WO3/BiVO4 heterojunctions: Photoelectrochemical performance for dexamethasone degradation and toxicity assessment in Lactuca sativa

Water contamination by dexamethasone (DEX) poses a significant threat to the global population. Developing an effective and affordable system for DEX removal remains a critical need, particularly in treating DEX and other contaminants at environmentally relevant concentrations. Chemical bath and spin coating techniques were applied to synthesize a custom-designed WO₃/BiVO₄ interface electrode on a fluorine-doped tin oxide (FTO) substrate. Each WO₃/BiVO₄, WO₃, and BiVO₄ layer was characterized both photochemically and electrochemically to identify enhanced light harvesting and electron transfer at the heterojunction. Compared to the pristine materials, more charge carriers, enhanced transfer, and separation of photogenerated pairs were observed. The effectiveness of the WO₃/BiVO₄ electrode in removing 10 mg L⁻¹ DEX was evaluated under photolysis, electrocatalysis (EC), and photoelectrocatalysis (PhEC) treatment conditions. The PhEC treatment at 1 mA cm⁻² under visible light irradiation exhibited an excellent DEX removal efficiency of 100 %, surpassing photocatalysis (54 %) and EC (14.6 %). The mineralization rate and the formation of short-chain acids (oxalic, succinic, glycolic, and adipic) depended on the processes investigated. The large formation of superoxide radicals from the photogenerated charges in WO₃/BiVO₄ was revealed by scavenger tests, elucidating the degradation mechanism in PhEC, which resulted in a final product with lower toxicity, proven by tests with Lactuca sativa. The application of reuse cycles and characterizations after the PhEC processes demonstrated the electrode's good quality and useful life. Therefore, it can be inferred that the WO₃/BiVO₄ electrode applied in the PhEC process efficiently removes DEX and presents itself as a promising proposal for treating residual drugs in environmental matrices.