Reengineering waste PET bottles into BiOBr/Bi4O5Br2 heterojunction materials for highly selective photocatalytic oxidation of benzyl alcohol

Abstract

The selective photocatalytic oxidation of benzyl alcohol (BA) to benzaldehyde (BAD) is a green and efficient strategy. In this study, Bi-MOF was synthesized from waste polyethylene terephthalate (PET) plastics, and BiOBr/Bi₄O₅Br₂ composites were prepared through bromination and annealing for the catalytic selective oxidation of BA to BAD. The effects of the BiOBr/Bi₄O₅Br₂ composite prepared at different annealing temperatures on photocatalytic performance were investigated. Results show that the BiOBr/Bi₄O₅Br₂-2 composite exhibits a higher conversion rate in the photocatalytic oxidation of BA compared with pure BiOBr and Bi₄O₅Br₂-4 under blue LED irradiation. This performance enhancement is primarily attributed to the dense heterojunction interface formed between BiOBr and Bi₄O₅Br₂, which effectively promotes the separation and transfer of photogenerated carriers while maintaining their strong redox capability. Through radical trapping experiments and electron paramagnetic resonance (EPR) tests, it was found that superoxide radicals (˙O₂⁻) and carbon-centered radicals are key active intermediates in the reaction. Furthermore, a photocatalytic enhancement mechanism of the heterojunction under the action of h⁺ and ˙O₂⁻ was proposed. This study provides a direct and efficient strategy for converting waste PET into Bi-MOF, thereby synthesizing MOF-derived photocatalysts. This approach holds significant potential for addressing environmental pollution and promoting sustainable economic development.