Ultrahigh Peroxymonosulfate Utilization Over a Single-Atom Iron-N-C Catalyst for Efficient Fenton-Like Chemistry via Surface-Bound Reactive Complexes

Transition metal single-atom catalysts (SACs) find extensive application in peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs). Yet, the disparity in intrinsic activity is often attributed to thermodynamics, but few studies focused on the electronic structure between different metals. Herein, transition metal catalysts in the form of single-atom M-N₄ moieties moored to graphitic carbon nitride (denoted MSA CN, M = Fe, Co, and Cu) are developed and used for activating PMS for the degradation of 4-chlorophenol. Remarkably, FeSA CN achieves a catalyst-dose-normalized kinetic rate constant of 34.2 L min⁻¹ g⁻¹, surpassing reported systems by 2–551 times ─ even at ultralow catalyst (0.06 mg L⁻¹) and PMS (0.2 mm) concentration. The in situ formation of surface-bound PMS* complexes enabled the degradation of 4-chlorophenol to achieve unprecedented utilization efficiency (≈100%) through highly efficient non-radical pathways. Density functional theory calculations revealed that large spin polarization of Fe-N-C sites facilitated the d orbitals to overlap with the PMS on the metal active sites and promoted electron transport, thereby facilitating PMS adsorption and enhancing the oxidation capacity. This work establishes a mechanistic foundation for designing a single Fe-atom catalyst/PMS system in Fenton-like water treatment.