Study On Structure And Properties Of Titanium Dioxide

Since the 1970 s, TiO₂ had been investigated widely because of the unique advantages. As semiconductor material, when TiO₂ irradiated by the light source, the electron in the valance band will transited to the conduction band, forming electron-hole pairs. In the electron-hole pairs, the photo-generated electrons have a strong reduction. And the oxygen atoms will convert to superoxide ions by complex with the electrons. Most organics can be oxidized by the photo-generated holes with strong oxidation. Compared with the general semiconductor materials, TiO₂ semiconductor belonging to wide band-gap semiconductor materials, the light-generated electron-hole pairs have a higher oxidation reduction potential, so the excited electrons and holes complex hardly. It is precisely because of this feature, TiO₂ has broad prospects in the super-hydrophilic properties, environmental management and energy development. But because of its wide band gap, so that the response of sunlight in the ultraviolet range of the following limitations, which greatly limits the use of TiO₂ material of sunlight.In practical applications of TiO₂ catalyst, mainly in three aspects: clean energy materials, photo-catalytic materials and super-hydrophilic material. And in this paper, the photo-catalytic and super-hydrophilic property is the focus of research. When TiO₂ as super-hydrophilic material, which exist mainly in the thin film state. As super-hydrophilic materials, TiO₂ has better Super-hydrophilicity irradiated by the light, but the TiO₂ film can’t keep Super-hydrophilicity for long time with loss of the light, in order to overcome the disadvantage, several ways have been adopted. Also as photo-catalytic materials, TiO₂ has several advantages, no secondary pollution and so on. In the catalytic processes, photo-generated electrons as the reducing agent, the photo-generated holes as the oxidation agent. so many of organics can be treated. However, because of the wide band gap, TiO₂ required lots of improvements, reducing energy consumption in the catalytic process.In this paper based on the sol-gel theory, discussed the influence of TiO₂ by Co、S codoped, the light absorption properties and corresponding mechanism of doped catalysts were studied. At the same time, the composite TiO₂ films were successfully obtained by dip-coating machines, then placed the films in the dark room. Investigating the super-hydrophilicity of the TiO₂ films precoated SiO₂ films. The experimental results shows:1. The TiO₂ powder catalysts and TiO₂ films had prepared successfully by sol-gel. The powders and the films was characterized by X-ray diffraction, the results showed that the powder catalysts exhibited a single crystal structure of anatase without rutile after heat treatment for one hour. But the films included two crystal structure after heat treatment for 1.5 hours, wherein the anatase content of 96.8%, rutile content of 3.2%. And this crystal structure is good for the super-hydrophilicity.2. The（Co, S） / TiO₂ grains size decrease as the doping concentration increases within a certain range of doping. Due to the lower crystallinity, the crystal spacing also had some shrinkage. Meanwhile, compared to the undoped TiO₂ catalyst,（Co, S） / TiO₂ powder catalyst absorption of visible light produced a clear red shift, and the threshold of undoped samples is nearly 400 nm. Samples（4,5） showed good light absorption properties, its optical response thresholds improved significantly, reaching near-infrared region of 785 nm. The results showed that the properties of visible light response had been significantly improved.3. The experiment results showed that the surface structure of TiO₂ films non-precoated TiO₂ films were smooth, but the precoated films were poly-porous. The non-precoated films were out of super-hydrophilicity after 6 hour. while the contact angle of TiO₂ films precoated SiO₂ kept under 10°after 30 hours. Among the films precoated SiO₂, two layers of TiO₂ films showed the excellent property, the contact angle was only 6.7°.