Unraveling the Mechanism of Singlet Oxygen‐Induced Phenol Polymerization on Fe‐N ₁ O ₃ Single‐Atom Sites

Transitioning advanced oxidation processes (AOPs) from deep mineralization to pollutant polymerization represents a promising strategy toward low‐carbon water decontamination. Single‐atom catalysts (SACs), with their well‐defined active sites, offer a unique platform to establish precise structure‐activity relationships and elucidate polymerization mechanisms. Herein, we synthesized Fe SACs with an Fe─N 1 O 3 configuration that exhibit superior activity in activating peroxymonosulfate (PMS) for phenol removal, achieving a rate constant of 0.204 min −1 and a total organic carbon removal efficiency of 82.05%. Mechanistic studies reveal that phenol removal followed a nonradical singlet oxygen‐driven polymerization pathway mediated by Fe active sites. The generated singlet oxygen possesses moderate redox potential, which drives surface‐absorbed phenol oxidation on support to form phenoxyl radicals through electrophilic attack, subsequently triggering the formation of high‐molecular‐weight chains (≤11 units). In‐depth theoretical calculations unveil that the asymmetric Fe─N 1 O 3 site exhibits a strong internal electric field and a moderate d‐band center. This electronic configuration enables enhanced PMS adsorption for sustained singlet oxygen generation and confers resistance to intermediate poisoning based on the Sabatier principle, thereby driving a continuous polymerization process. This fundamental mechanistic insight, bridging single‐atom coordination engineering with reaction selectivity control, provides a transformative blueprint for designing low‐carbon, high‐value water decontamination technologies centered on resource recovery.