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 use, 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 O^2–, 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 CQ-bearing organic wastewater.