Catalytic ozonation of thymol with a novel CoCe-MMO catalyst: Kinetics and mechanism

Abstract

In this study, a novel ozonation catalyst CoCe mixed metal oxide (CoCe-MMO) was prepared for the degradation of organic wastewater containing thymol. The results showed that the addition of CoCe-MMO could effectively enhance the effect of thymol degradation, and the thymol could be completely removed after 40 min of reaction. The reaction kinetics was calculated. It accords with the quasi-first order reaction kinetics, and the reaction rate constant is about 0.1357 min −1 . The enhancement mechanism was discussed and the CoCe-MMO could react with ozone to produce strong oxidizing free radicals-hydroxyl radicals (•OH). The catalyst was characterized by XRD, SEM, and XPS. The results showed that the catalyst continued the lamellar laminated structure of its precursor, and present a higher crystallinity and smaller crystal grain size (about 58-70 nm), which would promote the production of •OH. The •OH and O 3 could attack the ortho-position of thymol for peacekeeping, making it gradually converted into small molecule acids, and finally completely degraded into CO 2 and H 2 O. The stability and reusability of the catalyst were also studied and the CoCe-MMO catalyst could maintain high activity after three cycles. And the metal ion leaching rates of Co and Ce are 0.39 mg/L and 0.03 mg/L respectively, which is lower than the emission standard. This paper showed that the catalyst has good application prospect and could provide technical support for pharmaceutical wastewater pollution control with catalytic ozonation.