Preparation Of Nano-TiO₂ Powders And Gas-phase Photocatalytic Degradation Of Benzene

Volatile organic compounds (VOCs) constitute an important group of pollutants due to their toxicity and adverse biological effects, which are majoy pollutants and could be directly harmful to human beings. Cleaning indoor air have been concerned. Because of strong oxidation, chemical stability and non-toxic of TiO2 photocatalysts, TiO2 nanopowders are used for indoor air purification. However, its narrow spectrum response range and low efficiency of photocatalytic degradation of gas phase limit the practical applications. Therefore, modification of photocatalysts for enhance efficiency of photocatalytic degradation of gaseous pollutants under visible light (especially benzene and its homologues) is particularly important.In this dissertation, valuable explorations have been carried out on the fabrication, characterization and photocatalytic activity for decomposing gaseous benzene of doped titatia photocatalysts. The main points could be summarized as follows:Boron-doped TiO2 photocatalysts and N, F-codoped TiO2 photocatalysts were synthesized respectively by the improved sol-gel method. Tetrabutyl titanate, H3BO3 and NH4F were used as the source of Ti, B dopant and N, F-codoped respectively, and Ethanol or water were used as solvent. The crystalline phases, surface morphologies, surface element state and optical absorption properties of the as-synthesized samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy respectively. The optimum parameters of TiO2 nanopowders synthesis were obtained. The photocatalytic activity of the as-synthesized samples with degradation of gaseous benzene was detected by Gas Chromatography. Finally, the effect of B and N, F on the photocatalytic activity of TiO2 nanopowders were investigated.The results indicate that TiO2 photocatalysts with high catalytic activity are successfully obtained. The photocatalytic activity of boron-doped TiO2 photocatalyst with molar ratio of B to Ti 0.6, calcination temperature 600℃and calcination time 2.0 h is the highest. It can decompose benzene within 55 minutes completely under ultraviolet light, whose degradation efficiency is about twice as high as P25; under visible light, the degradation efficiency of the boron-doped TiO2 photocatalyst is about 1.4 times that of P25. For N, F-codoped TiO2 photocatalysts, the photocatalytic activity of TiO2 photocatalysts with molar ratio of N, F to Ti 0.1, calcination temperature 600℃and calcination time 2.0 h is better, which can decompose 90% benzene within 80 minutes. The degradation efficiency is about 1.3 times that of P25.B doping significantly enhances the intensity of light absorption of TiO2 photocatalysts and obviously improves the photocatalytic activities of TiO2. Furthermore, the incorporation of B makes the TiO2 nanopowders absorption edge red shift, enhancing the visible light activity of TiO2. The N, F codoping reduce the band gap of TiO2 and enhance its surface acidity, which provide more active sites and improve significantly the photocatalytic activity of TiO2 photocatalyst.