Photo-assisted Catalytic Ozonation Of Toluene Using Ce-based Catalysts

Volatile organic compounds（VOCs） are the precursors of O₃ and fine particles formed by atmospheric photochemistry,which seriously threaten human health and ecological environment.Effective control of VOCs has become an important measure to ensure the successful completion of China’s"Fourteenth Five-year"Ecological and Environmental Protection Plan.Energy consumption and efficiency are the main bottlenecks for the promotion and application of VOCs control technology in low concentration and high flow.As a renewable green energy,solar energy can meet energy demand and has the potential of sustainable development as well.Compared with traditional photocatalysts,photothermal catalysts can extend the range of sunlight utilization from ultraviolet and partial visible light to infrared light.The efficiency of catalytic ozonation of VOCs can be significantly increased with increasing reaction temperature at the temperature range of 10-100℃.Through the photothermal and photochemical conversions of solar energy,solar energy and catalytic ozonation technology can be combined to save energy and efficiently remove VOCs.In this study,we synthesized CeO₂nanoparticles coupled with PtO_x,NiCo₂O₄ and WC,respectively,to improve their catalytic performance by strengthening the light absorption and photothermal conversion.The contribution of photothermal and photochemical conversion in the process of photo-assisted catalytic ozonation for toluene was investigated by comparing the performance of catalytic ozonation under temperature control and light irradiation with that of thermal catalytic ozonation,in combination with the physical and chemical structure characterization of the materials.The separation behavior of photogenerated carriers was analyzed by atmosphere surface photovoltage spectrum.The specific results are as follows:（1）The enhancing mechanism of photo-assisted catalytic ozonation of toluene for CeO₂with PtO_x loading was clarified.The PtO_x loading increased the absorption of visible and infrared light and enhanced the photothermal conversion efficiency by 2.4 times compared with CeO₂（1）.The surface temperature of PtO_x-CeO₂（101.1℃）was 49.2%higher than that of CeO₂（1）under 450 m W/cm² illumination.The synergy factor of PtO_x loading under the full-spectrum irradiation was 4.05,which was 1.6 times higher than that of CeO₂（1）.The reaction rate of toluene removal by PtO_x-CeO₂ was 8853.9 mg/（m³·min）under the full-spectrum irradiation,which was 2.2 times higher than that of CeO₂（1）.Photogenerated carriers participated in toluene degradation by inducing ozone decomposition.PtO_x loading created selective pathways for the transfer of holes to adsorbed water,thereby enhancing the separation and utilization of photogenerated charges.（2）The improvement of synergy with sunlight and ozone for toluene degradation by NiCo₂O₄/CeO₂ was investigated.NiCo₂O₄ loading enhanced the absorption of incident light and the photothermal conversion capacity of absorbed light,and the photothermal conversion efficiency of incident light reached 77.4%.The surface temperature of 10%NiCo₂O₄/CeO₂ can be increased to 90.8℃under 300 m W/cm² illumination.The coupling with NiCo₂O₄ increased the amount of oxygen vacancies on CeO₂ surface,which significantly improved the performance of thermal catalytic ozonation for toluene degradation.The coupling did not improve the carrier separation efficiency,but increased the utilization rate of photogenerated carriers in toluene degradation reaction.The synergy factor of 10%NiCo₂O₄/CeO₂ reached 4.92,2.5 times higher than that of CeO₂（2）under the full-spectrum illumination.The removal rate of toluene by 10%NiCo₂O₄/CeO₂ under the full-spectrum illumination was 8594.6 mg/（m³·min）,and the mineralization rate was 58.5%.（3）The enhancement of the synergistic effect between sunlight and ozone by WC/CeO₂was studied.The photothermal conversion efficiency of incident light for WC/CeO₂ reached67.6%.The surface temperature（87.8℃）of 20%WC/CeO₂ was 62.9%higher than that of CeO₂（3）under 300 m W/cm² illumination.WC transferred electrons to CeO₂（3）,which significantly increased the amount of oxygen vacancies on the catalyst surface,thereby improving the catalytic ozonation performance of toluene.The coexistence of water and toluene on20%WC/CeO₂ surface promoted photogenerated carrier separation,whereas they showed the opposite effect on CeO₂（3）surface.The synergy factor of 20%WC/CeO₂reached 4.92,3.8times higher than that of CeO₂（3）.The coupling with WC significantly improved the photo-assisted ozonation catalytic performance of toluene.The reaction rate and mineralization efficiency of 20%WC/CeO₂ were 9274.5 mg/（m³·min）and 64.5%under the full-spectrum illumination,which were 4.7 and 6.2 times higher than those of CeO₂（3）,respectively.