Enhanced activation performance of peroxymonosulfate by NiCo2O4/SnO2 composite for metronidazole degradation under visible light

Abstract

In this study, a NiCo2O4/SnO2 complex was successfully synthesized by a convenient hydrothermal method and used for the catalytic degradation of metronidazole (MNZ) by activating peroxymonosulfate (PMS). The physicochemical properties of NiCo2O4/SnO2 were identified by a series of characterization methods. The remarkable PMS activation performance of NiCo2O4/SnO2 originated from the formation of a heterojunction between NiCo2O4 and SnO2, which led to the improvement of the light response ability and the electron conduction efficiency of the composite. The composite catalyst displayed almost 100 % MNZ degradation efficiency within 30 min under visible light. The degradation efficiency of MNZ can be maintained in a wide pH range (3−11). Furthermore, the effect of catalyst dosage, PMS concentration and MNZ concentration on the catalytic process were investigated by changing the experimental parameters. The various anions and different water substrates had only a minor influence on the degradation process of MNZ. In addition, quenching experiments and electron paramagnetic resonance techniques were employed to detect active groups in the reaction process. The results showed that superoxide radicals (O2•-), hydroxyl radicals (OH•), singlet oxygen (1O2), and sulfate radicals (SO4•-) were the main causes of MNZ degradation. Meanwhile, the liquid phase mass spectrometry (LCMS) and Toxicity Estimation Software Tool (T.E.S.T) were utilized to identify the intermediate products and their biological toxicity in the degradation process, and demonstrating a significant decline of biotoxicity compared with MNZ. Generally, this work will provide a new feasible scheme for the effective treatment of organic contaminants in water.