Ultrathin two-dimensional BiOBr_xI_1-x solid solution with rich oxygen vacancies for enhanced visible-light-driven photoactivity in environmental remediation

Photocatalysis is intensively investigated for environmental remediation, but suffering from moderate efficiency toward the colorless persistent organic contaminants, the major category of organic pollutants in water environment. Herein, a novel series of oxygen vacancy-rich ultrathin two-dimensional BiOBr_xI_1-x solid solution nanosheets (BBI-x) were successfully constructed via a one-step solvothermal method. Under visible light irradiation, the optimal BiOBr_0.85I_0.15 sample (BBI-0.85) exhibited over 90% degradation efficiency of 4-chlorophenol (4-CP) within 30 min, which was 4.4, 10.9 and 5.9 times greater than that of pure BiOI nanosheets, pure BiOBr nanosheets and oxygen vacancy-poor BiOBr_0.85I_0.15 nanoplates, respectively. Also, this excellent photoactivity can expand to other colorless organic contaminants, such as bisphenol analogues and sulfonamides, verifying the universal applicability of BiOBr_xI_1-x. The enhanced activity can be ascribed to the synergistic effect of solid solution and oxygen vacancies. Formation of solid solution promotes visible-light harvesting and photogenerated charge carriers’ separation efficiency, as well as endows photoinduced holes with sufficient oxidation capacity, unambiguously confirmed by multiple optical and photoelectrochemical characterizations. Meanwhile, the oxygen vacancies induce an intermediate level near the Fermi level, narrowing the band gap energy and impeding the recombination of photogenerated charge carriers, as evidenced by density functional theory (DFT) analyses. This work could give ideas for the design of highly active photocatalysts toward sustainable solar-to-chemical energy conversion and environmental remediation.