Oxygen vacancies in Z-scheme r-MIL-88A/OV-BiOBr heterojunctions enhance photo-Fenton degradation of chloroquine phosphate: Mechanisms insight, DFT calculations, degradation pathways and toxicity assessment

A low cycle of Fe2+/Fe3+, additional H2O2 dosage, and low mineralization efficiency have limited the wide application of Fe-MOFs. Herein, a novel Z-scheme r-MIL-88A/OV-BiOBr composites (OV-BM) with oxygen vacancies (OV) were fabricated by polyvinylpyrrolidone/ethylene glycol solvothermal method. The optimal OV-BM-25 showed the highest degradation efficiency of 97.8% for chloroquine phosphate (CQ) by initiating H2O2 under LED visible light irradiation within 60 min. The presence of oxygen vacancies enhanced the electron/hole separation in OV-BM composites and the electron transfer from OV-BiOBr to r-MIL-88A, driving Fe2+/Fe3+ cycling and in-situ H2O2 generation. Quenching experiments and EPR analysis demonstrated that O2–, 1O2, and e– were the main active species, inducing deamination, decarbonization, and cleavage of ring structures in CQ. The possible decomposition pathways of CQ and the ecotoxicity of intermediates were evaluated through UPLC-MS and QSAR analysis. This study provides a theoretical basis for developing Fe-MOFs-based heterojunctions photocatalysts in a Z-scheme photo-Fenton system to treat organic wastewater.