Hydroxyl Functionalization Regulates the Fe‐Site Microenvironment of MIL‐101(Fe) for Coupled Two‐Electron O 2 Reduction and Photocatalytic Self‐Fenton Oxidation

ABSTRACT In photocatalytic self‐Fenton systems, the overall oxidation efficiency depends on the effective coupling between in situ H 2 O 2 generation and its subsequent activation into hydroxyl radicals (•OH). Herein, hydroxyl‐functionalized MIL‐101(Fe) was developed to regulate the Fe‐site microenvironment and promote this coupled process under visible‐light irradiation. The optimized OH‐MIL‐101(Fe) increased the H 2 O 2 production rate in air from 2.64 to 171.02 µmol g −1 h −1 and achieved a high •OH generation rate of 9.07 µmol L −1 min −1 . Experimental results and density functional theory calculations indicate that hydroxyl functionalization enriches the electron density around Fe sites and facilitates charge transfer from the linker to the catalytic centers. This electronic modulation enhances O 2 adsorption and favors a preferential two‐electron O 2 reduction pathway, thereby promoting in situ H 2 O 2 generation and its subsequent self‐Fenton activation. As a result, OH‐MIL‐101(Fe) exhibits markedly improved visible‐light‐driven tetracycline (TC) degradation without the need for exogenous H 2 O 2 . This work highlights Fe‐site microenvironment engineering as an effective strategy for designing Metal‐organic frameworks (MOFs) based photocatalytic self‐Fenton systems.