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Recently, nanomaterials based adsorbents play a prominent role in the removal of toxic ions from aqueous solution. Hence in the present study, nano-graphene oxide (n-GO) fabricated hydrotalcite (n-GO@HT) composite was prepared by hydrothermal method for chromium removal. To improve the mechanical strength and chromium removal capacity, GO@HT composite was reinforced with chitosan (CS) to form hybrid composite namely n-GO@HTCS biocomposite. The synthesized biocomposite was characterized using various instrumental techniques like FTIR, SEM, TEM and EDAX with mapping analysis. To get the maximum chromium retention, the various sorption experiments like agitation time, dosage, pH, competing ions and temperature were optimized. The sorption capacity (SC) of n-GO@HTCS biocomposite was found to be 42.64 mg/g within 50 min. The obtained equilibrium data was explained with Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms wherein the chromium sorption process was best fitted with Langmuir isotherm. The thermodynamic results prove that the chromium sorption of n-GO@HTCS biocomposite was endothermic and spontaneous. The chromium sorbed n-GO@HTCS biocomposite could be easily regenerated with 0.1 M NaOH. The synthesized n-GO@HTCS biocomposite was also utilized in the field conditions. • Hydrothermal helped n-GO@HTCS composite was synthesized for Cr (VI) removal. • The maximum sorption capacity of n-GO@HTCS biocomposite was achieved 42.64 mg/g within 50 min. • The applicability of n-GO@HTCS biocomposite was tested at field experiments. [ABSTRACT FROM AUTHOR]

The magnetic hydrotalcite supported biopolymeric composites were synthesized by hydrothermal (Hydro) and in situ precipitation (in situ) methods for selective chromium removal. A comparative evaluation of chromium sorption capacity (SC) of both hydrothermal and in situ synthesized magnetic biocomposites namely Fe3O4@alginate/hydrotalcite (Fe3O4@AlgHT) composite, Fe3O4@chitosan/hydrotalcite (Fe3O4@CSHT) composite, and Fe3O4@gelatin/hydrotalcite (Fe3O4@GelHT) composite was carried out. The hydrothermally synthesized magnetic biocomposites demonstrated greater chromium SC than in situ method. The synthesized materials were characterized by Fourier transform infrared spectrometer, X-ray diffraction, Brunauer-Emmett-Teller, ultraviolet-visible spectrophotometer, vibrating sample magnetometer, transmission electron microscope, scanning electron microscope, and energy dispersive X-ray analysis. The equilibrium data of the synthesized magnetic biocomposites were explained by Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. The thermodynamic result shows that the nature of chromium sorption onto the magnetic biocomposites is spontaneous and endothermic. The kinetic models suggested that the chromium sorption behavior follow pseudo-second-order and intraparticle diffusion models. The chromium sorbed magnetic biocomposites can be easily regenerated using NaOH and can be effectively used up to five cycles. The suitability of the magnetic biocomposites at field conditions was inspected by field water sample. [ABSTRACT FROM AUTHOR]

This study focused on the hydrothermal synthesis of hydrocalumite (HC) incorporated biopolymer (alginate and chitosan) based hybrid composite materials for the selective removal of chromium. The synthesized hydrocalumite/alginate (HCAlg) and hydrocalumite/chitosan (HCCS) composites were characterized by FTIR, XRD, SEM, EDAX with mapping images and BET analysis. The synthesized HCCS composite possesses enhanced chromium sorption capacity (SC) compared to HCAlg composite, but both the hybrid composites showed a quick chromium sorption rate at 40 min. The depending adsorption parameters, namely equilibrium time, solution pH, competing co-ions, dosage, initial chromium concentration and temperature, were optimized for the maximum Cr(vi) sorption. The obtained equilibrium data was explained using Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. The thermodynamic result shows that the nature of the Cr(vi) adsorption attributed to the biopolymeric composites is spontaneous and endothermic. The possible Cr(vi) uptake mechanism of the synthesized biocomposites was occurred by electrostatic attraction and ion-exchange. The reusability of the synthesized adsorbents was carried out using NaOH and they can be used upto five cycles. Both the prepared biocomposites showed promising results against chromium contaminated ground water by reducing the chromium concentration below the tolerance limit. [ABSTRACT FROM AUTHOR]

The present study was performed to examine the probability of magnetic iron oxide fabricated hydrotalcite/chitosan (Fe 3 O 4 @HTCS) composite for the removal of excess fluoride content from drinking water. The developed Fe 3 O 4 @HTCS composite not only demonstrate the good separation ability but also display an extreme enhanced defluoridation capacity (DC) when compared to other base components and composite. The DCs of Fe 3 O 4 @HTCS composite, Fe 3 O 4 @HT composite, Fe 3 O 4 , HT and CS was found to be 5032, 3041, 1050, 1030 and 52 mgF − /kg respectively. The structure and morphology of the prepared adsorbent and fluoride sorbed adsorbent was analysed using FTIR, SEM and EDAX with mapping techniques. The dependence of DC on various parameters like initial fluoride concentration, pH, contact time, interfering anions and temperature was studied by batch method. From isotherm modeling, the equilibrium data is well described by Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms. Thermodynamic parameters confirm the spontaneity and endothermic nature of the fluoride adsorption. The performance of Fe 3 O 4 @HTCS composite to field water sample designates its adaptable nature at field conditions. [ABSTRACT FROM AUTHOR]

The present study was focused on Cr(VI) removal using eco-friendly materials like cellulose (Cel), hydrotalcite (HT), hydroxyapatite (HAp) and their composite forms. The cellulose/hydrotalcite (CelHT) and cellulose/hydroxyapatite (CelHAp) composites were synthesized by dispersing HT and HAp individually in cellulose polymeric matrix. To enhance the Cr(VI) sorption capacity (SC) and easy separation, cellulose supported magnetic composites namely iron-oxide coated cellulose/hydrotalcite (Fe 3 O 4 @CelHT) and cellulose/hydroxyapatite (Fe 3 O 4 @CelHAp) were synthesized by in situ fabrication method. The different adsorption influencing parameters like contact time, pH, co-ions, dosage, initial Cr(VI) concentration and temperature were optimized for maximum Cr(VI) sorption. The structure and morphology of cellulose supported magnetic composites were analyzed using FTIR, BET and SEM with EDAX analysis. The obtained equilibrium value was interpreted with Freundlich and Langmuir isotherms. The suitable Cr(VI) uptake mechanism for cellulose supported magnetic composites was demonstrated. The values of thermodynamic parameters helps in the prediction of nature of Cr(VI) sorption process. The suitability of these magnetic cellulose supported composites was tested at field conditions by collecting chromium contaminated water. [ABSTRACT FROM AUTHOR]

Biocomposites were synthesized by dispersing bentonite (Bent) clay in a biopolymer namely alginate (Alg) and cross-linked with bi (Ca 2+ ), tri (Ce 3+ ) and tetravalent (Zr 4+ ) metal ions viz., Ca@AlgBent, Ce@AlgBent and Zr@AlgBent composites respectively. The synthesized biocomposites were characterized by various instrumental techniques like FTIR, SEM and EDAX. Cr(VI) sorption capacities (SCs) of the biocomposites Ca@AlgBent, Ce@AlgBent and Zr@AlgBent were examined by batch process. Various adsorption influencing factors viz., contact time, dosage of the sorbent, pH of the medium, temperature, presence of common co-ions and initial Cr(VI) concentration were studied. Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherm models were adopted to examine the adsorption equilibrium. Kinetics of the sorption process was carried out by pseudo-first-order and pseudo-second-order models. The nature of the sorption process was explained using thermodynamic parameters like ΔS°, ΔG° and ΔH° and a possible mechanism for the sorption of Cr(VI) onto the biocomposites was given. The application of the biocomposites at field conditions was also examined by testing it with industrial water. The regeneration studies were carried to know about the reusability of the biocomposites. [ABSTRACT FROM AUTHOR]