Effective detoxification of hexavalent chromium using sulfate-crosslinked chitosan.

A sulfate-crosslinked chitosan (SCC) was prepared for effective detoxification of hexavalent chromium (Cr(VI)) from effluents. SCC was characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray studies. The maximum adsorption of Cr(VI) was observed at pH 6.0 with adsorption capacity of 157 mg/g in accordance with the Langmuir adsorption isotherm model. The adsorption process was found to follow the pseudo-second-order rate kinetics. From the study of various thermodynamic parameters (Gibbs energy, entropy and enthalpy changes), the adsorption capacity was found to decrease with increase in temperature. Column studies were carried out to obtain a breakthrough point of the adsorbent. The adsorbent was regenerated using sodium hydroxide with no change in the adsorption efficiency for up to 10 cycles. Effect of diverse ions on adsorption efficiency was studied and SCC was applied for Cr(VI) removal in synthetic effluents.

Stannic chloride impregnated chitosan for defluoridation of water.

Chitosan, a potent amino polysaccharide, has been impregnated with Sn(IV) chloride for effective adsorption of fluoride from water. The Sn(IV) chloride impregnated chitosan was synthesized using microwave assisted technique. The material was thoroughly characterized using FTIR, SEM, EDX and XRD. The decrease in surface area and pore volume has been revealed from BET studies. Enhanced thermal stability of this material was ascertained by TGA-DTA studies. This Sn(IV) chloride impregnated chitosan(Sn-Ch) has been exploited for its defluoridation property. Various parameters like pH, amount of adsorbent, adsorption time etc have been optimized to achieve maximum defluoridation efficiency. Under optimum conditions, Sn-Ch was found to have adsorption capacity of 17. 63mg/g. The equilibrium studies showed that the data fits well with Freundlich isotherm model. Thermodynamics and kinetics parameters have been evaluated. The material has been applied for the defluoridation of real water sample. It was found to be recyclable material and can be regenerated and reused multiple times adding a greener dimension.

Tin(IV) cross-linked chitosan for the removal of As(III).

Chitosan, a potent amino polysaccharide, has been cross-linked with Sn(IV) chloride. The material was thoroughly characterized using FT-IR, XRD, SEM, EDX, TGA-DTA and BET studies. This Sn(IV) chloride cross-linked chitosan (Sn-Ch) has been exploited for As(III) adsorption. Various parameters like pH, amount of adsorbent, adsorption time etc have been optimized to achieve maximum adsorption efficiency. Under optimum conditions of pH 7.0±0.2, adsorption time of 45min and adsorbent dose 200mg, Sn-Ch was found to have adsorption capacity of 17.10mg/g at 298K. Adsorption of As(III) by Sn-Ch follow non-linear Freundlich isotherm model. The equilibrium studies showed that the experimental data fits well with non-linear pseudo-second-order kinetic model. Adsorption process was found to be exothermic and spontaneous. Column study proves the applicability of Sn-Ch to the larger sample volumes. It was found to be recyclable material and could be regenerated and reused multiple times adding a greener dimension.

Removal of Cd(II) and Hg(II) from effluents by ionic solid impregnated chitosan.

Ethylhexadecyldimethyl ammonium bromide impregnated chitosan (EHDAIC) was prepared to remove cadmium and mercury from synthetic effluent. The adsorbent was characterized by FTIR, XRD, SEM, EDX and TGA-DTA. Adsorption studies were carried out under different conditions of pH, adsorbent dose, temperature, and contact time. The results showed that the adsorption capacity of EHDAIC is a function of the solution pH and the optimum pH for these metal ions was found to be 3.0. The equilibrium data has been described using Langmuir and Freundlich isotherm models. The maximum adsorption capacity of 341.30mg/g was observed for Cd(II) and 43.43mg/g for Hg(II) in accordance with Langmuir adsorption isotherm in the form of their chloro complexes. The kinetic data fitted well with pseudo-second-order model, and equilibrium data was found to follow Freundlich isotherm model. The calculated thermodynamic parameters showed that the adsorption process was feasible, exothermic and spontaneous. Effect of common excipient ions was studied. Also the material was tested for large sample volumes using column extraction process. The adsorbent material could be regenerated for repetitive applications.