Photo-catalytic titanium dioxide

GoB, D., Frach, P, Zywitzki, O., Modes, T., Klinkenberg, S. and Gottfried, C. (2005). Photo-catalytic titanium dioxide thin films prepared by reactive pulse magnetron sputtering at low temperature. Surf. Coat. Technol. 200( 1—4), 967-971. 

Baker MN, Taras Ml (1981) The quest forpure water. American Waterworks Association, Denver Bandala ER, Gelover S, Leal MT, Arancibia-Bulnes C, Jimenez A, Estrada CA (2002) Solar photocatalytic degradation of Aldrin. Catal Today 76(2-4) 189-199 Banerjee S, Gopal 1, Muraleedharan P, Tyagi AK, Raj B (2006) Physics and chemistry of photo-catalytic titanium dioxide visualization of bactericidal activity using atomic force nucroscopy. Curr Sci 90(10) 1378-1383... 

To be used as photocatalysts, especially in the so-called clean technologies, active materials must fulfill the following requirements (1) very low toxicity, (2) resistance to photo-corrosion, (3) high availability, (4) high catalytic efficiency, and (5) low cost. From all the materials cited above, titanium dioxide and its derivatives seem to offer the best answer to these requirements, being by far the most commonly utilized photocatalysts. To be used in gas-phase photocatalysis, in addition to the above requirements, two other conditions are still necessary, that is, a very small pressure drop and an easy recovery. 

The surfaces of mtile Ti02 have been the subject of intense research because of their photo-catalytic properties for the dissociation of water. The hydroxylation rate on the surface and the kinetics of the reaction were shown to depend strongly on the surface stoichiometry and detailed atomic structure. In addition, like the two above surfaces of sapphire and magnesium oxide, rutile titanium dioxide surfaces stand as model metal oxide surfaces. Their atomic structure is thus of fundamental interest. 

Photo-catalysis is the acceleration of a photochemical reaction in the presence of a catalyst. In photo-catalysis, hght is absorbed by the catalyst. In photo-generated catalysis, the photo-catalytic activity depends on the ability of the catalyst to create electron-hole pairs, which generate free radicals (e.g. hydroxyl radicals OH) able to undergo secondary reactions. Its practical application was made possible by the discovery of water electrolysis by means of titanium dioxide. 

Ti02 and metal-doped Ti02 are prone to a variety of applieations such as catalytic gas-phase conversion of moleeules or photo-oxidation of organic molecules in aqueous solutions [117]. For the first aspect, titanium dioxide exhibits a very rich surface organie chemistry, due to the ability of titanium cations to exist in different oxidation states and coordination envirorunents [118]. On the other hand, the interfaces between highly dispersed metal phases on the Ti02 substrate may deeply influenee the macroscopic behaviour of these materials, in view of the modifieations of the eleetronie structure, morphology and thermal stability of the metal [119]. 

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