Preparation and Characterization of Chitosan Thin Films on Mixed-Matrix Membranes for Complete Removal of Chromium

Herein we present a new approach for the complete removal of Cr-VI species, through reduction of Cr-VI to Cr-III, followed by adsorption of Cr-III. Reduction of chromium from water is an important challenge, as Cr-IV is one of the most toxic substances emitted from industrial processes. Chitosan (CS) thin films were developed on plain polysulfone (PSf) and PSf/TiO2 membrane substrates by a temperature-induced technique using polyvinyl alcohol as a binder. Structure property elucidation was carried out by X-ray diffraction, microscopy, spectroscopy, contact angle measurement, and water uptake studies. The increase in hydrophilicity followed the order: PSf < PSf/TiO2 < PSf/TiO2/CS membranes. Use of this thin-film composite membrane for chromium removal was investigated with regards to the effects of light and pH. The observations reveal 100% reduction of Cr-VI to Cr-III through electrons and protons donated from OH and NH2 groups of the CS layer; the reduced Cr-III species are adsorbed onto the CS layer via complexation to give chromium-free water.