. At the same time, the hardness values of the 2.5% carbon nanotubes, aluminum hydroxide, and zinc borate compositions increased steadily in comparison to the 2.5% composition. Because the epoxy created a strong link between the nanoparticles, the epoxy resin and nanomaterials helped to increase the nanocomposite’s hardness value. As a result, the samples of 2.5% to 7.5% carbon nanotubes, aluminum hydroxide, and zinc borate nanocomposite showed somewhat higher hardness values as well as a higher impact strength. Although the 2.5 to 5% aluminum hydroxide components helped to develop the crystal structure of the composite to some extent, the 7.5% aluminum hydroxide filled with 92.5% epoxy resin creates a hard nanocomposite. The aluminum hydroxide and zinc borate material’s impact strength was lower than that of the carbon nanotube’s materials because they were not stable during the microstructure process. At 35 J/m2, the impact strengths of 92.5% epoxy 7.5% aluminum hydroxide and hardness were attained, respectively. The 92.5% epoxy 7.5% zinc borate, on the other hand, attained impact strength at 30 J/m2 and hardness at the 85 D value. The 97.5% epoxy 2.5% zinc borate nanocomposite material achieved the highest hardness values overall, measuring 81 D. The impact strengths of the 2.5% zinc borate samples were quite weak, peaking at 13 J/m2.

15.4.3 Flammability properties Epoxy is more flame resistant when flame retardants such as carbon nanotubes, aluminum hydroxide, and zinc borate are present. The nanocomposite’s flame retardant performance had significantly improved. Zinc borate has the most effect on epoxy of all these flame retardants. With higher flame retardant fractions, flame retardant efficacy often improves. Therefore, a large volume fraction lowers the amount of combustible polymers that epoxy may use, which results in thicker and more even char layers. 7.5% has a substantially greater surface area per unit volume, a shorter reinforcement material distance, and a larger surface tension with the matrix material. It is confirmed that it performs better than 5% and 10%, which leads to a compact char layer. As shown in Tab. 15.2, adding 7.5% zinc borate causes the burning rate of epoxy

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Fig. 15.4: Impact strength (a) and hardness (b) of nanocomposite.

to rise from 0.5% to 9.7%, when compared to 7.5% aluminum hydroxide, and carbon nanotubes cause the burning rates of the composites to only reach 34.97 mm/min and 32.04 mm/min, respectively. The aluminum hydroxide and zinc borate’s flame retardant mechanisms of the compounds may account for this outcome. While zinc borate exhibits both a condensed phase and a gas phase mechanism, aluminum hydroxide

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and carbon nanotubes shield the composites via a condensed phase mechanism. Carbon nanotubes specifically grow to a pathogen retardant char layer, with a size of 20–30 times its initial size when the composite is subjected to a heat source. The thick char layers shield the composite by limiting the flow of mass and heat. Additionally, the expansion of carbon nanotubes may effectively absorb heat, cooling the composite material [29]. The larger surface area per unit mass of carbon nanotubes makes the van der Waal forces. By releasing water and the thermally stable aluminum oxide onto the composite’s surface during the endothermic dehydration of aluminum hydroxide, the epoxy matrix beneath is shielded. With respect to zinc borate, its oxidation in the condensed phase yields zinc oxide, which can react with water from the polymer’s breakdown to make boric acid, coating the composite’s surface. Zinc borate functions as a flame retardant in the vapor phase via a radical trapping mechanism by generating PO-free radicals during combustion, which can extinguish H and OH of the flame [17]. After the burning test, the composite surface develops an insulating char layer of expanded carbon nanotubes. These char layers can successfully shield the composite material from the flame, but high temperatures can cause them to oxidize. Poorly distributed flame retardants in a polymer provide uneven char coverage, which has an impact on the flame retardance and mechanical characteristics of the resultant composites. Tab. 15.2: Horizontal burning rate of nanocomposite. Sample

Burning rate (mm/min)

Dripping of burning specimen

Combustion up to holding clamp

.% epoxy .% carbon nanotubes

. No

No

% epoxy % carbon nanotubes

. No

No

.% epoxy .% carbon nanotubes

. No

No

.% epoxy .% aluminum hydroxide

. No

No

% epoxy % aluminum hydroxide

. No

No

.% epoxy .% aluminum hydroxide

. No

No

.% epoxy .% zinc borate

. No

No

% epoxy % zinc borate

. No

No

.% epoxy .% zinc borate

. No

No

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15.4.4 Thermogravimetric analysis In comparison to other polymers, the 7.5% carbon nanotubes/epoxy nanocomposite’s TGA measurement demonstrates the polymer’s exceptional mass-sustenance ability. Figure 15.5 shows that at 171.37 °C, the carbon nanotubes/epoxy nanocomposite started to lose weight. Even though the weight loss is ongoing at a range of temperatures, it only increases gradually as the temperature rises from 293.83 °C to 390.60 °C, showing the polymer’s capacity to withstand the high temperature without an abrupt mass loss. In comparison to the weight loss at lower temperatures, weight loss at the higher temperature of 664.19 °C is 7.235%. The nanocomposite retains just a residual weight of 6.39%, practically losing its whole weight.

Fig. 15.5: TGA curve for 7.5% carbon nanotubes/epoxy composite.

Figure 15.6 shows that at many different temperature ranges, weight loss is seen; however, it is most pronounced at temperatures between 314 °C and 382.91 °C. The flame retardant polymer’s nature has been changed by 7.5% aluminum hydroxide/epoxy, causing it to lose weight when heated. Even if mass loss happens at lower temperatures, the rate of loss is seen to be extremely low, and it has also demonstrated enhanced resistance to weight loss by reaching a final residual mass of 4.986% at a very high temperature of 853.24 °C. It is discovered that the whole residual weight percentage has significantly increased to 25.07%.

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Fig. 15.6: TGA curve for 7.5% aluminum hydroxide/epoxy composite.

Figure 15.7. shows that the weight loss of 7.5% zinc borate/epoxy starts at 63.63 °C and occurs at temperatures of 159.58 °C, 290.82 °C, 338.78 °C, 385.78 °C, and 385.11 °C, with a weight loss of up to 39.50%. The polymer is then seen to have a significant weight percentage loss at 465.63 °C and 624 °C up to 33.27 °C. But at 900 °C, the ultimate residual weight percentage is found to be 27.17%, which is not found in any other sample (carbon nanotubes and aluminum hydroxide). As a result, zinc borate is found to have stronger resistance to weight loss at higher temperatures (900 °C).

15.5 Conclusion In this chapter, the mechanical and thermal characteristics of nanofiller-reinforced epoxy nanocomposites were discussed. The charring ability of the epoxy composites as well as their mechanical and thermal stability are improved by adding fillers that are evenly scattered throughout the epoxy matrix. The mechanical properties indicated that the carbon nanotube structures were the most effective for the reaction. The 97.5% EP 7.5% carbon nanotubes composite had the highest elongation in the tensile test at 28.5 MPa, the highest flexural strength at 50.5 MPa, the highest impact strength at 66 J/m2, and the highest hardness value at 111 D. The thermal stability of the epoxy resin was improved by the addition of zinc borate. But carbon nanotubes/

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Fig. 15.7: TGA curve for 7.5% zinc borate/epoxy composite.

epoxy composites show a different pattern. The large surface area of the carbon nanotubes, their uniform dispersion in the epoxy matrix, and their strong interfacial binding are claimed to inhibit the mobility of the polymer chains, resulting in a lengthier relaxation period and, thus, a reduction in blazing characteristics. Because the segments of the polymer chain that are close to the nanofiller surface should have reduced mobility, the flaming characteristics of the zinc borate /epoxy nanocomposites likewise increase with increasing zinc borate concentration. Given the enormous range of polymer matrices, it has been established that the flammability of polymeric materials is a convolution for which there is no one-size-fits-all solution. Polymer additives that are most promising for creating high-strength materials that are fire-resistant and secure. Nanocomposite applications may be suggested for industries like covering and packaging, where load bearing and thermal insulation are not major concerns.

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Anjali Awasthi, Ashish Kapoor, Soma Banerjee✶

16 Recent advancements in polymer nanocomposites-based adsorbents for chromium removal Abstract: Chromium is a toxic heavy metal commonly found in industrial effluents. It remains a serious cause of environmental and health hazards in recent days. Adsorption is a very effective method of treatment for the removal of chromium from wastewater. Polymer nanocomposite-based adsorbents have gained increasing attention over time due to their unique physico-chemical properties and ease of functionalization. This chapter outlines the recent progress in polymer nanocomposite-based adsorbents for chromium decontamination from aqueous environments. Specific focus is given to the design and synthesis of various polymer nanocomposites, their adsorption characteristics, and the underlying mechanisms of chromium adsorption. Insights are provided into functionalization strategies that can not only increase the uptake of chromium but also improve mechanical integrity and thereby enhance adsorbent recyclability. A critical evaluation is made using key figures of merit, including adsorption capacity and chromium removal efficiency. The equilibrium and kinetic behavior of these systems are discussed. Major factors influencing the adsorption process are examined. Finally, the future perspective is discussed to identify subsequent research initiatives that need to be undertaken to overcome the existing challenges in nanomaterial-based chromium remediation to realize real-time, largescale industrial applications. Keywords: Chromium removal, polymer nanocomposite, adsorption, functionalization, heavy metal

16.1 Introduction Chromium is white silvery transition metal with atomic mass of 52.996 g/mol and an atomic number of 24. Chromium is caught up in human lipid and protein metabolism naturally at low concentrations; therefore, only very little amounts are required for

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Corresponding author: Soma Banerjee, Department of Plastic Technology, School of Chemical Technology, Harcourt Butler Technical University, Kanpur 208002, Uttar Pradesh, India, e-mail: [email protected] Anjali Awasthi, Ashish Kapoor, Department of Chemical Engineering, School of Chemical Technology, Harcourt Butler Technical University, Kanpur 208002, Uttar Pradesh, India https://doi.org/10.1515/9783111137902-016

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typical human life processes. The majority of the daily chromium intake comes from foods such as grains, vegetables, fruits, shellfish, potatoes, egg yolks, and mushrooms. Furthermore, low to moderate levels of chromium can be found in other potential sources such as nutritional and type II antidiabetic medicines [1]. Further, there are many industrial uses for compounds containing chromium, including the creation of plating, pigments, anticorrosive coatings, metal polishing, cement, and wood preservatives. Spent process streams and effluents from these industries become the pathways for chromium to enter the ecosystem and pose risks to public health and environment. Chromium toxicity is one of the most significant sources of pollution from tannery effluents [2]. Chromium is also found in considerably higher amounts in industrial operations that can pollute the air and water. There are nine distinct valence states of chromium, spanning from − 2 to + 6. Only the hexavalent [Cr (VI)] and trivalent [Cr (III)] forms of chromium are of primary environmental concern due to the fact that they are the most oxidized forms that are stable in the environment. Trivalent form [Cr(H2O)6]3+, [(H2O)5Cr(OH)]2+, Cr(OH)3), which in alkaline circumstances is more stable, when used as a supplement, remains less harmful. Second hexavalent forms, Cr2O72−, H2CrO4, CrO42−, and HCrO4− are more stable in acidic circumstances and have strong oxidant, carcinogenic, and genotoxic properties. Hexavalent chromium is also very harmful to animals due to the possible generation of reactive oxygen species in cells; hence the presence of chromium in industrial effluents has become a major problem worldwide. In contrast, the trivalent state of chromium is substantially less harmful and also acts as an essential element in trace amounts. The pH of the solution affects the existence of two chromium forms: chromate and dichromate. While these two divalent oxyanions are highly water soluble and are little absorbed by soil and organic matter, they float in groundwater. Because of their exceedingly poisonous, mutagenic, carcinogenic, and teratogenic nature, both chromate anions pose immediate and long-term health concerns in animals and humans. Unlike Cr (VI), Cr (III) species are mostly oxides, hydroxides, and sulphates, which are less mobile, less water soluble, 100 times less poisonous, and 1,000 times less mutagenic [3]. The LD50 limit of Cr(III) trivalent is 185–615 mg/kg and that of Cr(VI) hexavalent is 20–250 mg/kg [1]. Cr(VI) is also a strong dermal irritant that can be discharged from fabrics when clothing comes in direct contact with a person’s skin; chromate-based dyestuffs may be highly dangerous to human health [4]. Chromium removal from wastewater has recently been accomplished using a variety of biological, chemical, and physical treatment techniques [5, 6]. The crucial aspects in selecting an appropriate method include process efficiency, costs, energy consumption, and formation of byproducts. Adsorption has drawn a lot of attention recently in wastewater treatment due to their easy operation mechanism, low cost, minimum quantity of adsorbent materials, and simplicity of recycling [7, 8].

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16.2 Preparation of polymer nanocomposites Polymer nanocomposites (PNCs) can be synthesized in a number of ways, mainly under the broad class of in situ synthesis and direct compounding [9–13]. The synthesis methods are wide and have their own advantages and disadvantages. They are employed on the basis of requirements as per application areas. PNCs can be synthesized by in situ techniques with added functional groups to be utilized in waste water treatment enormously due to the homogeneous distribution of nanomaterials inside the matrix polymer [14, 15]. The introduction of functionalities imparts compatibility with the constituents in the composites due to the provision of strong interfacial interaction. The in situ synthesis method is broadly classified as in situ particle generation, in situ polymer formation, and simultaneous in situ particle and polymer generation. In the in situ polymerization method, the monomer with initiator is allowed to polymerize in the presence of a nanomaterial, say clay. The nanomaterial gets intermingled with the growing polymer chains with the progress of polymerization, leading to the development of PNCs. On the other hand, for in situ particle generation, the nanoparticles are synthesized from the metal precursor of the nanomaterials inside a polymer solution. With the progressive generation of the nanoparticles inside the polymeric phase, the nanocomposite eventually develops. In situ simultaneous development of both inorganic nanomaterials and polymer matrix is an area of interest recently [16]. In the very first step of preparation of PNCs, silver dedocacanoate is synthesized as silver precursor, followed by adding it to 3,3,5-trimethylcyclohexylmethacrylate monomer, which in the subsequent step, under proper reaction condition, is converted simultaneously to PNC. The blending of the nanomaterial with the polymer matrix is considered to be the simplest method of preparation of PNCs. Direct compounding with the nanomaterial is carried out either in the melt phase or the solution phase by the application of mechanical force for proper mixing of the polymer matrix with the nanomaterial [17, 18]. Direct compounding remains an easy and rapid fabrication method for the preparation of PNCs with the associated challenge of aggregation and non-uniform dispersion of nanomaterials, resulting in need for compatibilizers or a functionalization approach for further improvement in the properties of the nanocomposites. In solution blending, the polymer is dissolved in a suitable solvent and the nanomaterial is dispersed in the polymer solution by mechanical agitation. Upon evaporation of the solvent, polymer nanocomposites can be obtained and utilized. In melt mixing, the polymer is introduced with the nanomaterials in the molten form and mixed inside an extruder. The dispersion of the filler inside the matrix remains challenging and it decides the overall effectiveness of the nanocomposites. Figure 16.1 represents the various routes of synthesis of polymer nanocomposites and their advantages and associated challenges in brief. As already discussed, the removal of toxic ions is of prime interest for the sake of the benefit of the leaving organisms. Cr (III) and Cr (VI) ions are a point of concern in this respect. A number of technologies, e.g. ion exchange, adsorption, reverse osmosis,

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Fig. 16.1: Method of preparation of polymer nanocomposites, highlighting advantages and the associated challenges.

etc. are utilized to resolve this issue. Adsorption remains an interesting and fruitful method for the elimination of toxic metal ions, especially at low concentration. The nanostructured adsorbents prove to be excellent in the removal of toxic metal ions from wastewater as discussed in the subsequent section of this article. One of the best practices to utilize the nanoparticles is to convert them into nanocomposites and hence have been extensively explored in the recent past (Tab. 16.1). The removal efficiency is dependent on factors like adsorbent type, contact time, temperature, etc., contributing to the optimum performance of the polymer nanocomposites for the purification of the wastewater.

16.3 Removal of chromium using PNCs With the advancements in materials science, several novel materials have been developed for the sorption of Cr(VI) from aqueous systems. Among these, nanomaterialbased sorbents are highly promising by virtue of their physicochemical characteristics. However, there are some practical issues that limit their widespread adoption in water treatment. Nanoparticles easily tend to cluster, which affects their overall performance. The minute size of particles and their high surface energy make handling and separation from the solution difficult. Consequently, it limits their potential for

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recycling and reuse. The merits of nanoparticles in adsorption can be effectively realized in the form of nanocomposites. Significant developments have been made in the application of various nanocomposites for treating chromium-contaminated water. The developments of adsorbents that can facilitate the reduction of chromium from the hexavalent to the trivalent state as well as the sorption of reduced species have received increasing interest. Such materials should have two main features, namely, electron donating characteristics to enable reduction of hexavalent chromium and active binding sorption sites. The general chemistry of the removal of Cr ions has been briefly explained in Fig. 16.2. The process of removal broadly follows the mechanism of electrostatic attraction, hydrogen bonding, ion exchange, reduction, and complexation. The associated chemical bonding is briefly included below [19, 20].

Fig. 16.2: Chemistry of the removal of Cr from wastewater.

Polyaniline-based materials are suitable candidates with desirable properties. Environmentally friendly bacterial cellulose polyaniline aerogels, synthesized in the presence of anionic surfactants, were investigated for chromium remediation [21]. Nanocomposite aerogel, prepared with sodium dodecylbenzene-sulfonate, had a larger surface area and a relatively more homogeneous coverage of polyaniline on cellulosic nanofibers, in comparison to sorbents fabricated with sodium dodecyl sulfate. The existence of more amine functional groups facilitated the effective removal of chromium as they acted as electron-donating agents. Kumar et al. studied the oxidative polymerization technique to prepare para toluene sulfonic acid functionalized polyaniline carbon nanotube composites as adsorbents for Cr(VI). A strong linkage of Cr(VI) to the nanosorbent was observed with the highest uptake capacity of 166 mg/g. The amine, imine, and hydroxyl functional groups present on the nanocomposite played a key role in the sorption process.

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Clay-based polymer nanocomposites, prepared by mixing unmodified and modified clays in polymer matrices, have received increasing attention in recent years. These materials combine the advantages of clay minerals and polymeric resins in their applications as adsorbents [22]. A green clay-polymer nanocomposite was synthesized by using natural polymer derived from Moringa olifera and bentonite clay [23]. More than 99% removal efficiency was obtained for chromium as well as other heavy metals such as cadmium and lead by the coagulo-adsorption process. Ferromagnetic adsorbents provide capability for easy separation from liquid phase in the presence of magnetic field. Magnetite is a widely used magnetic material that is cheap, biocompatible, and possesses relatively lesser toxicity. The composites of magnetite with polymers exhibit good sorption uptake and reduction capability, which are desirable properties for the treatment of water contaminated with hexavalent chromium. Alsaiari et al. synthesized a nanocomposite adsorbent by combining Fe3O4 nanoparticles with polypyrrole and chitosan [24]. A single step co-precipitation procedure was followed for preparing magnetic chitosan, which was subsequently modified using polypyrrole. The maximum chromium sorption uptake of 105 mg/g was obtained via reductive and adsorptive mechanisms. Hydroxyl-functionalized magnetic fungus nanocomposites have also been employed for the decontamination of Cr (VI) [25]. The physicochemical characteristics of the fungi were greatly improved by magnetic graphene oxide nanoparticles. The mechanism revealed reduction of hexavalent chromium and mineralization into ferric chromate in residues. A magnetic nanocomposite synthesized using manganese dioxide (MnO2) nanowires, graphene oxide (GO), polypyrrole (PPy) and iron oxide (Fe3O4) nanoparticles was developed in a study for the elimination of Cr(VI) from aqueous solution based on the adsorption–reduction principle. For an effective absorption, GO offered enough surface area, a hydrophilic surface, and functional groups. The adsorption behavior of Cr(VI) by GMFP was substantially influenced by pH. The highest maximum chromium uptake was reported to be nearly 375 mg/g at pH 2. Through electrostatic attraction, GMFP was able to successfully adsorb Cr(VI), and the sorbed Cr(VI) ions were partially converted to Cr(III), resulting in the effective remediation of Cr(VI). Further, Fe3O4 nanoparticles could be easily separated and recovered after treatment due to their excellent magnetic characteristics. It must be noted that several other components can also be found in chromium-rich industrial effluents. Co-existing ions such as Cu2+, Zn2+, Ni2+, CO32− and SO42− may have an effect on the treatment method. However, as cations in the solution they have minimal interaction with the positively charged surface of GMFP at low values of pH, they have no effect on Cr(VI) elimination, suggesting the effectiveness of the adsorbent for practical applications [26]. Further, a polymeric-silica composite material was used for Cr(VI) removal in another investigation [27]. A one-pot approach was used to make PEI-silica nanoparticles. The PEI-silica nanoparticles removed a large amount of chromium; however, the pure nano-silica had no effect in the control test. A batch adsorption test was employed to measure the chromium ion uptake capacity. The pH

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value influenced the chromium ion sorption as it altered the interactions between chromium and the nanoparticle surface. The maximal Cr(VI) adsorption capacities for pH values of 2, 3, and 4 were 120.7, 138.2, and 183.7 mg/g, respectively. Another investigation was carried out for Cr(VI) remediation in a batch mode utilizing an adsorbent in the form of chitosan-grafted graphene oxide (CS-GO) nanocomposite [28]. The ultrasonic irradiation process was used to create the CS-GO nanocomposite material. At pH 2.0 and 420 min of contact time, a sorption capacity of 104.16 mg/g was attained. The CS-GO material can be recycled up to 10 times without losing its adsorption capacity. The influence of interferents (anions: SO42−, NO3− and HPO42−, cations: Mg2+ and Fe3+) on Cr(VI) adsorption by CSGO was investigated. Because of the opposition between the anionic species and Cr(VI) on the binding sites of the CS-GO nanocomposite, the anions tend to slow down the adsorption process, lowering the surface charge of the sorbent. In another study, a new modified polypyrrole/m-phenylediamine (PPy–mPD) composite was coated with Fe3O4 nanoparticles. It was generated by oxidative polymerization and utilized for the separation of hazardous oxyanion Cr(VI) from an aqueous solution [29]. Several approaches were used to confirm and examine the structure and characteristics of the PPy–mPD/Fe3O4 nanocomposite. With the appearance of Fe lattice fringes, high-resolution transmission electron microscopy established the presence of Fe3O4. At pH 2 and 25 °C, the nanocomposite was able to eliminate 99.6% of 100 mg/L of Cr(VI) in batch adsorption studies. Mohamed et al. investigated Cr(VI) removal utilizing a new nanocomposite, NFe3O4Starch-GluNFe3O4ED, which was made by microwave irradiation [30]. The maximal percentage removal of Cr(VI) ions on NFe3O4Starch-GluNFe3O4ED at pH 2.0 were 85.27%, 91.90%, and 96.47% for 10, 25 and 50 mg/L Cr(VI) containing feed solutions, respectively, at an equilibrium time of 30 min. Interfering salts such as NaCl, KCl, CaCl2, NH 4Cl, and MgCl2 had a substantial impact on the process. The highest uptake capacity was 210.74 mg/g under equilibrium conditions.

16.4 Adsorption analysis Adsorbents are materials that possess the capacity to adsorb or bind molecules or ions to their surface. They can be characterized based on several factors, including surface area, pore size, chemical composition, and morphology. High surface area adsorbents have a large number of pores on their surface that can adsorb a high number of molecules or ions. The pore size can also affect the adsorption capacity and selectivity of an adsorbent. Chemical composition can also play a role as certain adsorbents are more selective for specific types of molecules or ions. Surface properties, such as charge, can also affect adsorption.

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There are several methods that can be used to characterize the surface area of the synthesized sorbents. The Brunauer-Emmett-Teller (BET) method is a widely used approach based on the physical adsorption of nitrogen gas on the surface of the sorbent. The amount of nitrogen adsorbed is used to calculate the surface area. Multipoint BET is an extension of the BET method and allows for the determination of the surface area of adsorbent samples with a non-uniform pore size distribution. The Barrett-Joyner-Halenda (BJH) method uses the sorption isotherm to estimate the pore size distribution of the adsorbent. Various techniques can be employed to analyze the chemical characteristics of adsorbents. X-ray diffraction (XRD) technique makes use of X-rays to study the crystal structure of an adsorbent material. Fourier transform infrared spectroscopy (FTIR) utilizes infrared light to identify the functional groups present in an adsorbent material. Thermogravimetric analysis (TGA) involves the measurement of the weight change of an adsorbent material with respect to temperature, which can provide information about the composition and stability of the material. X-ray fluorescence (XRF) is another non-destructive methodology to identify the elemental composition of an adsorbent material. It is based on the measurement of the fluorescent X-rays emitted from the testing sample upon excitation by a primary X-ray source. Raman spectroscopy employs the principle of Raman scattering to identify the functional groups present in an adsorbent. Energy-dispersive X-ray spectroscopy (EDS) technique uses X-rays to identify the elemental composition of an adsorbent material. This is usually performed along with scanning electron microscopy (SEM) that makes use of a beam of electrons to produce images of the surface of adsorbent materials, which can provide information about the particle size and morphology. These are some of the common techniques to analyze the prominent characteristics of adsorbents, but different adsorbents may have specific properties of interest and may require other specialized techniques for characterization, such as vibrating sample magnetometry, dynamic light scattering, X-ray absorption near-edge structure spectroscopy, extended X-ray absorption fine structure spectroscopy, and solid state nuclear magnetic resonance spectroscopy.

16.5 Adsorption models Understanding the isotherm and kinetic behavior can help researchers get a better grasp on how different substances interact with one another during adsorption, which will lead to more efficient process designs and better products overall. Adsorption isotherms represent the relationship between the amount of a substance adsorbed by a solid and the concentration of that substance in a liquid or gas phase under equilibrium conditions at a given temperature. The adsorbate is a material that adheres to the surface of another material, while the adsorbent is a material

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that has an affinity for certain substances. The graphical representation of an isotherm displays how much of an adsorbate substance will adhere to a given amount of an adsorbent. An overview is provided here of the different types of isotherms, their uses, and how they can be used to describe the properties of adsorbed materials. The Langmuir equation was developed by Irving Langmuir in 1918 and it describes the monolayer coverage on a surface [31]. The relation is given by equation (16.1) below. q0e =

q,max KL CeðchromiunÞ 1 + q,max KL CeðchromiumÞ

(16:1)

Where, q0e =the quantity adsorbate adsorbed on the adsorbent surface (mg/g), q,max = the maximal sorption capacity of the adsorbent (mg/g), KL = Langmuir constant, CeðchromiumÞ = the amount of chromium present in the solution at equilibrium condition (mg/L). Langmuir equation describes the monolayer coverage because it assumes that all sites are equally likely to be occupied by an adsorbed species. It also assumes that there are no intermolecular interactions between the molecules in the same layer or between layers; this means that each molecule occupies its own site without affecting any other molecules on the surface. The Langmuir model does not take into account any chemical bonding between molecules in different layers, which could cause them to interact with each other and affect their ability to adhere to surfaces. The Freundlich isotherm represents a multilayer adsorption scenario [32]. It is mathematically denoted by the following equation (16.2). q0e = KF CeðchromiumÞ 1=n

(16:2)

Where, q0e = the quantity of adsorbate adsorbed on the adsorbent surface (mg/g), KF = Freundlich constants, CeðchromiumÞ = the concentration of chromium present in the solution at equilibrium condition (mg/L), n = Freundlich constant. The Freundlich equation differs from Langmuir because it assumes that each molecule interacts with its neighbors as well as with itself; this means that molecules are not isolated, rather they interact with other molecules in their vicinity. It also takes into account any chemical bonding between molecules in different layers, which affects their ability to adhere to surfaces. In the Temkin isotherm [33], the adsorption capacity rises with rising temperature and the process is endothermic as shown in equation (16.3).   (16:3) q0e = q,max ln KT CeðchromiumÞ q0e = The quantity of adsorbate adsorbed on the adsorbent surface (mg/g), KT = Temkin isotherm constants, CeðchromiumÞ = The amount of chromium present in the solution at equilibrium condition (mg/L)

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Anjali Awasthi, Ashish Kapoor, Soma Banerjee

It must be noted that the type of adsorbent, the pH of the solution, the presence of other ions, and the temperature can all affect the shape of the adsorption isotherm for chromium; so different conditions may produce different isotherm types. For chromium, several types of adsorption isotherms are observed, depending on the oxidation state of the chromium species. Cr(VI) ions adsorption isotherms are typically Langmuir or Freundlich types that are commonly observed for the adsorption of highly oxidized species. The data obtained from the isotherm models can help in optimization of the separation processes and the improvement of their efficiency by understanding how the different parameters affect the process being studied. Adsorption kinetics deals with how the sorption properties of a system evolve over time. The pseudo-first-order (PFO) kinetic model is applied to describe the timedependent adsorption behavior of a substance onto a solid surface. In this case, the rate of adsorption is reliant on the concentration of the adsorbate (the substance being adsorbed) in the liquid phase. The equation (16.4) for the PFO model [34] is given as:   (16:4) q0t = q0max 1 − eK1 t Where, q0max is the amount of adsorbate adsorbed at time t, K1 is the PFO rate constant, and q0t is the initial adsorption capacity of the solid. It is important to note that the PFO model is only valid for a certain range of adsorption conditions, and in some cases, more complex models such as the pseudo-second-order model are needed to accurately describe the adsorption process. The pseudo-second-order (PSO) kinetic model is an alternative to the PFO model for depicting sorption kinetics. In this model, the rate of adsorption is dependent on both the concentration of the sorbate in the liquid phase and the amount of sorbate already adsorbed onto the solid surface. The equation (16.5) represents the PSO kinetic model for adsorption as [35]: q0t

 2 K2 q0max t = 1 + K2 q0max t

(16:5)

where, t denotes the time, and K2 is the PSO rate constant. The PSO kinetic model is useful when adsorption is controlled by a chemical interaction between the adsorbate and the solid surface, rather than by diffusion or other physical processes. It is also used when the rate-limiting step is the chemical reaction between the adsorbate and the adsorbent, and the adsorbate molecules adsorbed on the surface are not available for further adsorption. This model gives more accurate and reliable results for the prediction of adsorption capacity and rate constant.

Polypyrrole magnetic chitosan

PEI-silica nanocomposite

Green-clay polymer nanocomposite

Starch–montmorillonite/polyaniline (St–Mt/PANI) nanocomposite

.

.

.

.

– – – –

– – – – –

– – – –

– – – – – –

– – – – –

Chitosan-clay nanocomposite

.

Temperature: 260 pH: 2 Time: 15 min Concentration: 10 mg/L

Coagulant dosage: 5 g/L Time: 0–300 min Chromium solution concentration: 2–20 mg/L pH: 2–4 Temperature: 25 °C

pH: 2–4 Adsorbent dosage: 20–30 mg Time: 24 h Chromium solution concentration: 10–200 mg/L

pH: 2–4.5 Adsorbent dosage: 100 mg Time: 0–300 min Chromium solution concentration: 100 mg/L Temperature: 25 °C Methyl orange concentration: 100 mg/L

pH: 1–9 Adsorbent dosage: 5–50 mg Time: 15–150 min Chromium solution concentration: 50–1,000 mg/L Temperature: 10–50 °C

Experimental conditions

S. Adsorbent No.

Adsorption capacity

Adsorption model – Langmuir . isotherm model mg/g Kinetic model – pseudo-second order

Kinetic model – pseudo-second order  mg/g Adsorption model – Freundlich and Langmuir isotherm model

Kinetic model – pseudo-second order . mg/g Adsorption model – Langmuir isotherm model

Kinetic model – pseudo-second order . mg/g Adsorption model – Langmuir (Cr VI) isotherm model

Kinetic model – pseudo-second order . Adsorption model – Freundlich and mg/g Langmuir isotherm model

Best-fit models

Tab. 16.1: Summary of experimental conditions, isotherm, and kinetics for the removal of chromium (VI) using various adsorbents.

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[]

[]

[]

[]

Reference

16 Recent advancements in polymer nanocomposites-based adsorbents

325

Copper ferrite-Polyaniline nanocomposite

ChitosanCDTA-GO nanocomposite

Bacterial cellulose

Guar gum polymer

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.

.

.

– – – –

– – – –

– – – –

– – – –

– – – –

(Maghemite/Chitosan/Polypyrrole) nanocomposites

.

Temperature: 25 °C pH: 2–11 Time: 8 h Concentration: 20 to 160 mg/L

Temperature: 25 °C pH: 1–7 Time: 0 to 24 h Concentration: 50 to 300 mg/L

Temperature: 25 °C pH: 3.5 Time: 60 min Concentration: 2 g/L

Temperature: 23 °C pH: 2 Time: 720 min Concentration below 10mg/L

Temperature: 23 °C pH: 2 Time: 720 min Concentration: