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ISSN : 1225-0112(Print)
ISSN : 2288-4505(Online)
Applied Chemistry for Engineering Vol.33 No.5 pp.502-522
DOI : https://doi.org/10.14478/ace.2022.1089

Advancement of Clay and Clay-based Materials in the Remediation of Aquatic Environments Contaminated with Heavy Metal Toxic Ions and Micro-pollutants

Lalhmunsiama, Ralte Malsawmdawngzela*, Chhakchhuak Vanlalhmingmawia*, Diwakar Tiwari*†, Yiyong Yoon**†
Department of Industrial Chemistry, School of Physical Sciences Mizoram University, Aizawl 796004, India
*Department of Chemistry, School of Physical Sciences Mizoram University, Aizawl 796004, India
**Department of Biosystems and Convergence Engineering, Catholic Kwandong University, Gangneung 25601, Korea
† Corresponding Author: Diwakar Tiwari: Department of Chemistry, School of Physical Sciences Mizoram University, Aizawl 796004, India; Yiyong Yoon: Department of Biosystems and Convergence Engineering, Catholic Kwandong University, Gangneung 25601, Korea Tel: Diwakar Tiwari: +91-389-2330642; Yiyong Yoon: +82-33-649-7538 e-mail: Diwakar Tiwari: diw_tiwari@yahoo.com; Yiyong Yoon: yoonyy@cku.ac.kr
August 24, 2022 ; September 14, 2022 ; September 15, 2022

Abstract


Clay minerals are natural materials that show widespread applications in various branches of science, including environmental sciences, in particular the remediation of water contaminated with various water pollutants. Modified clays and minerals have attracted the attention of researchers in the recent past since the modified materials are seemingly more useful and efficient for removing emerging water contaminants. Therefore, modified engineered materials having multi-functionalities have received greater interest from researchers. The advanced clay-based materials are highly effective in the remediation of water contaminated with organic and inorganic contaminants, and these materials show enhanced selectivity towards the specific pollutants. The review inherently discusses various methods employed in the modification of clays and addresses the challenges in synthesizing the advanced engineered materials precursor to natural clay minerals. The changes in physical and chemical properties, as investigated by various characterization techniques before and after the modifications, are broadly explained. Further, the implications of these materials for the decontamination of waterbodies as contaminated with potential water pollutants are extensively discussed. Additionally, the insights involved in the removal of organic and inorganic pollutants are discussed in the review. Furthermore, the future perspectives and specific challenges in the scaling up of the treatment methods in technology development are included in this communication.


Advanced clay based materials , Sorption mechanism , Micro-pollutants , Heavy metals , Synthesis of advanced materials

초록

    1. Introduction

    Rapid industrialization and urbanization resulted in the deleterious quality of fresh water. The occurrence of toxic heavy metals and emerging micro-pollutants in water resources is increased tremendously with the advent of enhanced industrial and anthropogenic activities, including the mining industry, electroplating industry, pesticides, metal rinse processes, tanning industry, textile industry, batteries, metal smelting, paper industry, electrolysis applications etc.[1,2]. Many heavy metals, including mercury, lead, copper, cadmium, arsenic, chromium, and many other (toxic) metals, are excessively released, which causes serious environmental and public health issues[3,4]. The primary sources, permissible levels in drinking water, and health effects of heavy metals are given in Table 1. The heavy metals are persistent and non-biodegradable; hence, even at low concentrations posing serious environmental concerns. The presence of these contaminants in water- bodies resulted in a slow accumulation in the biological systems, both in marine and human lives. Hence, eliminating these heavy metals is a viable and effective solution to safeguard the human and aquatic environment[5].

    Similarly, excess release of harmful endocrine-disrupting chemicals (EDCs), pharmaceuticals, dyes, personal care products etc. are entering the aquatic environment through various anthropogenic activities[6,7]. Micro-pollutants are usually detected at trace quantities ranging from μg/L to ng/L in waterbodies, including river and lake waters. Since the traditional wastewater treatment plants are not specifically designed to eliminate these emerging pollutants at low levels. Moreover, their potential persistency and bioactivity caused an additional pollutant load to the water bodies, which needs efficient removal of these emerging contaminants from the aquatic environment. Different types of micropollutants and their effects on human health are summarized in Table 2. Due to extensive and continuous usage of these pollutants with unmanaged disposal in the water bodies, they are detected in the aquatic environment. Therefore, these micro-pollutants pose several health issues in humans and living organisms and received a global concern [8,9].

    Removing of toxic heavy metals and micro-pollutants from water bodies is of great environmental concern. A literature survey reveals that several methods, including chemical precipitation, evaporation, re- verse osmosis, solvent extraction, ion exchange, biological, photocatalysis, electrochemical treatment, membrane filtration, etc. are employed for the decontamination of water polluted with toxic metal ions, including micro-pollutants[35,36]. Nevertheless, these methods have several disadvantages, for example, expensive, the requirement of skilled personnel for operation, incomplete removal, generation of by-products, and high energy requirement[37,38]. Moreover, these processes are not efficient for low-level metal pre-concentration. Adsorption is one of the most common methods used to remove of these pollutants from the aquatic environment due to its low cost, simplicity of operation, effectiveness, and high efficiency compared to other traditional removal methods[39-43]. Moreover, adsorbents could be reutilized by following an appropriate desorption procedure[44,45].

    Clays are the most common adsorbents used in adsorption methods due to their abundance, low cost, eco-friendly, high specific surface area, etc.[46]. Researchers around the globe are focusing on the use of natural and modified clays as adsorbents for treating wastewater since it contains exchangeable cations along with the surface functional groups, which facilitate the sorption of various water contaminants[47]. Clay minerals consist of alumino silicate sheets, of which the structural layers are firmly arranged, and each sheet is made up of two, three, or four layers. This constitutes tetrahedral silicate [SiO4]4-(T) and octahedral aluminate [AlO3(OH)3]6-(O). The smaller metal cations occupy the interiors of tetrahedrons and octahedrons, and the oxygen atom occupies the apices from which some are connected with protons (as OH). Thus, fundamental structural elements form the hexagonal network with each sheet. The charges of the layers depend upon the ratio and number of sheets in the fundamental structural units[48,49].

    Clay minerals are efficient in removing several heavy metal toxic ions effectively, however; the organic pollutants having non- or lowpolarity and anionic impurities such as As(V), As(III), Cr(VI) etc., are less attracted by these pristine clay minerals[48,50,51]. Anionic contaminants and hydrophobic or non-polar organic pollutants, are feebly adsorbed by these clays, which possess enhanced hydrophilic character and charges on the surface[52,53]. Moreover, the pristine clay particles are difficult to recover and regenerate after the adsorption process and usually lose a significant quantity of their adsorption capacities during the regeneration process[54]. Therefore, the raw clay minerals require suitable modifications to remove these water pollutants efficiently these water pollutants. The suitable modification of clay minerals results in useful and engineered material in environmental engineering[55,56] and material sciences[57,58]. Organic cations with short and long-chain compounds are introduced within the interlayer spaces with the available exchangeable cations and the permanent negative charge of clay minerals. Thus, these modifications considerably change the hydrophilic nature of clay to hydrophobic nature, which in turn is employed to remove efficiently several organic compounds or even anionic water pollutants[59]. The synthesis of nanocomposites and incorporation into clay minerals has become of great interest recently because of their physical and chemical properties and distinctive applications in the diverse area of research[60,61]. Modification of clay minerals mainly involved two processes, i.e., chemical and physical processes. Modifying natural clay minerals with surfactants has shown their efficient adsorption process but their combined surface and thermal potential still need to be studied. Removal of several contaminants could be achieved using hybrid materials having inorganic/organic moieties[62]. Clay minerals physically modified by thermal activation remove intercrystallite water molecules and increases porosity and surface area[63]. Therefore, this review focussed on the applicability of natural clay and its modified form for removing toxic heavy metals and micro-pollutants from aqueous solutions.

    2. Use of natural clay in the removal of heavy metals and micro-pollutants

    Kaolinite[64], montmorillonite[65], vermiculite[66], sepiolite[67], bentonite[68], and laterite soil[69] in their pristine form are used for the removal of toxic heavy metals from aqueous solutions. The sorption of diatrizoic acid (DAT), iopamidol (IOP), metformin (MTF), and carbamazepine (CBZ) was conducted using montmorillonite. It was reported that montmorillonite could remove 70% of MTF and CBZ, 30% of DAT, and no removal of IOP without generation of by-products. Further, it was observed that the adsorption rates depend on the pollutant concentrations[70]. Palygorskite-montmorillonite (PM) is used to treat the effluent filter material for carbamazepine. The sorption of carbamazepine onto PM mainly occurred through the hydrogen bonding between the hydrogen donor group of carbamazepine and the hydrogen acceptor group of the PM[71]. Montmorillonite and kaolinite are used for the sorption of antibiotic nalidixic acid (NA). The adsorption of NA on kaolinite and montmorillonite was higher at lower pH. The adsorption of NA on montmorillonite is promoted by a coordination bond between the keto oxygen or C=N group in the pyridine ring and the exchangeable cations in the interlayer of montmorillonite according as revealed by the FT-IR analyses[72]. The adsorption capacity of various natural clay for heavy metals and micro-pollutants is summarized in Table 3.

    3. Thermal modification of clay

    Thermal modification of clay minerals is termed calcination[85]. Clay minerals are usually heated up to 200~1000°C for 2~4 hrs. The thermal activation of clay minerals causes the activation of clay’s active sites, which promote the sorption of pollutants[86,87]. During calcination, dehydration and then dihydroxylation occurred, which resulted in the reduction of mass while the porosity was increased significantly; the clay surface became more exposed to the ion exchange process[88]. It was reported that the surface properties of bentonite and kaolinite were changed substantially on heat treatment. The volatile impurities and physico-adsorbed water molecules were removed at 100 °C, increasing the specific surface area of clay[89]. However, the specific surface area was reduced if the temperature was increased up to 500 °C, mainly due to the collapse of clay layers and the dihydroxylation process[85]. A similar decrease in surface area was observed in kaolinite and montmorillonite after the heat treatment at 750 °C[90]. Further, calcination of montmorillonite at 600 °C results in a decrease in surface area but increases with sorption capacity[91,92]. This showed that the sorption potential was also affected by other factors[93]. The cation exchange capacity (CEC) of clay is likely to be reduced once clays are treated at a very high temperature; however, the temperature must be maintained carefully during thermal treatment[85]. The adsorption capacity of bentonite and kaolinite was decreased by calcining the solids from 500 to 900 °C[94]. The maximum sorption capacity of various heavy metals and micro-pollutants using thermally treated clays is included in Table 4.

    X-ray diffraction analysis of thermally treated bentonite at 400 °C showed a significant decrease in the basal spacings from 1.48 nm to 0.97 nm[95]. A similar observation was also reported on the thermal treatment of bentonite clay[96]. The FT–IR spectra of thermally treated bentonite clay decrease in the intensity of H–O–H deformation band at 1600 to 1700 cm-1 and O–H stretching vibrations at 3100 to 3700 cm-1 [97].

    4. Activation of Clay

    Clay minerals are often treated with acids to modify their surface and remove impurities[104]. Activation of clay minerals with acids, caused by the opening of pores and exposure of clay edges, leads to an enhanced sorption capacity for several pollutants[105]. Activation of clay minerals with acid is found to be an effective method of modification[106]. Calcium, potassium, magnesium, iron, and metal oxides are also removed from clay minerals during acid treatment, increasing surface area and further providing open spaces for heavy metal adsorption[87,107,108]. Sulphuric, phosphoric, nitric, and hydrochloric acids are the most common acids used to activate clay minerals[109,110]. The structural changes on the surface and interlayer spaces of montmorillonite clay due to acid treatment are shown in Figure 1. Generally, the activation of clay minerals involves the treatment of clay with acid for the selected time at constant stirring and temperature. The excess free ions, such as Cl-, SO4- etc., are detached from the clay once it is activated and then washed with distilled water, dried, and employed for its applications[104].

    Acid activation of bentonite clay was performed using a clay concentration of 6 %(w/v) under mild conditions. The XRD results of activated bentonite significantly affected the crystallinity of bentonite, leading to a decrease in the peak intensity, and the width of the ‘001’ peak was increased. FT-IR results showed that the vibrations bands at 3417, 1640, and 3617 cm-1 are significantly changed after activation. Nevertheless, the layered structure of bentonite was not changed, which was affirmed by the presence of a weak vibrational band at 1039 cm-1. The increased intensity of band at 793 cm-1 and the band’s widening at 1041 cm-1 showed that amorphous silica is formed after activation. The specific surface area and pore volume were increased by 3.3 and 2.75 times, respectively. The SEM images showed that activated bentonite appeared highly compact and showed large pores than raw bentonite[14]. Further, the XRD results of two clays: raw green clay (RGC) and raw red clay (RRC), after treating with acid, showed an increase in silica due to its poor solubility in acid solutions, while the octahedral and exchangeable ions are significantly removed. Moreover, the textual analysis showed that the internal porosity, pore volume, specific surface area, and pore sizes were increased after activation with acid[112]. A similar result was also reported using bentonite activated with 0.35, 0.70, 1.0, 1.5, 2.0, 3.5, 7.0, and 10 N hydrochloric acid in the liquid-to-solid ratio 4 : 1 for 45 minutes[113]. Montmorillonite-illite type of clay was activated with sulphuric acid. The mineral phase analysis of montmorillonite-illite clay (MIC) and montmorillonite-illite activated clay MIC (AA) from XRD analyses showed that some magnesium and potassium, were activated during activation, and calcium was removed, and as a result, montmorillonite and illite phases disappeared in the clay sample. Moreover, quartz to quartz inversion was also observed. The XRD image is given in Figure 2[114].

    Further, it was observed that the adsorption of heavy metals by activated clay is also influenced by the strength of the acid used during activation. For example, the adsorption of Cu(II) on activated palygorskite clay activated by HCl showed substantial improvement with increasing the concentration of the acids[115]. The efficiency of various activated clays in removing toxic heavy metals is highlighted in Table 5.

    5. Clay modification using surfactants

    Clay minerals are often modified with organic compounds[120]. Over the past few decades, organoclays have drawn attention in many areas like medicine, engineering, environmental sciences, etc.[121,122]. Due to the presence of chelating functional groups in the organoclay, heavy metals are bonded onto its surface with a stronger bond than the pristine clay[123]. Quaternary ammonium organo-clays are classified into two groups. Firstly, quaternary ammonium cations (QACs) having short-chain alkyl groups such as tetramethylammonium (TMA)/trimethylphenylammonium (TMPA) or benzyltriethylammonium (BTEA), the groups of organo-clays is called adsorptive clay. Secondly, the QACs containing long-chain alkyl groups, for example, didodecyldimethylammonium (DDDMA) and hexadecyltrimethylammonium (HDTMA) -clays, are called organophilic clay[124]. The presence of benzyl groups, long and short chain aliphatic, and often hydroxyl groups caused to increase in the basal spacing of clay along with their adsorption capability[125]. Clay with higher charge density and the surfactant molecules’ length increases the interlayer spacings of clay structure[126]. The aqueous and ethanolic solutions of hexadecyltrimethylammonium (HDTMA) bromide reacts with the different charge of layer silicates, the intercalated HDTMA formed flat-lying molecules (monolayers), and the charges on the layer are < 0.5 e- (per unit cell basis); flat-lying molecules (bilayers) for layer charges between 0.5 and 1.0 e- and bent paraffin-like arrangements for layer charges < 1.0 e-. For smectites and vermiculites with layer charges > 0.5 e-, greater layer spacing is achieved by intercalating of salt molecules from an aqueous medium rather than an ethanol medium[127]. Organoclays are synthesized depending on the mechanisms of reactions that organic compounds are introduced into clay minerals. Polar molecules displace water molecules in the interlayer space of vermiculites and smectites. Several organic cations exchange interlayer cations. Cation exchange and solid-state reactions are mainly used to prepare organoclays[128]. Organoclays are mostly prepared by cation exchange reactions[129]. Quaternary alkylammonium cations (QAC) exchange the interlayer cations of clay minerals in aqueous solutions. Different physicochemical conditions are demonstrated in the preparation of organophilic clays[130-132]. The reaction of clay minerals and ammonium cations using a solid-state reaction was first reported by Ogawa et al.[133]. In a solid-state reaction, organic molecules are intercalated within the interlayer spaces of clay minerals in the absence of solvent since, without solvent, it is a more eco-friendly and reliable process for industrialization. Cation movement between silicate layers is not always taking part in the intercalation of neutral molecules[128]. Aniline salts are intercalated using the mechanochemical process with several counter ions in montmorillonite[134]. Ion-dipole interaction plays a key role in many solid-state reactions. The interlayer cations and organic molecules with polar groups are attached during ion-dipole interaction. Cations on the surface interact with the negative part of the molecule, thereby displacing water molecules from the interlayer cations[129,135].

    Inorgano-organo-clay minerals are developed for the treatment of industrial wastewater [136,137]. Both organic surfactant and hydroxide pillaring agents are intercalated for the modification of clay minerals with inorgano-organo compounds[138-141]. Hence hydrophobic and hydrophilic compounds are removed simultaneously. Polycations of iron (III), aluminium (III), or titanium (IV) are intercalated into the interlamellar spaces of montmorillonite and further modified with cetyl trimethylammonium bromide. The material showed enhanced removal efficiency for diuron and its three degradation products: 3-(3,4- dichlorophenyl)-1-methylurea, 1-(3,4-dichlorophenyl) urea, and 2,4- dichloroanilin. It was reported that hydrophobic interaction was the main mechanism for the adsorption of these pesticides by the organoinorgano- clays[138].

    Several organic cationic surfactants (Dodecyltrimethylammonium bromide, Hexadecyltrimethylammonium bromide, Tetradecyltrimethylammonium bromide, Tetraphenylphosphonium bromide, Zinc Stearate) were used for the modification of montmorillonite.

    Sericite was modified with hexadecyltrimetyl ammonium bromide (HDTMA) and alkyldimethylbenzyl ammonium chloride (AMBA). FT-IR results show that the vibrational band at 3443 cm-1 almost vanished for the modified sericite, indicating the replacement of organic molecules with the hydroxyl group. The two new bands at 2920 cm-1 and 2856 cm-1 were attributed to the C–H stretching and C–H scissoring vibrations, respectively, which infer that the hexadecyltrimetyl ammonium bromide and alkyldimethylbenzyl ammonium chloride are introduced within the sericite clay (Cf Figure 3)[142]. A similar observation was also observed when kaolinite was modified with HDTMA[143]. In other studies, montmorillonite was modified with cetyltrimethylammonium bromide (CTMAB); XRD results showed basal spacing of montmorillonite was increased from 1.52 to 1.81 nm, which confirmed that (CTMAB) was intercalated within the interlayer space. The insertion of Fe polycation, on the other hand, did not intercalate into the interlayer of montmorillonite[144]. The SEM image of bentonite modified with octadecyl benzyl dimethyl ammonium (SMB3) displayed a smoother surface than unmodified bentonite. Moreover, the SMB3 showed small size fragments and layers alike contexture, indicating that bentonite is evenly distributed while the modification was carried out using these surfactant molecules[145]. The kaolinite modified with HDTMA (SMK) showed a significant decrease in specific surface area from 8.61 to 3.39 m2/g, pore volume and diameter were increased from 0.04 to 0.07 cc/g and 9.53~20.41 nm, respectively[146]. These results indicated that HDTMA was successfully intercalated within the interspace of kaolinite. Similar findings were reported in the literature in which bentonite was modified with cetyltrimethyl ammonium bromide (CTMAB)/ hexadecylammonium bromide (HDTMA) or pillared with aluminium and then modified with CTMAB/ HDTMA [147,148].

    Montmorillonite was modified by polyamine Gemini surfactant and employed in the removal of Cu(II) with a maximum removal capacity of 29.30 mg/g at 75 mg/L of Cu(II) initial concentration[149]. In another study, modification of rectorite with stearyl trimethylammonium chloride removes Cr(VI) with approximately 400 mmol/kg via electrostatic interactions in acidic pH conditions[150]. A comparative study for the sorption of bentonite (BT), bentonite modified with hexadecyltrimethylammonium (BT-HDTMA), and phenyl fatty hydroxamic acid (BT-PFHA) showed that the monolayer adsorption capacities of BT, BT-HDTMA and BT-PFHA for Pb(II) were found to be 149.3, 227.3 and 256.4 mg/g, respectively. Further, the sorption data were fitted well to the Langmuir, Dubinin-Radushkevich, and Temkin models. The kinetic data is fitted well with the pseudo-second-order kinetic model, and the thermodynamic studies revealed that the adsorption was feasible, spontaneous, and exothermic[151]. Single and complex modified bentonite was synthesized using iron (hydr)oxides (Fex(OH)y), manganese oxides (MnxOy) and cationic surfactants, cetyltrimethylammonium bromide (CTMAB), and poly(dimethyldiallylammonium chloride) (PDMDAAC) and employed in the sorptive removal of arsenic. Results showed that arsenic removal greatly depends upon the combination, type, and amount of modifiers used in clay modification. The removal of arsenic in single modified bentonite was in the order Fex(OH)y-Bent > MnxOy-Bent > CTMABBent > PDMDAAC-Bent. Moreover, the complex modified bentonite, manganese oxide, and PDMDAAC showed the best arsenic removal due to the presence of several manganese oxide particles and the change in the surface properties of bentonite. The decrease in the removal of arsenic was observed with CTMAB-MnxOy-Bent, CTMAB-, or PDMDAACFex(OH)y-Bent[152]. The removal efficiency of heavy metals and micro-pollutants using organo- and organo-inorgano clays are summarized in Table 6.

    HDTMA: hexadecyltrimethylammonium, BH: bentonite modified with hexadecyltrimethylammonium, BAH: bentonite pillaring with aluminium and modified with hexadecyltrimethylammonium, LCH: local clay modified with hexadecyltrimethylammonium, LCAH: local clay pillaring with aluminium and modified with hexadecyltrimethylammonium, HDPy-Bn: bentonite modified with hexadecylpyridinium, HDTMA-Bn: bentonite modified with hexadecyltrimethylammonium, BE-Bn: bentonite modified with benzethonium, HDPy-Ver: vermiculite modified with hexadecylpyridinium, HDTMA-Ver: vermiculite modified with hexadecyltrimethylammonium, BE-Ver: vermiculite modified with benzethonium, CTMAB: cetyltrimethylammonium bromide.

    6. Grafting or silylation of clay

    Grafting or silylating the surface of clay minerals has drawn greater attention because the grafted materials showed varied applications in environmental and chemical engineering[162]. Various types of clay functionalized with different silanes are given in Table 7. In general, there are three possible sites for silylation/grafting of silane at the surface of the clay, i.e., the external surface, internal surface, and broken edges of clay minerals, as shown in Figure 4[163,164].

    The reactive sites of montmorillonite were increased on acid treatment, leading to greater silane molecules loading[56,165]. The interactions of clay minerals with silane molecules were facilitated by increasing the concentration of silane and the temperature of the reaction[166]. The surface of bentonite was grafted with 3-aminopropyltriethoxysilane (APTES), allowing its nano-space to be utilized for intercalation of cations, bio-molecules, polymeric materials, drug delivery, and several commercial uses[167]. “Flip mechanism” describes the mechanism of amine grafted onto silica minerals. Firstly, amine forms a hydrogen bond with the hydroxyl group on the surface of silica particles, or proton is transferred from the silica particles to amine forming an ionic bond. On the silicon side of silane molecules, self-catalyzation of hydrogen-bonded molecules occurred, forming a covalent bond with siloxane. Due to this condensation, the interaction of the amine group at the surface is lost, and the amine is far apart from the surface. Fast stabilization occurs when a higher amount of ethoxy group on the APTES is present. Therefore, the original amine-down position of the silane molecule is changed to the amineup- position resulting in a ‘flip mechanism’(Figure 5)[168,169].

    The grafting of silane was not favored using the nonpolar solvents (e.g., toluene)[50,161,162], while intercalation of silane was observed when polar solvents (e.g., water/ethanol mixture and ethanol) was used as a dispersing medium[172].

    Nano-texturization method was employed for the functionalization of palgorskite clay with mercapto and amino silane to efficiently remove cadmium from polluted soils and water. Results show that functionalized materials significantly increased the adsorption capacity compared to the unmodified palgorskite clay. The enthalpy change was positive, and the endothermic sorption process(Figure 6)[179].

    The interlayer spaces of vermiculite were incorporated with CYS and CTA and utilized for the adsorption of Hg(II). The intraparticle diffusion, controls the adsorption kinetics of Hg(II). Batch adsorption of Hg(II) using modified 3-MPS is similar to Na-VT and follows pseudo- second-order kinetics. Higher breakthrough volume was achieved using vermiculite modified with 3-MPS in column studies. The adsorption is irreversible[180]. As shown in Table 8, the adsorption capacities of various functionalized clay possessed relatively high adsorption capacity for heavy metals and micro-pollutants in the aqueous medium.

    7. Clay based composites

    Clay and clay-based composites materials are found to be promising in the remediation of toxic heavy metals from an aqueous environment due to their large surface area, low-cost, stability, high cation exchange capacity, high porosity, and the ability to swell to a large extent, which overcomes with the conventional methods. One or more components of composites are functionalized to increase the sorption efficiency [191-194]. Cellulose -montmorillonite[195], poly (acrylic acid)/organomontmorillonite[196], bentonite/NZVI[197]; Kaolinite/ZrO and kaolinite/ TBA[198]; chitosan-clay nanocomposite[199] are some clay-based composites employed in the removal of heavy metal ions. The adsorption capacity of various clay-based nanocomposites in the removal of heavy metal ions are summarized in Table 9.

    Liquid phase reduction was employed for the synthesis of bentonite- supported nanoscale zero-valent iron (B-nZVI) and utilized in the removal of Cu(II), Pb(II), and Cr(VI) from electroplating wastewater. More than 90% removal efficiency was achieved using the composite material. Further, ethylenediaminetetraacetic acid (EDTA) solution was used to desorb the heavy metals, but the removal capacity of Cr(VI) was decreased by approx. 70% using the reutilized material[200]. Single and mixed pillared clays (Zr-Bent, Al-Bent, Al−Zr-Bent, Ce-Zr-Bent, Ce-Al−Zr-Bent, Ce-Al-Bent) were utilized for the adsorption of Cu(II), Co(II) and Cd(II). The adsorption of heavy metals was higher for pillared clays rich in cerium. The experimental data is well fitted to the second-order-kinetic model and Langmuir adsorption isotherm[201]. 4-aminoantipyrine was immobilized onto bentonite and employed in the elimination of Hg(II), Cr(III), and Pb(II) from an aqueous solution. The maximum adsorption capacity of the solid material was found to be 52.9, 52.9, and 55.5 mg/g for Hg(II), Cr(III), and Pb(II), respectively[202]. E-coli-kaolinite nanocomposite was used in the adsorption of Cr(VI), Cd(II), Fe(III), and Ni(II) from water with adsorption capacity of 4.6 10.3, 16.5, and 6.9 mg/g, respectively[203].

    Synthesis of polymer-layered silicate nanocomposite includes solution blending, in-situ polymerization, and melt blending. In the solution blending method, prepolymer and polymer are soluble in a solvent such as toluene, chloroform, or water resulting in exfoliation of layered clay. After mixing the layered clay and polymer/prepolymer, intercalation of polymer chains and solvent displacement occurs within the clay’s interlayer[204,205]. Desorption of solvent molecules results in the gaining of entropy, which is responsible for intercalation in the solution blending[206]. Chitosan gold clay nanoparticles (Ch/AuNPs/clay) and chitosan silver clay nanoparticles (Ch/AgNPs/clay) were synthe- sized by solution blending method. From the SEM image[Figure 7(a), (b), (c), the (Ch)/Clay composite comprised several layered structures with bulky flakes and interlayer spaces. While in the case of (Ch)/AuNPs/Clay and (Ch)/AgNPs/Clay nanocomposites, there was a significant decrease in the interlayer spaces of clay, which reaffirmed the impregnation of the chitosan assembled on nanoparticles between the clay layers. It was also observed that (Ch)/AgNPs and (Ch)/AuNPs were primarily circular in shape and poly-dispersed from the transmission electron microscope (TEM) analysis. Moreover, the TEM images showed that the prepared nanoparticles are well stabilized due to the interaction with the free amino groups of chitosan Cf Figure 7(d) and (e)]. Further, in the EDX spectra, the intense and distinctive optical absorption peaks were observed around 3 keV and 2.1 keV due to the surface plasmon resonance (SPR) of metallic silver (Ag) and gold (Au) nanocrystals, respectively[Figure 7(f) and (g)][207].

    In situ polymerization method involves swelling of layered silicate inside the monomer solution resulting in polymer formation between intercalated sheets. Before swelling of layered silicate by monomer, heat, or radiation, organic initiator or diffusion of appropriate initiator or by fixing catalyst through cationic exchange inside the interlayer is employed for the initiation of polymerization[204]. Montmorillonite clay nanocomposite (PPy-OMMT NC) was prepared via in situ polymerization of pyrrole monomer. From the FT-IR spectrum of the Ppy-OMMT NC3, the C–H deformation, C–H stretching vibration, conjugated C–N stretching, and pyrrole ring stretching are observed at 824~958 cm-1, 1081 cm-1, 1423 cm-1, and 1513 cm-1, which confirmed the presence of PPy moieties in the nanocomposite[Fig. 8(c)]. The XRD data of Ppy-OMMT NC3 could not show any distinct peak, which suggests that almost all the clay sheets in the polymer matrix are exfoliated. The small angle X-rays (SAXS) pattern also revealed that no low angle diffraction occurred with the nanocomposite prepared by in situ polymerization. The studies show that the insertion of polypyrrole has successfully exfoliated the OMMT clay sheets[Fig. 8(b)]. High-resolution transmission electron microscopic images (HR-TEM) of OMMT show sheets as black strips, while in Ppy-OMMT NC3 these strips are well distributed(Fig. 8). The SEM image of OMMT show flaky structure, after modification with PPy, the OMMT clay structure was covered by polypyrrole(Fig. 8)[208].

    In the melt blending method, the molten form of polymer matrix was mixed with layered silicate. If the selected polymer and layer surfaces were appropriately suited, the polymer crept into the interlayer gallery, resulted from the formation of exfoliated or intercalated nanocomposite [204]. Al-pillared-montmorillonite (AlPMt)/poly(methyl methacrylate) (PMMA) nanocomposites wwer synthesized via melt blending method (MBM) and solution blending method (SBM). The FT-IR spectra of AlPMt/PMMA nanocomposite showed that the interaction of AlPMt and PMMA proceeded via C=O and C-O groups[Fig. 9(a)]. The XRD patterns of AlPMt/PMMA nanocomposite displayed in increased amorphous nature. The characteristic reflection of AlPMt was not found in XRD patterns since AlPMt was homogeneously dispersed within PMMA matrix[Fig. 9(b)]. The TEM image of AlPMt/PMMA (2.5 wt%) nanocomposite for MBM is shown in Fig. 9(c). Clay platelet (dark zone) was observed using this method. In the polymer matrix, the pillared clay layers were distributed evenly and homogeneously, which was evidence of the intercalated morphology. The homogeneity of dispersions from the image is on a nanometer scale, which agrees with the XRD results[209].

    It is observed that the mechanistic pathway in removing pollutants involved surface complexation[187,202-205,207,210]. The electrostatic interaction[212,213,218] and the hydrophobic interactions[130,181] significantly remove micro-pollutants using clay-based composites. Moreover, the ion exchange[214] and surface complexation[217] were found to occur in removing micropollutants’ toxic heavy metal ions from the aquatic environment by clay-based composite using clay-based materials.

    8. Conclusion and future perspective

    This review broadly discussed various techniques employed for modifying different types of clays. Also, different types of clay-based materials were comprehensively reviewed for their efficiency in the remediation of aqueous waste contaminated with toxic heavy metals and emerging micro-pollutants. The surface complexation is the prominent mechanism involved in removing toxic heavy metal ions by clay-based composite, whereas the electrostatic interaction plays a significant role in micro-pollutants removal using these types of composite. Thermal and acid-activated clay is simple, easy to prepare, and has an enhanced adsorption capacity. The modifications of clay minerals with surfactants are promising adsorbents for decontaminating different pollutants from wastewater. However, the intercalated surfactant might leach into the surrounding solutions, which leads to secondary contamination of water. Silylation of clay minerals is a promising method since the organosilanes are immobilized through strong covalent bonding into the clay network, which further prevents the leaching of the organic moieties into the surrounding environment. Moreover, the silylated materials exhibit more enhanced adsorption selectivity and efficiency for removing pollutants from aqueous solutions.

    Even though enormous work is carried out and much literatures has reported the removal of heavy metals and micro-pollutants using clay-based advanced materials from the aquatic environment, the perspective of scaling up the laboratory trials to the technology development for real application is still a challenge for researchers. The adsorbent is designed in such a way that the clay-based materials are eco-friendly, have no hazardous by-products, and have a high sorption capacity towards these pollutants. Moreover, simultaneous removal of anionic, cationic, and non-ionic pollutants is a real challenge using these advanced materials to simulate the complex matrix. Further, there is a challenge associated with the disposal of utilized materials and recovery of the pollutants, especially the toxic metal ions, for the potential future implications.

    Figures

    ACE-33-5-502_F1.gif
    Structural changes of montmorillonite by acid attack on the surface and interlayer spaces[111].
    ACE-33-5-502_F2.gif
    XRD image of montmorillonite-illite clay(MIC) and montmorillonite-illite activated clay MIC (AA)[114].
    ACE-33-5-502_F3.gif
    FT-IR spectra of sericite, HDTMA-sericite (H1) and AMBAsericite (A1)[142].
    ACE-33-5-502_F4.gif
    Probable sites for grafting or silylation, i.e. (a) internal clay surface, (b) external surface of clay, (c) broken edges of clay.
    ACE-33-5-502_F5.gif
    Interaction types between silicate surface material and APTES in absence of water (a) proton transfer, (b) Hydrogen bonding, (c) Condensation of APTES with silica particle[169].
    ACE-33-5-502_F6.gif
    Schematic of sorption mechanisms of Cd(II) on PAL, PAL-SH and PAL-NH2[179].
    ACE-33-5-502_F7.gif
    SEM images of Ch/Clay (a), Ch/Clay/AuNPs (b), Ch/Clay/AgNPs (c); TEM images of Ch/Clay/AuNPs (d), Ch/Clay/AgNPs (e); EDX image of Ch/Clay/AuNPs (f), Ch/Clay/AgNPs (g)[207].
    ACE-33-5-502_F8.gif
    Transmission electron microscopic images of (a) OMMT and (b) Ppy-OMMT NC3,and scanning electron microscope of (c) OMMT and (d) Ppy-OMMT NC3[208].
    ACE-33-5-502_F9.gif
    (a) FTIR-ATR spectra of AlPMt/PMMA nanocomposites with MBM, (b) XRD patterns of AlPMt/PMMA nanocomposites with MBM and (c) TEM images of AlPMt/PMMA (2.5 wt.%) nanocomposites synthesized via MBM[209].

    Tables

    The Major Sources, Permissible Level in Drinking Water and Health Effects of Heavy Metals
    Different Micro-Pollutants and its Effects on Human Health
    Adsorption Capacities of Raw Clays for the Removal of Various Heavy Metals and Micro-Pollutants
    Removal of Heavy Metals and Micro-Pollutants Using Thermally Treated Clays
    Removal Efficiency of Heavy Metals by Various Activated Clays under Batch Reactor
    Removal of Heavy Metals and Micro-Pollutants using Organo- and Organo-Inorgano Clays
    Characterization of Different Clay Functionalized with Different Silanes
    Removal of Heavy Metals and Micro-Pollutants using Functionalized Clay
    Clay Based Nanocomposites for the Removal of Toxic Heavy Metal Ions and Some Micro-Pollutants

    References

    1. M. Taseidifar, F. Makavipour, R. M. Pashley, and A. F. M. M. Rahman, Removal of heavy metal ions from water using ion flotation, Environ. Technol. Innov., 8, 182-190 (2017).
    2. Y. Zou, X. Wang, A. Khan, P. Wang, Y. Liu, A. Alsaedi, T. Hayat, and X. Wang, Environmental remediation and application of nanoscale zero-valent iron and its composites for the removal of heavy metal ions: A review, Environ. Sci. Technol., 50, 7290-7304 (2016).
    3. H. Bhandari, S. Garg, and R. Gaba, Advanced nanocomposites for removal of heavy metals from wastewater, Macromol. Symp., 397, 2000337 (2021).
    4. K. Buruga, H. Song, J. Shang, N. Bolan, T. K. Jagannathan, and K.-H. Kim, A review on functional polymer-clay based nanocomposite membranes for treatment of water, J. Hazard. Mater., 379, 120584 (2019).
    5. I. G. Wenten, K. Khoiruddin, A. K. Wardani, and I. N. Widiasa, Synthetic polymer-based membranes for heavy metal removal. In: A. M. Ismail, W. N. W. Salleh, N. Yusof, Synthetic Polymeric Membranes for Advanced Water Treatment, Gas Separation, and Energy Sustainability, 71-101 Elsevier (2020).
    6. R. Sabouni and H. Gomaa, Photocatalytic degradation of pharmaceutical micro-pollutants using ZnO, Environ. Sci. Pollut. Res., 26, 5372-5380 (2019).
    7. Z. Toušová, B. Vrana, M. Smutná, J. Novák, V. Klučárová, R. Grabic, J. Slobodník, J. P. Giesy, and K. Hilscherová, Analytical and bioanalytical assessments of organic micropollutants in the Bosna River using a combination of passive sampling, bioassays and multi-residue analysis, Sci. Total Environ., 650, 1599-1612 (2019).
    8. L. L. S. Silva, C. G. Moreira, B. A. Curzio, and F. V. da Fonseca, Micropollutant removal from water by membrane and advanced oxidation processes—A review, J. Water Resour. Prot., 9, 411-431 (2017).
    9. A. Tiwari, A. Shukla, Lalliansanga, D. Tiwari, and S. M. Lee, Nanocomposite thin films Ag0(NP)/TiO2 in the efficient removal of micro-pollutants from aqueous solutions: A case study of tetracycline and sulfamethoxazole removal, J. Environ. Manage., 220, 96-108 (2018).
    10. M. Hadavifar, N. Bahramifar, H. Younesi, and Q. Li, Adsorption of mercury ions from synthetic and real wastewater aqueous solution by functionalized multi-walled carbon nanotube with both amino and thiolated groups, Chem. Eng. J., 237, 217-228 (2014).
    11. USEPA, National Primary Drinking Water Regulation Table, (2001).
    12. H. Zeng, L. Wang, D. Zhang, F. Wang, V. K. Sharma, and C. Wang, Amido-functionalized carboxymethyl chitosan/montmorillonite composite for highly efficient and cost-effective mercury removal from aqueous solution, J. Colloid Interface Sci., 554, 479-487 (2019).
    13. I. Ogbu, K. Akpomie, A. Osunkunle, and S. Eze, Sawdust-kaolinite composite as efficient sorbent for heavy metal ions, Bangladesh J. Sci. Ind. Res., 54, 99-110 (2019).
    14. R. R. Pawar, Lalhmunsiama, H C. Bajaj, and S.-M. Lee, Activated bentonite as a low-cost adsorbent for the removal of Cu(II) and Pb(II) from aqueous solutions: Batch and column studies, J. Ind. Eng. Chem., 34, 213-223 (2016).
    15. WHO, Guidelines for drinking-water quality: First addendum to volume 1, World Health Organization; 3rd Ed. 188, Geneva (2006).
    16. Y. Bendezu Roca and W. S. Fuentes, Use of nanoclay as an adsorbent to remove Cu(II) from acid mine drainage (amd), Chem. Eng. Trans., 73, 241-246 (2019).
    17. K. C. Nebagha, K. Ziat, L. Rghioui, M. Khayet, M. Saidi, K. Aboumaria, A. El Hourch, and S. Sebti, Adsorptive removal of copper (II) from aqueous solutions using low cost Moroccan adsorbent. Part I: Parameters influencing Cu (II) adsorption, J. Mater. Env. Sci., 6, 3022-3033 (2015).
    18. R. Malsawmdawngzela, Lalhmunsiama, and D. Tiwari, Novel and highly efficient functionalized bentonite for elimination of Cu2+ and Cd2+ from aqueous wastes, Environ. Eng. Res., 27, 210355 (2021).
    19. G. A. Kloster, M. Valiente, N. E. Marcovich, and M. A. Mosiewicki, Adsorption of arsenic onto films based on chitosan and chitosan/nano-iron oxide, Int. J. Biol. Macromol., 165 1286-1295 (2020).
    20. M. Rajeswari, P. Agrawal, S. Pavithra, Priya, G. R. Sandhya, and G. M. Pavithra, Continuous biosorption of cadmium by Moringa olefera in a packed column, Biotechnol. Bioprocess Eng., 18, 321-325 (2013).
    21. M. Elmuntasir Ibrahim Ahmed, Selective Adsorption of Cadmium Species onto Organic Clay Using Experimental and Geochemical Speciation Modeling Data, Int. J. Eng. Technol., 8, 128-131 (2016).
    22. K. Rao, M. Mohapatra, S. Anand, and P. Venkateswarlu, Review on cadmium removal from aqueous solutions, Int. J. Eng. Sci. Technol., 2, (2011).
    23. J. Kent and J. H. Tay, Treatment of 17αethinylestradiol, 4nonylphenol, and carbamazepine in wastewater using an aerobic granular sludge sequencing batch reactor, Sci. Total Environ., 652, 1270-1278 (2019).
    24. J. J. Triviño, M. Gómez, J. Valenzuela, A. Vera, and V. Arancibia, Determination of a natural (17β-estradiol) and a synthetic (17α -ethinylestradiol) hormones in pharmaceutical formulations and urine by adsorptive stripping voltammetry, Sens. Actuators B Chem., 297, 126728 (2019).
    25. E.-J. Cho, J.-K. Kang, J.-K. Moon, B.-H. Um, C.-G. Lee, S. Jeong, and S.-J. Park, Removal of triclosan from aqueous solution via adsorption by kenaf‐derived biochar: Its adsorption mechanism study via spectroscopic and experimental approaches, J. Environ. Chem. Eng., 9, 106343 (2021).
    26. L. M. Weatherly and J. A. Gosse, Triclosan exposure, transformation, and human health effects, J. Toxicol. Environ. Health Part B., 20, 447-469 (2017).
    27. S. Bio and B. Nunes, Acute effects of diclofenac on zebrafish: Indications of oxidative effects and damages at environmentally realistic levels of exposure, Environ. Toxicol. Pharmacol., 78, 103394 (2020).
    28. J.-P. Chae, M. S. Park, Y.-S. Hwang, B.-H. Min, S.-H. Kim, H.-S. Lee, and M.-J. Park, Evaluation of developmental toxicity and teratogenicity of diclofenac using Xenopus embryos, Chemosphere, 120 (2015) 52-58.
    29. L. Xiang, Z. Xie, H. Guo, J. Song, D. Li, Y. Wang, S. Pan, S. Lin, Z. Li, J. Han, and W. Qiao, Efficient removal of emerging contaminant sulfamethoxazole in water by ozone coupled with calcium peroxide: Mechanism and toxicity assessment, Chemosphere, 283, 131156 (2021).
    30. M. Ershad, M. A. Ameer, and D. Vearrier, Ibuprofen Toxicity, In: StatPearls. StatPearls Publishing (2021).
    31. O. E. Abdel-Gelil, and S. R. Mansour, Tetracycline and toxicity induced, Gastroenterol. Hepatol., 10, 177-179 (2019).
    32. J. R. Rochester, Bisphenol A and human health: A review of the literature, Reprod. Toxicol., 42, 132-155 (2013).
    33. M. Saravanan, S. Karthika, A. Malarvizhi, and M. Ramesh, Ecotoxicological impacts of clofibric acid and diclofenac in common carp (Cyprinus carpio) fingerlings: Hematological, biochemical, ionoregulatory and enzymological responses, J. Hazard. Mater., 195, 188-194 (2011).
    34. 34. W. Li, R. Zhou, R. Zhou, J. Weerasinghe, T. Zhang, A. Gissibl, P. J. Cullen, R. Speight, and K. (Ken) Ostrikov, Insights into amoxicillin degradation in water by non-thermal plasmas, Chemosphere, 132757 (2021).
    35. T. O. Ajiboye, O. A. Oyewo, and D. C. Onwudiwe, Simultaneous removal of organics and heavy metals from industrial wastewater: A review, Chemosphere, 262, 128379 (2021).
    36. J. Qu, Y. Yuan, Q. Meng, G. Zhang, F. Deng, L. Wang, Y. Tao, Z. Jiang, and Y. Zhang, Simultaneously enhanced removal and stepwise recovery of atrazine and Pb(II) from water using β–cyclodextrin functionalized cellulose: Characterization, adsorptive performance and mechanism exploration, J. Hazard. Mater., 400, 123142 (2020).
    37. B. Szczepanik, Photocatalytic degradation of organic contaminants over clay-TiO2 nanocomposites: A review, Appl. Clay Sci., 141, 227-239, (2017).
    38. R. Zhu, Q. Chen, Q. Zhou, Y. Xi, J. Zhu, and H. He, Adsorbents based on montmorillonite for contaminant removal from water: A review, Appl. Clay Sci., 123, 239-258 (2016).
    39. V. K. Gupta, I. Ali, Suhas, and D. Mohan, Equilibrium uptake and sorption dynamics for the removal of a basic dye (basic red) using low-cost adsorbents, J. Colloid Interface Sci., 265, 257-264 (2003).
    40. M. A. Khan, M. K. Uddin, R. Bushra, A. Ahmad, and S. A. Nabi, Synthesis and characterization of polyaniline Zr(IV) molybdophosphate for the adsorption of phenol from aqueous solution, React. Kinet. Mech. Catal., 113, 499-517 (2014).
    41. R. A. K. Rao and M. Kashifuddin, Adsorption properties of coriander seed powder (Coriandrum Sativum): extraction and pre-concentration of Pb(II), Cu(II) and Zn(II) Ions from aqueous solution, Adsorpt. Sci. Technol., 30, 127-146 (2012).
    42. Lalhmunsiama, D. Tiwari, and S.-M. Lee, Physico-chemical studies in the removal of Sr(II) from aqueous solutions using activated sericite, J. Environ. Radioact., 147, 76-84 (2015).
    43. S. M. Lee, Lalhmunsiama, and D. Tiwari, Sericite in the remediation of Cd(II)- and Mn(II)-contaminated waters: batch and column studies, Environ. Sci. Pollut. Res., 21, 3686-3696 (2014).
    44. K. H. Vardhan, P. S. Kumar, and R. C. Panda, A review on heavy metal pollution, toxicity and remedial measures: Current trends and future perspectives, J. Mol. Liq., 290, 111197 (2019).
    45. V.B. Yadav, R. Gadi, and S. Kalra, Clay based nanocomposites for removal of heavy metals from water: A review, J. Environ. Manage., 232, 803-817 (2019).
    46. G. Crini, and P.-M. Badot, Sorption Processes and Pollution: Conventional and Non-conventional Sorbents for Pollutant Removal from Wastewaters, 191-192, Université de Franche Comté Besancon, France (2010).
    47. R. Srinivasan, Advances in Application of Natural Clay and Its Composites in Removal of Biological, Organic, and Inorganic Contaminants from Drinking Water, Adv. Mater. Sci. Eng., 2011, 1-17 (2011).
    48. S. M. Lee and D. Tiwari, Organo and inorgano-organo-modified clays in the remediation of aqueous solutions: An overview, Appl. Clay Sci., 59-60, 84-102 (2012).
    49. D. Tiwari and S. M. Lee, Thanhmingliana, Hybrid materials in the decontamination of bisphenol A from aqueous solutions, RSC Adv.,4, 43921-43930 (2014) .
    50. R. Malsawmdawngzela, Lalhmunsiama, D. Tiwari, and S. Lee, Synthesis of novel clay-based nanocomposite materials and its application in the remediation of arsenic contaminated water, Int. J. Environ. Sci. Technol. 19 (2022),
    51. Thanhmingliana and D. Tiwari, Efficient use of hybrid materials in the remediation of aquatic environment contaminated with micropollutant diclofenac sodium, Chem. Eng. J., 263, 364-373 (2015).
    52. Y. Park, G. A. Ayoko, and R. L. Frost, Application of organoclays for the adsorption of recalcitrant organic molecules from aqueous media, J. Colloid Interface Sci., 354, 292-305 (2011).
    53. S. M. Lee, Thanhmingliana, and D. Tiwari, Hybrid materials precursor to natural clay in the attenuation of bisphenol A from aqueous solutions, J. Water Process Eng., 11, 46-54 (2016).
    54. E. I. Unuabonah, and A. Taubert, Clay–polymer nanocomposites (CPNs): Adsorbents of the future for water treatment, Appl. Clay Sci., 99, 83-92 (2014).
    55. D. L. Guerra, S. P. Oliveira, R. A. S. Silva, E. M. Silva, and A. C. Batista, Dielectric properties of organofunctionalized kaolinite clay and application in adsorption mercury cation, Ceram. Int., 38, 1687-1696 (2012).
    56. H. He, Q. Zhou, W. N. Martens, T. J. Kloprogge, P. Yuan, Y. Xi, J. Zhu, and R. L. Frost, Microstructure of HDTMA+-modified montmorillonite and its influence on sorption characteristics, Clays Clay Miner., 54, 689-696 (2006).
    57. N. N. Herrera, J.-M. Letoffe, J.-P. Reymond, and E. BourgeatLami, Silylation of laponite clay particles with monofunctional and trifunctional vinyl alkoxysilanes, J. Mater. Chem., 15, 863 (2005).
    58. A. Okada and A. Usuki, Twenty Years of Polymer-Clay Nanocomposites, Macromol. Mater. Eng., 291, 1449-1476 (2006).
    59. U. F. Alkaram, A. A. Mukhlis, and A. H. Al-Dujaili, The removal of phenol from aqueous solutions by adsorption using surfactant-modified bentonite and kaolinite, J. Hazard. Mater., 169, 324-332 (2009).
    60. V. C. G. dos Santos, M. T. Grassi, and G. Abate, Sorption of Hg(II) by modified K10 montmorillonite: Influence of pH, ionic strength and the treatment with different cations, Geoderma., 237-238, 129-136 (2015).
    61. E. Ruiz-Hitzky, M. Darder, F. M. Fernandes, E. Zatile, F. J. Palomares, and P. Aranda, Supported Graphene from Natural Resources: Easy Preparation and Applications, Adv. Mater., 23, 5250-5255 (2011).
    62. A. M. Awad, S. M. R. Shaikh, R. Jalab, M. H. Gulied, M. S. Nasser, A. Benamor, and S. Adham, Adsorption of organic pollutants by natural and modified clays: A comprehensive review, Sep. Purif. Technol., 228, 115719 (2019).
    63. H. Chen, J. Zhao, A. Zhong, and Y. Jin, Removal capacity and adsorption mechanism of heat-treated palygorskite clay for methylene blue, Chem. Eng. J., 174, 143-150 (2011).
    64. M. Jiang, X. Jin, X.-Q. Lu, and Z. Chen, Adsorption of Pb(II), Cd(II), Ni(II) and Cu(II) onto natural kaolinite clay, Desalination, 252, 33-39 (2010).
    65. X. Gu, L. J. Evans, and S. J. Barabash, Modeling the adsorption of Cd (II), Cu (II), Ni (II), Pb (II) and Zn (II) onto montmorillonite, Geochim. Cosmochim. Acta, 74, 5718-5728 (2010).
    66. M. Malandrino, O. Abollino, A. Giacomino, M. Aceto, and E. Mentasti, Adsorption of heavy metals on vermiculite: Influence of pH and organic ligands, J. Colloid Interface Sci., 299, 537-546 (2006).
    67. E. Padilla-Ortega, R. Leyva-Ramos, J. Mendoza-Barron, R. M. Guerrero-Coronado, A. Jacobo-Azuara, and A. Aragon-Piña, Adsorption of heavy metal ions from aqueous solution onto sepiolite, Adsorpt. Sci. Technol., 29, 569-584 (2011).
    68. B. Anna, M. Kleopas, S. Constantine, F. Anestis, and B. Maria, Adsorption of Cd(II), Cu(II), Ni(II) and Pb(II) onto natural bentonite: study in monoand multi-metal systems, Environ. Earth Sci., 73, 5435-5444 (2015).
    69. Sunil, B. M., Faziludeen, and Saifiya, Removal of hexavalent chromium Cr (VI) by adsorption in blended lateritic soil, Adv. Environ. Res., 4, 197-210 (2015).
    70. L. Mahouachi, T. Rastogi, W.-U. Palm, I. Ghorbel-Abid, D. Ben Hassen Chehimi, and K. Kümmerer, Natural clay as a sorbent to remove pharmaceutical micropollutants from wastewater, Chemosphere, 258, 127213 (2020).
    71. T. M. Berhane, J. Levy, M. P. S. Krekeler, N. D. Danielson, and A. Stalcup, Sorption-desorption of carbamazepine by palygorskitemontmorillonite (PM) filter medium, J. Hazard. Mater., 282, 183- 193 (2015).
    72. Q. Wu, Z. Li, and H. Hong, Adsorption of the quinolone antibiotic nalidixic acid onto montmorillonite and kaolinite, Appl. Clay Sci., 74, 66-73 (2013).
    73. A. A. Taha, M. A. Shreadah, H. F. Heiba, and A. M. Ahmed, Validity of Egyptian Na-montmorillonite for adsorption of Pb2+, Cd2+ and Ni2+ under acidic conditions: characterization, isotherm, kinetics, thermodynamics and application study: Adsorption of heavy metals under acidic conditions, Asia-Pac. J. Chem. Eng., 12, 292-306 (2017).
    74. M. Barkat, S. Chegrouche, A. Mellah, B. Bensmain, D. Nibou, and M. Boufatit, application of algerian bentonite in the removal of cadmium (II) and chromium (VI) from aqueous solutions, J. Surf. Eng. Mater. Adv. Technol., 04, 210-226 (2014).
    75. S. Sen Gupta and K. G. Bhattacharyya, Immobilization of Pb(II), Cd(II) and Ni(II) ions on kaolinite and montmorillonite surfaces from aqueous medium, J. Environ. Manage., 87, (2008) 46-58.
    76. Ö. Etci, N. Bektaş and M. S. Öncel, Single and binary adsorption of lead and cadmium ions from aqueous solution using the clay mineral beidellite, Environ. Earth Sci., 61, 231-240 (2010).
    77. C.-J. Wang, Z. Li, and W.-T. Jiang, Adsorption of ciprofloxacin on 2:1 dioctahedral clay minerals, Appl. Clay Sci., 53, 723-728 (2011).
    78. P.-H. Chang, Z. Li, W.-T. Jiang, C.-Y. Kuo, and J.-S. Jean, Adsorption of tetracycline on montmorillonite: influence of solution pH, temperature, and ionic strength, Desalin. Water Treat., 1-13, 1380-1392 (2014).
    79. P.-H. Chang, Z. Li, J.-S. Jean, W.-T. Jiang, C.-J. Wang, and K.-H. Lin, Adsorption of tetracycline on 2:1 layered non-swelling clay mineral illite, Appl. Clay Sci., 67-68, 158-163 (2012).
    80. S. K. Behera, S.-Y. Oh, and H.-S. Park, Sorption of triclosan onto activated carbon, kaolinite and montmorillonite: Effects of pH, ionic strength, and humic acid, J. Hazard. Mater., 179, 684-691 (2010).
    81. H. Mabrouki and D. E. Akretche, Diclofenac potassium removal from water by adsorption on natural and pillared clay, Desalin. Water Treat., 57, 6033-6043 (2016).
    82. M. Kaur and M. Datta, Diclofenac sodium adsorption onto montmorillonite: Adsorption equilibrium studies and drug release kinetics, Adsorpt. Sci. Technol., 32, 365-387 (2014).
    83. E. K. Putra, R. Pranowo, J. Sunarso, N. Indraswati, and S. Ismadji, Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: Mechanisms, isotherms and kinetics, Water Res., 43, 2419-2430 (2009).
    84. H. Gallouze, D.-E. Akretche, C. Daniel, I. Coelhoso, and J. G. Crespo, Removal of synthetic estrogen from water by adsorption on modified bentonites, Environ. Eng. Sci., 38, 4-14 (2021).
    85. E. Bojemueller, A. Nennemann, and G. Lagaly, Enhanced pesticide adsorption by thermally modified bentonites, Appl. Clay Sci., 18, 277-284 (2001).
    86. A. Gil, Y. El Mouzdahir, A. Elmchaouri, M. A. Vicente, and S. A. Korili, Equilibrium and thermodynamic investigation of methylene blue adsorption on thermaland acid-activated clay minerals, Desalin. Water Treat., 51, 2881-2888 (2013).
    87. R. Rusmin, B. Sarkar, B. Biswas, J. Churchman, Y. Liu, and R. Naidu, Structural, electrokinetic and surface properties of activated palygorskite for environmental application, Appl. Clay Sci., 134, 95-102 (2016).
    88. J. A. Torres-Luna and J. G. Carriazo, Porous aluminosilicic solids obtained by thermal-acid modification of a commercial kaolinite-type natural clay, Solid State Sci., 88, 29-35 (2019).
    89. M. Toor, B. Jin, S. Dai, and V. Vimonses, Activating natural bentonite as a cost-effective adsorbent for removal of Congo-red in wastewater, J. Ind. Eng. Chem., 21, 653-661 (2015)..
    90. J. Nones, J. Nones, H. G. Riella, A. Poli, A. G. Trentin, and N. C. Kuhnen, Thermal treatment of bentonite reduces aflatoxin b1 adsorption and affects stem cell death, Mater. Sci. Eng. C, 55, 530-537 (2015).
    91. S. Aytas, M. Yurtlu, and R. Donat, Adsorption characteristic of U (VI) ion onto thermally activated bentonite, J. Hazard. Mater., 172, 667-674 (2009).
    92. Q. Zuo, X. Gao, J. Yang, P. Zhang, G. Chen, Y. Li, K. Shi, and W. Wu, Investigation on the thermal activation of montmorillonite and its application for the removal of U(VI) in aqueous solution, J. Taiwan Inst. Chem. Eng., 80, 754-760 (2017).
    93. L. Heller-Kallai, Chapter 7.2 Thermally Modified Clay Minerals, In: Dev. Clay Sci., Elsevier, 289-308 (2006).
    94. H. A. Talaat, N. M. El Defrawy, A. G. Abulnour, H. A. Hani, and A. Tawfik, Evaluation of heavy metals removal using some Egyptian clays, Int. Proc. Chem. Biol. Environ. Eng., 6, 37-42 (2011).
    95. E. Padilla-Ortega, N. Medellín-Castillo, and A. Robledo-Cabrera, Comparative study of the effect of structural arrangement of clays in the thermal activation: Evaluation of their adsorption capacity to remove Cd(II), J. Environ. Chem. Eng., 8, 103850 (2020).
    96. Z. Orolínová, A. Mockovčiaková, S. Dolinská, and J. Briančin, EFFECT OF THERMAL TREATMENT ON THE BENTONITE PROPERTIES, Arch. Tech. Sci., 4, 49-56 (2012).
    97. C. Bertagnolli, S. J. Kleinübing, and M. G. C. da Silva, Preparation and characterization of a Brazilian bentonite clay for removal of copper in porous beds, Appl. Clay Sci., 53, 73-79 (2011).
    98. M. G. A. Vieira, A. F. A. Neto, M. L. Gimenes, and M. G. C. da Silva, Sorption kinetics and equilibrium for the removal of nickel ions from aqueous phase on calcined Bofe bentonite clay, J. Hazard. Mater., 177, 362-371 (2010).
    99. V. Masindi and M. M. Ramakokovhu, The performance of thermally activated and vibratory ball milled South African bentonite clay for the removal of chromium ions from aqueous solution, Mater. Today Proc., 38, 964-974 (2021).
    100. S. T. Akar, Y. Yetimoglu, and T. Gedikbey, Removal of chromium (VI) ions from aqueous solutions by using Turkish montmorillonite clay: effect of activation and modification, Desalination, 244, 97-108 (2009).
    101. R. Antonelli, G. R. P. Malpass, M. G. C. da Silva, and M. G. A. Vieira, Adsorption of ciprofloxacin onto thermally modified bentonite clay: Experimental design, characterization, and adsorbent regeneration, J. Environ. Chem. Eng., 8, 104553 (2020).
    102. A. Maged, J. Iqbal, S. Kharbish, I. S. Ismael, and A. Bhatnagar, Tuning tetracycline removal from aqueous solution onto activated 2:1 layered clay mineral: Characterization, sorption and mechanistic studies, J. Hazard. Mater., 384, (2020) 121320.
    103. E. González-Pradas, M. Socías-Viciana, M. D. Ureña-Amate, A. Cantos-Molina, and M. Villafranca-Sánchez, Adsorption of chloridazon from aqueous solution on heat and acid treated sepiolites, Water Res., 39, 1849-1857 (2005).
    104. V. A. A. España, B. Sarkar, B. Biswas, R. Rusmin, and R. Naidu, Environmental applications of thermally modified and acid activated clay minerals: Current status of the art, Environ. Technol. Innov., 13, 383-397 (2019).
    105. K. G. Akpomie, and F. A. Dawodu, Acid-modified montmorillonite for sorption of heavy metals from automobile effluent, Beni-Suef Univ. J. Basic Appl. Sci., 5, 1-12 (2016).
    106. C. Volzone, Retention of pollutant gases: Comparison between clay minerals and their modified products, Appl. Clay Sci., 36, 191-196 (2007).
    107. W. T. Tsai, K. J. Hsien, and J. M. Yang, Silica adsorbent prepared from spent diatomaceous earth and its application to removal of dye from aqueous solution, J. Colloid Interface Sci., 275, 428-433 (2004).
    108. D. Tiwari, Lalhmunsiama, S. I. Choi, and S. M. Lee, Activated sericite: An efficient and effective natural clay material for attenuation of cesium from aquatic environment, Pedosphere, 24, 731-742 (2014).
    109. R. Shawabkeh, Experimental study and modeling of basic dye sorption by diatomaceous clay, Appl. Clay Sci., 24, 111-120 (2003).
    110. T. Vengris, R. Binkien, and A. Sveikauskait, Nickel, copper and zinc removal from waste water by a modified clay sorbent, Appl. Clay Sci., 18, 183-190 (2001).
    111. [111] P. Komadel and J. Madejová, Acid Activation of Clay Minerals, In: F. Bergaya, B.K.G. Theng, G. Lagaly, Developments in Clay Science, 263-287, Elsevier (2013).
    112. [112] M. Eloussaief and M. Benzina, Efficiency of natural and acid-activated clays in the removal of Pb(II) from aqueous solutions, J. Hazard. Mater., 178, 753-757 (2010).
    113. [113] P. Pushpaletha, S. Rugmini and M. Lalithambika, Correlation between surface properties and catalytic activity of clay catalysts, Appl. Clay Sci., 30, 141-153 (2005).
    114. [114] J. U. K. Oubagaranadin, Z. V. P. Murthy, and V. P. Mallapur, Removal of Cu(II) and Zn(II) from industrial wastewater by acid-activated montmorillonite-illite type of clay, Comptes Rendus Chim., 13, 1359-1363 (2010).
    115. [115] H. Chen, Y. Zhao and A. Wang, Removal of Cu(II) from aqueous solution by adsorption onto acid-activated palygorskite, J. Hazard. Mater., 149, 346-354 (2007).
    116. [116] Y. Bayrak, Y. Yesiloglu and U. Gecgel, Adsorption behavior of Cr(VI) on activated hazelnut shell ash and activated bentonite, Microporous Mesoporous Mater., 91, 107-110 (2006).
    117. [117] S. Arfaoui, N. Frini-Srasra, and E. Srasra, Modelling of the adsorption of the chromium ion by modified clays, Desalination, 222, 474-481 (2008).
    118. [118] Y. Deng, F. Wu, B. Liu, X. Hu, and C. Sun, Sorptive removal of β-blocker propranolol from aqueous solution by modified attapulgite: Effect factors and sorption mechanisms, Chem. Eng. J., 174, 571-578 (2011).
    119. [119] H. Zaghouane-Boudiaf and M. Boutahala, Kinetic analysis of 2,4,5-trichlorophenol adsorption onto acid-activated montmorillonite from aqueous solution, Int. J. Miner. Process., 100, 72-78 (2011).
    120. [120] B. Sarkar, Y. Xi, M. Megharaj, G. S. R. Krishnamurti, M. Bowman, H. Rose, and R. Naidu, Bioreactive Organoclay: A New Technology for Environmental Remediation, Crit. Rev. Environ. Sci. Technol., 42, 435-488 (2012).
    121. [121] M. Addy, B. Losey, R. Mohseni, E. Zlotnikov, and A. Vasiliev, Adsorption of heavy metal ions on mesoporous silica-modified montmorillonite containing a grafted chelate ligand, Appl. Clay Sci., 59-60, 115-120 (2012).
    122. [122] R. Celis, C. Trigo, G. Facenda, M. D. C. Hermosín, and J. Cornejo, Selective Modification of Clay Minerals for the Adsorption of Herbicides Widely Used in Olive Groves, J. Agric. Food Chem., 55, 6650-6658 (2007).
    123. [123] H. He, L. Ma, J. Zhu, R.L. Frost, B. K. G. Theng, and F. Bergaya, Synthesis of organoclays: A critical review and some unresolved issues, Appl. Clay Sci., 100, 22-28 (2014).
    124. [124] L. Groisman, Sorption of organic compounds of varying hydrophobicities from water and industrial wastewater by longand short-chain organoclays, Appl. Clay Sci., 24, 159-166 (2004).
    125. [125] V. A. Oyanedel-Craver and J. A. Smith, Effect of quaternary ammonium cation loading and pH on heavy metal sorption to Ca bentonite and two organobentonites, J. Hazard. Mater., 137, 1102- 1114 (2006).
    126. [126] P. LeBaron, Polymer-layered silicate nanocomposites: an overview, Appl. Clay Sci., 15, 11-29 (1999).
    127. [127] P. G. Slade and W. P. Gates, The swelling of HDTMA smectites as influenced by their preparation and layer charges, Appl. Clay Sci., 25, 93-101 (2004).
    128. [128] F. Bergaya and G. Lagaly, General introduction: clays, clay minerals, and clay science, Dev. Clay Sci., 1, 1-18 (2006).
    129. [129] G. Beall and M. Goss, Self-assembly of organic molecules on montmorillonite, Appl. Clay Sci., 27 179-186 (2004).
    130. [130] G. Gorrasi, M. Tortora, V. Vittoria, D. Kaempfer, and R. Mülhaupt, Transport properties of organic vapors in nanocomposites of organophilic layered silicate and syndiotactic polypropylene, Polymer, 44, 3679-3685 (2003).
    131. [131] M. Kozak and L. Domka, Adsorption of the quaternary ammonium salts on montmorillonite, J. Phys. Chem. Solids, 65, 441-445 (2004).
    132. [132] J. Zhu, H. He, L. Zhu, X. Wen and F. Deng, Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR, J. Colloid Interface Sci., 286, 239-244 (2005).
    133. [133] M. Ogawa, T. Handa, K. Kuroda and C. Kato, Formation of organoammonium-montmorillonites by solid-solid reactions, Chem. Lett., 19, 71-74 (1990).
    134. [134] S. Yoshimoto, F. Ohashi, and T. Kameyama, X-ray diffraction studies of intercalation compounds prepared from aniline salts and montmorillonite by a mechanochemical processing, Solid State Commun., 136, 251-256 (2005).
    135. [135] D. Merinska, Z. Malac, M. Pospisil, Z. Weiss, M. Chmielova, P. Capkova, and J. Simonik, Polymer/clay nanocomposites based on MMT/ODA intercalates, Compos. Interfaces, 9, 529-540 (2002).
    136. [136] T. S. Anirudhan and M. Ramachandran, Synthesis and characterization of amidoximated polyacrylonitrile/organobentonite composite for Cu(II), Zn(II), and Cd(II) adsorption from aqueous solutions and industry wastewaters, Ind. Eng. Chem. Res., 47, 6175-6184 (2008).
    137. [137] B. Cheknane, O. Bouras, M. Baudu, J.-P. Basly, and A. Cherguielaine, Granular inorgano-organo pillared clays (GIOCs): Preparation by wet granulation, characterization and application to the removal of a Basic dye (BY28) from aqueous solutions, Chem. Eng. J., 158, 528-534 (2010).
    138. [138] O. Bouras, J.-C. Bollinger, M. Baudu, and H. Khalaf, Adsorption of diuron and its degradation products from aqueous solution by surfactant-modified pillared clays, Appl. Clay Sci., 37, 240-250 (2007).
    139. [139] S.-Z. Li and P.-X. Wu, Characterization of sodium dodecyl sulfate modified iron pillared montmorillonite and its application for the removal of aqueous Cu(II) and Co(II), J. Hazard. Mater., 173, 62-70 (2010).
    140. [140] F. Zermane, O. Bouras, M. Baudu, and J.-P. Basly, Cooperative coadsorption of 4-nitrophenol and basic yellow 28 dye onto an iron organo-inorgano pillared montmorillonite clay, J. Colloid Interface Sci., 350, 315-319 (2010).
    141. [141] Thanhmingliana, C. Lalhriatpuia, D. Tiwari, and S.-M. Lee, Efficient removal of 17β-estradiol using hybrid clay materials: Batch and column studies, Environ. Eng. Res., 21, 203-210 (2016).
    142. [142] D. Tiwari, W. Kim, M. Kim, S. K. Prasad, and S.-M. Lee, Organo-modified sericite in the remediation of phenol-contaminated waters, Desalin. Water Treat., 53, 446-451 (2015).
    143. [143] X. Jin, M. Jiang, J. Du, and Z. Chen, Removal of Cr(VI) from aqueous solution by surfactant-modified kaolinite, J. Ind. Eng. Chem., 20, 3025-3032 (2014).
    144. [144] X. Ren, Z. Zhang, H. Luo, B. Hu, Z. Dang, C. Yang, and L. Li, Adsorption of arsenic on modified montmorillonite, Appl. Clay Sci., 97, 17-23 (2014).
    145. [145] J. Su, H.-G. Huang, X.-Y. Jin, X.-Q. Lu, and Z.-L. Chen, Synthesis, characterization and kinetic of a surfactant-modified bentonite used to remove As(III) and As(V) from aqueous solution, J. Hazard. Mater., 185, 63-70 (2011).
    146. [146] R. Mudzielwana, M.W. Gitari, and P. Ndungu, Performance evaluation of surfactant modified kaolin clay in As(III) and As(V) adsorption from groundwater: adsorption kinetics, isotherms and thermodynamics, Heliyon, 5, e02756 (2019).
    147. [147] S.M. Lee, Lalhmunsiama, Thanhmingliana, and D. Tiwari, Porous hybrid materials in the remediation of water contaminated with As(III) and As(V), Chem. Eng. J., 270, 496-507 (2015).
    148. [148] L. Zhu, and R. Zhu, Simultaneous sorption of organic compounds and phosphate to inorganic-organic bentonites from water, Sep. Purif. Technol., 54, 71-76 (2007).
    149. [149] Y. Chu, M. A. Khan, S. Zhu, M. Xia, W. Lei, F. Wang, and Y. Xu, Microstructural modification of organo‐montmorillonite with Gemini surfactant containing four ammonium cations: molecular dynamics (MD) simulations and adsorption capacity for copper ions, J. Chem. Technol. Biotechnol., 94, 3585-3594 (2019).
    150. [150] H. Hong, W.-T. Jiang, X. Zhang, L. Tie, and Z. Li, Adsorption of Cr(VI) on STAC-modified rectorite, Appl. Clay Sci., 42, 292-299 (2008).
    151. [151] I. Hamadneh, R. Abu-Zurayk, B. Abu-Irmaileh, A. Bozeya, and A. H. Al-Dujaili, Adsorption of Pb(II) on raw and organically modified Jordanian bentonite, Clay Miner., 50, 485-496 (2015).
    152. [152] J. Hua, Synthesis and characterization of bentonite based inorgano-organo-composites and their performances for removing arsenic from water, Appl. Clay Sci., 114, 239-246 (2015).
    153. [153] S. Dultz, J.-H. An, and B. Riebe, Organic cation exchanged montmorillonite and vermiculite as adsorbents for Cr(VI): Effect of layer charge on adsorption properties, Appl. Clay Sci., 67-68, 125-133 (2012).
    154. [154] X. Ren, Z. Zhang, H. Luo, B. Hu, Z. Dang, C. Yang, and L. Li, Adsorption of arsenic on modified montmorillonite, Appl. Clay Sci., 97-98, 17-23 (2014).
    155. [155] K. Tohdee and L. Kaewsichan, Asadullah, Enhancement of adsorption efficiency of heavy metal Cu(II) and Zn(II) onto cationic surfactant modified bentonite, J. Environ. Chem. Eng., 6, 2821-2828 (2018).
    156. [156] X. Jin, S. Zha, S. Li, and Z. Chen, Simultaneous removal of mixed contaminants by organoclays — Amoxicillin and Cu(II) from aqueous solution, Appl. Clay Sci., 102, 196-201 (2014).
    157. [157] Q. Yang, M. Gao, Z. Luo, and S. Yang, Enhanced removal of bisphenol A from aqueous solution by organo-montmorillonites modified with novel Gemini pyridinium surfactants containing long alkyl chain, Chem. Eng. J., 285, 27-38 (2016).
    158. [158] J. Wang, M. Gao, F. Ding, and T. Shen, Organo-vermiculites modified by heating and gemini pyridinium surfactants: Preparation, characterization and sulfamethoxazole adsorption, Colloids Surf. Physicochem. Eng. Asp., 546, 143-152 (2018).
    159. [159] A. E. Burgos, T. A. Ribeiro-Santos, and R. M. Lago, Adsorption of the harmful hormone ethinyl estradiol inside hydrophobic cavities of CTA(+) intercalated montmorillonite, Water Sci. Technol.J. Int. Assoc. Water Pollut. Res., 74, 663-671 (2016).
    160. [160] S. I. Rathnayake, Y. Xi, R. L. Frost, and G. A. Ayoko, Environmental applications of inorganic–organic clays for recalcitrant organic pollutants removal: Bisphenol A, J. Colloid Interface Sci., 470, (2016) 183-195.
    161. [161] A. (Fern) Phuekphong, K. Imwiset, and M. Ogawa, Adsorption of Triclosan onto Organically Modified-Magadiite and Bentonite, J. Inorg. Organomet. Polym. Mater., 31, 1902-1911 (2021).
    162. [162] H. He, Q. Tao, J. Zhu, P. Yuan, W. Shen, and S. Yang, Silylation of clay mineral surfaces, Appl. Clay Sci., 71, 15-20 (2013).
    163. [163] A. Di Gianni, E. Amerio, O. Monticelli, and R. Bongiovanni, Preparation of polymer/clay mineral nanocomposites via dispersion of silylated montmorillonite in a UV curable epoxy matrix, Appl. Clay Sci., 42, 116-124 (2008).
    164. [164] Negrete, J.-M. Letoffe, J.-L. Putaux, L. David, and E. BourgeatLami, Aqueous Dispersions of Silane-Functionalized Laponite Clay Platelets. A First Step toward the Elaboration of Water-Based Polymer/Clay Nanocomposites, Langmuir, 20, 1564-1571 (2004).
    165. [165] W. Shen, H. He, J. Zhu, P. Yuan, Y. Ma, and X. Liang, Preparation and characterization of 3-aminopropyltriethoxysilane grafted montmorillonite and acid-activated montmorillonite, Sci. Bull., 54, 265-271 (2009).
    166. [166] F. Piscitelli, P. Posocco, R. Toth, M. Fermeglia, S. Pricl, G. Mensitieri, and M. Lavorgna, Sodium montmorillonite silylation: Unexpected effect of the aminosilane chain length, J. Colloid Interface Sci. 351(1), 108-115 (2010)
    167. [167] S. B. Y. Abeywardena, S. Perera, K. M. Nalin de Silva, and N. P. Tissera, A facile method to modify bentonite nanoclay with silane, Int. Nano Lett., 7, 237-241 (2017).
    168. [168] M. Monasterio, J. J. Gaitero, E. Erkizia, A. M. Guerrero Bustos, L. A. Miccio, J. S. Dolado, and S. Cerveny, Effect of addition of silica- and amine functionalized silica-nanoparticles on the microstructure of calcium silicate hydrate (C–S–H) gel, J. Colloid Interface Sci., 450, 109-118 (2015).
    169. [169] A. Xue, S. Zhou, Y. Zhao, X. Lu, and P. Han, Effective NH2-grafting on attapulgite surfaces for adsorption of reactive dyes, J. Hazard. Mater., 194, 7-14 (2011).
    170. [170] A. M. Shanmugharaj, K. Y. Rhee, and S. H. Ryu, Influence of dispersing medium on grafting of aminopropyltriethoxysilane in swelling clay materials, J. Colloid Interface Sci., 298, 854-859 (2006).
    171. [171] L. M. Daniel, R. L. Frost, and H. Y. Zhu, Edge-modification of laponite with dimethyl-octylmethoxysilane, J. Colloid Interface Sci., 321, 302-309 (2008).
    172. [172] H. He, J. Duchet, J. Galy, and J.-F. Gerard, Grafting of swelling clay materials with 3-aminopropyltriethoxysilane, J. Colloid Interface Sci., 288, 171-176 (2005).
    173. [173] W. Carvalho, C. Vignado, and J. Fontana, Ni(II) removal from aqueous effluents by silylated clays, J. Hazard. Mater., 153, 1240-1247 (2008).
    174. [174] T. Şahan, F. Erol, and Ş. Yılmaz, Mercury(II) adsorption by a novel adsorbent mercapto-modified bentonite using ICP-OES and use of response surface methodology for optimization, Microchem. J., 138, 360-368 (2018).
    175. [175] X. Liang, Y. Xu, G. Sun, L. Wang, Y. Sun, Y. Sun, and X. Qin, Preparation and characterization of mercapto functionalized sepiolite and their application for sorption of lead and cadmium, Chem. Eng. J., 174, 436-444 (2011).
    176. [176] Lalhmunsiama, D. Tiwari, and S.-M. Lee, Surface-functionalized activated sericite for the simultaneous removal of cadmium and phenol from aqueous solutions: Mechanistic insights, Chem. Eng. J., 283, 1414-1423 (2016).
    177. [177] R. Malsawmdawngzela, D. Tiwari, and Lalhmunsiama, Facile synthesis and implications of novel hydrophobic materials: Newer insights of pharmaceuticals removal, Int. J. Biochem. Biophy., 58(6), 520-531 (2021).
    178. [178] R. Malsawmdawngzela, L. Siama, D. Tiwari, S.-M. Lee, and D.-J. Kim, Efficient and selective use of functionalized material in the decontamination of water: removal of emerging micro-pollutants from aqueous wastes, Environ. Technol. 1-15 (2021),
    179. [179] X. Liang, J. Han, Y. Xu, L. Wang, Y. Sun, and X. Tan, Sorption of Cd2+ on mercapto and amino functionalized palygorskite, Appl. Surf. Sci., 322, 194-201 (2014).
    180. [180] F. H. do Nascimento, D.M. de Souza Costa, and J. C. Masini, Evaluation of thiol-modified vermiculite for removal of Hg(II) from aqueous solutions, Appl. Clay Sci., 124-125, 227-235 (2016).
    181. [181] H. Cui, Y. Qian, Q. Li, Z. Wei, and J. Zhai, Fast removal of Hg(II) ions from aqueous solution by amine-modified attapulgite, Appl. Clay Sci., 72, 84-90 (2013).
    182. [182] V. Marjanović, S. Lazarević, I. Janković-Častvan, B. Potkonjak, Đ. Janaćković, and R. Petrović, Chromium (VI) removal from aqueous solutions using mercaptosilane functionalized sepiolites, Chem. Eng. J., 166, 198-206 (2011).
    183. [183] Ş. Yılmaz, T. Şahan, and A. Karabakan, Response surface approach for optimization of Hg (II) adsorption by 3-mercaptopropyl trimethoxysilane-modified kaolin minerals from aqueous solution, Korean J. Chem. Eng., 34, 2225-2235 (2017).
    184. [184] Ü. Ecer, Ş. Yılmaz, and T. Şahan, Highly efficient Cd(II) adsorption using mercapto-modified bentonite as a novel adsorbent: an experimental design application based on response surface methodology for optimization, Water Sci. Technol., 78, 1348-1360 (2018).
    185. [185] J. Han, X. Liang, Y. Xu, and Y. Xu, Removal of Cu2+ from aqueous solution by adsorption onto mercapto functionalized palygorskite, J. Ind. Eng. Chem., 23, 307-315 (2015)..
    186. [186] T. S. Anirudhan, S. Jalajamony, and S. S. Sreekumari, Adsorption of heavy metal ions from aqueous solutions by amine and carboxylate functionalised bentonites, Appl. Clay Sci., 65-66, 67-71 (2012).
    187. [187] T. Phothitontimongkol, N. Siebers, N. Sukpirom, and F. Unob, Preparation and characterization of novel organo-clay minerals for Hg(II) ions adsorption from aqueous solution, Appl. Clay Sci., 43, 343-349 (2009).
    188. [188] T. Undabeytia, F. Madrid, J. Vázquez, and J. I. Pérez-Martínez, Grafted Sepiolites for the Removal of Pharmaceuticals in Water Treatment, Clays Clay Miner., 67, 173-182 (2019).
    189. [189] Lalhmunsiama, R. R. Pawar, A. Chowdhury, Zirlianngura, and S. M. Lee, Removal of emerging micropollutants from water using hybrid material precursor to natural sericite clay, Int. J. Biochem. Biophy., 58 (2021).
    190. [190] R. Malsawmdawngzela and D. Tiwari, 17α-Ethinylestradiol elimination using synthesized and dense nanocomposite materials: Mechanism and real matrix treatment, Korean J. Chem. Eng., 39, 646-654 (2022).
    191. [191] Z. Danková, A. Bekényiová, I. Štyriaková and E. Fedorová, Study of Cu(II) Adsorption by Siderite and Kaolin, Procedia Earth Planet. Sci., 15, 821-826 (2015).
    192. [192] F. Fu and Q. Wang, Removal of heavy metal ions from wastewaters: A review, J. Environ. Manage., 92, 407-418 (2011).
    193. [193] D. J. L. Guerra, I. Mello, R. Resende, and R. Silva, Application as absorbents of natural and functionalized Brazilian bentonite in Pb2+ adsorption: Equilibrium, kinetic, pH, and thermodynamic effects, Water Resour. Ind., 4, 32-50 (2013).
    194. [194] Q. H. Zeng, A. B. Yu, G. Q. (Max) Lu, and D. R. Paul, Clay-Based Polymer Nanocomposites: Research and Commercial Development, J. Nanosci. Nanotechnol., 5, 1574-1592 (2005).
    195. [195] A.S.K. Kumar, S. Kalidhasan, V. Rajesh, and N. Rajesh, Application of Cellulose-Clay Composite Biosorbent toward the Effective Adsorption and Removal of Chromium from Industrial Wastewater, Ind. Eng. Chem. Res., 51, 58-69 (2012).
    196. [196] Y. Ma, L. Lv, Y. Guo, Y. Fu, Q. Shao, T. Wu, S. Guo, K. Sun, X. Guo, E. K. Wujcik, and Z. Guo, Porous lignin based poly (acrylic acid)/organo-montmorillonite nanocomposites: Swelling behaviors and rapid removal of Pb (II) ions, Polymer, 128, 12-23 (2017).
    197. [197] A. Soliemanzadeh and M. Fekri, The application of green tea extract to prepare bentonite-supported nanoscale zero-valent iron and its performance on removal of Cr(VI): Effect of relative parameters and soil experiments, Microporous Mesoporous Mater., 239, 60-69 (2017).
    198. [198] K. G. Bhattacharyya, S. S. Gupta, Kaolinite, montmorillonite, and their modified derivatives as adsorbents for removal of Cu(II) from aqueous solution, Sep. Purif. Technol., 50, 388-397 (2006).
    199. [199] V. N. Tirtom, A. Dinçer, S. Becerik, T. Aydemir, and A. Çelik, Comparative adsorption of Ni(II) and Cd(II) ions on epichlorohydrin crosslinked chitosan–clay composite beads in aqueous solution, Chem. Eng. J., 197, 379-386 (2012).
    200. [200] Y.-J. Shi, X.-H. Wang, Z. Qi, M.-H. Diao, M.-M. Gao, S.-F. Xing, S.-G. Wang, and X.-C. Zhao, Sorption and biodegradation of tetracycline by nitrifying granules and the toxicity of tetracycline on granules, J. Hazard. Mater., 191, 103-109 (2011).
    201. [201] S. Mnasri-Ghnimi, and N. Frini-Srasra, Removal of heavy metals from aqueous solutions by adsorption using single and mixed pillared clays, Appl. Clay Sci., 179, 105151 (2019).
    202. [202] Q. Wang, X. Chang, D. Li, Z. Hu, R. Li, and Q. He, Adsorption of chromium(III), mercury(II) and lead(II) ions onto 4-amino- antipyrine immobilized bentonite, J. Hazard. Mater., 186, 1076- 1081 (2011).
    203. [203] C. Quintelas, Z. Rocha, B. Silva, B. Fonseca, H. Figueiredo, and T. Tavares, Removal of Cd(II), Cr(VI), Fe(III) and Ni(II) from aqueous solutions by an E. coli biofilm supported on kaolin, Chem. Eng. J., 149, 319-324 (2009).
    204. [204] M. Alexandre and P. Dubois, Polymer-layered silicate nano- composites: preparation, properties and uses of a new class of materials, Mater. Sci. Eng. R Rep., 28, 1-63 (2000).
    205. [205] G. Beyer, Nanocomposites: a new class of flame retardants for polymers, Plast. Addit. Compd., 4, 22-28 (2002).
    206. [206] H. R. Fischer, L. H. Gielgens, and T. P. M. Koster, Nanocomposites from polymers and layered minerals, MRS Proc., 519, 117 (1998).
    207. [207] E. M. S. Azzam, Gh. Eshaq, A. M. Rabie, A. A. Bakr, A. A. Abd-Elaal, A. E. El Metwally, and S. M. Tawfik, Preparation and characterization of chitosan-clay nanocomposites for the removal of Cu(II) from aqueous solution, Int. J. Biol. Macromol., 89, 507-517 (2016).
    208. [208] K. Z. Setshedi, M. Bhaumik, S. Songwane, M. S. Onyango, and A. Maity, Exfoliated polypyrrole-organically modified montmorillonite clay nanocomposite as a potential adsorbent for Cr(VI) removal, Chem. Eng. J., 222, 186-197 (2013).
    209. [209] B. K. Kizilduman, M. Alkan, M. Doğan, and Y. Turhan, Al- Pillared-Montmorillonite (AlPMt)/Poly(Methyl Methacrylate)(PMMA) Nanocomposites: The effects of solvent types and synthesis methods, Adv. Mater. Sci., 17, 5-23 (2017).
    210. [210] R. Fu, Y. Yang, Z. Xu, X. Zhang, X. Guo, and D. Bi, The removal of chromium (VI) and lead (II) from groundwater using sepiolite-supported nanoscale zero-valent iron (S-NZVI), Chemosphere, 138, 726-734 (2015).
    211. [211] S. Bhowmick, S. Chakraborty, P. Mondal, W. Van Renterghem, S. Van den Berghe, G. Roman-Ross, D. Chatterjee, and M. Iglesias, Montmorillonite-supported nanoscale zero-valent iron for removal of arsenic from aqueous solution: Kinetics and mechanism, Chem. Eng. J., 243, 14-23 (2014).
    212. [212] C.M. Futalan, C.-C. Kan, M.L. Dalida, K.-J. Hsien, C. Pascua, and M.-W. Wan, Comparative and competitive adsorption of copper, lead, and nickel using chitosan immobilized on bentonite, Carbohydr. Polym., 83, 528-536 (2011).
    213. [213] A. B. Đukić, K. R. Kumrić, N. S. Vukelić, M. S. Dimitrijević, Z. D. Baščarević, S. V. Kurko, and L. Lj. Matović, Simultaneous removal of Pb2+, Cu2+, Zn2+ and Cd2+ from highly acidic solutions using mechanochemically synthesized montmorillonite–kaolinite/ TiO2 composite, Appl. Clay Sci., 103, 20-27 (2015).
    214. [214] A. Ramesh, H. Hasegawa, T. Maki, and K. Ueda, Adsorption of inorganic and organic arsenic from aqueous solutions by polymeric Al/Fe modified montmorillonite, Sep. Purif. Technol., 56, 90-100 (2007).
    215. [215] H. A. Sani, M. B. Ahmad, M. Z. Hussein, N. A. Ibrahim, A. Musa, and T. A. Saleh, Nanocomposite of ZnO with montmorillonite for removal of lead and copper ions from aqueous solutions, Process Saf. Environ. Prot., 109, 97-105 (2017).
    216. [216] L. Chen, P. Wu, M. Chen, X. Lai, Z. Ahmed, N. Zhu, Z. Dang, Y. Bi, and T. Liu, Preparation and characterization of the ecofriendly chitosan/vermiculite biocomposite with excellent removal capacity for cadmium and lead, Appl. Clay Sci., 159, 74-82 (2018).
    217. [217] A. C. S. Alcântara, M. Darder, P. Aranda, and E. Ruiz-Hitzky, Polysaccharide–fibrous clay bionanocomposites, Appl. Clay Sci., 96, 2-8 (2014).
    218. [218] A. Olad, M. Bastanian, and H. Bakht Khosh Hagh, Thermodynamic and kinetic studies of removal process of hexavalent chromium ions from water by using bio-conducting starch–montmorillonite/ polyaniline nanocomposite, J. Inorg. Organomet. Polym. Mater., 29, 1916-1926 (2019).
    219. [219] S. Piri, Z. A. Zanjani, F. Piri, A. Zamani, M. Yaftian, and M. Davari, Potential of polyaniline modified clay nanocomposite as a selective decontamination adsorbent for Pb(II) ions from contaminated waters; kinetics and thermodynamic study, J. Environ. Health Sci. Eng., 14, 20 (2016).
    220. [220] X. Wang, L. Yang, J. Zhang, C. Wang, and Q. Li, Preparation and characterization of chitosan–poly(vinyl alcohol)/bentonite nanocomposites for adsorption of Hg(II) ions, Chem. Eng. J., 251, 404-412 (2014).
    221. [221] T. H. Vu, T. M. V. Ngo, T. T. A. Duong, T. H. L. Nguyen, X. T. Mai, T. H. N. Pham, T. P. Le, and T. H. Tran, Removal of tetracycline from aqueous solution using nanocomposite based on polyanion-modified laterite material, J. Anal. Methods Chem., 2020, 1-9 (2020).
    222. [222] M. Chauhan, V. K. Saini, and S. Suthar, Ti-pillared montmorillonite clay for adsorptive removal of amoxicillin, imipramine, diclofenac-sodium, and paracetamol from water, J. Hazard. Mater., 399, 122832 (2020).
    223. [223] I. A. Shabtai and Y. G. Mishael, Polycyclodextrin–clay composites: regenerable dual-site sorbents for bisphenol a removal from treated wastewater, ACS Appl. Mater. Interfaces., 10, 27088-27097 (2018).
    224. [224] X. Jin, M. Zheng, B. Sarkar, R. Naidu, and Z. Chen, Characterization of bentonite modified with humic acid for the removal of Cu (II) and 2,4-dichlorophenol from aqueous solution, Appl. Clay Sci., 134, 89-94 (2016).
    225. [225] A. Ely, M. Baudu, J.-P. Basly, and M. O. S. O. Kankou, Copper and nitrophenol pollutants removal by Na-montmorillonite/alginate microcapsules, J. Hazard. Mater., 171, 405-409 (2009).
    226. [226] Y. Hu, C. Pan, X. Zheng, S. Liu, F. Hu, L. Xu, G. Xu, and X. Peng, Removal of ciprofloxacin with aluminum-pillared kaolin sodium alginate beads (CA-Al-KABs): kinetics, isotherms, and BBD model, Water, 12, 905 (2020).
    227. [227] T. M. Salem Attia, X. L. Hu, and D. Q. Yin, Synthesized magnetic nanoparticles coated zeolite for the adsorption of pharmaceutical compounds from aqueous solution using batch and column studies, Chemosphere, 93, 2076-2085 (2013).
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