| Volatile organic compounds(VOCs)are the focus of current social concern.PM2.5,photochemical smog and many other environmental pollution problems have a direct or indirect link with it.Therefore,effective measures should be taken to deal with it so as to reduce the harm to the environment.Because of the huge size of VOCs,it can not be investigated comprehensively.Therefore,toluene,the representative substance of VOCs,is selected as the target pollutant in this study.TiO2 has high photocatalytic activity and non-toxic.Therefore,the paper selected TiO2 based catalysts to degrade toluene.However,the catalyst is easy to intoxication and inactivation,which greatly limits its application in industry.Therefore,the cause of catalyst deactivation is studied,and the F-TiO2 catalyst is modified so that it can be used as soon as possible in the industry.A photocatalytic reaction system for toluene degradation in a 4 mm thick sandwich reactor was established by using scrape coating method as catalyst.F-TiO2 was screened for its high degradation activity against toluene.The maximum degradation rate of F-TiO2 was 91.2% in 60 min illumination time.The photocatalytic activity of F-TiO2 decreases with the increase of concentration and flow rate.The relative humidity(RH)has firstly promoting and then inhibiting effect on the photocatalytic activity of F-TiO2.When RH is 60%,the photocatalytic activity of the film is better.The presence of oxygen can promote the photocatalytic degradation efficiency of toluene.The photocatalytic activity of F-TiO2 thin film decreases with the increase of coating thickness.In order to explore the deactivation reasons,the fresh and deactivation catalyst were characterized by XRD,SEM,UV-Vis,low temperature nitrogen adsorption desorption,TG-DSC and XPS.It was found that there was no obvious change in crystal size and grain size for the fresh and post-reaction catalysts.The absorption of the deactivated catalyst in the visible region significantly is increased.There is the obvious agglomeration phenomenon for deactivated F-TiO2 particles.Specific surface area,pore size and pore volume are also significantly lower than the fresh catalyst.The deactivated catalyst has a significant weight loss process at 250 ℃ to 400 ℃,indicating that the surface of the catalyst accumulates low temperature aromatic hydrocarbons.The F loss of TiO2-x Fx in F-TiO2 lattice leads to the conversion of Ti3+ to Ti4+,which leads to the decrease of oxygen vacancy and the decrease of catalyst activity.The mainorganic intermediates on the surface of the F-TiO2 catalyst are butyl acetate.Based on the mechanism of F-TiO2 catalyst deactivation,the regeneration methods of two kinds of catalysts for ultrasonic and high temperature calcination were selected.Ultrasonic regeneration has a stronger ability to recover the specific surface area of the catalyst.But the improvement of carbon deposition in the catalyst is not obvious.When the ultrasonic time is 60 min,the photocatalytic activity is greatly restored.The highest degradation rate is 64.4%.High temperature calcination can oxidize the carbon deposition on the surface of the deactivated catalyst to improve the photocatalytic activity.However,when the temperature is higher than a certain value,the catalyst will agglomerate,which leading to the decrease of photocatalytic activity.When the calcination temperature is 450 ℃,the photocatalytic activity is the best,which is 80.6%.In order to improve the photocatalytic stability of F-TiO2,the TiO2@F-TiO2 encapsulated catalyst was prepared.The photocatalytic stability of the catalyst was improved to a certain extent.The photocatalytic degradation of toluene by TiO2@F-TiO2 was 18% higher than that of the original catalyst at 240 min illumination time. |
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