| TiO2 semiconductor photocatalytic oxidation has received considerable attention for the treatment of biorefractory wastewater, since many organic compounds have proved to be degraded effectively to CO2, H2O and small molecules. However, TiO2 can only utilize a relative small part (less than 5%) of the solar spectrum for photocatalytic oxidation and artificial UV light sources are unstable and expensive, which are main barriers to marketing the TiO2 photocatalytic processes. Therefore, the use of visible light of solar energy, which is free and inexhaustible, has recently drawn considerable attention. Early studies reported that dye pollutants can be degraded effectively in the presence of TiO2 particles under visible light irradiation, which provide a new method for the treatment or pre-treatment of dye-containing wastewater. In this work, silica gel supported titanium dioxide particles (TiO2/SiO2) prepared by acid-catalyzed sol-gel method was used as photocatalyst. The effects of preparing conditions and physical characterizations of the supported photocatalyst on the photoactivity were investigated. The photoactivity of supported catalyst was promoted significantly when the catalyst was modified by metallic silver. Moreover, the deactivation of the catalyst and the photodegradation pathway of Acid Orange 7 (AO7) under UV or visible light irradiation were also discussed in detail.Silica gel supported titanium dioxide particles (TiO2/SiO2) prepared by acid-catalyzed sol-gel method was used as photocatalyst for the photodegradation of AO7 under visible light irradiation. The effects of preparing conditions such as calcination temperature, TiO2 loading, initial pH and calcination time on the physical characterization and the photoactivity were investigated. The supported catalysts were characterized by X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (TG-DTA), BET specific surface area determination (BET), and scanning electron microscopy (SEM). The results indicated that the major phase of TiO2/SiO2 particles was pure anatase and the average crystallite size of anatase was about 5.0 nm. It was observed form SEM photograph that a layer of porous fractured TiO2 film adhered well to the surface of silica gel. The presence of silica gel inhibited the phase transformation of TiO2 from anatase to rutile and the TiO2 particles were dispersed well on the surface of the silica gel. Due to its large surface area, mesoporous structure, pure anatase structure and high adsorption capacity, the photoactivity of 31%TiO2/SiO2 was much higher than that of the puretitanium dioxide. Moreover, the supported catalyst had good sedimentation ability so that it was easy to recovery form the suspension.The influence of operational variables such as initial dye concentration, TiO2/SiO2 amount, pH and temperature on the photodegradation of AO7 under visible light irradiation was investigated. In TiO2/Vis system, AO7 could be decomposed easily; concomitantly, part of benzene and naphthalene ring of the dye was destroyed. After the suspensions were completely discolored, the reaction intermediates were no longer mineralized under further irradiation by visible light. The results suggested that the photodegradation of AO7 under visible light irradiation was through the photosensitization way. Under visible light irradiation, the adsorption was a precondition for the degradation and the strong adsorption was significantly effective to accelerate the rate of electron transfer from the conduction band to molecular oxygen, resulting hi the enhancement of the degradation rate of AO7. In addition, the strong adsorption could accelerate the mineralization rate of AO7, but could not promote the final mineralization yield of the dye.A set of supported TiO2 photocatalysts loaded with various ions of transition metal (Co2+, Cu2+, Fe3+, Mo6+) and silver were prepared by using wet impregnation and photodeposition methods. Loading TiO2 with Co2+, Cu2+, Fe3+and Mo6+ caused a significant decrease of TiO2 photocatalytic activit...
|
PDF Full Text Request