Preparation Of Controllable Crystalline Titania And Study On The Visible Light Photocatalytic Properties

In recent yeas, semiconductor photocatalysts have evoked tremendous interest in the light-stimulated degradation of aqueous pollutants and atmospheric pollutants. Titanium dioxide photocatalysis has been the focus of the investigation, particularly because of its high photocatalytic activity and its stability with respect to photocorrosion and chemical corrosion.Nanometer titanias in different crystal structures with high specific surface area have been prepared by the hydrolysis solvothermal method using titanium alkoxides as starting materials under acidic condition. The effect of reaction conditions on the crystal structure and the formation mechanism of controlled synthesis for titania nanocrystals in liquid media were investigated. Furthermore, the origin of photocatalytic activity under visible light irradiation and the mechanism of the photocatalytic reaction were discussed.In the paper, the influences of preparation condition such as the ration of water and raw material, temperature and time on the crystal phase, size of the products were discussed. The ratio of water and raw material has significant effect on the phase composition of the final titania powders. With the increasing of the ratio, the content of rutile increases. There is a linear relationship when the ration is more than 30:1. Thus, the phase composition can be controlled by just changing the ratio of water and raw material. The content of rutile will increases when the temperature increases or the time is prolonged, and the size of the nanoparticles will increases too.The results revealed that the formation of the mixed phase is related to the kinds of the TiO₆ octahedrons (growth units) and their modes of arrangement during reaction process. Under different synthesis conditions, the growth units which are consistent with different polymorphs by hydrolysis, olation and oxolation, transform subsequently to nuclei with a certain polymorph, finally form the crystallites of certain phase andsize.The titanias with different crystal structures have high visible light photocatalytic activity. The degradation of MO within 30min could achieve as high as 89.9% under visible light irradiation (> 450nm). The improvement of the photocatalysis in the aspects of the quantum efficiency and visible light response has been discussed on the base of the surface status and the properties of light absorption. Moreover, the transfer process of the charge between rutile and anatase under the visible light irradiation has been investigated. The effects of the mixed phase the particle size and surface status on the photocatalytic activity under visible light irradiation have been concluded.