Tunable Modulation of Oxygen Vacancies Regulating Surface Polarization in Bi ₄ TaO ₈ Cl Nanosheets for Enhancement of Photocatalytic CO ₂ Reduction

Unique Bi₄TaO₈Cl nanosheets were synthesized via a molten-salt method and then processed to introduce tunable oxygen vacancy (VO) concentrations through H₂/Ar treatment and in situ NaBH₄-assisted calcination reduction, respectively. Owing to the surface polarization induced by the VO, the modified BTOC exhibits significantly enhanced charge separation/transport efficiency and improved CO₂ activation capability. Consequently, the CO production rate increases substantially with the VO concentration. Density functional theory calculations reveal that this enhancement originates from the role of VO in regulating the local electronic structure and optimizing the adsorption free energy of the *COOH intermediate. This work provides theoretical insights and a practical strategy for designing high-performance, defect-regulated bismuth oxyhalide photocatalysts.