Enriched Oxygen Vacancy-Mediated Efficient Charge Transfer in S-Scheme ZnO-V_O@Zn_0.5Cd_0.5S Heterojunction for Rapid...

Efficient charge separation is critical for high-performance photocatalytic reduction of U(VI) in nuclear wastewater. Employing defect engineering, an oxygen vacancy (V_O)-enriched S-scheme ZnO-V_O@Zn_0.5Cd_0.5S (ZnO-V_O@ZCS) heterojunction is constructed for rapid U(VI) removal. The synergistic effect of oxygen vacancies and the S-scheme mechanism is shown to significantly enhance charge separation and photocatalytic U(VI) reduction. Remarkably, ZnO-V_O@ZCS achieves 99.10% U(VI) removal within 10 min at pH 4 under simulated sunlight without sacrificial agents, surpassing the V_O-free ZnO@ZCS reference and exhibiting 4.10-fold and 20.0-fold higher activity than pristine ZnO-V_O and ZCS, respectively. Meanwhile, the catalyst maintains robust performance across a wide pH range (3-8), complex matrices (interfering ions/dyes), natural sunlight, and diverse U(VI) containing wastewater. In situ X-ray photoelectron spectroscopy (In situ XPS) and Kelvin probe force microscopy (KPFM) confirm the S-scheme charge transfer between ZnO-V_O and ZCS. Femtosecond transient absorption spectroscopy (fs-TAS) and density functional theory (DFT) calculations reveal that V_O serve as transient electron traps, creating rapid charge-transfer channels that interplay with the S-scheme to enhance charge transfer efficiency and accelerate U(VI) reduction kinetics. This study provides new insights for designing defect-modulated S-scheme heterojunction photocatalysts, promising for sustainable nuclear wastewater treatment.