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|Titanium Dioxide Photocatalysis – one approach to self cleaning ceramic surfaces|
Titanium dioxide has recently gained a lot of interest in the development of the self-cleaning surfaces through photocatalysis. The oxidation of hydrocarbons, which are common contaminants on several surfaces, is a slow process, but can remarkably be accelerated with the help of photocatalyst, such as titanium dioxide, creating strongly oxidative conditions on the surface. Such semiconducting particles in contact with a liquid or gaseous medium generate under exposure of light exited states which are able to inititate redox reactions and molecular transformations.
In 1972 Fujishima and Honda  discovered the photocatalytic splitting of water on TiO2 electrodes. This was a beginning of strong development of heterogeneous photocatalysis. Titanium dioxide has three polymorphs: rutile, brookite and anatase. Anatase shows the highest photoactivity. TiO2 is a semiconductor with the band gap energy of 3.2 eV. The photons having the energy > 3.2 eV ( wavelength < 388 nm, UV light, about 5% of the solar light reaching the surface of the earth) can promote an electron from the valence to the conduction band which results in chemical reactions on the surface creating either highly reactive hydroxyl radicals or superoxide ions which both are very powerful oxidants capable to oxidize most organic contaminants.
The heterogeneous photocatalytic oxidation with TiO2:
Figure 1 describes the major areas of activity in titanium dioxide photosynthesis.
Recently a lot of research is done to extend the range of photocatalysis wider to the range of wave lengths of visible light [2,3]. This is also one aim in SHINE PRO -project. In addition to that further techniques, ALD (Atomic Layer Deposition), Sputtering, Thermal Spraying and Sol-Gel synthesis, are studied to produce such photocatalytically active surfaces on different materials.
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