Deciphering the Origin of Higher Shell Coordination on Single Iron Catalysts for Resilient Modulating Persulfate Oxidation Into Singlet Oxygen Pathway

Abstract Precise manipulation of coordination structure of single‐atom sites and establishment of schematic microenvironment‐oxidation pathway relations remain significant challenges in Fenton‐like chemistry. Herein, incorporating sulfur heteroatoms into the higher coordination shell of FeN ₄ structure (Fe‐NSC) exhibited a volcano trend of p ‐hydroxybenzoic acid oxidation, aligning with the number and positions of sulfur dopant. Specifically, higher shell S coordination with moderate electronegativity and larger atomic radii triggers long‐range electronic interactions, which provoke Fe 3d orbital splitting and spin electron rearrangement, resulting in a spin crossover with orbital states d _xy ² d _yz ¹ d _xz ² d _z ²¹ . As a result, the partial filling of e _g and t _{2 g} orbitals and moderate σ/π antibonding states between 3d and 2p atomic states optimized the adsorption–desorption behaviors of the key oxygenated intermediates from peroxymonosulfate activation. Thus, the optimal binding configuration weakens the Fe─O bonding and accelerates PMS dissociation to yield C‐S‐N ₄ Fe‐O*, which subsequently couples to form ¹ O ₂ with nearly 100% selectivity. The Fe‐NSC‐functionalized membrane exhibited outstanding long‐term reusability in a continuous flow reactor which further validated practical application perspective. This study provides insight at both atomic and electronic levels for rational design of spin‐polarized catalysts and its functions in fine‐tuning oxidation pathways in environmental catalysis.