Insights into the enhanced removal of sulfamethoxazole via peroxymonosulfate activation catalyzed by bimetallic (Co/Cu) doped graphitic carbon nitride: Reaction kinetics, mechanisms, and pathways

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have shown great potential for recalcitrant contaminants removal in wastewater treatment. Herein, we report the efficient activation of PMS by bimetallic oxides (cobalt and copper) co-doped graphitic carbon nitride (Co-Cu@g-C3N4) for removal of sulfamethoxazole (SMX). The morphology and chemical composition of the fresh and used Co-Cu@g-C3N4 were characterized by TEM, SEM, XRD, BET, and XPS. Nearly complete removal of SMX (50 mg/L) was observed in the presence of 50 mg/L Co-Cu@g-C3N4, 0.5 mmol/L PMS within 20 min at neutral pH with a degradation rate of 0.137 min-1. Moreover, the Co-Cu@g-C3N4 catalyst enabled more than 90 % removal of various typical pollutants within 20 min, including sulfapyridine, rhodamine B, acridine red, and malachite green, with rate constants of 0.083, 0.130, 0.096, and 0.160 min-1, respectively. Quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that sulfate radical (SO4 center dot- ) and singlet oxygen (1O2) were collectively responsible for SMX degradation. The efficient activation of PMS by Co-Cu@g-C3N4 was ascribed to the continuous conversion of Co(III) to Co(II) and Cu(I) to Cu(II), and the presence of oxygen vacancy (OV) on the catalyst. The Co-Cu@g-C3N4/PMS system exhibited superior durability and maintained high efficiency in real water samples. Finally, theoretical calculations of Fukui index were performed to determine the possible degradation pathways of SMX, and the ecotoxicity of the degradation products was evaluated by the ECOSAR program. This study significantly advances the understanding of the reaction between PMS and bimetallic oxides catalysts, as well facilitates the development and application of PMS-based AOPs in wastewater treatment.