| Summary: | 碩士 === 國立東華大學 === 化學系 === 93 === Titanium dioxide (TiO2), a semiconducting material, is the most popular photocatalysts due to its chemical stability, non-toxicity, and low cost. When a photon with energy of hn matches or exceeds the energy band gap, Eg, of TiO2, the electron-hole pairs are formed. These electrons and holes further react with oxygen and water to form free radicals which can decompose organic materials. Because of their high specific surface area, nanoscale TiO2 photocatalysts exhibit high organic chemical and microbe destruction rates under ultraviolet light. When used in powder form, TiO2 photocatalysts may suffer from several drawbacks, such as aggregation, secondary pollution, and hard to recycle. The objectives of this thesis are to prepare recyclable TiO2 photocatalysts with high photocatalytic activity, to apply them in the decomposition of organic dyes, and to study the kinetic behaviors of these systems.
The sol-gel method was applied to synthesize TiO2, and two forms of photocatalysts were prepared. First, TiO2 thin films were prepared by depositing TiO2 sol on the glass substrates with a spin-coater, followed by high temperature annealing. The morphology, crystallinity, and film thickness were analyzed with AFM/SEM, XRD, and ellipsometer, respectively. The effects of some parameters on the photocatalytic performance, including the type of precursor, the concentration of TiO2 sol, pH, the thickness of TiO2 films, and annealing temperature, were discussed. Second, magnetic core-shell photocatalysts were prepared, which could be recycled by magnet. In this experiment, micron-sized iron oxides were used as cores and coated with TiO2 via the sol-gel process. The core-shell structures were characterized by DLS, XRD, and TGA. The effects of precursor, concentration of precursor, and annealing temperature on the structure and photocatalytic activity of the core-shell photocatalysts were evaluated. The results for both the TiO2 thin films and the magnetic core-shell photocatalysts indicated that the use of titanium tetraisopropoxide (TTIP) as the precursor under pH of 3~4 and with annealing temperature of 450°C exhibited the best photocatalytic activity. The rate constants of the dye decomposition reaction under different experimental conditions were also measured and compared to examine the kinetic behaviors of TiO2 photocatalysts.
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