| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 100 === The purpose of this study was to develop a catalyst with high efficiency photocatalytic activity and had core/shell structure. It could be applied to the degradation of organic pollutants under UV light illumination. The literature shows that doping noble metal on the surface of titanium dioxide can enhance the photocatalytic activity because noble metal can form active sites to promote the electronic charge transfer in the interface of metal and titanium dioxide. Although the activity of this kind of structure is high, the exposed metal is easy to dissolve or corrosive, leading to catalyst decay. Core/shell structure can be used to overcome this shortcoming, noble metals located in the core, while titanium dioxide is in the shell. In this study, M@TiO2 (M = Pd, Ag, Au) catalysts with core/shell structure were synthesized by sol-gel method with hydrothermal treatment with different preparation parameters. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light and 250W halogen lamp as the light source. The concentration of MB in the degradation samples were measured by UV-vis spectrometer (UV-vis). This thesis is divided into two parts, the first part is on the preparation of M@TiO2 (M = Pd, Ag, Au) with core/shell structure and its photocatalystic activity. The TEM micrographs results show that the particle size of metal cores was about 3-12nm, and the shell thickness of titanium dioxide was about 6-20nm. The XRD pattern results show that Pd@TiO2 has highest crystallinity. The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light and 250W halogen lamp as the light source. Pd@TiO2 had the highest activity under UV light and halogen lamp illumination. Because Pd@TiO2 had higher crysallinity, lower band gap energy, and higher absorption at visible region. The second part is on discussion different preparation parameters: metals loading amount, and hytrothermal time, and found the relationship with the photocatalystic activity by methylene blue degradation under the UV light illumination. The optimal amounts of Pd, Ag, and Au loading were 0.5 wt. %, 0.5 wt. %, 1.0 wt. %.The optimal hytrothermal time was 18 hours. Furthermore, the sample for 18 hour had the highest activity due to the highest crystallinity. From these results, the photocatalytic activity of M@TiO2 (M = Pd, Ag, Au) catalyst mainly depended on the crystallinity of TiO2, the kind of metals, the amount of noble metal loading and the OH group contents.
Keywords: titanium dioxide, core/shell structure, photocatalyst, palladium, silver, gold, sol-gel method, hydrothermal method, methylene degradation.
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