MIL-101(Fe)/BiOBr S-scheme photocatalyst for promoting photocatalytic abatement of Cr(VI) and enrofloxacin antibiotic: Performance and mechanism

The development of highly active, economical, and robust bifunctional photocatalysts is a priority for sustainable photocatalytic water remediation. Inadequately available reactive sites and sluggish interface photocarrier transfer and separation remain significant challenges in the photoreaction progress. In this study, the Fe-containing metal-organic framework (MOF) MIL-101(Fe) was integrated with BiOBr microspheres to form a competent S-scheme heterostructure for the photocatalytic mitigation of Cr(VI) and enrofloxacin (ENR) antibiotics. The optimal MIL-101(Fe)/BiOBr exhibited the highest photoactivity, with 99.4% of Cr(VI) and 84.4% of ENR eliminated upon visible-light illumination in a single-pollutant system. The photoactivity of MIL-101(Fe)/BiOBr in the decontamination of the Cr(VI)-ENR co-existence system exhibited a substantial enhancement when compared to that in a single system, owing to the improved utilization of electrons and holes resulting from the synergism between Cr(VI), ENR, and the photocatalyst. The enhanced photoactivity is attributed to two aspects: (1) the incorporation of MIL-101(Fe) results in an increased number of available reactive sites and improved solar harvesting properties; and (2) the S-scheme mechanism enables the effective spatial disassociation of photoexcited carriers and optimization of the photo-redox capability of the system. Through scavenging experiments, electron spin resonance characterization, liquid chromatography-tandem mass spectrometry analysis, and T.E.S.T. theoretical estimation, the catalytic mechanism, antibiotic degradation process, and biotoxicities of the degraded products were analyzed and confirmed. This study provides a viable strategy for building competent MOF-inorganic semiconductor S-scheme photocatalysts with superior photocatalytic decontamination performance.