Adsorptive removal of Cr(VI) by Chitosan-SiO2-TiO2 nanocomposite

Abstract

A bio-nanocomposite was synthesized by incorporating amorphous SiO2 and nanocrystalline TiO2 into chitosan matrix using glutaraldehyde crosslinker (CsC@SiO2@TiO2). The structure of CsC@SiO2@TiO2 was characterized by various techniques like FT-IR, XRD, TGA, DTA, SEM and EDX. This composite was used selectively for the removal of Cr(VI) from aqueous solutions through batch adsorption studies. Under the optimum conditions of pH 3.0, contact time of 120 min, adsorbent dose of 50 mg and Cr(VI) concentration of 100 mg L-1, the monolayer adsorption capacity was found to be 182.43 mg/g. Kinetic studies reveal that the material follows the pseudo order kinetics towards Cr(VI) sorption process. Thermodynamic parameters studies reveal that the adsorption process was endothermic, spontaneous and entropy driven in nature. The sorption of Cr(VI) has been explained by Langmuir isotherm model indicating monolayer adsorption on homogeneous surface. The composite showed more than 90% uptake of Cr(VI) under optimum conditions and more than 80% uptake in the presence of other interfering ions proving its selectivity towards Cr(VI). The material has been regenerated by using 0.5 M NaOH with negligible change in adsorption capacity for the five adsorption–desorption cycles.