Fabrication of thiophene-chitosan hydrogel-trap for efficient immobilization of mercury (II) from aqueous environs.

The fabrication of thiophene-chitosan (TCS) hydrogel has been carried out to show the excellent binding performance of Hg(II) from an aqueous solution of heavy metal ions in presence of thiophene moiety within the hydrogel network. Thiophene moiety has been implanted within chitosan, a wild bio-resources, through a facile Schiff base condensation strategy with 2-thiophenecarboxaldehyde to develop a three-dimensional network of TCS hydrogel. The parameters influencing adsorption capacity such as pH, volume of functional agent, contact time, amount of the hydrogel are included to broaden the in-depth study for the adsorption window of Hg(II) followed by the desorption and reusability performance of TCS. The results indicate that the TCS hydrogel for Hg(II) followed pseudo-second-order kinetics. Ethylenediaminetetraacetic acid (EDTA), acts as a better eluent compared to HCl to desorb Hg(II) and even after recurring adsorption/desorption cycles, removal efficacy of TCS hydrogel could be retained.

Comparison of Monovalent and Divalent Ions Removal from Aqueous Solutions Using Agricultural Waste Biochars Prepared at Different Temperatures-Experimental and Model Study.

Copper (Cu) and silver (Ag) occur naturally in the environment but have toxic effects on organisms at elevated concentrations. This paper discussed the removal of Cu and Ag from aqueous solutions using biochars obtained at different pyrolysis temperatures. Three biomass sources-sunflower husks (SH), a mixture of sunflower husks and rapeseed pomace (SR) and wood waste (WW)-were pyrolyzed at 300, 400 and 500 °C. Biochars produced at 500 °C exhibited a higher specific surface area, lower variable surface charge and lower contents of surface functional groups than those obtained at 400 or 300 °C. The pseudo-second-order model and intra-particle diffusion (IPD) model well-described the Cu and Ag adsorption kinetics. The Cu adsorption was about 1.48 times slower than the Ag adsorption on the biochars obtained at 500 °C. The model of Langmuir-Freundlich well-described the equilibrium adsorption. Agricultural biochars obtained at >500 °C had a surface with a higher affinity to attract Ag than Cu and were able to remove a larger amount of heavy metals from aqueous media than those prepared at lower pyrolysis temperatures.

Adsorption of Cu(II) ions from aqueous solution using pyridine-2,6-dicarboxylic acid crosslinked chitosan as a green biopolymer adsorbent.

In this study, crosslinked chitosan (CCS) has been synthesized by anchoring a bifunctional ligand, namely pyridine-2,6-dicarboxylic acid (PDC) with chitosan through ion exchange. The functionalized biopolymer has been characterized using different instrumental analyses including elemental (CHN), spectroscopic (UV-visible, NMR, powder XRD, and FTIR), thermal analyses (TGA and DSC), surface and morphological (BET and SEM) analyses. The PDC-CCS was utilized for the recovery of Cu(II) from water contaminated with Cu. The adsorption limit/capacity of PDC-CCS has been examined for solution pH, temperature, Cu(II) ion concentration, and the contact time of the adsorbent. An extreme adsorption limit of 2186 mmol·g-1 has been found for the PDC-CCS. Equilibrium was quickly attained within 60 min from the start of adsorption. Also, it was discovered that the adsorption limit/capacity exceedingly relies upon temperature and pH. On testing the experimental data with the two most popular adsorption models (fundamentally, Freundlich and Langmuir), we found that Cu(II) ion adsorption suit both models. Similarly, the experimental adsorption kinetics is in reality, second-order. Thermodynamic studies also revealed that the adsorption process was spontaneous and enthalpy driven. DFT calculations suggest that the main adsorption mechanism is by chelation through charge transfer from the adsorbent to the Cu(II) ions in solution.

Adsorptive removal of strontium ions from aqueous solution by graphene oxide.

Graphene oxide (GO) was prepared, characterized, and applied for adsorption of Sr(II) in aqueous solution. The adsorption capacity was calculated to be 137.80 mg/g according to the Langmuir model. The observation by scanning electron microscope with energy dispersive X-ray detector (SEM-EDX), high-resolution transmission electron microscope (HRTEM), and X-ray diffraction (XRD) revealed the crystal structure of Sr compound on the surface of graphene sheets. The analyses by the Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the involvement of O-C=O, C-O, and C-O-C groups during the adsorption. The X-ray absorption fine structure (XAFS) analysis provided the detail information of GO-Sr composites, and the fitting results were given by Sr(HCOO)2 and SrCO3 model, and the coordination numbers (CN) and interatomic distances (R) of Sr-O shell and Sr-C shell were calculated. The adsorption mechanism of Sr(II) was attributed to complexation between Sr and the acidic oxygen-containing groups, which lead to the agglomeration of graphene oxide. Two types of crystals were proposed. Type 1 was formed by coordination between Sr(II) and O-C=O groups, and type 2 was formed by coordination between Sr(II) and C-O/C-O-C groups.

Selective capillary electrophoresis separation of mono and divalent cations within a high-surface area-to-volume ratio multi-lumen capillary.

In this study, the separation of inorganic mono and divalent cations using multi-lumen silica capillaries (MLCs) of 126 channels, each with either 4 or 8 µm inner diameter, was investigated using capillary electrophoresis and on-capillary capacitively coupled contactless conductivity detection (CE-C4D). MLCs provided sufficiently high surface area-to-volume ratios to generate significant wall ion-exchange interactions for the divalent cations, which significantly affected resultant selectivity, whereas monovalent cations were predominantly separated by simple electrophoresis. The resultant hybrid selectivity was seen for both 4 and 8 µm channel multi-lumen capillaries, without any preconditioning or capillary wall modification. Remarkably, the electrophoretic mobilities for the divalent cations Mg2+ and Ca2+ were reduced 7.5 times compared to those determined using a single channel open tubular capillary of 50 µm i.d., providing much improved selectivity. Apparent electrophoretic mobilities of divalent cations increased as the concentration of BGE increased, while those of monovalent cations decreased parallel to electroosmotic mobility. These results show the electrostatic interaction between the divalent cations and the silica wall. At least, this specific separation of mono- and divalent cations were clearly observed with a mixture standards solution of less than 200 µmol L-1. Using a MLC with 126 × 8 µm i.d. channels and 49.1 cm in length, together with a 20 mmol L-1 MES/His BGE, containing 2 mmol L-1 18-crown-6, monovalent cations (NH4+, K+ Na+ and Li+) and divalent cations (Ca2+ and Mg2+) could be completely separated within 4 min. For monovalent cations, on-capillary detection using C4D provided calibration curve (0-200 µmol L-1) correlation coefficients in the range R2 = 0.995-0.999, and limits of detection of 2.2-6.6 µmol L-1. Relative standard deviations for migration times were less than 0.6%, and recoveries ranged from the 93.8%-105.4%. The new method was applied to the separation and quantitative determination of monovalent and divalent cations in drinking waters and soil extracts.

CE-XRF-initial steps toward a non-invasive elemental sensitive detector for liquid separations.

The toxicity, bioavailability, and mobilization of elements within the biosphere is dependent on its species. CE has emerged as a strong separation technique for elemental speciation. Conventionally, CE has been coupled with UV-vis, C4 D, PIXE (proton-induced X-ray emission), and ICP-MS. UV-vis and C4 D are not elemental sensitive detection methods, PIXE requires the etching of the detection window resulting in a very brittle capillary, and ICP-MS is an expensive large footprint instrument. Here, we aim to develop an elemental specific detector, XRF (X-ray fluorescence spectrometry), for use with CE. A custom-built micro-XRF was tested and static LODs were determined for 19 elements (Ca-U) with both unmodified (20-926 ppm) and modified capillaries (20-291 ppm). A custom-built CE was combined with the micro-XRF and separation of Ca2+ and Co2+ was obtained. Sr2+ coeluted with Ca2+ in the mixture, but because of the elemental sensitivity of XRF, the Sr and Ca signals could be separated. After successful testing of the micro-XRF, the feasibility of using a low-cost X-ray source and detector was tested. Even lower LODs were obtained for Ga and Rb, showing the feasibility of a smaller, low-cost XRF unit as an elemental specific detector. However, the buffer selection that can be conveniently used with XRF is currently limited due to capillary corrosion, likely correlated to radiolysis.

Hybrid chitosan/polyaniline-polypyrrole biomaterial for enhanced adsorption and antimicrobial activity.

In this work, chitosan (CS) functionalized polyaniline-polypyrrole (Pani-Ppy) copolymer (CS/Pani-Ppy) was synthesized applying a facile one pot method for the enhanced adsorption of Zn(II) and antimicrobial activity for E. coli and E. agglomerans. The synthesized materials were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform inferred spectroscopy and X-ray photoelectron spectroscopy. The adsorption of the Zn(II) on the synthesized materials was highly dependent on the pH of the solution, the initial metal ion concentration, and temperature. The adsorption of Zn(II) on the studied materials was as follows: CS/Pani-Ppy>Pani-Ppy>Ppy>Pani>CS. The results reveal that adsorption of Zn(II) follows the Langmuir adsorption isotherm, and that chemisorption occurs through pendant and bridging interactions, with active adsorbent sites. Thermodynamic results show the adsorption is spontaneous and exothermic in nature. The synthesized materials show excellent antimicrobial activity against E. coli and E. agglomerans bacterial organisms, and an approximately 100% decline in the viability of both strains was observed with CS/Pani-Ppy and Pani-Ppy. The order of antimicrobial activity for the synthesized materials was as follows: CS/Ppy-Pani>Ppy-Pani>Ppy>Pani>CS. The results show that the greater activity of CS/Ppy-Pani resulted from the electrostatic interaction between positively charged amine groups and negatively charged bacteria.

Polyacrylamide-phytic acid-polydopamine conducting porous hydrogel for rapid detection and removal of copper (II) ions.

In this work, a conducting porous polymer hydrogel-based electrochemical sensor has been developed for rapid detection of copper (II) ions (Cu2+). The polymer (termed as PAAM/PA/PDA) hydrogel is prepared through multi-interactions of the monomers dopamine (DA), acrylamide (AAM) and phytic acid (PA) under mild ambient conditions: the AAM polymerizes through free-radical polymerization, DA occurs poly coupling reaction, and PA crosslinks polydopamine (PDA) and polyacrylamide (PAAM) by hydrogen bonds. The three dimensional (3D) network nanostructured PAAM/PA/PDA hydrogel not only provides a large surface area for increasing the amount of immobilized molecules/ions, but also exhibits a good conductivity. The PAAM/PA/PDA hydrogel-based electrochemical sensor exhibits a low detection limit (1nmolL-1, S/N=3) and wide linear range (from 1nmolL-1 to 1µmolL-1) for Cu2+ detection in aqueous samples. Furthermore, the Cu2+ can be sensitively detected by the electrochemical sensor in different sample matrices, indicating that the electrochemical sensor could be used to monitor Cu2+ with reasonable assay performance in practical samples. The PAAM/PA/PDA hydrogel also exhibits a good capacity to remove Cu2+(231.36±4.70mgg-1), which is superior to those of other adsorption materials reported in the literature. The facile synthesized PAAM/PA/PDA hydrogel provides a novel and regenerable platform for monitoring and removing Cu2+ in real samples.

Adsorptive removal of nickel(II) ions from aqueous environment: A review.

Among various methods adsorption can be efficiently employed for the treatment of heavy metal ions contaminated wastewater. In this context the authors reviewed variety of adsorbents used by various researchers for the removal of nickel(II) ions from aqueous environment. One of the objectives of this review article is to assemble the scattered available enlightenment on a wide range of potentially effective adsorbents for nickel(II) ions removal. This work critically assessed existing knowledge and research on the uptake of nickel by various adsorbents such as activated carbon, non-conventional low-cost materials, nanomaterials, composites and nanocomposites. The system's performance is evaluated with respect to the overall metal removal and the adsorption capacity. In addition, the equilibrium adsorption isotherms, kinetics and thermodynamics data as well as various optimal experimental conditions (solution pH, equilibrium contact time and dosage of adsorbent) of different adsorbents towards Ni(II) ions were also analyzed. It is evident from a literature survey of more than 190 published articles that agricultural solid waste materials, natural materials and biosorbents have demonstrated outstanding adsorption capabilities for Ni(II) ions.

Ion selectivity of graphene nanopores.

As population growth continues to outpace development of water infrastructure in many countries, desalination (the removal of salts from seawater) at high energy efficiency will likely become a vital source of fresh water. Due to its atomic thinness combined with its mechanical strength, porous graphene may be particularly well-suited for electrodialysis desalination, in which ions are removed under an electric field via ion-selective pores. Here, we show that single graphene nanopores preferentially permit the passage of K(+) cations over Cl(-) anions with selectivity ratios of over 100 and conduct monovalent cations up to 5 times more rapidly than divalent cations. Surprisingly, the observed K(+)/Cl(-) selectivity persists in pores even as large as about 20 nm in diameter, suggesting that high throughput, highly selective graphene electrodialysis membranes can be fabricated without the need for subnanometer control over pore size.

Thioether-Based Fluorescent Covalent Organic Framework for Selective Detection and Facile Removal of Mercury(II).

Heavy metal ions are highly toxic and widely spread as environmental pollutants. New strategies are being developed to simultaneously detect and remove these toxic ions. Herein, we take the intrinsic advantage of covalent organic frameworks (COFs) and develop fluorescent COFs for sensing applications. As a proof-of-concept, a thioether-functionalized COF material, COF-LZU8, was "bottom-up" integrated with multifunctionality for the selective detection and facile removal of mercury(II): the π-conjugated framework as the signal transducer, the evenly and densely distributed thioether groups as the Hg(2+) receptor, the regular pores facilitating the real-time detection and mass transfer, together with the robust COF structure for recycle use. The excellent sensing performance of COF-LZU8 was achieved in terms of high sensitivity, excellent selectivity, easy visibility, and real-time response. Meanwhile, the efficient removal of Hg(2+) from water and the recycling of COF-LZU8 offers the possibility for practical applications. In addition, X-ray photoelectron spectroscopy and solid-state NMR investigations verified the strong and selective interaction between Hg(2+) and the thioether groups of COF-LZU8. This research not only demonstrates the utilization of fluorescent COFs for both sensing and removal of metal ions but also highlights the facile construction of functionalized COFs for environmental applications.

Experimental study of the removal of copper ions using hydrogels of xanthan, 2-acrylamido-2-methyl-1-propane sulfonic acid, montmorillonite: Kinetic and equilibrium study.

In this paper, removal of copper ions from aqueous solution using novel xanthan gum (XG) hydrogel, xanthan gum-graft-2-acrylamido-2-methyl-1-propane sulfonic acid (XG-g-P(AMPS)) hydrogel and xanthan gum-graft-2-acrylamido-2-methyl-1-propane sulfonic acid/montmorillonite (XG-g-P(AMPS)/MMT) hydrogel composite were studied. The structure and morphologies of the xanthan-based hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). Adsorbents comprised a porous crosslink structure with side chains that carried carboxyl, hydroxyl and sulfonate. Maximum adsorption was observed in the pH=5.2, initial concentrations of Cu(2+)=321.8 mg/L, Temperature=45 °C, contact time=5 h with 0.2 g/50 mL of the hydrogels. Adsorption process was found to follow Langmuir isotherm model with maximum adsorption capacity of 24.57, 39.06 and 29.49 mg/g for the XG, XG-g-P(AMPS) and XG-g-P(AMPS)/MMT, respectively. Adsorption kinetics data fitted well with pseudo second order model. The negative ΔG° values and the positive ΔS° confirmed that the adsorption was a spontaneous process. The positive ΔH° values suggested that the adsorption was endothermic in nature.

Optimization, isotherm, kinetic and thermodynamic studies of Pb(II) ions adsorption onto N-maleated chitosan-immobilized TiO2 nanoparticles from aqueous media.

Chitosan, CS was chemically engineered by maleic anhydride via simple protocol to produce N-maleated chitosan, MCS which immobilized on anatase TiO2 to synthesize novel eco-friendly nanosorbent (51±3.8 nm), MCS@TiO2 for cost-effective and efficient removal of Pb(II) ions from aqueous media. The chemical structure, surface properties and morphology of MCS@TiO2 were recognized by FTIR, (1)H NMR, XRD, TEM, DLS and zeta-potential techniques. The relations between %removal of Pb(II) and different analytical parameters such as solution acidity (pH), MCS@TiO2 dosage, time of contact and initial Pb(II) concentration were optimized using response surface methodology (RSM) and Box-Behnken design (BBD) statistical procedures. The fitting of the experimental data to four different isotherm models at optimized conditions was carried out by various statistical treatments including the correlation coefficient (r), coefficient of determination (r(2)) and non-linear Chi-square (χ(2)) test analyses which all confirm the suitability of Langmuir model to explain the adsorption isotherm data. Also, statistics predicted that the pseudo-second-order model is the optimum kinetic model among four applied kinetic models to closely describe the rate equation of the adsorption process. Thermodynamics viewed the adsorption as endothermic and feasible physical process. EDTA could release the sorbed Pb(II) ions from MCS@TiO2 with a recovery above 92% after three sorption-desorption cycles. The novel synthesized nanosorbent is evidenced to be an excellent solid phase extractor for Pb(II) ions from wastewaters.

Selective extraction and release using (EDTA-Ni)-layered double hydroxide coupled with catalytic oxidation of 3,3',5,5'-tetramethylbenzidine for sensitive detection of copper ion.

Copper is an important heavy metal in various biological processes. Many methods have been developed for detecting of copper ions (Cu(2+)) in aqueous samples. However, an easy, cheap, selective and sensitive method is still desired. In this study, a selective extraction-release-catalysis approach has been developed for sensitive detection of copper ion. Ethylenediaminetetraacetic acid (EDTA) chelated with nickel ion (Ni(2+)) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent in dispersive solid-phase extraction for the enrichment of Cu(2+) at pH 6. Since Cu(2+) has a stronger complex formation constant with EDTA, Ni(2+) exchanged with Cu(2+) selectively. The resulting sorbent containing Cu(2+) was transferred to catalyze the 3,3',5,5'-tetramethylbenzidine oxidation reaction, since Cu(2+) could be released by the sorbent effectively and has high catalytic ability for the reaction. Blue light emitted from the oxidation product was measured by ultraviolet-visible spectrophotometry for the determination of Cu(2+). The extraction temperature, extraction time, and catalysis time were optimized. The results showed that this method provided a low limit of detection of 10nM, a wide linear range (0.05-100µM) and good linearity (r(2)=0.9977). The optimized conditions were applied to environmental water samples. Using Cu(2+) as an example, this work provided a new and interesting approach for the convenient and efficient detection of metal cations in aqueous samples.

Confined Flocculation of Ionic Pollutants by Poly(L-dopa)-Based Polyelectrolyte Complexes in Hydrogel Beads for Three-Dimensional, Quantitative, Efficient Water Decontamination.

The development of simple and recyclable adsorbents with high adsorption capacity is a technical imperative for water treatment. In this work, we have successfully developed new adsorbents for the removal of ionic pollutants from water via encapsulation of polyelectrolyte complexes (PECs) made from positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly(l-3,4-dihydroxyphenylalanine) (PDopa), obtained via the self-polymerization of l-3,4-dihydroxyphenylalanine (l-Dopa). Given the outstanding mass transport through the hydrogel host matrixes, the PDopa-PAH PEC guests loaded inside can effectively and efficiently remove various ionic pollutants, including heavy metal ions and ionic organic dyes, from water. The adsorption efficiency of the PDopa-PAH PECs can be quantitatively correlated to and tailored by the PDopa-to-PAH molar ratio. Because PDopa embodies one catechol group, one carboxyl group, and one amino group in each repeating unit, the resulting PDopa-PAH PECs exhibit the largest capacity of adsorption of heavy metal ions compared to available adsorbents. Because both PDopa and PAH are pH-sensitive, the PDopa-PAH PEC-loaded agarose hydrogel beads can be easily and completely recovered after the adsorption of ionic pollutants by adjusting the pH of the surrounding media. The present strategy is similar to the conventional process of using PECs to flocculate ionic pollutants from water, while in our system flocculation is confined to the agarose hydrogel beads, thus allowing easy separation of the resulting adsorbents from water.

A simultaneous electrochemical multianalyte immunoassay of high sensitivity C-reactive protein and soluble CD40 ligand based on reduced graphene oxide-tetraethylene pentamine that directly adsorb metal ions as labels.

A simplified electrochemical multianalyte immunosensor for the simultaneous detection of high sensitivity C-reactive protein (hsCRP) and soluble CD40 ligand (sCD40L) that uses reduced graphene oxide-tetraethylene pentamine (rGO-TEPA) that directly adsorbs metal ions as labels is reported. rGO-TEPA contains a large number of amino groups and has excellent conductivity, making it an ideal template for the loading of Pb(2+) and Cu(2+), which greatly amplifies the detection signals. The signals could be directly detected in a single run through differential pulse voltammetry (DPV), and each biorecognition event produces a distinct voltammetric peak. The position and size of each peak reflects the identity and the level of the corresponding antigen. Primarily designed for an application in a sandwich-type immunoassay based on Pb(2+) and Cu(2+) labels, two main challenges are accomplished with the herein presented nanosheets: fabrication of the template and the amination process for Pb(2+) and Cu(2+) adsorption. To further improve the analytical performance of the immunosensor, Au@bovine serum albumin (BSA) nanospheres synthesized through a "green" synthesis route were used as a sensor platform, which not only provides a biocompatible microenvironment for the immobilization of antibodies but also amplifies the electrochemical signals. Under optimal conditions, hsCRP and sCD40L could be assayed in the range of 0.05 to 100 ng mL(-1) with detection limits of 16.7 and 13.1 pg mL(-1) (S/N=3), respectively. The assay results on clinical serum samples with the proposed immunosensor were in acceptable agreement with those using the standard single-analyte test of the enzyme-linked immunosorbent assay (ELISA). This novel immunosensing system provides a simple, sensitive and low-cost approach for a multianalyte immunoassay.

Synthesis and application of ion-imprinted polymer nanoparticles for the determination of nickel ions.

Novel Ni(II) ion-imprinted polymers (Ni-IIP) nanoparticles were prepared by using Ni(II) ion-1,5-diphenyl carbazide (DPC) complex as the template molecule and methacrylic acid, ethylene glycol dimethacrylate (EGDMA) and 2,2'-azobisisobutyronitrile (AIBN) as the functional monomer, cross-linker and the radical initiator, respectively. The synthesized polymer particles were characterized physically and morphologically by using infrared spectroscopy (IR), thermo gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. Some parameters such as pH, weight of the polymer, adsorption time, elution time, eluent type and eluent volume which affects the efficiency of the polymer were studied. The preconcentration factor, relative standard deviation, and limit of detection of the method were found to be 100, 1.9%, and 0.002 µg mL(-1), respectively. The prepared ion-imprinted polymer particles have an increased selectivity toward Ni(II) ions over a range of competing metal ions with the same charge and similar ionic radius. The method was applied to the determination of nickel in tomato and some water samples.

Adsorption and desorption of nickel(II) ions from aqueous solution by a lignocellulose/montmorillonite nanocomposite.

A new and inexpensive lignocellulose/montmorillonite (LNC/MMT) nanocomposite was prepared by a chemical intercalation of LNC into MMT and was subsequently investigated as an adsorbent in batch systems for the adsorption-desorption of Ni(II) ions in an aqueous solution. The optimum conditions for the Ni(II) ion adsorption capacity of the LNC/MMT nanocomposite were studied in detail by varying parameters such as the initial Ni(II) concentration, the solution pH value, the adsorption temperature and time. The results indicated that the maximum adsorption capacity of Ni(II) reached 94.86 mg/g at an initial Ni(II) concentration of 0.0032 mol/L, a solution pH of 6.8, an adsorption temperature of 70°C, and adsorption time of 40 min. The represented adsorption kinetics model exhibited good agreement between the experimental data and the pseudo-second-order kinetic model. The Langmuir isotherm equation best fit the experimental data. The structure of the LNC/MMT nanocomposite was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), whereas the adsorption mechanism was discussed in combination with the results obtained from scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectroscopy analyses (FTIR). The desorption capacity of the LNC/MMT nanocomposite depended on parameters such as HNO3 concentration, desorption temperature, and desorption time. The satisfactory desorption capacity of 81.34 mg/g was obtained at a HNO3 concentration, desorption temperature, and desorption time of 0.2 mol/L, 60 ºC, and 30 min, respectively. The regeneration studies showed that the adsorption capacity of the LNC/MMT nanocomposite was consistent for five cycles without any appreciable loss in the batch process and confirmed that the LNC/MMT nanocomposite was reusable. The overall study revealed that the LNC/MMT nanocomposite functioned as an effective adsorbent in the detoxification of Ni(II)-contaminated wastewater.

Synthesis of ethylenediamine modified chitosan microspheres for removal of divalent and hexavalent ions.

Ethylenediamine modified chitosan was obtained in the form of microspheres by chemical crosslinking with gluteraldehyde and evaluated for the effective removal of metal ions. The present modification results in additional nitrogen centers which function as potential binding sites and the microsphere form enhances the specific surface area during adsorption of metal ions. The adsorbent was used in batch experiments to evaluate the adsorption of Cu(II), Zn(II), Pb(II) and Cr(VI) in a individual metal salt solutions. The samples exhibited highest affinity for Cu(II) and least for Cr(VI) ions. The adsorption data were interpreted based on Langmuir and Freundlich isotherm models. The maximum adsorption capacity obtained from Langmuir model is 60.9 mg g(-1). The modified microspheres can be regenerated with high efficiency, suggesting that this adsorbent is satisfactory to reuse.

A novel hierarchical nanobiocomposite of graphene oxide-magnetic chitosan grafted with mercapto as a solid phase extraction sorbent for the determination of mercury ions in environmental water samples.

New mercapto-grafted graphene oxide-magnetic chitosan (GO-MC) has been developed as a novel biosorbent for the preconcentration and extraction of mercury ion from water samples. A facile and ecofriendly synthesis procedure was also developed for modification of GO-MC with 3-mercaptopropyltrimethoxysilane. The prepared nanocomposite material (mercapto/GO-MC) was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and energy-dispersive X-ray spectroscopy (EDX). The mercury analysis was performed by continuous-flow cold vapor atomic absorption spectrometry. The parameters affecting the extraction and preconcentration processes were carried out. The optimum conditions were found to be 60mg of sorbent, pH of 6.5, 10min for adsorption time, 3mL of HCl (0.1mol L(-1))/thiourea (2% w/v) as the eluent and 250mL for breakthrough volume. An excellent linearity was achieved in the range of 0.12-80ng mL(-1) (R(2)=0.999) at a preconcentration factor of 80. The limit of detection and quantification were achieved as 0.06ng mL(-1) and 0.12ng mL(-1), respectively. A good repeatability was obtained with the relative standard deviation (RSD) of 4.7%. Furthermore, real water samples were analyzed and good recoveries were obtained from 95 to 100%.