Oxidative degradation of sulfamethoxazole antibiotic catalyzed by porous magnetic manganese ferrite nanoparticles: mechanism and by-products identification

Abstract

Magnetic porous manganese ferrite nanoparticles (MnxFe3-xO4) with diverse ingredient Mn/Fe mole ratios were synthesized to degrade sulfamethoxazole (SMX) antibiotic residues involving peroxymonosulfate (PMS) dissociation to produce free radical SO4•−, •OH and singlet oxygen 1O2 in the absence of heat and light. With the increase in proportion of manganese, the degradation efficiency of SMX increased from 19 to 70% in 30 min. The removal efficiency of SMX increased following the concentration increase of PMS (from 1 ~ 10 mM). After 60 min, the total organic carbon went down by 20%, and the concentration of NH4+ and NO3− accumulated obviously simultaneously. EPR study and chemical probe method, depending on scavenging revealed that SO4•−, •OH and 1O2 were generated and contributed to the degradation system. Based on the capture of eleven decomposition by-products by LC/MS, two different degradation pathways of SMX were determined, mainly consisting of cleavage of the S–N bond, hydroxylation of benzene and heterocyclic ring, oxidation of amino group and ring-opening cleavage processes. The nanoparticle reuse tests showed that the porous magnetic manganese ferrite nanoparticles could still maintain a high degradation efficiency after five oxidative degradation reactions. The magnetic porous manganese ferrite nanocrystals could activate the PMS to oxidize SMX antibiotic residue without additional energy.