Anti-Interference Fe-N-C/PMS System: Synergistic Radical-Nonradical Pathways Enabled by sp2 Carbon and Metal-N Coordination

Phenol is a refractory organic pollutant that is difficult to degrade in wastewater treatment, and efficiently and stably degrading phenol presents a significant challenge. In this study, iron-doped humic acid-based nitrogen–carbon materials were prepared to activate peroxymonosulfate (PMS) for the degradation of phenol. The Fe-N-C/PMS system achieved a phenol degradation rate of 99.71%, which follows a first-order kinetic model, with the reaction rate constant of 0.1419 min−1. The phenol degradation rate remained above 92% in inorganic anions (Cl−, SO42−, HCO3−) and humic acid and the system maintained a 100% phenol removal rate over a wide pH range (3–9). The iron in the catalyst predominantly exists in the forms of Fe0 and Fe3C, and Fe0, Fe2+/Fe3+ are the main active sites that promote PMS activation during the reaction. Additionally, Fe-N-C has a large specific surface area (1041.36 m2/g). Quenching experiments and electron spin resonance (ESR) spectroscopy detected the active free radicals in the Fe-N-C/PMS system: SO4•−, •OH, O2•−, and 1O2. The mechanism for phenol degradation was discussed, involving radical pathways (SO4•−, •OH, O2•−) and the non-radical pathway (1O2), in the Fe-N-C/PMS system activated by Fe0, Fe2+/Fe3+, sp2 hybridized carbon, C-O/C-N, C=O, and graphitic nitrogen active sites. This study provides new insights into the synthesis of efficient carbon-based catalysts for phenol degradation and water remediation.