Insight into heterogeneous catalytic degradation of sulfamethazine by peroxymonosulfate activated with CuCo2O4 derived from bimetallic oxalate

CuCo2O4 was synthesized via the calcination of a copper-cobalt bimetallic oxalate precursor and was used as a heterogeneous catalyst of peroxymonosulfate (PMS) for the degradation of sulfamethazine (SMZ). The results demonstrated that the CuCo2O4 had higher catalytic activity than the monometallic CuO and Co3O4. The degradation efficiency of SMZ (50 mg/L) by PMS (1 mmol/L) activated with CuCo2O4 (0.1 g/L) was above 98% within 30 min at initial pH 5. Electron paramagnetic resonance (EPR) and radical quenching experiments proved that both sulfate radicals (SO4−) and singlet oxygen (1O2) were responsible for the efficient removal of SMZ, especially 1O2. The superoxide radicals (O2−) produced from the reaction improved the generation of SO4− and 1O2. Cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and hydrogen temperature- programmed reduction (H2-TPR) investigations revealed that the synergy of Cu and Co species in PMS activation resulted from higher electroconductibility, more electron transfer, and better redox potential of the CuCo2O4. The synergy between the Co(III)/Co(II) and the Cu(II)/Cu(I) couples enhanced the turnover frequency (TOF) of CuCo2O4. The possible degradation pathways are further proposed according to the identification of the SMZ degradation products and the theoretical calculations of the frontier electron densities (FEDs) of the SMZ molecule.