Usage of nanoparticles as adsorbents for waste water treatment: An emerging trend

Sustainable Materials and Technologies 22 (2019) e00128

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Usage of nanoparticles as adsorbents for waste water treatment: An emerging trend Priya Kumari ⁎, Masood Alam, Weqar Ahmed Siddiqi Department of Applied Sciences & Humanities, Faculty of Engineering and Technology, Jamia Millia Islamia, New Delhi 110025, India

a r t i c l e

i n f o

Article history: Received 22 April 2019 Received in revised form 31 August 2019 Accepted 5 September 2019

Keywords: Nano-particles Green synthesis Isotherms Kinetics

a b s t r a c t Nanotechnology is the most promising and under explored branch of science of 21st century. It has the capability of generating materials with unique and unusual properties, hitherto unknown to mankind. In recent years, it has presented its potential to contribute in solving one of the greatest issues of the modern world, i.e., waste water treatment. The present review emphasizes on the potential, the nano-particles (NPs) hold in advancing the waste water treatment and augmenting the water supply by developing the unconventional resources of water. The concept of adsorption is discussed and various nano-adsorbents mostly used in waste water treatment have been discussed categorically. The review also discusses the types of pollutants that can be removed by nanoadsorbents with a special mention of regeneration of the nano-adsorbents. The purpose of this review is to emphasize upon the importance of adsorption and NPs in the waste water treatment industry and to showcase how the NPs have the ability to revolutionise the waste water treatment industry. This review is an attempt to compile most of the relevant knowledge of the nano-adsorbents scattered over decades of literature. It also presents the harmful effects of dyes, pesticides and most common heavy metals present in waste water, showcasing the various adsorbents researchers have used to efficiently remove them. There have been several review articles in the literature but, to the best of our knowledge, there are none that cover the nano-adsorbents and their targeted pollutants across so many categories so comprehensively. The review convincingly establishes the potential of nano-adsorbents for waste water treatment. © 2019 Elsevier B.V. All rights reserved.

Contents 1. 2. 3.

4.

Introduction . . . . . . . . . . . . . . . . . . Adsorption . . . . . . . . . . . . . . . . . . . Types of nano-adsorbents . . . . . . . . . . . . 3.1. Carbon based . . . . . . . . . . . . . . 3.2. Metal NPs . . . . . . . . . . . . . . . . 3.3. Metal oxide based . . . . . . . . . . . . 3.3.1. Nano iron oxides . . . . . . . . 3.3.2. Nano manganese oxides . . . . . 3.3.3. Nano aluminium oxides . . . . . 3.4. Nano composites. . . . . . . . . . . . . Pollutants and their removal using nano-adsorbents 4.1. Inorganic pollutants . . . . . . . . . . . 4.1.1. Arsenic (As) . . . . . . . . . . . 4.1.2. Chromium (Cr) . . . . . . . . . 4.1.3. Cadmium (Cd) . . . . . . . . . 4.1.4. Lead (Pb) . . . . . . . . . . . . 4.1.5. Copper (Cu) . . . . . . . . . . . 4.1.6. Nickel (Ni) . . . . . . . . . . .

⁎ Corresponding author. E-mail address: [email protected] (P. Kumari).

https://doi.org/10.1016/j.susmat.2019.e00128 2214-9937/© 2019 Elsevier B.V. All rights reserved.

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4.1.7. Miscellaneous metal ions 4.2. Organic pollutants . . . . . . . 4.3. Biological pollutants . . . . . . 5. Regeneration of adsorbent . . . . . . . 6. Conclusion . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . References. . . . . . . . . . . . . . . . .

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1. Introduction Water is the fundamental for all the life forms to exist on this planet. With increasing population and industrialisation, the naturally occurring water resources are getting more and more contaminated [1–5]. Industrialization and improving lifestyle is driving up the demand of clean water. Clean water is not only needed in our houses, but in most of the industries as well. This ever growing pressure on existing water supplies to meet the needs of people is forcing them to opt and develop the methods for tapping into unconventional sources of water like rain water harvesting, contaminated fresh water, waste water, brackish water and sea water, to name a few. But these additional new resources cannot be used directly. The water needs to be treated and made fit for usage in household activities, industries or agricultural activities. In this scenario, waste water treatment becomes of utmost importance. Today, waste water treatment, in itself, has become an industry, which, in turn, adds to environmental pollution in some form or the other. The water treatment methods had been very limited up till recently, but with ever expanding human knowledge and advancing technologies, the researchers have developed various environment friendly and effective methods for waste water treatment [6–11]. In 2011, Ali et al., presented electro coagulation and electro-dialysis techniques for removing arsenic from water [6]. T.A. Saleh et al. (2012) used a CNT/ Magnesium oxide composite column to treat water with lead (II) ions contamination [7]. Similarly, V.K. Gupta et al., in 2011, presented alumina coated CNTs for removing lead [11]. In 2015, M. Ghaedi et al., used an apparatus combining adsorption and ultrasonic action to show that the combined usage of these techniques improved the quality of waste water purification significantly [12]. In the bygone decade, the NPs have emerged as an excellent option for tackling the global issue of water pollution and treatment. Recently, there has been a lot of research and development in the field of fabrication of NPs with specifically controlled morphologies and properties, making it an area of high interest. NPs, basically, are nano scale versions of their bulk counterpart. NPs are usually b100 nm in at least one spatial dimension. Owing to their extremely high specific surface area and reduced surface imperfections, they have very unique chemical, physical, optical, electrical, magnetic and biological characteristics. All these properties make them excellent adsorbents, effective towards a huge range of pollutants. Nano-technology powered modular and multifunctional processes for water treatment provide highly efficient and affordable solutions that rely less on large infrastructures and more on the technology [13]. Nano-technology and NPs based methods of waste water treatment not only overcome the current challenges of conventional methods but also offer the scope of optimum utilisation of unconventional water sources which were not tapped in until now. The impact of NPs on human health and our ecosystem or any potential adverse effects of treatment processes are huge.

2. Adsorption Out of the various methods of waste water treatment available and discussed in the literature, including Biotechnology [14], Catalytic processes [15], Membrane processes [16–21], Ionizing radiation processes [22], Magnetically assisted processes [23], etc., Adsorption is one of

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the most investigated techniques for removal of pollutants from aqueous mix [24–27]. Adsorption is preferred, mostly due to its high efficiency and simplicity [28]. Adsorption, by large, is preferred over other techniques of Waste water treatment in terms of initial cost, flexibility, ease of operation and effectiveness towards wide range of pollutants. Nano-adsorbents are NPs from organic or inorganic sources having high affinity for adsorption. Because of their high specific surface area, high porosity and active surface, they are highly effective in isolating wide range of contaminants of varying molecular sizes [29]. The nanoadsorbents work efficiently and rapidly, without releasing any toxic payload [30]. Another significant characteristic of nano-adsorbents is Regeneration. This means that after adsorption, the same NPs can be reused after a regeneration process wherein the adsorbate is separated from the NPs. K. Yang et al., in 2007, performed the experiments for desorption of hydrocarbons from carbon NPs in water [31]. 3. Types of nano-adsorbents There are a large number of nano-adsorbents used for waste water treatment. They have been found to be highly effective in removal of pollutants from water. However, a direct capacity comparison cannot be made as it depends upon various aspects, including the size and shape of the NPs, the operating conditions (like pH, temperature, reaction time) or experimental form(whether the study is conducted via batch experiments or column runs). The Nano-adsorbents are broadly categorised as below. 3.1. Carbon based For any nano-adsorbent, most important and defining characteristics would be its large surface area and its porosity. Literature shows that presently, a wide range of such materials are available like activated Carbon, zeolites, pillared clays, metal-organic frameworks, polymers, etc [32–36]. However, most prominent category, among all, can be the Carbon based adsorbents like Carbon Nano Tubes (CNTs), Activated carbon [37], Porous Carbon [38,39], Graphene and Fullerenes, all of which exhibit high thermal stability and high adsorption capability [40–43]. Carbon nano tubes [44–46] are an allotrope of Carbon. Simply put, CNTs are cylindrically shaped structural form rolled up in a tube-like structure. They are, in majority, of two types: (a) Single Walled Carbon Nano-tubes (SWCNTs), which have a single graphene sheet rolled up as a tube; (b) Multi Walled Carbon Nano-tubes (MWCNTs), which have multiple graphene sheets rolled up as a tube like structure. Fig. 1 shows a simple structure of both types of CNTs. CNTs are one of the most researched nano-sorbents amongst the various Carbon based adsorbents. Literature survey shows that the CNTs are highly effective towards adsorption of organic and inorganic pollutants present in water [47,48].The CNTs have a very high surface active sites to volume ratio and hence, an exceptionally high sorption capabilities as compared to powdered activated carbon [49]. The activated surface for adsorption of a CNT is its external surface [50]. In 2008, Pan et al. [51] showed that CNTs, in water, form loose aggregates or clusters, thus, reducing the surface area. However, the interstitial grooves and gaps between them provide very highly active sites for adsorption for organic molecules.

P. Kumari et al. / Sustainable Materials and Technologies 22 (2019) e00128

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Fig. 1. Carbon nano structures with potential for the adsorption application a) graphene b) fullerene and c) carbon nanotubes (Reprinted with permission from ref 236. Copyright 2015 Springer).

Activated carbon is another widely used Carbon based adsorbent. In comparison to CNTs, activated carbon, despite having comparable surface area, is not fit for large organic molecules. Ji et al. (2009) showed that its micro-pores are often not accessible to these bulky organic molecules such as most of the antibiotics [52] and pharmaceuticals [53]. CNTs, hence, are more suitable for adsorption of such molecules due to their larger pores in the bundles formed in aqueous medium and their more accessible adsorption sites. In 2010, Yang and Xing [51] used Carbon NPs for adsorption of organic compounds in aqueous solution. It was observed that Activated carbon has comparatively low adsorption affinity for low molecular weight organic compounds. On the other hand, CNTs strongly adsorb most of these organic compounds due to its diversified pollutant-CNT interactions [54]. Despite its shortcomings, activated carbon is an effective and very popularly used adsorbent. Literature survey reveals that it can be easily prepared from waste rubber tyres. Using waste rubber tyres for its synthesis not only gives us a cheap raw material, it also helps in waste disposal as well [55]. Graphene family adsorbents [56], though effective towards a large number of water pollutants, have not been researched as extensively as CNTs and activated carbon. A number of authors have reported and demonstrated the capabilities of graphene based adsorbents (like graphene oxide and reduced graphene oxide) to adsorb various pollutants like synthetic dyes [52,57] and heavy metals [58]. In many instances, Graphene Oxide (GO) has been used as a substitute of CNTs and ideal material for waste water treatment. GO has comparatively lower production cost. Single layered GO offers two basal planes for adsorption [41,59–61]. In contrast, the inner walls of CNTs are not available for adsorption in aqueous medium [59]. Similarly, the adsorption activities of Fullerenes for organic pollutants [47,58] present in aqueous media have also been studied but at much lower level as compared to the other allotropes of carbon. 3.2. Metal NPs The literature is full of a number of metal NPs being used as adsorbents for waste water treatment. A few of them have been discussed and reviewed here. Traditionally, Gold and Silver symbolise wealth and prosperity. Gold has been making human life better ever since ancient times. Even today, Gold nano-particles (Au-NPs) are used in cosmetics [62] and other

human health products. The Au-NPs have anti-cancerous and unique optical properties which have high medical relevance. Patra et al. (2010) described the synthesis process of Au-NPs aimed for Pancreatic Cancer Therapy [63]. Cui et al. (2012) gave a detailed mechanism of Au-NPs functioning against Escherichia coli [64]. The green synthesis of anti-bacterial Au-NPs was demonstrated by Abdel-Raouf et al., using ethanolic extract of a marine algae Galaxaura elongate [65] (Fig. 2). The silver nano-particles (Ag-NPs) are easily the most widely used Metal NPs. Silver has, since always, been considered effective in controlling bodily infections, minor injuries as an anti-bacterial agent [66,67] and ulcer treatments [68]. Silver is also used to prevent food spoilage [69]. Ag-NPs/Graphene Oxide composites are used for Quercetin and Morin determination in various vegetables and fruits [70]. Ag-NPs have found immense applications in medicine field. Monteiro et al., 2009, studied the usage of silver in anti-microbial medical devices [71]. Sondi et al., 2004, through a case study, suggested that Ag-NPs penetrate the bacterial membrane of E-coli [72] and other gram-negative bacteria [73]. In 2008, Martinez-Castanon et al., conducted a series of experiments studying the effect of varying the size of Ag-NPs on their Anti-bacterial prowess [74]. Ag-NPs have been incorporated in the wound dressings, bone cement as well as in implants [75]. In 2016, Mojgan Goudarzi et al., used pomegranate peel extract and cochinealdye precursor to synthesise monodispersed Ag-NPs [76]. Fatemeh Mohandes and Masoud Salavati-Niasari, in 2013, used sonochemical method for synthesis of silver vanadium oxide nano rods [77]. Similarly, ultrasound assisted methods were used to synthesize nano-particles of HgSe [78], NiMoO4 nanorods [79] and Zn2SiO4 nanostructures [80] as well. Merin et al., (2010), biosynthesized Ag-NPs by micro-algal strains Chlorella salina, Chaetocerus calcitrans, Tetraselmis gracilis and Chaetocerus calcitrans [81]. The synthesized NPs had antimicrobial properties against Proteus vulgaris, E. coli, Pseudomonas aeruginosa and K. pneumoniae. The table given below, gives the anti-bacterial, anti-fungal and antiviral properties of Ag / Au NPs studied and stated in the literature of Metal NPs (Table 1). 3.3. Metal oxide based Another major category of nano-adsorbents is metal oxides (Table 2). Amongst them, the oxides of Zn [94], zirconium [95,96],

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Fig. 2. SEM image of (a) metal-based NPs (Ag-NPs) and (b) metal oxide NPs (Fe3O4-Ag CSNPs).

Table 1 Antibacterial, antifungal and antiviral activity of Ag and Au nano-particles. NP Organism/Plant/Chemical used for synthesis

Activity against

References

Ag Ag Au Au Ag

Azadirachta indica Curcuma longa Terminalia chebula Galaxaura elongata Alternaria alternata

[82] [83] [84] [85] [86]

Ag Au Au Ag Ag Au Au

Amylomyces rouxii Abelmoschus esculentus Tin chloride (SnCl2), sodium borohydride (NaBH4) 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) Lactobacillus fermentum Aliphatic-tetra-ethylene glycol Sodium 2-mercaptoethanesulfonate (MESNA), Sodium borohydride NaBH4

S. aureus, E. coli on cotton fabrics E. coli on cotton fabrics S. aureus, E. coli E. coli, K. pneumonia, S. aureus, P. aeruginosa Phoma glomerata, Phoma herbarum, Fusarium semitectum, Trichoderma sp. and Candida albicans Candida albicans, Fusarium oxysporum Puccinia graminis tritci, Aspergillus flavus, Aspergillus niger and Candida albicans Candida Hepatitis B virus Bacteriophage UZ1, application to NanoCeram filter HIV Herpes simplex virus type 1

lead [97], manganese, iron, titanium, magnesium, cerium and aluminium are the most prominent and promising ones [98–100]. Literature survey shows that the Nano Metal Oxides (NMOs) have high tendency of adsorption towards heavy metals. That means NMOs can be used to purify water by removing various toxic metal pollutants from water, as per the increasingly stringent regulations [101]. The major drawback of NMOs is that if the size is reduced from micro level to nano level, the surface energy increases to such a level that it leads to a very poor stability. Hence, at this size, due to Van der Waals forces and other interactions [102], they tend to agglomerate, thus decreasing their

Table 2 Adsorption capacities of NMOs for various pollutants S. Adsorbent no 1 2

3 4 5 6

MgO

Adsorbate

Reactive Blue 19 Reactive Red 198 ү-Fe2O3 Cr (IV) Cu (II) Ni (II) Goethite (α-FeOOH) Cu (II) Hematite (α-Fe2O3) Cu (II) γ-Al2O3 Ni (II) ZnO Pb (II)

pH

Adsorption capacity (mg g-1)

Refs.

8

166.7 123.5 17 26.8 23.6 100% 84.46 176.1 6.7

[104]

2.5 6.5 9.5 6 5.2 ± 0.1 -

[105]

[112] [125] [106] [107]

[87] [88] [89] [90] [91] [92] [93]

adsorption capability to a minimal level. NMOs have poor mechanical strength and hence, to broaden their applications and usability, they are often impregnated into large sized porous supports so as to form a composite adsorbent [103]. The table below gives the details of adsorption capacity comparison of various NMOs for adsorption of heavy metals and dyes. However, the adsorption capacity varies with the experimental conditions, which has varied greatly. Hence, a direct linear comparison cannot be made. For example, each study/ experiment will be using a different sized NMO for adsorption. Additionally, the various operating conditions, like pressure, temperature, reaction run time, pH, etc., will also be varying. Hence, a simple comparison for few selective NMOs has been presented in the table below. 3.3.1. Nano iron oxides Iron is one of the most abundantly available metals on Earth. The ease of synthesis and abundance of resources make Ferrous oxides a low-cost option for toxic metals adsorption from aqueous media. Iron is mostly environment friendly. For this reason, Nano Iron Oxides (NFeOs) can easily be pumped directly into the contaminated water site with low or zero risk of secondary contamination [108]. The most researched and studied NFeOs include maghemite (ү-Fe2O3) [109,110], amorphous hydrous Iron Oxides [111], hematite (α-Fe2O3) [112,113], magnetite (Fe3O4) [114–119], goethite (α-FeOOH) and iron / Iron oxide (Fe/FexOy) [120].

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Hematite (α-Fe2O3) and Goethite (α-FeOOH): The high specific surface area and the chemical nature of goethites make them very efficient for adsorption of metal cations [121]. Grossl et al., (1994), studied the kinetics of Cu cations adsorption (and desorption) on (and from) goethite (α-FeOOH) employing the p-jump (pressure jump) relaxation method [112]. This revealed both mechanistic and kinetic information for the reaction occurring at millisecond time-scale level. It was observed that the adsorption of Cu2+ increased when the pH was increased from 4.5 to 5.5. The process was found to be unaffected by the background electrolytes. It was observed that the Cu cations, on adsorption on goethite, form an inner-sphere surface complex. The value of calculated intrinsic rate constant for adsorption was found to be 106.81 Lmol-1s-1. On the other hand, the value of intrinsic rate constant of desorption (104.88 Lmol-1s-1) was found to be two orders of magnitude lower than that of adsorption. This combination of p-jump method/ technique and surface complexation modelling is also used to describe the adsorption (and desorption) of Co2+, Zn2+, Pb2+ on Gamma-Al2O3 [122] as well as Pb2+ adsorption (and desorption) on α-FeOOH [123]. The analysis done by Eigen and Tamm steady-state model [124] had also showed similar observation where the metal cations, which are divalent, tend to form an inner-sphere surface complex with the oxide surfaces. The adsorption of Cu2+ on nano hematite is also quite similar to that on nano goethite in terms of the kinetics and dynamics, though goethite has higher specific surface area and comparatively more maximum adsorption capacity (149.25 mg g-1) towards Cu2+ than that of hematite (84.46 mg g-1) [125]. Maghemite (γ-Fe2O3) and magnetite (Fe3O4): The Maghemite nano-gels are prepared from the sol-gel method, wherein, NH4OH solution is added to the mixture of FeCl2 and FeCl3 in purified water which is deoxygenated and then bubbled with nitrogen gas. The result is a redbrown γ-Fe2O3 nano-gel which is collected by simply subjecting the mixture to an externally created temporary magnetic field after adding ethanol. Hu et al. (2005), studied the removal of Cr4+ using the maghemite nano-gel [126]. It was observed that the equilibrium period remained unaffected by the initial concentration of Cr cations in the aqueous media and the adsorption capacity increased if the mixture pH was decreased. The adsorption capacity of maghemite nano-gel towards Cr2+ was found to be higher than that of commercially available activated carbon (15.47 mg g-1) [127], beech saw dust (16.13 mg g-1) [128], diatomite (11.55 mg g-1) [129] and anatase (14.56 mg g-1) [130]. In 2006, Hu et al., conducted another study of removal of a number of heavy metal ions like Cr4+, Ni2+ and Cu2+ using the same maghemite nano-gel [131]. It was seen that the adsorption capacity was highly dependent on the pH level of the contaminated wastewater used for the experiment. The ideal pH level for Cr4+, Ni2+ and Cu2+ were found to be 2.5, 8.5 and 6.5 respectively. On maintaining the optimal pH levels, the cations uptake was mainly due to the electrostatic attraction. Nano magnetite (Fe3O4) is another important form of NFO. The most widely used method for preparation of nano magnetite is chemical coprecipitation by adding alkaline carbonate to the solution having Fe3+ and Fe2+ in the molar ratio of 2:1 [132,133]. On addition of a surfactant, such as oleic acid, a smaller particle size was attained during the synthesis [134]. Nano magnetite is mostly used as a core of composite adsorbents [114,115,117,118,135–137] for adsorption of heavy metals. Hydrous ferric oxides: Precipitation of ammonia with ferric nitrate or chloride solutions by purging with N2 in a carbonate free environment yields nano hydrous ferric oxides [111]. Dzombak and Morel followed a similar method and synthesized nano HFOs with surface area of 600 m2g-1 and mean pore diameter of 3.8 nm [138]. 3.3.2. Nano manganese oxides The nano manganese oxides (NMnOs) [139] have a polymorphic structure and high specific surface area [140], making them much more effective adsorbent as compared to their bulk counterpart. The

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NMnOs are effective to a wide range of pollutants and have been exploited [141,142] for adsorption of both cationic and anionic from water, like arsenate [143], phosphate [144], heavy metal ions [145], etc. Some of the most researched NMnOs are Hydrous Manganese Oxides and nano-tunnel Manganese Oxides. Hydrous manganese oxides (HMOs): Parida et al., (1981), synthesized HMO by mixing MnSO4·H2O with NaClO solution having active chlorine [146]. The resulting precipitate was, then, washed with HCl so as to remove the excess alkali and then was rinsed with double ionised water. Gadde and Laitenen, in 1974, had used a different method for the synthesis. They added manganese nitrate to an alkaline solution of sodium permanganate and re-disbursed the particles in sodium nitrate solution. The heavy metal cations, like, Cd (II), Pb (II) and Zn (II), usually form inner-sphere complex on adsorption on HMOs. The HMO’s affinity towards adsorption of these heavy metals, in increasing order, is Zn2+b Cd2+b Pb2+. This might be because of the varied softness of these metals [147].

3.3.3. Nano aluminium oxides Alumina has been the traditional adsorbent for removal of heavy metals. The γ-Al2O3 is expected to be comparatively more effective adsorbent than α-Al2O3 [148,149]. The nano sized γ-Al2O3 [150] is prepared by using sol-gel method. The adsorption capability of γ-Al2O3 towards heavy metals is expected to increase on physical or chemical modification with a certain functional groups having donor atoms such as sulphur, nitrogen, phosphorous and oxygen [151–154]. Fatemah Davar et al., used modified sol-gel method for synthesis of spinel–type zinc aluminate (ZnAl2O4) NPs [155]. The lowest temperature for NPs preparation was found to be 550oC. Sol-gel method was also used by Masoud Salavati-Nisari et al., to prepare CoAl2O4 nano-crystals [156].

3.4. Nano composites Nano Metal oxides are often characterised by poor mechanical strength and for this reason, they are mostly impregnated or supported by other large sized porous supports, i.e., nano materials like zeolites [157] or CNTs so as to form nano-composites which have comparatively better usability and applications. NMOs like ZnO [158–162], CdO [163] and TiO2 [164] are used to form nano-composites with Ag, CNTs, CeO2 [165] and γ-Mn2O3 [166] and their enhanced photocatalytic activities are exploited to remove the industrial textile effluents from the waste water. Tawfik A. Saleh and V. K. Gupta, in 2011, successfully synthesized the nano composite of carbon nanotube/tungsten oxide (MWCNT/WO3) and studied its catalytic activity for rhodamine B removal from waste water under sunlight [167]. Sahar Zinatloo-Ajabshir et al., in 2017, synthesised Dy2Sn2O7SnO2 nano-composite for removal of organic contaminants using photocatalytic mechanism [168]. Freeze-drying synthesis technique was used by F. Mohandes and M. Salavati-Niasari in 2014 to synthesise chitosan / graphene oxide / hydroxyapatite nano-composite [169]. Similarly, Graphene/Pd/TiO2 [170] nano-composite is also used for photocatalytic degradation of dyes.

4. Pollutants and their removal using nano-adsorbents In order to qualify as NPs, the particle has to lie within the size range of 1–100 nm [171,172]. The size of the NPs is of utmost importance. It defines its versatility and adsorption capability. The various pollutants found in water today can be broadly categorised into three categories, viz., Organic, Inorganic and Biological pollutants. Literature shows that the Nano-adsorbents have been found capable to adsorb organic as well as inorganic pollutants, along with biological pollutants equally.

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4.1. Inorganic pollutants Adsorption technology has a proven track record in removal of inorganic pollutants form waste water. A simple survey of the available literature reveals that most commonly, the removal of inorganic ions is done by using NPs of oxides of aluminium, iron and titanium [173]. According to some researchers, the ease of preparation and large surface area of iron oxide NPs make them very good adsorbent for efficient removal of inorganic species [174,175]. Various metal and metal oxide NPs have been used to remove various heavy metal pollutants, including As, Cd, Cr, Cu, etc.

capacity was found to be ≥90% and further increase in contact time led to 100% removal of pollutants. Maximum adsorption occurred in acidic conditions. The study on adsorption of Cr (VI) revealed that the mechanism clearly followed pseudo-second-order kinetic model [184]. Gupta et al., synthesized CuO NPs and applied them into water treatment techniques. The average size of NPs was 8 nm which is good to provide larger surface area and better adsorption quality. In order to obtain maximum adsorption of Cr (VI) on these NPs, the influential parameters like pH, time, metal concentration, adsorbent dose etc. were optimized using batch experiments. The adsorption process was observed to be endothermic and the kinetic data was more in agreement with the pseudo-second-order kinetic model. Isotherm model suggested that a monolayer of Cr (VI) ions was developed on the surface of CuO NPs and adsorption energy was distributed uniformly on the surface of the adsorbent [185]. In 2012, Vinod Kumar Gupta et al. used waste rubber tyres for synthesis of activated carbon and use it for removal of chromium from water. It was observed that the process was pH dependent and equilibrium was achieved in 1 hour [186].

4.1.1. Arsenic (As) Arsenic, probably, is the most harmful of all the metal pollutants as it contaminates the ground water. All over the world, people are drinking arsenic contaminated water because of arsenic ground water contamination [176]. In a study performed in Bangladesh, sampling thousands of hair, nail, water and urine samples, it was concluded that about nine hundred of the villages had higher concentration of arsenic in ground water than the permissible maximum limit [177,178]. To remove arsenic from ground water effectively, researchers have studied and performed several methods and techniques. Adsorption has proven as one of the most effective method for this purpose. Vargas et al., [179] synthesized cobalt and manganese ferrite NPs to remove arsenic [As (III)]. In case of both the NPs, the adsorption data was best fitted to Freundlich adsorption isotherm. The maximum adsorption capacity was observed to decrease with increase in Mn in the ferrite composition (from 24.17 to 16.96 mg g-1). On the other hand, in case of Co ferrites, the adsorption capacity was found to be less sensitive to change in Co in the ferrite composition (24.81 to 24.40 mg g-1). To predict the As adsorption behaviour and assessing the iron oxide NPs in the biogeochemical cycling of As metal ions, Dickson et al. [180] synthesized hematite NPs and performed adsorption of arsenite [As (III)] and arsenate [As(V)]. As hematite NPs tend to form aggregates, arsenic adsorption was considered with both NPs and their micron-sized aggregates. The kinetic data was best described by the pseudo-secondorder model. Adsorption of As (V) (4122 ± 62.79 μg g-1) was found to be more effective than As (III) (2899 ± 71.09 μg g-1) at equilibrium. Adsorption data was best described by Freundlich adsorption isotherm model and adsorption was better in case of hematite than the aggregates. In the year 2014, Hokkanen et al., used magnetic iron NPs modified micro fibrillated cellulose (Fe NP/ MFC) for arsenate (As (V)) removal from aqueous solutions. It was found to be an exceptionally good adsorbent material due to its high surface area, magnetic property and good adsorption capability. The adsorption data was best described by Langmuir isotherm model. The kinetics was best explained by pseudosecond-order kinetic equation. The FeNP/ MFC showed highly improved As (V) adsorption properties as compared to original Fe-NPs [181].

4.1.3. Cadmium (Cd) Cd is highly toxic, non biodegradable heavy metal which causes long term damage by accumulation in the body [187]. Once it enters the body, it remains deposited in the body and keeps on getting accumulated throughout life. It causes kidney damage and bone demineralization. To tackle the problem of Cd contamination in water, many researchers are working towards the efficient removal of Cd ions from waste water. Adsorption, again, can be one of the most efficient methods for the removal of Cd from water bodies. Li et al., used plasma reduction method to develop nanoscale zerovalent iron particles supported on reduced graphene oxide (NZVI/ rGOs) for the adsorption of Cd (II) metal ions. The adsorption capacity of these NPs for Cd (II) was noted to be 425.72 mg g-1, which is very high. The adsorption was very fast and completed within 50 min. The adsorption process was found to be spontaneous and endothermic in nature [188]. Synthesis of ascorbic acid-stabilized zero valent iron nanoparticles (AAs-ZVIN) was done by Savasari et al., for Cd (II) removal. Adsorption study was done under response surface methodology. The adsorption capacity was found to be 79.68% at pH 7 within the contact time of 60 min [189]. Tabesh et al., prepared γ-Al2O3-NPs and characterized them using various techniques like XRD, SEM, TGA and IR. Then removal efficiency for Cd (II) on γ-Al2O3-NPs was studied varying the parameters like pH, contact time, metal concentration and adsorbent dosage. The adsorption process followed Freundlich isotherm model. The adsorption capacities were found to be 47.08 mg g-1 and 17.22 mg g-1 for Pb2+ and Cd2+, respectively. The NPs were regenerated and reused for 3 times in a row [190].

4.1.2. Chromium (Cr) Cr is widely used in the mining and pigment manufacturing industries. Cr exists in two oxidation states in aqueous solution, one is Cr (III) which is comparatively less toxic and the other is Cr (VI) which is extremely mobile in environment and carcinogenic to living beings [182]. Hence, there is a need to develop methods that can effectively remove it from water on a large scale. Nafiey et al., performed adsorption of Cr (VI) on reduced graphene oxide-cobalt oxide nano-particles (rGO–Co3O4 NPs) and got excellent results. Under mild conditions, a one step synthesis of rGO–Co3O4 NPs was done. The adsorption capacity (208.8 mg g-1) was found to be very efficient compared to other graphene based adsorbents [183]. A novel green synthesis of zero valent iron nanoprticles (NZVI) using plant extracts was done by Faztadeh et al., for removal of Cr (VI) from aqueous media. After synthesis, the NPs were characterized and then Cr (VI) adsorption was done in batch experiment. The adsorption

4.1.4. Lead (Pb) With the rapid increase in chemical manufacturing industries, amount of heavy metals used is also increasing, rapidly. Out of all heavy metals, Pb is one of the most dangerous one. Pb2+ has continuous toxicity and can cause serious blood disease [191]. The permissible limit of Pb in drinking water is 0.010 mg L-1 [192]. Earlier, the copper pipes were used for plumbing water in buildings and were soldered using Pb. If the pipes or fixtures have Pb as a constituent, the water can easily be Pb contaminated. For this reason, now days, galvanized or plastic plumbing is preferred. Fan et al., carried out a study, wherein, first, magnetite Fe3O4/ Chitosan nano-particles (Fe3O4/CSNPs) were synthesised and then were applied for efficient removal of heavy metals. The strong chelating capability of chitosan leads to a better adsorption capacity of Fe3O4/ CSNPs for Pb (II) than that of pure Fe3O4 and faster adsorption rates also. The maximum adsorption capacity was found to be 79.29 mg g-1.

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The adsorption data was in favour of Langmuir isotherm model suggesting monolayer adsorption. The NPs were recyclable which made them very good adsorbent for water treatment [193] (Table 3). Chen et al., used sulfonated magnetic NPs to remove Pb (II) ions from water. These NPs are very efficient adsorbents due to their additional active site, “sulfo-group”. It was observed that adsorption reaches up to 99% in 24 h of contact time. The adsorption followed Langmuir isotherm model over Freundlich isotherm model. The reaction was very fast, aligning with pseudo-second-order kinetics. Subjected to the super paramagnetic power of the NPs, they can be easily regenerated after adsorption from the reaction solution [194]. Xiong et al., investigated the efficiency and mechanism of Pb (II) removal by MgO NPs from aqueous media. Adsorption studies were done by using batch experiments and kinetics was found to be pseudosecond-order. The adsorption followed Langmuir isotherm model. The maximum adsorption capacity was found to be 2614 mg m-1. Easy preparation, remarkable removal efficiency makes them better adsorbent for treatment of waste water containing heavy metals [195]. 4.1.5. Copper (Cu) Cu is one of the essential nutrients required in our body, but in very small quantity. However, it has been found that oral intake of Cu ions can have harmful effects on heath like nausea, vomiting, etc. For the efficient removal of Cu ions from waste water, adsorption technique had been used by many researchers. Davarnejad et al., in 2016, modified henna with Fe3O4 NPs and used them to remove Cu (II) from wastewater. The maximum adsorption achieved was up to 99.11% with variable pH. Freundlich isotherm model confirmed that the modified henna was a perfect adsorbent for Cu (II) removal. The adsorption data was in good agreement with the Langmuir isotherm model [196]. The nanocomposite of ZnO with montmorillonite (MMT) was used by Sani et al., for the removal of Cu (II) ions from aqueous solutions. XRD revealed that the ZnO/MMT nanocomposite has hexagonal wurtzite structure. The role of ZnO in enhancing the adsorption efficiency of ZnO/MMT was investigated. Isotherm models were applied to adsorption data and it was more in agreement with Langmuir isotherm model rather than Freundlich isotherm model. The kinetics was better explained by pseudo-second-order kinetic model [197]. Fouladgar et al., used γ-alumina for single and binary adsorption of Cu (II) ions from aqueous media and further kinetic and equilibrium

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modelling was done. The maximum adsorption capacity for Cu (II) was found to be 31.3 mg g-1. Out of Langmuir and Freundlich isotherm models, the adsorption data was in best agreement with the Freundlich isotherm model. The time dependent data was used to check the kinetics and it was found to be a successful pseudo-second-order reaction [198]. 4.1.6. Nickel (Ni) Agarwal et al., synthesized γ-alumina NPs and MWCNTs for the rapid removal of noxious Ni (II) from liquid phase. The maximum Ni (II) removal using γ-alumina NPs and MWCNTs was 99.41% and 87.65%, respectively. The adsorption equilibrium and the kinetic data were well fitted and found to be in good agreement with Langmuir isotherm model and pseudo-second-order kinetic model [199]. Gautam et al., removed Ni (II) by using super paramagnetic Fe3O4 NPs from aqueous solution. The process of adsorption was very fast (30 min) and was found to be pH dependent. The kinetics of the removals showed better agreement with pseudo-second-order rate kinetics. Out of all isotherm models, the adsorption data showed good agreement with the Freundlich isotherm model. The process was endothermic in nature and the adsorption capacity ranged from 209.205 to 362.318 mg g-1 [200]. Ma et al., studied adsorption and desorption of Ni (II) over aluminium substituted goethite (Al-FeOOH). Using batch technique, adsorption of Ni (II) on Al-FeOOH NPs was found to be successful by optimizing environmental factors including contact time, ionic strength, temperature and pH. Adsorption reaction followed pseudo second order kinetics. The maximum adsorption capacity was calculated from Langmuir isotherm model and was found to be 94.52 mg g-1. This experiment implied that Al-FeOOH can be used as an effective adsorbent in removal of Ni (II) from aqueous solutions [201]. 4.1.7. Miscellaneous metal ions In the above discussion, we focused on removal of a single metal ion on specific adsorbent, but there have been studies where researchers have performed adsorption of two or more metal ions on single adsorbent, which are being discussed below. In year 2014, Liu et al., used hydrothermally synthesized titanate nanotubes (TNTs) to remove highly toxic thallium ions from environment. TNTs were found to be very efficient in adsorption of thallium ions. The adsorption was very fast and adsorption equilibrium was

Table 3 Removal of inorganic water pollutants by adsorption using Nano-adsorbents. S. no.

Pollutants

Adsorbents (Nano-Particles)

Removing capacities

Contact time

pH

Refs.

1 2

As (III) As (III) and As (V)

Cobalt (10-20 nm) and manganese (10-50 nm) ferrite Hematite

4h 8h

2 6-8

[179] [180]

3 4 5 6 7

As (V) Cr (VI) Cr (VI) Cr (VI) Cd (II)

5–600 min (75 min) 12 h 10–30 min 180 min 50 min

2 3 2 3 5

[181] [183] [184] [185] [188]

8 9 10 11 12 13 14 15 16 17 18 19 20

Cd (II) Cd (II) Pb (II) Pb (II) Pb (II) Cu (II) Cu (II) Cu (II) Ni Ni Ni Th (I) and Th (III) Pb (II), Cd (II), Cu (II), Ni (II)

Iron NPs modified micro fibrillated cellulose Graphene oxide-Cobalt oxide Zero valent iron nanoparticles (NZVI) Copper oxide Nanoscale zerovalent iron particles supported on reduced graphene oxide Ascorbic acid-stabilized zero valent iron nanoparticles γ-Al2O3 NPs Magnetite Fe3O4 / Chitosan nanoparticles (Fe3O4 / CSNPs) Sulfonated magnetic NPs MgO Modified henna with Fe3O4 Nanocomposite of ZnO with montmorillonite γ-alumina γ-alumina NPs and MWCNTs Superparamagnetic Fe3O4 Aluminium substituted goethite (Al-FeOOH) Titanate nanotubes Nano scale zero valent iron particles (nZVI)

24.81 and 24.17 mg g-1 2899 ± 71.09 μg g-1 and 4122 ± 62.79 μg g-1 2.460 mmol g-1 208.8 mg g-1 100% 15.62 mg g-1 425.72 mg g-1 79.58% 17.22 mg g-1 79.29 mg g-1 108.93 mg g-1 2614 mg m-1 99.11% 31.3 mg g-1 99.41% and 87.65%, 209.205 to 362.318 mg g-1 94.52 mg g-1 709.2 mg g-1 -

60 min 30 min 12 hr 24 h 180 min 85 min 90 min 4h 30 min 35 min 6h 10 min 30 min (Pb), 20 min (Cd, Cu, Ni)

7 5 6 7 4 4 5 10 8 5 2-7

[189] [190] [193] [194] [195] [196] [197] [198] [199] [180] [181] [182] [202]

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attained within 10 min. The adsorption isotherm followed the Langmuir model and the maximum adsorption capacity was observed to be 709.2 mg g-1. The mechanism for Th (I) adsorption was ion-exchange but for Th (III), ion-exchange and co-precipitation mechanisms were opted. Furthermore, it was concluded that after desorption, regeneration of TNTs can be done and TNTs can be used again for the adsorption [202]. Azzam et al., used nano scale zero valent iron particles (nZVI) to remove heavy metal ions (Pb (II), Cd (II), Cu (II) and Ni (II)) from aqueous media or polluted water for the betterment of environment. Batch experiment was conducted to study the adsorption of heavy metal ions. The adsorption kinetics was best fitted with the pseudo-secondorder kinetic model. These NPs showed great capability to adsorb heavy metal ions from several natural ground water specimen and ability to adsorb multiple metal ions simultaneously. Hence nZVI offers potential remediation method for the elimination of heavy metal ions from water and environment [203]. In 2007, Yantasee et al., performed surface functionalization of iron oxide (Fe3O4) NPs, with dimercaptosuccinic acid (DMSA) and showed that this was an effective adsorbent for the removal of toxic soft metals (Hg, Ag, Pb, Cd,and Tl) from aqueous solution. Surface area of the NPs was found to be 114 m2g-1. DMSA- Fe3O4 had a capacity of 227 mg g-1, for Hg, and showed quick adsorption for the rest of the metals [204]. Similarly, functionalised iron NPs were synthesised by Imran Ali et al. using black tea and ferrous sulphate for removal of 17-β-estradiol traces, an endocrine disturbing and carcinogenic steroid, from water [205]. The wastewater residue from the Electroplating industry has got higher concentration of heavy metal ions and to remove those ions from wastewater, Hu et al., synthesized maghemite NPs. This was done using the sol-gel method. TEM analysis revealed that the assynthesized nano-particles had an average diameter of 10 nm. The maghemite NPs (10 nm) were used for the adsorption of heavy metals (Cr, Cu and Ni ions) from waste water. To determine the adsorption kinetics and mechanism, batch experiments were conducted. The process was found to be highly pH dependent. The adsorption data well fitted with Langmuir isotherm model. Desorption of metal ions was also demonstrated using 0.01 M NaOH for adsorbed-Cr and 0.05 M HCl for adsorbed-Cu/Ni with the efficiency of 92% and 94% respectively. This is evident from the systematic study that maghemite NPs can be used as an effective adsorbent for the reduction of pollutants like heavy metals from waster waters and environment [131]. 4.2. Organic pollutants Many organic pollutants [206] including dyes, pesticides, hydrocarbons, etc. are removed from wastewater using adsorption technology. Large numbers of scientists are working in the field of adsorption to develop good adsorbents effective against the organic pollutants, which form a prominent category of water pollutants. Dye: The major source of dyes, as a pollutant in water bodies, are industries like textile, rubber, paper, printing, painting etc. which require huge number of colouring agents for various purposes in their manufacturing processes. As per today’s scenario, the demand of using dyes (especially azo dyes), in making things attractive, is increasing which is resulting in increase of concentration of dyes in the water bodies where these effluents are dumped. Eriochrome black T (EBT) is an azo dye. Large numbers of synthetic dyes used in the industries are composed of azo dyes. So, if an adsorbent is developed to be effective against azo dyes, it can be used for removal of a large range of dyes from the wastewater. A reactive azo dye will have one or more azo group (\\N_N\\), which acts as chromophore in the molecular structure [207]. There are several studies in literature wherein the researchers have used photocatalytic treatment for dyes decontamination in waste water [208–211]. R. Saravanan et al., synthesised ZnO nano-particles using several different techniques and did a comparative study of its

usage for photocatalytic degradation of organic dyes [212]. Similarly, CeO2/V2O5 and CeO2/CuO can be used as nano-catalysts for visible light induced treatment of methylene blue in waste water [213]. Arash Asfaram et al., performed an ultrasound assisted treatment of wastewater with Auramine-O (AO) contamination using ZnS:Cu NPs loaded on activated carbon [214]. The maximum adsorption capacity of ZnS:Cu-NP-AC for AO was found to be 183.15 mg g-1, showing its high potential as an adsorbent. Quaternary ammonium polyethylenimine (PEI) was modified to silica NPs (QPEI/SiO2) by Liu et al., as a novel adsorbent to remove methyl orange (MO) from aqueous media. The equilibrium time was very short, i.e., 10 min and the adsorption capacity was found to be 105.4 mg g-1. The adsorption data was well fitted to Langmuir isotherm model. It was clear from the results that QPEI/SiO2 was very efficient and could be considered as a viable adsorbent for removing MO from wastewater [215]. Alok Mittal et al., investigated the potential of bottom ash for removal of chrysoidine Y, an azo dye used in textile factories, from wastewater. The monolayer adsorption was observed and the adsorption capacity at 30 °C was found to be 7.27 × 10-5 mol g-1, as per the Langmuir analysis [216]. Mak et al., used polyacrylic acid (PAA)-bound iron oxide magnetic NPs for the efficient removal of methylene blue (MB) from aqueous solutions. In their work, adsorption was done in batch experiments. Adsorption of MB on (PAA)-bound iron oxide magnetic NPs followed Langmuir isotherm model. The monolayer adsorption capacity was calculated to be 0.199 mg mg-1 between 10 and40 °C. As per thermodynamic data, the process was spontaneous, endothermic and physicochemical in nature. The results revealed that the (PAA)-bound iron oxide magnetic NPs is an efficient and very cheap adsorbent for the removal of MB from aqueous solution and can contribute effectively in environment clean up [217]. Tang et al., used cobalt nano-particles embedded magnetic ordered mesoporous carbon (Co/OMC) for the highly effective adsorption of rhodamine B (Rh B). The NPs used in adsorption were synthesized involving infusion and calcinations method. The maximum adsorption value was 468 mg g-1 at 200 mg L-1 initial Rh B concentration. Data obtained from batch experiments was in good agreement with pseudosecond-order model and showed significant correlation with intraparticle diffusion model. Langmuir isotherm model was followed during the course of adsorption indicating the monolayer formation on the surface of Co/OMC by Rh B. The thermodynamic studies revealed that the reaction was endothermic and spontaneous in nature. The results concluded that Co/OMC had good potential for the removal of Rh B from aqueous solution [218]. Mekatal et al., used ion-exchange method and prepared CuO supported on a NaA zeolite (CuO/NaA). The parameters such as contact time, temperature, pH, adsorbent dosage and dye concentration were optimised during the batch experiments for better study of adsorption on CuO/NaA NPs. The adsorption equilibrium was achieved in 240 min of contact time. Among all the isotherm models, the data was well fitted on Langmuir isotherm model. Kinetic data was in agreement with second-order kinetic model. The evaluation of the thermodynamic parameters revealed that the reaction was spontaneous in nature [219]. Pesticides: The major sources of pesticide introduction to the environment are industries (like food, cosmetic, textile etc.), forestry and agriculture along with domestic activities [220]. However, studies also revealed that the pesticide pollution also takes place through air. The dust particles present in the air adsorb pesticides used in agriculture, forest and various other domestic activities and travel in air and in turn, polluting the water bodies, sediments and soil. Many researchers are working towards developing methods to deal with the pesticide pollution. Malathion and Lindane are amongst the most commom and toxic pesticides available and used in India [221]. The adsorption of pesticides using NPs has been found to be most promising and effective. Dehaghi et al., performed synthesis of chitosan-zinc oxide nanoparticles (CS-ZnONPs) composite beads for the effective removal of

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permethrin pesticide from water. Adsorption application of NPs was performed using batch experiments. After optimizing the parameters (pH, contact time, adsorbent dose and concentration of pesticides) maximum removal obtained was 99%. Complete regeneration of the adsorbent can be done by NaOH solution (0.1M) and then can be used for adsorption application again. This makes these NPs very important from economic and environmental point of view [222]. Liu et al., used Porous Hollow Silica nano-particles (PHSNs) for the removal of water soluble pesticide, validamycin. PHSNs offers many active sites for adsorption of validamycin like on the external surface, inter-space of the surface or at the pore channels on the shell are internal core of PHSNs. After adsorption, further characterization of valiPHSNs revealed that there is no change in chemical properties of validamycin after adsorption. Desorption of validamycin was also performed successfully. As validamycin was adsorbed at different sites, the releasing process took large amount of time due to the porous structure of adsorption. The releasing capacity of the adsorbent varies depending on the dissolution medium condition and can be accelerated by increasing or decreasing the parameters like pH and temperature [223]. Nair et al., used gold and silver in solution phase supported over activated alumina as an effective system for the removal of the two most common pesticides namely chlorpyrifos and malathion from the aqueous media. A coating of gold and silver was done over activated alumina and the water containing pesticides was run through the column of NPs. Characterization of NPs by UV-Vis spectroscopy and gas chromatography confirmed that the adsorption was successful. This device was used for comparatively longer practice for this purpose of reducing water pollution. Alumina, when used alone as an adsorbent, is not as effective for the removal of pesticides as compared with when used in conjunction with the gold and silver solution for wastewater treatment [224].

4.3. Biological pollutants Shimabuku et al., used continuous flow experiment in the filters commonly used in households to investigate the removal efficiency of activated carbon modified with silver (Ag) and copper oxide (CuO) NPs for T4 bacteriopahse. During the experiment, water at a speed of 450 ml min-1 was passed through the filter made up of these NPs. After that, the filtered water was analysed to check the presence of bacteriophase and the release of Ag and CuO. The porous structure containing Ag and CuO showed high molecular capacity for the bacteriophase. The level of Ag and CuO released in water was found to be very low, i.e., below the permissible limit (100 ppb for Ag and 1000 ppb for copper) in drinking water. From this study, it can be concluded that activated carbon modified with Ag and CuO NPs can be used as a filter to remove virus from drinking water [225]. Asghar et al., performed an environment-friendly synthesis of copper (Cu), silver (Ag) and iron (Fe) NPs using black tea and green tea leaves extracts. To assess the antibacterial activity of NPs, methicillinand vancomycin- resistance staphylococcus aureus strains were used and for antifungal activity, Aspergillus flaves and A paraciticus fungal species were used. Adsorption capability for Aflatoxin B1 (AFB1) was also determined in solution. Ag-NPs showed better antibacterial/antifungal activities and reduced the aflatoxin generation in comparison to Fe-NPs and Cu-NPs. Adsorption capacities with AFB1 contamination was high in Fe-NPs. The equilibrium data best fitted to Langmuir isotherm model with adsorption capacity of 110–115 ng mg-1 (Ag-NPs), 11–118 ng mg-1 (Cu-NPs) and 131–139 ng mg-1. The kinetic and thermodynamic data showed that the reaction was spontaneous, endothermic and followed pseudo-second-order kinetics. Thus, these NPs can be used as an effective alternative antibacterial/antifungal agent against diseases caused by pathogens. In addition, these NPs can also be used as aflatoxin adsorbent in human food and animal feed effectively [226].

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Darabdhara et al., performed top down (mechanical ball milling) and bottom up approaches (chemical reduction method) for the synthesis of magnetic Fe3O4 NPs. It was observed that the adsorption capacity of the synthesized NPs was surface charge dependent for both gram negative bacterium Escherichia coli and gram positive bacterium Staphylococcus aureus. Adsorption kinetics was evaluated at pH 5, considering four different temperatures, viz., 20, 25, 30 and 35 °C. Adsorption analysis showed that the process followed Langmuir isotherm model and pseudo-second-order kinetic model was the best fit kinetic model for the adsorption of gram positive and gram negative bacteria on Fe3O4 NPs. Hence, these NPs can be used as a less costly adsorbent option for the removal of harmful pathogens and bacteria from water by simple and easy adsorption technique [227]. 5. Regeneration of adsorbent The regeneration ability of any spent adsorbent material is an important aspect so as to determine and justify its cost effectiveness. The ease with which any adsorbent can be regenerated, vastly determines its usage and adaptability in any water treatment technique. The researchers, now a days are working towards the synthesis of magnetic adsorbents simply because of the fact that they can be regenerated efficiently after adsorption, by simply applying an external magnetic field. Given the choice, any adsorbent which can be regenerated easily will always be preferred over any other adsorbent due to the economical and environmental advantage. In 2014, Vinod Kumar Gupta et al., synthesised Fe@Au bimetallic nano-particles involved Graphene Oxide (Fe@Au-ATPGO) and used them for catalytic reduction of 2-nitrophenol and 4-nitrophenol. He showed that the nano-particles, after usage, can be easily regenerated within 15 seconds by a simple magnetic field and can be reused at least 10 times without any significant decrease in stable conversion efficiency [228]. Babaee et al., studied regeneration of Fe/Cu NPs after adsorption of As (III) and As (V). They used 0.10 and 0.01 mol L-1 NaOH as regeneration agent. It was observed that the adsorption was enhanced in acidic medium and in basic medium, desorption is possible very easily. 100% desorption of As (V) and 70.3% desorption of As (III) was achieved by 0.10 mol L-1 NaOH. These amounts reduced to 79.4% and 57.5% for As (III) and As (V), respectively while using 0.01 mol L-1 NaOH [229]. Further, Ghasemi et al., performed desorption of heavy metal on the surface of a new and highly efficient superparamagnetic nanoadsorbents (EDTA functionalized Fe3O4 NPs). Different concentrations of HCl (0.001, 0.01, 0.1, 0.5 and 1 mol L-1) were used as eluent for desorption of heavy metals. The coordinated cations (heavy metal ions) on EDTA can be replaced by H+ ion in acidic medium and that way metal ions were released. It was found that the regeneration of EDTA functionalized Fe3O4 NPs reaches up to 98% after simultaneous removal of heavy metal ions using 0.5 mol L−1 HCl as an eluent. Thirty consecutive adsorption/desorption cycles were performed to evaluate reuse of EDTA functionalized Fe3O4 NPs. It was observed that EDTA functionalized Fe3O4 NPs could be effectively regenerated and reused with a rapid and simple process using 0.5 mol L−1 HCl [230]. Zhao et al., synthesized ternary magnetic composite consisting of graphene oxide (GO), diethylenetriamine and Fe3O4 NPs (AMGO) for the adsorption of Cr (VI) from aqueous solution. Further, regeneration of AMGO was done using NaOH solution (0.1 M). Cr (VI)-adsorbed AMGO was placed in 7 ml NaOH solution for 3h and then thoroughly washed with milli-Q water to remove adsorbed alkali. The adsorption capacity (106.5 mg g-1) of the regenerated AMGO decreased from the adsorption capacity (123.4 mg g-1) of the original AMGO after five consecutive cycles but still promising for further usage [231]. Srivastava et al. [232] and Lu et al. [233] synthesized Cu2(OH)2CO3 NPs and magnetic nanoparticle-multi walled carbon nanotubes composites (MNP-MWCNTs) respectively for the adsorption of As (VI) and then performed desorption of the same from the nano-adsorbents.

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Regeneration of Cu2(OH)2CO3 NPs was done by using different concentrations of NaOH and maximum amount of NPs were regenerated by using 0.15 M NaOH. Desorption of As (VI) increased with the increase in volume of NaOH. Same way, MNP-MWCNTs were regenerated using NaOH (0.5 mol L) solution. After desorption, external magnetic field was applied to MNP-MWCNTs for their separation and were ready for reuse. The easy recovery of the adsorbents makes them cost effective and efficient for their application in water treatment. Karimi et al., used dimethylglyoxim/sodium dodecyl sulfateimmobilized on alumina-coated magnetite nanoparticles (DMG/SDSACMNPs) for the efficient recovery (by adsorption) of Ni (II) from soil, spinach, tomato, black tea, tobacco and different water samples. The magnetite adsorbents were recovered successfully using a magnet and decanted directly. Further, 2.5 mL of 0.1 mol L-1 HNO3 solution was added as eluent and found to be efficient for quantitative recovery of Ni (II). Again, magnets were used to settle the magnetic NPs. These can be used, at least, three times in a row without any decrease in their removal efficiency [234]. As we are aware that, the exhausted adsorbents are very toxic and hazardous for health and environment, proper disposal of them should be done by the users. The best way of managing their disposal is regeneration of adsorbents. Recovered organic pollutants, on the other hand, should be treated as the main pollutants. These should be filled in some steel cylinders and dumped deep beneath the earth [173]. 6. Conclusion An expository evaluation of nano-adsorbents in this article indicates that NPs are being used for successful removal of inorganic, organic as well as biological pollutants form waste water. The adsorption method has been convincingly proven to be equally effective across all the categories of pollutants present in the water. A large variety of NPs have been synthesized using simple and eco-friendly techniques and have been reported efficient in the literature for easy removal of most of the pollutants. These NPs are capable of removing pollutants even at very low concentrations (i. e., μg L-1). The adsorption of pollutants on NPs is, mostly, pH dependent and thermodynamics of the process also affects the course of adsorption. It is clear from the literature that adsorption involving NPs is very fast, as most of the adsorption equilibriums were achieved within 1 to 15 min. Another important aspect, for the widespread use of NPs, from economical and ecological point of view, is their regeneration capabilities. Having said that, the most preferred and commonly synthesized NPs are metal-based NPs (including silver, iron, manganese, copper, Aluminium NPs), owing to their ease of synthesis with high yield and regeneration capability after adsorption. In comparison to regular iron based materials, iron NPs have higher efficiency of removal or reduction of contaminants in both in-situ and ex-situ environmental engineering applications [235]. It should be noted that the management of recovered pollutants and exhausted adsorbents is another point of major concern. There is not much literature available addressing the disposal of exhausted adsorbents and recovered pollutants post regeneration process. Therefore, to tackle this problem, researchers need to develop eco-friendly waste management techniques. Mostly, the adsorption studies were performed in batch experiments which gave potentially good results. However, these were limited to laboratory conditions only. Few of the researchers used NPs in water filters at homes for the treatment of drinking water. But, in order to evolve these methods from miniature lab conditions to large scale actual world applications, there is a need for collaboration between the water treatment industries and the researchers. Only then, we can hope to resolve this issue globally. Nevertheless, the article presented sufficient references from the literature that the waste water treatment using nano-adsorbents is not only comparatively quick and efficient; it is also eco-friendly, versatile and easily expandable to large scale as well. However, it has huge potential for further research and development so as to make it more economic and effective.

Declaration of Competing Interest There is no conflict of interest. Acknowledgement One of the authors Priya Kumari is thankful to UGC (University Grants Commission), New Delhi, India for financial assistance by providing Non-NET fellowship. References [1] A.D.N. Nemerow, Industrial and Hazardous Waste Treatment, Van Nostrand Reinhold, New York, 1991. [2] H.Y.A.-E.I. Ali, Chiral Pollutants: Distribution, Toxicity and Analysis by Chromatography and Capillary Electrophoresis, John Wiley & Sons, Chichester, UK, 2004. [3] R. Helmer, I. Hespanhol, Water Pollution Control – A Guide to the Use of Water Quality Management Principles, E & FN Spon, London, Great Britain, 1997. [4] J.H. Lehr, T.E. Gass, J. Pettyjohn De Marre, Domestic Water Treatment, McGraw-Hill Book Company, New York, 1980. [5] N.L. Nemerrow, Industrial Water Pollution: Origins, Characteristics, and Treatment, Addison-Wesley Publishing Company, Massachusetts, 1978. [6] I. Ali, T.A. Khan, M. Asim, Removal of arsenic from water by electro coagulation and electrodialysis techniques, Sep. Purif. Rev. 40 (2011) 25–42. [7] T.A. Saleh, V.K. Gupta, Column with CNT/magnesium oxide composite for lead (II) removal from water, Environ. Sci. Pollut. Res. 19 (2012) 1224–1228. [8] V.K. Gupta, A. Nayak, Cadmium removal and recovery from aqueous solutions by novel adsorbents prepared from orange peel and Fe2O3 nanoparticles, Chem. Eng. J. 180 (2012) 81–90. [9] T.A. Saleh, V.K. Gupta, Functionalization of tungsten oxide into MWCNT and its application for sunlight-induced degradation of Rhodamine B, J. Colloid Interface Sci. 362 (2011) 337–344. [10] T.A. Saleh, S. Agarwal, V.K. Gupta, Synthesis of MWCNT/MnO2 and their application for simultaneous oxidation of arsenite and sorption of arsenate, Appl. Catal. B 106 (2011) 46–53. [11] V.K. Gupta, S. Agarwal, T.A. Saleh, Synthesis and characterization of alumina coated carbon nanotubes and their application for lead removal, J. Hazard. Mater. 185 (2011) 17–23. [12] M. Ghaedi, S. Hajjati, Z. Mahmudi, I. Tyagi, Shilpi Agarwal, A. Maity, V.K. Gupta, Modeling of competitive ultrasonic assisted removal of the dyes – methylene blue and Safranin-O using Fe 3 O 4 nanoparticles, Chem. Eng. J. 268 (2015) 28–37. [13] X.L. Qu, J. Brame, Q. Li, J.J.P. Alvarez, Nanotechnology for a safe and sustainable water supply: enabling integrated water treatment and reuse, Acc. Chem. Res. 46 (3) (2013) 834–843. [14] Richard E. Speece, Anaerobic biotechnology for industrial wastewater treatment, Environ. Sci. Technol. 17 (9) (1983). [15] N.N. Fathima, R. Aravindhan, J.R. Rao, B.U. Nair, Dye house wastewater treatment through advanced oxidation process using Cu-exchanged Y zeolite: a heterogeneous catalytic approach, Chemosphere 70 (2008) 1146–1151. [16] E.M.V. Hoek, A.K. Ghosh, Nanotechnology-based membranes for water purification, in: N. Savage, M. Diallo, J. Duncan, A. Street, R. Sustich (Eds.), Nanotechnology Applications for Clean Water, William Andrew Publishing, Boston 2009, pp. 47–58. [17] P. Le-Clech, V. Che, T.A.G. Fane, Fouling in membrane bioreactors used in wastewater treatment, J. Membr. Sci. 284 (2006) 17–53. [18] P. Xu, C. Bellona, J.E. Drewes, Fouling of nanofiltration and reverse osmosis membranes during municipal wastewater reclamation: membrane autopsy results from pilot-scale investigations, J. Membr. Sci. 353 (2010) 111–121. [19] J. Zhang, H.C. Chua, J. Zhou, A.G. Fane, Factors affecting the membrane performance in submerged membrane bioreactors, J. Membr. Sci. 284 (2006) 54–66. [20] H.-H. Ngo, W. Guo, Membrane fouling control and enhanced phosphorus removal in an aerated submerged membrane bioreactor using modified green bioflocculant, Bioresour. Technol. 100 (2009) 4289–4291. [21] T.A. Saleh, V.K. Gupta, Synthesis and characterization of alumina nano-particles polyamide membrane with enhanced flux rejection performance, Sep. Purif. Technol. 89 (2012) 245–251. [22] W. Jianlong, W. Jiazhuo, Application of radiation technology to sewage sludge processing: A review, J. Hazard. Mater. 143 (2007) 2–7. [23] R.D. Ambashta, M. Sillanpaa, Water purification using magnetic assistance: A review, J. Hazard. Mater. 180 (2010) 38–49. [24] A. Da˛browski, Adsorption-from theory to practice, Adv. Colloid Interf. Sci. 93 (1–3) (2001) 135–224. [25] Q. Jiuhui, Research progress of novel adsorption processes in water purification: a review, J. Environ. Sci. 20 (1) (2008) 1–13. [26] S.J.T. Pollard, F.E. Thompson, G.L. Mcconnachie, Microporous carbons from moringa oleifera husks for water purification in less developed countries, Water Res. 29 (1) (1995) 337–347. [27] G. Reschke, D. Gelbin, Application of adsorption for water-purification – a literature-review, Chem. Technol. 34 (3) (1982) 114–120. [28] R. Han, D. Ding, Y. Xu, W. Zou, Y. Wang, Y. Li, L. Zou, Use of rice husk for the adsorption of congo red from aqueous solution in column mode, Bioresour. Technol. 99 (2008) 2938–2946.

P. Kumari et al. / Sustainable Materials and Technologies 22 (2019) e00128 [29] A.N. Grace, C. Santhosh, V. Velmurugan, G. Jacob, S.K. Jeong, A. Bhatnagar, Role of nanomaterials in water treatment applications: A review, Chem. Eng. J. 306 (2016) 1116–1137. [30] S. Pacheco, M. Medina, F. Valencia, J. Tapia, Removal of inorganic mercury from polluted water using structured nanoparticles, J. Environ. Eng. 132 (2006) 342–349. [31] K. Yang, B. Xing, Desorption of polycyclic aromatic hydrocarbons from carbon nanomaterials in water, Environ. Pollut. 145 (2007) 529–537. [32] S. Wang, Y. Peng, Natural zeolites as effective adsorbents in water and wastewater treatment, Chem. Eng. J. 156 (2010) 11–24. [33] W.S. Wan Ngah, L.C. Teong, M.A.K.M. Hanafiah, Adsorption of dyes and heavy metal ions by chitosan composites: a review, Carbohydr. Polym. 83 (2011) 1446–1456. [34] S. Sen Gupta, K.G. Bhattacharyya, Adsorption of heavy metals on kaolinite and montmorillonite: a review, Phys. Chem. Chem. Phys. 14 (2012) 6698–6723. [35] A.A. Adeyemo, I.O. Adeoye, O.S. Bello, Metal organic frameworks as adsorbents for dye adsorption: overview, prospects and future challenges, Toxicol. Environ. Chem. 94 (2012) 1846–1863. [36] Y. Kim, J. Yi, Advances in environmental technologies via the application of mesoporous materials, J. Ind. Eng. Chem. 10 (2004) 41–51. [37] V.K. Gupta, A. Nayak, S. Agarwal, I. Tyagi, Potential of activated carbon from Waste Rubber Tire for the adsorption of phenolics: Effect of pre-treatment conditions, J. Colloid Interface Sci. 417 (2014) 420–430. [38] V.K. Gupta, T.A. Saleh, Sorption of pollutants by porous carbon, carbon nanotubes and fullerene - An overview, Environ. Sci. Pollut. Res. 20 (2013) 2828–2843. [39] N. Mohammadi, H. Khani, V.K. Gupta, E. Amereh, S. Agarwal, Adsorption process of methyl orange dye onto mesoporous carbon material–kinetic and thermodynamic studies, J. Colloid Interface Sci. 362 (2011) 457–462. [40] X. Ren, C. Chen, M. Nagatsu, X. Wang, Carbon nanotubes as adsorbents in environmental pollution management: a review, Chem. Eng. J. 170 (2011) 395–410. [41] G.P. Rao, C. Lu, F. Su, Sorption of divalent metal ions from aqueous solution by carbon nanotubes: a review, Sep. Purif. Technol. 58 (2007) 224–231. [42] M.B. Seymour, C. Su, Y. Gao, Y. Lu, Y. Li, Characterization of carbon nanoonions for heavy metal ion remediation, J. Nanopart. Res. 14 (2012) 1–13. [43] S. Wang, C.W. Ng, W. Wang, Q. Li, L. Li, A Comparative study on the adsorption of acid and reactive dyes on multiwall carbon nanotubes in single and binary dye systems, J. Chem. Eng. Data 57 (2012) 1563–1569. [44] S. Iijima, Helical microtubules of graphitic carbon, Nature 354 (1991) 56–58. [45] S. Iijima, T. Ichihashi, Single-shell carbon nanotubes of 1-nm diameter, Nature 363 (1993) 603–605. [46] D.S. Bethune, C.H. Klang, M.S. De Vries, et al., Cobalt-catalysed growth of carbon nanotubes with single-atomic-layer walls, Nature 363 (2003) 605–607. [47] V.K. Gupta, T.A. Saleh, Sorption of pollutants by porous carbon, carbon nanotubes and fullerene—an overview, Environ. Sci. Pollut. Res. 20 (2013) 2828–2843. [48] F.M. Machado, C.P. Bergmann, T.H.M. Fernandes, et al., Adsorption of reactive red M-2BE dye from water solutions by multi-walled carbon nanotubes and activated carbon, J. Hazard. Mater. 192 (2011) 1122–1131. [49] B. Pan, D.H. Lin, H. Mashayekhi, B.S. Xing, Adsorption and hysteresis of bisphenol A and 17 alpha-ethinyl estradiol on carbon nanomaterials, Environ. Sci. Technol. 42 (15) (2008) 5480–5485. [50] K. Yang, B.S. Xing, Adsorption of organic compounds by carbon nanomaterials in aqueous phase: Polanyi theory and its application, Chem. Rev. 110 (10) (2010) 5989–6008. [51] B. Pan, B.S. Xing, Adsorption mechanisms of organic chemicals on carbon nanotubes, Environ. Sci. Technol. 42 (24) (2008) 9005–9013. [52] S. Chowdhury, R. Balasubramanian, Recent advances in the use of graphene-family nanoadsorbents for removal of toxic pollutants from wastewater, Adv. Colloid Interf. Sci. 204 (2014) 35–56. [53] L.L. Ji, W. Chen, L. Duan, D.Q. Zhu, Mechanisms for strong adsorption of tetracycline to carbon nanotubes: a comparative study using activated carbon and graphite as adsorbents, Environ. Sci. Technol. 43 (7) (2009) 2322–2327. [54] X. Qu, P.J.J. Alvarez, Q. Li, Applications of nanotechnology in water and wastewater treatment, Water Res. 47 (2013) 3931–3946. [55] T.A. Saleh, V.K. Gupta, Processing methods, characteristics and adsorption behavior of tires derived carbons: a review, Adv. Colloid Interf. Sci. 211 (2014) 93–101. [56] K.S. Novoselov, A.K. Geim, S.V. Morozov, et al., Electric field effect in atomically thin carbon films, Science 306 (2004) 666–669. [57] Y. Li, Q. Du, T. Liu, et al., Comparative study of methylene blue dye adsorption onto activated carbon, graphene oxide, and carbon nanotubes, Chem. Eng. Res. Des. 91 (2013) 361–368. [58] Z.H. Huang, X. Zheng, W. Lv, M. Wang, Q.H. Yang, F. Kang, Adsorption of lead(II) ions from aqueous solution on low-temperature exfoliated graphene nanosheets, Langmuir 27 (2011) 7558–7562. [59] R. Sitko, B. Zawisza, E. Malicka, Graphene as a new sorbent in analytical chemistry, TrAC Trends Anal. Chem. 51 (2013) 33–43. [60] A. Stafiej, K. Pyrzynska, Adsorption of heavy metal ions with carbon nanotubes, Sep. Purif. Technol. 58 (2007) 49–52. [61] J. Zhao, Z. Wang, J.C. White, B. Xing, Graphene in the aquatic environment: adsorption, dispersion, toxicity and transformation, Environ. Sci. Technol. 48 (2014) 9995–10009. [62] F.K. Alanazi, A.A. Radwan, I.A. Alsarra, Biopharmaceutical applications of nanogold, Saudi Pharm. J. 18 (2010) 179–193. [63] C.R. Patra, R. Bhattacharya, D. Mukhopadhyay, P. Mukherjee, Fabrication of gold nanoparticles for targeted therapy in pancreatic cancer, Adv. Drug Deliv. Rev. 62 (2010) 346–361.

11

[64] Y. Cui, Y. Zhao, Y. Tian, W. Zhang, X. Lü, X. Jiang, The molecular mechanism of action of bactericidal gold nanoparticles on Escherichia coli, Biomaterials 33 (2012) 2327–2333. [65] N. Abdel-Raouf, N.M. Al-Enazi, I.B.M. Ibraheem, Green biosynthesis of gold nanoparticles using Galaxaura elongata and characterization of their antibacterial activity, Arab. J. Chem. 10 ( (2017) S3029–S3039. [66] N. Grier, Silver and its compounds, in: S.S. Block (Ed.), Disinfection, Sterilization and Preservation, Lea and Febiger, Philadelphia 1983, pp. 375–389. [67] A.D. Russell, F.R.C. Path, S.R. Phram, W.B. Hugo, Antimicrobial activity and action of silver, Prog. Med. Chem. 31 (1994) 351–370. [68] S. Singh, J.P. Saikia, A.K. Buragohain, A novel ‘green’ synthesis of colloidal silver nanoparticles (SNP) using Dillenia indica fruit extract, Colloid Surf. B 102 (2013) 83–85. [69] P. Kuppusamy, M.M. Yusoff, G.P. Maniam, N. Govindan, Biosynthesis of metallic nanoparticles using plant derivatives and their new avenues in pharmacological applications – an updated report, Saudi Pharmaceutical. J. 24 (2016) 473–484. [70] M.L. Yola, V.K. Gupta, T. Eren, A.E. Sen, N. Atar, A novel electro analytical nanosensor nanoparticles based on graphene oxide/silver for simultaneous determination of quercetin and morin, Electrochim. Acta 120 (2014) 204–211. [71] D.R. Monteiro, L.F. Gorup, A.S. Takamiya, A.C. Ruvollo, E.R. de Camargo, D.B. Barbosa, The growing importance of materials that prevent microbial adhesion: antimicrobial effect of medical devices containing silver, Int. J. Antimicrob. Agents 34 (2009) 103–110. [72] I. Sondi, B. Salopek-Sondi, Silver nanoparticles as antimicrobial agent: a case study on E-coli as a model for gram-negative bacteria, J. Colloid Interface Sci. 275 (2004) 177–182. [73] J.R. Morones, J.L. Elechiguerra, A. Camacho, K. Holt, J.B. Kouri, J.T. Ramirez, M.J. Yacaman, The bactericidal effect of silver nanoparticles, Nanotechnology 16 (2005) 2346–2353. [74] G.A. Martinez-Castanon, N. Nino-Martinez, F. Martinez-Gutierre, J.R. MartinezMendoza, F. Ruiz, Synthesis and antibacterial activity of silver nanoparticles with different sizes, J. Nanopart. Res. 10 (2008) 1343–1348. [75] K. Chaloupka, Y. Malam, A.M. Seifalian, Nanosilver as a new generation of nanoproduct in biomedical applications, Trends Biotechnol. 28 (2010) 580–588. [76] M. Goudarzi, M.S. Niasari, N. Mir, M.M. Kamazani, S. Bagheri, Biosynthesis and characterization of silver nanoparticles prepared from two novel natural precursors by facile thermal decomposition methods, Sci. Rep. 6 (2016), 32539. [77] F. Mohandes, M.S. Niasari, Sonochemical synthesis of silver vanadium oxide micro/ nanorods: Solvent and surfactant effects, Ultrason. Sonochem. 20 (2013) 354–365. [78] M.E. Zare, M.S. Niasari, A. Sobhani, Simple sonochemical synthesis and characterization of HgSe nanoparticles, Ultrason. Sonochem. 19 (2012) 1079–1086. [79] G. Kianpour, M.S. Niasari, H. Emadi, Sonochemical synthesis and characterization of NiMoO4 nanorods, Ultrason. Sonochem. 20 (2013) 418–424. [80] M.M. Arani, M.S. Niasari, A simple sonochemical approach for synthesis and characterization of Zn2SiO4 nanostructures, Ultrason. Sonochem. 29 (2016) 226–235. [81] D.D. Merin, S. Prakash, B.V. Bhimba, Antibacterial screening of silver nanoparticles synthesized by marine micro algae, Asian Pac J Trop Med 3 (2010) 797–799. [82] A. Tripathi, N. Chandrasekaran, A.M. Raichur, A. Mukherjee, Antibacterial applications of silver nanoparticles synthesized by aqueous extract of Azadirachta indica (Neem) leaves, J. Biomed. Nanotechnol. 5 (2009) 93–98. [83] S. Kumar, K. Sneha, Y.-S. Yun, Immobilization of silver nanoparticles synthesized using Curcuma longa tuber powder and extract on cotton cloth for bactericidal activity, Bioresour. Technol. 101 (2010) 7958–7965. [84] K.M. Kumar, B.K. Mandal, M. Sinha, V. Krishnakumar, Terminalia chebula mediated green and rapid synthesis of gold nanoparticles, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 86 (2012) 490–494. [85] A. l-Raouf, N.M. Al-Enazi, I.B.M. Ibraheem NM, Green biosynthesis of gold nanoparticles using Galaxaura elongata and characterization of their antibacterial activity, Arab. J. Chem. 10 ( (2017) S3029–S3039. [86] M. Gajbhiye, J. Kesharwani, A. Ingle, A. Gade, M. Rai, Fungus-mediated synthesis of silver nanoparticles and their activity against pathogenic fungi in combination with fluconazole, Nanomedicine 5 (2009) 382–386. [87] J. Musarrat, S. Dwivedi, B.R. Singh, A.A. Al-Khedhairy, A. Azam, A. Naqvi, Production of antimicrobial silver nanoparticles in water extracts of the fungus Amylomyces rouxii strain KSU-09, Bioresour. Technol. 101 (2010) 8772–8776. [88] C. Jayaseelan, R. Ramkumar, A.A. Rahuman, P. Perumal, Green synthesis of gold nanoparticles esculentus using seed aqueous extract of Abelmoschus and its antifungal activity, Ind. Crop. Prod. 45 (2013) 423–429. [89] I.A. Wani, T. Ahmad, Size and shape dependant antifungal A activity of gold nanoparticles: case study of Candida, Colloids Surf. B: Biointerfaces 101 (2013) 162–170. [90] L. Lu, R.W. Sun, R. Chen, C. Hui, C. Ho, J.M. Luk, G.K.K. Lau, C. Che, Silver nanoparticles inhibit hepatitis B virus replication, Antivir. Ther. 13 (2008) 253–262. [91] D. Gusseme, G. Du Laing, T. Hennebel, P. Renard, D. Chidambaram, J.P. Fitts, et al., Virus removal by biogenic cerium, Environ. Sci. Technol. 44 (2010) 6350–6356. [92] P.D. Gianvincenzo, M. Marradi, O.M.M. Ávila, L.M. Bedoya, J. Alcamí, S. Penadés, Gold nanoparticles capped with sulfate-ended ligands as anti-HIV agents, Bioorg. Med. Chem. Lett. 20 (2010) 2718–2721. [93] D.B. Pinto, S. Shukla, A. Gedanken, R. Sarid, Inhibition of HSV-1 attachment, entry, and cell-to-cell spread by functionalized multivalent gold nanoparticles, small 6 (2010) 1044–1050. [94] R. Saravanan, V.K. Gupta, T. Prakash, V. Narayanan, A. Stephen, Synthesis, characterization and photocatalytic activity of novel Hg doped ZnO nanorods prepared by thermal decomposition method, J. Mol. Liq. 178 (2013) 88–93.

12

P. Kumari et al. / Sustainable Materials and Technologies 22 (2019) e00128

[95] M.S. Niasari, M. Dadkhah, F. Davar, Synthesis and characterization of pure cubic zirconium oxide nanocrystals by decomposition of bis-aqua, tris-acetylacetonato zirconium(IV) nitrate as new precursor complex, Inorg. Chim. Acta 362 (2009) 3969–3974. [96] S.Z. Ajabshir, M.S. Niasari, Facile route to synthesize zirconium dioxide (ZrO2) nanostructures: structural, optical and photocatalytic studies, J. Mol. Liq. 216 (2016) 545–551. [97] M.S. Niasari, F. Mohandes, F. Davar, Preparation of PbO nanocrystals via decomposition of lead oxalate, Polyhedron 28 (2009) 2263–2267. [98] P.G. Tratnyek, R.L. Johnson, Nanotechnologies for environmental cleanup, Nano Today 1 (2006) 44–48. [99] A.-F. Ngomsik, A. Bee, M. Draye, G. Cote, V. Cabuil, Magnetic nano- and microparticles for metal removal and environmental applications: a review, C.R. Chim. 8 (2005) 963–970. [100] A. Vaseashta, M. Vaclavikova, S. Vaseashta, G. Gallios, P. Roy, O. Pummakarnchana, Nanostructures in environmental pollution detection, monitoring, and remediation, Sci. Technol. Adv. Mater. 8 (2007) 47–59. [101] E.A. Deliyanni, E.N. Peleka, K.A. Matis, Modeling the sorption of metal ions from aqueous solution by iron-based adsorbents, J. Hazard. Mater. 172 (2009) 550–558. [102] T. Pradeep, Anshup, Noble metal nanoparticles for water purification: a critical review, Thin Solid Films 517 (2009) 6441–6478. [103] B. Pan, B. Pan, W. Zhang, L. Lv, Q. Zhang, S. Zheng, Development of polymeric and polymer-based hybrid adsorbents for pollutants removal from waters, Chem. Eng. J. 151 (2009) 19–29. [104] G. Moussavi, M. Mahmoudi, Removal of azo and anthraquinone reactive dyes from industrial wastewaters using MgO nanoparticles, J. Hazard. Mater. 168 (2009) 806–812. [105] J. Hu, G. Chen, I.M.C. Lo, M. ASCE, Selective removal of heavy metals from industrial wastewater using maghemite nanoparticle: performance and mechanisms, J. Environ. Eng. 132 (2006) 709–715. [106] Y.I. Tarasevich, G.M. Klimova, Kaolinite, Complex-forming adsorbents based on aluminium oxide and polyphosphates for the extraction and concentration of heavy metal ions from water solutions, Appl. Clay Sci. 19 (2001) 95–101. [107] X.F. Ma, Y.Q. Wang, M.J. Gao, H.Z. ZnO, G.A. PbS Xu, A. Li, Novel strategy to prepare heterostructured functional adsorption nanocomposite utilizing the surface property of ZnO nanosheets, Catal. Today 158 (2010) 459–463. [108] E.A. Deliyanni, N.K. Lazaridis, E.N. Peleka, K.A. Matis, Metals removal from aqueous solution by iron-based bonding agents, Environ. Sci. Pollut. Res. 11 (2004) 18–21. [109] J. Hu, G.H. Chen, I.M.C. Lo, Removal by and recovery of Cr (VI) from wastewater maghemite nanoparticles, Water Res. 39 (2005) 4528–4536. [110] G.H. Chen Hu, I.M.C. Lo, Selective wastewater removal of heavy metals from industrial using maghemite nanoparticle: environ. performance and mechanisms, J. Eng.-ASCE. 132 (2006) 709–715. [111] M. Fan, T. Boonfueng, Y. Xu, L. Axe, T.A. Tyson, Modeling Pb sorption to microporous amorphous oxides as discrete particles and coatings, J. Colloid Interface Sci. 281 (2005) 39–48. [112] P.R. Grossl, D.L. Sparks, C.C. Ainsworth, Rapid kinetics of Cu(II) adsorption– desorption on goethite, Environ. Sci. Technol. 28 (1994) 1422–1429. [113] Y.H. Chen, F.A. Li, Kinetic study on removal of copper (II) using goethite and hematite nano-photocatalysts, J. Colloid Interface Sci. 347 (2010) 277–281. [114] A.R. Mandavian, M.A.S. Mirrahimi, Efficient separation of heavy metal cations by anchoring polyacrylic acid on superparamagnetic magnetite nanoparticles through surface modification, Chem. Eng. J. 159 (2010) 264–271. [115] J. Wang, S. Zheng, Y. Shao, J. Liu, Z. Xu, D. Zhu, Amino-functionalized Fe3O4 @SiO2 core–shell Magnetic nanomaterial as a novel adsorbent for aqueous heavy metals removal, J. Colloid Interface Sci. 349 (2010) 293–299. [116] A.Z.M. Badruddoza, A.S.H. Tay, P.Y. Tan, K. Hidajat, M.S. Uddin, Carboxymethylbeta-yclodextrin conjugated magnetic nanoparticles as nano-adsorbents for removal of copper ions: synthesis and adsorption studies, J. Hazard. Mater. 185 (2011) 1177–1186. [117] J.F. Liu, Z.S. Zhao, G.B. Jiang, Coating Fe3 O4 magnetic nanoparticles with humic acid for high efficient removal of heavy metals in water, Environ. Sci. Technol. 42 (2008) 6949–6954. [118] S.H. Huang, D.H. Chen, Rapid removal of heavy metal cations and anions from aqueous solutions by an amino-functionalized magnetic nano-adsorbent, J. Hazard. Mater. 163 (2009) 174–179. [119] X.-h. Guan, Y.-c. Qin, L.-w. Wang, R. Yin, M. Lu, Y.-j. Yang, Study on the disposal process for removing heavy metal ions from wastewater by composite biosorbent of nano Fe3O4 /Sphaerotilus natans, Chin. J. Environ. Sci. 28 (2007) 436–440. [120] J.E. Macdonald, J.G.C. Veinot, Removal of residual metal catalysts iron/iron with oxide nanoparticles from coordinating environments, Langmuir 24 (2008) 7169–7177. [121] U. Schwertmann, R.M. Taylor, Natural and synthetic poorly crystallized lepidocrocite, Clay Miner. 14 (1979) 285–293. [122] K. Hachiya, M. Sasaki, T. Ikeda, N. Mikami, T. Yasunaga, Static and kinetics studies of adsorption desorption of metal-ions on a gamma-Al2O3 surface. 2. Kinetic-study by means of pressure-jump technique, J. Phys. Chem. 88 (1984) 27–31. [123] K.F. Hayes, J.O. Leckie, Pressure-jump kinetic-studies of lead-ion adsorption at the goethite aqueous interface, Abstr. Am. Chem. Soc. 193 (1987) 205–209. [124] M. Eigen, K. Tamm, Schallabsorption In elektrolytlosungen als folge chemischer relaxation. 2. Messergebnisse und relaxationsmechanismen fur 2-2-wertige elektrolyte, Z. Elektrochem. 66 (1962) 107–121. [125] Y.H. Chen, F.A. Li, Kinetic study hematite on removal of copper (II) using goethite and nano-photocatalysts, J. Colloid Interface Sci. 347 (2010) 277–281. [126] J. Hu, G.H. Chen, I.M.C. Lo, Removal by and recovery of Cr (VI) from wastewater maghemite nanoparticles, Water Res. 39 (2005) 4528–4536.

[127] S. Babel, T.A. Kurniawan, Cr (VI) Removal from synthetic wastewater using coconut shell charcoal and commercial activated carbon modified with oxidizing agents and/or chitosan, Chemosphere 54 (2004) 951–967. [128] F.N. Acar, E. Malkoc, The removal by fagus of chromium (VI) From aqueous solutions orientalis L. Bioresour. Technol. 94 (2004) 13–15. [129] T.N.D. Dantas, A.A.D. Neto, M. Moura, Removal of chromium from aqueous solutions by diatomite treated with microemulsion, Water Res. 35 (2001) 2219–2224. [130] C.H. Weng, J.H. Wang, C.P. Huang, Adsorption of Cr (VI) onto TiO2 from dilute aqueous solutions, Water Sci. Technol. 35 (1997) 55–62. [131] J. Hu, G.H. Chen, I.M.C. Lo, Selective Wastewater removal of heavy metals from industrial using maghemite nanoparticle: Environ. Performance and mechanisms, J. Eng.-ASCE. 132 (2006) 709–715. [132] P. Tartaj, M.D. Morales, S. Veintemillas-Verdaguer, C.J. Serna, T. Gonzalez-Carreno, The preparation of magnetic nanoparticles for applications in biomedicine, J. Phys. D. Appl. Phys. 36 (2003) 182–197. [133] P. Tartaj, M.P. Morales, T. Gonzalez-Carreno, S. Veintemillas-Verdaguer, C.J. Serna, Advances In magnetic nanoparticles For biotechnology applications, J. Magn. Magn. Mater. 290 (2005) 28–34. [134] D. Maity, D.C. Agrawal, Synthesis of iron oxide nanoparticles under oxidizing environment and their stabilization In aqueous and non-aqueous media, J. Magn. Magn. Mater. 308 (2007) 46–55. [135] S. Shin, J. Jang, Thiol containing polymer encapsulated magnetic nanoparticles as reusable and efficiently separable adsorbent for heavy metal ions, Chem. Commun. (41) (2007) 4230–4232. [136] Y.C. Chang, D.H. Chen, Preparation chitosan-bound and adsorption properties of monodisperse Fe3O4 magnetic colloid nanoparticles for removal of Cu(II) ions, J. Interface Sci. 283 (2005) 446–451. [137] C.L. Warner, R.S. Addleman, A.D. Nash, T.C. Cinson, M.H. Droubay, M.A.W. Engelhard, M.G. Warner Yantasee, nanoparticle-based high-performance, superparamagnetic, heavy metal natural sorbents for removal of contaminants from waters, ChemSusChem 3 (2010) 749–757. [138] D.A. Dzombak, F.M.M. Morel, Sorption of cadmium on hydrous ferric-oxide at high sorbate/sorbent ratios equilibrium, kinetics, and modeling, J. Colloid Interface Sci. 112 (1986) 588–598. [139] F. Mohandes, F. Davar, M.S. Niasari, Magnesium oxide nanocrystals via thermal decomposition of magnesium oxalate, J. Phys. Chem. Solids 71 (2010) 1623–1628. [140] H.Q. Wang, G.F. Yang, Q.Y. Li, X.X. Zhong, F.P. Wang, Z.S. Li, Y.H. Li, Porous nanoMnO2: large scale synthesis via a facile quick-redox procedure and application in a supercapacitor, New J. Chem. 35 (2011) 469–475. [141] P. Larger-Trivedi, L. Axe, A comparison of strontium sorption to hydrous aluminum, iron, and manganese oxides, J. Colloid Interface Sci. 218 (1999) 554–563. [142] S.P. Mishra, Vijaya, Removal behaviour of hydrous manganese oxide and hydrous stannic oxide for Cs (I) Ions from aqueous solutions, Sep. Purif. Technol. 54 (2007) 10–17. [143] T. Takamatsu, M. Kawashima, M. Koyama, The role of Mn2+ -rich hydrous manganese - oxide in the accumulation of arsenic in lake-sediments, Water Res. 19 (1985) 1029–1032. [144] M. Kawashima, Y. Tainaka, T. Hori, M. Koyama, T. Takamatsu, Phosphate adsorption onto hydrous manganese (IV) Oxide in the presence of divalent-cations, Water Res. 20 (1986) 471–475. [145] S.P. Mishra, S.S. Dubey, D. Tiwari, Rapid and efficient removal of Hg (II) by Hydrous manganese and tin oxides, J. Colloid Interface Sci. 279 (2004) 61–67. [146] K.M. Parida, S.B. Kanungo, B.R. Sant, Studies on MnO2.1. chemical- composition, microstructure and other characteristics of some synthetic MnO2 of various crystalline modifications, Electrochim. Acta 26 (1981) 435–443. [147] M. Misono, E.I. Ochiai, Y. Saito, Y. Yoneda, A new dual parameter scale for strength of Lewis acids and bases with evaluation of their softness, J. Inorg. Nucl. Chem. 29 (1967) 2685–2691. [148] J.D. Li, Y.L. Shi, Y.Q. Cai, S.F. Mou, G.B. Jiang, Adsorption of di-ethyl-phthalate from aqueous solutions with surfactant-coated nano/microsized alumina, Chem. Eng. J. 140 (2008) 214–220. [149] M. Hiraide, J. Iwasawa, S. Hiramatsu, H. Kawaguchi, Use of surfactant aggregates formed on alumina for the preparation of chelating sorbents, Anal. Sci. 11 (1995) 611–615. [150] G. Chang, Z. Jiang, T. Peng, B. Hu, Preparation of high-specific-surface-area nanometer-sized alumina by sol–gel method and study on adsorption behaviors of transition metal ions on the alumina powder with ICP-AES, Acta Chim. Sin. 61 (2003). [151] M. Hiraide, M.H. Sorouradin, H. Kawaguchi, Immobilization of dithizone on surfactant-coated alumina for preconcentration of metal-ions, Anal. Sci. 10 (1994) 125–127. [152] M. Ghaedi, K. Niknam, A. Shokrollahi, E. Niknam, H.R. Rajabi, M. Soylak, Flame atomic absorption spectrometric determination of trace amounts of heavy metal ions after solid phase extraction using modified sodium dodecyl sulfate coated on alumina, J. Hazard. Mater. 155 (2008) 121–127. [153] S. Dadfarnia, A.M.H. Shabani, H.D. Shirie, Determination of lead in different samples by atomic absorption spectrometry after preconcentration with dithizone immobilized on surfactant-coated alumina, Bull. Kor. Chem. Soc. 23 (2002) 545–548. [154] A.M.H. Shabani, S. Dadfarnia, Z. Dehghani, On-line Solid phase extraction system using 1,10-phenanthroline immobilized on surfactant coated alumina for the flame atomic absorption spectrometric determination of copper cadmium, and, Talanta 79 (2009) 1066–1070. [155] F. Davar, M.S. Niasari, Synthesis and characterization of spinel-type zinc aluminate nanoparticles by a modified sol–gel method using new precursor, J. Alloys Compd. 509 (2011) 2487–2492.

P. Kumari et al. / Sustainable Materials and Technologies 22 (2019) e00128 [156] M.S. Niasari, M.F. Khouzani, F. Davar, Bright blue pigment CoAl2O4 nanocrystals prepared by modified sol–gel method, J. Sol-Gel Sci. Technol. 52 (2009) 321–327. [157] M.S. Niasari, Ship-in-a-bottle synthesis, characterization and catalytic oxidation of styrene by host (nanopores of zeolite-Y)/guest ([bis(2-hydroxyanil) acetylacetonato manganese(III)]) nanocomposite materials (HGNM), Microporous Mesoporous Mater. 95 (2006) 248–256. [158] R. Saravanan, E. Thirumal, V.K. Gupta, V. Narayanan, A. Stephen, The photocatalytic activity of ZnO prepared by simple thermal decomposition method at various temperatures, J. Mol. Liq. 177 (2013) 394–401. [159] R. Saravanan, E. Sacari, F. Gracia, M.M. Khan, E. Mosquera, V.K. Gupta, Conducting PANI stimulated ZnO system for visible light photocatalytic degradation of coloured dyes, J. Mol. Liq. 221 (2016) 1029–1033. [160] R. Saravanan, V.K. Gupta, E. Mosquera, F. Gracia, Preparation and characterization of V2O5/ZnO nanocomposite system for photocatalytic application, J. Mol. Liq. 198 (2014) 409–412. [161] R. Saravanan, M.M. Khan, V.K. Gupta, E. Mosquera, F. Gracia, V. Narayanan, A. Stephen, ZnO/Ag/Mn2O3 nanocomposite for visible light-induced industrial textile effluent degradation, uric acid and ascorbic acid sensing and antimicrobial activities, RSC Adv. 5 (2015) 34645–34651. [162] M.S. Niasari, F. Davar, Z. Fereshteh, Synthesis and characterization of ZnO nanocrystals from thermolysis of new precursor, Chem. Eng. J. 146 (2009) 498–502. [163] R. Saravanan, M. Mansoob Khan, Vinod Kumar Gupta, E. Mosquera, F. Gracia, V. Narayanan, A. Stephen, ZnO/Ag/CdO nanocomposite for visible light-induced photocatalytic degradation of industrial textile effluents, J. Colloid Interface Sci. 452 (2015) 126–133. [164] T.A. Saleh, V.K. Gupta, Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide, J. Colloid Interface Sci. 371 (2012) 101–106. [165] S. Rajendran, V.K. Gupta, M.M. Khan, F. Gracia, J. Qin, S. Arumainathan, Ce3+-ioninduced visible-light photocatalytic degradation and electrochemical activity of ZnO/CeO2 nanocomposite, Sci. Rep. 6 (2016), 31641. [166] R. Saravanan, V.K. Gupta, V. Narayanan, A. Stephen, Visible light degradation of textile effluent using novel catalyst ZnO/g-Mn2O3, J. Taiwan Inst. Chem. Eng. 45 (2014) 1910–1917. [167] T.A. Saleh, V.K. Gupta, Functionalization of tungsten oxide into MWCNT and its application for sunlight-induced degradation of rhodamine B, J. Colloid Interface Sci. 362 (2011) 337–344. [168] S.Z. Ajabshir, M.S. Morassaei, M.S. Niasari, Facile fabrication of Dy2Sn2O7-SnO2 nanocomposites as an effective photocatalyst for degradation and removal of organic contaminants, J. Colloid Interface Sci. 497 (2017) 298–308. [169] R. Saravanan, S. Joicy, V.K. Gupta, V. Narayanan, A. Stephen, Visible light induced degradation of methylene blue using CeO2/V2O5 and CeO2/CuO catalysts, Mater. Sci. Eng. C 33 (2013) 4725–4731. [170] H. Safajou, H. Khojasteh, M.S. Niasari, S.M. Derazkola, Enhanced photocatalytic degradation of dyes over graphene/Pd/TiO2 nanocomposites: TiO2 nanowires versus TiO2 nanoparticles, J. Colloid Interface Sci. 498 (2017) 423–432. [171] L.B. Kiss, J. So derlund, G.A. Niklasson, C.G. Granqvist, New approach to the origin of lognormal size distributions of nanoparticles, Nanotechnology 10 (1999) 25–28. [172] C. Buzea, I. Pacheco, K. Robbie, Nanomaterials and nanoparticles: sources and toxicity, Biointerphases 2 (4) (2007) 17–71. [173] I. Ali, New generation adsorbents for water treatment, Chem. Rev. 112 (2012) 5073–5091. [174] E.A. Deliyanni, N.K. Lazaridis, E.N. Peleka, K.A. Matis, Metals removal from aqueous solution by iron-based bonding agents, Environ. Sci. Pollut. Res. 11 (2004) 18–21. [175] Y.H. Huang, C.I. Hsueh, H.P. Cheng, L.C. Su, C.Y. Chen, Thermodynamics and kinetics of adsorption of Cu(II) onto waste iron oxide, J. Hazard. Mater. 144 (2006) 406–411. [176] H. Brammer, P. Ravenscroft, Arsenic in groundwater: a threat to sustainable agriculture in South and South-east Asia, Environ. Int. 35 (2009) 647–654. [177] A. Chatterjee, D. Das, B.K. Mandal, T.R. Chowdhury, G. Samanta, D. Chakraborti, Arsenic in ground water in six districts of West Bengal, India: the biggest arsenic calamity in the world. Part I. Arsenic species in drinking water and urine of the affected people, Analyst 120 (1995) 643. [178] D. Das, A. Chatterjee, B.K. Mandal, C. Samanta, D. Chakraborti, B. Chanda, Arsenic in ground water in six districts of West Bengal, India: the biggest arsenic calamity in the world. Part 2. Arsenic concentration in drinking water, hair, nails, urine, skinscale and liver tissue (biopsy) of the affected people, Analyst 120 (1995) 917. [179] S. Martinez-Vargas, Arturo I. Martı´nez, Elias E. Herna´ndez-Beteta, O.F. MijangosRicardez, V. Va´zquez-Hipo´lito, C. Patin˜o-Carachure, H. Hernandez-Flores, J. Lo´ pez-Luna, Arsenic adsorption on cobalt and manganese ferrite nanoparticles, J. Mater. Sci. 52 (2017) 6205–6215. [180] D. Dickson, G. Liu, Y. Cai, Adsorption kinetics and isotherms of arsenite and arsenate on hematite nanoparticles and aggregates, J. Environ. Manag. 186 (2017) 261–267. [181] S. Hokkanen, E. Repo, S. Lou, M. Sillanpää, Removal of arsenic(V) by magnetic nanoparticle activated microfibrillated cellulose, Chem. Eng. J. 260 (2015) 886–894. [182] F. Depault, M. Cojocaru, F. Fortin, S. Chakrabarti, N. Lemieux, Genotoxic effects of chromium(VI) and cadmium(II) in human blood lymphocytes using the electron microscopy in situ end-labeling (EM-ISEL) assay, Toxicol. in Vitro 20 (2006) 513–518. [183] A. Al Nafiey, A. Addad, B. Sieber, G. Chastanet, A. Barras, S. Szunerits, R. Boukherroub, Reduced graphene oxide decorated with Co3O4 nanoparticles (rGO-Co3O4) nanocomposite: a reusable catalyst for highly efficient reduction of

[184]

[185]

[186]

[187]

[188]

[189]

[190]

[191]

[192]

[193]

[194]

[195]

[196]

[197]

[198]

[199]

[200] [201] [202]

[203]

[204]

[205]

[206] [207]

[208]

[209]

[210]

13

4-nitrophenol, and Cr(VI) and dye removal from aqueous solutions, Chem. Eng. J. 322 (2017) 375–384. M. Fazlzadeh, K. Rahmani, A. Zarei, H. Abdoallahzadeh, F. Nasiri, R. Khosravi, A novel green synthesis of zero valent iron nanoparticles (NZVI) using three plant extracts and their efficient application for removal of Cr(VI) from aqueous solutions, Adv. Powder Technol. 28 (2017) 122–130. V.K. Gupta, R. Chandra, I. Tyagi, M. Verma, Removal of hexavalent chromium ions using CuO nanoparticles for water purification applications, J. Colloid Interface Sci. 478 (2016) 54–62. V.K. Gupta, I. Ali, T.A. Saleh, M.N. Siddiqui, S. Agarwal, Chromium removal from water by activated carbon developed from waste rubber tires, Environ. Sci. Pollut. Res. 20 (2013) 1261–1268. A. Keshavarz, Z. Parang, A. Nasseri, The effect of sulfuric acid, oxalic acid, and their combination on the size and regularity of the porous alumina by anodization, J. Nanostruct. Chem. 3 (2013) 34–38. J. Li, C. Chen, K. Zhu, X. Wang, Nanoscale zero-valent iron particles modified on reduced graphene oxides using a plasma technique for Cd(II) removal, J. Taiwan Inst. Chem. Eng. 59 (2016) 389–394. M. Savasari, P. Biparva, M. Emadi, M.A. Bahmanyar, Optimization of Cd (II) removal from aqueous solution by ascorbic acidstabilized zero valent iron nanoparticles using response surface methodology, J. Ind. Eng. Chem. 21 (2015) 1403–1409. S. Tabesh, F. Davar, M.R. Loghman-Estarki, Preparation of γ-Al2O3 nanoparticles using modified sol-gel method and its use for the adsorption of lead and cadmium ions, J. Alloys Compd. 730 (2018) 441–449. L.F. Chen, H.W. Lang, Y. Lu, C.H. Cui, S.H. Yu, Synthesis of an Attapulgite clay@carbon nanocomposite adsorbent by a hydrothermal carbonization process and their application in the removal of toxic metal ions from water, Langmuir 27 (2011) 8998–9004. S. Luo, T.T. Lu, L. Peng, J.H. Shao, Q.R. Zeng, J.D. Gu, Synthesis of nanoscale zerovalent iron immobilized in alginate microcapsules for removal of Pb (II) from aqueous solution, J. Mater. Chem. A 2 (2014) 15463–15472. H. Fan, S. Zhou, W. Jiao, G. Qi, Y. Liu, Removal of heavy metal ions by magnetic chitosan nanoparticles prepared continuously via high-gravity reactive precipitation method, Carbohydr. Polym. 174 (2017) 1192–1200. K. Chen, J. He, Y. Li, X. Cai, K. Zhang, T. Liu, Y. Hu, D. Lin, L. Kong, J. Liu, Removal of cadmium and lead ions from water by sulfonated magnetic nanoparticle adsorbents, J. Colloid Interface Sci. 494 (2017) 307–316. C. Xiong, W. Wang, F. Tan, F. Luo, J. Chen, X. Qiao, Title: Investigation on the efficiency and mechanism of Cd(II) and Pb(II) removal from aqueous solutions using MgO nanoparticles, J. Hazard. Mater. 299 (2015) 664–674. R. Davarnejad, P. Panahi, Cu (II) removal from aqueous wastewaters by adsorption on the modified Henna with Fe3O4 nanoparticles using response surface methodology, Sep. Purif. Technol. 158 (2016) 286–292. H. A. Sani, M. B. Ahmad, M. Z. Hussein, N. A. Ibrahim, A. Musa, T. A. Saleh, Nanocomposite of ZnO with montmorillonite for removal of lead and copper ions from aqueous solutions Process. Saf. Environ. Prot., 109 (17) 97-105. M. Fouladgar, M.B.H. Sabzyan, Single and binary adsorption of nickel and copper from aqueous solutions by γ-alumina nanoparticles: equilibrium and kinetic modelling, J. Mol. Liq. 211 (2015) 1060–1073. S. Agarwal, I. Tyagi, V.K. Gupta, M.H. Dehghani, J. Jaafari, D. Balarak, M. Asif, Rapid removal of noxious nickel (II) using novel γ-alumina nanoparticles and multiwalled carbon nanotubes: kinetic and isotherm studies, J. Mol. Liq. 224 ( (2016) 618–623. R.K. Gautam, P.K. Gautam, S. Banerjee, S.S.K. Singh, M.C. Chattopadhyaya, Removal of Ni(II) by magnetic nanoparticles, J. Mol. Liq. 204 (2015) 60–69. M. Ma, H. Gao, Y. Sun, M. Huang, The adsorption and desorption of Ni(II) on Al substituted goethite, J. Mol. Liq. 201 (2015) 30–35. W. Liu, P. Zhang, A.G.L. Borthwick, H. Chen, J. Ni, Adsorption mechanisms of thallium(I) and thallium(III) by titanate nanotubes: Ion-exchange and coprecipitation, J. Colloid Interface Sci. 423 (2014) 67–75. M. Ahmed, T. Azzam Shaimaa, B. El-Wakeel Bayaumy, Mostafa Fathy M. El-Shahat, Removal of Pb, Cd, Cu and Ni from aqueous solution using nano scale zero valent iron particles, J. Environ. Chem. Eng. 4 (2016) 2196–2206. W. Yantasee, C.L. Warner, T. Sangvanich, R. Shane Addleman, T.G. Carter, R.J. Wiacek, G.E. Fryxell, C. Timchalk, M.G. Warner, Removal of heavy metals from aqueous systems with Thiol functionalized superparamagnetic nanoparticles, Environ. Sci. Technol. 41 (2007) 5114–5119. I. Ali, Z.A. Alothman, A. Alwarthan, Supra molecular mechanism of the removal of 17-β-estradiol endocrine disturbing pollutant from water on functionalized iron nano particles, J. Mol. Liq. 241 (2017) 123–129. O.M. Alharbi, A.A. Basheer, R.A. Khattab, I. Ali, Health and environmental effects of persistent organic pollutants, J. Mol. Liq. 263 (2018) 442–453. A.A. Ahmad, B.H. Hameed, Fixed-bed adsorption of reactive azo dye onto granular activated carbon prepared from waste, J. Hazard. Mater. 175 (2010) 298–303. R. Saravanan, S. Karthikeyan, V.K. Gupta, G. Sekaran, V. Narayanan, A. Stephen, Enhanced photocatalytic activity of ZnO/CuO nanocomposite for the degradation of textile dye on visible light illumination, Mater. Sci. Eng. C 33 (2013) 91–98. V.K. Gupta, R. Jain, A. Nayak, S. Agarwal, M. Shrivastava, Removal of the hazardous dye—Tartrazine by photodegradation on titanium dioxide surface, Mater. Sci. Eng. C 31 (2011) 1062–1067. R. Saravanan, N. Karthikeyan, V.K. Gupta, E. Thirumal, P. Thangadurai, V. Narayanan, A. Stephen, ZnO/Ag nanocomposite: an efficient catalyst for degradation studies of textile effluents under visible light, Mater. Sci. Eng. C 33 (2013) 2235–2244.

14

P. Kumari et al. / Sustainable Materials and Technologies 22 (2019) e00128

[211] M.S. Niasari, F. Soofivand, A.S. Nasab, M.S. Arani, A.Y. Faal, S. Bagheri, Synthesis, characterization, and morphological control of ZnTiO3 nanoparticles through solgel processes and its photocatalyst application, Adv. Powder Technol. 27 (2016) 2066–2075. [212] R. Saravanan, V.K. Gupta, V. Narayanan, A. Stephen, Comparative study on photocatalytic activity of ZnO prepared by different methods, J. Mol. Liq. 181 (2013) 133–141. [213] R. Saravanan, S. Joicy, V.K. Gupta, V. Narayanan, A. Stephen, Visible light induced degradation of methylene blue using CeO2/V2O5 and CeO2/CuO catalysts, Mater. Sci. Eng. C 33 (2013) 4725–4731. [214] A. Asfaram, M. Ghaedi, S. Agarwal, I. Tyagi, V.K. Gupta, Removal of basic dye Auramine-O by ZnS: Cu nanoparticles loaded on activated carbon optimization of parameters using response surface methodology with central composite design, RSC Adv. 5 (2015) 18438–18450. [215] J. Liu, S. Ma, L. Zang, Preparation and characterization of nanoparticle ammoniumfunctionalized silica as a new adsorbent to remove methyl orange from aqueous solution, Appl. Surf. Sci. 265 (2013) 393–398. [216] A. Mittal, J. Mittal, A. Malviya, V.K. Gupta, Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials, J. Colloid Interface Sci. 344 (2010) 497–507. [217] S.Y. Mak, D.H. Chen, Fast adsorption of methylene blue on polyacrylic acidbound iron oxide magnetic nanoparticles, Dyes Pigments 61 (2004) 93–98. [218] L. Tang, Y. Cai, G. Yang, Y. Liu, G. Zeng, Y. Zhou, S. Li, J. Wang, S. Zhang, Y. Fang, Y. He, Cobalt nanoparticles-embedded magnetic carbon ordered mesoporous for highly effective adsorption of rhodamine B, Appl. Surf. Sci. 314 (2014) 746–753. [219] H. El, D. Mekatel, S. Nibou, A. Amokrane, M. Trari Aid, Adsorption of methyl orange on nanoparticles of synthetic zeolite NaA/CuO, C. R. Chim. 18 (2015) 336–344. [220] M. Ahmaruzzaman, V.K. Gupta, Rice husk and its ash as low-cost adsorbents in water and wastewater treatment, Ind. Eng. Chem. Res. 50 (2011) 13589–13613. [221] V.K. Gupta, C.K. Jain, I. Ali, S. Chandra, S. Agarwal, Removal of lindane and malathion from wastewater using bagasse fly ash-a sugar industry waste, Water Res. 36 (2002) 2483–2490. [222] S.M. Dehaghi, P.A. Azar, B. Rahmanifar, A.M. Moradi, Removal of permethrin pesticide from water by chitosan-zinc oxide nanoparticles composite as an adsorbent, J. Saudi Chem. Soc. 18 (2014) 248–355. [223] F. Liu, Li-Xiong Wen, Z. Li, H. Sun, W. Yu, J. Chen, Porous hollow silica nanoparticles as controlled delivery system for water-soluble pesticide, Mater. Res. Bull. 41 (2006) 2268–2275. [224] A. Sreekumaran Nair, T. Pradeep, Extraction of chlorpyrifos and malathion from water by metal nanoparticles, J. Nanosci. Nanotechnol. 7 (2007) 1–7.

[225] Q.L. Shimabuku, F.S. Arakawa, M.F. Silva, P.F. Coldebella, T.U. Nakamura, M.R.F. Klen, R. Bergamasco, Water treatment with exceptional virus inactivation using activated carbon modified with silver (Ag) and copper oxide (CuO) nanoparticles, Environ. Technol. 38 (2016) 2058–2069. [226] M.A. Asghar, M.A. Asghar, E. Zahir, S.M. Shahid, M.N. Khan, J. Iqbal, G. Walker, Iron, copper and silver nanoparticles: Green synthesis using green and black tea leaves extracts and evaluation of antibacterial, antifungal and aflatoxin B1 adsorption activity, LWT Food Sci. Technol. 90 (2018) 98–107. [227] G. Darabdhara, P.K. Boruah, N. Hussain, B.B. Sharma Priyakshree, Pinaki Sengupta, Manash R. Das, Magnetic nanoparticles towards efficient and adsorption of gram positive gram negative bacteria: An Investigation parameters of adsorption and interaction mechanism, Colloids Surf. A Physicochem. Eng. Aspects 516 (2017) 161–170. [228] V.K. Gupta, N. Atar, M.L. Yola, Z. Ustundag, L. Uzun, A novel magnetic Fe@Au coreshell nanoparticles anchored graphene oxide recyclable nanocatalyst for the reduction of nitrophenol compounds, Water Res. 48 (2014) 210–217. [229] Y. Babaee, C.N. Mulligan, Md S. Rahaman, Removal of arsenic (III) and arsenic (V) from aqueous solutions through adsorption by Fe/Cu nanoparticles, J. Chem. Technol. Biotechnol. 93 (2018) 63–71. [230] E. Ghasemi, A. Heydari, M. Sillanpaa, Superparamagnetic Fe3O4@EDTA nanoparticles as an efficient adsorbent for simultaneous removal of Ag(I), Hg(II), Mn(II), Zn(II), Pb (II) and Cd (II) from water and soil environmental samples, Microchem. J. 131 (2017) 51–56. [231] D. Zhao, X. Gao, C. Wu, R. Xie, S. Feng, C. Chen, Facile preparation of amino functionalized with graphene oxide decorated Fe3O4 nanoparticles for the adsorption of Cr(VI), Appl. Surf. Sci. 384 (2016) 1–9. [232] V. Srivastava, Y.C. Sharma, M. Sillanpaa, Response surface methodological approach for the optimization of adsorption process in the removal of Cr(VI) ions by Cu2 (OH)2CO3 nanoparticles, Appl. Surf. Sci. 326 (2015) 257–270. [233] W. Lu, J. Li, Y. Sheng, X. Zhang, J. You, L. Chen, One-pot synthesis of magnetic iron oxide nanoparticle-multiwalled carbon nanotube composites for enhanced removal of Cr(VI) from aqueous solution, J. Colloid Interface Sci. 505 (2017) 1134–1146. [234] M.A. Karimi, M. Kafi, Removal, preconcentration and determination of Ni(II) from different environmental samples using modified magnetite nanoparticles prior to flame atomic absorption spectrometry, Arab. J. Chem. 8 (2015) 812–820. [235] L. Li, M. Fan, R.C. Brown, J. Van Leeuwen, J. Wang, W. Wang, Y. Song, P. Zhang, Synthesis, properties, and environmental applications of nanoscale iron-based materials: a review, Crit. Rev. Environ. Sci. Technol. 36 (2006) 405–431. [236] C.P. Bergmann, F.M. Machado, Carbon Nanomaterials as Adsorbents for Environmental and Biological Applications, Springer, 2015.