| Summary: | 碩士 === 國立高雄第一科技大學 === 環境與安全衛生工程研究所 === 101 === Gas-phase photocatalytic oxidation process is an emerging control technology for volatile organic compounds control, which uses semiconductor oxides as photocatalysts to decompose many retardant organic pollutants by forming reactive species (e.g., hydroxyl radicals) on their surfaces while irradiated with suitable light energy. These reactive species are mainly originated from formation of electron-hole pairs on photocatalyst, and the recombination rates of electron-hole pairs dominantly determine the activities of photocatalysts. The photocatalysts with retarded recombination rates of electron-hole pairs usually have high activities.
Accordingly, this study aimed to develop a high efficient gas-phase photocatalytic oxidation process by retarding the electron-hole recombination rate of TiO2 thin-film photocatalyst with an additional external bias. The tested TiO2 thin film photocatalysts were prepared with RF magnetic sputtering processes by depositing thin-film TiO2 onto Al2O3 ceramic substrates. For enhancing the photocatalytic activity of TiO2, the TiO2 was composited with a CuO thin layer before depositing onto the Al2O3 substrate. As a matter of fact, this additional layer of CuO is beneficial for absorption light red-shift. This study used methyl tert butyl ether (MtBE) as a target pollutant. Several experimental parameters including reaction temperature, water vapor content, and applied bias were investigated in the study.
The experimental results demonstrated that the degradation of MtBE followed pseudo first-order reaction kinetics. Higher MtBE degradation rates were achieved by being provided with suitable external bias. The applied bias can delay the electron-hole recombination rate and accelerate the overall reaction rate. In comparison of pure TiO2, the CuO/TiO2 composite photocatalyst achieved higher MtBE degradation rates. In the test range of 45~105℃, the photocatalytic degradation of MtBE peaked at 90℃, showing the intrinsically behaviors of heterogeneous reactions for the photocatalysis of MtBE. Similarly, proper amount water vapor was beneficial for the photocatalysis of MtBE. More hydroxyl radicals can be formed in the presence of water vapor, but the MtBE degradation rates were inhibited in the presence of too much water vapor.
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