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

CuCo 2 O 4 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 CuCo 2 O 4 had higher catalytic activity than the monometallic CuO and Co 3 O 4 . The degradation efficiency of SMZ (50 mg/L) by PMS (1 mmol/L) activated with CuCo 2 O 4 (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 (SO 4 − ) and singlet oxygen ( 1 O 2 ) were responsible for the efficient removal of SMZ, especially 1 O 2 . The superoxide radicals (O 2 − ) produced from the reaction improved the generation of SO 4 − and 1 O 2 . Cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and hydrogen temperature- programmed reduction (H 2 -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 CuCo 2 O 4 . The synergy between the Co(III)/Co(II) and the Cu(II)/Cu(I) couples enhanced the turnover frequency (TOF) of CuCo 2 O 4 . 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.