Direct Z-scheme charge transfer in a Bi₄O₅Br₂/Sn-based mental-organic framework composite enabling efficient...

Metal-organic frameworks (MOFs) are promising visible-light photocatalysts for eliminating recalcitrant antibiotics from water, owing to their structurally tunable properties and enhanced light-harvesting abilities. In this study, a series of Bi₄O₅Br₂/Sn(II)-2-methylimidazole framework (Sn-MIM) heterojunctions (BSM) was constructed via a facile hydrothermal process. Structural, morphological, and surface-chemical analyses confirmed the intimate interfacial coupling between layered Bi₄O₅Br₂ nanosheets and Sn-MIM, with the BSM-3 composite (3 wt% Sn-MIM) exhibiting the most favorable architecture and the largest specific surface area. Under visible-light irradiation, BSM-3 achieved a high oxytetracycline (OTC) degradation efficiency of 94.2% within 90 min and demonstrated excellent stability and recyclability. Both photoelectrochemical and photoluminescence evidence supports a direct Z-scheme charge-transfer pathway in the Bi₄O₅Br₂/Sn-MIM system, which enhances charge separation while preserving the high oxidative and reductive potentials of the respective components. Electron spin resonance characterization and scavenger experiments collectively suggest that the photocatalytic degradation of OTC mainly proceeds via O₂^•- and •OH-mediated pathways. Time-resolved probe electrospray ionization mass spectrometry was employed to monitor the degradation process. Seventeen transformation products were detected, based on which multiple degradation pathways were proposed. In silico toxicity assessment further evaluated the environmental relevance of OTC transformation products. This work establishes a versatile approach to integrating MOFs with Bi-based oxyhalides and offering insights into the development of advanced photocatalytic materials for environmental decontamination.