Asymmetric electric field-induced modulation on MOFs for boosting heterogeneous photo-Fenton process: Porous coordination structure and selective oxidation

Heterogeneous photo-Fenton process is among the most important advanced technologies for removing micropollutants in water nowadays. However, limited H₂O₂ utilization and slow reaction efficiencies are two main bottlenecks that limit potential applications. Herein, the novel mechanism for enhancing the photo-Fenton reaction was explored over the construction of asymmetric metal clusters within the iron-metal organic framework. The enhancement of the photocatalytic mechanism could be attributed to the averaged separation of Mn on defective Fe-O clusters in MIL-101 (Fe), with coordination number (CN) calculated to be 5.7 (Fe-O) and 5.8 (Mn-O) using extended X-ray absorption fine structure (EXAFS) analysis, which offers an ideal support in developing photocatalysts. Density functional theory (DFT) calculations and electrochemical measurements prove that the asymmetry in electron distribution and decreasing Fermi level increased the electron transfer performance of MOFs. The dual metal cluster framework significantly enhances the adsorption for H₂O₂ as well as carrier separation efficiency. As a result, the steady-state concentration of ·OH is approximately 1.64 times higher than that of pristine MIL-101(Fe). On the other hand, the adsorption process of degradation intermediates of DF over MIL by the electrostatic and hydrophobic interaction greatly facilitates the charge transfer process by the formation of an asymmetric electric field. Under the irradiation of visible light, micropollutants can be completely removed (>99 %) within 30 min over the dual asymmetry structure (MIL-101-Fe₅Mn₅) under the simulated solar-light irradiation, with the reaction kinetics 6.8 times higher than that of pristine MIL-101(Fe). This study offers a novel strategy for developing Mn-based photocatalysis for effectively removing micropollutants.