The mechanism of water pollutant photodegradation by mixed and core–shell WO3/TiO2 nanocomposites

Abstract

Environmental pollution is one of the biggest concerns in the world today, and solar energy-driven photocatalysis is a promising method for decomposing pollutants in aqueous systems. In this study, the photocatalytic efficiency and catalytic mechanism of WO₃-loaded TiO₂ nanocomposites of various structures were analyzed. The nanocomposites were synthesized via sol–gel reactions using mixtures of precursors at various ratios (5%, 8%, and 10 wt% WO₃ in the nanocomposites) and via core–shell approaches (TiO₂@WO₃ and WO₃@TiO₂ in a 9 : 1 ratio of TiO₂ : WO₃). After calcination at 450 °C, the nanocomposites were characterized and used as photocatalysts. The kinetics of photocatalysis with these nanocomposites for the degradation of methylene blue (MB⁺) and methyl orange (MO⁻) under UV light (365 nm) were analyzed as pseudo-first-order reactions. The decomposition rate of MB⁺ was much higher than that of MO⁻, and the adsorption behavior of the dyes in the dark suggested that the negatively charged surface of WO₃ played an important role in adsorbing the cationic dye. Scavengers were used to quench the active species (superoxide, hole, and hydroxyl radicals), and the results indicated that hydroxyl radicals were the most active species; however, the active species were generated more evenly on the mixed surfaces of WO₃ and TiO₂ than on the core–shell structures. This finding shows that the photoreaction mechanisms could be controlled through adjustments to the nanocomposite structure. These results can guide the design and preparation of photocatalysts with improved and controlled activities for environmental remediation.