Preparation of Crosslinked Chitosan/TiO2 Composite Beads for Photocatalytic Removal of Reactive Black 5: Effect of Material Composition and Process Parameters on Decolorization and Mineralization

Abstract

The immobilization of photocatalysts onto biodegradable polymeric supports has emerged as an effective strategy to overcome catalyst recovery limitations associated with conventional slurry photocatalytic systems. In this study, chitosan/TiO2 composite beads with different chitosan properties and TiO2 loadings were synthesized and evaluated for the photocatalytic removal of Reactive Black 5 (RB5), a recalcitrant azo dye commonly encountered in textile wastewater. The effects of chitosan molecular weight, degree of deacetylation, and crosslinking treatment on the structural characteristics and photocatalytic performance of the composite beads were systematically investigated. The synthesized composites were characterized through physical property measurements, point of zero charge (pHpzc) determination, and FTIR analyses. Photocatalytic performance was evaluated under various operational conditions, including pH, catalyst dosage, initial dye concentration, and temperature. Among the prepared materials, the crosslinked chitosan/TiO2 composite bead produced from chitosan with an 85% degree of deacetylation exhibited the highest mineralization efficiency, achieving 76.23% total organic carbon (TOC) removal. FTIR analyses performed before and after treatment indicated that RB5 removal occurred through the combined effects of adsorption and photocatalytic oxidation. The effects of operational parameters revealed that acidic conditions significantly enhanced RB5 removal, while increasing temperature improved reaction kinetics and overall degradation efficiency. Kinetic studies indicated that the photocatalytic degradation process was best described by the pseudo-first-order kinetic model, with correlation coefficients ranging from 0.9841 to 0.9976. Arrhenius analysis yielded an apparent activation energy of 11.76 kJ mol-1, indicating a low energy barrier for the degradation process. The results demonstrate that crosslinked chitosan/TiO2 composite beads are promising, environmentally friendly, and sustainable photocatalytic materials for the treatment of dye-containing wastewater and advanced water purification applications.