Citric acid-modified MIL-88A(Fe) for enhanced photo-Fenton oxidation in water decontamination

Fe-based metal organic framework with high active site exposure, wide light absorption and fast H2O2 activation are pivotal for photo-Fenton degradation of contaminants. However, insufficient active site exposure, weak visible light adsorption and low charge transfer efficiency in iron-oxo clusters usually lead to the slow Fe(II)/Fe(III) cycle. In this study, we develop a novel citric acid (CA)-modified MIL-88A(Fe) strategy to boost photo-Fenton efficiency by accelerating Fe(II)/Fe(III) cycle for emerging contaminants removal. Relationship between CA coordination mode and photo-Fenton performance was studied by using methylene blue (MB) and carbamazepine (CBZ) as model contaminants. It was found that the degradation rate constants of MIL-88A(Fe)-CA-3 were 6.5 and 2.6 times higher than those in the pristine MIL-88A(Fe) for MB and CBZ degradation, respectively. The optimized MIL-88A(Fe)-CA-3 also exhibited good recyclability, enabling multiple cycles in photo-Fenton reaction. The results of experimental characterizations and density functional theory calculations demonstrated that ligand substitution was conductive to active site exposure, visible light absorption, charge carrier transfer and Fe2+/Fe3+ redox cycle, which are responsible for an improved photo-Fenton performance.