Study On Photocatalytic Degradation Of Gaseous Organic Pollutants-Toluene

In recent years, the elimination of VOCs pollutants becomes the hot issue of indoor air pollution control. Toluene is one of the main pollutants in indoor air; it can be absorbed by the skin, respiratory and gastrointestinal, which threatens human health. Therefore, research on the degradation of toluene has important theoretical and practical value.TiO2 has been widely used in photocatalytic degradation of pollutants; it has such advantages of chemical stability and low cost, non-toxic, high catalytic activity and oxidation ability. But TiO2 has shortcomings such as low utilization of solar energy, prone to complex electron and hole. To solve this problem, the author use precious metals Ag and Pd modified TiO2. prepared Ag, Pd doping (with Ag-TiO2 and Pd-TiO2 indicated) and Ag, Pd load (with Ag/TiO2 and Pd/TiO2 indicated) two types of TiO2 photocatalyst by sol-gel process and impregnation, respectively. Then, their photocatalytic activity of toluene was investigated in the continuous flow reactor. Finally, the photocatalyst were characterized by XRD, SEM, and BET techniques. The results are as follows:1. The results of using the Ag-modified TiO2 photocatalyst prepared by sol-gel process and impregnation in photocatalytic degradation of toluene showed that the Ag doped nanometer TiO2 photocatalysts prepared by sol-gel process with compositions (nAg/nTi=1.6%) have the maximum degradation rate (43%). And the best heat treatment temperatures of the Agx-TiO2 is 550℃.Agx/TiO2 prepared by impregnation has lower toluene degradation rate than that of Agx-TiO2 prepared by sol-gel process.2. The Pd-TiO2 photocatalysts prepared by sol-gel process with compositions (nPd/nTi=0.3%) have the maximum toluene degradation rate of 45.2%. And the best treatment temperatures for the photocatalyst is 500℃。Pd/TiO2 prepared by impregnation has a lower toluene degradation rate than that of Pd-TiO2 prepared by sol-gel process.3. XRD results exhibited that Ag and Pd modified TiO2 by sol-gel has a structure of anatase when calcination temperature is 500℃.The doping of Pd can make the transformation of anatase to rutile harder than Ag. The photocatalyst by impregnation is rutile because of calcination time extended. With the increase of calcination temperature, the catalyst particle size increases, the specific surface area decreases.4. The test results of SEM showed that catalysts prepared by sol-gel and impregnation have uniform particle distribution. As the role of surface energy of nanoparticles, there are agglomerations of crystal more or less. Of all of the catalysts, the doping of Pd by sol-gel has the smallest catalyst particle, indicating that Pd doping can effectively inhibit the agglomeration of nanoparticles.5. O2-TPD results displayed that the pure TiO2 has desorption peaks of both surface lattice oxygen and bulk lattice oxygen. However, Ag and Pd-modified TiO2 have only desorption peak of surface adsorbed oxygen. Activity tests showed that the presence of adsorbed oxygen is beneficial to improve on the catalytic activity.6. Analysis of UV-visible diffuse reflectance spectra showed that the absorption wavelength of Ag and Pd doped catalyst shifted to higher wavelengths, and the absorption intensity in the visible light region have increased compared with that of the pure TiO2.