In-situ and ex-situ preparation of Bi2S3 on the BiVO4/TiO2 to construct Bi2S3/BiVO4/TiO2 heterojunction for efficient Cr(VI) reduction

The environmentally friendly and rapid removal of hexavalent chromium (Cr(VI)) from wastewater has garnered significant attention, driven by the severe acute toxicity and carcinogenic properties associated with Cr(VI). The design and synthesis of heterojunctions are recognized as effective solutions for enhancing the photocatalytic performance of TiO2 based materials. BiVO4/TiO2 and Bi2S3/BiVO4/TiO2 composite films (BVT) were prepared via a simple hydrothermal method. The influence of Bi2S3 preparation methods (In-situ and Ex-situ) on the morphology, structure and properties of BVT was studied. The relative crystallinity of TiO2, BiVO4/TiO2, BVT(Insitu) and BVT(Ex-situ) were 50 %, 62 %, 72 % and 92 %, respectively. SEM shows that the morphology of Bi2S3 in BVT(In-situ) was nanoribbon and that of Bi2S3 in BVT(Ex-situ) was radioactive sphere. Compared with pure TiO2 and BiVO4/TiO2, the light absorption range of BVT composite material has been expanded from the ultraviolet light region to the visible region, the bandgap has been significantly narrowed, and the photocurrent density has been increased. The BVT(In-situ) shows stronger photoelectrical performance and reduction efficiency of Cr (VI) compared to BVT(Ex-situ), reaching 93.9 %. The photocatalytic reaction rate of BVT(In-situ) and BVT(Ex-situ) are 0.0291 min(-1) and 0.0266 min(-1), respectively. Density functional theory (DFT) calculations indicate that the work function of BiVO4 is higher than that of Bi2S3, and electrons will transfer from Bi2S3 to BiVO4 at the heterojunction interface. The BVT(In-situ) heterojunction constructed in this experiment greatly improves the separation and transport efficiency of photo-generated carriers, laying the foundation for the wide application of BVT heterojunction in the field of optoelectronics and providing a strategy for photocatalytic reduction of Cr(VI). The BVT(In-situ) with FTO conductive glass, it also can be applied to photovoltaic fields such as solar cells, photocatalysis and photodetectors.