Efficient heterogeneous activation of peroxymonosulfate by Ag-doped CoFe2O4 nanoparticles for sulfamethoxazole degradation

In this work, silver-doped cobalt ferrite catalysts Agx-CoFe2O4 (x = n(Ag+): n(Fe3+); x = 0, 0.02, 0.04, 0.06, and 0.08) were synthesized through the reverse co-precipitation method and employed to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) degradation. Ag0.06-CoFe2O4 exhibited the best catalytic activity and PMS utilization efficiency, indicating the optimal silver doping ratio. The characterization results revealed that Ag doping led to the exposure of more active sites and the increase of the concentration of oxygen vacancies (OV). The effects of Ag0.06-CoFe2O4 dosage, PMS concentration, initial pH, inorganic ions, and humic acid on SMX degradation by Ag0.06-CoFe2O4/PMS system were investigated. The utilization of 0.1 g/L Ag0.06-CoFe2O4 and 0.1 mM PMS resulted in a remarkable 95.1 % degradation efficiency of 10 μM SMX in 30 min at initial pH of 5.0. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed the presence of both radical species (HO•, SO4•− and O2•−) and non-radical species (1O2) in Ag0.06-CoFe2O4/PMS system, among which SO4•− and 1O2 played a predominant role in SMX degradation. The catalytic cycle between≡CoOH+/≡CoO+ and PMS and the interaction of OV with adsorbed oxygen should contribute to PMS activation. The cycling experiments and X-ray diffraction (XRD) patterns before and after the reaction showed that Ag0.06-CoFe2O4 exhibited remarkable stability and reusability. The transformation products (TPs) of SMX were identified, and three possible degradation pathways were proposed. Most of these TPs demonstrated lower toxicity compared to SMX, as predicted by the Ecological Structure−Activity Relationship Model.