Synthesis, Mechanism Analysis, and Degradation Pathways of Fe-Based Metal–Organic Frameworks/BiOBr Heterojunctions for Effective Photocatalytic Organic Pollutant Degradation

Conventional photocatalysts suffer from rapid electron-hole recombination, severely limiting their practical application in wastewater treatment. Moreover, many organic degradation systems require the addition of hydrogen peroxide or persulfate to enhance photocatalytic activity, but this not only often leads to secondary pollution but also results in low oxidant utilization efficiency. To overcome this fundamental constraint, a novel direct Fe-based Metal-Organic Frameworks (Fe-MOF)/BiOBr heterojunction was innovatively constructed via hydrothermal synthesis. Without the need for additional oxidizing agents, this catalyst relies solely on light energy to initiate and maintain the photocatalytic degradation reaction. The optimized MIL-101/BiOBr composite demonstrated outstanding performance, achieving over 99% degradation of Rhodamine B (RhB) within 60 min under UV light, retaining an 88% degradation rate at an ultrahigh dye concentration (80 mg/L), and maintaining exceptional cycling stability (89.57% after 5 cycles). Mechanistically, ESR/trapping experiments identified h⁺ and ·O₂^- as the dominant species, while comprehensive characterization (SEM, XRD, XPS, BET) and photoelectrochemical analyses confirmed the successful preparation of the heterojunction. Furthermore, density functional theory (DFT) calculations combined with the analysis of degradation intermediates allowed the prediction of the Rhodamine B degradation pathway from both theoretical and experimental perspectives. The catalyst also exhibited versatile degradation capability, efficiently removing methylene blue (73.1-97.7%) and tetracycline with accelerated kinetics. Overall, the Fe-MOF/BiOBr synthesized in this study represents a photocatalytic material with significant practical potential for wastewater degradation thanks to its innovative advantages such as light-driven operation, high electron-hole separation efficiency, stable performance, broad organic degradation capability, and well-elucidated degradation pathways.