Fe 3 d Electron Delocalization in Asymmetric Fe Single Atoms Enables Nonradical Peroxymonosulfate Activation for Micropollutant Degradation

Abstract

Abstract Nonradical peroxymonosulfate (PMS) activation provides a selective route for micropollutant degradation, yet the orbital-level origin of oxidant speciation at single-atom sites remains unclear. Herein, an asymmetric Fe single-atom catalyst (Fe–N3–VN–C) is synthesized via molten-salt-assisted pyrolysis of a zeolitic imidazolate framework precursor, where NaCl etching enriches pyrrolic-N anchors and stabilizes low-coordination Fe centers. Fe–N3–VN–C exhibits efficient degradation of electron-rich micropollutants, exemplified by sulfamethoxazole, over a wide pH range of 3.5–9.5 and in wastewater matrices. The study through quenching experiments and electron paramagnetic resonance spectroscopy indicates singlet oxygen (1O2) as the dominant reactive species, with only minor radical contributions. The density functional theory calculations reveal that asymmetric coordination induces Fe 3d electron delocalization, which reinforces Fe 3d–O 2p coupling, strengthens Fe–O covalency, accelerates interfacial charge transfer, and stabilizes Fe–O intermediates. In addition, adjacent pyrrolic N cooperates with Fe to polarize adsorbed pollutants, forming a dual-site center that promotes selective 1O2 generation. This work establishes Fe 3d electron delocalization as a key electronic origin of nonradical PMS activation and provides a mechanistic basis for designing single-atom catalysts for practical water purification.