Synergistic Multivalent States and Oxygen Vacancies in W/S Codoped Bi₂O₄ Oxysulfide for Enhanced Pollutant Reduction...

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 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(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.