Construction of direct Z-scheme BPQDs-modified BiOBr thin film for enhanced photocatalytic performance under visible light irradiation

Surface modification on photocatalytic thin films is long considered as an effective strategy to improve the degradation performance, which in turn helps to alleviate the worldwide environmental pollution issue. In this study, a direct Z-scheme photocatalytic system is constructed successfully by integrating black phosphorus quantum dots (BPQDs) on the surface of BiOBr thin film prepared by hydrothermal method. The optimal BPQDs/BiOBr-1 thin film presents remarkable enhanced photocatalytic activity for degrading methyl violet (MV) and tetracycline hydrochloride (TC), which is 3 and 3.65 times higher than that of pure BiOBr counterpart. The active species involved in the reaction are h⁺, •O₂⁻, and •OH, which determined by radical trapping experiments. The formation of direct Z-scheme photocatalytic system makes electrons assembled in the conduction band (CB) of BPQDs and holes gathered in the valence band (VB) of BiOBr, which supports the generation of h⁺ and •O₂⁻ and in turn accelerates the photocatalytic reaction. Besides, the improved efficiency of charge separation, enhanced visible light absorption and enlarged specific surface area also contributed to the enhanced photocatalytic performance of BPQDs/BiOBr. This work provides a feasible strategy for optimizing photocatalytic thin films via detailed analyzing the role of BPQDs in the construction of direct Z-scheme photocatalysts.