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Preparation , Characterization and Photocatalytic TiO 2 -based degradation properties of hollow spheres

Author: LvZuoZhen
Tutor: LiJie
School: Central South University
Course: Physical Chemistry of Metallurgy
Keywords: hollow sphere WO3/TiO2 Ag/TiO2 photo-degradation methylene blue
CLC: O643.32
Type: Master's thesis
Year: 2011
Downloads: 130
Quote: 0
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Abstract


As the energy crisis and environmental problem becoming worse, visible-light driven semiconductor photocatalysts have become a hot research area. Among the oxide semiconductor photocatalysts available, titanium dioxide has proven to be the most widely used one for environmental catalysis due to its various merits, such as excellent photocatalytic activity, low cost, nontoxicity, and chemical biological inertness. In this study, four chemical materials, i.e., glucose, silver nitrate, tetrabutylortitanate and ammonium metatungstate, were used as raw material. Mesoporous carbon spheres, WO3/TiO2 hollow spheres, and Ag/TiO2 hollow spheres were prepared by hydrothermal-template method which was first used. The results show that the photoelectrochemical properties of TiO2 were enhanced by doping WO3 and Ag, expanding its potential application in solar energy. The main contents are as the following:(1)W03/TiO2 hollow spheres were successfully prepared using template method. UV-vis diffuse reflectance spectra illustrated that the main absorption edges of the WO3/TiO2 hollow spheres were red-shifted compared to the TiO2 hollow spheres, indicating an extension of light absorption into the visible region for the composite photocatalyst. The photocatalytic activity of the as-prepared WO3/TiO2 hollow spheres was investigated by the mineralization of methylene blue (MB) in an aqueous solution, and compared to TiO2. The photocatalytic mineralization of MB, catalyzed by TiO2 or WO3/TiO2 proceeded at a significantly higher rate under UV irradiation than that under visible light. Coupling TiO2 with WO3 more than doubles the rates of mineralization of MB, compared to TiO2 samples, which are due to the more efficient separation of the electron-hole charges generated upon irradiation. However, more significant was the increase in the apparent rate constant with the WO3/TiO2 composite semiconductor material which was 3.2 to 3.5 times larger than with the TiO2 material, under both UV and visible light irradiation. Moreover, the MB solution is almost completely degraded within 75 min by WO3/TiO2 hollow spheres irradiated under visible light. Under the same conditions, the degradation rate of MB is only 64% for TiO2 hollow spheres. Meanwhile, the mechanism of photocatalytic activity of WO3/TiO2 was studied.(2)Ag/TiO2 hollow spheres were prepared by hydrothermal method using Ag/C spheres as template. The UV-vis diffuse reflectance spectra (DRS) show an extension of light absorption into the visible region for the composite photocatalyst. The photocatalytic activity of the as-prepared Ag/TiO2 hollow spheres has been determined by degradation of MB in aqueous solution, and compared to TiO2. Moreover, the MB solution has been almost completely degraded at 45 min of reaction catalyzed by Ag/TiO2 hollow spheres. More significant was the increase in the apparent rate constant with the Ag/TiO2 composite semiconductor material, which was 12 and 1.5 times larger than that with the TiO2 material, under UV and visible light irradiation respectively.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalytic reaction
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