Efficient degradation of sulfamethazine with CuCo2O4 spinel nanocatalysts for peroxymonosulfate activation

CuCo2O4 spinel nanoparticles (NPs) synthesized using a solvothermal method were used as catalysts to activate peroxymonosulfate (PMS) with sulfamethazine (SMZ) as the target pollutant. A degradation efficiency of 87.2% was achieved in 20 min with 20 mg L-1 PMS and 0.01 g L-1 CuCo2O4 catalyst. In contrast, only 51.1%, 11.3%, 12.5%, and 7.9% degradations of SMZ were observed with Co3O4, CuFe2O4, CuO, and Fe3O4, respectively, as the catalysts. The superior catalytic reactivity of CuCo2O4 was explained with the presence of Co2+ on the catalyst surface and the combined catalytic reactivity of copper and cobalt towards PMS. Based on the XPS results and the relative catalytic reactivity of Cu2+ and Cu+, it was proposed that the Cu2+/ Cu+ circulation was least likely the key reaction steps. Instead, a complex reaction mechanism involving the generation of Cu3+ was used to explain the activation of PMS by Cu2+. The investigation on the reaction parameters showed that the SMZ degradation efficiency responded positively to increases in the PMS dose and the scavenger effect. A mild alkaline condition favored the degradation of SMZ, and an optimized operational condition was found to achieve 98% SMZ degradation with 20 mg L-1 PMS, 0.04 g L-1 CuCo2O4, and 5 mg L-1 SMZ at pH 7.7. The activation energy of SMZ degradation was thus estimated to be 21.0 kJ mol(-1) for the CuCo2O4/PMS system and 38.4 kJ mol(-1) for the CuFe2O4/PMS system. Finally, a degradation mechanism on the basis of analyzing the degradation products of SMZ was proposed and the stability and reusability of the CuFe2O4 NPs were evaluated. (C) 2015 Elsevier B.V. All rights reserved.