Photo-induced dissolution of Bi2O3 during photocatalysis reactions: Mechanisms and inhibition method

Highlights: • Concentration of Bi³⁺ produced from Bi₂O₃ under UV was 27-fold that in the dark. • O^2- in the Bi₂O₃ crystal lattice was oxidized by h⁺ to form O₂ under light. • Concentration of Bi³⁺ was lowered from 2.02 to 0.27 mg/m² after modification. • Transfer of h⁺ from VB-Bi₂O₃ to HOMO-PANI inhibited the dissolution of Bi₂O₃. Photo-induced dissolution greatly limits the application of Bi₂O₃ photocatalyst in water treatment. In this study, mechanisms for the photo-induced dissolution of Bi₂O₃ were proposed. (1) Under UV light, h⁺ forms and diffuses through Bi₂O₃. (2) The h⁺, which reaches the surface of Bi₂O₃ and can be regarded as a monatomic oxygen ion (O_S^-), is weakly bonded to the crystal lattice. (3) Two O_S^- combine and the generated (O-O)^2- ionic group is oxidized by h⁺, resulting in the release of O₂ and dissolution of Bi₂O₃. However, modification of Bi₂O₃ using polyaniline (PANI) greatly inhibits Bi₂O₃ dissolution under UV. Under the PANI to Bi₂O₃ mass ratio of 1.5%, the concentration of produced Bi³⁺ significantly decreased from 2.02 to 0.27 mg/m² with a high methylene blue (MB) degradation efficiency of 98.3%, thanks to the separation of h⁺ from VB-Bi₂O₃ to HOMO-PANI. This study provided the theoretical foundation for the modification and application of Bi₂O₃ in water treatment.