Abstract: The molten salt method focuses on improving the crystallinity of synthetic materials and avoiding the high energy consumption of traditional synthesis processes. In this work, a novel BiOBr/Bi₂S₃ high-low junction with large contact area was constructed by the molten salt method combined with the ion exchange strategy. Its unique energy band structure and new charge transfer mechanism realize the rapid migration of photogenerated charges between different components. Specifically, Bi₂S₃ was grown on BiOBr in situ by a high-temperature molten salt reaction. Due to the deep valence band position of BiOBr and the narrow band gap of Bi₂S₃, an intrinsic internal electric field and band bending are produced at the interface, forming a high-low junction photocatalyst with an intimate interface. In addition, the BiOBr/Bi₂S₃ composite maintains a high oxidation potential and produces high and robust photocatalytic oxidation activity. In the molten state, the close binding of BiOBr and Bi₂S₃ can be promoted through the ion-exchange strategy, resulting in excellent photocatalytic degradation rates of bisphenol A and tetracycline and in-situ generation of H₂O₂. Finally, the mechanism of carriers separation and transfer in BiOBr/Bi₂S₃ high-low junction is also discussed. Density functional theory (DFT) results found that the improvement of O₂ adsorption ability would promote the occurrence of oxygen reduction reaction (ORR), and make positive contributions to the enhanced H₂O₂ production activity. This study will provide a new perspective for broadening the spectral response range of Bi-based photocatalytic materials and preparing high-low junction photocatalysts with dense interface by the molten salt method.

Key words: Photocatalysis, BiOBr, Bi₂S₃, High-low junction, Molten salt