The enhanced catalytic degradation of sulfamethoxazole over Fe@nitrogen-doped carbon-supported nanocomposite: Insight into the mechanism

An environmentally friendly Fe@nitrogen-doped carbon nanocomposite catalyst (Fe@N-CNs) was prepared via a facile and economical process using carboxymethyl chitosan (CMCs) hydrogel as a template to achieve Fe anchoring and N-doping simultaneously for peroxymonosulfate (PMS) activation to efficiently degrade sulfamethoxazole (SMX). The "core-shell " structure of Fe@N-CNs displayed that Fe nanoparticles identified as Fe3C and Fe3N were encapsulated in nitrogen-doped carbon nanosheets. The formation of FexNy sites and the high content of graphitic N obtained from CMCs facilitated the catalytic reaction. With excellent catalytic activity to achieve complete degradation of SMX in less than 10 min, Fe@N-CNs/PMS system also exhibited stable catalytic degradation efficiency over a wide pH range (3.0-9.0) and under high-salinity conditions. Singlet oxygen was identified as the dominant reactive species in catalytic oxidation and played a vital role in the non-radical pathway. The potential SMX degradation pathway and mechanism in the Fe@N-CNs/PMS reaction system were proposed according to DFT calculations and product detection results. Quantitative structure-activity relationship (QSAR) prediction verified the efficient elimination of SMX degradation products toxicity. Moreover, the Fe@N-CNs/PMS system was also confirmed to be effective towards the inactivation of antibiotic resistant bacteria (ARB) and antibiotics resistance genes (ARGs).