A series of Ag/TiO2 with various Ag loadings were prepared by incipient-wetness impregnation method. P25 TiO2 from Evonik-Degussa was used because it has both anatase and rutile phase and is very active. The aim of this study was to improve the activity of this material under twilight illumination. The catalysts were characterized by X-ray diffraction, high resolution-transmission electron spectroscopy, and X-ray photoelectron spectroscopy. Methylene blue dye was chosen for destruction to test its photocatalytic activity under low intensity UV light and visible light illumination, similar to twilight. Some of the Ag cations were incorporated into the surface structure of TiO2, resulting in more hydroxyl groups and defect sites on the surface. This would lift the valence band. The presence of Ag could trap electrons and have plasmon effect. However, too much amount of Ag would cover the surface of TiO2 and suppress activity. Adding Ag on TiO2 increased activity significantly under UV light irradiation. Pure TiO2 does not have activity under visible light illumination. Adding Ag on TiO2 would have activity even under low intensity of visible light illumination. The activity of 1.5 Ag/TiO2 was 7 times higher than pure TiO2 under UV light illumination, and only 2.5 times higher under visible light illumination.
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