Efficient decolorization of azo dye solution by visible light-induced photocatalytic process using SnO 2/ZnO heterojunction immobilized in chitosan matrix

Abstract

SnO 2/ZnO quantum dot (3–5 nm diameters) heterojunction immobilized on crosslinked chitosan films (SnO 2/ZnO/chitosan films) were prepared successfully and characterized by high-resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM) and X-ray diffraction (XRD). In the presence of SnO 2/ZnO/chitosan films and under visible light irradiation, decolorization of azo dye methyl orange (MO) in aqueous solution was studied. The effects of key operational parameters such as aeration, photocatalyst dosage, MO initial concentration and electrolytes were discussed. SnO 2/ZnO/chitosan films exhibited a good adsorption–photocatalytic activity for decolorization of MO and could be reused expediently by simple filtration from treated solution. The decolorization process of MO solution was accelerated with increased photocatalyst dosage and decreased initial MO concentration. The presence of coexisting anions had impeditive effects on photocatalytic decolorization of MO dye. Kinetics analysis indicated that the dye photocatalytic decolorization rates could be approximated by pseudo-first-order model. With weak aeration MO solution was decolorized successfully excess 99% by SnO 2/ZnO/chitosan films after 210 min of visible light irradiation. As an inorganic/organic composite material, SnO 2/ZnO/chitosan films exhibited enhanced properties due to the combination of SnO 2/ZnO quantum dot heterojunction and organic matrix at nanometer scale. Cycling experiments indicated that SnO 2/ZnO/chitosan films were efficient and stable visible light photocatalyst.