Synergistic Multivalent States and Oxygen Vacancies in W/S Codoped Bi2O4 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 Bi2O4 oxysulfide (WBiOS) is developed for pollutant reduction under dark conditions. By introducing the W cation and S anion, the electronic structure of Bi2O4 is reconstructed, accompanied by the formation of abundant oxygen vacancies (Ov) and dual Bi3+/5+ and W4+/6+ redox couples. The Bi3+/5+ and W4+/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(Bi3+)/n(Bi3+ + Bi5+) (39.46%) and n(W4+)/n(W4+ + W6+) (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 NaBH4 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.