Ornidazole degradation by PMS activated by Co-Zr-TiO2 with abundant oxygen vacancies: Performance, mechanism and degradation pathway

Peroxymonosulfate (PMS) activation through free radical and non-free radical synergism is a promising technique for the removal of difficult-to-degrade organic contaminants. Due to the insufficient sites of action or low activation efficiency of existing activation materials, there are still significant hurdles to enhancing the performance of PMS activation for the degradation of organic matter. In this paper, a bimetallic cobalt- and zirconium-doped TiO2 catalyst (Co-Zr-TiO2) with abundant oxygen vacancies was effectively prepared and employed to activate PMS for the removal of ornidazole (ONZ). The degradation rate of ONZ in the Co-Zr-TiO2/PMS system reached 100% within 20 min, and catalytic performance was approximately 49.6, 52.7 and 4.1 times higher than that of TiO2, Zr-TiO2 and Co-TiO2. Furthermore, the Co-Zr-TiO2 catalyst showed strong catalytic activity in aqueous solutions for various pollutants in addition to good adaptability in the pH range of 3–11. The mechanisms for the generation of multi-reactive oxygen species are activation of PMS by surface Co3+/Co2+ to generate free radicals (SO4•- and •OH); bimetallic doping leading to an increase in oxygen vacancies, which generates 1O2; and Zr4+ doping leading to an increase in the specific surface area, which results in the accessible active sites increase. Radical scavenging and EPR experiments confirmed that SO4•- and 1O2 were the main active substances in the Co-Zr-TiO2/PMS system. Finally, HPLC-MS analysis of degradation intermediates provided a possible catalytic degradation pathway for ONZ. The study proposes a strategy for the construction of efficient PMS activation catalysts for environmental cleanup that combines free radicals with non-free radicals.