Visible light-driven photoactivity of zinc oxide impregnated chitosan beads for the detoxification of textile dyes

Abstract

The photocatalytic decolorization of model textile dyes, namely, Methylene Blue (MB) and Rhodamine B (RB) dyes using zinc oxide (ZnO) and zinc oxide impregnated chitosan beads (ZCB) under UV and visible light irradiations were investigated. ZCB was synthesized in order to enhance the photoresponse of ZnO toward visible light using chitosan, a well-known biopolymer. The ZnO and ZCB photocatalysts were characterized by Fourier transform-infrared spectra (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), diffuse reflectance spectra (DRS) and X-ray diffraction studies (XRD). In order to optimize various experimental parameters viz., irradiation time, the amount of catalyst, pH, co-ions, initial concentration of dye, experiments were conducted under UV and visible light irradiations. The percentage of decolorization of MB and RB dyes using ZnO and ZCB is in the order of ZnO/UV>ZCB/vis>ZnO/vis. The mineralization of dyes was assessed by measuring chemical oxygen demand (COD) at optimized conditions. The rate of photodecolorization of MB and RB dyes follows the pseudo-first-order kinetics. The reuse of ZCB in the photocatalytic decolorization of textile dyes has also been studied.