Synergistic Radical and Non-Radical Pathways in Phenol Degradation: Electron Transfer Mechanism Dominated by N-Doped Carbon/Peroxymonosulfate System

Phenolic compounds constitute the predominant group of recalcitrant organic contaminants in coal chemical wastewater. In this study, humic acid and urea were used as carbon and nitrogen sources to prepare nitrogen-doped carbon material (labeled as NC-800) through a two-step calcination process. Using this catalyst (NC-800) to activate PMS for phenol degradation achieved 100% phenol removal across a wide pH range (1–9). The removal rate remained at 99.62% even with high concentrations of inorganic anions or natural organic matter, breaking through the limitations of traditional Fenton-like reactions in terms of acid–base environment and anion influence. The quenching experiment and electron spin resonance (ESR) spectroscopy results indicated that the N-C/PMS system generated three active species hydroxyl radicals (•OH), superoxide radicals (O2•−), and singlet oxygen (1O2) through the active sites in electron-rich regions such as graphite nitrogen, pyrrole nitrogen, and C=O. An electrochemical test revealed that the system formed a metastable NC-800-PMS* complex during the reaction, indicating the existence of a non-radical pathway of electron transfer. The combination of free radicals (•OH, O2•−) and non-free radicals (1O2, electron transfer) facilitated the rapid degradation of phenol, providing a theoretical basis for phenol degradation.