Exploitation of zinc oxide impregnated chitosan beads for the photocatalytic decolorization of an azo dye

Abstract

Investigations were made to evaluate and distinguish the photocatalytic decolorization of Reactive Red 2 (RR) dye using zinc oxide (ZnO) and zinc oxide impregnated chitosan beads (ZCB) under UV and visible light irradiations. To enhance the photoresponse of ZnO toward visible light, the modification of ZnO using biopolymer, chitosan, has been carried out and synthesized the ZCB. Both ZnO and ZCB photocatalysts were characterized by Fourier transform-infrared spectra (FT-IR), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and diffuse reflectance spectra (DRS). Experiments were conducted to optimize various parameters, viz., irradiation time, the amount of catalyst, pH, co-ions and initial concentration of dye under UV and visible light irradiations. The percentage of decolorization of RR dye using ZnO and ZCB under UV as well as visible light is in the order of ZnO/UV>ZCB/vis>ZnO/vis>ZCB/UV. The mineralization/detoxification of RR dye was assessed by measuring chemical oxygen demand (COD) at optimized conditions. The kinetic studies demonstrated that the photocatalytic reactions followed the pseudo-first-order model. The reusability of as-synthesized ZCB was assessed.