Synthesis of hierarchical bismuth-rich Bi4O5BrxI2-x solid solutions for enhanced photocatalytic activities of CO2 conversion and Cr(VI) reduction under visible light

Bismuth oxyhalides (BiOX, X = Br, I) photocatalysts are rarely applied for photocatalytic reduction reaction withthe photo-induced electron, as this is impeded by their low conduction band. As a widely used approach for enhancing the photocatalytic reduction activity, bismuth-rich strategy results the bismuth content of BiOX photocatalysts increasing. In this paper, a solid solutions of bismuth-rich Bi4O5BrxI2-x were prepared applying the molecular precursor method. Bi4O5BrxI2-x were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), element mapping, Brunauer–Emmett–Teller surface analysis (BET), UV–vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The obtained photocatalytic data showed that Bi4O5BrxI2-x solid solutions had higher photocatalytic activities than Bi4O5Br2 and Bi4O5I2. At an optimal ratio of x = 1, the Bi4O5BrI photocatalyst showed the highest photocatalytic reduction activity for CO2 conversion (22.85 μmol h−1 g−1 CO generation, AQE was 0.372 at 400 nm) and Cr(VI) removal (88%). CO2 adsorption data and CO2 temperature programmed desorption (CO2-TPD) revealed that Bi4O5BrI exhibited the highest chemical adsorption ability of CO2 molecules Photocurrent and electrochemical impedance (EIS) spectroscopy demonstrated the enhanced photo-induced carrier separation efficiency of Bi4O5BrI. These mechanistic studies suggest that Bi4O5BrxI2-x solid solutions are excellent photocatalysts for solar fuel generation and environmental remediation.