Mechanistic study of vacuum UV catalytic oxidation for toluene degradation over CeO2 nanorods

The present study specifically investigates vacuum ultraviolet (VUV) catalytic oxidation for toluene degradation over CeO2 nanorods. Synergetic effects of ultraviolet photocatalytic oxidation (UV-PCO) and ozone catalytic oxidation (OZCO) were manifested in the results of toluene removal and COx generation, while the combination of UV-PCO and OZCO (UV-OZCO) did not lead to improvement of mineralization. All the processes contribute to ozone decomposition, but no obvious synergetic effects of the different processes can be observed. Intermediate analysis results indicated that more toluene was oxidized into by-products, such as benzyl alcohol and benzaldehyde, by UV-OZCO rather than forming COx. Both hydroxyl radical (center dot OH) and superoxide radical (center dot O-2(-)) were found in all the processes of the VUV-PCO-OZCO system (combination of VUV photolysis, UV-PCO, OZCO and UV-OZCO processes). In the UV-OZCO process, the formation of hydroxyl radical was promoted, while that of superoxide radical was impeded, resulting in lower mineralization level of toluene. The mechanistic study of toluene degradation over CeO2 nanorods in the VUV-PCO-OZCO system revealed that with the formation of center dot O-2(-) and center dot OH, toluene is first oxidized to intermediates, followed by further ring-opening reaction and, finally, degradation into CO2 and H2O. CeO2 nanorods function as both ozonation catalyst and photocatalyst, and the redox pair of Ce3+ and Ce4+ are interconvertible and can keep a balance. (C) 2020 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.

Automated summary

This study investigates the application of CeO2 nanorods in vacuum ultraviolet (VUV) catalytic oxidation for toluene degradation. The results show that the synergistic effects of ultraviolet photocatalytic oxidation (UV-PCO) and ozone catalytic oxidation (OZCO) play a role in the removal of toluene and COx generation. However, the combination of UV-PCO and OZCO (UV-OZCO) does not improve mineralization. Furthermore, the study reveals the generation of hydroxyl radical (center dot OH) and the inhibition of superoxide radical (center dot O-2(-)) in the UV-OZCO process, leading to lower mineralization level of toluene.