Photocatalysis
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In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalysed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis the photocatalytic activity (PCA) depends on the ability of the catalyst to create electron–hole pairs, which generate free radicals (hydroxyl ions; OH-) able to undergo secondary reactions. Its comprehension has been made possible ever since the discovery of water electrolysis by means of the titanium dioxide. Commercial application of the process is called Advanced Oxidation Process(es) (AOP) [1]. There are several methods of achieving AOP's, that can but do not necessarily involve tiO2 or even the use of UV. Generally the defining factor is the production and use of the hydroxyl ion.
Examples:
- Conversion of water to hydrogen gas by water splitting photocatalysis [1]. An efficient photocatalyst in the UV range is based on an tantalum oxide NaTaO3 with cocatalyst nickel oxide. The surface of the tantalum oxide crystals is grooved with so called nanosteps (3-15 nm range, see nanotechnology). The NiO particles from which the hydrogen gas evolves are present on the edges, the oxygen gas evolves from the grooves.
- Use of titanium dioxide in self cleaning coatings. Free radicals [1]generated from TiO2 oxidize organic matter. [2]
- Oxidation of organic contaminants using magnetic particles that are coated with titanium dioxide nanoparticles and agitated using a magnetic field while being exposed to UV light [2].
[edit] External source
- [1] Strategies for the Development of Visible-light-driven Photocatalysts for Water Splitting Akihiko Kudo, Hideki Kato1 and Issei Tsuji Chemistry Letters Vol. 33 (2004) , No. 12 p.1534
- [2] Kostedt, W. L., IV.; Drwiega, J; Mazyck, D. W.; Lee, S.-W.; Sigmund, W.; Wu, C.-Y.; Chadik, P. Magnetically agitated photocatalytic reactor for photocatalytic oxidation of aqueous phase organic pollutants. Environmental Science & Technology 2005, 39(20), 8052-8056.
