Synergistic Multivalent States and Oxygen Vacancies in W/S Codoped Bi ₂ O ₄ Oxysulfide for Enhanced Pollutant Reduction under Dark Conditions

Conventional photocatalytic systems rely on light irradiation to activate catalytic reactions, which significantly limits their practical applicability under real environmental conditions. Herein, a W/S codoped Bi 2 O 4 oxysulfide (WBiOS) is developed for pollutant reduction under dark conditions. By introducing the W cation and S anion, the electronic structure of Bi 2 O 4 is reconstructed, accompanied by the formation of abundant oxygen vacancies (Ov) and dual Bi 3+/5+ and W 4+/6+ redox couples. The Bi 3+/5+ and W 4+/6+ species establish efficient electron-transfer pathways, while the Ov acts as an electron-trapping center and active sites, thereby accelerating electron transport and surface reaction kinetics. Benefiting from these synergistic effects, optimized WBiOS-2 with n (Bi 3+ )/ n (Bi 3+ + Bi 5+ ) (39.46%) and n (W 4+ )/ n (W 4+ + W 6+ ) (30.64%) exhibits the largest electrochemically active surface area (1.87 mF cm –2 ). It achieves complete reduction of 100 mL of 20 ppm 4-nitrophenol, methylene blue, nitro compounds, and Cr(VI) within 16, 8, 6, and 14 min, respectively, using NaBH 4 as the reducing agent, with corresponding kinetic rate constants of 0.17, 0.13, 0.18, and 0.19 min –1, respectively. WBiOS-2 demonstrates sustained performance toward mixed pollutants across a wide pH range and maintains structural stability during cyclic operation. This work provides a promising strategy for the design of oxysulfide catalysts for environmental remediation.