Coordination-tailored high-spin Fe-MOF membrane electrode ensures selective singlet oxygen electrosynthesis: Non-radical emerging contaminants removal

Selective electrosynthesis of singlet oxygen (¹O₂) provides a promising non-radical route for precise and efficient degradation of persistent emerging contaminants (ECs). Herein, a coordination-tailored Fe-MOF membrane electrode was developed by constructing nitro-functionalized MIL-53(Fe)-NO₂ with stabilized high-spin (HS) Fe(III) sites and immobilizing the catalyst in a porous PVDF matrix on carbon cloth, yielding the M53NO₂(50)@P/CC membrane electrode. This membrane electrode architecture enabled highly selective ¹O₂ generation, and achieved rapid non-radical removal of sulfamethoxazole (SMX) with a kinetic rate constant of 0.103 min⁻¹. In situ Raman and FTIR spectroscopy, XPS, EPR, and DFT calculations collectively reveal that nitro-ligand-field engineering stabilizes catalytically favorable HS Fe(III) sites and regulates O₂ activation at the Fe center. Compared with pristine MIL-53(Fe), MIL-53(Fe)-NO₂ induces a more moderate end-on O₂ adsorption mode, reduces excessive charge transfer and Fe-O coupling, preserves the O-O moiety, and lowers the free-energy penalty of the rate-determining *OOH to OOH• conversion step. This balanced oxygen-intermediate binding suppresses excessive intermediate retention and undesired O-O bond cleavage, thereby favoring selective ¹O₂ generation. The M53NO₂(50)@P/CC system shows broad applicability toward diverse ECs, strong matrix tolerance, and stable cycling performance. Moreover, the flow-through configuration integrates membrane filtration with electrocatalysis, improving mass transfer while in situ generated ¹O₂ mitigates membrane fouling and prolongs membrane electrode service life. This work provides a coordination-tailored strategy for selective ¹O₂ electrosynthesis and advances Fe-MOF membrane electrodes for sustainable non-radical water purification.