Controllable Synthesis of BixOyBrz/TiO2 Heterojunctions with Excellent Visible-Light-Driven Photocatalytic Activities for Phenol

Abstract

Bi_xO_yBr_z/TiO₂ composites have been synthesized by hydrothermal method, with TiO₂ nanoparticles being employed as substrate. During the process of hydrothermal reaction, both temperature and pH have been utilized to effectively regulate the Bi/Br atomic ratio of Bi_xO_yBr_z/TiO₂ composites. In essence, the competitive reaction between OH⁻ and Br⁻ in the solution is the key factor to form Bi_xO_yBr_z with different Bi/Br atomic ratios. Under visible light, the prepared Bi₄O₅Br₂/TiO₂ heterojunction demonstrates higher photocatalytic activity than other Bi_xO_yBr_z/TiO₂ composites for phenol and Rh B. The removal rate of phenol with Bi₄O₅Br₂/TiO₂ heterojunction is up to 92.1% after irradiation for 75 min. The excellent photocatalytic activities of Bi₄O₅Br₂/TiO₂ heterojunction are mainly attributed to its optimized microstructure and the matching band energy structure, whereby TiO₂ nanoparticles with ≈10 nm diameter uniformly arranged on ≈10.2 nm thick Bi₄O₅Br₂ nanosheets. Moreover, the heterojunction structure promotes the separation of photo-generated electrons and holes in Bi₄O₅Br₂/TiO₂, while $·O_2^{-}$ and h⁺ are the main active species during its photocatalytic processes.