| Summary: | 碩士 === 國立高雄科技大學 === 環境與安全衛生工程系 === 107 === Powder-form photocatalysts are widely tested in various studies for developing advanced oxidation processes for organic pollutants removal. However, they are difficult to be used in real application, since that powder-form photocatalysts are difficult to stay in the photocatalytic reactors for a long time. It is necessary to develop immobilized form photocatalysts for practical application purposes. Thin-film form photocatalysts should be one of the best choices.
Accordingly, this study developed and prpared TiO2-PVDF composite thin-films as photocatalysts for controlling typical a volatile organic pollutant, benzene (C6H6), from contaminated gaseous streams. The thin-film photocatalysts were prepared with an immersion precipitation method by mixing P-25 TiO2 and PVDF powders with some suitable solvents. Other than good photocatalytic oxidation capabilities, the prepared TiO2-PVDF thin films have several superior physical properties including high plasticity, low mechanical resistance, and high flexibility. In addition, easy to modify their activities by co-doping with other nano-carbon containing substances, such as, carbon nanotubes and graphene oxide, is another advantage, which has been demonstrated in this study. For confirming the prepared sample with good photocatalytic activities, some typical affecting factors for photocatalytic oxidation, such as, reaction temperature (35~75 oC), humidity, and types of light sources, were tested as well.
Some important results have been achieved in this study. The photocatalytic decomposition of benzene vapor basically followed the first-order reaction kinetics. Fast photocatalysis of benzene was observed under the illumination of near-UV light, but slow degradation rate of benzene was detected while using visible blue light as an only light source. For simple TiO2-PVDF thin-film as the photocatalyst, benzene peaked its decomposition rate at a reaction temperature 35oC in dry environment (k= 0.328 hr-1). Less degradation rate for benzene was also detected in higher temperature environment. The occurrence of water vapor would retard the photocatalysis of benzene due to adsorption competition among water and benzene vapor for the activated sites on photocatalysts.
On the other hand, after being doped with suitable amount of carbon-nanotube (CNT), the photocatalytic activities of TiO2-PVDF thin films were enhanced. Higher benzene degradation rates were demonstrated in the study. It is expected that the recombination rate of electron-hole pairs of photocatalysts was retarded due to CNT co-doping. It was found that the TiO2-PVDF thin film co-doped with 1% CNT achieved the highest benzene degradation rate (k= 0.354 hr-1, in dry condition). It was also observed that higher degradation rate of benzene was achieved in the presence of 10 g/cm3 water vapor, which might be due to more hydroxyl radicals formed while some humidity presenting if water vapor was not too much. One benefit for adding some CNT to the TiO2-PVDF thin films was to keep them with good photocatalytic activities in high temperature and humid conditions.
Finally, the photocatalytic activities of prepared TiO2-PVDF thin films were not enhanced much while co-doping with graphene oxide below 2%. It might be that the bonding between TiO2 and graphene oxide was not good enough by the current using preparation recipies or the amount of doped graphene oxide was not suitable. More investigation required is suggested.
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