| dc.description.abstract | The objective of this research was to develop a photocatalyst which is active in photoreaction to destruct organic compounds in waste gas and waste water. Noble metal deposited on titanium dioxide has been widely studied as a modified photocatalyst in organic pollutants destruction under UV light irradiation. However, noble metals such as Pt, Pd, Rh, and Au are too expensive to be used in industrial application. In order to find an efficient way to improve the quantum efficiency of photocatalyst, we increase the numbers of active sites by silver deposition. The materials we studied were silver modified titanium dioxide synthesis by sol–gel method, chemical deposition, and photodeposition.
In sol–gel process, neutral suspension silver titanium dioxide sol was successfully prepared using titanium tetrachloride, ammonia, hydrogen peroxide, and silver nitrate. The nanoparticles in the sol were characterized by X–ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR–TEM) and X–ray photoelectron spectroscopy (XPS). Titanium dioxide has anatase–type structure in rhombus shape and the size of silver was about 2 nm. The sol of titanium dioxide and silver titanium dioxide are easy coating on the surface of glass substance by dip–coating method, and properties of the films were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), and contact angle analysis. The thickness of the films was 700 to 1200 nm depending on the coating times and the films showed super–hydrophilic property under UV light scattering. Both the sols and the films of titanium dioxide and silver titanium dioxide were completely destruct methylene blue under UV light irradiation, and the concentration of methylene blue was measured by UV–vis spectroscopy (UV–vis). The results showed that the photoefficiency of silver titanium dioxide is higher than titanium dioxide.
In chemical deposition process, silver titanium dioxide was prepared using P–25 titanium dioxide, silver nitrate, cetyltrimethyl ammonium bromide, and sodium borohydride as materials. Inductively–coupled plasma–mass spectrometry (ICP–MS) were used to determined the contents of silver in the silver titanium dioxide. The particle size of silver on TiO2 was about 5–10 nm. The results of MB degradation under UV light irradiation showed that Ag/TiO2 had a higher activity than TiO2.
In photodeposition process, silver titanium dioxide was prepared using P–25 titanium dioxide, and silver nitrate as materials, and UV light scattering time was 15 minutes at room temperature. Inductively–coupled plasma–mass spectrometry (ICP–MS) was used to determined the contents of silver in the silver titanium dioxide. The particle size of silver on TiO2 was about 1.5–2.5 nm. The results of MB degradation under UV light irradiation showed that Ag/TiO2 had a higher activity than TiO2.
Silver titanium dioxide synthesized by photodeposition showed the best photoactivity in this study due to the smaller silver particles attached on titanium dioxide surface with high dispersion. Silver nanoparticles could successfully deposit on TiO2 surface and play important roles as electron traps. Without being recombination centers of electrons and holes, silver nanoparticles increase the actives sites and make electrons easily act with the adsorbed substances such as O2 and OH– and form O2– and OH radical. The reactive species could degrade the MB efficiently into small molecules like CO2, H2O, and etc. However, silver amounts is proposed not to be the determined factor in the synthesis, but the dispersion, particle size and attachment style of Ag.
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