N, O co-doped porous carbon by ammonia/steam synergistic activation: An efficient peroxymonosulfate activator for acetaminophen degradation via electron transfer-dominated mechanism

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have emerged as a promising wastewater treatment technology, where developing cost-effective non-metallic catalysts is crucial for practical applications. Herein, N, O co-doped porous carbon (TNS-X) was fabricated from renewable gallotannin through a one-step synergistic activation strategy employing ammonia and steam. The optimized catalyst, TNS-800, exhibited exceptional PMS activation performance, achieving 100% removal of acetaminophen (20 mg L⁻¹) within 60 min at a low dosage of 0.15 g L⁻¹. Remarkably, its apparent rate constant (k_obs = 0.131 min⁻¹) surpassed that of oxygen-doped carbon (TS-800) by 4.85-fold. Quantitative structure-activity analysis identified graphitic N and C=O groups as the primary active sites (R² > 0.92). Comprehensive investigations, including quenching experiments, electron paramagnetic resonance (EPR), electrochemical tests, and in situ Raman spectroscopy, unveiled a non-radical-dominated pathway consisting of electron transfer (68.0%) and singlet oxygen generation (32.0%). Crucially, nitrogen doping induced a mechanistic shift from radical- to non-radical-dominated PMS activation, achieving a 61.2% TOC mineralization efficiency. The system demonstrated robust practical potential with >86.2% acetaminophen degradation in real water matrices (tap water, Yangtze River water, and secondary effluent) and excellent recyclability. Furthermore, the treated effluent exhibited significantly reduced phytotoxicity, with mung bean germination rates increasing from 33.3% to 62.7%. This work provides a facile, green strategy for synthesizing high-performance carbon materials and offers theoretical insights into designing efficient non-radical systems for sustainable water remediation.