Sustainable Materials for Sensing and Remediation of Noxious Pollutants

By Inderjeet Tyagi and Rama Rao Karri

Due to rapid urbanization and development, water get polluted by the noxious waste released from industrial, sewage and agricultural runoffs. Sustainable Materials for Sensing and Remediation of Noxious Pollutants covers two most widely used aspects in the field of wastewater i.e. sensing and rapid remediation with a possible solution of successful technology commercialization.

Chapters include information on low cost materials as sensing and remediating agents for the rapid removal of noxious impurities from wastewater. It includes chapters on the sensing of noxious metals, low cost adsorbents for the removal of noxious impurities i.e. inorganic (metal ions) and organic (dyes). Additional chapters include future/upcoming scopes of work and one chapter on the general introduction of the field. The book content will be technical and focused for the audience like graduate students, academicians, researchers and industrial professionals.

Sustainable Materials for Sensing and Remediation of Noxious Pollutants is single reference source for environmental scientists and engineers interested in low cost sensing and remediation strategies.

• Assists readers in developing new strategies to address the issues related to sensing and remediation activities
• Includes low cost materials for sensor and adsorbent development allowing professionals to make decisions based on economic considerations
• Provides alternatives for the development of socioeconomically sustainable products for sensing and remediation application

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 5, 2022
• ISBN: 9780323994262

Book preview

Introduction

Dr. Inderjeet Tyagi, Centre for DNA Taxonomy, Molecular Systematics Division, Zoological Survey of India, Ministry of Environment, Forest and Climate Change (MoEFCC), New Alipore, Kolkata, West Bengal, India

Prof. Dr. Joanna Goscianska, Department of Chemical Technology, Faculty of Chemistry, Adam Mickiewicz University in Poznań, Poland

Prof. Dr. Mohammad Hadi Dehghani, Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran, Institute for Environmental Research, Center for Solid Waste Research, Tehran University of Medical Sciences, Tehran, Iran

Dr. Rama Rao Karri, Petroleum and Chemical Engineering, Faculty of Engineering, Universiti Teknologi Brunei (UTB), Gadong, Brunei Darussalam

Water scarcity is one of the major problems in many parts of the world, and, as a result, water pollution is receiving increasing attention. Water plays a crucial role in accomplishing sustainable livelihood, and achieving clean water is one of the main sustainable development goals (SDGs). Surging human population and resource consumption are the two major issues the human race is trying to address to lead a sustainable lifestyle. Water is an essential component for the sustenance of life. However, the available water resources on the earth are being depleted owing to pollution. It is very evident that urbanization and industrialization have resulted in the exploitation of natural resources all across the globe. Pollution of natural water resources with organic (carbohydrates, dyes, fertilizers, oil and grease, pesticides, pharmaceuticals, plasticizers, polyaromatic hydrocarbons, proteins, etc.) and inorganic (heavy metals) pollutants has become a challenging issue in many countries.

Urban and industrial wastewaters constitute the most important contamination sources of rivers, lakes, reservoirs, and oceans, and increasing industrialization has put pressure on the demand for water resulting in a huge increase in wastewater production as well. Since there is water shortage globally, wastewater treatment and water reuse have become highly significant. Therefore, removing pollutants to prevent pollution of water sources seems to be very necessary. Recent advances have made it possible to partially solve many of the problems associated with water quality and pollution, as well as the protection of water resources using various water treatment techniques. Even though several approaches have been developed for efficient water purification, optimal water purification methods available at a low cost have been undertaken and they are affordable to the developing nations. The adsorption technique using a solid adsorbent meets the above requirements because it offers low installation cost and easy operation with high efficiency and is affordable and environmentally friendly, thus making it one of the preferred methods for water purification.

Green technology appears to be one of the effective strategies to alleviate toxicity by utilizing natural resources to produce nanomaterials and, simultaneously, offers extensive benefits such as reduced operating costs, good biocompatibility, thermal and chemical stability, and reduced environmental impacts. With the salient features of nanotechnology and nanomaterials, in the last decade, there has been a rising interest in the growth of eco-friendly, solid material-based nanoparticles and nanoadsorbents. Nanoadsorbents are widely used to treat contaminated water to remove organic and inorganic contaminants. Nanoparticles have important properties that have enabled them to be widely considered as a suitable adsorbent. They act as a sorbent selective for the adsorption of metal ions and anions. In addition, nanomaterials can be functionalized with different chemical groups to increase their affinity to certain compounds. Due to their high surface area, size, and optical, electronic, and catalytic properties, nanomaterials make it possible to create better and more cost-effective water treatment approaches.

This book provides an overview of the various methods of detecting and removing organic and inorganic contaminants from aqueous solutions. The compiled chapters describe smart and advanced porous nanomaterials, which are applied in the relatively low-cost and effective processes of adsorption and sensing of dyes, pesticides, pharmaceuticals, and heavy metal ions. An important aspect is a thorough analysis of the impact of these pollutants on the environment and human health and highlighting the benefits of removing them from the environment using the most promising technologies, taking into account the possibility of their transfer from the laboratory scale to the industrial scale. In addition, the book presents the most effective methods for removing toxic contaminants from water solutions and air using sustainable nanoporous adsorbents.

This edited book will be very useful for MSc and PhD students who are working in the environmental chemistry field; students who are working in the environmental science field; students who are working on water and wastewater purification technologies; researchers working on environmental nanotechnology; researchers and academics who are working on environmental remediation technologies; researchers and managers who are working in water and wastewater plants and industries; researchers who are working in the environmental toxicology field; researchers and engineers who are working on water treatment and green chemistry; managers and industries that wish to implement professionally advanced technologies; and policymakers working on environmental pollutants and remediation.

Chapter 1: Sustainable materials for sensing and remediation of toxic pollutants: An overview

Inderjeet Tyagia,⁎; Pratibha Singhb; Rama Rao Karric; Mohammad Hadi Dehghanid,e; Joanna Goscianskaf; Kaomud Tyagia; Vikas Kumara    a Centre for DNA Taxonomy, Molecular Systematics Division, Zoological Survey of India, Ministry of Environment, Forest and Climate Change, Government of India, Kolkata, West Bengal, India

b Department of Chemistry, University of Delhi, New Delhi, India

c Petroleum and Chemical Engineering, Faculty of Engineering, Universiti Teknologi Brunei, Bandar Seri Begawan, Brunei Darussalam

d Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

e Institute for Environmental Research, Center for Solid Waste Research, Tehran University of Medical Sciences, Tehran, Iran

f Faculty of Chemistry, Department of Chemical Technology, Adam Mickiewicz University in Poznań, Poznań, Poland

⁎ Corresponding author.

Abstract

Water pollution is a global issue and researchers as well as policy makers are coming up with new approaches and mitigation techniques to provide remediate the water pollution. The present chapter provides a general overview of the sustainable materials for sensing and remediation of noxious inorganic and organic impurities. The characteristic properties required for the material to be an excellent adsorbent and sensor, along with different characterization methods, were discussed. Various commonly used detection techniques are also discussed. Further, the details about different types of sensors and adsorbents used for sensing and remediation of noxious organic and inorganic impurities have been provided for better understanding to the readers.

Keywords

Sustainable material; Sensing; Remediation; Heavy metals; Dyes; Wastewater treatment

Abbreviations

AB1 

Acid black 1

AB117 

Acid blue 117

AB25 

Acid blue 25

AO19 

Acid orange 17

AO3 

Acid orange 3

AY36 

Acid yellow 36

BBG 

Basic brown G

BO2 

Basic orange 2

BV14 

Basic violet 14

CR 

Congo red

CV 

Crystal violet

DO13 

Disperse orange 13

DB3 

Disperse blue 3

DB86 

Disperse blue 86

DB9 

Disperse blue 9

DNB106 

Direct navy blue 106

DO26 

Direct orange 26

DR11 

Direct red 11

DR81 

Direct red 81

DV28 

Direct violet 28

DY211 

Direct yellow 211

DY3 

Direct yellow 3

DY50 

Direct yellow 50

EBT 

Eriochrome Black T

MB 

Methylene blue

MG 

Malachite green

MO 

Methyl orange

MV 

Methyl violet

RB 19 Reactive blue 19

RB2 

Reactive blue 2

RB74 

Reactive blue 74

RhB 

Rhodamine B

RR15, RB2, RB19,RB74 Reactive red 15, Reactive blue 2, 19,74

VBE 1, 4, 5,6,14 Vat blue 1, 4, 5, 6, 14

VBR 1, 68, 72, Vat brown R 1, 68, 72.

VR13 

Vat red 13

VV1 

Vat violet 1

VY1 

Vat yellow 1

Acknowledgment

Dr. Inderjeet Tyagi is thankful to the Director, Zoological Survey of India, Ministry of Environment, Forest and Climate Change, Kolkata, for continuous motivation and moral support. Further, Dr. Tyagi extends his sincere thanks to the RAMC for considering the project entitled "DNA Metasystematics studies for the assessment of Macrobiome and Microbiome in fresh water ecosystem with relation to the Noxious Pollutants" under ZSI core funding.

1: Introduction

Water being the most essential element and basic requirement of the living creatures on planet earth, water bodies cover > 70% of the entire earth’s surface area, out of which only 0.002% is considered as appropriate for human consumption.¹ Due to rapid urbanization and industrialization, it is a tough challenge for us to prevent this important resource from getting polluted from inorganic and organic pollutants.²

Inorganic pollutants majorly include trace elements (heavy metals) having a density greater than 4 ± 1 g/cm³, such as Nickel (Ni), Lead (Pb), Arsenic (As), Chromium (Cr), Copper (Cu), Cadmium (Cd), Zinc (Zn), Mercury (Hg), Iron (Fe), etc.³–¹¹ They are introduced into the water or wastewater through natural and anthropogenic activities from sectors such as mining, agricultural activities, industrial outlets (textile, tanneries, nuclear, etc.), domestic sewage, and others. These metal impurities have a detrimental impact on human health and prevailing flora and fauna.¹² Heavy metals such as Copper (Cu) in an excess amount above the permissible limit may lead to liver damage, kidney disorders, muscle impairment, insomnia, and inhibits enzymatic activities.¹³ Besides, Chromium (Cr) intake (even in trace amounts) may lead to nausea, headache, and diarrhea.¹⁴ Further, the intoxication of Mercury (Hg) leads to disorders such as circulatory, nervous and rheumatoid arthritis, etc.¹³ On the other hand, the characteristics of heavy metals such as high solubility, non-biodegradable nature, and high stability tends them to migrate throughout the aqueous system and gets accumulated in the food chain which in turn hampers the growth of food chain elements. These heavy metals not only deteriorate the faunal and human health but also possesses negative impact on the plants through inhibiting photosynthesis, stunting growth, altering chlorophyll synthesis, altered enzymatic activities, etc.¹⁵

Organic impurities majorly constitute dyes not just limited to toxic cationic (methylene blue, safranin-O, malachite green, crystal violet, etc.) and anionic dyes (Eriochrome Black T, methyl orange, Congo red, Alizarin red S, etc.).¹⁶–²³ Polyaromatic hydrocarbons (PAHs),²⁴ Chlorophenols (CPs)²⁵ etc. Thus, it is essential to detect and remediate these impurities from water and wastewater to make it fit for day-to-day activities. These dye molecules and organic impurities pose a serious threat to the ecosystem and lead to several disorders such as cancer, mutation, and other irregularities in vital organs such as reproductive, nephrological, hepatic, and neurological disorders etc.²⁶–²⁸ In addition to this, these impurities pose a serious threat to the floral ecosystem, it hampers photosynthesis by limiting the transmission of sunlight which in turn affect the food chain of the aquatic community.²⁹–³¹ The different sources responsible for the release of dyeing impurities are textile, paint, and pigment industries, etc.³²–³⁶ Approximately more than 0.1 million different types of dyes are commercially available, and these contribute directly or indirectly to the detrimental on the ecosystem due to complex aromatic structure.³⁷–⁴⁰ The classification of dyes can be better understood from Table 1.

Table 1

Reproduced with permission from ref. 41.

Keeping in view these noxious pollutants, to date, several efforts have been made to detect and remediate these noxious impurities from water and wastewater. Different materials such as coumarin,⁴² rhodamine,⁴³ Schiff bases,⁴⁴ and phthalocyanine tetrafonic acid⁴⁵ were used as a sensor for the detection of metal as well as organic impurities. Moreover, the sensor used in environmental applications can be classified into two on-site for real applications and others that require a laboratory environment. Although the second one has great technological advantages, but its non-portable nature and bulkiness are major drawbacks. As a result, it is limited to only labs and not considered for on-site sensing and environmental monitoring. Attempts have been made to subside this major drawback to make them eligible candidates for the on-site environmental monitoring through tuning them under real environmental conditions. As a result, electrochemical and potentiometric sensors have emerged as potential candidates for sensors.⁴⁶–⁵⁰

For remediation of noxious impurities, different techniques such as oxidation, membrane process, coagulation/flocculation, biological treatment methods, and adsorbents were applied. The advantages and disadvantages associated with different removal techniques explored to date can be better understood from Fig. 1. Some of the novel adsorbents derived from waste products, bio-materials, metal oxides, naturally occurring materials, cellulose-lignin derived, nanoparticles, etc., were used as sustainable material across the globe for the remediation of noxious pollutants.³–¹³,¹⁵–²⁰

Fig. 1

Fig. 1 Advantages (A) and disadvantages (D) associated with removal techniques in general. (Reproduced with permission from ref. 41.)

The present chapter presents an overview of the characteristics of sustainable material for an application as adsorbent and sensor for the remediation and detection of noxious impurities, characterization methods, detailed overview of different materials used as adsorbents, and sensors for inorganic and organic impurities.

2: Characteristics of sustainable material for adsorbent and sensor

To remove noxious impurities, the sustainable adsorbent must possess characteristic properties such as cost-effectiveness, facile eco-friendly routes of synthesis, high selectivity, exponential adsorption capacity, and long shelf life. Further, other properties which play a significant role in the adsorptive removal of noxious impurities were active sites, specific surface area, pore-volume, pore structure, and surface functional moieties.⁵¹ Based on the pore size, IUPAC classified the porous materials as macroporous (> 50 nm diameter), mesoporous (2 to 50 nm), and microporous (less than 2 nm diameter).⁵²

On the other hand, the characteristics properties of sensors have no boundaries as it is a devices used to transform the different information related to chemical or physical properties in the form of a signal. The designing of sensors is always a challenge. It essentially requires a basic understanding of the nature of inter and intramolecular interactions, its ability to create certain nanosized architectures, and computing of the signal/response produced due to the interaction of these architectures. Thus, it can be concluded that the synthesis or designing of modern era sensors has no boundaries, and it works on the interfaces of different science, i.e., chemical, physical, material science, and engineering.⁵³

3: Characterization techniques

Characterization is essentially required to understand the properties of the material. It is one of the significant steps before applying the material in different fields, whether it be wastewater treatment or sensing. Furthermore, it has emerged as an independent research field and is widely recommended by researchers across the globe.⁵⁴–⁵⁶ The general overview of different techniques and their role in material characterization can be better understood from Fig. 2. Thus, the commonly adopted characterization techniques are as follows:

•Proximate and ultimate analyses: It includes moisture, ash, fixed carbon, volatile matter, elemental analyses such as C, H, O, N, and S, and chemical compounds.

•Brunauer-Emmett-Teller (BET), Barret-Joyner-Halender (BJH): It includes analyzing the specific surface area, pore volume, and pore size distribution.

•Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HR-TEM), Scanning transmission electron microscopy (STEM): It includes morphological analyses such as surface morphologies and microscopic features.

•Energy-dispersive X-ray spectroscopy (EDX): It is widely used for mineral elements and their dispersion.

•SEM-EDX: It is widely used for surface elemental composition and distribution analyses.

•X-ray photoelectron spectroscopy (XPS): This advanced technology is used to analyze the surface chemical composition and chemical state of each element.

•Fourier transform-infrared spectroscopy (FT-IR), Raman spectroscopy,Böehm titration: It is used to analyze the surface functionalization’s, i.e., functional group present on the surface of the material and structures such as graphite/amorphous.

•Thermogravimetric analyzer (TGA): It elucidates the activation energy and structural thermal stability.

•X-ray diffraction (XRD): It is used for the mineralogical analyses and nature of the material, i.e., crystalline or amorphous.

•X-ray fluorescence spectroscopy (XRF): It is used to quantify compounds and inorganic matters.

•Solid-state nuclear magnetic resonance (NMR): It is used to elucidate the aromaticity and the content of aromatic carbons.

•Electron spin resonance (ESR) and Electron paramagnetic resonance (EPR): It is used to elucidate the spin of unpaired electrons.

•Scanning transmission soft X-ray microscopy (STXM): It is widely used for species distribution, state, behavior, and chemical composition analyses.

•Synchrotron-based near-edge X-ray absorption fine structure spectroscopy (NEXAFS): It is used to decipher the electronic states, C species structure, and surface chemistry.

•X-ray absorption near-edge structure spectroscopy (XANES): It is used to study the oxidation states and density of redox-sensitive heavy metals.

•Extended X-ray absorption fine structure spectroscopy (EXAFS): It is used to elucidate the metal-surface coordination status, atomic types, and number.

Fig. 2

Fig. 2 A general overview of different techniques and their role in material characterization. (Reproduced with permission from ref. 56.)

4: Detection techniques for noxious organic and inorganic impurities

Detection of noxious impurities is essentially required before remediation from water or wastewater. Keeping in view the cost-effectiveness of the whole process, the selected technique must possess properties such as eco-friendly, high-selectivity, and precise low limit detection etc.⁵⁷ The detailed overview of some of the techniques used to detect noxious pollutants are as follows.

4.1: Advanced instrumental techniques

Noxious organic and inorganic impurities were generally detected with great ease and precision using different spectroscopic methods. For detecting heavy metal impurities, techniques such as AAS, ICP-OES, ICP-MS, XRF/TXRF, ICP-AES, etc.,⁵⁷–⁵⁹ were preferred. The major advantage of these techniques is their ability to detect heavy metals, even trace quantity (Femtomolar range), with great precision.⁶⁰ Shirkhanloo and Mousavi used AAS to detect metals such as Cu² +, Pb² +, and Cd² + in aqueous solution even in trace quantities 2, 3, and 0.2 μg/L, respectively.⁶¹ Other advanced techniques such as ICP-MS can detect the metal impurities in the range of parts per billion (ppb) to parts per trillion (ppt).

Further, with the synchronization of these techniques with chromatography and laser ablation, the detection limit can be optimized.⁶² Although the spectroscopic technique is most precise, and it involves expensive instruments and a complex mode of operation, which requires trained personnel to run and calibrate from time to time.⁶³ The Limit of Detection (LOD) of different techniques for different metal ions can be better understood from Table 2.

Table 2

Reproduced with permission from ref. 64.

The detection of organic impurities was carried out using techniques such as HPLC, fluorescence detection (FD), mass spectroscopy, tandem mass spectroscopy, real time-time of flight mass spectrometry, UV-Vis, Raman spectroscopy, and surface-enhanced Raman spectroscopic methods (SERS).⁶⁸–⁷⁴

4.2: Sensors

4.2.1: Electrochemical

It is a class of chemical sensors in which electrodes act as transducer elements in the presence of analytes. As discussed in Section 2, sensors used diverse characteristics properties to detect environmental pollutants in water and wastewater, and these parameters vary from case to case, whether it be physical, chemical, or biological parameters.⁷⁵ It works on the principle of generating electrical signal/response in the presence of analytes.⁷⁵ It is widely used as the techniques involving the electrochemistry principles that have great potential with respect to other techniques due to properties such as cost-effectiveness and facile eco-friendly routes to detect noxious environmental pollutants such as heavy metals, dyeing impurities, complex organic compounds such as pesticides, PAHs, CPs, and herbicides etc.⁷⁶ Further, electrochemical sensors are different origins such as amperometric, voltammetric, and potentiometric etc.⁷⁷

Amperometric sensors were based on the redox mechanism, and they measured current as a result of oxidation and reduction of electroactive substance in a particular system undergoing electrochemical reaction.⁷⁸,⁷⁹ Some of the efforts that have been made using amperometric-based electrochemical sensors for the detection of environmental pollutants are as follows.

Tucci et al. developed a microbial amperometric-based sensor for sensing herbicides such as atrazine and diuron in the aqueous samples.⁸⁰ On the other hand, amperometric sensors based on competitive reactions at nitroreductase@Layered double hydroxide (NLDH) for the detection of mesotrione were developed by researchers.⁸¹ Ayenimo and Adeloju developed an amperometric sensor from Ultrathin Polypyrrole-based glucose biosensor to detect noxious heavy metal impurities such as lead, mercury, cadmium, and copper in their ionic form (2 +).⁸² Moreover, an electrochemical for detecting phenols and catechol was developed by Quynh et al. It was a non-enzymatic sensor.⁸³

Voltammetric sensors were based on a powerful electroanalytical technique called Voltammetry. They are widely applied for detecting several environmental pollutants such as metal ions⁸⁴–⁸⁶ and complex organic molecules such as pharmaceutical compounds, pesticides, dyes, and herbicides in the aqueous samples.⁸⁷–⁹³

4.2.2: Optical

The most widely used optical sensors were mainly based on fluorescence sensors and colorimetric sensors, and the details related to each of them are mentioned below.

The former involves the use of specific fluorescence probes, and it was analyzed through changes in the intensity of fluorescence after its interaction with analytes and based on this the concentration of analytes was measured. Apart from the conventional single fluorophore sensor, the advanced technique, i.e., fluorescence resonance energy transfer (FRET), was actively used to detect the impurities with great sensitivity. As a part of the mechanism, the acceptor (Quencher species), when located at a certain distance, can quench the donor (fluorescent species) fluorescence during the energy transfer process, and the change in fluorescence intensity of acceptor or donor species will result in the analysis of the concentration of analytes.⁹⁴ On the other hand, colorimetric sensing is a cost-effective, simple and facile technique that generally relies on the change in color of a mixture solution having gold nanoparticles (AuNPs) and the analytes.⁹⁵,⁹⁶ This is because optical absorption of AuNPs is strongly affected by the refractive index of the surrounding media and the interparticle surface plasmon coupling, and the analytes present triggered in the aggregation and redispersion of the AuNPs and results in the significant color change. Further, the NPs were functionalized with specific molecules that only bind with the analytes understudy for high sensitivity and specificity.⁹⁵,⁹⁶ Several optical sensors for different environmental pollutants all⁴²–⁴⁵,⁹⁷–¹⁰³ have been developed to date, and it is not practically possible to discuss them all.

5: Remediation methods for the noxious organic and inorganic impurities

Water and wastewater treatment technologies for the remediation of noxious impurities in terms of materials and techniques were classified into two, i.e., conventional treatment and non-conventional treatment. The conventional treatment technologies include chemical precipitation, coagulation/flocculation, membrane technologies, ion-exchangers, electrochemical technologies, etc. On the other hand, non-conventional technologies involved adsorption, Fenton-like reactions, microbial fuel cell, and nanotechnology. A general overview of the conventional and non-conventional treatment technologies can be obtained from Figs. 3 and 4.

Fig. 3

Fig. 3 A general overview of different conventional wastewater treatment technologies. (Reproduced with permission from ref.64.)

Fig. 4

Fig. 4 A general overview of different non-conventional wastewater treatment technologies. (Reproduced with permission from ref. 64.)

Further, adsorption is the most widely used wastewater treatment technology, as indicated from the Scopus database. Different sustainable adsorbents such as activated carbon, naturally occurring materials, biochar (agricultural wastes), industrial wastes, nanoparticles, nanomaterials, functionalized adsorbents, etc.,³–¹³,¹⁵–⁴⁰ were majorly used for remediation of noxious impurities.

As the present chapter is majorly focused on sustainable materials. So, our major focus will be on the non-conventional wastewater treatments methods that involve various materials. Further, it is not feasible to provide details about all the developed/synthesized adsorbents in this chapter, but details of some most widely used adsorbents are presented below.

5.1: Activated carbon

It is one of the most widely used adsorbents for the remediation of noxious inorganic and organic impurities. Due to properties such as porous nature, high specific surface area, and ease to surface functionalization, it shows excellent adsorbent properties. Some of the common materials that were used as activated carbon upon physical and chemical activation are coal, naturally occurring materials, lignin and cellulose derivatives, agricultural waste, rubber tire, industrial wastes, fruit stones, etc.¹⁰⁴–¹¹⁵

Ghaedi et al. developed the activated carbon from oak tree wood to remove noxious sunset yellow; results obtained revealed that maximum adsorption of 5.8377–30.1205 mg/g was observed from the adsorbent dosage of 0.05–0.25 g.¹⁰⁴ An adsorbent based on functionalized activated carbon with Ag nanoparticles to remove noxious methylene blue dye. Results revealed that the developed adsorbent possesses excellent adsorption capacity, and ~ 95% removal of MB dye was observed within 4 min.¹⁰⁵ Nekouei et al. used Ni(OH)2 functionalized activated carbon (Ni(OH)2-NP-AC) for the removal of malachite green (MG). The synthesized adsorbent possesses a specific surface area ~ 960 m²/g with excellent removal properties.¹⁰⁶ Dehghanian et al. synthesized SnS NPs modified activated carbon (SnS-NP-AC) to remove toxic Congo red (CR) dye from the aqueous solution. The synthesized adsorbent possesses excellent adsorption capacity, and ~ 99% dye removal was observed.¹⁰⁷ In one other study, Al-Aoh used coconut husk fiber-based activated carbon for the adsorptive removal of nitrophenol, methylene blue, and acid red-27 dye.¹⁰⁹ Ghasemi et al. synthesized tetraethylenepentamine functionalized activated carbon from Rosa canina L. The synthesized adsorbent shows a maximum adsorption capacity of 333.3 mg/g.¹¹⁰ Heibati et al. used activated carbon prepared from walnut and poplar woods to remove noxious AR18 dye. The developed adsorbent took around 90 min for the removal of AR18 dyes.¹¹¹ Asfaram et al. used ZnS: Cu NPs modified activated carbon for the removal of Auramine-O; the findings obtained revealed that the optimized parameter for the removal of 99.76% of this noxious dye was 0.02 g (adsorbent dosage), 20 mg/L (initial dye concentration), 7 (pH) and 3 min (sonication time) with the maximum adsorption capacity of 183.15 mg/g.¹⁶

Gupta et al. used scrap tire as activated carbon to remove noxious Ni (II) ion from the aqueous solution, and the synthesized adsorbent shows maximum adsorption capacity of 25 mg/g with approximately 95% removal within 50 min of contact time.⁵ Karmacharya et al. used activated carbon derived from tire and functionalized its alumina composite, and the results obtained revealed that maximum adsorption capacities for both the ionic form of As (V) and As (III) were 23.8 and 14.28 mg/g, respectively.⁸ Karri et al. used palm kernel shell-based activated carbon to remove Zn (II) from the aqueous solution. The findings revealed that the optimized values of effective parameters such as pH, residence time, adsorbent dosage, and temperature for the 90% removal were 5, 53.2 min, 44.8 mg/L, 15.5 mg/L, and 40°C, respectively.¹⁰ On the other hand, Sankaran et al. derived activated carbon from eggshell wastes to remove noxious metal impurities such as copper, zinc, nickel, and cobalt along with microbial products.¹² Wong et al. reported the 95% removal of noxious Cr⁴ + onto the activated carbon obtained from rice husk.¹¹⁶ Wang et al. modified activated carbon with tartaric acid and applied it to remove copper and lead ions from the aqueous solution.¹¹⁷ Bernard et al. modified activated carbon derived from coconut shell using ZnCl2 for the removal of heavy metals such as lead, iron, copper, and zinc.¹¹⁸

5.2: Carbon nanotubes

Carbon nanotubes (CNTs) have developed the great interest of researchers across the globe to be used as adsorbents for the removal of noxious inorganic or organic impurities due to their unique physical and chemical properties. Two well-known forms of CNTs are Single-walled carbon nanotubes (SWCNTs) and Multiwalled carbon nanotubes (MWCNTs).¹¹⁹ An in-depth analysis revealed that the enhanced adsorption capacities of CNTs were due to the morphology, number of active sites, and fundamental structural features along with π-conjugative structures.¹¹⁹

Chen et al. used CNTs for the adsorptive removal of Ni² + and Sr² + and observed that it depends on the effective parameter such as pH and ionic strength. Further, the MWCNTs shows great removal potential for Sr² +.¹²⁰ In one another study, Yang et al. carried out the removal of Ni² + onto the MWCNTs, finding obtained revealed that adsorption increases as the pH increases, but the optimized pH for this process was 8.¹²¹ Lu et al. used SWCNTs and MWCNTs as adsorbents for the removal of Ni² + and observed that both the adsorbent possesses excellent adsorption capacity even after several regenerative cycles.¹²² Li et al. used MWCNTs to remove Pb² + ions; results obtained revealed that adsorption capacity increases with an increase in temperature with the endothermic nature.¹²³ Moreover, Atieh functionalized MWCNTs and observed that upon acidification, MWCNTs shows enhanced adsorption capacity up to 20 times and 5 times with respect to un-modified MWCNTs and other surfaces, respectively.¹²⁴ Xu et al. applied oxidized MWCNTs for the removal of noxious Pb² + ions and observed that the adsorption process depends on the pH and followed pseudo-second-order model.¹²⁵ Likewise in metal impurities, CNTs were used for the remediation of several dyes such as Procion red MX-5B, Sufranine O, acid red 18, bromothymol blue, methyl blue, methyl violet, methylene blue etc.¹²⁶–¹³⁰

Moreover, the detailed overview of multiple adsorbents is available in a different chapter of the current book, and it will be of no use to furnish similar information in this chapter as it provides only a brief overview of technologies used in wastewater treatment.

6: Conclusion and future scopes

Although water is the most essential element for human life, it is one of the most exploited natural resources. Rapid urbanization and industrialization are majorly responsible for the deterioration of this natural resource through their toxic effluents in the form of inorganic and organic impurities to the nearby aquatic sources. These noxious impurities deteriorate the water and make them unfit for drinking and other day-to-day activities. Approximately 800 million people across the globe do not have access to safe drinking water. Keeping in view the importance of this natural resource, a sustainable material focussed on wastewater treatment and strict environmental policies implementation is essentially required across the globe so that zero-discharge limit of these noxious effluents from their sources may be achieved for the upliftment of the society.

References

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2 Vardhan K.H., Kumar P.S., Panda R.C. A review on heavy metal pollution, toxicity and remedial measures: current trends and future perspectives. J Mol Liq. 2019;290:111197.

3 Dehghani M.H., Taher M.M., Bajpai A.K., et al. Removal of noxious Cr (VI) ions using single-walled carbon nanotubes and multi-walled carbon nanotubes. Chem Eng J.