Oxygen vacancy-enriched Bi4O5Br2/InVO4 S-scheme heterojunction for efficient visible-light photocatalytic degradation of ciprofloxacin

Constructing heterojunctions is an effective strategy to enhance charge carrier separation and photocatalytic performance. In this study, a Bi 4 O 5 Br 2 /InVO 4 S-scheme heterojunction composite was prepared by a solvothermal method. The physicochemical properties were thoroughly investigated using various characterization techniques. Visible-light degradation experiments of ciprofloxacin (CIP) showed that the optimal sample, 5% Bi 4 O 5 Br 2 /InVO 4 (BI-5), exhibited the highest degradation activity (92.77%) along with excellent cycling stability. The effects of different environmental factors on the degradation performance were also systematically studied. The enhanced activity is attributed to the synergistic effect of the S-scheme heterojunction and increased oxygen vacancies. The S-scheme charge transfer, driven by the IEF at the heterointerface, enables spatial separation of photogenerated electrons and holes while preserving strong redox potentials, with reductive electrons accumulating in Bi 4 O 5 Br 2 and oxidative holes remaining in InVO 4 . Meanwhile, the introduction of InVO 4 creates abundant oxygen vacancies. These vacancies act as electron capture centers to suppress bulk recombination, introduce in-gap states that facilitate interfacial charge transfer, and provide additional active sites for surface reactions. Consequently, the S-scheme junction and oxygen vacancies jointly promote the separation, migration, and surface utilization of charge carriers, leading to significantly improved photocatalytic performance.