New Frontiers of Nanomaterials in Environmental Science 9811592381, 9789811592386

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Rajeev Kumar Raman Kumar Gurpreet Kaur  Editors

New Frontiers of Nanomaterials in Environmental Science

New Frontiers of Nanomaterials in Environmental Science

Rajeev Kumar • Raman Kumar • Gurpreet Kaur Editors

New Frontiers of Nanomaterials in Environmental Science

Editors Rajeev Kumar Department of Environment Studies Panjab University Chandigarh, India

Raman Kumar Department of Biotechnology Maharishi Markandeshwar (Deemed to be University) Ambala, Haryana, India

Gurpreet Kaur Department of Chemistry and Centre of Advanced Studies in Chemistry Panjab University Chandigarh, Haryana, India

ISBN 978-981-15-9238-6 ISBN 978-981-15-9239-3 https://doi.org/10.1007/978-981-15-9239-3

(eBook)

# Springer Nature Singapore Pte Ltd. 2021 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Contents

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Environmental Pollution, Its Causes and Impact on Ecosystem . . . . Sushma Negi, Smriti Batoye, Kunal Singh, and Jaskaran Singh Waraich

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Nanomaterials; Applications; Implications and Management . . . . . Varsha Dogra, Gurpreet Kaur, Rajeev Kumar, and Sandeep Kumar

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Environmental Nanotechnology: Its Applications, Effects and Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Teenu Jasrotia, Ganga Ram Chaudhary, Sesha Srinivasan, and Rajeev Kumar

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Nanoscavengers for the Waste Water Remediation . . . . . . . . . . . . . Anupreet Kaur

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Development of Environmental Nanosensors for Detection Monitoring and Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Urmila Chakraborty, Gurpreet Kaur, and Ganga Ram Chaudhary

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Nanotechnology for the Remediation of Heavy Metals . . . . . . . . . . 145 Nikita Dhiman, Raman Kumar, Ajeet Kaushik, and Rajeev Kumar

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Emerging Potential of Nano-Based Techniques for Dye Removal . . . 165 Savita Chaudhary and Pooja Chauhan

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Nanomaterials for Remediation of Pesticides . . . . . . . . . . . . . . . . . . 193 Bhupinder Dhir

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Application of Carbon-Based Nanomaterials for Removal of Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 Avtar Singh, Jaspreet Singh Dhau, and Rajeev Kumar

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Nanofertilizers and Their Applications . . . . . . . . . . . . . . . . . . . . . . 229 Bhupinder Dhir

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Nanopesticides in Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 Anupreet Kaur

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Management of Waste Using Nanotechnology . . . . . . . . . . . . . . . . . 253 Surbhi Vyas, Nikita Dhiman, Sushma Negi, and Rajeev Kumar

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Phytoremediation and Nanoremediation . . . . . . . . . . . . . . . . . . . . . 281 Parveen Kumar, Ashwani Kumar, and Rajeev Kumar

About the Editors

Rajeev Kumar is working as an Assistant Professor in the Department of Environment Studies, Panjab University, Chandigarh, since 1 July 2010. He has completed his B.Sc. (Honours School) and M.Sc. (Honours School) degree in Chemistry from the Department of Chemistry and Centre for Advanced Studies in Chemistry, Panjab University, Chandigarh. His main research areas include organometallic, nanochemistry and bioremediation of environmental pollutants with the help of fungi. He has completed one DST-SERB project funded by the Department of Science and Technology (SERB), Government of India, New Delhi, and also the Project Director of “Indo-US Partnership on Green Chemistry/ Engineering and Technologies Education, Research and Outreach for Sustainable Development funded by University Grant Commission and MHRD, New Delhi”. He has published 52 International research papers with more than 180 citations and also published 15 international book chapters; his H index is 11. Raman Kumar is working as an Associate Professor in the Department of Biotechnology, Maharishi Markandeshwar (Deemed to be University), Mullana (Ambala), Haryana, India, since 2011. He has also worked as Senior Research Fellow, Division of Soil and Crop Management, Central Soil Salinity Research Institute, Karnal, India, from 2007 to 2010. He has experience of about 13 years in the field of Teaching and Research in the area of Microbial and Environmental Biotechnology. He has published more than 40 publications and 02 books in various national and international peer-reviewed journals. He developed many bacterial and fungal strains for removal of heavy vii

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About the Editors

metals from wastewater. His current research areas are bioremediation and biodegradation of toxic pollutants, pesticides and azo dyes using microbial consortium from the industrial effluents, mechanisms involved in heavy metal bioremediation. Gurpreet Kaur is working as an Assistant Professor in the Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University. She did her B.Sc. (Hons school), M.Sc. (Hons school) and Ph.D. from the same department. Dr. Kaur is one of the recipients of DST Inspire Faculty Award. She is a physical chemist and works in the field of colloidal chemistry. Her area of research includes fabrication of metal functionalized surfactants for wide spectrum application including formation of bioactive materials and their interaction with biomolecules (DNA, proteins, etc.), antimicrobial surfactants, microbial corrosion inhibitors, and electrocatalyst. She has more than 50 publications including review articles, 5 book chapters, and 3 Indian patents [one granted and two filed (and one applied for)].

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Environmental Pollution, Its Causes and Impact on Ecosystem Sushma Negi, Smriti Batoye, Kunal Singh, and Jaskaran Singh Waraich

Abstract

Pollution is one of the major concerns for our society, and it has gained serious importance in the past couple of decades, as it is not only degrading the quality of our health but is also shaking the roots of our beautiful and well-balanced ecosystem. In this chapter, various types of pollution are discussed, which are disturbing our ecosystem. The remedies and their impact on ecosystem have been discussed in details. Anthropogenic activities causing pollution have also been discussed. Pollution are generally classified as air, water, soil and solid waste have been discussed. Toxicology of every pollution is discussed. Keywords

Environment · Pollution · Solid waste · Treatment · Ecosystem · Hazards · Toxicity of ecosystem

S. Negi (*) Department of Environmental Science, Maharaja Agrasen University, Baddi, Himachal Pradesh, India S. Batoye Department of Zoology, Maharaja Agrasen University, Baddi, Himachal Pradesh, India K. Singh Department of Mechanical Engineering, Maharaja Agrasen University, Baddi, Himachal Pradesh, India J. S. Waraich Department of Defence and National Security Studies, Panjab University, Chandigarh, Haryana, India # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_1

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1.1

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Introduction

The term pollution as we speak can be broadly subdivided into many forms. Specifically speaking each type of pollution weather in air, water or land affects the ecosystem in different ways. With the recent advancement in science and technology it is now easily possible to detect the complex effect of this pollution on our ecosystem, but still it is not possible to recycle or totally eliminate the hazardous effects of this increasing toxicity on our ecosystem. However, it may be noted that the harmful effects of pollution can not only be reduced through recycling waste but can also be reduced through awareness among common being. Through multimedia and social networking such awareness can be spread and the effects of pollution can be reduced by minimizing the disposal of harmful waste in our environment (Ibanez et al. 2007). In this chapter, the impact of pollution on ecology has been discussed in detail. It may be noted that one of the most difficult and most hazardous type of pollution is the air pollution. In this era of rapid urban development, air pollution bears some serious toxicological as well as carcinogenic impact on living beings. The emissions due to industrial processes and automobiles contribute to the majority of air pollution. It may be noted that air pollution can be broadly subdivided into various categories like air particulate (Sweileh et al. 2018) pollution which is somewhat easy to control in closed confined spaces. Another form of air pollution is the increase in hazardous gases such as carbon monoxide, sulfur oxides as well as gases generated due to high temperature processes in industries and automobiles such as nitrogen oxides. Air pollution is difficult to control due to its ability to occupy large spaces as well as distribute homogenously in the environment. Air pollution is the major cause of respiratory, skin allergies and cardiovascular and neuropsychiatric diseases (Gaddi and Capello 2018). In this chapter, various remedies to prevent air pollution have been discussed in detail. Figure 1.1 displays the division of pollution into its various forms. If fresh air is required for a living being to sustain a healthy and happy life, fresh water also shares an equal important part in the lifecycle of any living being. Fresh water is a valuable resource which in today’s era of urbanization is easily being contaminated to an extent that it is considered polluted. It may be noted that there are processes to restore the quality of water but these processes are also costly and

Fig. 1.1 Division of pollution into its various forms

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Fig. 1.2 Solid waste dumping site in Ghaziabad, India

difficult to maintain and apply. It is however much wise and easy to prevent such water contaminating activities on prior basis. The pollutants in waters can broadly be classified into synthetic as well as biological pollutants (Sharma and Bhattacharya 2017). With recent advancements in industrial processes, synthetic pollutants hold the maximum share of water pollution in terms of toxicity as well as its quantity in the aquatic environment. However, the impact of organic matter can also not be neglected; such organic material which decomposes in aquatic region consumes oxygen and hence decreases its oxygen levels, creating a low oxygen aquatic region for the living aquatic beings such as fish. The excess nitrates used in crops result in growth of algae (Venkateswarlu 1969) and therefore harm the aquatic beings by preventing the proper exposure of sunlight to the plants deep inside the aquatic region. In this chapter various types of water pollution and their impact on aquatic ecology have been discussed in detail. Some methods and means to reduce and treat such activities have also been discussed. In recent years, the increasing toxic effects of solid waste have not only degraded the quality of land but have also affected the health of living being by disturbing the ecosystem. Excessive use of fertilizers and e-waste has raised concerns over our ability to even sustain a healthy life for our future generations. Therefore, it is essential in this era of rapid industrial growth to dispose such waste effectively and quickly to reduce its toxic effects on our precious land which is limited in size. Figure 1.2 displays an example of dumping ground in Ghaziabad, India which depicts the dumping of solid waste near urban cities. In this chapter, the impact of solid waste on ecosystem has been discussed in detail and methods and means to eliminate the effects of waste have also been discussed. Various techniques (Keyu

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2012) like disposing, incineration, landfills and some chemical processes such as pyrolysis to gain energy advantage from the waste have been discussed in detail. Note that the purpose of discussing such techniques is to generate awareness among people to use such techniques locally if possible and motivate innovators to develop such techniques which are inexpensive and easy to conduct to minimize solid waste. It may be noted that all the different types of pollutions as discussed above are interrelated with each other and each type affects the ecosystem altogether. For example, excess air pollution is responsible for acid rain which affects the water as well as soil by disturbing its pH and contaminating it with carcinogenic and toxic pollutants. Excess use of harmful fertilizers and pesticides not only deplete the nutritional value of soil but also destroys its ability to grow healthy organic food for decades if not centuries. Seepage of water from dumps (Naveen et al. 2018) not only contaminates the underground water but also poisons the land on which these dumps are situated. In this chapter, the impact of contaminated soil on ecosystem has been discussed in detail along with some remedies to minimize the effect of soil pollution.

1.2

Pollution: Types and Causes

Increase in population and money-making increase to rapid change in our ecosystem which is considered necessary to be enhanced by protection and sustainable use, so that they can fortify all aspects of human life. With the period of time human have changed natural ecosystem more rapidly and extensively this transformation has changed and contribute a lot in human well-being and economic development. But not all have been benefited with these contributions. Although goods and services used rapidly from environment and these dependencies make people more complex toward resources used which has adverse impact on global climate change. However, the natural environment should be preserved for the future.

1.2.1

Air Pollution

The substances accumulate in the atmosphere contribute to air pollution which further expose to increase in passable concentrations and expose to human health or produce other deliberate effects on living matter and other materials (Millennium Ecosystem Assessment 2005). Major sources of pollution are generated from power and heat generated industries, burning of solid wastes, industrial processes especially from transportation (Adetunde and Glover 2010; Baig et al. 2009). The main types of pollutants are carbon monoxide, hydrocarbons, nitrogen oxides, particulates, sulfur dioxide, and photochemical oxidants. Tables 1.1, 1.2 and 1.3 shows the major sources of different types of air pollutants and their effect of health and ecosystem along with an approximate duration of such pollutants in atmosphere.

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Table 1.1 Sources of air pollution and consequence of pollutants on health Pollutants Nitrogen oxides Carbon monoxide

Sources Industries, vehicles and power plants Fossil fuels emission

Carbon dioxide

Burning of fossil fuels

Suspended particulate matter

Vehicular emission and burning of fossil fuels Industries and power plant Industries and vehicular pollution Burning of fossil fuels

Sulfur oxide Smog Hydrocarbons

Chlorofluorocarbons

Refrigerators, emission from jets

Health effects Problems in the lungs, respiratory systems and causes asthma and bronchitis Severe headache, irritation to mucous membrane, unconsciousness and death Vision problem, severe headache and heart strain Lung irritation reduces development of RBC and pulmonary malfunctioning Irritation in eyes and throat, allergies, cough etc Respiratory and eye problems Kidney problems, irritation in eyes, nose and throat, asthma, hypertension and carcinogenic effects on lungs Ozone layer depletion, global warming

Table 1.2 Lifetimes of atmospheric pollutants (adapted from (GEO 4 2007)) Pollutant O3 NOx SO2 NH3

Atmospheric lifetime Weeks to months Days Days to weeks Days to weeks

Scale of impacts Regional to hemispheric Local to regional Local to regional Local

Table 1.3 Ecological effects of air pollution and their impacts on ecosystem Pollutant ecological effect Plant growth reduced Increased plant susceptibility to stress Acidification eutrophication

Ecosystem service impact Provisioning Regulating Reduced plant and Altered climate biomass production regulation through C sequestration

NH3

Eutrophication

Reduced food provision from aquatic systems

SO2

Acidification

Pollutant O3

Nox

Altered nutrient cycling and increased system losses Altered nutrient cycling and increased system losses

Supporting Reduced net primary Productivity

Increased net primary Productivity Increased net primary Productivity Loss of biodiversity

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Water Pollution

The quality of water is degrading day by day due to its physical, chemical and biological changes and adversely affecting the quality of water and living organism. Addition of such pollutants like pesticides, heavy metals, and nondegradable, bioaccumulative, chemical compounds dissolved or suspended solids pollutants into water which are most insidious and persistent toxic pollutants of these polluted water drains out with rain water and are responsible for polluting water and can be grouped under conventional and nonconventional. • Conventional/Classical Pollutants: These are normally associated with the undeviating input through human waste products. Rapid urbanization and rapid population increase have produced sewage problems because treatment facilities have not set aside pace with need. Untreated and incompletely treated sewage from municipal wastewater systems and septic tanks in unsewered areas contribute significant quantities of nutrients, suspended solids, dissolved solids, oil, metals (arsenic, mercury, chromium, lead, iron, and manganese), and biodegradable organic carbon to the water environment. Also, high concentrations of suspended solids silt up rivers and navigational channels, necessitating frequent dredging. Excess dissolved solids make the water undesirable for drinking and for crop irrigation (Kumar et al. 2005; Mian et al. 2010). • Nonconventional Pollutants: These are the particulate forms of metals, they are highly toxic untested chemicals which are discharged into water pollutants from biologically inert materials such as clay and iron residues from building and demolishing wastes to the most toxic and dangerous materials such as halogenated hydrocarbons (DDT, kepone, mirex, and polychlorinated biphenyls—PCB). The chronic low-level pollutants are proving to be the most difficult to correct and abate because of their ubiquitous nature and chemical stability (Bhatnagar and Minocha 2006; Murad 2010). Figure 1.3 display the blockage of water water due to house hold waste which is a common picture in almost every part of rural and semi-urban India.

1.2.2.1 Effects of Water Pollution on Human Health If the presence of heavy metals such as fluoride, arsenic, lead, cadmium, mercury, etc are high in water then it is dangerous for human health. Concentrations of floride below 0.5 mg/L causes dental caries and mottling of teeth, but exposure to higher levels above 0.5 mg/L for 5–6 years may lead to adverse effect on human health leading to a condition called fluorosis (Murad and Krishnamurthy 2004). Such toxic chemicals like arsenic and cadmium are highly dangerous for human health causing respiratory cancer and skin lesion. Long exposure to these toxic elements leads to bladder and lung cancer. Lead contamination in the drinking water is also caused by pipes, fitting, solder, and household plumbing systems. It may be noted that lead exposure also affects adversely the blood, central nervous system and the kidneys of human being, which may proove fatal for the health of child and pregnant women (Murad and Krishnamurthy 2008).

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Fig. 1.3 Effect of pollution on water

1.2.3

Soil Pollution

Contamination of soil with inconsistent concentrations of heavy metals makes the environment harmful to human beings and other living organisms. The root cause of soil pollution is agriculture by the use of pesticides, excessive industrial activity, poor management or inefficient disposal of waste which are challenges with the greater requirement of remediation (Chibuike and Obiora 2014). The presence of substances in soil so called as xenobiotic which are carcinogenic and may accumulate in the environment causing toxic effects to humans primarily through food, inhalation or drinking water, affect the mobility and biological impact of these toxins (Giller et al. 1998). The large quantity of xenobiotic compounds in soil has been increased rigorously by the accelerated rate of extraction of minerals and fossil fuels and by highly technological industrial processes (Adham et al. 2011) and not all soil pollutants are xenobiotic compounds. Crop production problems in agriculture are encountered when excess salinity salt accumulation occurs in soils in arid climates where the rate of evaporation exceeds the rate of precipitation. As the soil dries, ions released by mineral weathering or introduced by saline ground water tend to accumulate in the form of carbonate, sulfate, chloride, and clay minerals (Li et al. 2014; Lim et al. 2008). The sustained use of water resources for irrigating agricultural land in an arid region requires that the applied water not damage the soil environment. Crop utilization of water and fertilizers has the effect of concentrating salts in the soil; consequently, without careful management irrigated soils can become saline or develop toxicity (Zhao et al. 2012).

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Solid Waste Pollution

Waste generation in a broader sense is understood as any household, industrial and agricultural materials that have been used up. Since such waste accumulates in the territories managed by municipalities responsible for its removal and storage which is a major contributor to increasing municipal solid waste, infrastructure development that meets the needs of the people and protects the environment is fundamental to achieving effective economic growth. Rapid population growth in India has led to depletion of natural resources. The transition from wastes to resources can only be achieved through investment in SWM as this depends on a coordinated set of actions to develop markets and maximize recovery of reusable/recyclable materials.

1.3

Impact of Pollution on Ecosystem and Its Treatment/ Remediations

The following sections explain in detail the toxicology of different types of pollutions. Their impact, causes and their treatment have been discussed in detail.

1.3.1

Toxicology of Air Pollution and Its Treatment

The air pollution effects on existing organisms will only be inadequate to the human beings and animal but also includes the whole environment. Ecologically, air pollutants can severely damage the air, soil and groundwater (Mellouki et al. 2016). Various studies on the link between air pollution and species diversity evidently show the deleterious effects of environmental pollutants on the extinction of flora and fauna (Camargo and Alonso 2006). Air poised may also affect reproductivity in animals (Veras et al. 2010). It may be noted that climate change because of greenhouse gas emissions as well as acid rains and inversion of temperature are some of the main impacts of air pollution on ecology (Schneider 1989).

1.3.1.1 Impact of Air Pollution Particle pollutants constitute the major parts of air pollutants. These are mostly related with respiratory and cardiovascular-associated diseases and mortality (Sadeghi et al. 2015; Sahu et al. 2014). Their size mostly ranges from 2.5 to 10μm. Besides, many scientific studies have confirmed that the fine particle pollutants can cause early demise in individuals with cardiac or pulmonary disease such as nonfatal heart attacks, cardiac dysrhythmias and declined lungs function. Coughing, constraint activities due to lung problems are the most common clinical sign of pulmonary disease due to air pollution (Bentayeb et al. 2013; Gao et al. 2014). O3 is the major constituent of the atmosphere. Ground-level ozone is released by chemical reaction of nitrogen and volatile organic compounds or due to anthropogenic activities with increased risk of lung diseases, chiefly asthma (Gorai et al.

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Fig. 1.4 Effect of air pollution on health and ecosystem

2014). These are thought to increase the concentration of free radicals which causes lipid peroxidation of cellular membranes and macromolecules. Also affects DNA leading to decreased cellular function (McCarthy et al. 2013). Carbon monoxide is a hazardous gas and is generated during the incomplete combustion of coal, wood and other fossil fuels. Its affinity toward hemoglobin molecule is much more around 250 times, then the molecule of oxygen. The result of carbon monoxide poisoning is severe headache, nausea, loss of consciousness etc. (Akyol et al. 2014). SO2, is a highly reactive gas chiefly released due to consumption of fossil fuel, volcanic activities and industrial processes. Patients having a lung disease, infants and people who are exposed to SO2 are more prone to skin and pulmonary diseases. As a sensory irritant, it can cause bronchospasm and mucus secretion in humans, SO2 is responsible for acid rain and acidification of soils due to its water soluble property. Figure 1.4 depicts the effect of air pollution on health and ecosystem. As per different studies, the major lethal effects of air pollutants are primarily on the pulmonary, cardiovascular, immune, dermatologic, nervous, hematological and reproductive systems. Additionally, the cellular and molecular toxicity may also produce different types of cancers in long term (Kampa and Castanas 2008). • Pulmonary disorders Mostly the air pollutants enter the body via airways; hence, the pulmonary system, depending upon the amount of inhaled pollutants and their accumulation in target cells, latter on it causes asthma (Brunekreef et al. 2009). Air pollutants, such as PMs, dust, O3 and benzene cause severe injury to the respiratory tract (Valavanidis et al. 2013; Bahadar et al. 2014; Johannson et al. 2014). Various studies have validated the relationship between both traffic-related or industrial air pollutants and the increasing risk of COPD (Ko and Hui 2012).

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• Cardiovascular dysfunctions Various studies have revealed that the air pollutants cause cardiovascular illnesses (Snow et al. 2014; Andersen et al. 2012). They are also associated with changes in leucocytes which also might be responsible for cardiovascular functions (Steenhof et al. 2014). However, a study on animal models suggested the close association between hypertension and exposure of air pollutants. The traffic effluents, especially high levels of NO2, cause hypertrophy of right and left ventricle (Leary et al. 2014; Van Hee et al. 2009). • Neuropsychiatric complications The correlation between the exposure of suspended air toxins and nervous system has constantly been argued. The toxicity of air pollutants on nervous system includes neurological problems and psychiatric disorders (Newman et al. 2013; Haynes et al. 2011). Some workers have also shown that the association between air pollutants causes elevated risk of neuro-inflammation, Alzheimer’s and Parkinson’s diseases (Calderon-Garciduenas et al. 2008). • Long-term effects The first line of defense against foreign pathogens is skin. It is also a target organ for pollution as it absorbs environmental pollutants equivalent to the respiratory tract (Goldsmith 1996; Singh and Maibach 2013). The research has proved that air pollutants like PAHs, VOCs, oxides, and PM affect skin aging and cause pigmented spots on the face (Vierkötter et al. 2010; Drakaki et al. 2014). Several air pollutants are hepatocarcinogenic chemicals, which also increases the incidence of autism and its related disorders in fetus and children (Ito et al. 2011; Roberts et al. 2013; Becerra et al. 2013). Due to the deteriorating quality of air, severe problems in the immune system such as an abnormal augmentation in the serum levels of the immunoglobulin; IgA, IgM, and the complement component C3 in humans as well as chronic inflammatory diseases of the lungs are caused (Vawda et al. 2014; Behrendt et al. 2014). Chronic exposure of eye to air pollutants, results in retinopathy and adverse ocular outcomes (West et al. 2013; Ghorani-Azam et al. 2016).

1.3.1.2 Remediations/Treatment of Air Pollution It is not only an economic burden on a global scale, but also bears serious health related issues to our environment. Some of the major sources of air pollution are industries, thermal plants and IC engines, etc. With the latest technological advancements, it is now possible to utilize efficiently the energy within fossil fuel. For example, latest technologies used in engines like (MPFI) multipoint port fuel injection system or (CRDI) which is common rail direct injection system (Sharma et al. 2018) can be employed to minimize the use of fuel in engines and minimize its toxic byproducts. Also, other techniques like (IDI) indirect injection engine system and (GDI) which is gasoline direct injection system can be employed to reduce the pollutants generated during road transport. It may be noted that quality of fuel burnt also determines the amount and toxic levels of pollutants, example diesel engines require high temperature to burn and because this fuel is used in (CI) compression ignition engines, the fuel injected is compressed at high temperatures causing NOx

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Fig. 1.5 A diagram of wet scrubber. (Image downloaded from https://energyeducation.ca/ encyclopedia/Wet_scrubber on 13 December, 2019)

formation and unburnt carbon particulates. With recent advancements, the combustion chamber of diesel engines is being designed to employ smarter electronic fuel injection systems which are designed for precise injection and creates a homogenous mix of fuel, such techniques are called active techniques (Shukla et al. 2018) and effectively control the generation of pollutants. Also, passive techniques like after treatment devices used in tail pipe of the vehicle help reduce the level of air pollution to a level which satisfies the modern emission regulations. Such techniques involve hydrocarbon particulate trap, selective catalytic reduction system and NOx absorbers. Now considering the contamination of air due to industries, various techniques can be employed to recycle and filter the flue gases generated during any industrial process (Fig. 1.5). Wet scrubbers (Bhargava 2016) are known to be an effective pollution control device to arrest particle matter in the flue gases. There are different types of wet scrubbers like chemical scrubbers/gas scrubbers, particulate scrubbers/venturi scrubbers, Ammonia scrubbers and chlorine scrubbers and sulfuric acid scrubbers

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(Bhargava 2016) employed in industries. The principle of operation is injection of water into waste gas stream. The droplets of water trap the particulates form waste gas stream and it is collected in a sump, after that the treated air is exhausted. Apart from this, it is also advisable to employ strict government policies regarding domestic waste burning in societies and dumps which contaminate our local environment.

1.3.2

Toxicology of Water Pollution and Its Treatment

Water is a key element of not only our body but of almost all the living beings on this planet. Life without fresh and clean water is not possible. Also, it is very easy to contaminate water, and if contaminated to an extent it is may lead to uncured diseases in long run, as same water flows through our bodies. The following subsections explain in detail the serious implication of water pollution on ecology of our planet as well as some techniques to control it.

1.3.2.1 Impact of Water Pollution Water pollution has negative effects on the human beings and also on the environment. Due to untreated sewage, Indians have no access to a proper toilet, children’s die of diarrhea/day and in other countries too (Owa 2014), when great amount of toxic materials like pesticides, heavy metals, etc. are released into the streams, lakes and coastal waters in the ocean. These toxicant gets bioaccumulated and biomagnified in the aquatic ecosystem and due to this large amount of aquatic pollutants are consumed by humans (Evans et al. 2018). Water pollutants also lead to damage to human health carrying infection such as bacteria and viruses. Plant nutrients like nitrogen, phosphorus and other substances that support the growth of aquatic plant life could be in excess causing algal gloom and excessive weed growth. This makes water to have odor, taste and sometimes color. Eventually, the ecological balance of a water body is altered. 1.3.2.2 Remediations/Treatment of Water Pollution In view of the aforementioned effects, nowadays additional interest has been focused on the growth of more effective, low-cost, robust techniques for the treatment of wastewater, without further stressing the ecosystem or human health by the treatment itself (Shannon et al. 2008). In recent years, extensive studies have been done with the aim of finding alternative and economically feasible technologies for water and wastewater treatment. Various methods like coagulation, dialysis, membrane process, adsorption, osmosis, foam flotation, photocatalytic degradation and biological methods have been introduced for the elimination of lethal pollutants from water and wastewater (Pontius 1990). Although, numerous factors such as processing efficiency, engineering expertise, energy requirement, economic benefit and infrastructure have been restricted their applications. Figure 1.6 depicts a water treatment plant in Agra, note that the complexity of treatment is still making the process expensive and hindering its mass application.

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Fig. 1.6 Waste water treatment plant in Agra, India. (Image courtesy of CEEW, image downloaded from https://www.thethirdpole.net/en/2017/05/15/rethinking-wastewater-manage ment-in-india/ on 13 December, 2019)

Because of the complexity of the chemical mixtures in wastewater, conventional wastewater treatment is not always enough to eradicate the entire contaminant load. Ozonation and chlorination are important disinfection steps that have been introduced to control human pathogens. These highly developed treatments are very efficient at eliminating many chemicals and unwanted pathogens (Escher et al. 2011). The photocatalytic process which consists of semiconductors is a popular method to treat waste water from industries and is being widely researched nowadays. It is a low-cost, environment friendly, and sustainable technology to align with the “zero” waste scheme in the waste water industry (Chong et al. 2010). This advanced oxidation technology was used to remove microorganisms, persistent organic compounds, and arsenic metal ions in water. At present, the major technical barriers that obstruct its commercialization remained on the post-recovery of the catalyst particles after water treatment. Adsorption is one of the most effective advanced waste water treatment technologies, which is widely used by industry and academic researchers for removal of various pollutants. Activated carbon is the most widely examined adsorbent by researchers in water treatment process (Reddy et al. 2012). Nowadays, the term “adsorption” became more popular as “biosorption” due to the use of biomaterials as adsorbents for contaminated water treatment. Conversely, this has not been usually working in industries for waste water treatment. Moreover, the practice of magnetic adsorbent technology for the separation of water pollutants has received substantial attention in recent years. Immense efforts have been dedicated to the preparation of variety of magnetic adsorbents for waste water treatment. They

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are an attractive solution for metallic and dye pollutants, principally based on the process of simple magnetic separation (Kumar Reddy and Lee 2012). The importance of recuperation of resources from waste water is increasing globally and, attracted the interest of most of the researchers. Still, as far the contained nutrients are concerned, there has been relatively limited transfer of important research finding into practical operational outcomes. Desalination is another logical option which is used widely in a world where there is scarcity of fresh water and in many cities, which are situated near the ocean.

1.3.3

Toxicology of Soil Pollution and Its Treatment

Soil is a precious resource. Our ecosystem requires clean and healthy soil for healthy crop production. Anything that we consume as a food comes directly or indirectly from our soil. But due to unrestrained industrial activities and unregulated government policies toward waste disposal of societies, our soil is being polluted at a rapid rate. Following subsections explain in detail the harmful effects of soil pollution on environment along with some methods to treat this polluted soil.

1.3.3.1 Impact of Soil Pollution Anthropogenic activities such as industrial activity, chemicals used in agriculture and improper disposal of waste are the main reason for soil pollution. Soil pollution disturbs the ecological balance and causes hazardous health effects in human beings. Moreover, crops cannot grow and flourish in a contaminated soil, however if grow, they might have absorbed toxic chemicals and cause severe health issues in humans consuming them. Sometimes, the increased salinity of the soil causes soil pollution which becomes harmful for vegetation. It modifies the soil structure causing deaths of various valuable organisms (e.g., Pheretima posthuma). Furthermore, also reducing the ability of the soil to support life, thus affect the larger predators like birds and force them to move in the search of food. There is an occurrence of higher incidences of migraine, nausea, fatigue, skin diseases and even miscarriages in humans living near polluted lands (Pierzynski et al. 2000). Depending on the types of pollutants and their concentration present in the soil, several long-term effects of soil pollution are reproductive disorders, cancer, leukemia, liver and kidney damage, and failure of central nervous system. These health problems could be because of direct poisoning by the contaminated land (e.g. children playing on land filled with toxic waste) or by indirect poisoning (like consuming crops grown on polluted land, drinking water infected by the leaching of chemicals from the contaminated land to the water supply, etc.) (Mishra et al. 2016). Health effects will be different depending on what kind of pollutant is in the soil. It can range from developmental problems, such as in children exposed to lead, to cancer from chromium and some chemicals found in fertilizer, whether those chemicals are still used or have been banned but are still found in the soil. Some soil contaminants increase the risk of leukemia, while others can lead to kidney

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Fig. 1.7 Causes of soil pollution

damage, liver problems and changes in the central nervous system (Owa 2014; Evans et al. 2018). The short-term effects of soil pollutants are nausea, headaches, fatigue and skin diseases. The causes of soil pollution are many; Fig. 1.7 depicts some of the major causes of soil pollution in pictorial form.

1.3.3.2 Remediations/Treatment of Soil Pollution There are several ways to acquire soil back to its pristine state or to eliminate the polluted soil so, that the land can be utilized again for agriculture. • It can be controlled by a variety of forestry and farm practices e.g., planting trees on barren slopes. Contour cultivation and strip cropping may be applied instead of shifting cultivation. • In the long-term, soil erosion can be arrested by avoiding deforestation and substituting chemical manures by animal wastes. • Proper dumping of unwanted materials: Open dumping is the most commonly practiced technique. • Manufacture of natural fertilizers: Biopesticides and organic fertilizers should be used in place of toxic pesticides and synthesized chemical fertilizers. E.g., organic wastes in animal dung may be utilized to prepare compost manure. • Proper hygiene: People should be educated about sanitary habits. • Public awareness: People should be educated by informal and formal public awareness programs on health hazards by environmental education. E.g., mass media, educational institutions and voluntary agencies can achieve this. • Recycling and reuse of wastes: The wastes like paper, metals, plastics, organics, glasses, petroleum products, industrial effluents, etc. should be recycled and reused. Industrial wastes should be properly treated at source. Integrated waste treatment methods should be adopted.

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Fig. 1.8 Polluted soil turned red by a nearby closed dye factory in china. (Image courtesy of REUTERS/Stringer, image downloaded from https://www.reuters.com/article/us-china-environ ment-soil/china-needs-patience-to-fight-costly-war-against-soil-pollution-governmentidUSKBN19D0N6 on 13 December, 2019)

• Ban on toxic chemicals: Ban must be imposed on pesticides and chemicals like DDT, BHC, etc. which are lethal to plants and animals. There should a ban on nuclear explosions and improper disposal of radioactive wastes. It may be noted that public awareness and use of organic fertilizers also bears equal importance in reducing soil pollution. Also, ban on toxic and hazardous chemicals such as DDT, BHC, etc. much be imposed by the government to prevent its fatal effects on environment. Tree plantation on big scale and proper government regulations to maintain such plantation is essential for minimizing soil pollution as well as create a better pathway to deal with such soil pollution for our future generation. Some of the countries like China are already facing the crisis of not only air pollution but also soil pollution, due to heavy metal disposal in soil the quality of soil in china is so much degraded that it requires expensive and complex technology to regain its quality of soil (Fig. 1.8).

1.3.4

Toxicology of Solid Waste Pollution and Its Treatment

Solid wastes are the major source of land pollution as it is generated by both the communities as well as industries. Further improper disposal of this solid waste contributes to water and air pollution. It may be noted that if proper disposal techniques are employed along with awareness and strict government policies, the

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toxic effects of this waste can be minimized as solid waste are much easier to segregate on prior basis and use less expensive techniques then required for the treatment of water or air pollution. Following subsections explains in detail the impact of solid waste on ecosystem and its treatment.

1.3.4.1 Impact of Solid Waste Pollution Due to increasing population and rapid industrialization the world is facing some serious negative impacts from the solid waste. Lack of awareness among people as well as improper and lenient govt. policies have created a self-granted mindset among people without realizing the serious toxic impact of such wastes. If on one side like China, which is the world’s largest global electronics giant is producing inexpensive but toxic devices by involving the use of heavy metals in their products at a rapid rate, on other, developing Asian countries like India have become a dumping ground of these items. As a result, toxic mountains of such solid waste are a common site in developing countries. It may be noted that toxic fumes from such dumps not only contaminate our environment but also it degrades the quality of soil on which it is located to such an extent that it becomes useless for any agriculture use for centuries. The rain water seeps through such dumps and percolates into the permeable soil, pollutes the underground water, and makes it useless for not only consumption but also for washing and other community activities. It may be noted that not only such big dump mountains are responsible for increase in pollution but also the dumps at localized level in urban cities have such implications. This localized dumped waste pollutes societies and communities and creates an unhygienic environment for people. The waste gets clogged in sewers and creates a flooding situation during rains. Also, due to clogging the proper flow of water in sewers is obstructed. The flies on the dumped waste are the major carrier of diseases, and it is also responsible for the generation of excess number of mosquitoes. 1.3.4.2 Remediations/Treatment of Solid Waste Pollution Solid waste can be controlled by various means such as disposal, incineration, composting, recycling, etc. Disposing the solid waste can be achieved via sanitary landfills or by incineration. In today’s world of growing population, the compactness of solid waste in sanitary landfills is crucial, therefore these fills are designed on impermeable soil. Heavy machinery is required to achieve the required compactness of solid waste which is then covered with a layer of compact soil for proper disposal each day. Another method of disposal is incineration, which is the process of burning the waste within a specified temperature range by the municipal authorities. It may be noted that using incineration the weight of solid waste may be reduced by 75% which makes it an effective technique for solid waste disposal. Figure 1.9 displays the process of incineration. Composting is a technique of decomposition of solid waste and it generates humus from the organic waste. Such process is beneficial to generate manure for agriculture. While composting helps in decomposing organic waste, the nonorganic waste can be recycled to gain some economic advantage. In today’s era of rapid industrial

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Fig. 1.9 Solid waste incineration process. (Image courtesy of Northern California Compactors, Inc., image downloaded from https://www.norcalcompactors.net/wp-content/uploads/2014/02/ Incineration.jpg on 13 December, 2019)

manufacturing, the products can be recycled to obtain valuable components for the disposed devices. It may also be noted that such recycling also reduces air or water pollution which is a by-product of manufacturing such components. Pyrolysis is another technique which is a process of destructive distillation, in this process the waste products are heated in a reactor at around 650  C to 1000  C in an oxygen less environment which results in the generation of chemical gases for this waste. Such valuable gases such as methane, carbon, charcoal, etc. can be used for energy generation in various applications. Design optimization and resource reduction is another technique to minimize the use of materials while production of industrial goods. In recent years, design optimization has gained popularity as it helps design a product which bears equal strength and complexity with reduced number of components. Various CAD (Computer Aided Design) software’s help develop such design models in which the product is simulated for the desired characteristics before actual manufacturing.

1.4

Conclusion

The purpose of this chapter is to create an educated awareness among reader to understand the hazardous impact of pollution whether its air, water, soil or solid waste on ecosystem. The impact of each type of pollution has been discussed in detail and their remedies have been discussed. Causes of every pollution have been discussed to understand the effect of harmful industrial and human activities which is

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polluting our precious ecosystem. It may be observed that some of the pollutants like air pollutants and water pollutants involve complex and expensive technologies to regain its quality, however, land pollution can be minimized by using appropriate disposal techniques by industries as well as strict government policies toward industries and societies. Also, the techniques involved in solid waste disposal are less expensive and can be widely applied through awareness. It may be concluded that mother earth is our only home in this vast ocean of universe and if it is our right to utilize its resources, it is also our duty to respect its constituent elements likes air, water, and soil.

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Nanomaterials; Applications; Implications and Management Varsha Dogra, Gurpreet Kaur, Rajeev Kumar, and Sandeep Kumar

Abstract

In today’s time, the field of nanotechnology is getting huge attention and priority in the area of research because of its diverse applications that cover almost every field. Nanotechnology comprises fabrication, characterization, controlled size nanomaterials having different potentials, research, and development in the nanometer scale. Nanotechnology is playing the most important roles in science and technology; the medical field, food industries, agriculture, and commercial industries. Applications of nanotechnology and engineered nanomaterials (ENM) are growing very vastly that is creating a marked impact on human health and everyday life. However, there are some uncertainties, and anomalies in the properties, chemical composition, size, and shape of the nanomaterials that cause an adverse impact on the public health and ecosystem. Thousands of nano-based consumer products are already in the market without proper checking of possible risks on the earth and the human body. A very little is known about the toxicity of nanomaterials toward biotic and abiotic components of the environment and their management. This book chapter provides the summary of nanomaterials, their classifications, applications, impacts or implications, and their management strategies.

V. Dogra · R. Kumar Department of Environment Studies, Panjab University, Chandigarh, India G. Kaur (*) Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh, India e-mail: [email protected] S. Kumar Department of Bio and Nano Technology, Guru Jambheshwar University of Science and Technology, Hisar, Haryana, India # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_2

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Keywords

Nanomaterials · Applications · Nanotoxicity · Management

2.1

Introduction

An overview of nanotechnology and nanomaterials: Nano word represents extremely small or one billion of stated unit i.e., 10–9. One nanometer length is nearly equivalent to 5 silicon atoms or 10 hydrogens bring into line. Richard P Feynman introduced the concept of nanotechnology in December 1959 in his lecture entitled ‘There’s plenty of room at the bottom’ at American Physical Society meeting (Wu and Yu 2017). From that time, there have been very innovative and revolutionary developments that have proved the Feynman’s perception of materials at the nanoscale. The term ‘nanotechnology’ was first invented by Norio Taniguchi (a professor at the Tokyo University of Science) in 1974 to explore and describe the ultra-precision and fine dimensions. In 1986, K. Eric Drexler used the term ‘nanotechnology’ in his book Engines of Creation: The Coming Era of Nanotechnology after getting inspired by Feynman’s notions. Presently, the nanotechnology field considered to have huge applications in different areas such as in various commercial products, biomedical field, drug development, and delivery, in decontamination of water, in various technologies, and the formation of smaller, stronger and lighter substances. The use of nanomaterials (NMs) is getting advanced and creating a great revolution in the field of nanotechnology. From the last few decades, this field has developed immensely and has produced different types of NMs including metallic, oxides, and metal oxides (Ostiguy et al. 2006; Aitken et al. 2004). Nanoscience deals with the fabrication, characterization, examination, and exploitation of nanosubstances. Materials at nanoscale exhibit unique properties and unpredictable characteristics such as extremely small size, surface charge, shape, chemical reactivity, superparamagnetic behavior, conductivity, unexpected strength, etc. that same material at macro or microscale doesn’t possess. Nanosubstances with size less than 100 nm possess various types of morphology that depends on the orientation of the nanocrystals. Various types of morphologies are documented in the literature such as rods, tubes, fibers, wires, petal-shaped, spinel, floral shape, spherical, cubic, trigonal, tetrahedral, hexagonal, octahedral, decahedral, polyhedral, etc. (Imasaka et al. 2006; Warner et al. 2008). NMs have exclusive properties such as unique magnetic, electrical, catalytic, mechanical, and optical (Qin et al. 1999; Webster et al. 1999; Webster 2000; Vasir et al. 2005; Ferrari 2005). Small size, large surface area, and exclusive physicochemical properties of nanosubstances make them extremely oversensitive leading to cause adverse effects on biotic and abiotic components of the ecosystem (Oberdörster et al. 2005b). Consequently, more focus is given on the public health and environment safety. Royal Society and Royal Academy of Engineering in 2004 gave the first report on nanotoxicity and emphasized the current requirement to study and inspect the

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toxicity of nanosubstances on different levels such as physiological, cellular, and genomic to ensure the safety of NMs before the utilization. Since many studies have been done on the physiological toxicity, oxidative stress, inflammation, cytotoxicity, and genotoxicity of nanosubstances but still the evidence is inadequate and there’s a need for in-depth investigation (Nel 2006; Xia et al. 2006; Stone et al. 2006; Sayes et al. 2007). Nanotechnology is an interdisciplinary science that includes: 1. Nanophysics: This field includes quantum physics, spintronics, photonics which is meant for the synthesis of NMs and also for the research area. 2. Nanochemistry: This field comprises nanocolloids, quantum chemistry, and sol-gel which are linked with the NMs fabrications and different research areas. 3. Nanoelectronics, optoelectronics, and nanoengineering: These fields relate with the development of unique technologies, nanodevices, nanomotors, nanoactuators, nanorobots, ultra-large integrated circuits (ULCI), microoptoelectronic-mechanical systems (MEMS, MOEMS), etc. 4. Nanomaterials science: This research area comprises of nanoceramics compounds, nanopowder technology, nanosintering, nanotribology, and other nano processes which are connected with the research, development, and synthesis of novel NMs architectures, functional and smart nanosubstances with exceptional properties. 5. Nanometrology, Nanodevice-building, and Nano-hand-craft: This field concerns the development of smart nanotools, instruments, and computational systems to advance the nanotechnology field. 6. Nanobionics: This field is related to the advancement of nanobiorobots, nanobiochips, etc.

2.2

Nanomaterial Sources

2.2.1

Engineered Nanomaterials

These NMs are man-made for human benefits. Humans are intentionally fabricating the NMs for commercial benefits and upgrading the lifestyles (Martin et al. 2013). Engineered NMs are fabricated by using various methods such as physical, chemical and biological methods. Examples of physical methods are inert gas condensation, pulse vapor decomposition, laser pyrolysis, electrospraying, etc. Wet chemical methods include microemulsion, microwave, thermal decomposition, precipitation/ coprecipitation, hydrothermal/solvothermal synthesis, biological and green methods (Fig. 2.1). Biological methods include plant extract-assisted biogenesis, microorganism-assisted biogenesis, and bio template-assisted biogenesis.

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Fig. 2.1 Different wet chemical methods used for the fabrications of nanoparticles

2.2.2

Ultrafine or Incidental Nanomaterials

Ultrafine or incidental NMs are defined as the NMs fabricated indeliberately either directly or indirectly by anthropogenic processes. These NMs are produced by industries non-intentionally as a by-product of various processes. Other than industries, ultrafine nanoparticles (NPs) released from automobile engine exhausts, household combustion processes like cooking, smelting, fires, fuel combustion, welding fumes, and volcanoes fuel also (Oberdörster et al. 2005b; Duffin et al. 2007). It was documented that fullerenes (one type of NMs) are released from candle fumes, burning gas, and biomass, as a by-product of corrosion products (Barceló and Farré 2012). Aerosol research, environmental and occupational health communities used the term ‘ultrafine’ to define airborne particles in the range of 1–100 nm (Barceló and Farré 2012).

2.2.3

Natural Nanomaterials

These NMs are defined as the nanosubstances made by nature through biogeochemical processes, without anthropogenic connection. Natural NMs have always been

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abundantly present in the 4.54-billion-year-old earth system. Therefore, ever since life first appeared on this planet, natural NMs and living things have coevolved.

2.3

Classification of Nanomaterials

NMs are classified based on dimensionality (Fig. 2.2), composition, uniformity, morphology, and agglomeration (Royal 2004; Buzea et al. 2007).

2.3.1

Dimensionality

(a) 0D nanomaterials: Zero-dimension NMs are those materials that are measured within the nanoscale. Examples of zero-dimensional NMs are NPs and nanopores.

Fig. 2.2 Classification of nanomaterials based on dimensionality

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(b) 1D nanomaterials: At the nanometer scale, NMs having one dimension includes nanotubes, nanowires, fibers, fibrils, and dendrimers. (c) 2D nanomaterials: These are materials that are measured outside the nanoscale. Two-dimensional NMs are generally surface coatings or thin films. Surface coatings have potential applications in electronics, optics, and magneto-optic devices, fiber-optic systems, information storage systems, biological and chemical sensors. At an atomic level (monolayer), thin films can be controlled (Seshan 2002). (d) 3D nanomaterials: In all three dimensions materials at the nanoscale are known as 3D NMs that constitute nanocrystals, fullerenes, quantum dots, colloids, and precipitates. Some common types of NMs are nanofibers, nanotubes, quantum dots, dendrimers, and fullerenes.

2.3.2

Morphology and Nanocomposites

(a) Morphology: Different NPs have different morphology and it occurs according to high and low aspect ratio particles. High aspect ratio NPs are nanowires and nanotubes whereas NPs with low aspect ratio include spherical, cubic, oval, helical, prism and pillar shapes. (b) Nanocomposites: Significant progress has been made in recent years associated with nanocomposites with the increasing development of new technologies in fields like ferrofluids, magnetic nanospheres, and microspheres. Microspheres and nanospheres comprising of a magnetic core surrounded by non-magnetic matrix are utilized in various biological applications (Krishnan 2010). These types of nanocomposites are used as a carrier by utilizing the magnetic field. Nanocomposites having biocompatible coatings help in preventing the aggregation and protects the body from toxicity also. According to few reports, it was documented that for in vitro applications, biocompatible coatings are not necessary, and particles can be coated with nontoxic materials. Supermagnetic types of composites are made by surrounding the supermagnetic nanocrystals in a non-magnetic matrix, for example, nanoporous silica or polystyrene (Leun and SenGupta 2000; Jain et al. 2008; Behrens 2011). Under the external magnetic field, formed colloidal particles maintain the superparamagnetic behavior and display higher magnetization. NMs chemical composition constitutes of one or several materials. Naturally formed NPs are often formed of materials agglomerations with different types of compositions, whereas pure NMs having a single composition can be synthesized in vitro using various methods. There are basically different chemical orderings by which elemental atoms are arranged within the NMs (Borbón 2011; Tiruvalam et al. 2011).

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1. Mixed nanomaterials: In this type, the arrangement of atoms can be either ordered or random. Ordered arrangement corresponds to the positioning of A and B atom. 2. Core-shell nanomaterials: In this form of ordering, NMs composed of two different types of atoms in which one type of atom surrounds another type of atom forming a shell kind of structure. There’s one more subcategory of coreshell NMs i.e., multishell or onion-like NPs. The arrangement is in the form of AB-C in the case of three different atoms and A-B-A form for two different atoms in an alternating form. 3. Layered nanomaterials: This type of arrangement is also known as dumbbell-like NPs. This form comprises of two different NPs having a mutual interface that inclines to lessen the bonds among the atoms. Apart from these types, there are other types of NMs having different compositions which were synthesized after looking at the increasing need for multi-functional NMs i.e., multicore shell structure in which core is in the shape of onion-like or dumbbell-like (Shi et al. 2006; Llamosa Pérez et al. 2013; Benelmekki et al. 2014, 2015; Benelmekki and Sowwan 2015).

2.3.3

NP Uniformity and Agglomeration

According to the properties of the NPs, NPs can be formed as a suspension/colloids, solid, dispersed aerosol, or in agglomerated form. Agglomerated NPs synthesized due to the van der Waals forces and Brownian motion. Agglomeration caused by Brownian motion is known as coagulation. Many processes help in the removal of agglomeration of NPs, one of the ways to avoid the agglomeration is by coating the NPs by another organic or inorganic material. In the case of magnetic NPs also, agglomeration of NPs is documented unless NPs are coated with any non–magnetic substance.

2.3.4

NP Characterization

After the fabrication of NPs, it is important to characterize the particles to understand the NPs in detail like their structure, composition, uniformity, charge, etc. To understand these properties of NPs, many techniques can be utilized for their characterization. The main techniques of characterizations are transmission electron microscopy (TEM), scanning TEM (STEM), scanning electron microscope (SEM), electron energy loss spectroscopy (EELS), X-ray powder diffraction (XRD) and X-ray photoelectron ppectroscopy (XPS) (Mourdikoudis et al. 2018).

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Nanotechnology Applications in Different Fields

Nanotechnology is a very overpowering technology that taking over the world enormously and rapidly. Nanotechnology is spreading all over the world because of its unique and supremacy properties like durability, hardness, strength, catalytic, electrical, magnetic, etc. and also due to its ability to control the materials at the atomic level (10 9 m). Because of these unique properties, nanotechnology has widespread applications in every commercial field such as nanofluid, nanostructured coatings, nanoremediation, microbial fuel cell, nanocatalyst, nanophosphors development, computer nanochips, removal of environmental contaminants, nanoparticles in sunscreen creams and lotions, etc.

2.4.1

Nanofluid

Nanofluids are heat transfer fluid consisting of particles in nanoscale dispersed uniformly and stably in the base fluid. Different factors change the properties of nanofluids that depend on various parameters such as pH control, surfactant, ultrasonication, stability, uniformity, properties of the base fluid, particle geometry and dimensions, and effects of fluid-particle interfacial. Nanofluids are better than conventional fluids because of better thermal performance as NMs have a high surface to volume ratio that advances the thermal conductivity of nanofluids. Heat exchangers are required to transfer the heat at a maximum amount. Heat transfer rate depends on the surface area, properties of heat exchanger material, and working fluid properties such as thermophysical properties (Peyghambarzadeh et al. 2011). NMs commonly used are CuO, NiO, TiO2, ZnO, Cu, Au, Al2O3, single-walled carbon nanotubes (SWCNT), multiwalled carbon nanotubes (MWCNT), SiC, TiC, etc. (Bognár and Vencl 2019).

2.4.2

Nanostructured Coatings

NMs are utilized as a coating material to prevent erosion and corrosion to increase the mechanical properties of the metal substances. NMs coating is a unique way to enhance the surface properties of any substance to improve the working efficiency (Higuera Hidalgo et al. 2001). According to many reports, nanocoating increases the service life of various materials (Keshavamurthy et al. 2014; Kusmoko et al. 2015; Shukla et al. 2015). There are different methods for nanostructured coatings such as physical vapor deposition, chemical vapor deposition, etc. but the most widespread method is the thermal spray process as this method gives more throughput in minimum time (Roy et al. 2006).

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Nanoremediation

Among other applications, nanoremediation is attaining superior attention because of the pollutants decontamination properties (Bartke et al. 2018; Corsi et al. 2018). Nanoremediation is the employment of the NPs in the remediation of the environment by degrading or immobilization of the pollutants (Kadu et al. 2017; Wang and Wang 2018). The commercial industries of nanoremediation have increased over the past few years. Under a set of favorable conditions, nanoremediation is employed using different types of nano-sized particles. To decontaminate the soil or groundwater, NPs are either directly injected in it or pump and treat method is used. Remediation takes place by adsorption of the xenobiotics for the treatment of water. In some cases, after the treatment of nanoremediation, NPs can be recovered and can be utilized in the subsequent treatment. The main scenario of decontamination or environmental remediation is the removal of the harmful substances, elements and molecules from the in situ conditions without harming or disturbing the environment.

2.4.4

Carbon Nanotube-Microbial Fuel Cell

In this type of fuel cell, microorganisms are utilized to consume organic waste such as starch, sugar, etc. to generate electricity and clean water. This is an innovative technology to produce electricity by treating industrial effluents and also domestic wastewater. Carbon nanotubes (CNTs) have a high surface area, chemical stability, and good mechanical properties making them suitable for designing electrodes and sensors as they are ideal for the growth of cells. CNTs support the growth, proliferation, and immobilization of bacteria. Multiwalled CNT provides a self-supporting structure for the growth and proliferation of hydrogen-producing bacteria (E. coli) (Thepsuparungsikul et al. 2012). Single-walled CNTs and MWCNTs are affirmed to be compatible with the growth of various eukaryotic cells.

2.4.5

Nanocatalyst

Various NPs have extraordinary surface activity making them ideal nanocatalyst. Aluminum in nanosize has high reaction rate and is employed as solid fuel in rocket propulsion, however in bulk form, aluminum is generally utilized in utensils (Brousseau and Anderson 2002; Galfetti et al. 2006). Nanocatalysis is a growing field that comprises the utilization of nanosubstances as a catalyst in various catalytical applications that benefits the chemical industries. Nanocatalysts have various applications such as in water purification, biodiesel production, carbon nanotubes, in solid rocket propellants, photocatalytic activity, photodegradation of methylene blue, photocatalytic degradation of phenol, photocatalytic degradation of azo dyes, photocatalysis, photovoltaic, wastewater treatment, etc. (Chaturvedi et al. 2012).

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Nanophosphors Development

Nanophosphors have been extensively studied in the last decade due to their application in high-performance displays and devices. Nanophosphors are generally fabricated in the form of powders but there are few reports of nanophosphors synthesized as matrix and film form also (Chander 2005). The resolution of the TV, monitor, or different screens depends on the pixel size. These pixels are made from materials called phosphors which glow when hit by electron stream inside the cathode ray tube (CRT). As the size of the pixel or phosphors reduces, the resolution improves. By utilizing the nanophosphors, the resolution of display devices can be improved and also reduce the cost of manufacturing (Chander 2005).

2.4.7

Computer Nanochips

Nanotechnology is helping the industries by providing long-lasting, durable, better thermal, and ultra-high purity NMs. A nanochip is a product of nanotechnology which is a very small electronic integrated circuit measured in nanoscale in which individual particles show major characters. Smaller the size of the electronic system, the processing system can work more powerfully in given physical space, less energy is utilized for working, and in miniature form rate of work is faster because the components of the system are closer to each other and also reduces the chargecarrier transit time. Nanochip is composed of three main constituents i.e., transistors, interconnections, and architecture (Alagarasi 2011).

2.4.8

Removal of Environmental Contaminants

Nanotechnology has developed innovative and unique materials that possess enhanced physical, chemical and mechanical properties. NMs are utilized as a catalyst to interact with the various pollutants such as toxic and lethal gases (such as carbon monoxide, nitrogen oxide released from automobiles; carbon dioxide, hydrocarbons, chlorofluorocarbons, volatile organic compounds, etc.) which harms the environment and also public health (Falahi and Abbasi 2013; Mohamed 2017). An example of nanocatalysts is catalytic converters which are used in automobiles and in power generation equipment to avoid environmental contamination. Small size NMs have a high surface/volume ratio and are effectively designed to interact with the environmental pollutants and convert them into non-toxic materials. Using the nanofilters in air pollution control devices, air pollution can be decreased (Ngô and Van de Voorde 2014).

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Nanoparticles in Sunscreen Creams and Lotions

UV exposure from sunlight is the cause of sunburn and cancer. NPs are getting huge attention from cosmetic industries because of different unique properties. It was reported that nano-TiO2 enhances the sun protection factor (SPF) without causing stickiness in the creams and lotions. ZnO and TiO2 NPs in the lotions and creams act as nano skin blockers as they do not cross the skin and remain outside making a layer on the skin. These nano-based lotions and creams are very effective for a long time. ZnO and TiO2 NPs protect the skin from UV-A and UV-B radiations without causing any irritation and disrupting the endocrine system. These NPs are transparent and pleasing to touch (Lorenz et al. 2010; Wiesenthal et al. 2011).

2.4.10 Advanced Applications of Nanomaterials • Metallic NMs are utilized as a strengthening material in alloys to construct lightweight material with high strength and solidity. These alloys are mainly used in the automotive sector and aerospace sector. For example, titanium NPs are employed as an alloying element in steel making it more durable by enhancing the properties such as strength, temperature, corrosion resistance, and ductility (Fiiipponi and Sutherland 2012). • In the field of civil engineering, nanotechnology plays a huge part in providing improved designs and building methods. Nanotechnology aids in the advancement of the various structural constituents, their properties, strong composition, lightweight and self-disinfecting surfaces. Saurav (2012) reported that by using SiO2 nanopowder instead of using conventional SiO2 as a part of traditional concrete, the mechanical properties of the concrete can be increased (Saurav 2012). • In the field of power production, nanotechnology also plays a significant role, for example, MnO2 is utilized in rechargeable batteries (Sayle et al. 2009). TiO2 films and nano-silicon are utilized in the formation of thin-film solar cells (O’Regan and Grätzel 1991). Plastic solar cells or organic solar cells are a type of photovoltaic cell that helps in the conversion of sunlight energy into electrical energy 50 times more than conventional cells (Brabec et al. 2001). • In the field of biomedical, NPs are employed for therapeutic purpose (Giljohann et al. 2010). Various NPs have antimicrobial and antifungal properties as shown in Fig. 2.3 (Shrivastava et al. 2007). • In drug delivery: nanomaterials assist in the target delivery of a drug by entering the bloodstream, and also improves the delivery of drugs that are poorly soluble in water (Bahrami et al. 2017; Kumar et al. 2017; Nejat et al. 2017).

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Fig. 2.3 Applications of nanoparticles (NPs) in the field of biomedicine

Besides, • Various elemental properties can be enhanced such as conductivity (Dongliang et al. 2017; Abdel Aal et al. 2017), redox properties, magnetic, and thermal (Pourgolmohammad et al. 2017; Tebaldi et al. 2018). • In the preparation of advanced polymer solar cells (Shen et al. 2017), dye-sensitized solar cells (Wu et al. 2016), and thin layer solar cells (Khanaki et al. 2015; Choi et al. 2016; Jang et al. 2016; Kim et al. 2016; Park et al. 2016) with high efficacies. • NPs are utilized in decontamination (Gupta and Sengupta 2017; Walekar et al. 2017), dye adsorption (Wang et al. 2015), in gas sensors (Van Duy et al. 2016). • Nano-silicon dioxide crystals are utilized in various fields, the finest example of their use is in the formation of tennis racquets strings as these NPs gives extra strength (Dolez 2015). • Nanoporous graphene and doped graphene complexes are employed in environmental remediation (Thomas and Ramaswamy 2016). • Other benefaction of the nanotechnology field includes the formation of powerefficient LED’S (Jeong et al. 2014), water-resistant coatings (Hassan et al. 2016), solar stucco (Luévano-Hipólito and Martínez-de la Cruz 2018), and auto-cleaning glasses (Rifai et al. 2017).

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Implications and Fate of Nanotechnology in the Environment

NPs are getting huge attention in various fields because of the diverse applications and unique properties but industries are commercializing the NPs without proper detail study, and tests of nanotoxicity leading to create nano-ecotoxicity. Overuse, overproduction, commercialization, and disposal of the NPs have led to their uncontrolled release in the ecosystem. Effluent streams from industries and factories, landfills, commercial products, and incinerated products are the main sources of NPs released in the environment. The fate and NPs interaction depend on various factors such as shape, surface charge, etc. but the significant factor that regulates the nanotoxicity is the small size of the NPs. An extremely small particle with the size range of 1–10 nm acts analogous to a gas molecule and can enter the human body effortlessly. Workers of nano-based commercial industries are more prone to occupational exposure to NPs. NPs that enters through the respiratory system can interfere with the functioning of the cell (Khalili Fard et al. 2015; Bahadar et al. 2016). Other parameters that impact the nanotoxicity are shape, surface charge, surface morphology, chemical composition, accumulation ability, and solubilization (Caballero-Díaz et al. 2013; Conway et al. 2015). From all the nano-ecotoxicity investigations, it has been concluded that the toxicity of NPs is dependent on various factors and it is not controlled through any one factor. Therefore, every nanomaterial should be assessed at the individual level in detail to confirm its safety. After entering the environment, NPs undergoes dissolution, agglomeration, settling, biological, or chemical transformation, mineralization, speciation (Conway et al. 2015; Kent and Vikesland 2016; Peng et al. 2017). Some NPs remain in the environment and also display biomagnification in organisms that depend on its stability (Smita et al. 2012).

2.5.1

Disadvantages and Implications of Nanomaterials

1. Nanomaterials unpredictability and instability: The kinetics of the nanosubstances is very rapid and thus controlling their properties is extremely challenging. To avoid the agglomeration of the particles, the encapsulation of the NPs technique is used. Nanosubstances are corrosion resistant and vastly soluble. Maintaining the structure of NMs is very challenging as their properties deteriorate. 2. Fine metal nanopowders act as strong explosives in the presence of oxygen due to their high surface area. Some nanopowders can effortlessly cause an explosion by exothermic combustion. 3. Impurity: NMs are very reactive and root to agglomeration causing impurities. Encapsulation of nanosubstances becomes essentials when they are fabricated through chemical routes. Stabilization of NMs achieved when reactive particles are coated with the nonreactive complex. But still, attaining the purity of NMs is very problematic as impurities become part of the fabricated NMs.

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Fig. 2.4 Sources, exposure routes, and effects of nanoparticles in human body

4. Harmful for flora and fauna: Because of the small size of the NMs, they are harmful to the biotic and abiotic components of the ecosystem. NPs are known to cause cytotoxicity, genotoxicity, and ecotoxicity. NPs easily enter the cells and interrupt the cell functioning such as transcription and translation process (Byrne and Baugh 2008). The main cause of the toxicity is the extremely small size, high surface area, and improved surface activity. NMs are also known to cause biomagnification after entering the food chain leading to various complications in the different organs of the human body such as lungs, liver, blood, etc. (Fig. 2.4) (Byrne and Baugh 2008). 5. The problem in fabrication, isolation, and utilization of nanosubstances: Maintaining the stability, and uniformity of the NPs is very difficult. Therefore, to maintain stability, NMs have to be coated with a stable substance. Isolation of nanosubstances is very complicated as particles tend to merge and grow in size because of agglomeration.

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6. Impact on human health: NMs gets in contact with the human through various commercial products such as body lotions, facial creams, cosmetics, and various medicinal drugs (Oberdörster et al. 2005b; Curtis et al. 2006; Hagens et al. 2007). The human body gets exposed to NMs through various routes such as skin, respiratory tract, and gastrointestinal tract. Through inhalation, small size nanosubstances pass the respiratory tract and pass down to the alveoli of lungs affecting and disturbing the respiratory system (Oberdörster et al. 2005a; Lam et al. 2006; Nel 2006; Donaldson et al. 1999, 2006). Various NMs are known to enter and interact with the body organs such as lymph nodes, lungs, kidney, spleen, bone marrow, heart, intestinal tract, and liver causing various complications (Fig. 2.4) (Oberdörster et al. 2005a; Chen et al. 2006a, b; Hagens et al. 2007). 7. Disposal and Recycling: Disposal of NMs is a very complicated and difficult process as it requires the full understanding and knowledge of NPs properties. NMs are difficult to recycle as they act in an uncertain manner because of their unique properties. Therefore, a detail investigation is required to combat the toxic effects of nanosubstances on flora and fauna. 8. Impact on earth: Various parts or components of the earth are getting disturbed by NMs. The reason could be a small size and high reactivity which causing alterations in the earth’s system and impacting globally (Qafoku 2010). NMs instigating climate change, alterations in the earth components and various cycles, changes in the soil environment (Gislason et al. 2009; Qafoku 2010b). The concentration of CO2 has increased from about 320 to 410 parts per million (in 2018) leading to an increase in earth temperature and climate change (Hochella et al. 2019). Various changes in the climate have caused variations in every day, periodic and interannual temperatures; local rainfall; and prolonged phase of drought, heatwaves, wildfires, and permafrost (Pachauri et al. 2014) that is disturbing the ecosystems, forests, agronomy, and food production; and also changing earth water quality (Fig. 2.5) (Qafoku 2010b).

2.6

Management

To investigate the nano substances effects on the flora and fauna, a detailed study of the nanotoxicity is required. The chief components of the environment are air, water and soil and these components are interlinked and also related to biota. Contamination of one component can contaminate the other components over the time leading to nano-ecotoxicity. The prediction of the factors causing nanotoxicity and affecting the biotic and abiotic components of the ecosystem is often problematic and difficult. But the nano-ecotoxicity can be overcome by regulating the conditions and fabrication methods (Rollins 2009; Davies 2008).

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Fig. 2.5 Various implications of nanomaterials on the earth system

2.6.1

Methods to Overcome the Nanotoxicity

Because of the severity of nanotoxicity, there is an immediate requirement of advance strategies to minimize the toxic effects of nanosubstances. The following are a few ways to avoid and regulate the nano-ecotoxicity: • By coating the NPs with biocompatible complexes. For example, ZnO NPs have exceptional antimicrobial potential but their utilization as food additives is restricted as they are toxic in nature. Considering this, Chia and Leong (2016) studied the coating of ZnO NPs with Si to lessen the toxicity. It was confirmed that the Si layer did not change the antimicrobial potential of the ZnO NPs against S. aureus and E. coli. Additionally, Si coating averts the dissociation of ZnO NPs into zinc ions (Chia and Leong 2016). • By coating with natural substances or with complexes that mimic the properties of the natural substances to overcome the toxicity.

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• By changing the protocol of NPs fabrication to prevent the nanotoxicity. For example, Kansara et al. (2018) developed the biocompatible Fe3O4 NPs using a safe-by-design approach by the coprecipitation method (Kansara et al. 2018).

2.6.2

Limiting the Nano-Contamination

Nano-contamination can be controlled by restricting the NPs into the environment that can only be achieved by utilizing sieve-like materials or instruments that can filter the NPs. One such filter is HEPA (High-Efficiency Particulate Air Filter). Bortolassi et al. (2017) investigated the potential of HEPA filters to remove NPs. In this study, three filters were utilized i.e., HEPA 1 filter with 99.995% MPPS (most penetrating particle size) efficiency, HEPA 2 filter (EPM2000) and HEPA 3 filter (QM-A). HEPA 1 and HEPA 2 filter were made of glass but HEPA 3 filter was of micro quartz fibers. From the study, it was confirmed that all the filters blocked the NPs passage. HEPA 2 filter affirmed the filtration capacity of 99% (Bortolassi et al. 2017). Using this kind of technology, the entry of NPs into the atmosphere or ecosystem can be controlled. Another method of controlling the NPs into the environment is recommended by Mikelonis et al. (2016). According to the study, changes in the fabrication methodology led to a decrease in the Ag release from ceramic water filters (CWFs) and in disinfection efficiency (Mikelonis et al. 2016). Four different molecules i.e., polyvinylpyrrolidone, casein, branched polyethyleneimine and citrate were utilized to stabilize the silver NPs.

2.7

Conclusion

The emergence of nanotechnology is a sign of revolution in the field of technology that will enter eventually every dimension of life. Nanotechnology has various commercial applications that cover practically every sector such as catalysis, environment, biomedical, food industries, agriculture, sensing, energy, and photovoltaic. NPs have the potential to effectively remove the pesticides, dyes, heavy metals, and decontaminate the air, water, and soil. Besides various applications, nanotechnology has also countless concerns regarding nanotoxicity. Nanotechnology is an untested technology that has many downsides. This field is fabricating a significant quantity of nanosubstances that could potentially be released into the ecosystem and can enter the groundwater aquifers. According to the various reports, NMs have potential harmful impacts on the human body and earth system as they interact with the living system. In view of this, many researchers are doing investigation considering different parameters for the safety of the environment and public health. Considering this, the field of nano-toxicology is growing to assess the possible risks of nanomaterials.

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Acknowledgments G. K. is thankful to DST for Inspire Faculty award (IFA-12-CH-41) and PURSE grant II. R. K. is thankful to UGC (F. No. 194-2/2016 IC) for providing financial support. V. D. is thankful to UGC for SRF.

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Environmental Nanotechnology: Its Applications, Effects and Management Teenu Jasrotia, Ganga Ram Chaudhary, Sesha Srinivasan, and Rajeev Kumar

Abstract

Environmental nanotechnology is holding an immense position in modern days’ science and engineering. These advanced ‘nanomaterials’ are being utilized for diverse range of applications but with the ideology of saving environment. Environmental sector is being tackled with the aim of developing sensors for detecting, monitoring and analysing the toxic contaminants so as to protect and remediate environment. In the presented chapter we have tried to illustrate applications of nanofields, and resulting impacts on the four spheres of the earth. Many efforts are being taken to have a check on the negative impacts of the nanotechnology but still there are many prevailing discrepancies that need to be confronted. Keywords

Nanotechnology · Sensors · Environment · Toxic

T. Jasrotia Department of Environment Studies, Panjab University, Chandigarh, India Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh, India G. R. Chaudhary Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh, India S. Srinivasan Florida Polytechnic University, Lakeland, FL, USA R. Kumar (*) Department of Environment Studies, Panjab University, Chandigarh, India e-mail: [email protected] # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_3

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3.1

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Introduction

Nanotechnology has the potential to be called ‘technology of choice’ because of its probable key factors of sustainability, precised application and eco-friendliness (Mishra et al. 2019). It has provided manipulation of science to merge various fields in one domain (Subramani et al. 2019). Nanotechnology has presented technological developments for managing phenomenon at their smallest constituent levels (Nasrollahzadeh et al. 2019a). The emergence of nanotechnology with our day-today life has led the conventional processes to a new and improved level. Their unique and incomparable optical sensitivity and reactivity is resultant of their size downscaling (Nel et al. 2006). Installation of nanosystems into larger systems provides completely different physical, chemical as well as biological grounds to them. Nanotechnology has stood up as the common and efficient solution for the addressal of challenges in diverse technological as well as environmental fields as shown in Fig. 3.1. With the help of divulgation at nanoscale, new techniques have been worked upon for maximal functional outflux with minimal resource and energy influx (Subramani et al. 2019). Researchers are running for exploration of untapped potential of nanotechnology (Mishra et al. 2019). Nanotechnology is developing with an expanding pace for ground-breaking developments in framing new and improved equipments but without paying considerate attention towards its devastating outcomes on environment (Nasrollahzadeh et al. 2019b). With the introduction of new products in the market, public supported with organizations working on national and international platforms has aggravated the discussions on the health concerns of nanotechnology (Murphy et al. 2017). As a result research work to disclose potential hazards associated with technology has been coming on practical grounds but still it is too far to understand the whole implications of nanotechnology on environmental aspects (Serrano 2010). For the concerned purpose the safety issues associated with same, need to be incorporated in the mandatory regulatory system of nations. As per present times data, only few countries have nanoregulation as their legislating agenda. With the stances of public safety, the swift upsurgence of unguarded applications of nanoparticles (Nps) in diverse fields has raised the safety concerns with respect to basic commodities, organisms and environment as well (Saitoh et al. 2001). The ongoing research reflects towards the potential of nanotechnology to drive the future towards different inclination than todays, which totally depends on the route-plans of usage (Karn 2004).

3.2

Nanotechnology

The nanoscale concision of elements leads them in the sphere of Nps. Precise designing of material at atomic level to form functional units in real world, can be ascribed to nanotechnology (National Science and Technology Council 2000). After the statement of Feynman—‘there are plenty of room at the bottom’, nanoengineering proved to be a leading edge of development (Purohit et al. 2017).

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Fig. 3.1 Applications of nanotechnology in different fields

3.3

Environmental Nanotechnology

Nanotechnology that embraces the field of environment comes under the domain of environmental nanotechnology. Nanotechnology can be interfaced with the environment on the addressal of three aspects—biological congruity and resulting impacts on living beings, transformation procedures on grounds of geochemical as well as biological cycles ultimately describing the fate of the materials in biotic and abiotic components and lastly how the technological hands can be provided to tackle environmental problems (Jiang et al. 2019). The concerned aspect of nanotechnology emphasizes the introduction of sustainability terms for the designing of nanoentities (Ai et al. 2011; Yang et al. 2012) along with addressal of the associated

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Fig. 3.2 Nanoparticles interaction with four spheres of the earth

ecological concerns (Wiesner and Bottero 2007) and benefits. While talking about environmental nanotechnology all the four spheres of earth (Fig. 3.2) are need to be addressed.

3.4

Applications of Environmental Nanotechnology

Completely changed properties of nanosystems from their macro-sized counterparts or parent elements make them materials of interest for different environmental applications (Louie et al. 2016). Most of the interest is shown by the researchers for designing of nanomaterials to treat pollution problems. One such example is of nano-cellulose owing to its mechanical properties accompanied with property of film formation, has been used for fabrication of separating membranes for air and liquid

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(Isogai et al. 2011). For treating pollution laden environment, nanostructures could be metal driven or metal free. Metal-Free Nanostructures Nanostructures without the involvement of metals do possess inimitable two-dimensional properties such as mechanical, optical, physical and chemical as well, which made them material of choice for treating pollution. Production of stable BN nanosheets with the doping of carbon have higher potential of electron-hole pairs generation with the stimulation of visible light (Huang et al. 2015). Metal-Nanostructures High surface to volume ratio synchronized with shorter diffusion distances of nano-photocatalysts augments their enactment manifolds (Ren et al. 2017). Sun et al. had reported synthesis of photo catalytically efficient nanotubes of monoclinic BiVO4 with 60 times enhanced surface area than its bulk counterparts (Sun et al. 2010). The enhanced activity is attributable to lower electron-hole recombination rates along with generation of radical and active sites on surface of nanotubes for adsorption of pollutants. It has been reported that CdS-loaded TiO2 nanotubes take visible spectrum of light to trigger the photocatalytic activity (Banerjee et al. 2008). Coupling of g-C3N4 with different semiconductors such as SnO2 (Yin et al. 2014), CeO2 (Huang et al. 2013), and ZnO (Sun et al. 2012) has been successfully carried out. The resultant coupling offers better results in the form of more efficient photocatalyst because of effective band gap convergence and enhanced resistance to photocorrosion. Day-by-day increasing concerns of pollution has deviated most of the attention of research world towards the treatment and abatement of pollution. This concerned threat is tackled on two fronts: firstly by preventing the pollution and secondly by treating the already polluted spheres. Most of the undiscovered portion of hydrosphere still comes in contact to the human interference in the form of pollution. Run-off from land areas along with the intentional discharge from industrial plants has a serious considerable share in polluting the surface water bodies. In addition to this, human mobility and export-import conducted via waterways aggravates the situation with the accidental instances of oil-spillage resulting in arousal of life threatening concerns for aquatic micro as well as macro flora.

3.4.1

Nanotechnology in Hydrosphere

Hydrosphere covering around 71% of geographical area of earth is the abode of more than billions of creatures. For meeting global water crisis, nanoscience is emerging as a best possible tool with the fabrication of separation membranes of high efficiency and enhanced performance. Different categories of nanomaterials (such as nanospheres, nanofiber, nanocomposites, nanorods) with anti-pathogenic and antifouling properties, symbiotic with enhanced permeation properties paved their way for being designed as pollutant specific and briskly active water purifying membranes (Ying et al. 2017). One of the recent advancements in nanofield is attainment of membrane synthesis in the form of nanofiber membranes with high aspect ratio (Wang and Hsiao 2016), 2-D layered self-assembled membranes (Ying

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et al. 2016), rigorous packed nanoparticle membranes (Kim and Van der Bruggen 2010) or membranes of nanocomposites. Silk nanofibrils based nanofiber membranes performed filtration of proteins, Nps colloidal and dyes such as Rhodamine B from contaminated water with the efficiency enhancement factor of more than 1000 times than its commercial counterparts (Ling et al. 2016). Oil-water separation has been successfully achieved using TiO2 nanostructures because of higher water capturing potential of membrane layers along with its property of selfcleaning (Tan et al. 2015). Composite membranes such as MgSi@RGO/PAN put in force the physical sieving and electrostatic interaction for selective rejection of small molecules of dye and neutral solutes from waste water (Liang et al. 2016). Regeneration potential of the membrane, achieved by just autoclavation or ultrasonication has provided it an extra admiration in pollution removal context (Srivastava et al. 2004). CNTs has been used as nanofilter for the eradication of poliovirus (Madaeni et al. 1995) and MS2 virus (Mostafavi et al. 2009) with highest possible efficiency. Many organic compounds such as polyaromatic hydrocarbons, DDT, phenols and pesticides are found susceptible to these CNTs (Gotovac et al. 2006; Yang et al. 2006; Zhou et al. 2006). Widespread use of personal care and pharmaceutical products pave their way into surface water (Wu et al. 2015) and ground water (Gottschall et al. 2012) with considerable concentrations of ng/L-μg/L and ng/mg respectively, thus detrimentally affecting aquatic organisms. The toxic metals leached out from them are being captured and tried to remediate with the help of nanotechnology. CeO2 Nps show the potential of capturing chromium (IV) on its surface thus treating chromium loaded water. Organic load is successfully unloaded with the help of highly photooxidant TiO2 nanostructures (Wilcoxon 2000). Surface coating of ethylenediamine on TiO2 is efficient to decontaminate ground water containing anionic metal content (Mattigod et al. 2005). Nps can reduce the toxic content of contaminants by initiating their breakdown cycle or by settling them via sedimentation or by adsorbing them onto their surface areas (Deng et al. 2017).

3.4.2

Nanotechnology in Atmosphere

To separate pollutants and toxic gases from the air, nanoadsorbents are proved to be an efficient and promising method. Nanoproducts are being commercialized as building blocks, self-cleaning gases and architectural coatings because of their property of eliminating metal contaminants which are dispersed in air. The increasing assembly and complexities of the nanomaterials to form morphologies of nanotubes and nano-meshes is found to augment air purification manifolds. Adsorption works on the principle of surface attachment, which occurs when toxicants pass through the surface of nanomaterials (Nowack 2010; Qu et al. 2013; Gehrke et al. 2015). Nanoadsorbents are solids with tunable pore sizes on their larger surface areas and having dispersion distance of the magnitude of short intraparticle size to separate and collect adsorbates on their surfaces (Sharma et al. 2009; Qu et al.

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2013; Gehrke et al. 2015). Carbon nanotubes (CNTs) on account of generation of oxidative stress in microbes causes rupturing of cell membranes, thus disinfecting the air carrying tonnes of harmful bacteria and viruses (Brady-Estévez et al. 2008; Nepal et al. 2008; Mostafavi et al. 2009). CNTs show competence for elimination of even trace concentrations of toxic constituents of air (Long and Yang 2001). CNTs have also been explored to be used as chemical sensors for the sensing of carbon monoxide, carbon dioxide (Varghese et al. 2001), ammonia and nitrogen dioxide (Kong et al. 2000). Adsorption of vapours of organic compounds like hexane, toluene and cyclohexane fits them in the category of heterogeneous adsorbents (Agnihotri et al. 2005). Treatment of noxious gases and pathogens is successfully carried out with the help of nano-photocatalysts, which have more potential than their macro-sized counterparts. Many efforts have been made by researchers to develop catalysts driven by sunlight for the detoxification of the air. TiO2 working in conjunction with other metals have the potential of escalating the prevailing standards of cleanup. When it gets doped with nitrogen, the resultant material TiO2-XNX showed enhanced photocatalytic activity even in the visible region of sunlight by increasing the absorption capacity (Asahi et al. 2001). In addition to it, various other nonmetallic doping elements such as bromide, chloride (Luo et al. 2004), fluorine (Ho et al. 2006) and carbon (Sakthivel and Kisch 2003) have been tested and showed a greater plunge in the energy levels of TiO2, thus enhancing the photocatalytic edges of the concerned naturally occurring oxide of metal. The resultant shifting of energy bands to lower levels has been exploited for the degradation of carbon monoxide, benzene, acetaldehyde and other related organic vapours in air. Combustion involving processes results into the release of harmful elements containing vapours like mercury. Silica Nps have been incorporated in titania to form nanocomposites of silica-titania for oxidizing adsorbed mercury into mercuric oxide with less volatile nature (Pitoniak et al. 2005). Nanomaterials of silica offers the application of heavy metal removal like that of cadmium and lead from the combustion gases (Biswas and Zachariah 1997; Lee et al. 2005). Nano-catalysts derived from oxides of metal have been installed in thermal power plants to remove nitrogen oxides from effluents (Rickerby and Morrison 2007). Formaldehyde pollution of air is photocatalytically degraded by Zhang et al. using 3-D macroporous Au-CeO2 Nps (Zhang et al. 2009). Successful efforts have been made to degrade benzene and acetone using Ag/AgBr/ TiO2 nanocomposites (Zhang et al. 2011).

3.4.3

Nanotechnology in Lithosphere

Soil is considered as a sink for pharmaceutical products with concentrations ranging in units of μg/kg (Gottschall et al. 2012). Ziari et al. had postulated the positive impact of Nps on the strength of soil. Zycosoil, modified version of glasphalt stands at higher strength profile with resistance to rutting and stiffness modulus than its conventional counterpart – asphalt (Ziari et al. 2015). Nanotechniques have made successful contribution in improving soil quality which have pushed the agriculture

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sector to stand with an increase growth rate of 25% and carry the potential of aggravating economic growth to hit the target of three trillion USD by the 2020 (McKee and Filser 2016). Many cordless sensors have been designed for the monitoring and diagnosis of diseases, health and prevailing conditions of crop plants along with the evaluation of nutrient holding capacity of soil. With the aid of nanotechnology it is possible to track the pathways of pesticides and chemical herbicides in the plants tissues and soil even when present in trace amounts. The resultant real-time monitoring has boost up the crop-production by a huge margin by enhancing the production rate and eliminating the percentile of crop losses. By using nanoherbicides, nanofertilizers and nanopesticides we are successful in managing food scarcity and hence famine and drought like conditions with a wide margin. Nanotechnology holds prospects of fertilization improvement with the soil engineering techniques.

3.4.4

Nanotechnology in Biosphere

Biosphere or life supporting sphere comprises all the living beings interacting in one or another way with each other either directly or indirectly. For improving life of crops and protect them from different pesticides and harsh environmental conditions, market is already flooded with agrochemicals nano formulations in the form of nanocapsules (Pérez-de-Luque and Rubiales 2009). Nanocapsules filled with required nutrients are proved to be more efficient than direct application of nutrients because of the controlled release mechanism of nanocapsules (Liu et al. 2008). Nanoscience has successfully provided a common alternative to environmentally harsh rodenticides, miticides and pesticides. Nano-alumina has shown considerate results for controlling food insects (Stadler et al. 2010). Biocide tracking has been made possible with the help of nanotechnology using smart dust-as a sensor. Biocides has been treated and nullified with the help of nanostructured photocatalytic nanomaterials (Elliott and Zhang 2001). Applications for Humans Nanomedicine field deals with human body at molecular level involving diagnosis, treatment, regulation and control of body functioning (Emerich 2005). Biomedical applications of Nps owes to their defense mechanism against cellular level damages caused by toxic stimulators like radiations, chemicals or pathological situations such as neurological defects along with retinal neurodegeneration or cardiac complexities (Pulido-Reyes et al. 2015). Most of the synthesized Nps are potential anticancerous agents (Gao et al. 2014), like silica NPs encapsulated with nanoshells, because of its photothermal property (Akerman et al. 2002). Implementation of nanotechnology with medical fields provides extraordinary results for human health as mentioned below:

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Drug Delivery Applications

The damaged or diseased tissues provide a platform for easy penetration and mobility of numerous nanoproducts, as being different from normal physiology it is easy to alter them for drug targeting (Vasir and Labhasetwar 2005). Many nanomaterials are being devised as efficient drug carriers for brain related abnormalities as they are found to modify distribution of cells and tissues, enhance performance of drugs and curtails toxicity of drugs to a remarkable level (Kattan et al. 1992; de Kozak et al. 2004; Feng et al. 2004). Nanotechnology has aloofed obstructions for brain drugs to reach their target sites by crossing blood-brain barriers, thus helping neurology to touch new achievements (Alyautdin et al. 1998; Garcia-Garcia et al. 2005). Nanocoated capsules provide longer efficacy with longer residence time in circulatory system so as to provide adequate dose at the target organ. Control-drug release has also been successfully achieved by the incorporation of Nps in polymer matrix. Intracellular abnormalities are effectively treated with the extravasation nature of nano-sized drugs carriers (Allen 2004). Macrophages of liver and spleen are successfully encountered with required drugs using nanotechnology, as they can easily localize in reticuloendothelial system (Vasir et al. 2005).

3.4.6

Gene Delivery Applications

Nanotechnology is being utilized for treating genetically transferred diseases by replacing the segments carrying defective genes with the repaired ones. Nps acting as non-viral vectors for gene transplant provide a great alternate for the viral-vectors that hold the risk of immunogenicity with complications of reversion of modelled virus and effective pharmaceutical processing (Young et al. 2006). Plasmid DNA has been successfully transported with the help of 50–500 nm sized Nps (Davis 1997). PLGA polymer coated Nps have been a choice for gene transfer because of their biodegradable nature, biological congruence, continuous and prolonged release and providing a resistant encapsulation to DNA against degradation inside endolysosomes (Panyam and Labhasetwar 2012). Higher amount of DNA release from the PLGA polymer Nps because of its higher molecular weight enables higher rate of gene transfection in cases of breast cancer and prostate cancer (Prabha and Labhasetwar 2004).

3.4.7

Body Imaging Technology

Nanotechnology has successfully captured the internal body happenings on the screen as molecular disease imaging (Lin and Datar 2006). Biochemical reactions carried out inside the human body are investigated by the incorporation of nanoscience with the mimics of internal molecules such as proteins (Guccione et al. 2004). Quantum dots are used for biomedical imaging because of their unique

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and extraordinary optical and electrical properties (Weng and Ren 2006). Apart from this they have been explored for detecting cancer biomarkers from blood samples or tissue biopsies (Smith et al. 2006). Quantum dots when tagged with antibodies can easily target and image the tumours simultaneously on screen or radiographic sheets (Chan and Nie 1998). In vivo tracking of progenitor cells is made possible with the help of iron Nps using MRI technique.

3.4.8

Other Applications

3.4.8.1 Nanotechnology as Energy Sources and Energy Convertors Not only in treatment but nanotechnology has also inserted its claw in the development of green energy sources. Energy sector of world is highly boosted up because of the involvement of nanofield. Nanotechnology has been successfully explored for the designing of materials and technology for cleaner energy production, energy storage for saving, energy conversion along with improvement of energy efficiency (Pathakoti et al. 2018). One of the attention seeking work in this field is usage of nanotechnology for controlling the extensive energy carrying X-rays and γ-rays by obstructing, storing and converting them for bio imaging or other related applications (Maldiney et al. 2014). Nanotechnology has provided successful, clean and efficient alternative to the energy sources such as improved and proficient solar cells, fuel cells and batteries. Aerogels fabricated with the help of nanotechnology for insulation purpose is far ahead from its other counterparts for their porous nature and lightweight, which aids up in saving energy to a remarkable level. Using nanomaterials, more lightweight, durable, stronger and efficient blades are being designed for the easy and fast movement of wind turbines, thus cutting the pollution costs caused by fossil fuel fed energy channels.

3.4.8.2 Nanotechnology for Remediation of Contamination In this field, nanotechnology acts as an important and unquestionable tool for the remediation of the contaminated water or soil either on-site (in situ remediation) or off-site (ex situ remediation). Nps application for remediation is more successful because of its ability to reach upto the points where larger particles fail to reach. Moreover the efficiently coated Nps avoid interactions with unwanted entities present in the medium. Ground water has been efficaciously treated to filter out chlorinated solvents leached out from menacing waste sites. Zerovalent iron Nps have been explored by Li et al. for the dechlorination of perchloroethylene and trichloroethylene to produce carbon dioxide with faster reaction rates (Li et al. 2006). Waste sites with heavy accumulated dose of lead, arsenic and chromium have been successfully immobilized with the help of nanoscale iron particles (Kanel et al. 2006; Rickerby and Morrison 2007).

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3.4.8.3 Nanotechnology for Carbon Storage and Carbon Sequestration Global warming, one of the top most threat of twenty-first century is mainly caused and contributed by the huge amount of emissions of carbon dioxide (CO2) gas from natural as well as anthropogenic sources (IPCC 2007). To maintain carbon balance of environment, carbon capture, sequestration and storage is an important required action of time. Many efforts are being made to make it happen but each one of them has some associated cons. As a result attention is now diverted towards the fabrication of such nanomaterials that are efficient carbon capturers with long life and regeneration potential. Carbon sequestration of a material is directly proportional to number of assembled carbon adsorbing nanolayers in the unit. Layer-by-layer assembly of nanocoatings of CO2 adsorbing materials for the sorption of gas provides a potential alternate of conventional methods (Srivastava and Kotov 2008; Li et al. 2011). Metal organic framework of silica with nanopores incorporated in it provides a porous substrate for the storage of CO2 gas due to adjustable chemical functionality and enhanced thermal stability (Millward and Yaghi 2005). A zeotype porous nanocubic structure (chromium terephthalate) is utilized to capture and store CO2 emission from smokestacks and tailpipes of thermal power plants (Ferey et al. 2005). Using molecular simulation Chen and Jiang had made efforts for exploring pre and post combustion CO2 capture with the help of bio-metal-organic framework decorated with nano-sized channels having numerous sites of Lewis bases (Chen and Jiang 2010). Nanotechnology has cut short the time required for natural process of carbonate formation with the help of nanocrystals of magnesium oxide to force CO2 to get attached to the solid adsorbing substrates with significant rate and quantity (Ruminski et al. 2011). From the grounds of present data this technology is considered to be facile, easy to operate and deprived of any serious environmental constrains. 3.4.8.4 Nanotechnology for Food Safety Nanotechnology has been marketed as enhancer of food industry in terms of taste, production efficiency, safety and food characteristics. Mostly they have been utilized in out-of food industries but recently efforts are being made to include them in edible stuffs. Iron oxide Nps have been utilized as food colorant whereas titanium dioxide Nps are used as edible food pigment (He et al. 2019). Temperature sensitive Nps act as indicators for food storage which shows colour change when the temperature of the foodstuff fluctuate from the required reference range, thus avoiding the chances of food poisoning in the consumers (Cerqueira et al. 2018). Nps derived from naturally occurring polysaccharides are excellent food coating material because of the associated properties of thermal sensitivity and photo protective nature along with enhanced antioxidant potential and antimicrobial activity against variety of microbes (Kritchenkov et al. 2019). Nanotechnology provides better dispersion capacity of poorly soluble or insoluble materials along with sustained-release potential of drugs (Chuacharoen and Sabliov 2016). Curcumin loaded nanoemulsions showed negligible or delayed degradation in the presence of visible and UV-light and alter in vitro digestion of lipolysis of nanoemulsions

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(Li et al. 2016). These emulsions provide additional benefits of having different rheological properties with longer duration potential for storage and have remarkable optical transparency to be used in beverages (Joung et al. 2016; Li et al. 2016).

3.5

Effects of Environmental Nanotechnology

Before evaluating nanotechnology for environmental applications on a commercial scale we are required to confront questions regarding its impacts on one or another section of ecosystem. To explore the probable impacts of nanomaterials on the health of environment and its residents, various studies ranging from molecular level to particle and macro-level have been conducted with the help of simulations and modelling of mechanisms. Owing to tiny size dimensions of Nps, the complexity of associated risks also increases many a times. Effects of Nps get intensified with the symbiosis of toxins available in the environment irrespective of their origin. High surface to volume ratio increases the affinity of the toxins to get adsorbed on the surface of Nps and enhances complexity of the system to remediate (Hu et al. 2012). The joint venture of toxicants with Nps of Ag (Völker et al. 2014), TiO2 (Zhu et al. 2011), ZnO (Oleszczuk et al. 2015), and Al2O3 (Li et al. 2016) has been explored in literature. The smaller dimensions of Nps leads them to undesirably interact with biological units and the environment, thus leading to the generation of serious toxicity concerns that need to be assessed. Number of studies have already reported the unique properties of small dimensioned particles (reactivity, size, designing and shape) to be the major culprit for imparting them toxic terms (Maynard et al. 2006; Handy and Shaw 2007; Hillie and Hlophe 2007; Klaine et al. 2008). Many reports reflect the unforeseen vulnerabilities of this technology towards environmental and human health (Bianco 2013; Tonelli et al. 2015). It is impossible to find the connecting link between toxic impacts of different Nps because of their different properties, thus an urgent need of hour is to standardize the toxicity evaluation methods. A large number of parameters of NPs like size dimensions, morphology, charge, nature along with physicochemical properties decides the magnitude of toxicity (Yang and Watts 2005). These NPs affects aquatic and terrestrial life along with the air they are surrounded with by exerting complications in these systems. Thus in other words, nano-size implicates their impacts on soil, plants, animals, humans, atmosphere and hydrosphere.

3.5.1

Effects on Hydrosphere

With the advancement in the field of nanotechnology, the dumping and release of nanomaterials and their by-products in the water ecosystem is becoming inevitable. Influx of nanomaterials in water bodies imposes remarkable footprints on the aquatic life (Scown et al. 2010). The degraded by-products has also become an important causative agent of many serious problems in water organisms, when ingested in large

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quantities (Fabrega et al. 2011). Many studies have been conducted from time to time to show irreparable damage to the exposed aquatic animals. An ecotoxicological indicator, largemouth bass, is susceptible to C60 fullerenes as they cause serious brain injuries to the bass. A huge population of water fleas is reported to diminish because of the presence of fullerenes (C60) (Lyon et al. 2006). Quantum dots owing to their extreme small dimensions along with higher reactivity and association with heavy metals contributes to the toxic impacts of nanomaterials (Moore 2006). They can cause serious damage to the cells of the organisms by the relocation of energy to adjacent oxygen molecules due to the formation of reactive oxygen species (Derfus et al. 2004). Most of the contaminants of emerging concerns commonly termed as CECs are carcinogenic in nature, thus aggravating the situation aroused by legacy pollutants. Many studies have authenticated the presence of these contaminants in water even in ppm levels (Ashton et al. 2004). A study conducted by Hughes et al. on water bodies testified the presence of around 180 medicinal drugs that proved their toxic nature against water life (Hughes et al. 2013). Hydrogeochemistry of the pollutants is greatly influenced by their geogenic sources, thus causing the longterm effects when released out from the leftover personal care products (Kumar et al. 2018).

3.5.2

Effects on Atmosphere

Nps have potential of imparting negative impacts on the air quality by altering the composition ratio of constituents. Airborne source of Nps can be indoor such as heating or may be outdoor arising from either natural cause such as coal fires (Sehn et al. 2016) or might be due to anthropogenic factors working on industrial levels such as spanning industry and power plants (Saikia et al. 2018). Transportational emissions are the core emitter of Nps laden pollution in the city areas, contributing nearly 90% of the share (Johansson et al. 2007). Being in nanoscale these particles are easily carried out by air and get dispersed for several days, thus causing health concerns as they can easily drip from pulmonary clearance and get deposited in the lungs of animals and humans (Mao et al. 2014). Vehicular emissions from the roads are a major contributor of air pollution laded with Nps. Magnetite Nps owing to their small dimensions ranging from 2–200 nm, abundance formation and toxic terms are categorized as malicious and chronic neurotoxicants that have the potential of causing damage to brain by crossing blood–brain barrier (Levesque et al. 2011). Many cases have been reported which reflects the direct and irreversible relation between airborne Nps exposure and damages and injuries to olfactory nerves of brains (Maher et al. 2016). Workers of welding industries who deals with the manufacturing of magnetic Nps are among the higher risk groups with extremely higher chances of inhalation of magnetic Nps that can cause Alzheimer’s disease (Maher 2019). Air-driven Nps hold a greater risk to the living communities because of their highly reactive nature and toxicity that can boost their affinity with living cells, tissues, organs and organ systems as well (Li et al. 2003). Once entered in the body through nasal path, they can either take the pathway of blood circulation or get

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distributed in the whole body via axons of nerves (Garcia et al. 2015). Secretion of proteins such as MIP-1α, tumour necrosis factor-α and IL-6 gets aggravated with the exposure of Nps released from the combustion of diesel which can damage brain’s functionality (Levesque et al. 2011). Nps released in environment as a resultant of biomass burning are carcinogenic in nature because of surface bounded PAHs associated with them (Halsall et al. 2008). Carbon black Nps are one of the leading negative input of fuel industries in the atmosphere which leads to a variety of body impairments such as pulmonary disorders (Zhou et al. 2020). The suspended NPs effects the scenic view of environment by clustering together to form dust clouds (Kabir et al. 2018).

3.5.3

Effects on Biosphere

Significant impact of nanotechnology on the living beings both biotic and abiotic can be seen with evidences from literature.

3.5.3.1 Plants Floral component of ecosystem is an important link for cycling of Nps in the living world (Zhu et al. 2008). Nps trigger a series of processes that can potentially alter important plant processes such as photosynthesis, growth rate and structure of organelles of plant cells (Kibbey and Strevett 2019). Most of the imposed changes are long-term effects. Phytotoxicity associated with Nps is validated by a considerable number of scientists with terms of biomagnification and bioaccumulation (Hussain et al. 2019). Yang and Watts had conducted a study in which they had reported the toxic effects of alumina Nps on the seeds of Avena sativa, Brassica oleracea, Cucumis sativus, Glycine max and Zea mays in the form of root length inhibition (Yang and Watts 2005). Zinc Nps and zinc oxide Nps have been reported as seed germination inhibitor for ryegrass and corn respectively and possess potential of being a terminator of root elongating enzymes (Lin and Xing 2007). In a study conducted by Zhu et al. when Cucurbita maxima was grown in hydroponics assisted with the Nps of Fe2O3, they gets translocated to each part of the plants wherein they were adsorbed and accumulated in the tissues (Zhu et al. 2008). 3.5.3.2 Animals Carbon Nps have potential of causing inflammation and liver degeneration along with the impairment of central veins and functioning of hepatocytes, thus weakening both cellular and organ systems of mouse (Zhang et al. 2019). The toxic effect of Nps on aquatic organisms has also been reported very well in literature. Citrate coated silver Nps of 40 nm range leads to ion binding and alters the mechanism of protein digestion and absorption, causing toxic effects in the invertebrate class of Daphnia magna (Hou et al. 2017). Silver Nps (AgNPs) accumulation by Nereis (Hediste) diversicolor has led to a considerable decrement in their burrowing activity. Nereis coelomocytes showed a direct proportionality relation between concentration of Nps and their toxic impacts. AgNps impose a considerable damage

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to genetic makeup and permeability mechanisms of lysosomal membranes (Cong et al. 2014). AgNPs effect the fecundity rate of Caenorhabditis elegans and is further carried down to generations by damaging germ cells (Luo et al. 2016). Vignardi et al. had conducted a study in which they had evaluated the impacts of TiO2 Nps on Trachinotus carolinus—an aquatic member. They had jotted down their findings in which they had mentioned about the cytotoxic and mutagenic effects of the Nps that drive their toxicity terms against genetic material (DNA) and erythrocyte viability by forming micronucleus and erythrocyte nuclear abnormalities (Vignardi et al. 2015). Mytilus galloprovincialis when provided with the exposure of copper Nps and AgNps, induces a chain of abnormalities such as generation of oxidative stress, metallothionein activation, DNA damage and many more (Gomes et al. 2013). Hu et al. had found fluorescence enhancement in the cytoplasm of Isochrysis galbana, showing penetration of nano-Al2O3 inside the cell which when present in higher concentrations have synergistic effect on the toxicity of lead. Nano-Al2O3 laden lead proved to be more deleterious than the free lead ions (Hu et al. 2018). Living beings in marine ecosystems for instance fishes, are prone to toxicity of Ag+ when it gets deposited on the gills in place of their analogue (Na+ ions) (Cáceres-Vélez et al. 2019). A considerable note of toxic perspectives associated with nanomaterials has been jotted down by Nel et al. The small dimensions of the nanomaterials pave their easy transport and accumulation in the body systems at different locations, which when get adsorbed in the body fluids and tissues results in devastating impacts on the body functioning and ultimately ends in severe injuries and diseases (Nel et al. 2006). Countable frequency of literature is available which stipulates the toxicity of the bare graphene on genetic levels that cannot be ignored (Bianco 2013; Guo and Mei 2014; Tonelli et al. 2015). CeO2 Nps have potential of exerting pro-oxidative effect because of the alterations in intracellular redox reactions or generation of reactive oxygen species which in turn causes cell damage followed by cell death (Pešić et al. 2015). In the presence of protons, cells are prone to cytotoxic effects of nano oxidases (Forest et al. 2017). Metal oxides NPs are being evaluated against animals wherein they have showed a number of deviations from normal functioning such as kidney and liver damage, degeneration of neurons, alterations in genetic pool, cytoplasm dysfunctioning, and generation of reactive oxygen species which in turn generates oxidative stress in the cells of the body (Zhu et al. 2019).

3.5.3.3 Microorganisms Bacteria, because of greater and quick proliferating rate and diminutive lifespan are often considered as indicator organisms for nanotoxicity studies (Jackson et al. 2013). When Nps comes in contact with the micro-biota, they alter the composition and number of microbial communities (Chen et al. 2017) in one of the mentioned ways: by dissolving out the rigidity of cell membranes, by altering the DNA and protein structures, or by the formation of clusters with enhanced agglomeration number (Turan et al. 2019). Freixa et al. had concluded that gram-positive strains of bacteria are more susceptible to toxic effects of NPs than the gram negative strains (Freixa et al. 2018). Partial solubility of AgNPs when applied to microbes without

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sludge, they intermittently release silver ions, thus imparting toxic effects on the ammonium oxidizing bacteria (Schlich et al. 2018). AgNPs are very well known for their antimicrobial activities, so they will create a havoc for beneficial microbes when released in the environment (Schlich et al. 2017). Microbial community of the ecosystems such as Aeromonas hydrophila and E. coli is severely affected with the combined exposure of TiO2NPs and ZnONPs (Tong et al. 2015). These nanoentities leads to the generation of reactive oxygen species thus causing bacterial wall destruction (Das et al. 2017). Higher influx of multiwall carbon nanotubes in the soil profile alter the biodiversity of microbes by enhancing the population of MWCNTs tolerant microbes (Shrestha et al. 2013).

3.5.4

Effects on Lithosphere

Soil is the ultimate sink of Nps wherein they are dispensed after being released from the concerned applications (Nowack and Bucheli 2007). Their enormous use and ever-increasing demand heap the landfills with the leftover nanomaterials (Gajjar et al. 2009). Nps when released in the environment, can trigger their own associated environmental concerns which are hard to avoid (Abbott and Maynard 2010; Grieger et al. 2010). Release of nanomaterials in environment results in alterations of activities and composition of microbial community, thus effecting services like agricultural outgrowth, breakdown of waste constituents and supply of clear ground water (Frenk et al. 2013). Antimicrobial property of designed Nps leads them to be an unwanted tool for beneficial microflora and fauna of the soil. They create disruptions in the conduction of signals between symbiotic partners, thus imparting negative impacts on the thriving plants and ecosystem (Gurunathan 2015). Many Nps such as those of palladium and silica have shown deleterious impact on the soil ecosystem (Shah and Belozerova 2009). AgNPs when released in the environment attack soil microbes which are beneficial for important soil activities such as rock weathering, xenobiotics degradation and plant growth (Xu and Zhang 2018). Graphene oxide Nps proved to be the altering driver for the working machinery of beneficial soil microbes thus hindering essential biogeochemical processes like nutrients cycling, mineralization and degradation of organic carbon (Prosser et al. 2007). Nps which are entrapped in soil molecules pave their way to plant tissues wherein they get accumulated with time and finally enters into the food chain, thus ending up in non-tolerant organisms (Saha and Dutta Gupta 2017). Many studies have reported the interaction of nanomaterials like pristine graphene oxide with the soil which causes a lot of changes in the latter (Du et al. 2015). Apart from the toxicological impacts, aggregates of nanomaterials dumped into the soil aggravates the formation of new and undiscovered plant microbes interaction because of creation of new and different bacterial isolates, thus imparting changes in the soil ecosystems (Gurunathan 2015).

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Management of Environmental Nanotechnology

A remarkable mount of attention is required for managing environmental concerns arising with the involvement of nanotechnology in our world. But as per the present data only 7% of finance is owed to the analysis of health and safety implications of human and environment. Funding for the development of nanotechnology in environmental sector is still lacking notable attention. The stock market has raised the shares of nano-concerned materials owing to the driving forces of anticipated market demands and government driven incentives, which results in more influx from the R&D sector (Jiang et al. 2019). Tracking the pathway of the nanomaterials present in nature after their release is a noteworthy challenge. For the proper management of technology of tiny dimensioned materials, their complete profiling should be carried out ensuring the disclosure of their detailed impacts from manufacturing stage to dumping one. For the synthesis ground more attention should be paid towards surface coating materials than towards core materials because it is only the surface area of Nps that interacts and enhances the reactivity thus imparting toxic template to them. Hence life cycle assessment of the nanomaterials should be a must regulation incorporated in the regulatory guidelines of the nations. Careful scrutinization processes should pass only the materials that have benefits outweighing the harmful aspects by a significant margin. Long-term benefits and risks should be counted on both biotic and abiotic components of the environment with sufficient clarification regarding structures, applications and size aspects of the nanomaterials. Efforts should be made for making systems for social alertness regarding proper handling and disposal of these Nps as they can have immense long-term impacts on the humans as well as on their environment. So the judging point should be derived on the terms of benefits—carried on long term with negligible risk factors. There is a still growing on conflict regarding the safety issues of the Nps because of immense use of nanotechnology, their exposure, release and disposal. As a result many efforts are still required for complete elucidation of the whereabouts of these structures. The ongoing confusion proved to be a driving force for compelling OECD (Organization for Economic Cooperation and Development) to amend its priority list of toxicological evaluation with the addition of Nps (Peng et al. 2014).

3.7

Conclusion

Diverse novel applications of Nps in disparate realms have stretched them to all the four spheres of the earth viz. atmosphere, hydrosphere, lithosphere and biosphere. Designing and fabrication of novel nanomaterials for environmental applications is adding up day by day, but it still lacks conversion from laboratorial set ups to commercialized grounds. One of the key challenges faced by the nanofield is establishment of equilibrium between production cost and ease of manufacturing operations. Diverse applications of nanomaterials have placed it as a ‘technology of choice’. But many efforts are still required for the placement of this technology of modern era in indubitable place regarding its harsh and inevitable impacts on the

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environment and its inhabitants by the proper management during synthesis and application phase.

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4

Nanoscavengers for the Waste Water Remediation Anupreet Kaur

Abstract

Water on earth is present in abundance but only 1% of this is available for human health. Environmental pollution and water pollution are increasing day by day due to the urbanization and industrialization. Release of discharge from urbanization and effluent from industries is the major concern of pollution and it’s the threat to humanity. So there is dying need to develop new technologies and method for water remediation. Nanotechnology is the technology which meets many of the above conditions. Nanomaterials and their properties make these highly beneficial technologies for water remediation. This chapter is an overview of nanomaterials for water remediation. Keywords

Nanomaterials · Alumina nanoparticles · Zerovalent nanoparticles · Silica nanoparticles · MOFs · NMs · Graphene · CNTs

4.1

Introduction

Water is the main source for all the living beings on the earth and the environmental pollution have serious impact on the fresh water supply (Crittenden et al. 2005; Mara 2003; Moore et al. 2003; Johnson et al. 2008). Almost 10–20 million people die every year due to water borne infections and nonfatal infections cause about 20million deaths. Unavailability of safe water is the major problem and 0.78 billion people around world do not have safe drinking water (Montgomery and Elimelech 2007; Theron and Cloete 2002; Eshelby 2007). The unmanageable pollution and A. Kaur (*) Basic and Applied Sciences Department, Punjabi University, Patiala, Punjab, India e-mail: [email protected] # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_4

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pollutants in water is the major concern in the environment (Leonard et al. 2003; Hutton et al. 2007). The rapid development of industries such as batteries, metal plating, mining operation, fertilizers, tanneries, and pesticides (World Health Organization and UNICEF 2013; L’vovich 1979). Nanotechnology is the emerging technology, which meets the above problem. Nanomaterials used for the preconcentration and separation of environment pollutants from various environmental samples such as water, soil, and environment. The nanomaterials have atoms and molecules joining to create material with extraordinary physical and chemical properties. The application of nanomaterials in water and waste water treatment has drawn wide role in water purification and remediation. This is due to the unique properties of nanomaterials such as small size and thus large specific surface area, strong adsorption capacity, and high reactivity (Postel et al. 1996; Gleick, and Pacific Institute for Studies in Development, Environment and Security,
Stockholm Environment Institute 1993; Shiklomanov 2000; Seckler et al. 2003; El-Dessouky and Ettouney 2002). Nanotechnology and nanomaterials play important role for waste water treatment due to their high surface area and high reactivity. With the ever increasing population, the water resources get polluted by industrial effluents and burden our society. Nanomaterials provide more application in water purification by different techniques like adsorption, membranes and membrane process, photocatalyst, disinfection and microbial control, sensing and monitoring. Nanotechnology it is the manipulation of materials and process that are engineered to the molecular scale of 1–100 nm and by the bottom-up approach significance improve in the efficiency of waste water treatment. The physical and chemical modification of nanomaterials improve the sensitivity and selectivity (Shannon et al. 2008; Brumfiel 2003). Nanomaterials are the drivers of the nanotechnology revolution and a key bottleneck to the applications of nanotechnology to solve this world water crisis. Nanomaterials have a number of key physicochemical properties that make them particularly attractive as separation media for water purification. On a mass basis, they have much large surface areas than bulk particles. Nanomaterials can also be functionalized with various chemical groups to increase their affinity toward a given compound. They can also serve as high capacity/selectivity and recyclable legends for toxic metal ions, organic and inorganic solutes/anions in aqueous solutions (Cloete 2010). Nanomaterials also provide unprecedented opportunities to develop more efficient water-purification catalysts due to their large surface areas and their size and shape-dependent optical, electronic and catalytic properties. Water is the most essential important commodities of life which is required for survival of living beings as well as for food preparation, processing, and sanitation. But unfortunately, about half of billion people have to face water scarcity in various countries like India, China, Bangladesh, Pakistan, Nigeria, Mexico, and arid and semi-arid regions of the USA. This water scarcity problem spreads a number of preventable diseases like legionellosis, hepatitis, malaria, and dengue. Due to global warming, there is constant increase in the salinity of land water as well as sea water and this also causes the scarcity of drinking water. One of the major problems in water pollution is as water is the universal solvent it dissolves all kinds of

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Table 4.1 Water relating problems in various countries Figures 3.4 millions 63 millions 6 km 80% 40%

Facts Water-related problems in developing countries Countries like Bangladesh, India, and Nepal people suffer with arsenic pollution Women from Asia and Asian continent have to walk to fetch water for daily use Rate of water-related deaths in children aged between 0 and 14 years Diarrhea due to water-related deaths

contaminants like metal ions, inorganic anions, organic dyes, pesticides and insecticides, radioactive elements, etc. The interesting facts are shown in Table 4.1. This chapter is mainly concerned with providing a review of the interests of scientists and researchers in the application of nanomaterials in the improvement of water treatment, and application of nanotech in water treatments has several advantages than the traditional water treatments and this review is also identifying the grand challenges and directions for future avenues in the field of nanotechnology applications in water treatment.

4.2

Properties of Nanomaterials

Materials reduced to the nanoscale can suddenly show a variety of properties, compared to microscale, due to two effects: (1) Firstly it comprises the surface effects, which can be explained by (a) having more surface atoms compared to inner atoms, (2) so having more free energy surface available in the increases rate of a chemical reaction, (3) superparamagnetism that occurs when the particle is smaller than the magnetic domain in a material, (4) the fact that, in a free electron model, average energy spacing increases as the number of atoms is reduced and this enhances the catalytic properties of nanoparticle, (5) the agglomeration state, shape, and fractal dimension, (6) the solubility and, (7) the chemical composition and crystal structure.

4.3

Mechanisms of Nanomaterials

(a) Innate Surface Properties: The physical, material, and chemical properties of NMs are directly related to their intrinsic compositions, apparent sizes, and extrinsic surface structures. As mentioned earlier, it is widely recognized that as particle size decreases to the nanometer scale, there are a variety of reasons, including quantum confinement effects, that cause their physical and chemical properties to differ from those associated with their bulk form. Equally important and widely acknowledged, but seemingly less understood, is recognition that a large portion of the atoms in nanoparticles are at or near the surface of the particles. Determining the nature and distribution of active sites on

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nanostructured surfaces is an important challenge. The following are the basic innate factors which influence the function as adsorbent of nanoparticles in solution or substrate: location of the most atoms in the surface, high surface area, high chemical activity, high adsorptive capacity, lack of internal diffusional resistance, and high surface binding energy. Each of the above properties successively leads to the significant fraction of atoms or molecules associated with surfaces and interfaces and increases the potential impact of surface accessibility and affinity, surface enrichment, number of active sorption sites, and, accordingly, surface energy toward specific analytes. Because of capillary and sorption effects, the high surface area present in nanomaterials may retain solvents in circumstances that can surprise researchers. Even using surface tools, it can sometimes be difficult to characterize the nature of the actual nanomaterials surfaces. (b) External Functionalization: Using the various functional groups, a number of changes emerge in the surface properties of nanomaterials. Coupling the wide variety of nanomaterials with different external functionalization methods will result in excellent adsorption properties. Further functionalization of the surface prevents NMs from aggregating and provides their selectivity. Intended coatings may have a significant impact on a variety of nanoparticle properties. Functionalized groups induce important characteristics to the adsorbents such as high absorption capacity (often measured as the breakthrough volume for a flowing system) and rapid desorption. The quest for functionalized groups is an important factor to improve analytical parameters such as selectivity, affinity, stability, and adsorption capacity. This is done by introducing various organic donor atoms to the nanomaterials’ surface and improving the interactions with the analytes of interest, such as hydrophilicity or polarity. Amino and oxygen groups are known to be able to coordinate to transition metals via electrostatic interactions.

4.4

Nanoparticles in Water Treatment

Nanoparticles have two key properties that make them particularly attractive as sorbents. First, on a mass basis, they have much larger surface areas than bulk particles. Second, they can also be functionalized with various chemical groups to increase their affinity toward target compounds. Applications of nanoparticles as adsorbents for high efficient removal of pollutants from wastewater must satisfy the following criterions: 1. The nanoparticles act as nanosorbents are nontoxic. 2. These nanosorbents must show relatively high sorption capacities and selectivity even to the low concentration of pollutants. 3. The adsorbed pollutant could be removed from the surface of the nanoadsorbent very easily.

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4. The sorbents could be infinitely recycled many times and this is best property of nanosorbents and the process should be reversible so that we can get our adsorbent back. 5. The Nanoparticles show high adsorption capacity.

4.4.1

Alumina Nanoparticles for Water Remediation

Alumina is generally known as corundum. It is white oxide and having several phases such as gamma, delta, theta, and alpha. Out of these four phases alpha alumina is the most thermodynamically stable phase. Alumina has many interesting properties, for example high hardness, high stability, high insulation, and transparency (DeFriend et al. 2003). Nanosized Al2O3 can be prepared by various methods and has been employed as solid phase extraction materials for separation/ preconcentration of trace pollutants. Functional groups containing donors atoms such as nitrogen, oxygen, and phosphorus have improved selectivity and sensitivity of the nanoparticles and this is done by physical and chemical modifications. (Saha and Sarkar 2012; Dousová et al. 2006; Pacheco et al. 2006; Medina et al. 2010). CH3 H3C

CH2 O O Al H 2C

CH2

O SH

CH3

Al2O3–3-mercaptopropyltriethoxysilane nanoparticles

CH3 H3C

CH2 O O Al H2C

CH2

O

CH3 Al2O3–3-aminoropyltriethoxysilane nanoparticles

NH2

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CH3 H3C

CH2 O O Al H2C

CH2

O Cl

CH3 Al2O3–3-cholropropyltriethoxysilane nanoparticles

4.4.2

Silica Nanoparticles for Water Remediation

Silica nanoparticle is a most promising material as a SPNE because of its large surface area, high adsorption capacity, low temperature modification, less degree of unsaturation, and low electrophilicity (Kaur and Gupta 2009a) (Figs. 4.1 and 4.2). The sequence of reactivity of silica nanoparticles as compared to other nanoparticles is expressed as follows: ZrðORÞ4 , AlðORÞ4 > TiðORÞ4 > SnðORÞ4 >> SiðORÞ4 Most pollutants are weakly adsorbed on nanoparticles surface because of low selectivity and sensitivity. To increase the sensitivity and selectivity for the pollutant, physical or chemical modification of surface of these nanoparticles with certain functional groups containing some donor atoms such as oxygen, nitrogen, sulfur, and phosphorus is done and experimented by many researchers. The most common is the adsorption in which the specific chelating reagent is to load chelating reagent by physical or chemical procedure. This method is simple but the loaded reagent is prone to leaking out from the sorbent, while the chemically bonded material is more stable and can be used repeatedly and this is the drawback of this method. Selectivity of suitable specific functional groups toward pollutant depends on certain factors such as (1) size of the modifiers, (2) activity of loaded group, and also (3) on the basis of the concept of hard–soft acids and bases. Chemical adsorption is more useful technique of nanoparticles provides immobility, mechanical stability, and water insolubility, thereby increases the efficiency, sensitivity, and selectivity. Chemical modification is a process that leads to change in chemical characteristics of surface of nanoparticles and mainly the adsorption properties are significantly affected. This provides immobility, mechanical stability, and water insolubility, thereby increases the efficiency, sensitivity, and selectivity of nanoparticles for the analytical application (Zhang et al. 2010). Chemical modification of nanoparticles by silylation procedure using different silylating agents such as 3-aminopropyltriethoxysilane, 3-chloropropyltriethoxysilane, and 3-mercaptopropyltriethoxysilane provides immobility, mechanical stability and water insolubility (Kaur and Gupta 2008, 2009b, c, d, e, 2010a, b, c, 2015).

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Fig. 4.1 Chemical modification of silica nanoparticles with various silanes and ligands

4.4.3

Titania Nanoparticles for Water Remediation

Titanium dioxide is mainly found as a key ingredient in wall paints, sunscreens, and toothpaste; and it acts as reflectors of light or as abrasives. TiO2 has been widely used as photocatalyst because of its high stability, wide source, acid–base resistance, low cost, their high chemical stability, good photoactivity, relatively low cost, and nontoxicity. This is mostly widely as photocatalyst used for environmental applications because of its high oxidative power, nontoxicity, photostability, and water insolubility properties under most conditions. Superoxide anions are produced when electrons will react with oxygen and holes will react with water to produce the hydroxyl radicals to degrade and mineralize the pollutant. In the photocatalyst mechanism, a photocatalyst is irradiated with UV light with energy greater than the bandgap energy, electron (e) in the valence band will move to conduction band, leaving a hole in the valence band and these holes and electrons have strong energy potentials and migrate to the semiconductor surface generating highly reactive free radicals. TiO2 nanoparticles have emerged as promising photocatalysts for water purification. The removal of total organic carbon from waters contaminated with organic wastes was greatly enhanced by the addition of TiO2 nanoparticles in the presence of ultraviolet light. It was successfully used to degrade organic compounds (e.g., chlorinated alkanes and benzenes, dioxins, furans) pentacholorophenol and aromatic chlorinated compounds had been photocatalytically studied using titania nanoparticles (Kaur 2016; Mills and Hoffmann 1993; Jardim et al. 1997; Shunxin et al. 1999). TiO2 nanoparticles were used for preconcentration and separation of rare earth metals and their determination in geological samples (Liang et al. 2001a, b; Hang et al. 2003; Choi et al. 2007).

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Fig. 4.2 Photocatalytic studies by titania nanoparticles

Overall reaction: TiO2 þ hv ! e þ hþ

ð4:1Þ

e þ O2 ! O 2 Oxidative reaction: hþ þ pollutant organic moiety ! CO2

ð4:2Þ

hþ þ H2 O !
OH þ Hþ

ð4:3Þ

OH þ pollutant organic moiety ! CO2

ð4:4Þ

Reductive reaction:


4.4.4

Nanoscale Zerovalent Metals

Iron is the most abundant element on earth and it has many advantages as zerovalent nanomaterials for water remediation. It has excellent adsorption properties, precipitation and oxidation (in the presence of dissolved oxygen), and low cost. This makes, these nanoparticles is the most effective nanoscavengers for water remediation. This

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concept of using zerovalent metals, such as iron, as remediation is based on reduction–oxidation or “redox” reactions, in which a neutral electron donor (a metal) chemically reduces an electron acceptor (a contaminant). It is in nanoscale so their surface area becomes large. ZVI iron is the moderate reducing agent that reacts with dissolved oxygen and water resulting in oxidization of the iron from its zero oxidation to iron (II) state and the free electrons are used for the reduction of pollutants (Laurent et al. 2008; Zhang and Elliot 2006; Quinn et al. 2005). 2þ 2Fe0ðsÞ þ 4Hþ ðaqÞ þ O2ðaqÞ ! 2FeðaqÞ þ 2H2 OðlÞ : Fe0ðsÞ þ 2H2 OðlÞ ! Fe2þ ðaqÞ þ H2ðgÞ þ 2OHðaqÞ

To increase the efficiency of the zerovalent iron nanoparticles, a commonly used strategy is to incorporate iron nanoparticles within support materials, such as polymers, porous carbon, and polyelectrolytes. Dissolved As(III) had been removed by iron nanoparticles-embedded macroporous composites (Savina et al. 2011; Huang et al. 2010; O’Carroll et al. 2013; Nagpal et al. 2010; Su et al. 2011; Xu and Bhattacharyya 2008).

4.5

Other Materials for Nanoremediation

2D graphene such as pristine graphene, graphene oxide, and reduced graphene is one of the important and promising materials for water remediation (Gao et al. 2008; Wang et al. 2013). It is the allotrope of carbon. The membranes of graphene have thinness of atomic level providing better filtration as compared to the conventional polyamide membranes (Sudibya et al. 2011; Yazari and Koratkar 2012). The 2D graphene have good adsorption capacity for sodium cation and this can effectively remove the salts from water. In this brief review, we will summarize recent achievements of effective strategies for synthesizing high-quality graphene–metal oxide composites and their photocatalytic applications. Photocatalytical degradation of volatile aromatic pollutant had done by TiO2-graphene nanocomposites. Graphene oxide sheets used for removal of Pb(II) ions from aqueous solutions (Zhao et al. 2011a) and also preconcentration of U(VI) ions by few-layered graphene oxide nanosheets (Zhao et al. 2012). Folding/aggregation of graphene oxide used for the removal of Cu2+ (Yang et al. 2010). Graphene-based PANI nanocomposites have also been used as sensing platforms due to their good electrocatalytic activity, high specific surface area, excellent reliability, and low cost properties (Xu et al. 2008; Al-Mashat et al. 2010; Ramesha and Sampath 2011). These composites are successfully used for DNA, 4-aminophenol, dopamine, artesunate, hydrogen peroxide and hydrazine detection, as well as hydrogen (H2), methane (CH4) and ammonia (NH3) gas sensing. Innovative sensors with high sensitivity and selectivity, and fast response are in great need, and also we know fast response is in great need. Biosensors and affinity

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sensor devices have been shown to have the ability to provide rapid, cost effective, specific and reliable quantitative and qualitative analysis. To date the developments in nanomaterials and biosensor fabrications technology is moving rapidly with new and novel nano-biorecognition materials being developed which can be applied as the sensing receptors for mycotoxin analysis. Biosensors, as tools, have proofed to be able to provide rapid, sensitive, robust, and cost-effective quantitative methods for on-site testing. Developing biosensor devices for different mycotoxins are attracting much research interest in recent years with a range of devices are being developed and reported in the scientific literature. However, with the advent of nanotechnology and its impact on developing ultrasensitive devices, mycotoxins analysis is benefiting also from the advances taking place in applying nanomaterials in sensors development (Saini and Kaur 2012a, b, 2013; Wang et al. 2009; Liu 2008). It was established that gold supported on various metal oxides is a useful candidate for alkenes hydrogenation. A few interesting revelations arose from this research. Thiol–modified gold coated polystyrene particles had been used for adsorption of aromatic compounds (Qu et al. 2008). Dansyl-norvaline stereospecific recognition had been done by albumin gold nanoparticles (Kobayashi et al. 2006). Gold nanoparticles were also employed for an immunoassay for the detection of aflatoxin B1 (AFB1) in foods (Liu et al. 2003). Recently, MOFs, obtained by linking metal cations (or cationic metal clusters) with organic linkers, have attracted significant interest in the last years mainly due to the advantage of showing a large variety of structural types and chemical compositions, high surface area and permanent nanoscale porosity (Abhijith and Thakur 2012; Jiang and Xu 2011). MOFs have been widely studied as materials for catalysis gas storage and separation sensing and drug delivery and, more recently, the analytical applications of MOFs have emerged (Li et al. 2011, 2012; Surblé et al. 2006; Sumida et al. 2011; Chae et al. 2004; Shekhah et al. 2011). In this field, MOFs have shown to be promising materials as sorbents for sample preparation as chromatographic stationary phases, as well as for the development of improved detection systems and sensors. However, MOFs crystalline powders generally possess a random crystal size and shape, which makes troublesome their direct application and have led to engineer hybrid materials containing them, such as through supports, magnetic beads, beads coated with a MOF shell, or MOF crystals entrapped porous monolith. Porous materials are defined as solids containing empty voids which can host other molecules. The fundamental features of these materials are their porosity, the ratio between total occupied and empty space, the (average) size of the pores and the surface area (Li et al. 2011; Surblé et al. 2006; Sumida et al. 2011; Shekhah et al. 2011; Bagheri et al. 2012; Furukawa et al. 2013; Meek et al. 2011). Typical surface area values for the porous materials applied in technological processes range between 2000 and 8000 m2 g1. The most important applications of such materials are the storage of small molecules and filtering.The metal organic frameworks are defined as a nanocomposite material which can be consisted of either inorganic or organic materials. MOFs have shown high potential in gas storage, separation, chemical sensing, drug delivery, and heterogeneous catalysis applications. In

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general, the flexible and highly porous structure of MOFs allows guest species such as metal ions to diffuse into their bulk structure. The shape and size of the pores lead to selectivity over the guests that may be adsorbed. These features make MOFs an ideal sorbent in solid phase extraction of heavy metals. However, there is little information about MOFs as an adsorbent. Nanomaterials are well known to possess excellent electrical, optical, thermal, catalytic properties and strong mechanical strength, which offer great opportunities to construct nanomaterials-based sensors or devices for monitoring environmental contaminations in air, water, and soil. Various nanomaterials, such as carbon nanotubes (Forzani et al. 2006), gold nanoparticles, silicon nanowires, and quantum dots, have been extensively explored in detecting and measuring toxic metal ions, toxic gases, pesticides, and hazardous industrial chemicals with high sensitivity, selectivity and simplicity (Kim et al. 2009; Patzke et al. 2002; Wen et al. 2010, 2011). CNTs and graphene have been extensively studied for nanodevices or nanosensors (Bagheri et al. 2012; Douglas and Alexander 2008; Kong et al. 2000; Guo and Dong 2011; Goh and Pumera 2011; He et al. 2010; Male et al. 2007). Many metallic nanoparticles, such as gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs), have been used in the received in chemical and biological sensors (Zhao et al. 2011b), medical diagnostics, and therapeutics and biological imaging (Rosi et al. 2006; Sperling et al. 2008; Daniel and Astruc 2004). AuNPs or AgNPs exhibit high extinction coefficients and strong size- and distance-dependent optical properties, and are considered as a new class of reporters and have been applied in colorimetric sensing (Lee et al. 2007, 2008; Daniel et al. 2009; Xue et al. 2008; Liu and Lu 2003, 2004; Liu et al. 2007; Mirkin et al. 1996; Chen et al. 2010; He et al. 2008). Silicon-based nanomaterials are an important type of nanomaterial, which have been extensively studied due to their with single-molecule sensitivity (Li et al. 2010a, b; Nie and Emory 1997; Cao et al. 2002; Liu et al. 2012; Dasary et al. 2009; Zamarion et al. 2008; Wang and Irudayaraj 2011). Other nanomaterials also have been used in environmental monitoring, such as Fe3O4 (Liu et al. 2008; Zuo et al. 2009), SiO2 (Zhang et al. 2006), ZrO2 (Du et al. 2011; Liu and Lin 2005), etc.

4.6

Conclusion

Clean and fresh water and air are essential for the existence for life. Water and air are two vital components of life on earth; the existence of life on earth is made possible largely because of their importance to metabolic processes within body. Decontamination is the reduction or removal of chemical and biological agents by means of physical, chemical neutralization, or detoxication techniques. More than half of the world is facing problem of water purification. This condition is worse in the developing countries. Nanomaterials are being used in more than 1600 commercial products including food, and the consumers are already exposed to these nanomaterials. Nanotechnology revolution will play an essential role in solving the problem of rising demands of clean water and decreasing of the available

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supplies of fresh water. Nanotechnology has shown huge potential in areas as diverse as drug development, water decontamination, information and communication technologies, and the production of stronger, lighter materials and human health care. The recent development of nanotechnology is the technology which raised the possibility of environmental decontamination through several nanomaterials, processes, and tools. This chapter summarizes the expertise of various approaches of decontamination for successful realization of remediation in environment.

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5

Development of Environmental Nanosensors for Detection Monitoring and Assessment Urmila Chakraborty, Gurpreet Kaur, and Ganga Ram Chaudhary

Abstract

Regular detection, monitoring and assessment of the environmental samples is extremely essential for checking the levels of environmental contaminants, evaluation of the effects due to their presence in the environment and taking suitable measures for the maintenance of essential environmental resources. With the advancement of nanotechnology, extensive research work has been focussed on utilizing the unique chemical and physical properties of nanostructures and nanomaterials for the development of nanosensors. These nanosensors have great advantage over the conventional sensors due to their better interaction with nanoscale analytes, high sensitivity, selectivity, portability, fast response and ease of operation. Nanosensors have huge and important applications in almost all areas of our lives like daily use gadgets, industries, environmental detection, medical, defence and security, agriculture, food processing, etc. Nanosensors have significant use for detection and monitoring of environmental samples. For environmental applications, nanosensors can be categorized based on the nanomaterials used as the sensing material, transduction principle, application for different samples (air, soil and water) and sensors for various analytes. The combination of nanotechnology and biotechnology has resulted in the development of more selective and efficient nanobiosensors. Nanosensors are mainly based on optical, electrochemical, mechanical and magnetic transduction principles. A large variety of sensor materials for nanosensor fabrication such as, metal-based, metal-oxide-based, carbon-based, and polymer-based nanomaterials have been developed. These nanosensors have been used for the detection of various analytes like pathogens, toxic gases, organic chemicals, heavy metals and

U. Chakraborty · G. Kaur · G. R. Chaudhary (*) Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh, India e-mail: [email protected] # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_5

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pesticides from the environmental samples. Besides detection of single analytes, nanotechnology can be applied to develop devices like multianalyte nanosensor arrays, which can be designed for simultaneous detection of multiple analytes. In this work, we have discussed various types of nanosensors based on the nanomaterials and transduction principle for detection, monitoring and assessment of different harmful environmental contaminants. Limitations of these nanosensors challenging their practical and potential applications have also been discussed in this chapter. Keywords

Nanosensors · Nanomaterials · Environment · Nanoscale · Contaminant

5.1

Introduction

We are living in a rapidly progressive world, with regular technological advancement, agricultural and industrial growth, new scientific research and changing human lifestyle. All these developments affect the environment due to constant direct and indirect human interactions with their living and nonliving surroundings. The modernization have in one side led to many positive effects like development of facilities for a better and comfortable lifestyle, but in turn have also resulted in numerous negative impacts on our environment. The excessive use and production of different kinds of chemical and biological compounds for growth of various sectors of human life have led to excessive emission of harmful gases into the atmosphere and discharge of harmful effluents into the water sources and soil. When such chemical and biological species enter the environment beyond a certain limit, they lead to the contamination of air, water and soil, leading to change in physical, chemical and biological properties of these natural resources, thus causing environmental pollution. As a consequence, such effects give rise to dangerous phenomenon like ozone layer depletion, acid rain, climate changes and melting of the glaciers due to global warming, and numerous fatal diseases causing harm to humans as well as all the other living species on our planet. Therefore, detection of the amount of such species in the environmental samples and regular monitoring of the impacts of developmental projects releasing such substances is very important. Also, proper environmental studies for identification, evaluation and estimation of the consequences of proposed and ongoing projects, i.e. environmental assessment for reducing the negative effects before making commitments and decision regarding such projects is extremely necessary (Balaman 2019). Many technologies for detection and monitoring of environmental samples have been developed and used over years including sample analysis by techniques like flow injection analysis, atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), high performance liquid chromatography (HPLC), gas chromatography (GC), inductively coupled plasma mass spectrometry (ICP-MS), etc., but they have certain limitations like expert handling, time consuming sample preparation, high operating costs, portability

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issues, etc. Thus, the monitoring, assessment and detection of any kind of changes in the environmental systems require certain types of devices which can respond to particular chemical, biochemical and physical stimulus for which they are designed and result in an output which can be recorded and analyzed. Such types of devices are known as “Sensors”. Currently technological and scientific advancement has led to the development of various kinds of sensors, but revolutionary progress in the field of sensors have been observed with the advancement in nanotechnology, which deals with the materials and systems in the nanoscale dimensions (10 to 100 nm or 10
9 m). According to most of the definitions, “Nanosensors” can be defined as sensors which have at least one of the dimensions less than 100 nm and have the ability to collect information at nanoscale and convert it to analyzable data. Nanosensors should not necessarily be devices manufactured at nanoscale but they can also be large devices which utilize the unique property of nanomaterials to make nanoscale measurements. Nanomaterials possess unique properties due to their nanoscale dimensions, they have high ratio of surface area to volume, giving rise to distinct physical and chemical properties, including, optical, mechanical and electrical properties different from those of bulk materials. Nanosensors utilize such unique characteristics of nanoscaled materials due to the ability of these materials to interact with the surrounding environment at a nanoscale level. Also, in many cases they have similar dimensions to the analytes of interest and hence can give information for nanoscale matrices which is far more accurate, and highly sensitive (Grieshaber et al. 2008) than the information obtained from normal sensors. Hence, the main advantages of nanosensors over conventional sensors are:• • • • • • •

the low energy required for operation due to nanosizes, opportunities to design miniaturized and portable sensors, high selectivity and sensitivity, low analyte detection limit, ease of surface functionalization to design target specific sensors, fast response time, applications in real time sensing, tuneable size dependent properties making them useful for efficient detection of large variety of samples.

Further, recognizing the natural sensing abilities of many biological systems, the combination of nanotechnology with biotechnology have resulted in the development of nanobiosensors with rapid response and more enhanced sensitivity and selectivity (Dubey and Mailapalli 2016). Nanosensors are used is almost all areas of life. These are present in the systems we use everyday like on automatic doors, cars, phones, etc., and their applications range to a wide variety of devices in various industrial, environmental and agricultural fields (Rodrígues-Mozaz et al. 2004) for instance:• In food processing and technology for analysis of food quality and food toxicants. • For medical applications for designing reliable diagnostic tools and therapeutic systems, point-of-care devices, measurement of temperature of living cells, etc.

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• In the area defence and military for designing special equipments, detection of toxic chemicals, forensics, etc. • In agricultural sector for devising humidity sensors for automatic irrigation systems, for detection of levels of harmful chemicals such as pesticides and fungicides, monitoring of soil conditions and crop growth, etc. • Significantly important utilization in environmental assessment, detection and monitoring. They can be effectively used for the detection of toxic and harmful gaseous pollutants released from industrial, domestic, vehicular, and natural emissions, dangerous organic and inorganic chemicals contaminating the water and soil, quality control of these natural resources, designing real time environment monitoring systems to check and regulate the levels of any contaminants etc. There are numerous other important applications of nanosensors, but this chapter focuses on the applications of nanosensors in the field of detection, monitoring and assessment of the environmental samples, with discussion of various types of nanosensors based on different classifications applicable for this field. This chapter also discusses the limitations and future scopes for the use of nanosensors in environmental applications.

5.2

Working Principle of Nanosensors and Methods for Nanosensors Development

The main components of a basic sensor are: (1) sensor material (2) transducer. In principle, in the presence of the target analytes, the sensor materials are responsive and sensitive to variation in environmental stimuli, which act as the transduction principle, such as thermal (temperature, heat flow, entropy, specific heat etc.), chemicals (concentration, pH, composition, oxidation/reduction potential, rate of reaction etc.), magnetic (magnetic moment, flux density, permeability, field intensity), optical (absorbance, transmittance, fluorescence etc.), mechanical (volume, area, length, pressure, mass flow, acoustic intensity and acoustic wavelength, etc.), electrical (current, voltage, resistance, charge, etc.) variations (Middlehoek and Noorlag 1982). These variations are converted to mostly electrical signals by the transducer to give an output that can be analyzed. In case of biosensors, another important component is the bio-recognition element such as enzymes, oligonucleotides and antibodies. These elements interact with the target analyte to produce biological response which can be converted to electrical response by the transducer. The methods for production of nanosensors include three main approaches: (1) top-down lithography, (2) bottom-up method and (3) self-assembly. Most of the integrated circuits are developed by top-down lithography, which involves carving out the required design from larger block of material. This method is mostly used to prepare devices for micro electromechanical systems, but recently, nanosized components have also been incorporated by this technique.

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Bottom-up approach is an additive process, and involves sensor preparation by one by one assembly of individual molecules or atoms into particular positions using tools like atomic force microscopes (AFM). But this method is mainly used to build starting molecules for self-assembling sensors. The third and fastest method for nanosensors fabrication is self-assembly, which entails growing specific nanostructures for sensors applications. In this method, mostly set of components that are already complete, are automatically assembled to give finished products. This technique is more accurate, cost-effective and fast than the other methods, as it involves assembly of numerous molecules with minimum or no outer influence.

5.3

Classification of Nanosensors

Nanosensors can generally and broadly be classified on the basis of: 1. 2. 3. 4.

Structure and type of nanomaterials used for fabrication of nanosensors. Transduction principle. Applications. Various types of analytes for which the nanosensors are used.

Figure 5.1 represents main components of nanosensors and their various types for environmental applications.

5.3.1

On the Basis of Transduction Principle

Nanosensors can be classified on the basis various techniques employed for transduction of signal. There are different methods for signal transduction but the nanosensors can be categorized on the basis of main transduction mechanisms: (1) optical nanosensors, (2) electrochemical nanosensors (3) mechanical/acoustic nanosensors (Munawar et al. 2019) and (4) magnetic nanosensors.

5.3.1.1 Optical Nanosensors Optical nanosensors are based on the distinctive optical behaviour displayed by nanomaterials upon interaction of light signals. The sensitivity of the optical nanosensors depends mainly on the techniques for detecting the optical phenomenon (Qu et al. 2012). These nanosensors respond to variation in optical signal transduction and can be further classified according to their particular optical properties like absorption and emission, surface plasmon resonance (SPR), light scattering, fluorescence, etc. Many fluorescence-based nanosensors are designed on the either properties of non-fluorescent nanomaterials to quench the fluorescence of fluorophores or fluorescence quenching of the fluorescent nanomaterials by other species. The Jablonski diagram for fluorescence, and fluorescence quenching in the presence of quencher

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Fig. 5.1 Main components of nanosensors and their various types according to types of nanomaterials used, transduction principle and recognition elements (for nanobiosensors) for environmental applications

have been represented in Fig. 5.2a, b. For instance gold nanoparticles (AuNPs), when brought to close proximity to fluorescein isothiocyanates (FITCs) result in the quenching of fluorescence emitted by FITCs (Munawar et al. 2019). Another types of fluorescence-based nanosensors are based on the phenomenon of Föster resonance energy transfer (FRET), which involves energy transfer between two fluorophores, one of which act as a donor and other as an acceptor. This is the energy transfer that is non-radiative in nature and doesn’t include photon emission but involves long range dipole–dipole interaction between the two fluorophores. For the phenomenon of FRET to occur, the distance between the FRET pair should be less than 10 nm and there must be more than 30% overlap between the donor’s emission spectrum and acceptor’s absorbance spectrum (Stanisavljevic et al. 2015; Elangovan et al. 2002). The basic principle of FRET is shown in Fig. 5.2c, d. The principle of FRET has been utilized for development of highly sensitive analytical techniques in various research fields. But, the combination of nanotechnology with the principle of FRET has led to the development of FRET-based nanosensors with improved sensor properties. Among various nanomaterials,

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Fig. 5.2 (a) Jablonski diagram for fluorescence, (b) quenching of fluorescence of fluorophore donor (D) in the presence of quencher (Q), (c) Jablonski diagram representing the principle of FRET, (d) figurative representation of FRET between donor (D) and acceptor (A) fluorophores

nanoparticles, especially quantum dots (QDs) present huge potential for fabrication of FRET-based nanosensors. QDs are semiconductor nanoparticles within the size range of 1–10 nm. These nanomaterials display quantum confinement giving rise to distinctive electronic and optical properties, depending on their size. QDs offer better optical properties and FRET characteristics over organic fluorophores (OFs). The core size of QDs can be controlled during synthesis, which results in quantum confinement and this gives emission range tuning potential to the QDs, hence, providing advantage for FRET than OFs. QDs show strong chemical degradation and/or photo bleaching resistance due to inorganic core, brighter probes due to molar extinction coefficient 10–100 times greater than OFs, large Stokes shift, longer fluorescence lifetime (20–50 ns) than OFs, excitation of multicoloured QDs from single source without overlap of emission peaks due to narrow emission and broad absorption peaks, elimination of background auto fluorescence in biological samples and simultaneous detection of multiple targets. Table 5.1 (Stanisavljevic et al. 2015) represents benefits of QDs over OFs based on desirable characteristics for FRET. However, QDs also face shortcomings like insolubility and inorganic nature, but such problems can be overcome by modification using capping agents and different coatings. Luminescence intermittency is another drawback for applications of QDs,

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Table 5.1 Benefits of quantum dots (QDs) over organic fluorophores (Ofs) based on desirable characteristics for FRET S. no. 1. 2.

3.

Property Fluorescence lifetime (ns) Molar extinction coefficient Photostability

OFs Few

QDs 20–50

Less than 2  105 M
1 cm
1

10–100 times more than fluorophores

Varies with choice of fluorophore Generally narrow

Strongly resistant to photobleaching Broad

4.

Absorption spectra

5.

Emission spectra

Broad, tailed and asymmetric

Narrow (20–40 nm bandwidth)

6. 7.

Stokes Shift Quantum yield

>100 nm Varies with choice of fluorophore

300–400 nm 40–90%, depends on surface modifications and choice of buffer

Ref Walling et al. (2009) Sun and Goldys (2008) and Yu et al. (2003) Zrazhevskiy et al. (2010) Alivisatos et al. (2005) and Probst et al. (2013) Alivisatos et al. (2005) and Probst et al. (2013) Fu et al. (2005) Zrazhevskiy et al. (2010)

which can be controlled by surface engineering (Li et al. 2013; Stopel et al. 2013). QD-FRET sensors have been used for detection of various analytes like nucleic acids, and enzymatic activities. QD-FRET-based immunoassays have been used for sensing organic compounds including some organic pollutants. For instance, Zhang et al. reported the FRET-induced fluorescence quenching of CdTe QDs by dithiazone (DZ), which is a bidentate ligand. This sensor was used for detection of organophosphorothionate pesticides with chlorpyrifos as model pesticide. The detection was based on the recovery of luminescence of CdTe upon the replacement of DZ in the presence of the pesticide. Successful detection of organophosphorothionates was done in apple samples (Zhang et al. 2010). Guo et al. showed the QD-FRET-based sensing of broad-spectrum herbicide, glyphosate using cysteamine-stabilized gold nanoparticles (CS-AuNPs) with positive charge as acceptor, and negatively charged CdTe QDs capped with TGA as energy donor (Guo et al. 2014). QD-FRET-based nanosensors have also been used for prominent detection of heavy metal ions. For instance, Li et al. designed nanosensors for detection of mercury Hg(II). They used butyl rhodamine B dye and electronegative TGA-capped CDTe (cadmium telluride) QDs. For better FRET efficiency, the two fluorophores were brought closer by cetyltrimethylammoniumbromide addition in Tris-HCl buffer. The presence of Hg(II) quenched the photoluminescence of QDs by displacement of Cd(II) ions from the surface of TGA-CdTe QDs due to higher affinity of Hg(II) towards Te. With the decrease in fluorescence of TGA-CdTe QDs, there was a corresponding increase in the rhodamine B dye’s fluorescence (Li et al. 2008). Many harmful microorganisms and their toxins have also been detected by QDs-FRET-based nanosensors. Kattke et al. reported the detection of Aspergillus amstelodami using QDs-FRET-based immunoassay. They designed the nanosensor

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by using CdSe/ZnS QDs coated with PEG and derivatized by amine functional group, and conjugated anti-Aspergillus antibody to thee QDs using a crosslinker and BHQ3-labelled mold analyte quencher with lower antibody affinity as compared to A. amstelodami. The detection was based on the recovery of fluorescence of QDs due to displacement of BHQ3-labelled mold analyte in the presence of A. amstelodami. Low concentrations (103 spores/mL) were detected in 5 min or less by the immunoassay (Kattke et al. 2011). PEBBLES (Probes Encapsulated by Biologically Localized Embedding) PEBBLES-based optical sensors are submicron probes which consist of an inert matrix encapsulating fluorescent dyes, whose fluorescence can be quenched due to the target analyte. These are mainly applied for intracellular sensing. The main types of PEBBLES nanosensors are based on sol-gel silica, crosslinked poly (decylmethacrylate) and polyacrylamide matrices, which have been used for sensing of inorganic ions like Na+, Cl
, Zn2+, Cu2+, Mg2+, Ca2+, H+, K+. So far, most of the PEBBLE sensors have been fabricated on the basis of single fluorescence peak intensity measurement. However, fluctuations of signal at the source of excitation are major challenge for practical applications of PEBBLE. This problem can be tackled by designing ratiometric PEBBLE sensors, which consist of an inert matrix encapsulating two fluorescent dyes one of which act as an indicator and other as a reference. The ratios of intensity of the indicator and reference dyes, determine the sensor sensitivity. More accurate results are provided by ratiometric PEBBLES, because fluctuations of fluorescence have same effect on the indicator and reference dyes (Buck et al. 2004). Ratiometric PEBBLES sensors for oxygen detection was fabricated using organically modified silica (ormosil) NPs with fluorescent reference and indicator dyes, whose fluorescence were quenched with introduction of oxygen (Koo et al. 2004). This sensor can be used for monitoring dissolved oxygen as an indication of the bacteria present in aqueous media (Rodrígues-Mozaz et al. 2004). Wang et al., developed PEBBLE sensor with 1-pyrenemethylamine organic NPs for the detection of Cr(VI) in with selective and satisfactory results wastewater samples (Wang et al. 2004). Surface Plasmon Resonance (SPR) Another important optical phenomenon displayed by nanomaterials, especially noble metal nanoparticles (NPs) is the surface plasmon resonance (SPR). Unlike bulk materials, noble metal nanostructures with size less than electron’s de Broglie wavelength, result in strong absorption in the near-UV/visible region. For NPs in 5–20 nm size range, there is confinement of electrons into the nanosized “metal boxes”. These conduction electrons undergo collective oscillation, and upon interaction with light, when the frequency of incident photon resonates with the frequency of conduction electrons collective oscillation, distinct excitation-band known as surface plasmon band (SPB) is visible near 530 nm. This phenomenon is known as localized surface plasmon resonance (LSPR) (El-Sayed 2001; Daniel and Astruc 2004). The brilliant colours of metallic NPs are a result of this phenomenon of LSPR.

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Dependence of the LSPR spectrum on the internal properties of NPs (shape, size, type of material) as well as on the external environment of NPs (Kelly et al. 2003), make noble metal NPs extremely important for designing optical nanosensors (Bogue 2004). Detection is based on attachment of target molecule on the surface of NPs, producing change in the local refractive index, and thus resulting in the shift in LSPR spectrum. A wide array of molecular recognition elements like DNA, antibodies or enzymes can be incorporated as self-assembled monolayers (SAMs), which can be used for chemical modification of NPs and enhance their selectivity. A portable, cost-effective and simple instrument for transmission mode UV-vis extinction spectroscopy can be used to implement LSPR nanosensors. The device consists of a white light source and a small spectrometer, NPs arrays inside a flow cell and coupling these components using an optical fibre. The target analyte is stored in a solvent reservoir, and this reservoir and a syringe are also connected to the cell in the LSPR nanosensors setup. LSPR nanosensors based on single NPs have also been designed (Haes and Van Duyne 2004). As the absorbance of individual noble metal NPs is closer to the limit of detection, LSPR spectrum of single NPs can’t be measured by using UV-visible spectroscopy. Instead, the LSPR spectra of single NPs can be measured using resonant Rayleigh scattering spectroscopy, which offers detection of scattered signal in very low background (McFarland and Van Duyne 2003). LSPR nanosensors can be used for the detection of analytes at very low concentrations as low as zeptomole (10
21 mols) sensitivity and very low volume of analyte (attolitres: 10
18 L). For instance, McFarland et al. detected the molecules of hexadecanthiol at zeptomolar levels. LSPR single-NPs nanosensors provide potential sensing platforms for multianalyte (McFarland and Van Duyne 2003). Biotin functionalized gold NPs were used as single-NPs optical sensor for detection of protein streptavidin by Raschke et al., and this sensor showed sensitive detection for detecting about 50 bound streptavidin molecules (Raschke et al. 2003). LSPR-based nanobiosensors prepared by NPs functionalized with antibodies have shown sensitive detection towards microbial toxins and these could be used for successful sensing of water contaminating microorganisms (Rodrígues-Mozaz et al. 2004). Colorimetric Nanosensors Noble metal NPs have also been used for colorimetric sensing applications due to their unique optical properties depending on the particle size. For e.g., Liu and Lu, reported colorimetric detection of Pb2+ using gold NPs functionalized with enzyme specific for Pb2+. The sensing is based on aggregation of gold NPs, displaying blue colour, and change in colour to red with the presence of Pb2+ due to cleavage of the substrate by the enzyme and inhibition of aggregation (Liu and Lu 2004). Surface-Enhanced Raman Scattering (SERS) As a result of LSPR excitation displayed by metallic NPs, there is a generation of electromagnetic field on the NPs surface, which can result in increase in the spontaneous Raman scattering of species at close distances to the surfaces (Rodriguez-Lorenzo and Alvarez-Puebla 2014). This phenomenon gives rise to SERS spectroscopy, which can be used as an

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effective analytical tool. NPs of gold and silver have shown enhancement in the SERS factor by upto 1014 (Fritzsche and Taton 2003; Kneipp et al. 1999). Recently, SERS technique based nano-dielectrophoretic microfluid device biosensors were prepared and these were used for the sensing of water contaminating pathogens (Wang et al. 2017).

5.3.1.2 Electrochemical Nanosensors Voluminous research has been done of the development of electrochemical-based detection techniques due to low cost, high sensitivity, ease of operation, lesser time consumption, and ease of miniaturization and portability of electrochemical devices. Hence, these techniques offer a convenient approach towards nanosensors development for detection of environmental contaminants. The basic operating principle behind electrochemical based sensors is the detection of measurable change in current or potential, which takes place upon the chemical reaction of the analyte, which involves any kind of electron transfer between the analyte and the sensor material. Electrochemical nanosensors can be categorized mainly into: (1) conventional three or two electrode electrochemical systems, (2) chemiresistive/field-effect transistor (FET) systems (Nehra et al. 2019). Three and Two Electrode Systems These types of electrochemical nanosensors can be designed by fabrication of nanomaterials modified electrodes which can be used as working electrodes for three electrode or two electrode (for I–V method) electrochemical systems. Different materials, usually conductive materials like gold, silver, platinum, glassy carbon, indium tin oxide (ITO) and graphite can be used as substrates for deposition or growth of nanomaterials. Various methods for surface modification of these substrates using nanomaterials can be applied, like dip coating, drop casting, polymer-based coatings, direct growth on substrate, screen printing, use of binders (like Nafion). The analytes undergo redox reactions on the electrode surface and can be detected by electrochemical techniques like amperometry, voltammetry, impedance, potentiometry, etc. The nanomaterials act as electro catalysts by providing greater surface for analyte adsorption, improving the electron transfer properties between the analyte and electrode, and decreasing the over potential for electrochemical reactions taking place on the electrode surface. A number of different types of nanomaterials like metal, metal oxides, carbon-based, etc., have been used for fabrication of electrochemical nanosensors. The surfaces of these nanomaterials could further be chemically or biologically modified to show specificity for a particular analyte. Thus, these nanomaterials modified electrode surfaces display higher sensitivity, greater selectivity and much lower limit of detection for analytes. Screen-printed electrodes (SPE) are designed to integrate the working, reference and counter electrodes into small, compact, low cost and disposable electrochemical strips. These devices are based on inks like silver, platinum, carbon nanotubes (CNTs). Similar to the conventional system, the working electrode can be modified with various nanomaterials to devise nanosensors. SPE are designed to detect samples in microvolume and provide convenient, cheap and portable

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Fig. 5.3 (a) Three electrode electrochemical system, (b) Screen-printed electrode (SPE)

Fig. 5.4 (a) Illustration of FET sensors consisting of a source, channel material, gate electrode, gate oxide and drain (b) the effect adsorption and desorption of gas on the sensor current

nanosensor devices. Figure 5.3a, b represents conventional three electrode electrochemical system and SPE. (FET) Sensors Another kind of electrochemical sensor systems are the chemiresistive/field-effect transistor (FET) sensors. These types of sensors have the advantages of potential for designing miniaturized systems, parallel sensing, rapid response time and direct signal translation from target molecules interactions taking place on the surface. FET sensors have shown promising potential for the detection of gases, heavy metal ions, pathogens and proteins. FET sensors generally consist of source, channel material, gate electrode, gate oxide and drain (Mao et al. 2017) as shown in Fig. 5.4a and the effect of gas adsorption and desorption on the sensor current is demonstrated in Fig. 5.4b. FET sensor operates by monitoring the variation in conductance by pre- and postadsorption of target molecules on the channel material. Thus, channel material plays an important role in the working of FET sensors, as the intrinsic properties (band

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gap, work function, carrier mobility, etc.) of channel materials govern the performance of the sensor. 1-dimensional (1-D) nanomaterials like SWCNTs, silicon nanowires (SiNWs), metal oxide nanowires (MONWs), and 2-D nanomaterials have been used successfully as FET channel materials (Mao et al. 2017). The lack of specificity for a particular target molecule, limits the applications of pristine nanowires. To overcome this problem, researchers have developed surface functionalized and hybrid gas sensors, for e.g., Chen et al. (2009) developed an electronic nose hybrid nanosensor composed of SWCNT and nanowires of In2O3, ZnO, SnO2 and used this for sensing ethanol, NO2 and H2 gases. Choi et al. functionalized SiNWs with palladium to design FET-based hydrogen gas sensor (Choi et al. 2015). Besides, nanowires-based FET sensors have also been applied in the field of biomedical sensor applications (Ambhorkar et al. 2018). Metal oxides nanomaterials used for conducting channel like SiO2, ZnO, SnO2 and TiO2 are highly reactive and hence, can act as suitable materials for surface functionalization. The oxide surfaces can be modified by different self-assembled monolayers (SAMs). For instance, oxide surfaces are provided with covalent bonds by carbonyl, phosphoric acid and silanol groups. Properties of SAM layer modified surface depend on the functional groups present on them, for e.g., amine-terminated SAMs show selectivity for H+ ions. Surface functionalization of SiNW FETs with receptors like antigens, biotin and amine-terminated silanol has made them applicable for efficient detection of bio-substances in aqueous medium samples. Nanomaterials with 2-D layered structures, like graphene and reduced graphene oxide (RGO) possess unique electronic properties and large ratio of surface area to volume, thus making them suitable materials for FET sensors. For gas sensing applications, the target gases and 2-D nanomaterials interact with physical adsorption, and the 2-D nanomaterials undergo enhancement or reduction in the conductance, depending on the type of both the gas species (electron acceptor oxidizing gases like NO2/electron donor reducing gases like NH3) and the semiconductor (n-type/p-type) (Mao et al. 2017). The selectivity/sensitivity of the gas sensors can be improved by nanoparticles (NPs like WO3, Ag, SnO2 and Pt) deposition on the channel materials. For e.g., NPs and 2-D nanomaterials can be used to form hybrid structures for sensitive and selective gas sensing applications. The gases interact directly with the coated NPs, leading to the conductivity change of the hybrids, while the 2-D materials work as underlying conducting channel. Besides gas sensing, 2-D semiconductor nanomaterials with tunable and appropriate band gap can also be used favourably for water sensor and biosensor applications (Mao et al. 2017). Electrochemical nanosensors can also be modified for detection of proteins. Conjugation of immunoassays with nanosensors can be used to develop immunosensors. Electrochemical sensing techniques have been used for the detection of a large variety of analytes for environmental applications.

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5.3.1.3 Mechanical/Acoustic Detection Nanomechanical sensors are sensitive to mass and these are based on detection of displacements, mechanical forces and changes in mass. Overall mass of the mechanical device is related to the mass to be determined. Hence, when mechanical sensor’s mass is reduced to nanoscale, there is enhancement in the detection of mass (Ku et al. 2013). The major obstacle in mechanical nanosensors is the reduction of sensor sensitivity due to viscous damping (Burg et al. 2007). Cantilevers enclosed with fluid filled channels can be used for fluid measurements. However sensitivities achieved for such cantilevers is lower than that obtained in gas phase. Barun et al. devised resonant cantilever sensing array, which were used against E. coli (Barun et al. 2009). Piezoelectric cantilever sensors (PECS) were reported for detection of S. typhimurium, which showed greater sensitivity than array biosensors and ELISA (Shih and Shih 2007; Rowe et al. 1999). PECS sensors are types of mass sensors based on the change in mechanical resonance frequency due to binding of analyte molecules resulting in a change in mass. PECS can be miniaturized, and involve electrically driven mechanical resonance and sensing, giving them advantage over other techniques. Target molecules can attach with the receptors coated on the surface of piezoelectric device (Sakti et al. 1999; Ward and Buttry 1990). This change in resonant frequency can be monitored and simple electrical measurements with PECS can be used for fast, label-free and quantitative in situ pathogen detection (Shih and Shih 2007). 5.3.1.4 Magnetic Transduction Magnetic properties of some nanomaterials can be explored to design nanosensors which can work on the principle of magnetic transduction. Nanosensing devices like magnetic relaxation switching assays-(MRWs) based nanosensors, utilize these properties of magnetic nanoparticles (MNPs) such as superparamagnetic iron oxide nanoparticles (SPIOs), and such types of nanosensors can be applied for the detection environmental contaminants like biological macromolecules, small organic molecules and heavy metal ions. Upon interaction with the target analyte, the individual nanomagnetic probes (MNPs) get clustered into larger assemblies, causing inhomogeneity in the magnetic field. As a result, the surrounding water protons experience enhancement in the dephasing of spins. The detection of this subsequent variation in the spin-spin (transverse; T2) relaxation of the water molecules can be done using techniques like magnetic resonance relaxometry (Willner and Vikesland 2018). Rational design of MNPs with high T2 relaxivity can result in high sensitivity of MRWs-based nanosensors. Also, the specificity of receptor (oligonucleotides, proteins, small-molecule ligands, etc.) is important for designing the nanosensor. Mostly iron oxide (Fe2O3) NPs are used for these applications due to their high mass magnetization value (Ms). Doped and core/ shell MNPs have also been developed for improved magnetic properties, as discussed in detail in Sect. 5.3.2.2. MRWs operation involves radio frequency (RF), and due to the deep-penetrating power of RF radiations, MRWs-based sensing can be performed in light-

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impermeable and turbid media, hence eliminating the necessity of sample purification steps, unlike the cases of optical and electrochemical based sensors. Also, most of the practical samples don’t contain magnetic properties, hence, the MRWs-based nanosensors can be used for background-free detections of harmful water pollutants. In their work, Zhang et al. (2017b) have summarized the recent advances on MRWsbased nanosensors.

5.3.2

On the Basis of Shape and Types of Nanomaterials Used for Fabrication of Nanosensors

The type of nanomaterials and their structure plays an important role in determining their chemical and physical properties. By variation in their synthesis techniques and precursors used for fabrication of nanomaterials, various morphologies can be obtained like rods, dendimers, nanocubes, nanocones, nanowires, nanoflowers, nanofibers, quantum dots, nanosheets, etc. Also, different kinds of nanomaterials, like carbon-based, metal, metal oxides, etc. can be used for fabricating nanosensors for environmental applications. Here we are summarizing some major classes of nanomaterials and their applications for fabrication of nanosensors analyzing environmental samples.

5.3.2.1 Carbon-Based Nanomaterials Carbon-based nanomaterials have been implemented as suitable transduction elements for fabrication of highly selective and sensitive sensors due to their unique geometry, broad potential window, rapid electron transfer properties, low residual current, easy renewal and modification of their surfaces, and optical properties (Nehra et al. 2019). These carbon-based nanomaterials can be classified on the basis of the number of dimensions in nanorange as: • 0 D, with all the three dimensions in nanoscale (fullerenes, nanodiamond, carbon dots, etc.) • 1 D, with two dimensions in nanoscale (carbon nanofibres (CNFs), carbon nanotubes (CNTs), etc.) • 2 D, with one dimension in nanoscale (graphene, graphene oxide, etc.) Due to their excellent electrocatalytic behaviour, and ability to stay chemically inert during redox reactions, these materials have found huge application as electrochemical sensors, and have been used for the detection of a numerous environmental contaminants. Carbon-based materials have been used for modification of working electrode surfaces for three and two electrode electrochemical detection systems, and used for sensing analytes using electrochemical techniques like voltammetry, amperometry, impedance, etc. (Nehra et al. 2019). These materials have also been used as platforms for immobilization of biomolecules for designing biosensors.

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Carbon-based nanomaterials find a useful application as the functional channel in the chemiresistor/FET nanosensors systems. For instance, the respective planar and tubular geometries of graphene and CNTs provide greater binding of electrode surface with analyte molecules due to maximum exposure of the atoms on the surface. CNTs possess many desired properties for nanosensing applications, some of which are (Riu et al. 2006): 1. Unidirectional properties of CNTs-based materials can be greatly controlled due to high ratio of length-to-radius for CNTs. 2. Based on their diameter, chirality and any other surface functionalization, CNTs can behave as insulating, metallic or semiconducting materials. 3. CNTs can be encapsulated with gases and can be used to store separating gases or hydrogen. Metals can also be encapsulated inside CNTs to make magnetic or electrical nanocables. 4. CNTs are inert, robust and have high mechanical strength. Carbon-based nanostructures can ensure highly sensitive, low limit and label-free sensing of analyte due to the comparability of their dimensions to the Debye length (λD), which is a measure of penetration of electric field into the bulk material and is also responsible for modification of the electrode material’s properties upon analyte exposure (Nehra et al. 2019). Additionally, these nanomaterials also have the advantage for their ability of concurrent detection of multiple analytes. The use of graphene-based 2-D nanomaterials has gained much interest as channel materials for FET sensors due to their unique structure and excellent electronic properties. Graphene is a zero-gap semiconductor material with high room temperature electron mobility. Nanostructure based on graphene and RGO have high sensitivity to electronic changes upon the adsorption of target analyte molecules, and also have high specific surface area, thus making them important for sensor applications. Further, functionalization of the surfaces of carbon-based nanomaterials by incorporation of some inorganic nanomaterials or through covalent/non-covalent interactions, enhance the surface properties of the electrode materials. The surfaces of single-walled carbon nanotubes (SWCNTs) have been modified for their successful application as biosensors. The conductance of the nanotubes can be modified by substitution of the solid-state gate by detecting molecules (Besteman et al. 2003). Nanocarbon-modified electrodes can be applied for detection of various biological and chemical analytes. They have been used as efficient gas sensors for the detection of both indoor and outdoor harmful gas molecules. Highly sensitive gas sensors for NO2, CO2, H2, etc., have been fabricated using carbon-based nanomaterials. For e.g., NO2 gas sensor was designed by using n-p-n heterojunction of SnO2 nanowires and CNTs (Nguyet et al. 2017). These nanomaterials have also been used for hazardous organic molecules detection. For instance, highly sensitive and rapid detection of 2,4,6-trinitrotoluene (TNT) was reported by Castro et al., using a novel biosensor fabricated with reduced graphene oxide/CNT nanocomposites (Castro et al. 2018). Ren et al. reported colorimetric nanosensor for the detection of 2,4,6 trinitrophenol (TNP) compounds using orange fluorescence

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emitting carbon nanodots. Appreciable limit of detection (LOD) value of 5  10
5 M was obtained by visual detection and 0.127 μM by fluorescence measurements (Ren et al. 2018). Yan et al., reported specific electrocatalytic sensing of endocrine disrupting chemical bisphenol A (BPA) using graphitic carbon nitride modified with molecular imprinted polymer (Yan et al. 2018). Chiu et al. designed screen-printed carbon electrode sensor using conducting polymer (melamine) modified MWCNTs, based on the high stability and large surface area of CNTs. This sensor was efficiently used for electrochemical sensing of nitro furans in milk and lake water samples (Chiu et al. 2018). Detection of bacterial pathogens and viruses has also been done using carbon-based nanomaterials modified sensors. Carbon-based nanomaterials modified pyrolytic graphite electrode (Banks and Compton 2005) and glassy carbon electrode (Dekanski et al. 2001) have been successfully explored for this purpose. Sensing of pathogens is facilitated by high sensitivity and selectivity of carbon nanomaterials based nanobiosensors. Bharadwaj et al., proposed antibody-conjugated SWCNTs for electrochemical immunosensing of S. aureus (Bhardwaj et al. 2017). Carbon-nanomaterials-based sensors have been applied for detection of harmful heavy metal ions. Zhou et al., reviewed the recent progress in detection of heavy metal ions using biosensors prepared by nanostructures modified with DNAzymes/DNA (Zhou et al. 2016). The use of carbon-based nanomaterials for detection of different organic, inorganic and biological pollutants has been listed in Table 5.2. Carbon-based nanomaterials also exhibit excellent optical properties and these materials have also been used for developing optical nanosensors. Zhang et al. reported ultrasensitive glucose and hydrogen peroxide (H2O2) detection using FRET between polyaniline and carbon quantum dots (Zhang et al. 2015b). Recently, Bhaisare et al., reported the fluorescent sensing of urine sample with pathogenic bacteria (Escherichia coli (E. Coli) and Staphylococcus aureus (S. aureus)), based on their strong adhesion over carbon dots decorated magnetic nanoparticles functionalized with amine group (Bhaisare et al. 2016).

5.3.2.2 Magnetic Nanoparticles Magnetic nanoparticles also find significant use in important nanosensors applications. They can be fabricated with many forms like different types of ferrites (MeO.Fe2O3, Me ¼ Mn, Mg, Co, Ni, Zn, etc.), maghemite (γ-Fe2O3), greigite (Fe3S4), superparamagnetic magnetite (Fe3O4), etc. (Šafařik and Šafaříková 2002). Magnetization of the MNPs can be enhanced by introduction of chemical dopants like Co2+, Mn2+, Ni2+, Zn2+ which have higher magnetic moment (Cheon and Lee 2008; Jang et al. 2009). Magnetic properties can also be enhanced by fabricating core/shell MNPs with both the core and shell having high Ms. Magnetic moment possessed by Fe, Ni and Co NPs is stronger than iron oxide NPs, but these NPs are highly reactive in the aqueous medium making their direct application difficult. Designing core/shell NPs with these NPs as core and iron oxide or other metals as shell results in preserving the large magnetic moment of the cores and also gives them higher colloidal stability. For instance, different core-shell NPs Fe@MnFe2O4, Fe@Fe3O4, Fe@CoFe2O4 with Fe core were reported (Lee et al. 2011). The shells

Electrochemical Electrochemical

NO2 and N2

Carbon adhesive tape

MWCNTs/rGO

Electrochemical

Trinitrobenzene Dinitrobenzene Nitrobenzene 2,4,6 TNT

Electrochemical

Electrochemical

Fluorescence

S. aureus

Hydroquinone Catechol BPA Phenol Parabenes

Fluorescence

Chemiresistive

Transduction principle Electrochemical

S. aureus and E. coli

Analyte Staphylococcus aureus S. Typhimurium

Hydroxyl-rich carbon submicrospheres

Fe3O4/MWCNTs composite

Ag NPs/MWCNTs

Carbon dots decorated aminefunctionalized magnetic iron oxide NPs CDs@BONs

Carbon nanowires

Carbon-based nanomaterials modified electrodes SWCNTs

– 1–200 CFU mL
1 2.5–260 μM 20–260 μM 5.0–152 μM 2.4–152 μM 0.5–150 ng mL
1 0.2–1 mgL
1 0.01–16.8 mgL
1 0.2–12.3 mgL
1 0.5–1100 μM

3  102 and 3.5  102 CFU mL
1 – 0.16 μM 0.2 μM 2.4 μM 3.0 μM 0.03–2.0 ng mL
1 1.8 μgL
1 0.88 μgL
1 1.3 μgL
1 0.010 μM ~5 ppm

–

–

–

–

Anti-S. aureus antibody –

–

10 CFU mL
1

–

Salmonellaspecific aptamer probes –

Linear range –

LOD 13 CFU mL
1

Bioreceptor Antibody

Table 5.2 Detection of some organic, inorganic and biological pollutants using carbon-based nanomaterials

Castro et al. (2018) Lee et al. (2018)

PastorBelda et al. (2018) Pan et al. (2016)

Yang et al. (2018a) Goulart et al. (2018)

Bhaisare et al. (2016)

Ref Bhardwaj et al. (2017) Thiha et al. (2018)

108 U. Chakraborty et al.

Hg(II)

MoS2 nanosheet/DNA/CDs Fluorescence

Electrochemical DNA

– 1.02 nM

70 ppm 0–10 nM

– Septiani et al. (2018) Srinivasan et al. (2016)

CDs carbon dots, CDs@BONs breakable organosilica nanocapsules encapsulated with carbon dots, Fe3O4 iron oxide, LOD limit of detection, MWCNTs multiwalled carbon nanotubes, rGO reduced graphene oxide, Ag NPs silver nanoparticles, SWCNTs single walled carbon nanotubes, TNT trinitrotoluene, ZnO zinc oxide

SO2

3D wool-ball-like ZnO/MWCNTs

5 Development of Environmental Nanosensors for Detection Monitoring. . . 109

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protected the Fe cores from oxidations, and the core/shell NPs had higher Ms. than ferrite NPs. It was reported that Ms. of Fe@MnFe2O4 NPs was highest. Thus the development of multifunctional MNPs from such heterostructured MNPs can be used for designing multimodal MRSw-based nanosensors (Zhang et al. 2017b). These magnetic NPs can be conjugated with biorecognitive molecules (enzymes, DNA, etc.), and can be used for enrichment for the target analyte. Hence, these sensors can be applied to improve sensor sensitivity (Jianrong et al. 2004). Chemla et al. (2000) used magnetic NPs labelled with antibodies for sensing biological targets. They used sensitive SQUID technique which is highly sensitive and specific for detection of labelled magnetic NPs. Antibodies functionalized magnetic NPs can also be applied for detection of toxins from environmental samples.

5.3.2.3 Bio-Nanomaterials and Polymeric Nanomaterials Bio-nanomaterials and polymeric nanomaterials possess excellent thermal, mechanical, catalytic, physical and electrical properties. Hence these types of nanomaterials can be used for fabrication of highly selective and responsive nanobiosensors and electrochemical sensors (Yang et al. 2016). These nanomaterials can be combined with novel scientific and analytical techniques for application as electrochemical sensors (Wang et al. 2016). Bio-nanomaterials based sensors: a large number of nanosensors have been fabricated by combining the unique features of nanomaterials with the catalytic activity of biomolecules. Biomolecules, through self-organization can result in the formation of proper nanostructures with biomaterials. Sabela et al., designed electrochemical biosensor for capsaicin, using nanobiocomposites of enzyme Lphenylaniline ammonia-lyase and MWCNTs (Sabela et al. 2016). Li et al., developed portable biosensor for E. coli O157:H7 using self-assembled monolayers (SAMs) method (Li et al. 2015b). Polymer-based nanomaterials: Polymeric nanomaterials have been combined with various sensing technologies for the sensing of gaseous and liquid environmental pollutants and food contaminants (Rother et al. 2016). The electrochemical sensing properties of polymer-based nanomaterials can be improved by integration of graphene, CNTs, metal and metal oxide NPs, etc. (Villalonga et al. 2012; Dai et al. 2016). The selectivity and sensitivity and biocompatibility of nanosensors can be enhanced by combination of nanofillers and matrix. Navele et al. reported the room temperature sensing of reducing (NH3, H2S, C2H5OH, CH3OH) and oxidizing (Cl2 and NO2) gases using nanocomposite of polypyrrole (PPy)/a-Fe2O3 (Navale et al. 2014). Pramanik reported gas sensor for toxic gases like toluene, ethanol, benzene and acetone using bentonite nanohybrid modified polyaniline (PANI) nanofibers (Pramanik et al. 2013). 5.3.2.4 Metal Oxide (MOX)-Based Nanomaterials Metal oxide nanoparticles (NPs) and thin films are cost-effective ceramic-based nanomaterials with high surface area and unique properties. These materials have been well-explored for highly efficient nanosensors for various environmental

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applications (Yu et al. 2014). MOX display high sensitivity towards chemical environment changes, and these have many physical, chemical and electronic properties. Doped and well-structured MOX (mainly ZnO and SnO2) have been used for commercially available stable solid-state chemical sensors with low cost of production, and these sensors have been utilized for highly sensitive gas detection applications. The basic mechanism of MOX-based gas sensors involves charge transfer between analyte molecules and surface complexes (O2
,O
, H+, OH
), leading to electrical conductivity change. This process demands energy of activation, hence, classical MOX sensors only work at high temperatures (>200  C) (Francia et al. 2009). MOX nanomaterials have properties like stability, distinct electrochemical activity, high capacity for adsorption and large surface area, which are significant for electrochemical sensor fabrication. Features like particle size, morphology, functionality on the surface, and surface area, determine the analytical performance of MOX nanomaterials (Zhang and Gao 2019). Semiconductor MOX nanostructures like ZnO, In2O3, TiO2, NiO, WO3 and SnO2 have been explored for preparation of resistive gas sensors for the detection of volatile organic compounds (VOCs) and toxic pollutant gases. The principle of operation of such sensors involves change in resistance on variation of the molecules of test gas on the surface of electrode. For improvement in the LOD and sensitivity, numerous research activities have been performed for designing hierarchical MOX nanostructures (Shimizu et al. 2001). 1-D MOX nanostructures have also shown great potential for electrochemical detection of environmental contaminants. Nanosensors fabricated from pure and composite MOX nanomaterials like ZnO, SnO2, TiO2, etc., have been well explored for environmental applications. Tin oxides (SnO2) NPs have been the most applied materials for gas sensing applications. For e.g., Khoang et al., reported highly selective and sensitive detection of ethanol using hierarchical SnO2/ZnO nanostructures (Khoang et al. 2012). Apart from gas sensing, ultra-trace detection of heavy metal ions was reported with SnO2 combined with rGO, the analysis was done in drink water samples (Maduraiveeran and Jin 2017). Zinc oxide (ZnO) in a n-type semiconductor material, and ZnO nanostructures have numerous advantages over bulk ZnO, like excellent properties for electron transfer, low cost, eco-friendly, cost-effective, high ratio of surface to volume, and ability to be synthesized with many morphologies like nanorods, nanowires, nanotubes, nanoflakes, etc., making them suitable for sensing of a large variety of analytes (Napi et al. 2019). ZnO nanomaterials are suitable materials for gas sensing applications due to high conductivity, biocompatibility, and chemical/thermal stability resistance to oxidation., etc. Zhang et al. reported the fabrication of 3D flowerlike ZnO nanostructures and discussed their excellent gas sensing properties for n-butanol due to their large surface area and higher number of surface active sites (Zhang et al. 2012). ZnO nanostructures have also been used for other sensing application. For instance, Kumar et al. (2019) prepared low cost pH nanosensor for pH measurements in water, using interdigited electrodes (IDEs) synthesized using hydrothermally grown ZnO nanorods (NRs).

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Nickle oxide (NiO) nanostructures have also been well explored for gas sensing applications. NiO with flower-like morphology could provide large area of contact between electrolyte and active material, and increase the electrode’s electrochemical activity. For e.g., rose-like NiO NPs have displayed highly sensitive gas sensing for formaldehyde (Maduraiveeran and Jin 2017).

5.3.2.5 Metal-Based Nanomaterials Different metals including noble and rare earth metals, have been explored for sensing applications (Maduraiveeran and Jin 2017; Franke et al. 2006). Metal NPs based nanosensors provide advantage of sensitivity and selectivity enhancement by amplification of tuned signals. Lots of research has been focused for designing pure and bio-functionalized metal nanoparticles and nanocomposites, and application of these nanomaterials for the development of analytical techniques for environmental monitoring (Wang et al. 2011). Noble metals i.e., gold (Au), platinum (Pt), silver (Ag), palladium (Pd), osmium (Os), rhodium (Rh), iridium (Ir), ruthenium (Ru), display excellent corrosion and oxidation resistance even at high temperatures (Azharuddin et al. 2019), and thus, can be used for potential sensing applications. As mentioned in earlier sections, metal-based NPs show unique optical properties and can be used for fabrication of LSPR and SERS-based optical sensors. Metal NPs like Au, Ag, Pt, Cu and Pd also display outstanding electrocatalytic behaviour. Au NPs have distinct features like tunable optical properties, surface modification capacity, high surface area, high stability, electrocatalytic activity, and total recovery during electrochemical redox reactions. Au NPs have been used for modification of electrodes for electrochemical sensing and utilized them for detection of environmental contaminants, with advantages like high sensitivity, better catalytic activity, more signal-to-noise ratio, and better electroactive species diffusion (Wolfrum et al. 2016). Ratner and Mandler (2015) applied Au NPs for modification of electrode surface and highly sensitive and reproducible mercury (Hg) detection. Chen and Huang (2014) reported arsenic ion (As3+) detection with low detection limit of 32.5 pM using gold-based electrochemical nanosensors, fabricated by an easy and cost-effective method. Au NPs have also been used for successful fabrication of nanobiosensors due to improvement of bioanalytical performances and better electron transfer between biomolecules and transducer, with inclusion of Au NPs (Lebégue et al. 2015). Extensive research work has been done for utilizing platinum (Pt) NPs for electrochemical sensing, due to their electrocatalytic behaviour. The choice of methods for incorporation of Pt NPs on the surface of electrodes play significant role in the development of stable, chemically inert, highly catalytic nanosensors with low background current (Govindhan et al. 2016). Several techniques for fabrication of Pt NPs modified sensors like electrochemical deposition, chemical reduction, photochemical deposition, metal-vapour synthesis, etc., have been well-explored. Characteristics of Pt NPs like crystal structure, chemical composition, surface conditions, orientation of crystallographic axis, also plays major role in their mechanism for electron transport (Govindhan et al. 2016). Pt NPs based nanosensors have also been applied for the detection of major environmental contaminants. For

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instance, Mahmoudian et al. (2016) reported the synthesis of nanosensor using nanospherical Pt coated with polypyrrole (Pt/PPy NSs) and used this for highly sensitive detection of Hg2+ in presence of other ions like Zn2+, Cu2+, Ag+, K+, Pd2+, Sn2+, Pb2+, Ni2+. Zhang et al. (2015a) prepared nanosensor for detection of trinitrotoluene (TNT) with low detection limit of 0.8 ppb and linear range of 0.01–3 ppm, using hydrothermally synthesized PtPd nanocubes dispersed in graphene nanoribbons (PtPd-rGO NRs). Rismetov et al., reported electrodeposition of Pt NPs on boron doped diamond (BDD) surface for detection of hydrogen peroxide (H2O2) (Rismetov et al. 2014). Silver (Ag) NPs possess excellent catalytic and SERS activities, and are extensively used for designing nanosensors and nanobiosensors (Wu et al. 2006). These NPs have also been applied for detection of environmental pollutants. For e.g., Sebastian et al., reported microwave assisted synthesis of Ag NPs and applied them for fabricating nanosensors for mercury Hg(II) ions with 2.1 μM limit of detection (Sebastian et al. 2018). Ag NPs in conjugation with different matrices like silicate network, polymers, metal oxides, graphene, have shown high stability and outstanding sensing abilities. Kariuki et al. (2016) reported selective detection of nitrobenzene using poly(amic) acid (PAA) embedded with Ag NPs (PAA-Ag NPs). Ag NPs based immunosensors have also been used for highly selective, sensitive and rapid detection of analytes like virus, microorganisms and other small inorganic and organic molecules. Sepunaru et al. (2016) developed technique for sensing influenza viruses which were tagged with Ag NPs. The sensing was based on linear enhancement in the magnitude and frequency of current with increase in virus concentration and increment in the surface coverage of Ag NPs. Karthiga et al., reported colorimetric detection of toxic metal ions using Ag NPs synthesized by green method (Karthiga and Anthony 2013). Various plant extracts (green tea, pepper seed, sun-dried, neem bark, and fresh mango and neem leaf) were used to prepare green Ag NPs. Pepper tea extract-based Ag NPs showed colorimetric sensing for Zn2+, Hg2+ and Pb2+ ions. Green tea and mango leaf extracts based Ag NPs showed colorimetric detection for Hg2+ and Pb2+ ions. Selective colorimetric sensing for Zn2+ and Hg2+ was exhibited by neem bark extract-based Ag NPs. Fresh neem and sun-dried neem leaf based Ag NPs displayed selective detection of Hg2+ and Hg2+ and Pb2+ ions, respectively. The detection was carried out at wide pH range of 2–11. Copper (Cu) and palladium (Pd) NPs have gained recognition as suitable materials for nanosensors due to their relatively low cost as compared to Au, Ag and Pt and their excellent electrocatalytic behaviour and electrical conductivity. Cu nanostructures exhibit unique features for electroanalytical measurements like better signal-to-noise ratio, high surface area and high rate of mass transport (Abdel-Karim et al. 2020). Li et al. (2015a) used single step electrodeposition for synthesis of Cu nano-clusters, which showed high electrocatalytic performance, and were successfully applied for highly sensitive detection of nitrate. Pd NPs have been extensively used for sensing applications for hazardous gases, toxic species and biomolecules. Pd-based nanocomposites have exhibited better analyte mass diffusion, which also enabled transfer of electrons between electrode and active site due to electron tunnelling, resulting in excellent performance for electrochemical sensing (Xi et al.

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2019). In their work, Yaqoob et al. reported simple chemical synthesis of foldable nanosensor by using rGO assisted MWCNTs-supported Pd nanocubes and used the nanosensor for hydrogen detection (Yakoob et al. 2015). Pd can be incorporated to micro- or nanostructures of other metals or semiconducting MOX to improve their gas sensing and optical properties. For e.g., Yi et al. reported Pd NPs decorated nanogold wires (Pd/NPG) and used them for nanobiosensors for highly sensitive detection of traced dopamine (DA) with a low LOD of 1 μM, and 1–220 μM broad detection range (Yi et al. 2017).

5.3.2.6 Nanosensor Fabrication with Electrospun Nanofibers Fabrication of nanofibers (NFs) is economical, and these have properties like high efficiency, low sample requirement, multifunctionality, direct detection of analyte, high stability, less power consumption and low LOD (Veisi 2013; Asmatulu and Khan 2019). These properties of NFs arise due to their flexibility, small dimensions, tunable conduction properties, and higher specific surface area, making them useful for integration into sensing elements, and other industrial applications. Further, the dimensions and surface functionalities of NFs can be tailored to enhance absorption and diffusion rates for rapid response and signal transfer for better sensitivity, labelfree sensing and dynamic behaviour (Veisi et al. 2013; Veisi 2013; Asmatulu and Khan 2019). Electrospinning is a useful technique for nonwoven and woven, micronanoscale fibres production. The NFs produced by this method have smaller diameters leading to high porosity, more surface functionality, greater permeability, and better mechanical strength, resulting in making them suitable materials for nanosensors applications. Basic setup of electrospinning is shown in Fig. 5.5. Various types of Micro- and nanoscale fibres for application as nano- and biosensors can be produced by adjusting parameters like flow rate, concentration of polymer, screen and capillary distance, electrical potential, temperature, air velocity and humidity (Asmatulu and Khan 2019). Ding et al. discussed the most extensive application of electrospun NFs for medical purposes. It was also reported that due to porous and flexible nature along with high specific surface area, NFs can be used for designing ultrasensitive nanosensors for different industries. Recent progress in sensing approaches (optical, photoelectric, impedance etc.,) were also summarized in their work (Ding et al. 2010). Wang et al., have also discussed the recent development of electrospun nanofiberbased nanosensors, and their application for detection of different hazardous analytes (Wang et al. 2014). 5.3.2.7 Quantum Dots (QDs) QDs are nanocrystals with semiconductor nature. These have typical MX composition where, M is commonly Zn or Cd and X is Se, S or Te (Willner and Vikesland 2018). As discussed above, QDs can act as outstanding optical transducers due to broad absorption bands and narrow fluorescence emission bands. Emission bands of QDs can be tuned by variation in their composition, size and shape. Often, a shell or a second MX alloy is coated on QDs to generate highly tuneable core/shell QDs.

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Fig. 5.5 Electrospinning of nanofibers

ZnSe/ZnS (Ke et al. 2012), ZnS (Koneswaran and Narayanaswamy 2009), CdTe/ CdS (Gui et al. 2012) are some QDs used for sensor applications. These can be employed for efficient sensing of multiple analytes.

5.3.2.8 Porous Silica Porous silicon consists of silicon threads with thickness in nanorange (2–5 nm), arranged in the form of a complicated network, with surface having tiny pores ranging from nano- to micrometre dimensions. Due to these small pores, this material is capable of light absorption and emission. This material is semiconductor in nature with very high internal surface area/volume ratio. The light is emitted in visible region due to phenomenon of quantum confinement, and the material’s porosity controls the wavelength of the light emitted. Longer wavelengths are emitted by less porous silica, while shorter wavelengths are emitted by highly porous silica. For e.g., silica with porosity >70% emit blue/green light, and porosity ~40% emit red light. There is also variation in luminescence of porous silica by incorporation of molecules into the porous surface, making them suitable for application as gas sensors. Visual colour change can be monitored in the porous silica in the presence of analyte gas molecules, hence causing efficient detection of these molecules. The properties of porous silica can be modified to have suitable detection of particular analyte (Dahman et al. 2017).

5.3.3

On the Basis of Applications

As mentioned above, nanosensors find huge applications in almost all areas of life. Major threat to our health and environment is possessed by chemical pollutants like aromatic compounds, microorganisms, heavy metals, pesticides, etc., which are

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widely used and discharged into the environment directly or indirectly due to various human activities. Nanosensors find an important application for detection and monitoring of such harmful compounds from environmental samples. Here, in this portion of the chapter, we are mainly discussing the nanosensors classified according to their environmental applications. Table 5.3 displays some recently developed nanosensors for some major chemical and biological environmental pollutants.

5.3.3.1 Monitoring of Air Quality: Gas Sensors Various industrial activities, combustion of biomass and fossil fuels for energy production, vehicular emissions, natural causes like volcanic eruptions etc., result in the release of various organic and inorganic gases, which beyond a certain limit are the major sources of air pollution. Sulphur oxides (SOX), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOX), chlorofluorocarbons (CFCs), ammonia (NH3), volatile organic compounds (VOC) are included as major air pollutants. These pollutants can be further categorized as organic, inorganic and carcinogenic gases. Extensive research work has been performed for the utilization of nanomaterials for development of nanosensors for detection of different gaseous pollutants. Semiconducting nano-MOX like NiO, Fe2O3, WO3, TiO2, ZnO, SnO2 have been used as highly sensitive, rapid and cost-effective materials for fabrication of resistive gas sensors. These nanosensors can detect multiple gases and have simple electronic interface. Limitations with MOX-based gas sensors is their long-term instability, and working ability between 200  C to 500  C (Maduraiveeran and Jin 2017; Wetchakun et al. 2011). On the other hand polymer-based gas sensors can operate under room temperatures (Bai and Shi 2007). Therefore, these challenges can be overcome by combining both MOX nanomaterials and conductive polymers into nanocomposites for the development of gas sensors with high performance. The operating principles for most of these gas sensors is the variation in electrical properties (like resistance) resulted from transfer of charge or gas adsorption on the sensor surface (Hatchett and Josowicz 2008). Major organic gas pollutants are the VOCs these are types of flammable and greenhouse gases including ethanol, styrene, vinyl acetate, butadiene, acetonitrile, acetone, ethylene oxide, etc. These chemicals are mostly released from chemical industries and these have acute toxic effects (Lu et al. 2019). Detection of VOCs using efficient gas sensors is very important for monitoring of air quality. In their work, Zhou et al. (2018) reported the gas sensing applications of branched nanostructure based on one dimensional (1 D) nanomaterials. The heterostructures were prepared by combination of Zn2SnO4 nanorods and Mn3O4 nanowires, synthesized by a two-step hydrothermal method. The nanosensors exhibited outstanding and selective detection of acetone. Recently, Pramanik et al. (2013) reported nanohybrid designed with bentonite modified polyaniline (PANI) nanofibers. These nanohybrids were tested for detection of ethanol, toluene, benzene and acetone, and the 0.23 wt% PANI containing nanohybrid displayed higher sensitivity for acetone as compared to other gases. Khoang et al. (2012) produced ethanol sensors with high performance using hierarchical nanostructures synthesized

2,4,6 TNT DNB

Ag NPs modified electrochips

Ag2O QDs 2,4,6 TNT

Electrochemical

Electrochemical

4-NP

PtPd-rGONRs

Electrochemical (DPV) Electrochemical (voltammetric) Electrochemical

Nitrobenzene

4-NP 2-NP 2-NT

Electrochemical

BPA

GCE/NiDMG-AuNP

Fe3O4NPs-Si4Pic+Cl
/Au NPs-Si4Pic+Cl
/ GCE AuAg alloy NDs in SSG silicate sol-gel matrix AgNWs-PANI nanocomposite

Electrochemical (CV, EIS) Electrochemical

BPA

–

0.103 μM 0.58 μM 4.3 ppm

0.01–3 ppm 1  10
10–0.1 M 1  10
7–0.1 M

0.8 ppb –

5–40 ppm

0.6–32 μM

1–80 μM

– 52 nM

2–1400 nM

0.1–10 nM

–

0.5–20 ppm

7 nM

0.05 nM

500 ppm

Electrochemical

PANI NFs-based TENG Organic pollutants f-MWCNTs/AuNPs

NH3

SO2

MWCNTs/carbon nanospheres

5–100 ppm

– 0.5 ppm

Chemiresistive

NO2

Linear range

LOD

Chemiresistive

Transduction principle

(continued)

Deiminiat et al. (2017) Santana et al. (2017) Manivannan et al. (2017) Zhang et al. (2017a) Olorundare et al. (2016) Bhanjana et al. (2018) Zhang et al. (2015a) Singh et al. (2016)

Navale et al. (2014) Altal and Sekhaneh (2020) Cui et al. (2018)

Ref.

Table 5.3 Nanosensors for the detection of some major chemical and biological contaminants Analyte

Development of Environmental Nanosensors for Detection Monitoring. . .

Nanosensor material Gaseous pollutants CSA doped PPy/α-Fe2O3

5 117

Electrochemical

Pb (II) Pb (II) Cd (II) Ni(II) As (III)

Au NPs with detached fragments of truncated 8–17 DNA enzyme Bi NPs porous carbon Nanocomposite modified SPE

Nanosized biomaterials amyloid-fibril

Au/GNE

Optical (colorimetric)

Hg (II)

AuNCs/MIL68(In-NH2/Cys

Cr (VI)

Electrochemical (SWASV) Optical (colorimetric)

Optical (fluorescence)

Optical (fluorescence)

Hg (II)

Atrazine

Anti-atrazine monoclonal antibodies functionalized Au NPs/Au electrode Heavy metals AuNCs/MOFs

Transduction principle Optical (SERS)

Electrochemical (CV, Amperometric) Electrochemical (DPV)

Analyte (FL) (NAP) (BaP) Organophosphates

Pesticides Au-Ppy-rGO-based AChE nanobiosensors

Nanosensor material DS-C10H21 functionalized Au nanorods arrays

Table 5.3 (continued)

0.1–9 ppb –

–

–

Babar et al. (2019) Leung et al. (2013)

Memon et al. (2019) Niu et al. (2015)

Huang and Chang (2006) Wu et al. (2019)

– 20 pM–0.2 μM; 0.2 μM–60 μM 0.5 nM–5 nM

Yang et al. (2014) Liu et al. (2014b)

Ref. Tijunelyte et al. (2017)

–

Linear range –

0.65 ppb 0.81 ppb 5.47 ppb 0.1 ppb

0.2 nM

6.7 pM

2.0 ppb

74 pM

–

LOD 0.064 mgL
1 3.94 mgL
1 0.026 mgL
1

118 U. Chakraborty et al.

P. aeruginosa Legionella pneumophila

Optical (LSPR-based) Electrochemical (amperometric)

– 10 CFU mL
1

10–103 CFU mL
1 –

Hu et al. (2018) Martín et al. (2015)

Ag2O QDs Silver oxide quantum dots, GCE/NiDMG-AuNP Glassy carbon electrode modified with nickel dimethylglyoxime complex-gold nanoparticles, AgNWs-PANI Silver nanowires-polyaniline, AuAg Alloy NDs SSG gold/silver alloy nanodots in silicate solgel matrix, PANI NFs-based TENG polyaniline nanofibers based triboelectric nanogenerator, MWCNTs multi-walled carbon nanotubes, CSA camphor sulphonic acid, PPy/α-Fe2O3 polyoyrrole/iron oxide, Au-Ppy-rGO gold-polyoyrrole-reduced graphene oxide nanocomposites, AChE acetylcholinesterease, AuNCs/MIL68(In-NH2)/Cys Cysteine gold nanoclusters/ indium-based metal-organic frameworks, Bi NPs Bismuth nanoparticles, Au/GNE electrogenerated nanotextured gold assemblage, Bt-PEG biotinylated polyethylene glycol, DS-C10H21 diazonium salt, Fe3O4@pDA-C-Ab disposable core-shell iron oxide@poly(dopamine) magnetic nanoparticles, SPE screenprinted electrode, -Si4Pic+Cl
: polymer solution of 3-n-propyl-4-picolinium silsesquioxane chloride; PtPd-rGONRs: Ag NPs silver nanoparticles, BPA Bisphenol A, TNT Trinitrotoluene, 2-NP 2-Nitrophenol, 4-NP 4-nitrophenol, DNB dinitrobenzene, FL fluoranthene, NAP naphthalene, BaP benzo[a]pyrene

Pathogens (Bt-PEG) thiol/PEG thiol (1:3) nanosensor MNPs@pDA-C-Ab

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by growing ZnO nanorods on SnO2 nanowires backbone. This hierarchical nanosensors displayed enhanced and selective response for ethanol, as compared to bare SnO2 nanowires sensor. Nanosensors have also been effectively used for the detection of carcinogenic (cancer causing) gases from air. One of the major human carcinogens is benzene. Wang et al., fabricated a highly sensitive, and rapid gas sensor for benzene and toluene, using Au NPs modified ZnO nanowires (Au-ZnO NWs) (Wang et al. 2013). Chlorinated aliphatic hydrocarbons are also carcinogenic in nature and these chemicals also result in numerous other serious health issues. These chemicals include dichloromethane (CH2Cl2), chloroform (CHCl3), carbon tetrachloride (CCl4), etc., Kar and Choudhury (2013) reported nanocomposites developed with PANI doped with carboxylic acid functionalized MWCNTs (PANI/c-MWCNTs) for detection of chloroform. PANI/c-MWCNTs showed better response from chloroform as compared to pure PANI, due to better interactions of modified PANI backbone with chloroform. Besides organic gases, inorganic gases like ammonia (NH3), the oxides of sulphur (SOX) and nitrogen (NOX) also act as toxic air pollutants. Sulphur dioxide (SO2) is released into the environment as a result of activities like combustion of petroleum or coal with sulphur content and volcanic eruptions. In the presence of catalysts like NO2, SO2 released in the atmosphere is also prone to H2SO4 acid formation, causing acid rain. For the detection of SO2, Tyagi et al. (2017) developed an efficient gas sensor by integrating SnO2 thin film with NiO dotted cluster (10 nm thin). The sensor displayed much better response for SO2 as compared to bare SnO2 thin film. Hydrogen sulphide (H2S) is also a gaseous pollutant, which can affect the human nervous system, and is released into the environment during fuel production or biological processes. In their work, Su and Peng (2014) developed PPy/WO3 nanocomposite film based gas nanosensors for H2S detection at room temperature. The sensor displayed long-term stability (~54 days), higher response than pure PPy or WO3 films, and long linear working range (100–1000 ppb). Cui et al. (2018) recently developed a highly selective, sensitive, portable and flexible self-powered NH3 nanosensor. Triboelectric nanogenerators (TENG) based on polyaniline nanofibers (PANI NFs) were used for developing the nanosensor. The gas sensor was integrated with the power supply to form a single device. The sensing principle involves change in the electroconductivity of PANI after NH3 exposure resulting in reduction in the output voltage of TENG. The sensor exhibited a LOD of 500 ppm at room temperature. Nitrogen dioxide (NO2) is another harmful gas released mainly from vehicular emissions and from chemical industries due to combustion at high temperatures. NO2 also involves in atmospheric reactions, leading to the formation of ozone (O3) at ground level. Navale et al. developed camphor sulphonic acid (CSA) doped PPy/α-Fe2O3 hybrid nanocomposite, and used these hybrid nanocomposites as room temperature gas sensor (Navale et al. 2014). The nanosensors exhibited highly selectivity for NO2 in the presence of other reducing and oxidizing gases with low LOD of 5 ppm.

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Prajapati et al. (2020) reported ultralow-power nanosensor array platform by using four nanosensors, integrated with four nanoheaters (4 μM  100 nm). ZnO, 1% Ag doped BaTiO3-CuO, WO3 and V2O5 were used as sensing materials for the detection of CO, CO2, NO2 and SO2, respectively. The nanosensor displayed simultaneous detection of SO2 (~94% for 3 ppm; 265  C), CO (~93.2% for 3 ppm; 300  C), NO2 (~23.01% for 3 ppm; 150  C) and CO2 (~76.3% for 1000 ppm; 265  C). As mentioned in earlier sections, CNTs are robust with inert nature and display excellent electrical properties, making them appropriate materials for FET-based nanosensors. Many greenhouse gases and contaminating gases like NH3 and NO2 can be efficiently detected by gas sensors based on CNTs-FET. Kong et al. (2000) displayed the enhancement or reduction of the electrical resistance of single-walled carbon nanotubes (SWCNTs) upon exposure to electron donating (e.g., NH3) or electron withdrawing (eg., NO2) gaseous molecules, thus making CNTs applicable for electrochemical gas sensing operations. They also noted that as compared to solid-state sensors, CNT sensors exhibited higher sensitivity and rapid response at room temperature. By heating the CNT sensors to high temperature or by recovering under ambient conditions, the CNT sensors also displayed reversible behaviour. Change in resistance of SWNTs under the presence of O2 was reported by Collins et al. (2000) thus, making them suitable for the applications of gas sensing. Zahab et al. reported change in SWCNT conductivity to n-type from p-type upon exposure of H2O (water vapours) in surrounding atmosphere (Zahab et al. 2000). Varghese et al. (2001) demonstrated qualitative detection of CO2, CO and NH3 using CNT-FET electrochemical nanosensors with two geometries. One with resistive geometry having multi-walled carbon nanotube (MWCNTs) grown on SiO2 with serpentine pattern, and the other one with capacitative geometry, with a planar interdigital capacitor decorated with MWNTS-SiO2 composite.

5.3.3.2 Detection of Soil Samples Soil is an important environmental resource and, soil quality assessment and monitoring is extremely necessary because all the living beings are dependent on soil for food, habitat, fibres, recreation, even for waste and bi-products assimilation (Arrouays et al. 2012). The quality of soil has direct effect on human food safety, health, social development and sustainable growth of economy (Liu et al. 2013). Major soil contaminants are released by urban and industrial solid wastes and atmospheric depositions, metal smelting and mining, agricultural activities and sewage irrigation (Lu et al. 2019). Such activities directly or indirectly release dangerous soil contaminants like heavy metals and plastics, asbestos, herbicides, fungicides, pesticides, and polyaromatic hydrocarbons (PAHs) into the soil. Hence, regular surveys for soil monitoring and detection of these contaminants are essential for maintaining the soil quality. Conventional analytical methods for soil monitoring include, XRF, AAS, ICP-AES, etc., but more time consumption, high cost, need of expert handling and lack of portability, make the use of these techniques less convenient. These disadvantages can be tackled by using suitably designed nanosensors, which are emerging as useful analytical tools for soil monitoring

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(Lu et al. 2019). Some nanosensors designed for detecting soil contaminants have been discussed here. Carbendazim is a highly used fungicide. It is a benzimidazole fungicide, and the difficult decomposition of the benzimidazole ring makes carbendazim remain in soils for longer periods. It can be uptaken and transferred to trees and plants through the soil (Huebra et al. 2000). For electrochemical detection of carbendazim, Luo et al. (2013) fabricated nanosensors with glassy carbon electrode (GCE) modified with MWCNTs-GO nanocomposite. Carbendazim was detected with detection limit of 5 nm and detection in tap water and soil samples were also verified. Many aromatic hydrocarbons like BTEX (benzene, toluene, ethylbenzene and xylene) are toxic and can result in serious short- and long-term health problems. Matin et al. (2013) reported detection of such complex hydrocarbons at low levels in soil and water samples. They prepared PVC/MWCNTs nanocomposites by incorporating polyvinyl chloride (PVC) with MWCNTs. Heavy metal pollution is a serious matter of concern because of their toxic nature and long-term presence in the environment. These heavy metals affect the soil quality, crop yield, and hydrological cycles. Exposure to heavy metals can lead to dangerous health issues. The platinum group elements (PGMs) include Pt, Rh, Ir, Os, Ru and Pd. The use of these elements is increasing rapidly as catalysts, jewellery materials, drugs for cancer treatment etc. Excess of these elements possess potential threat to human health and environment. Horst et al. (2015) have developed a nanosensor for detection of PGMs using DPAdsV electrochemical technique. They modified a glassy carbon electrode with bimetallic NPs of bismuth-silver, and used DMG as chelating agent. Pd, Pt and Rh were detected with low detection limit. The applicability of the nanosensors was also displayed in soil and road side dust samples.

5.3.3.3 Detection of Water Contaminants ‘Water is life’, this indeed is very true, water is essential for survival. Though earth is called the blue planet as 71% of earth is covered with water, but out of that only 0.3% is available for human use. Safe water is necessary for consumption, sanitation, irrigation, household use and industrial growth. But unfortunately, these very activities especially the release of industrial effluents, are also direct or indirect causes for polluting the water sources. Every year millions of people get affected with water-borne diseases caused by water pollution, and many even lose their lives. Water pollution not only threatens the human existence but it is dangerous for our whole ecosystem, including the aquatic life, flora and fauna. Major water pollutants are discharged from agricultural and industrial activities. For e.g., mercury is released from chloralkali industries; battery industries discharge cadmium, mercury and lead; pharmaceutical industries release many toxic and harmful chemicals like persistent organic compounds (POCs); toxic dyes are used in tanneries and fabric manufacturing plants, and are ultimately discharged in water sources; toxic pesticides flow into water bodies from the fields, and so forth. Besides these contaminants, harmful water-borne pathogens also deteriorate the water quality, and are responsible for causing numerous water-borne diseases. Proper and

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regular detection and monitoring of the levels of such harmful contaminants is essential for maintenance of suitable water quality. The application of nanosensors for detection of some major pathogens, organic and heavy metal water pollutants are discussed in this chapter. Mercury (Hg), lead (Pb), cadmium (Cd), chromium (Cr) and arsenic are major highly toxic heavy metal contaminants of aquatic systems. Exposure to these metals can cause health problems like kidney failure, effect on central nervous system, high blood pressure, etc. Recently, extensive research has been performed for development of nano- and nanobiosensors for detection of these pollutants from water sources. Majorly, electrochemical and optical methods have been used for sensing applications due to their rapid response and high sensitivity. Cho et al. (2010) developed porphyrin derivative modified Au@SiO2 NPs for efficient colorimetric detection of Hg2+. Niu et al. (2015) developed bismuth (Bi) NPs and porous carbon nanocomposite modified screen-printed electrodes (SPE), and used this nanosensor for electrochemical detection of Ni2+, Pb2+ and Cd2+ with LOD of 5.47, 0.65 and 0.81 ppb, respectively. Detection was performed in tap water and waste water samples. The high surface area of Bi NPs and porous nature of carbon matrix facilitated the detection. Veera Kumar et al. (2016) developed a Pd NPs/porous activated carbons (PACs) modified GCE nanosensing platform for highly sensitive simultaneous detection of Hg2+, Pb2+, Cu2+ and Cd2+ with respective LOD values 54, 50, 66 and 41 nM. Nanosensors technology has emerged as an promising platform for detection of a large number of organic compounds from water sources, such as amino acids, thiols, poly aromatic hydrocarbons (PAHs), phenol and its derivatives, nitro-aromatic compounds, pesticides, etc. Sadeghi et al. (2013) reported effective voltammetric detection of phenol in water using p-chloranil and CNTs modified graphite paste composite electrode. The nanosensors displayed high selectivity for phenol without interference of 800-times presence of other potential interfering substances. Nitro-aromatic compounds also constitute major water contaminants. Compounds like paranitrophenol (4-NP) are highly used industrial chemicals. While, chemicals like trinitrotoluene (TNT), and dinitrotoluene are released from explosives. These chemicals can cause numerous severe health issues, thus making their detection significant for monitoring water quality. Cerruti et al. (2009) achieved highly selective detection of TNT by using phage display method. TNT oligopeptide receptor was immobilized on PEGM polymer matrix, and deposited on a quartz crystal microbalance (QCM). Decrease in the QCM resonance frequency on the presence of TNT was used for detection. The sensor showed selectivity for TNT over DNT. Highly selective 4-NP fluorescent detection was reported by Zhou et al. (2014) by using a composite of molecularly imprinted polymer (MIP) and graphene QDs (GQDs). Good specificity for recognition of 4-NP was provided by MIP, and GQDs act as donor for resonance energy transfer.

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Fig. 5.6 (a) Extraction of RNA fragments from bacteria (b) Specific negative control probes (NPs) and capture probes (CP) functionalized biochips for detection of three different pathogens simultaneously, with introduction of 16S rRNA resulted in reflectivity variation and with addition of gold nanoparticles modified detection probe (GNP-DP) there is enhancement in the signal (c) variation in the reflectivity with introduction of RNA resulting in SPRi-based RNA detection

Detection of water-borne pathogens like Escherichia coli (E. coli), Vibrio cholerae, Legionella pneumophila, Staphylococcus aureus (S. aureus), hepatitis B virus (HBV), etc., is necessary as these pathogens are the source of several serious water-borne ailments like cholera (by bacterium Vibrio cholerae). For e.g., between 2011 and 2012, Legionella pneumophila was responsible for outbreak of more than 50% water-borne diseases (Willner and Vikesland 2018). Melaine et al. (2017) reported multiplex detection of 16S rRNA from Salmonella typhimurium, Pseudomonas aeruginosa and Legionella. They used gold nanoparticles (GNPs) graftedDNA detection probes as substrate for SPR imaging (SPRi). DNA specific for each targets were captured on a DNA microarray, and these were assembled on the SPRi substrate. The detection was based on change in reflectivity signal, when the DNA isolated with 16 rRNA undergoes hybridization. Schematic representation of SPRibased RNA detection is shown in Fig. 5.6a–c.

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5.3.3.4 Nanosensors Used for Different Types of Analytes Nanosensors can further be classified on the basis of their application for sensing specific chemical and biological analytes. Current development in the field of nanosensors for detection of some major environmental contaminants has been discussed in this section:

Pesticides Pesticides were developed and introduced for their applications to destroy pests. Pesticides also include chemicals like insecticides, herbicides, fungicides, etc. But, despite their applications, pesticides have emerged as one of the major environmental pollutants due to their toxicity, and potential for bioaccumulation. Major pesticide classes include triazines, carbamates, organophosphorus (OPs) and neonicotinoids. Detection of these pesticides from environmental samples is of utmost importance. Nanosensors and nanobiosensors have been efficiently employed for highly sensitive and selective detection of pesticides. These sensors can be used for direct sensing of pesticides from sample. Pesticides often affect a particular enzyme. Hence, another method for pesticide detection involves direct or indirect monitoring of such enzymes. Carbamates and organophosphates inhibit the formation of acetylcholinesterase (AChE) enzyme. Thus, AchE has been immobilized on solid electrode surface for sensitive and fast electrochemical detection, and indirectly sensing of the associated pesticides (Willner and Vikesland 2018). For detection of AchE inhibition, hydrolysis of acetylthiocholine is used as an analogous reaction. Yang et al. (2014) used PPy-rGO (polyoyrrole-reduced graphene oxide) and Au NPs (~ 20 nm) for fabrication of Au-PPy-rGO-based AChE nanobiosensors for detection of OPs (Fig. 5.7). They used organophosphate paraxon-ethyl as a model pesticide. Electrodeposition of Au NPs was done on PPy-rGO to improve the conductivity and surface area of the electrode. Sulphonated rGO was electrochemically co-deposited with pyrrole. rGO aggregation was avoided by incorporation into PPy. AChE was co-deposited with a biocompatible silica matrix. The cyclic voltammetric (CV) and

Fig. 5.7 Illustration of organophosphorus pesticide detection using AChE biosensor fabricated using Au-Ppy-rGO nanocomposite

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amperometric methods were used for analysis. The AChE biosensor exhibited outstanding activity, high stability and rapid detection for OPs. (Yang et al. 2014). Yu et al. (2015) developed nanobiosensors for organophosphorus pesticide using GCE modified with amino functionalised CNTs (CNT-NH2). AChE incubation was subsequently performed on the electrode, and differential pulse voltammetry (DPV) was used for detection with LOD of 0.08 nM. Atrazine is a herbicide widely used in the United States. Liu et al. (2014b) developed anti-atrazine monoclonal antibodies functionalized Au NPs decorated Au electrode. The electrode was used for highly sensitive determination of atrazine using DPV technique. The variations produced on the electrode surface due to the interaction of antigen and antibody were measured, and a LOD value as low as 74 pM was achieved. Neonicotinoids are the largely used neuro-active insecticides. Apart from destroying insects, these also have harmful effects on human health. Acetamiprid is a neonicotinoid insecticide with chloropyridinyl group. Currently, aptamer-based nanosensors for detection of acetamiprid are being explored for effective neonicotinoids detection. In her review, Verdian have summarized such recently developed aptamer-based nanosensors (Verdian 2018). Heavy Metals Chromium

Chromium pollution is a cause of concern due to carcinogenic effects of Cr(VI). This chemical is released to the environment mainly by industrial activities. For e.g., chromium is used and released during dyes/pigments production, metal chrome plating and leather tanning. For detection of Cr (VI), Leung et al. (2013) reported colorimetric nanosensors using nanosized biomaterials amyloid-fibril. El-Safty et al. (2008) reported visual detection of Cr (VI), Co(II), Pb(II) and Pd (II) using optical nanosensor based on three dimensional (3D) nanostructures. The nanosensor exhibited rapid detection of Cr (VI) and other analyte ions with sub-picomolar recognition sensitivity. Lead

Lead (Pb) is a poisonous heavy metal, and lead exposure can lead to serious diseases like cancer, neurological and subtle cognitive defects. Several methods for detection of Pb2+ are based on label-free and label-based nanosensors. Recently, Memon et al. (2019) reported the development of label-free colorimetric nanosensor for sensing Pb2+ in water. They designed the nanosensor with unmodified Au NPs adsorbed with detached fragments of truncated 8–17 DNAzyme. The adsorbed AuNPs were protected against aggregation induced by salt concentration. The presence of Pb2+ was detected by change in the colour from blue to pink. High sensitivity and low LOD of 0.2 nM was obtained along with selectivity for Pb2+. Gao et al., developed a nanosensor for the detection of Pb2+ and Cd2+ using AlOOH-graphene oxide (GO) nanocomposite. SWASV method was used for the electrochemical detection of analytes. High adsorption capacity of AlOOH coupled

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with GO, resulted in the fast electron transfer kinetics. AlOOH-GO nanocomposite could be used for multiple detection due to unique stripping peak of each metal. Mercury

Mercury (Hg2+) is extremely toxic and human exposure to Hg2+ can cause dangerous health effects including negative effects on the neurological system. The presence of Hg2+ results in the formation of metal base pair, which can stabilize the thiaminethiamine (T-T) mismatch in DNA. Based on this effect, DNA-based probes can be potentially utilized for development of nanosensors for the detection of Hg2+. In the literature, two major Hg2+ oligonucleotides probes have been reported: (1) one which unfolds i.e., G-quadruplexes, (2) which hybridizes i.e., nearly complimentary single strands. Many nano-elements have been used for the construction of Hg2+ nanosensors. In their work, Liu et al. (2014a) reported an assay designed by Au shells encapsulated with magnetic silica spheres. They used complementary DNA sequences with 5 mismatched thiamine site, for functionalization of the Au NPs. Selection of the DNA sequences was done so that full hybridization was not permitted due to insufficient binding energy between the strand’s complimentary aspects. In the presence of Hg2+, plasmonic hotspot formation occurred due to reduction in the inter-probe spacing, resulting from full hybridization with introduction of Hg2+. The recovery and recycling of the nanoprobes was easily possible due to the magnetic nature of the particle cores. The fabrication and application of DNA-MSS@Au NPs and DNA-Au NPs as SERS-based nanosensor for detection of Hg2+ is represented schematically in Fig. 5.8 (Liu et al. 2014a). Nanoparticles like, Ag, Au, QDs have been reported in the literature for developing thiol-mediated assays for Hg2+ detection. Colometric response is obtained on the basis of aggregation and disaggregation principles. Huang and Chang (2006) reported fluorescence-based nanosensor with Au NPs for Hg2+ detection. The fluorescence of Rhodamine B (RB) was quenched on getting adsorbed on the Au NPs surface due to FRET and collision. The fluorescence signal was emitted by the on-sensor with the introduction of Hg2+ in the system, due to the displacement of RB from the surface of nanoparticles. The authors explored three sensor designs, and found an increase in the specificity of the assay for Hg2+, with the thiol coatings. The sensor exhibited low LOD values of 2.0 ppb and fast time of analysis i.e., less than 10 min. Cadmium

Nanosensors fabricated with SWCNTs, QDs, antimony (Sb) nanoparticles etc., have been used for cadmium detection. Gui et al. (2012) reported on/off-fluorescence sensor based on photoluminescent CdTe/CdS QDs for Cd2+ detection. APDC was used for quenching (turn off) the photoluminescence (PL) of CdTe/CdS QDs as a result of surface passivation due to partial loss of the surface layer of Cd-S. In the presence of Cd2+ the ADPC were displaced from the QD surface resulting in restoration of PL i.e., turning-on the sensor. The LOD was 6 nM and the sensor showed selectively 3-folds increase in PL in the presence of Cd2+.

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Fig. 5.8 Schematic representation of application of DNA-MSS@Au NPs and DNA-Au NPs as SERS-based nanosensor for detection of Hg2+

Gui et al. (2013) also reported a ratiometric sensor for greater accuracy for their Cd2+ sensing devices. For reduction of error by fluctuation in PL of QDs, two different chromophores were taken for fluorescence measurement. PEI polymer was coated on the CdTe QD cores, to reduce interactions between the secondary dye and QDs, after that fluorescein isothiocyanate (FITC) was conjugated in the system. Thus, signal of FITC was maintained, when the signals of QDs were quenched. In the presence of Cd2+, PL of QDs was restored. LOD was slightly more (12 nM) than the previous reported sensor (6 nM), but the linear detection range was much higher, i.e., 0.1–15 μM in comparison to 0.1–2 μM obtained in the previous work. Pathogens Water-borne pathogens cause great threat of water contamination. Serious waterborne diseases like cholera are spread by such pathogens. WHO have listed 2 helminths, 7 protozoas, 8 viruses and 12 bacteria as potentially significant pathogens in drinking water supply. Pathogen detection is an important and emerging research area. There are mainly three pathogen associated analytes considered for pathogen detection: (1) products e.g., toxins produced by pathogens, (2) genetic material, (3) representative epitome on cell membrane or whole analyte (cell). In their reviews, Willner and Vikesland (2018), Mocan et al. (2017) and Kumar et al. (2018) have provided detailed discussion about different water-borne pathogens and the methods of detection. Here we are presenting some recent

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progress in the development of nanosensors and nanobiosensors for the detection of some harmful water contaminating pathogens. Contamination of bacterium Vibrio cholerae in the water is the cause of cholera. Cholera toxin (CT) is secreted by the bacteria inside the intestines. Hence, the nanosensors have been designed for detection of both CT-B and V. cholerae. Majority nanosensors are based on the detection of CT-B due to the induction of toxin uptake by the CT-sub unit B (CT-B). Antibodies like β-galactose and ganglioside GM1 can be used for label-based CT detection. Ahn et al., reported FRET-based sensor for CT-B sensing, with theoretical LOD of 280 pM. Binding of cholera toxin on Au NPs modified with β-galactose results in prohibition of fluorescence quenching of QDs. Legionella pneumophila is a harmful bacterium which can grow in the building plumbing. People can get infected by this when they inhale this infective agent contaminated aerosol, or through the bacterium species present in fresh water. This bacterium can cause pneumonia like disease known as Legionnaires. For the detection of Legionella, Martin et al. (2015) designed a whole organism nanoprobe by combination of amperometric transduction with a sandwich immunoassay for capturing the bacteria. They used poly(dopamine) (pDA) for modification of magnetic NPs (MNPs) and then functionalized them with C-Ab which is a specific capture antibody, to develop MNPs@pDA-C-Ab probes. The post incubation step was introduction of horseradish peroxidase labelled antibody which acts as a second detector. Then the immuncomplexes were captured on a screen-printed carbon electrode (SPCE), using magnetic field. The assay exhibited specific detection of Legionella and low LOD after certain preconcentration steps, and can be used as a fast first screening method for water systems with high contamination. Pseudomonas aeruginosa is a harmful pathogen present in sewage, faeces, soil and water. It can be exposed through dermal contact with stool or infected water. P. aeruginosa can also colonize in premise plumbing. It has been a cause of nosocomial infection outbreaks in hospitals. Whole pathogen detection is mainly used as the method for detection of P. aeruginosa. Bacteriophages, antibodies and oligonucleotides recognition elements have also been used for the detection. In 2011, Wang et al. were the first to discover P. aeruginosa aptamer. Currently, in their works, Yoo et al. and Hu et al. developed LSPR-based optical nanosensors with nanotextured substrates for detection of P. aeruginosa. Yoo et al. (2015) followed a fabrication approach with three steps. First, a glass slide was deposited with gold (Au), this was followed by deposition of silica NPs, and then in the third step, a second Au layer was deposited. Then they directly attached aptamers on the surface of electrode via gold-thiol bond. On the other hand, Hu et al. used standard nanosphere lithography for fabrication of biotinylated polyethylene glycol (Bt-PEG) thiol/PEG thiol (1:3) nanosensor. Aptamers were immobilized using Bt-PEG thiol via Bt-neutravidin-Bt linkage, PEG thiol spacer was used to reduce the aptamers stearic hindrance. Hu et al. were successful in achieving low LOD values and lower concentration linear response (10–103 CFU mL
1) as compared to Yoo et al. But in Yoo et al.’s work, LOD was obtained at low sample volume of 3 μL (Hu et al. 2018).

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Phenolic and Nitro-Aromatic Compounds Phenols are extensively use organic chemicals. Many different synthetic organic compounds used as agricultural and industrial chemicals contain the phenolic group as their basic structural units. Mainly, paper, petroleum, plastic pesticides and pharmaceutical manufacturing industries use and release these phenolic compounds into the environment (Naghibi et al. 2003). Among the organic contaminants discharged into the aquatic environment, a large percentage consists of phenolic compounds. The potential of free radical formation and hydrophobicity of such compounds is the major reason for their toxicity (Hansch et al. 2000). Due to their highly toxic nature, many phenolic compounds have been listed as high priority pollutants by the United States environmental protection agency (USEPA) (Laine and Jorgense 1996). The maximum of individual and total permitted phenol levels in water suitable for human consumption has been set as 0.1 and 0.5 mg/L by the European Union (Daskalaki et al. 2011). These compounds possess serious threat to the environment and human health. Conventional methods for detection of these compounds include gas chromatography (GC), mass spectrometry, high performance liquid chromatography (HPLC) etc. But as mentioned above, these techniques have their own limitations for practical applications. Hence, methods for effective and convenient detection of such compounds in a serious issue, and the advancement of nanosensors technology can be used potentially to overcome this challenge. Nanosensors based detection of some phenolic compounds which are major environmental pollutants and matter of current concern has been discussed here. Recently, Mazhari et al. (2017) have reported the development of a paper-based nanobiosensor for the efficient and cost-effective detection of phenol from effluents of plastic, paper and wine industries. The sensor was prepared using Whatman no. 2 filter paper modified with Tyr-AuNPs bioconjugates. Streptomyces tuirus DBZ39 was used for bioconjugate formation of tyrosinase and Au NPs. The sensor displayed high efficiency for the detection of phenol from the effluents due to the SPR exhibited by AuNPs and substrate specific catalytic behaviour of tyrosinase. Thus, the sensor provides potential for cost-effective detection of phenol from the environmental samples. Bisphenol A (BPA) is a phenolic compound. This compound is extensively used in products like plastics, thermal papers and epoxy resins. BPA can leach out from product linings, and cause contamination of soil and water sources. It is a harmful endocrine disruptor (EDC) and can result in health issues like physiological abnormalities and reproductive dysfunction in humans. Elderly people, pregnant women and children are most vulnerable to BPA exposure. Although, nowadays, BPA-free products are being developed, but its detection is still important. Recently, various nanosensor based BPA detection methods have been developed and reported. Lee et al. (2019) reported optical nanosensor for sensitive detection of BPA using modified aptamer/AuNP conjugated with fluorescing single-stranded DNA aptamer. The sensor detected BPA with LOD as low as 9 pg mL
1 . An efficient, cheap and rapid electrochemical method for BPA detection was reported by Bolat et al. (2018) using poly(CTAB)-MWCNTs based nanosensor.

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They used cyclic voltammetry (CV) for electro polymerization to combine CTAB and MWCNTs on the surface of a pencil graphite electrode (PGE). Square wave voltammetry (SWV) was used to analyze the sensor performance for BPA detection. Low LOD value of 134 pM was obtained and effective performance in real matrices were also reported. In their work, Yang et al. (2018b) reported sensitive SERS-based BPA detection in milk samples using nanosensor developed with halides modified Au NPs with Zn2+ as aggregation agents. BPA detection at trace levels was achieved using the sensor. Though, they reported this sensor for detection in milk samples, but such methods can also be employed for environmental samples. Nitro-aromatic compounds (NACs) such as nitrobenzene, 4-nitrophenol (4-NP), mononitrotoluenes (MNTs), di- and trinitrotoluenes (DNTs and TNTs) are widely used organic compounds having numerous industrial applications like in explosives, pesticides, pharmaceuticals and dyes manufacturing industries. These are harmful carcinogenic chemicals. Detection of these compounds from the environmental samples is crucial. Numerous research works are based on electrochemical detection of NACs as a result of the electrochemical activity of these compounds due to the presence of nitro- functional group. Some recent developments in electrochemical nanosensors for the detection of NACs have been discussed in this section. Nitrobenzene (NB) falls under the category of NACs and it has been certified as major pollutant by USEPA. NB has poor wastewater biodegradability, and can result in methemoglobinemia, and even death. For electrochemical detection of NB, Emmanuel et al. (2013) reported GCE modified with AuNPs synthesized at room temperature by green method using Acacia nilotica extract. The analyte was electrochemically analyzed using DPV method and exhibited trace level detection of NB with low LOD value of 0.016 μM. The nanosensor also displayed appreciable NB detection in real water samples. 4-Nitro phenol (4-NP) is another harmful phenol based compound, it also falls under the category of nitro-aromatic compounds. 4-NP is widely used in pharmaceuticals, dyes and pesticides. 4-NP has long-term stability and once discharged into the environment, they remain there for a long time, making them harmful for humans, plants and animals. Exposure to 4-NP can cause undesirable health issues. In waste water, USEPA have confined maximum limit of 4-NP concentration as 4 nm 5 8

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7 4

Hydrothermal Calcinations

Ginger juice Orange peel

3–4 nm 3–5 nm

12 10 5 9

Wheat straw Seeds of wheat, rice, sorghum, pellet Egg white

Hydrothermal Oxidation and hydrothermal

Bamboo leaves Coffee seeds

9–10 nm >4 nm 4–5 nm 2–3 nm

Quantum yield 10.2

13 36

Hydrothermal Solvothermal Hydrothermal Heating in presence of ethanol Hydrothermal Calcination

Lemon peel Lemon juice Carrot juice Banana

Size >6 nm

4–5 nm >10 nm

Used method Hydrothermal heating

Precursor source Lemon juice

325 350

360 350

365

315

304 340

325 340

365 365

422 365 360 360

λexc 365

392 420

430 425

450

420

418 435

400 430

440 440

510 450 442 465

λem 450

Bioimaging Therapeutic agent

Metal ion detection and bioimaging Sensing of hydrogen peroxide Preparation of microfibers Therapeutic agent

Metal ion detection Metal ion sensing

Metal ion detection Fluorophore, bioimaging agent Therapeutic agent Good photo catalyst

Good photocatalyst Antimicrobial agent Useful in bioimaging Biomedical application

Application Useful in bioimaging

Table 7.3 Application of different kind of natural biomass for the production of C-dots and related properties

Essner et al. (2016) Pramanik et al. (2018)

Liu et al. (2014a) Yao et al. (2017)

Wang et al. (2016)

Li et al. (2014) Prasannan and Imae (2013) Yuan et al. (2015) Chaudhary et al. (2016a, d) Zhang et al. (2015)

Ref Tadesse et al. (2018) Anmei et al. (2018) Shaikh et al. (2019) Liu et al. (2017) De and Karak (2013) Liu et al. (2014b) Hsu et al. (2012)

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Carbonization and calcination Microwave assisted heating

Hydrothermal heating Hydrothermal heating Hydrothermal heating Hydrothermal heating Hydrothermal Carbonization

Calcination Low temperature carbonization Hydrothermal

Pyrolysis

Simple heating Hydrothermal Hydrothermal Ultrasonication Microwave method

Sepals of egg plant

Honey Sweet potato Corn flour Fresh tulsi leaves Spinach Almond husk

Mango peels Watermelon peels

Haemoglobin

Starch BSA DNA of E. coli Glucose Vitamin C

Rose petals

Tomato puree

Radish

Hydrothermal Hydrothermal heating and sonication Hydrothermal

Paper Bee pollen

10 11 – 6 15

4

10

8 7

350 360 366 350 330

230

320

310 365

325 315 390 340 330 390

340

390

360

360 340

450 448 445 445 405

380

397

425 444

406 420 460 430 405 470

440

470

450

449 440

Anion sensing Bioimaging Drug delivery Photo catalyst Bioimaging

Fluorophore

Sensing

Detection of Fe2+ ion Bioimaging

Detection of Fe2+ ion Metal ion sensing Detection of Hg2+ ion Detection of Pb2+ ion P-nitrophenol sensing Bioimaging

Bacteria sensing

Sensing of p-nitrophenol

Sensor for acetic acid

Pollutant sensing Bio fertilizer

(continued)

Sharma et al. (2019b) Chakraborty et al. (2018) Basu et al. (2015) Zhang et al. (2012) Ding et al. (2015) Ma et al. (2012) Gong et al. (2014)

Praneerad et al. (2019) Wang and Jiang (2016) Bukasov et al. (2018) Yang et al. (2014) Shen et al. (2017) Wei et al. (2014b) Kumar et al. (2017) Ren et al. (2018) Tripathi et al. (2016) Jiao et al. (2019) Zhou et al. (2012)

Wei et al. (2014c) Zheng et al. (2017)

Emerging Potential of Nano-Based Techniques for Dye Removal

4–5 nm 2–6 nm 6 nm 10 nm 3 nm

4 nm

4–5 nm

1–3 nm 2

25 – 25 12 53 2

15

>10 nm ~5 nm >4 nm 10 nm >4 nm 1–5 nm 5–20 nm

11

15

11 7

7–8 nm

4–5 nm

4–5 nm 2–3 nm

7 175

Precursor source Uric acid Sucrose Lipase

Table 7.3 (continued)

Used method Pyrolysis Hydrothermal Microwave method

Size 4 nm 2 nm 5 nm

Quantum yield 52 6 – λexc 350 350 360 λem 442 421 400 Application Metal ion detection Detection of picric acid Metal ion detection

Ref Qin et al. (2019) Li et al. (2018) Liu et al. (2016)

176 S. Chaudhary and P. Chauhan

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Fig. 7.4 Scheme for scale-up synthesis of C-dots from glucose and hydrochar. (Adapted figure from [Jing et al.] with permission from copyright (2019), American Chemical Society, (Washington, DC, USA))

biocompatible and less toxic particles. Therefore, it is not wrong in saying that transformation of waste biomass to useful C-dots has made a significant impact in finding new technologies for handling environmental concerns. For instance, Jing et al. (2019) have used the application of glucose and hydrochar for the preparation of C-dots. The synthesis involved the carbonization and decomposition of the starting source at 200  C for 6 h (Fig. 7.4). The formed C-dots have the tendency to display blue-green light emission under the UV light. The synthesis has mainly involved the structural rearrangement in the carbon sources used during the synthesis. The main processes involved hydrolysis, dehydration, decarboxylation, aromatization, and re-condensation of starting materials. The formed particles have displayed the XPS peak of C 1 s at 285.0 eV and O 1 s at 531.9 eV, respectively. The UV-vis. Absorption band has been observed between 250 and 350 nm. The fluorescence spectra have displayed the excitation-dependent aptitude. This aspect has been aroused due to the presence of emissive traps in C-dots. The existence of aromatic conjugate structure and free zigzag sites in C-dots has also produced the fluorescence variation in C-dots. Wang et al. (2018) have employed the application of intestine materials of pigs for the formation of C-dots via a single step processing. The as prepared

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nanoparticles have displayed the higher rate of dispersion in polymer matrix and act as an efficient material for ink-free patterned compound. The as formed particles have further been used for the detection of latent fingerprints of living beings. The process was found to be quite simple and affordable for the generation of large scaled C-dots. The technique employed in this work has provided the stability and clarity in latent fingerprints methodologies employed so far. The other advantage is the non-toxic nature of the employed material and better control over the colour tuning of samples.

7.7

Characteristic Properties of C-Dots

The zero dimensional with sp2 hybridized carbon-based nanoparticles with size in the range of 2–10 nm and having quasi-spherical shape and amorphous nature are generally termed as carbon dots. In certain cases, the group of carbon dots with small amount of N, O or H are also came under the category of carbon quantum dots (Kaur et al. 2018; Muhulet et al. 2018; Torres et al. 2019). The presence of surface modifiers over C-dots has provided them good water solubility and made them effective in water treatment application (Hasija et al. 2019; Lin et al. 2018). The chemical features of C-dots are mainly dependent over the nature of the synthetic procedure and the nature of the starting source for preparation of C-dots. The difference of size range made graphene oxide and carbon dots two separate materials in nanotechnology. Otherwise their physical and chemical structures are comparable with each other. The X-ray diffraction patterns have displayed characteristic peaks in the region of 2θ ¼ 20 to 26 with interlayer spacing distance value of around 0.3 and 0.38 nm, respectively. These values have confirmed the similarities of C-dots with graphene oxide. In addition, the existence of broad diffraction peaks in case of C-dots has clearly pointed out the existence of amorphous character in C-dots (Singh et al. 2019a; Huo et al. 2019). The mechanistic behavior of optical and luminescemce properties in C-dots is very attractive and considered as the most researched topic amongst the scientist (Ling et al. 2017; Peng et al. 2018). It has mainly been believed that C-dots have displayed a characteristic peak between 230 and 270 nm and 300 and 340 nm. These two peaks are mainly aroused due to the π!π* and n!π* transitions in C-dots, respectively. The variation in the peak position has mainly associated with the existence of mixture of sp2 and sp3 hybridized carbon atom in C-dots. The variation in the number and their respective distribution in the C-dots have produced direct impact over the optical properties of C-dots. In addition, the presence of quantum confinement effect and surface defects with the existence of aromatic kind of structure has also contributed towards the optical properties of C-dots. Along with optical properties, the presences of radioactive recombination of excitons and nature of surface defects in C-dots have generated multicolour fluorescence emission properties in C-dots (Ding et al. 2016). The existence of emissive traps in C-dots has produced the emission peaks in region of 320 to 480 nm. The well-known blue to green to yellow emissions is quite common in C-dots. The changes in the size, surface properties and defects in C-dots are

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mainly responsible for excitation-dependent emission profiles in C-dots. The quantum yield (ɸ) of C-dots is also associated with the colour variations in C-dots. In addition, the annihilation effect of C-dots is found to be minimum as compared to conventionally used fluorophore for bioimaging applications (Huang et al. 2018; Wang et al. 2019). C-dots have also displayed the single photon or two or multiphoton emission with down and up conversion fluorescence. The disordered band due to sp3 hybridized surface defects and G band due to the vibration of sp2 hybridized carbon in C-dots have displayed characteristic peaks between 100 and 1580 cm
1 in Raman spectra. The amount of graphitization and crystallization in C-dots can be easily estimated from the ratio of the two peaks. The binding energy peak profile for C1s and O1s is mainly observed at 287 and 534 eV in XPS spectra of C-dots. Recently C-dots have found the potential application in the fabrication of economically viable photosensitizers. The lower efficiency has mainly been tackled during the synthesis of photosensitizer with high rate of stability. The photoluminescence activity and photosensitization power can be easily modulated by doping the particles with N atoms during the synthesis of C-dots (Zhang et al. 2018a, b; Li et al. 2018). The photo-oxidation property of C-dots can be easily controlled via doping the C-dots. The response time of as prepared particles has been found to be quite fast. These properties have further enhanced the water solubility of C-dots and made them effective material in oxidase-mimicking nanozyme. These enzymes have further been used for the photodynamic antimicrobial chemotherapeutic applications.

7.8

Dye Removal Activities of C-Dots for Waste Water Cleanup

The aspiration for the secure and pleasurable living standards by living individual has produced unscrupulous discharge of harmful toxins including dye molecules into water resources and causing considerable effect on the environment (Devi et al. 2019; Kaur et al. 2017; Zhou et al. 2019; Sharma et al. 2019a). The tremendous growth in the textile industries, rapid urbanization and significant changes in the living styles of human beings all over the world has also contributed to the deterioration of the environment. There is an urgent requirement to find new expertise for handling environmental concerns especially water pollution. The extent of water pollution is so hard that the existence of water resources is shrinking in an exponential manner. In this regard, C-dots have attained colossal interest among the researchers for finding better alternatives for generating sustainable and economical methods for dye removal from waste resources (Sharma et al. 2019a; Singh et al. 2019c; Natrajan et al. 2018; Asadian et al. 2019). The application of luminescent C-dots in water cleanup has provided a boon for researchers in the field of toxin sensing by using fluorescence technique (Sun and Lei 2017; Wei et al. 2014; Zhang et al. 2016). The use of renewable biomass as a starting material for preparing C-dots has significantly reduced the cost of the process as compared to the available synthetic methods for producing chemosensor. The utilization of harmful and toxic chemicals during preparation of C-dots has also

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been reduced with the application of biomass as starting source. The other main advantage of the bio-inspired C-dots is the use of water as a reaction medium for the conversion of biomass into C-dots. In addition, the nutrient contents of this biomass will also be shown higher percentage concentrations of protein, crude lipid, carbohydrate and crude fibre contents in C-dots which will further supplement their role in water cleanup. Therefore, the chosen resources act as a good source of starting material for the synthesis of C-dots and their application in waste water treatment (Das et al. 2019; Meng et al. 2019; Hoang et al. 2019; Sun et al. 2019). The as prepared particles will also offer better control over the stability and luminescence activities of C-dots and act as sensitive and selective sensor for toxins. The presence of the different type of the functional group over the surface of C-dots has further made them one of the potential materials for the dye molecules present in the aqueous media. The conjugating ligand materials over the surface of C-dots are quite effective for the selective detection of dye toxin ions by using the fluorescencebased signals in presence of C-dots (Fu and Cui 2016). Additionally, the presence of a conjugated π electron system will further enhance the probability of C-dots to form complexes with a diverse range of aromatic nitro compounds containing dye molecules present in waste water sources. Thus C-dots will further open up its scope in chemo-sensing applications for the identification of dyes from the aqueous media. The low toxicity, higher stability, well-suited biocompatibility, excellent water solubility due to the functionalization make the as biomass derived C-dots as budding aspirant for monitoring dye pollutants with great efficacy. The practical utilities and average recovery of dye molecules in presence of C-dots synthesized by using different resources have also enhanced their role in waste water management. This method will offer a simple, rapid, cost-effective and harmless mean to determine metal ion as well as aromatic nitro compounds as impurities with higher selectivity and sensitivity and usefulness for water treatment purpose. For instance, Zhang et al. (2014) have employed the application of environmentfriendly nanocomposites of C-dots with positively charged double layered hydroxides for the removal of dye molecules from aqueous media. The presence of large quantity of oxygen containing surface functional group over the surface of C-dots has made them effective for the treatment of toxic dye molecules (Fig. 7.5). It has been observed that the adsorption tendency of this new material was as high as 185 mg/g for methyl blue. The adsorption behaviour follows Langmuir isotherm with pseudo-second-order kinetics. The adsorption mechanism was mainly explained due to the hydrogen bonding between the dye molecules and C-dots. In addition, the electrostatic interaction between the dye molecules and double layered hydroxides has further complimented the removal tendency of dyes (Zhang et al. 2014). Recently, Singh et al. (2019c) have developed a novel methodology for the waste water management by using the cost-effective hydrogel coated C-dots. The highwater retention power of hydrogel has provided the efficient photothermal mediations for adsorbed sunlight. Additionally, the presence of C-dots has provided the thermal and mechanical strength to the hydrogel matrix. The presence of the C-dots has further enhanced the absorption rate of sunlight and induced the higher

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Fig. 7.5 Adsorption of methyl blue over the surface of LDh doped C-dots. (Adapted figure from [Zhang et al.] with permission from copyright (2014), American Chemical Society, (Washington, DC, USA))

rate of water evaporation from the hydrogel. In addition, the application of C-dots is quite significant in the generation of competent and economically viable photocatalytic material for water splitting and dye removal. The photocatalytic activity was mainly achievable due to the promising light-harvesting and electron transference aptitude of C-dots (Martindale et al. 2015). The C-dots prepared via using the waste orange peels have the tendency to degrade the azo dye, i.e. naphthol blue-black from aqueous media by using UV irradiation method. The complete degradation of dye was achieved within 45 min of UV exposure in presence of C-dots. The effective photo-degradation behaviour of C-dots can be explained on the basis of successful electronic charge interaction over the surface of nano dots. The transference of photo-generated species has also displayed higher rate in presence of C-dots (Prasannan and Imae 2013). The application of C-dots prepared by using the expired milk has currently been used for the sensing of harmful toxic dyes from the aqueous media. The easy up take of as prepared C-dots has enhanced their role in bioimaging application. The as prepared nanoparticles have also been employed for the solid-state fluorescent sensing, security labelling applications and wearable optoelectronic devices with combining them with dye molecules. The fluorescent nature of prepared C-dots has made them useful as substitute for inks or dye and employed them in drawing patterns. The base plates for various types of textile materials, flexible type of plastic films are easily printed by using the highly biocompatible C-dots prepared by using the raw expired milk. The high adsorption

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power of C-dots has also been employed for the widely used surfactant, i.e. SDS from the aqueous media. The respective changes in the absorption rate of C-dots toward SDS have been monitored by varying the temperature and pH range of the reaction media. The effect of addition of external salt, i.e. NaCl has also been checked on presence of C-dots. The results were found to be quite impressive for the management of waste water from industrial sources having dye as toxins and enhanced the potential of C-dots in environmental remediation applications (Chavez-Sumarriva et al. 2016) This can be possible via the presence of different type of functional groups over the surface of C-dots which has provided the extra space for the complexation of dyes with C-dots (Liu et al. 2014). The surface modification with DNA has provided the extra affinity for dyes and provided the stable complexation (Song et al. 2015). Ramanan et al. (2018) have used the application of waste expanded polystyrene materials for the preparation of C-dots. As such these waste materials are considered to be one of the toxic non-biodegradable substances and its management is considered to be quite troublesome. By using their strategy, the conversion of these toxins into useful luminescent C-dots has provided a better option for dye removal. The prepared C-dots have shown high quantum yield value and long shelf life with controlled size. In addition, the PL activity of C-dots is not affected by the changes in the pH and ionic strength of the reaction media. The adsorption aptitude of as prepared C-dots is found to be quite effective towards dye molecules. Ma et al. (2018) have presented the single step route for fabricating the magnetic hybrid carbon nanotubes with Fe and C-dots by using the applications of APCNTs treated with NaClO. The formed composite has possessed high surface area and acts as a good adsorbent for the removal of dyes molecules. For instance, the adsorption capacity of methylene blue was found to be as high as dyes 132.58 mg/g. On the other hand, the system works well for methyl orange and nile red dyes with adsorption capacities of 28.41 mg/g and 98.81 mg/g, respectively. The system works well for the removal dyes in binary mixture systems. It has been found that the cooperative adsorption was possible over the surface of CNTs/Fe@C for removing MB-MO dyes from aqueous media (Fig. 7.6). On the other hand, the MB-NR dyes have displayed competitive adsorption during the treatment (Ma et al. 2018). In a separate report, Sansuk et al. (2016) have provided a new approach for the removal of anionic dyes from the waste water resources by using the combination of layered double hydroxides with C-dots. The electrostatic interaction between the LDHs and acid yellow 25 has mainly responsible for the dye removal. Just within 5 min, the 97% of dye molecules are able to get removed from the aqueous media with very high removal capacity of around 186 mg/g. Singh et al. (2019b) have used the application of in-situ synthesized magnetic IO nanoparticles inside CSGO hybrid hydrogel matrix for the removal of MB dye. The presence of carboxyl and epoxy groups of oxide form of C-dots has the ability to react with CS molecules to form amide and resulted in the formation of hydrogel for the effective removal of dye molecules. The formed hybrid has possessed large surface area for the effective removal of MB from aqueous media. The formed

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Fig. 7.6 Dye removal mechanism of (a) MB-MO, (b) MB-NR onto CNTs/Fe@C and (c) adsorption steps in binary dye systems. (Adapted figure from [Ma et al.] with permission from copyright (2018), American Chemical Society, (Washington, DC, USA))

nanocomposites have exhibited high magnetic response for removing the dyes (Fig. 7.7). The existence of high surface area with active functional groups has increased the availability of the active binding sites for the adsorptive removal of MB. In addition, the high pH of the reaction media has supported the electrostatic attraction of MB with negatively charged nanoparticles. The resultant kinetic studies have shown the presence of pseudo-second-order model with applicability of Freundlich adsorption isotherm. In addition, the adsorption process was found to be endothermic and spontaneous in nature. The reproducibility of the system was found to be higher after four successive cycles. Therefore, the combination of C-dots for dye removal has provided an excellent cost-effective means for waste water purification process. Till date, wide research has been carried out on the synthesis, characterization and application of C-dots due to their extraordinary applications in dye removal. Different parameters such as low cost, easy synthetic procedure and size controllable approaches make C-dots an exceptional material of nano-field. The field of C-dots

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Fig. 7.7 The mechanistic view showing the removal of dye using magnetic separation. (Adapted figure from [Singh et al.] with permission from copyright (2019), American Chemical Society, (Washington, DC, USA))

still encouraging enormous attention to discover further extraordinary potential with high efficiency for the removal of dyes. Summary In this book chapter we explored the synthesis of carbon dots by utilizing green biomass sources such as fruits, vegetables and kitchen waste. As green approach for the synthesis of C-dots has received greater attention because it reduces both costs, time and results in high yield formation of environment-friendly material. The biomass derived C-dots were found to be highly biocompatible and non-toxic in nature. The adsorption properties of developed C-dots further investigated out in dye removal. The large surface area, high chemical stability and superior catalytic activities made the nanomaterials as potential candidate for the removal of dyes. The correlation between the morphology and size of nanomaterials has also been discussed with reference to their dye removal efficiency.

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8

Nanomaterials for Remediation of Pesticides Bhupinder Dhir

Abstract

Nanomaterials have been considered as effective agents for remediation of contaminants present in the environment. Properties of nanoparticles such as high surface area, high reactivity, and effectiveness have mainly contributed to their high efficiency. Nanomaterials including carbon, metal oxides, bimetallic nanoparticles, nanoscale zero-valent iron (nZVI) have shown potential for treating pesticides including chlorinated organic compounds, organophosphorus compounds, and volatile organic compounds. The potential of nanomaterials in removing pesticides from the various components of the environment needs to be explored for developing large scale technologies. Keywords

Organochlorine · Organophosphorus · Nanomaterials · Pesticides · Remediation

8.1

Introduction

Pollution is a major environmental problem faced by human race all over the globe. The chemical compounds that provide effective protection against pests, fungi, and weeds to plants are referred as pesticides. They are widely used in providing protection to agricultural field all over the world. Excessive use of agrochemicals including insecticides, herbicides, and fungicides contaminates environment via their leaching in water and soil. Leaching of chemicals results in addition of their residues in drinking water, groundwater, and soil. Large quantities of pesticides get added to various components of the environment because of runoff from agricultural

B. Dhir (*) School of Sciences, Indira Gandhi National Open University, New Delhi, India # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_8

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land and foliar application. The presence of pesticide residues produces harmful effect on environment and organisms present in the water and land ecosystems. Exposure of these chemicals for long period produces various health effects in humans. Pesticides have been removed from the environment using various technologies. Some of the techniques found effective in getting high removal of pesticides mainly include physico-chemical treatment processes, surface adsorption, membrane filtration, and biological degradation (include bioremediation, phytoremediation processes). These techniques have been found effective in removing pesticides but sometimes show slow response, less specificity, less sensitivity, and release of many by-products. Nanotechnology that utilizes the nanoscale materials for removal of contaminants has emerged as a good alternate in the last few years (Guerra et al. 2018). Enhanced reactivity, high surface-to-volume ratio, unique physical properties, ideal size (small size ranging from 1 nm to 100 nm), magnetism make nanomaterials as ideal materials that prove useful in removing contaminants from the environment effectively (Rani et al. 2017). The functional groups present on the nanomaterials (surface chemistry) help in targeting specific pollutants to achieve efficient remediation (Joo and Cheng 2006; Patil 2016). Studies conducted by several workers established the role of nanoparticles in remediation/treatment of various inorganic or organic environmental pollutants (Yunus et al. 2012; Das et al. 2018). The role of nanotechnology in removing pesticides from various components of the environment has been proved. Use of nanoparticles for sensing and remediation of organochlorine and organophosphorus pesticides has been established (Uma Shanker and Jassal 2017; Firozjaee et al. 2018; Rawtani et al. 2018). Titanium oxide (TiO2) and monovalent iron are the nanoparticles found to act as excellent adsorbents and efficient photocatalysts that can degrade organochlorine compounds as well as their toxic metabolites. The present chapter provides detailed information about recent advances in field of nanotechnology and use of nanomaterials in remediation of pesticides.

8.2

Removal of Pesticides Using Nanotechnology

Nanotechnology that involves the use of nanomaterials, nanoparticles, nanomembranes, and nanopowders has proved efficient in detection, monitoring, and remediation of contaminants (Rajan 2011; Aragay et al. 2012). Nanoparticles possess high capacity to treat contaminants because they possess ability to (1) transform various types of environmental contaminants, (2) assist in in situ and ex situ remediation of contaminants, (3) show rapid mobility and high reactivity (Tosco et al. 2014). The functional groups present on nanomaterials facilitate the removal of pesticides. Nanoparticles have shown potential to remove chlorinated compounds, hydrocarbons, and organic compounds. High removal of broad range of pesticides by nanomaterials occurs because of their high adsorption capacity, faster kinetics, high surface area, and larger number of surface reaction sites. Research studies have

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shown that nanobiosensors that detect the presence of persistent organic pollutants have been developed (Xiong et al. 2018). Various pesticides can be removed from water bodies with the help of nanomaterials via adsorption. Attachment of organic compounds to functional groups increases the affinity of the nanomaterials towards target molecule (Liang et al. 2004; Savage and Diallo 2005). The mobile electrons and positive surface charges of nanoparticles accelerate oxidation and reduction reactions thereby assisting in degradation of pollutants. Transformation and detoxification of pesticides have been successfully reported after use of metal nanoparticles, bimetallic nanoparticles, metal oxide nanoparticles, and carbon nanotubes (Chen et al. 2007; Yang et al. 2008; Ren et al. 2011; Smith and Rodrigues 2015). Enzyme-based biosensors that help in detection of pesticides have also been developed (Willner and Vikesland 2018).

8.3

Removal of Pesticides by Nanoparticles

Various nanoparticles can be used in the removal of pesticides. Nanoscale particles possess the capacity of degradation of pesticides (Sun et al. 2006; Tratnyek and Johnson 2006; Satapanajaru et al. 2008; Garner and Keller 2014). Nanoparticles viz. nanoscale ZVI (nZVI) and reactive nanoscale iron product (RNIP) have shown capacity to remove pesticides (Kim et al. 2007, 2008). nZVI particles are composed of iron (Fe) and have a diameter of 100–200 nm, while RNIP particles are composed of Fe and Fe3O4 present in equal proportion (50:50) (Bardajee and Hooshyar 2013). ZVI nanoparticles lead to dechlorination of highly recalcitrant pesticides and herbicides (Thompson et al. 2010). The Fe(II) provides electrons for dechlorination. Dechlorination of compounds such as PCE (perchloroethylene) has been achieved using these materials. Oxidation of halogenated organic pollutants has been achieved after treatment with ZVI. The nZVIs get transformed from Fe0 to Fe2+ followed by oxidative transformation to Fe3+ (Crane and Scott 2012). These nanomaterials assist in chemical reduction and catalysis of organochlorine, organophosphorus pesticides, polychlorinated biphenyls, etc. (Karn et al. 2009). Removal of pesticides such as lindane, DDT, chlorinated solvents (PCE, TCE, DCE) using nZVI has been reported. Transformation of organic compounds like nitrates has also been reported using nZVI (Karn et al. 2009). Nanoscale ZVI also showed capacity to remove pesticides and herbicides such as atrazine, molinate, picloram, chlorpyrifos, diazinon, and diuron (Keum and Li 2004; Satapanajaru et al. 2008). Removal of compounds such as hexachlorobutadiene, pentachlorobenzene, hexachlorobenzene, lindane, dichlorodiphenyltrichloroethane (DDT), heptachlor has been reported using nano zero-valent iron (nZVI) (Šimkovič et al. 2015; Yildiz 2017). Reduction of nitroaromatic pesticides resulted in formation of amines after treatment of zero-valent iron powder (Keum and Li 2004). Studies indicated that silver, carbon, and alumina nanoparticles mineralize pesticides. The mineralization of the pesticides such as chlorpyrifos and malathion using silver nanoparticles has been reported (Manimegalai et al. 2014). Chitosan

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contains silver nanoparticles which assist in removal of pesticides from water. The removal of pesticide, namely atrazine after treatment of silver nanoparticle composite bioadsorbent present in the chitosan has been reported. The pesticide content noted a sharp decline in water when the adsorbent dose was increased from 0.5 to 2.0 g. Cross-linked chitosan-silver nanoparticles composite microbeads showed adsorption capacity of 115 μg mL 1 (Saifuddin et al. 2011). Removal of compounds like hexachlorobenzene and chlorinated hydrocarbons has been reported after treatment with bimetallic nanoparticles, viz. Ag/Fe, Ni/Fe, Cu/Fe (Yan et al. 2010; Koutsospyros et al. 2012; Nie et al. 2013). Bimetallic coreshell Fe/Ni and Fe/Pd nanoparticles showed capacity to dechlorinate toxic chlorinated organic compounds (Xu and Bhattacharyya 2005). Gold nanospheres and nanorods have shown capacity for adsorption of organophosphorus pesticides such as dimethoate. Adsorption of nanospheres resulted in aggregation (Momić et al. 2016). Nanospheres and nanorods have shown adsorption capacity of 456 mg g 1 for 57.1 mg g 1, respectively. These nanoparticles have been used successfully for removing dimethoate from drinking water. Carbon nanotubes (CNTs) composed of graphitic carbons have shown great capacity to remove pesticides (Pyrzynska 2011). Pore structure and surface functional groups present in CNTs help in the adsorption of pollutants. The mechanisms such as hydrophobic effect, covalent bonding, π–π interactions, hydrogen bonding, and electrostatic interactions help in adsorption of organic chemicals on CNTs. Transformation of organic compounds such as pesticides, pharmaceuticals, and drugs present in wastewater has been reported using single walled (SWNTs) or multiwalled CNTs (MWCNTs) (Deng et al. 2012; Yu et al. 2014). These nanotubes have also been found effective in removing volatile organic compounds and dioxins (Li et al. 2003; Long and Yang 2005; Peng et al. 2005; Rao et al. 2007). Polar aromatic compounds and polycyclic aromatic hydrocarbons (PAHs) get adsorbed on CNT through π–π interaction. Adsorption of compounds has been achieved when hydrogen bonding occurs between functional groups such as -COOH, -OH, -NH2, and organic molecules. The wet ability of CNTs surfaces get altered with functional groups. These groups make them more hydrophilic and suitable for sorption of low molecular weight and polar compounds (Shi et al. 2010). Both SWCNTs and MWCNTs possess thermal stability and specific chemical properties (Cho et al. 2008). The removal of compounds such as diuron and dichlobenil via adsorption on MWNTs has been noted. Adsorption of compounds gets increased with an enhancement in the surface area and total pore volume of MWNTs. Adsorption of atrazine by SWNTs and MWNTs has been reported. Multiwalled carbon nanotube (MWNT), nano-clay, and nano-alumina have shown capacity for adsorbing dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCBs). MWNT proved to be good adsorbent material for both contaminants. Removal of 88.9% and 77% for DDT and PCB at 10% of MWNT has been reported (Taha and Mobasser 2015). Unique physical and chemical properties of graphene, a carbon nanomaterial contributed to its capacity to remove pesticides (Maliyekkal et al. 2012; Nodeh et al. 2019). The pesticides removal by graphene occurs mainly via adsorption (ranging

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from 600 to 2000 mg g 1) (Wu et al. 2011; Pei et al. 2013; Sen Gupta et al. 2015). Removal of persistent halocarbon pesticides using graphene has been reported. Halogenation and/or dehalogenation reaction assists in the removal of pesticides. Aromatic rings of graphene adsorb contaminants through π–π interactions. Graphene-coated silica (GCS) has also shown high potential for removing residual organophosphorus pesticides from water (Liu et al. 2013; Zhang et al. 2015). Studies also reported removal of chlordane, a persistent organic pollutant from water using reduced graphene oxide supporting silver nanoparticles. The degradation of chlordane involved two-steps which include removal by silver nanoparticles and subsequent adsorption of the degraded products (Sarno et al. 2017). Nanocrystalline metal oxides remove broad range of pesticides including organophosphorus compounds. These compounds act as effective adsorbents. Ferric oxides, manganese oxides, aluminum oxides, zinc oxides, titanium oxides, magnesium oxides, and cerium oxides are the metal oxides which act as low cost effective adsorbents (Daneshvar et al. 2007; Navarro et al. 2009). Metallic nanoparticles showed adsorption capacity for pesticides such as lindane, aldrin, dieldrin, and endrin. Hexagonal mesoporous silica (HMS) showed adsorption capacity for organochlorine compounds such as DDT. Al2O3 and MgO activated carbon showed adsorption capacity for diazinon (Daneshvar et al. 2007; Firozjaee et al. 2017). The removal of heptachlor, lindane, and hexachlorobenzene has been reported using an effective reactant—nanoiron NANOFER 25. The removal of selected organochlorinated pesticides has been noted when commercial suspension of Nanofer 25 nZVI particles was used. High removal efficiency of 97% has been noted for lindane (LIN), hexachlorocyclohexane (HCH), hexachlorobutadiene (HCHB) within time period of 4 h. Removal efficiency of 99.6% has been noted for HCH followed by removal of 98.9% for LIN, 97.3% removal efficiency for HCHB followed by 84.8% removal efficiency for pentachlorobenzene (PCHB), and 72.7% for HCHBD with 24 h (Šimkovič et al. 2015). Materials such as ZnO, TiO2, Fe2O3, CdS, and WO3 remove pesticides by photocatalytic degradation (Yu et al. 2007; Rajeswari and Kanmani 2009; Mohagheghian et al. 2015). Removal of the wide range of recalcitrant organic pollutants occurs by photocatalytic oxidation. The photocatalytic degradation of organochlorine pesticides has been noted after using nano-TiO2 coated films (Yu et al. 2007). The TiO2 nanoparticles showed photocatalytic degradation of dicofol under UV light irradiation (Senthilnathan and Philip 2009). Active hydroxyl radicals (∙OH) react with dicofol to produce chloride ions and less toxic compounds that contain less chlorine content (Daneshvar et al. 2007; Senthilnathan and Philip 2010). In this way degradation of dicofol has been obtained. Photocatalytic degradation of isoproturon pesticide using TiO2 has also been reported (Police et al. 2010). Magnetic nanoparticles also possess capacity to remove pesticides. Magnetic nanoparticles whose surface has been modified exhibit high adsorption efficiency and hence show high capacity for removal of pesticides (Kaur et al. 2014; Maddah and Hasanzadeh 2017). Magnetic nanoparticles remove non-polar and moderately polar pesticides. This occurs due to their separation ability, excellent stability, and convenient operation (Šimkovič et al. 2015). Alumina nanoparticles also possess the

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Table 8.1 Various types of pesticides removed by nanoparticles Pesticide Organochlorine compounds

Nanoparticles used Chitosan-silver oxide nanoparticles Magnetic nanocomposite

DDT

Nano zero-valent iron, multiwalled carbon nanotube (MWNT), nano-clay and nanoalumina Chitosan-zinc oxide nanoparticles composite MWNT, nano-clay, nano-alumina Magnetic Fe3O4/red mud-nanoparticles

Dehaghi et al. (2014)

MWNT Gold nanospheres, nanorods MgO nanoparticles

Dehghani et al. (2017) Momić et al. (2016) Ahmadifard et al. (2019)

Permethrin PCBs Organophosphorus compounds Malathion Dimethoate Diazinon

Reference Rahmanifar and Dehaghi (2014) and Hubetska et al. (2018) Poursaberi et al. (2012) and Taha and Mobasser (2015)

Taha and Mobasser (2015) Aydin (2016)

potential to remove organophosphate pesticides. The surface of nanocrystalline alumina possesses high surface area and high concentration of hydroxyl groups which prove effective in absorption of organophosphate pesticides (Table 8.1). Hazardous organic pesticides can also be removed through the technique of nanofiltration (NF) (Plakas and Karabelas 2012). The properties (physical and chemical) of the membrane such as reverse osmosis (RO) and ultrafiltration (UF) play an important role in the removal of pesticides. The material for membrane is selected on the basis of properties such as molecular weight cut-off (MWCO), desalting degree, and porosity. Nanofiltration membranes target different molecules based on their molecular weight. The removal of pesticides is regulated by porosity, polarity (dipole moment), hydrophobicity/hydrophilicity of the membrane. The size and polarity affect the retention of pesticides (Van der Bruggen et al. 1998). Hydrophobic compounds such as aromatic pesticides, non-phenolic pesticides, and alkyl phthalates showed rejection at very high degrees on the nanomembranes. High polarity of membranes prevents the rejection of pesticides. The desalination property of NF membranes causes rejection of aromatic and non-phenyl pesticides. Composite membranes exhibit better rejection of pesticides. The surface of the membrane possesses negative charges that help in removal of contaminants. At the membrane surface electrostatic repulsion of the negatively charged pesticides increases their rejection (Van der Bruggen et al. 1999, 2001). The rejection of aromatic pesticides by NF membranes has been studied (Kiso et al. 2001). The pesticides get adsorbed to the surface via formation of hydrogen bonds between organic molecules and the hydrophilic groups of the membrane polymer. Studies proved that formation of macromolecular complexes due to presence of one more than one pesticide or pesticide complexes improves pesticide retention (Musbah et al. 2013). Treatment of NF membrane with high-molecular weight organic compounds such as humic acids increases the elimination of the pesticides (Boussahel et al. 2002). Water quality parameters such as pH, ionic strength,

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Table 8.2 Pesticides removed from water using nanoparticles Type of nanoparticle Cysteine-capped Ag nanoparticles

Name of the pesticide Chlorpyrifos, malathion

Ag nanoparticles Au nanoparticles, TiO2

Lindane Malathion

TiO2, ZnO

Monocrotophos

Graphene oxide supporting silver nanoparticles Chitosan-siloxane functionalized magnetic nanoparticles

Chlordane

Nanocomposite composed of magnetic Fe3O4 nanoparticles (M), graphene oxide (GO) Gold nanospheres Composite of chitosan-silver nanoparticles TiO2

Reference Singhal and Lind (2018) Gupta et al. (2015) Fouad and Mohamed (2012) Anandan et al. (2006) and Gomez et al. (2015) Sarno et al. (2017)

Abamectin, diazinon, fenamiphos, imidacloprid, cyhalothrin Hexaconazole, chlorpyrifos

Badawy et al. (2018)

Dimethoate Atrazine

Momić et al. (2016) Saifuddin et al. (2011) Baneshi et al. (2017)

Diazinon

Nodeh et al. (2019)

presence of organic matter also influence the rejection of pesticides. Increase in pH decreases the rejection rate, while decrease in pH improves adsorption and ionic strength. High ionic strength reduces membrane permeability resulting in a better rejection. This happens because electrostatic forces and pore size inside the membrane decrease. Two pesticides, namely hexaconazole and chlorpyrifos have been effectively adsorbed from water samples using nanocomposite composed of magnetic Fe3O4 nanoparticles (M), graphene oxide (GO), and N-methyl-D-glucamine functionalized calixarene (NGC). Both chlorpyrifos and hexaconazole showed high adsorption capacities of 78.74 and 93.46 mg g 1, respectively. Though nanomaterials offer several advantages for removal of pesticides, properties such as unstability, toxicity, and recovery costs need to be considered while designing technologies using nanomaterials for remediation processes (Table 8.2).

8.4

Conclusions

Nanotechnology has been used for the treatment and remediation of environmental contaminants. The nanoscale particles have shown diverse applications in remediation of organic compounds. Nanomaterials have shown capacity to remove pesticides from water. Individual or composite nanomaterials possess significant potential for removal of pesticides.

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Zero-valent iron (ZVI), metallic oxide nanoparticles, carbon nanotubes are some of the nanomaterials that have shown great capacity to degrade various organic compounds. Activated carbon, alumina, silver, and iron nanoparticles cause mineralization of pesticides. Ecological implications (such as biodegradability, recyclability) and toxicity of nanomaterials need to be assessed before using these materials in development of larger scale nanotechnologies for pesticide removal/remediation. More research studies need to be focused on development of new technologies that can target specific contaminants.

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9

Application of Carbon-Based Nanomaterials for Removal of Hydrocarbons Avtar Singh, Jaspreet Singh Dhau, and Rajeev Kumar

Abstract

Monoaromatic hydrocarbons, polyaromatic hydrocarbons, volatile organic compounds (VOCs), heavy metals, inorganic salts, particular matters are the main forms of environmental pollution. Hydrocarbons (monoaromatic and polyaromatic) are of special concerns because some of them are highly toxic and persistent pollutants which threaten all life forms on earth. Main sources of hydrocarbon contamination in environment are crude oil, petroleum-based products, pesticides, or different harmful organic matters which are discharged into the water bodies as effluents. Environmental researchers are continually devoting their efforts to solve environmental concerns. Nanotechnology promises a solution to challenges associated with environmental pollution caused by modernization and advancement of technology. The last three decades have seen a significant interest in carbon-based nanomaterials for their novel applications across physics, chemistry, biotechnology, and engineering. Carbon-based nanomaterials (CNMs) have shown unique physical and chemical properties such as large surface area, high mechanical strength, high conductivity, and stability. Carbon-based nanomaterials include mainly: fullerenes, carbon nanotubes, graphene, and graphene derivatives. This chapter provides an overview of carbon-based nanomaterials research for their application to removing A. Singh (*) Clean Energy Research Center, Department of Chemical and Biomedical Engineering, University of South Florida, Tampa, FL, USA Department of Chemistry, Sri Guru Tegh Bahadur Khalsa College, Anandpur Sahib, Punjab, India e-mail: [email protected] J. S. Dhau Research and Development, MolekuleInc, Tampa, FL, USA R. Kumar Department of Environment Studies, Panjab University, Chandigarh, India # Springer Nature Singapore Pte Ltd. 2021 R. Kumar et al. (eds.), New Frontiers of Nanomaterials in Environmental Science, https://doi.org/10.1007/978-981-15-9239-3_9

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hydrocarbons from the environment. The various applications of CNMs associated with removing of hydrocarbon in the environment such as in adsorption technology, in analytic chemistry, and in photocatalysis process have been discussed in the present chapter. Keywords

Environment · Pollution · Hydrocarbon · Polyaromatic hydrocarbon · Carbonbased nanomaterial

Abbreviations BTEX CNFs CNMs CVD GCMS GN GO GONPs HCNTs HPLC LOD LOQ MARG MCRG MGO MSPE MWCNTs NTE PAHs POPs RGO RSD SPE SPME SWCNTs USEPA WHO

Benzene, Toluene, Ethylbenzene, Xylene Carbon nanofibers Carbon-based nanomaterials Chemical vapor deposition Gas chromatography mass spectroscopy Graphene Graphene oxide Graphene oxide nanoparticles Hybrid carbon nanotubes High performance liquid chromatography Limit of detection Limit of quantification Magnetic annealing-reduced graphene Magnetic chemically reduced graphene Magnetic graphene oxide Magnetic solid-phase extraction Multi-walled carbon nanotubes Needle type extraction Polyaromatic hydrocarbons Persistent organic pollutants Reduced graphene oxide Relative standard deviation Solid-phase extraction Solid-phase microextraction Single-walled carbon nanotubes United States Environmental Protection Agency World Health Organization

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9.1

207

Introduction

With the modernization and advancement of technology lead to most serious environmental pollution problems facing humanity and other life forms on earth. Environmental pollution is defined as “the contamination of the physical and biological components of the earth/atmosphere system to such an extent that normal environmental processes are adversely affected” (Kemp 1998). Examples of environmental pollutants are carbon monoxide, nitrogen oxide, sulfur dioxide and particulate matter, chlorofluorocarbons, heavy metals, monoaromatic hydrocarbons, polyaromatic hydrocarbon, volatile organic compounds (Yunus et al. 2012). The rise in human population density and anthropogenic activity has led to more environmental deterioration (Sherbinin et al. 2007). Environmental pollutants have various adverse health effects like respiratory disorders, cardiovascular disorders, physical and mental disorders, organ dysfunction, neurological disorder, cancer (Kelishadi et al. 2009; Kargarfard et al. 2011; WHO 2013). Monoaromatic and polyaromatic hydrocarbons are of special concerns because some of them are highly toxic and persistent nature (USEPA 1984; Ma et al. 2010; Valavanidis et al. 2008; Masih et al. 2016). Main sources of hydrocarbon contamination in environment are crude oil, petroleum-based products, pesticides, or different harmful organic matters which are discharged into the water bodies as waste (Al-anzi and Siang 2017; Osin et al. 2017). In petroleum industries, oil spillage during exploration, transportation, storage, and refining of crude oil, whether accidentally or due to human activities, leads to main cause of hydrocarbon contamination of soil, water, and air pollution (Al-anzi and Siang 2017; Osin et al. 2017). The crude oil/petroleum sludge contains 200–300 different compounds, mainly aliphatic series (C1-C50), monoaromatics (BTEX), polyaromatic hydrocarbons, phenols, volatile organic compounds, and heavy metals (Younis et al. 2020). Aliphatic series compounds (in the form of gases, liquids, or solids) have relatively low toxicity and are biodegradable. BTEX are group of four volatile organic compounds: benzene, toluene, ethylbenzene, and xylene (mixture of ortho, para, and meta). BTEX have been identified as toxic, carcinogenic, and mutagenic (Masih et al. 2016), and are listed as Hazardous Air Pollutants in the US Clean Air Act Amendments of 1990. United States Environmental Protection Agency reported that the source for 47–75% of BTEX (benzene, toluene, ethylbenzene, and xylene) detected in environment is petroleum-based industries (Younis et al. 2020; Jafarinejad 2017a, b). Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds consisting of two or more fused aromatic rings, and are referred to as persistent organic pollutants (POPs) because of their chemical stability and biodegradation resistance (Borji et al. 2020). PAH contaminants pose a significant hazard to the environment and human health because of their chemical stability and biodegradation resistance (USEPA 1984; Ma et al. 2010; Valavanidis et al. 2008). Hydrocarbons have been widespread used in our day to day lives. They are the main source of fuel for the industrial and manufacturing sector. Thus, we need technologies for hydrocarbon pollution prevention which able to monitor and treatment of hydrocarbon contaminants in the environment. In the past two decades,

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considerable research has been published focusing on environmental application using carbon-based nanomaterials. An overview of current research is on carbonbased nanomaterials for their use in application of removal of hydrocarbons in environment.

9.2

Hydrocarbons

Hydrocarbons are simplest class of an organic chemical compound composed of carbon and hydrogen atoms. Hydrocarbons occur naturally throughout the world and are principal constituents of crude oil, natural gas, and other important energy sources (Al-anzi and Siang 2017; Osin et al. 2017). In our day to day life, they are used as fuels, lubricants, and raw materials for the production of paints, plastic, solvents, and industrial chemicals (Abdel-Shafy and Mansour 2016). They make good fuels because their covalent bonds store a large amount of energy, which is released when the molecules are burned to form carbon dioxide and water. Even though they are composed of only two types of atoms, due to carbon’s unique bonding patterns there is a wide variety of hydrocarbons with single, double, or triple bonds between the carbon atoms. The bonding of hydrocarbons allows them to form open chains and rings. Hydrocarbons can be classified into two main categories, namely aliphatics and aromatics (Fig. 9.1).

9.2.1

Aliphatic Hydrocarbons

Based upon structure and bonding of carbon skeleton, aliphatic hydrocarbons can be categorized into four groups: alkanes, cycloalkanes, alkenes, and alkyne. Alkanes are saturated hydrocarbons which mean that compounds consist entirely of single bonds, so that each carbon atom forms four single bonds with the H and other C atoms. They can be described by the formula CnH2n + 2. Examples of compounds in this group are hexane, heptane, octane, and decane. Cycloalkanes: Cycloalkanes are also saturated hydrocarbons where carbon atoms are connected in a ring through single bonds. Hydrocarbons

Aliphatics

Alkanes

Cycloalkanes

Aromatics

Alkenes

Fig. 9.1 Classification of hydrocarbons

Alkynes

Monoaromatics

Polyaromatics

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Alkenes and alkynes are known as unsaturated hydrocarbons because some of the carbons are connected to fewer than four neighboring atoms. Alkenes contain at least one double bond, while alkynes contain at least one triple bond. Alkenes are characterized by the general molecular formula CnH2n, alkynes by CnH2n
2. Ethene (C2H4) is the simplest alkene and ethyne (C2H2) is the simplest alkyne.

9.2.2

Aromatic Hydrocarbons

Aromatic hydrocarbons contain at least one benzene ring. These are also called as arenes. These compounds possess special properties due to the delocalized electron density in benzene, including additional stabilization. Aromatic hydrocarbons can be classified into two types: monoaromatic hydrocarbons and polyaromatic hydrocarbons. Examples of monoaromatics are benzene, toluene, ethylene, and xylene (BTEX) (Fig. 9.2). Compounds in this group that contain more than two closed rings are termed polynuclear or polycyclic aromatic hydrocarbons (PAHs). Phenanthrene and pyrene are examples in this group. The main sources of PAHs in environment are incomplete combustion of several organic materials such as coal, oil, petrol, natural gas, wood, and some other petroleum products (Abdel-Shafy and Mansour 2016). There are more than 100 different PAHs present and they generally occur as complex mixtures. 16 candidates of them have been selected as priority pollutants by the United States Environmental Protection Agency (Fig. 9.3) (USEPA 1984).

9.3

Carbon-Based Nanomaterials

Carbon is the sixth most common element in the universe with approximately 0.2% of the total mass of earth (Nasir et al. 2018). However, carbon is one of the versatile elements in the universe. Carbon with a unique feature known as “allotropy” forms compounds that have completely different properties depending on the arrangement of the adjacent carbon atoms. Based upon bonding relationships with the neighboring atoms, carbon hybridize into a sp, sp2, or sp3 configuration. Diamond in sp3 as hardest and graphite in sp2 as fragile and brittle are two classical examples of carbon allotropes in three-dimensional structures (Mauter and Elimelech 2008). In applied nanotechnology research, carbon-based nanomaterials have attracted wide attention

Fig. 9.2 Structures of BTEX

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1) Naphthalene

2) Phenanthrene

5) Anthracene

6) Indeno[1,2,3-c,d]pyrene

7) Acenaphthene

10) Benzo[a]anthracene

11) Benzo[b]fluoranthene

9) Chrysene

13) Benzo[g,h,i]perylene

14) Benzo[k]fluoranthene

3) Pyrene

15) Fluorene

4) Dibenzo[a,h]anthracene

8) Acenaphthylene

12) Benzo[a]pyrene

16) Fluoranthene

Fig. 9.3 Structures of 16 PAHs

due to special features of these materials such as large surface area, high mechanical strength, high conductivity, and stability (Li et al. 2020; Mauter and Elimelech 2008). Based on their dimensionality, carbon-based nanomaterials are classified into different categories: 0D carbon nanostructures having all the three dimensions less than 100 nm (e.g. Buckminster fullerenes and quantum dots); 1D carbon nanostructures having only one dimension larger than 100 nm and two dimensions smaller than 100 nm (e.g. carbon nanotubes (CNTs) and carbon nanofibers (CNFs)); 2D nanostructures having one dimension smaller than 100 nm (e.g. graphene); and 3D carbon nanostructures all dimensions are greater than 100 nm (e.g. carbon sponges) (Visakh and Morlanes 2016).

9.3.1

Fullerenes

After diamond and graphite, fullerene (C60) is third allotrope form of carbon, was discovered in 1985 by Harold W. Kroto (University of Sussex, Brighton, England), Robert F. Curl, and Richard E. Smalley (Rice University, Houston, Texas, USA) (Kroto et al. 1985). Fullerene is excellent example of zero-dimensional carbon nanostructures having all the three dimensions less than 100 nm. In addition to the C60 molecule, fullerene may have smaller (C28 and C36) and larger (C70, C76 and C78) structures. Fullerene, C60 has icosahedral symmetrically closed-cage structure

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Fig. 9.4 Structure of Fullerene (C60)

with 20 hexagons and 12 pentagons in which each carbon atom is bonded to 3 other carbon atoms with sp2 hybridization linked together by covalent bonds, is the most common and more investigated fullerene. Due to its shape similarity with soccer ball, fullerene is also known as buckyball (Fig. 9.4). Fullerene (C60) has received significant attention due to its unique photophysical and photochemical properties (Snow et al. 2012; Ou et al. 2014; Barendt et al. 2018; Moor et al. 2015).

9.3.2

Nanotubes

Carbon nanotubes (CNTs) were discovered by the Japanese researcher SumioLijima in 1991, which boosted the research in the field of carbon related nanomaterials (Iijima 1991). Carbon nanotubes belong to the fullerene structural family are the one-dimensional analogues of zero-dimensional fullerene. Carbon nanotubes with a diameter of several nanometer are formed by rolling of graphene sheets into a hollow cylinder. The diameter of a CNT can be 50,000 times thinner than a human hair, yet a nanotube is stronger than steel per unit weight (Akbar et al. 2015). Carbon nanotubes (CNTs) have high mechanical strength, good electrical conductivity, and chemical stability. CNTs can be classified into two main types: single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). SWCNT is formed by rolling of a single layer of graphene into a hollow cylinder. An MWCNT can similarly be considered to be a coaxial assembly of cylinders of SWCNTs. Generally, multi-walled CNTs have a diameter from 0.4 nm up to a few nanometers and outer diameter varies characteristically from 2 nm up to 30 nm (Eatemadi et al. 2014). Each layer in MWCNTs interacts through Van der Waals force with interlayer spacing of MWCNTs ranging between 0.34 and 0.39 nm (Zhbanov et al. 2010). Based upon the graphene sheets rolled, CNTs categorized into three types, namely armchair, zigzag, and chiral. CNTs can be synthesized with either of the methods reported in literature such as chemical vapor deposition, vapor phase growth, arc discharge, laser ablation and thermal chemical vapor deposition, etc. (Szabo et al. 2010). CNTs with different functional group have shown potential

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A) Defect-group functionalization

B) Covalent sidewall functionalization

SWNT

C) Noncovalent exohedral functionalization with Surfactants

D) Noncovalent exohedral functionalization with polymers

E) Endohedral functionalization with C60

Fig. 9.5 Methods for functionalization of single-walled carbon nanotubes (SWCNTs) (Hirsch 2002)

applications such as supercapacitors, sensors, solar cells, photovoltaic cells and absorbers, etc. The main functionalization possibilities of CNTs are: (a) functionalization of defect sites at the tube ends and side walls by oxidation and subsequent conversion into derivatives, (b) covalent sidewall functionalization using addition reactions and subsequent nucleophilic substitution, (c) noncovalent exohedral functionalization with surfactants, (d) noncovalent exohedral functionalization with polymers, and (e) endohedral functionalization with C60 (Hirsch 2002). These are represented in Fig. 9.5.

9.3.3

Graphene Oxide and Its Derivatives

Graphene (GN) was discovered in 2004 by Andre Geim and Konstantin Novoselov from the University of Manchester, England (Novoselov et al. 2004) awarded with a Nobel prize in 2010. Graphene is a two-dimensional allotropic form of carbon. GN in layered two-dimensional stable structure has carbon atoms exhibiting sp2hybridization connected by σ- and π-bonds (Yang et al. 2018). GN can be synthesized using various methods such as mechanical exfoliation, liquid phase exfoliation, and chemical vapor deposition (CVD) (Bhuyan et al. 2016). GN has many unique physical properties, such as large surface area, extremely high mechanical rigidity, high thermal stability, exceptional electric and chemical properties (Thangamuthu et al. 2019; Novoselov et al. 2004, 2005). GN can be used in various applications such as solar cells, energy storage device, supercapacitors, batteries,

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Fig. 9.6 Surface functionalization of graphene (Priyadarsini et al. 2018)

Fig. 9.7 Application of carbon-based nanomaterials

sensors, and environmental remediation (Thangamuthu et al. 2019; Novoselov et al. 2004, 2005). Graphene derivatives such as graphene oxide (GO) and reduced graphene oxide (RGO) are high performance carbon materials which has high specific surface area and rich functional groups on its surface (Geim 2009; Allen et al. 2010; Patel et al. 2019; Pei and Cheng 2012; Mauter and Elimelech 2008) (Fig. 9.6). With the help of oxidation processes the GN can be oxidized to form graphene oxides (GOs), with a range of surface O-functionalities such as carboxyl, carbonyl, hydroxyl, and phenol groups. With functional group manipulations, these high surface nanomaterials can be used for various applications (Smith et al. 2019; Kuilla et al. 2010; Zhu et al. 2010).

9.4

Application of Carbon-Based Nanomaterials for Removal of Hydrocarbons

In applied nanotechnology research, carbon-based nanomaterials have attracted wide attention due to special features of these materials, such as high specific surface area, adjustable pore volume, reactivity, strong sorption, hydrophilic and hydrophobic interactions (Li et al. 2020; Mauter and Elimelech 2008). Based upon these unique properties, carbon-based nanomaterials have been enabled significant progress in their environmental remediation applications. In this section, applications of carbon-based nanomaterials for removal of hydrocarbons from environment are divided into three parts (Fig. 9.7).

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Carbon-Based Nanomaterials in Adsorption Technology

Nano-adsorbents have been used for removal of heavy metals, fluoride, chlorophenols, dyes, hydrocarbons, and radionuclide (Schnorr and Swager 2011; Ren et al. 2011). Adsorption technique has proven to be very efficient for removing of contaminants from wastewaters. Conventional adsorption using activated carbon as adsorbents has been widely used for this purpose (Li et al. 2020). Adsorption is based upon surface chemistry, whereby the pollutants are selectively removed from an aqueous solution by attaching the solute (adsorbate) into a solid surface (adsorbent). Compared to other alternative processes including coagulation, filtration, precipitation, and oxidation, adsorption is economical, simpler in design, and higher efficiency in removing hazardous pollutants. Researchers are in quest of the new improved adsorbents with high adsorption capacity, high sensitivity, high selectivity, easy recyclable, and low cost (El-Din et al. 2017; Bandura et al. 2017; Al-Jammal et al. 2020). Carbon-based nanomaterials possessing high surface-areato-volume ratio and good surface modification ability have inspired widespread attention as a new type of adsorbents for the removal of various inorganic and organic pollutants from different matrix (Schnorr and Swager 2011; Ren et al. 2011; Chin et al. 2007). Large numbers of articles published on the adsorption of pollutants using variety of carbon-based nanomaterials including CNTs, GN, and GO. Bina et al. (2014) studied removal of benzene, toluene, ethylbenzene, and xylene (BTEX) from aqueous solution by MWCNTs, SWCNTs, and hybrid carbon nanotubes (HCNTs). Tubes of MWCNTs were opened as a sheet using hybrid of MWCNTs and silica (HCNTs). This study showed that SWCNTs showed better adsorption capacity for BTEX than the MWCNTs and HCNTs. The adsorption capacity for MWCNTs and SWCNTs follows the following order: xylene>ethylbenzene>toluene>benzene; for HCNT, the order is ethylbenzene > xylene > toluene > benzene. The results of desorption study showed that BTEX adsorbed on SWCNTs can easily be desorbed at 105  2  C and recycled. Organic pollutant structure and adsorptive interactions with CNTs play important role in their removal. Chen et al. (2007) evaluated adsorption of organic compounds with varied physical-chemical properties (hydrophobicity, polarity, electron polarizability, and size) to three different types of CNTs (one SWNT and two MWNTs). They found that the adsorption affinity correlated poorly with hydrophobicity but increased in the order of nonpolar aliphatic < nonpolar aromaticsm-xylene >o-xylene >p-xylene > toluene (227.05, 138.04, 63.34, 249.44, and 105.59 mg/g). The adsorption isotherms fitted well with the Langmuir and D-R models and followed the pseudosecond-order model for the adsorption of all TEX pollutants. Abbas et al. (2017) used wet impregnation technique for synthesizing iron oxide impregnated CNTs and used for removal of toluene and p-xylene. They studied effect of contact time, adsorbent amount, and initial concentration. Results demonstrated higher removal of p-xylene compared with toluene under almost similar experimental conditions. Adsorption capacity of p-xylene was calculated using Langmuir model fit as 219 mg/g and 458 mg/g for pure and iron oxide impregnated CNTs while it was 127 mg/g and 381 mg/g for toluene adsorption using pure and iron oxide impregnated CNTs. Graphene (GN) has a large theoretical specific surface area of 2620 m2g
1 and large delocalized π -electrons which indicate its potential for the adsorption of various pollutants in environment (Guo et al. 2014). With the help of oxidation processes the GN can be oxidized to form graphene oxides (GOs), with a range of surface O-functionalities such as -OH, –CO, and –COOH, -OC6H5 (Geim 2009; Allen et al. 2010; Patel et al. 2019; Pei and Cheng 2012; Mauter and Elimelech 2008). With functional group manipulations, these structures can easily disperse in aqueous solution through bonding with polar structure. In literature, graphene and its derivatives have been widely employed for adsorption of various pollutants such as heavy metals, dyes, phenol, pesticide, pharmaceuticals, and hydrocarbons. Some studies have reported the efficiency of GN and GO for adsorption of PAHs. Wang et al. (2014a) studied the adsorption of polycyclic aromatic hydrocarbons by GN and GO nanosheets and evaluated the role of morphology and the delocalized π-electron system in the adsorption of organic molecules (PAHs) onto adsorbent (graphene nanomaterials). 3-PAHs, namely naphthalene, phenanthrene, and pyrene were chosen as the adsorbates for this study. In results, GN displayed high affinity to the polycyclic aromatic hydrocarbons (PAHs), whereas after attaching oxygen to GN, GO adsorption was significantly reduced. The high affinities of the PAHs to GN are dominated by π
π interactions. The relative adsorption affinity of the contaminants was naphthalene