Rapid self-heating synthesis of nitrogen-doped carbon materials for peroxymonosulfate activation to degrade benzohydroxamic acid: Crucial role of persistent free radicals.

Nitrogen-doped carbon materials (NCM) have been widely employed to activate peroxymonosulfate (PMS) for wastewater remediation. Nevertheless, the traditional pyrolysis method used in synthesizing NCM suffers from issues such as slow heating rates and high energy consumption. Besides, the intrinsic mechanism on persistent free radicals (PFRs) in NCM-driven PMS activation remains ambiguous. Here, the flash joule heating (FJH) technology, a new heating technology, was applied to realize the rapid self-heating synthesis of NCM (FJH-NCM). The FJH-NCM synthesized at higher temperature (FJH-NCM-H) showed superior catalytic performance in activating PMS to eliminate benzohydroxamic acid (BHA). And 100% of BHA could be completely removed within 30 min, with the rate constant (k) reaching 0.3300 min. The oxidation efficiency of FJH-NCM-H/PMS system was less affected by natural organic matters and inorganic anions while maintaining stability across a wide pH range (3.50-11.00). Various methods, such as electron paramagnetic resonance, quenching experiments, probe tests, and electrochemical measurements, were employed to systematically elucidate the role of traditional reaction mechanisms (including radicals, O, and electron transfer) and PFRs in BHA removal. Results indicated that surface-attached PFRs mainly contributed to the BHA degradation in the FJH-NCM-H/PMS system. Surface-attached PFRs were generated from the direct reaction between PMS and organic precursors on the surface of FJH-NCM-H. Notably, the graphitization structure of FJH-NCM significantly influenced the catalytic performance. This study provides a new heating technology for biomass pyrolysis and rapid synthesis of NCM and reveals the crucial role of PFRs in NCM-driven PMS activation.