Rapid oxidation of 4-cholorphenol in the iron-based Metal-Organic frameworks (MOFs)/H2O2 system: The ignored two-steps interfacial single-electron transfer

Fe-based metal-organic frameworks (MOFs) are popular in activating oxidants e.g.H2O2 and persulfate (PS) for degrading recalcitrant organic substances, generally regarded with a simple interfacial efficient iron cycle. This study has revealed that a novel two-steps single-electron transfer mechanism would occur initially to activate the rapid degradation 4-chlorophenol (4-CP) in the MIL-88B(Fe)/H2O2 system (88B/H2O2 system). The degradation of 4-CP was acidic favorable (pH(0) <= 6.0) and could be divided into two reaction stages, i.e., initial lag phase (0-10 min) and following rapid decay phase (10-50 min). In the first stage, H2O2 was slowly activated on the surface of 88B to form superoxide radical (O-2(.-)), which would lead to the accumulation of the key intermediate hydroquinone (HQ) through reducing 4-CP. Afterwards, HQ could reductively dissolve iron ions which would lead to the subsequent efficient homogeneous Fenton reaction for the rapid oxidation of 4-CP by hydroxyl radical (.OH) in the following rapid decay phase. It was interesting to note that specific aromatic compounds, which would form reductive benzenediols intermediates by O-2(.-), could be efficiently degraded in the 88B/H(2)O(2)system. The result of this study is expected to provide a new insight for understanding the catalytic oxidation process based on MOFs, and its application if possible.