Nanomaterials: An Approach Towards Environmental Remediation

Environmental pollution has become biggest threat to mankind due to its adverse effects on human health and the ecosystem. Rapid industrialization, expansion of urbanization and adoption of latest technologies lead to the release of hazardous byproducts and effluents that contaminate the environment. Nanotechnology has proved to be a potential technique for environmental remediation. It involves the most advanced processes that can be successfully utilized in overcoming the issues of environmental contamination due to their unique properties. Multifunctional characteristics of nanomaterials offer unparalleled opportunities in the elimination of pollutants in the nanoscale like volatile compounds, heavy metals, inorganic and organic ions, drugs, pesticides, aromatic heterocycles, biological toxins, pathogens, etc. Nanomaterials with smaller size, higher surface area, quantum confinement and low reduction potential bring versatility in their functionality. These nanomaterials can be utilized as chemical oxidants, catalysts, adsorbents, nanosensors, etc. Surface engineering of nanomaterials can be utilized to enhance their surface area and maximize their reactivity for adsorption of pollutants and promote catalytic reactions by oxidation or reduction of pollutants from contaminated medium. Besides surface area, the selectivity of specific nanoparticles also affects the remediation process. In this chapter, we have given a brief introduction to the nanoremediation pathways broadly categorized into four categories: adsorption, photocatalysis, nano-membrane, nanosensors for different classes of nanomaterials like carbon-based, metal and metal oxides, magnetic, two dimensional, etc. Nanomaterials can prove to be efficient in energy harvesting and storage applications due to the interplay between surface and interface. Hence, there has been continuous demand for nanomaterials with new architectures and physically controlled properties for the purpose of energy harvesting. 

In recent years, scientists have been interested in spinel ferrite-based nanomaterials because of their exceptional characteristics, such as their high saturation magnetisation (Ms ), excellent chemical stabilities, and huge surface-to-volume ratios. Spinel nanoferrites for wastewater clean-up are the subject of this chapter, which goes into great depth. Spinel ferrite has been discussed in detail, along with some of its key features. Moreover, the synthesis method and structural and magnetic characteristics of spinel ferrites are also reviewed in this chapter. There has also been a discussion of conventional wastewater treatment methods and their limitations in handling different organic and inorganic pollutants. It is possible to remove inorganic and organic pollutants from wastewater using adsorption and photocatalysis therefore, in view of this, these methods are addressed in detail. The importance of spinel ferrite nanoparticles in pollutant degradation of wastewater and its recovery has been explored. Additionally, it has been discussed how adsorption and photocatalysis can improve the efficacy of currently used conventional wastewater treatment techniques. Towards the end, the future scope of spinel nanoferrites for wastewater treatment is discussed. 

Carbon quantum dots are sp2 /sp3 -hybridized carbon atoms with sizes ranging from 2-10nm. They are zero-dimensional florescent nanomaterials that are less toxic, more biocompatible and highly stable in nature. Carbon quantum dots have attracted the attention of many research groups due to their novel characteristics and have found several applications in industries. They are used in various scientific fields which include synthesis and design of inexpensive biological and chemical sensors. Carbon quantum dots have several uses in optical sensing, bio imaging, bio-sensing, optoelectronics photovoltaic and photocatalysis because of their superior electronic, optical, photocatalytic, up-conversion, photoluminescence and light harvesting properties. Using CQD, a cost-effective and environmentally friendly method of cleaning up environmental pollutants is introduced. They have lately been employed in remediation experiments in place of or together with metal semiconductors due to their optoelectronic features. Recently, the world has been facing serious threats due to environmental contamination of various kinds, which has become more serious due to lesser affordable means for treating it. Industrial waste, pesticides, heavy metal ions, pharmaceutical waste and sewage are some of the commonly observed water contaminants. Compared to the earlier studied forms of quantum dots, carbonaceous quantum dots are the most prevalent ones and can be a better option. The goal of this chapter is to explain the significance of carbonaceous quantum dots in environmental remediation. In addition, the advantages of carbonaceous quantum dots over conventional quantum dots, methods for synthesizing carbonaceous quantum dots (top down and bottom up), their functionalization or doping to improve their selectivity and sensitivity, their applications in various fields such as sensing, photocatalysis and biosensing have also been reviewed. By adding surface defects or interstitial states between electron holes, these alterations have a major impact on the optical characteristics of carbonaceous quantum dots. Additionally, the methods of removal of pollutants have also been explored by physical, chemical conventional and biological methods. Lastly, future perspectives and conclusion speculations have been considered.

In recent decades, considerable attention has been directed toward wastewater remediation through various processes, including adsorption, advanced photo-reduction/oxidation processes, ion exchange, and more. The linchpin of these processes lies in the judicious selection of appropriate materials, capable of not only meeting the primary requirements but also exhibiting suitable availability. The exploration of carbonaceous materials such as activated carbon, biochar, hydrochar, etc., emerges as a cost-effective strategy for wastewater remediation. The surface area, a well-established pivotal factor, assumes a critically influential role in the wastewater remediation process. Therefore, it is paramount, during the fabrication of such materials, to adopt appropriate strategies to ensure the fulfillment of the targeted material requirements. Due to their extensive surface area, carbonaceous materials hold immense potential in wastewater treatment through advanced oxidation processes (AOPs). The efficacy of these AOPs, encompassing photo-catalysis and photoreduction/oxidation, hinges upon the materials employed, including nanoparticles and hetero-structures. In turn, all AOPs are orchestrated by reactive oxidation species (ROS) generated at the active sites of catalysts, such as nanoparticles and heterostructures. This study comprehensively summarizes the pivotal role of carbonaceous materials, underscores their significance, and elucidates the fabrication techniques essential for their multidisciplinary application in wastewater treatment processes.

An enormous growth in the concentration of various poisons and pollutants in the environment has resulted from the ongoing expansion of industrial, agricultural, and urban activities. So, environmental remediation should be given equal attention to scientific efforts in the fields of industrial and technological developments. When it comes to the adsorption and desorption of several environmental contaminants, magnetic nanoparticles have proven to be superior to other contenders. Ferrites, among other magnetic nanoparticles, have gained attention as viable options for environmental cleanup because of their tiny size, high surface to volume ratios, superior catalytic capabilities, strong magnetic properties, and favourable optical characteristics. Additionally, ferrites have demonstrated the ease with which their structural, morphological, magnetic, and optical properties may be tailored, and these changes have further improved the effectiveness of pollution removal. Additionally, formation of composites of ferrites with different materials such as CNTs, graphene, rGO, cellulose, TiO2 , ZnO etc. has also led to enhancement in the catalytic properties. The role of pure and modified ferrites in eliminating different poisons and pollutants from the environment, as well as their possible uses in environmental remediation, are thoroughly discussed in this chapter.

Wastewater and other environmental concerns have an impact on every area of our life. Combining novel functional carbon nanomaterials (such as carbon nanotubes, graphene oxide and graphene) with established remediation techniques will provide fresh perspective on environmental problems, their causes and potential solutions for coexisting peacefully with nature. All around the world, water contamination has grown to be a major, enduring and increasing issue. It has detrimental effects on population health, aquatic flora and wildlife and the sustainability of water resources. Because there aren't enough efficient facilities for treating pollutants, the overall amount of water that is available is drastically reduced. Current methods of water filtration take long time, cost lot of money and are ineffective in removing newly discovered micropollutants. Carbon Nanotubes (CNTs) are a class of materials with special physicochemical, electrical and mechanical characteristics that can be used as environmental adsorbents, sensors, membranes and catalysts. CNTs can be created using particular functionalization or modification procedures, depending on the intended application and the chemical make-up of the target pollutants. Designer CNTs can significantly increase the effectiveness of contaminant removal and help with nanomaterial regeneration and recovery. Different chemical, inorganic, and biological pollutants have been treated using an expanding number of CNT-based products. These success stories show how they have lot of potential for real-world uses like desalination and wastewater treatment. In this chapter, the existing research on the interactions between different pollutants and CNTs in soil and water settings has been critically reviewed. The chapter will also assist in identifying the research voids that need to be filled in order to increase CNTs' economic via bility in the environmental remediation sector. Additionally, this makes an effort to present a broad overview of the prospective low-dimensional carbon nano-materials and their composites as adsorbents, catalysts, or catalytic support for the social sustainable environmental remediation solutions to the various difficulties arising.

In recent times, water pollution has become an issue of major concern. Various materials and techniques have been adopted for the purification of water. Among many, cellulose-based nanomaterials have gained valuable use in water remediation processes. These cellulose-based materials are highly biocompatible, abundantly available natural biopolymers and enjoy the advantage of containing many functional groups. The functional groups attached to cellulose biopolymers ensure their capability of modification with various nanoparticles like silver (Ag), graphene oxide (GO), and zinc oxide (ZnO) nanoparticles. These can then be easily applied for the remediation of wastewater by removing pollutants like organic dyes, microbial species, various drugs and heavy metal ions as well. In this chapter designing of various cellulose-based nano-materials has been discussed for the extraction of valuable metals from various wastewater. Mainly static and dynamic absorption processes through cellulose-based nano-materials have been also explained. Adsorption by various chemical transformations such as reduction, chelation and electrostatic interaction are discussed for the extraction of various metals from different wastewater sources. Lastly, composite systems consisting of cellulose and metal oxide nanoparticles have been reviewed for the extraction of rare earth metals from the mining industry. Metals from the recycling of battery and semiconductor devices that mostly constitute noble metals and rare earth elements are also discussed in this chapter.

The use of electronic devices is an integral part of our everyday life and a major part of our activities with these devices is related to receiving, sending, and storing information. Some of these devices used for sensing, analysing, and transmitting signals require a very small amount of energy. An alternative source to power these devices could be through harvesting tiny mechanical motions associated with different types of motions. Nanogenerators (NG) are potential sources of energy harvesting by converting waste mechanical energies into useful electrical energy. NGs have already been commercialized in the health and automobile industry as pacemakers and tyre pressure monitoring systems, respectively. However, there is a wide scope of using them for common household and environment remediation applications, which is currently restricted due to the high cost of fabrication and low energy conversion efficiency. Vibrational energy associated with wind, flow of fluid, body movements, roads, train tracks, etc. can be converted to power devices locally and reduce the carbon footprint due to the energy produced by fossil fuels. This book chapter reviews the basic working of different nanogenerators based on piezoelectricity, triboelectricity pyroelectric, and flexoelectricity. Many non-lead-containing piezoelectric materials are promising candidates for piezoelectric nanogenerators (PENG) that can also be used for various self-powered electronic and biomedical devices. Many metal-oxides such as zinc-oxides and hafnium-oxides could be of special interest to this. Triboelectricnanogenerators (TENG) could be the most preferred device for harvesting water-wave blue-energy and integration with conventional electromagnetic-induction (generators) that can be deployed at a large-scale.

Piezoelectric energy harvesting has attracted wide attention to fulfill day-byday increasing energy demand. Owing to its benefits, which include scalability, high power density, and simple architecture, piezoelectric ceramics have become the first choice of researchers over their counterparts such as electromagnetic and electrostatic energy harvesters. Despite extensive research and widespread use of lead-based piezoelectric ceramics, removing lead from these applications for environmental concerns is still difficult. Modern lead-free piezoelectric energy harvesting technology is reviewed in this chapter. Fundamental piezoelectric concepts and several piezoelectric material qualities are presented in a succinct theory part. A literature review on the advancement of lead-free piezoelectric ceramics, specifically KNN, BT, and BNT-based ceramics, since 2010 is presented. Applications for energy harvesting have also been described and assessed. Finally, based on their current developments, different challenges and future perspectives are also encompassed.

Thermal spray coating processes are commonly employed to manufacture surfaces for distinct harsh industrial applications including power generation and aerospace. Application of various thermal spray techniques is significant for diverse applications, which can affect the mining of critical raw materials (titanium, nickel, cobalt, tungsten, yttrium etc.). As a result, thermal spraying alone has contributed to reducing mining through reuse, reduction and recycling of coated base materials. Thermal spraying also prevents the need to discard costly superalloys by enabling selective repair of gas turbine and aero engine parts, which would otherwise donate to increased greenhouse gas emissions from casting, remelting and additional downstream operations like machining. Recently, cold spray additive manufacturing (CSAM) has played a significant role in manufacturing industries owing to many benefits such as high process flexibility, less production time, high accuracy and quality reduced power consumption, and powder and gas requirement than traditional manufacturing processes. This advanced manufacturing process can build 3D parts and has the potential to alter the future of the manufacturing world with significant sustainable merits. Thus, the aim of this chapter is to offer an overview of CSAM including their advantages for sustainable manufacturing in terms of environmental concerns. Thereafter, the share of various processes and industries to greenhouse gas emissions has been studied. Finally, the challenges associated with cold spray additive manufacturing have been discussed.

Nanomaterials have shown promising environmental remediation solutions owing to their unique chemical and physical properties. However, their probable impacts on human health and the environment must be evaluated before widespread implementation. This chapter aims to assess the ecotoxicity and risk associated with nanomaterials in environmental remediation. A comprehensive literature review has been conducted to evaluate the available data on ecotoxicity of nanomaterials, including their effects on aquatic and terrestrial organisms and mechanisms of toxicity. In addition, a risk assessment framework has been developed to assess the risks associated with nanomaterials in environmental remediation, taking into account the hazards, exposure, and vulnerability of different environmental receptors. Investigation of this study proposes that though nanomaterials have the potential to be effective in environmental remediation, there are significant concerns about their potential toxicity and risks. Further, research is needed to better understand the ecotoxicity and risk of nanomaterials, as well as to develop effective risk management strategies for their use in environmental remediation. Overall, this chapter highlights the importance of careful consideration of the ecological impacts and risks of nanomaterials before implementing them in environmental remediation programs.