Solvothermal Synthesis of Cu-Bi₄O₅Br₂ Photocatalyst Enhanced Visible Light Degradation of Ciprofloxacin

Cu-doped Bi₄O₅Br₂ photocatalyst was synthesized via a solvothermal method, and the influence of Cu doping on its structure, morphology, and photoelectric characteristics was comprehensively investigated by adopting various characterization techniques. Furthermore, the photocatalytic performance of the material was assessed through the degradation of ciprofloxacin (CIP) under visible light. The characterization results demonstrated that compared to the intrinsic Bi₄O₅Br₂, the introduction of Cu resulted in a decreased bandgap, an expanded visible light absorption range, an enhanced visible light absorption intensity, and improved separation efficiency of electrons and holes, thereby enhancing the photocatalytic activity. In the ciprofloxacin degradation experiment, 3%Cu-Bi₄O₅Br₂ exhibited superior performance, achieving a degradation rate of 80.1%, which was more than twice as high as the intrinsic Bi₄O₅Br₂ (53.2%). Moreover, it maintained excellent stability even after undergoing five cycling experiments. The free radical capture experiments indicated that h⁺, •O₂⁻ and •OH played a dominant role in the photodegradation reactions of ciprofloxacin. Finally, this study discussed the possible photocatalytic mechanism and deduced three degradation pathways of ciprofloxacin on the basis of the 8 intermediate products detected by LCMS. In summary, Cu-Bi₄O₅Br₂ demonstrated remarkable photocatalytic performance and stability under visible light response, positioning it as a promising catalyst for future sunlight-based removal of diverse pollutants.

The doping of Cu enhances the absorption of visible light by Bi₄O₅Br₂, improving its photocatalytic performance. The photocatalytic degradation mechanism of Cu-doped Bi₄O₅Br₂ photocatalyst mainly includes three approaches. The holes can interact with electrons in ciprofloxacin (CIP), thereby directly oxidizing it. Next, photogenerated electrons combine with dissolved oxygen to form superoxide negative ions, and some of these are further oxidized to produce hydroxyl radicals. Both superoxide negative ions and hydroxyl radicals participate in the degradation of CIP. Last, Cu²⁺ captures photogenerated electrons and transforms into Cu⁺, which promotes the reduction of dissolved oxygen molecules to generate superoxide radicals (•O₂^-), accelerating the degradation of CIP. Meanwhile, Cu⁺ can be oxidized back to Cu²⁺. This conversion is dynamic and continuously cycles as long as the illumination persists