CoFe2O4/MWCNTs as peroxymonosulfate activator for sulfadiazine degradation in wastewater: Performance, mechanisms, degradation pathway, and products toxicity assessment

Bimetal oxide-based compounds have potential in the degradation of antibiotics in wastewater. In this study, cobalt-ferrite-coated multi-walled carbon nanotubes (CoFe2O4/MWCNTs) have been synthesized by solvothermal method and characterized. Then, the degradation of sulfadiazine (SDZ) by CoFe2O4/MWCNTs activated peroxymonosulfate (PMS) system was determined, mainly including the effects of CoFe2O4/MWCNTs dosage, PMS concentration, solution pH, initial SDZ concentration, and co-existing anions on the degradation of SDZ. Based on reactive oxygen species identification and XPS analysis, the possible reaction mechanisms were investigated. In addition, the potential degradation pathways of SDZ were discussed. The results showed that CoFe2O4/MWCNTs exhibited superior catalytic activity and stability toward SDZ removal, and 97.5% of SDZ was degraded within 30 min under the condition of CoFe2O4/MWCNTs dosage 0.3 g/L, PMS concentration 0.5 mM and solution pH 7. The possible mechanism of PMS activation by CoFe2O4/MWCNTs involved both free-radical and non-radical pathways, and the generated reactive species (SO4•−, •OH, O2•− and 1O2) were responsible for the degradation of SDZ. In addition, four potential degradation pathways were proposed and 15 intermediates were identified. In view of the ecotoxicity assessment, it was found that the toxicity of the degradation intermediates was lower than that of SDZ. Overall, this study established an effective strategy for PMS activation to remove recalcitrant organic pollutants in wastewater.