Efficient degradation of sulfamethazine with CuCo2O4 spinel nanocatalysts for peroxymonosulfate activation

Abstract CuCo 2 O 4 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 CuCo 2 O 4 catalyst. In contrast, only 51.1%, 11.3%, 12.5%, and 7.9% degradations of SMZ were observed with Co 3 O 4 , CuFe 2 O 4 , CuO, and Fe 3 O 4 , respectively, as the catalysts. The superior catalytic reactivity of CuCo 2 O 4 was explained with the presence of Co 2 + 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 Cu 2 + and Cu + , it was proposed that the Cu 2 + / Cu + circulation was least likely the key reaction steps. Instead, a complex reaction mechanism involving the generation of Cu 3 + was used to explain the activation of PMS by Cu 2 + . 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 CuCo 2 O 4 , 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 CuCo 2 O 4 /PMS system and 38.4 kJ mol −1 for the CuFe 2 O 4 /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 CuFe 2 O 4 NPs were evaluated.