| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 91 === Photocatalytic Titanium dioxide becomes the most attractive green product in recent years owing to the serious worldwide environmental problem. In this thesis, photocatalytic titanium dioxide powders and thin films were synthesized at low temperature via the high-pressure processes, and effects of various process parameters on photocatalytic activities of titanium dioxide were studied. In addition, photo-induced superhydrophilicity of titanium dioxide thin films were also investigated.
Photocatalytic titanium dioxide (TiO2) powders were synthesized via the hydrothermal microemulsion process. Monophasic anatase TiO2 powders were obtained after the microemulsion-derived precursors were hydrothermally treated. The specific surface area of TiO2 powders was increased with the oil/water ratio leading to the enhancement of photocatalytic activity of TiO2 powders. As the hydrothermal temperature was elevated, the morphology of TiO2 particles changed from rod-like shape into spherical shape, whereas the extension of the hydrothermal period at the same temperature of 150oC led to the grain growth of TiO2 particles without shape change. The decrease of specific surface areas made the photocatalytic activities of TiO2 powders become lower.
TiO2 thin films with monophasic anatase structure were synthesized via the metalorganic deposition method. The crystallization temperature from amorphous films to anatase TiO2 films was significantly lowered from 350oC to 150 oC via the high-pressure crystallization (HPC) process. TiO2 thin films with crack-free surface were obtained via the HPC process owing to low-temperature crystallization process. During the HPC process, crystallization process took place simultaneously at each depth of TiO2 thin films resulting in TiO2 thin films with uniform crystallinity. The problem of Si diffusion from substrates was effectively inhibited via the HPC process due to low-temperature annealing. The high-pressure annealing led to high wettability of TiO2 thin films before UV illumination, and the hydrophilicity increased as the temperature was elevated under high-pressure annealing. Under UV illumination, TiO2 thin films annealed via the high-pressure process showed better photo-induced superhydrophilicity than those annealed via the atmospheric-pressure process. TiO2 thin films synthesized via the high-pressure annealing process also exhibited better photocatalytic activities than those prepared via the conventional annealing process. In conclusion, the HPC process provides a new route to synthesize TiO2 thin films with high photocatalytic activity and high wettability at low temperature.
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