Facile fabrication of BUC-21/Bi₂₄O₃₁Br₁₀ composites for enhanced photocatalytic Cr(VI) reduction under white light

In this study, the Bi₂₄O₃₁Br₁₀ nanosheets were successfully synthesized using hydrothermal method. Subsequently, series binary BUC-21/Bi₂₄O₃₁Br₁₀ composites were fabricated by facile ball-milling method. The results suggested that the introduction of a specific quality of Bi₂₄O₃₁Br₁₀ on the surface of BUC-21 could enhance the utilization efficiency of white light and suppress the photo-induced carriers recombination to promote the photocatalytic efficiency. The BB-100 (the mass ratio of BUC-21/Bi₂₄O₃₁Br₁₀ being 1) exhibited the best performance, in which 99.9% Cr(VI) ions were photoreduced into Cr(III) upon the white light irradiation within 120 min. As well, the influences of small organic acids, initial pH, light intensities along with the co-existing matters on the Cr(VI) removal were investigated. Furthermore, the Box-Behnken experimental design methodology proved that the photoreduction process was significantly influenced by the co-existing inorganic anions and negatively charged dissolved organic matters (DOM). After 4-run recycling for the adsorption-photoreduction of Cr(VI) experiments, the BB-100 still exhibited satisfied reduction activity with good stability and reusability. A possible reaction mechanism was proposed and clarified through the electrochemical determination, time-resolved photoluminescence decay spectra, active species trapping experiments, electron spin resonance analyses (ESR) and density functional theory (DFT) calculation.