(physical chemistry) The phenomenon by which a relatively small amount of light-absorbing material, called a photocatalyst, changes the rate of chemical reaction without itself being consumed.
Photocatalysis
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(′fōd·ō·kə′tal·ə·səs)
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Promotion or stimulation of a chemical reaction by light.
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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 radicals: ·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 (AOP). 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 radical.
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Applications
- Conversion of water to hydrogen gas by photocatalytic water splitting.[1] An efficient photocatalyst in the UV range is based on a sodium tantalum oxide NaTaO with cocatalyst nickel oxide. The surface of the sodium tantalum oxide crystals is grooved with so called nanosteps that is a result of doping with lanthanum (3-15 nm range, see nanotechnology). The NiO particles which facilitate hydrogen gas evolution are present on the edges, the oxygen gas evolves from the grooves.
- Use of titanium dioxide in self-cleaning glass. Free radicals[2] generated from TiO2 oxidize organic matter.[3]
- Disinfection of water by titanium dioxide photocatalysis.[4]
- 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.[5]
- Conversion of carbon dioxide into gaseous hydrocarbons using titanium dioxide in the presence of water.[6] As an efficient absorber in the UV range, titanium dioxide nanoparticles in the anatase and rutile phases are able to generate excitons by promoting electrons across the band gap. The electrons and holes react with the surrounding water vapor to produce hydroxyl radicals and protons. At present, proposed reaction mechanisms usually suggest the creation of a highly reactive carbon radical from carbon monoxide and carbon dioxide which then reacts with the photogenerated protons to ultimately form methane. Although the efficiencies of present titanium dioxide based photocatalysts are low, the incorporation of carbon based nanostructures such as carbon nanotubes[7] and metallic nanoparticles[8] have been shown to enhance the efficiency of these photocatalysts.
See also
References
- ^ Kudo, Akihiko; Hideki Kato; Issei Tsuji (2004). "Strategies for the Development of Visible-light-driven Photocatalysts for Water Splitting". Chemistry Letters 33 (12): 1534.
- ^ "Snapcat Photo Catalytic Oxidation with Titanium Dioxide (2005)". CaluTech UV Air. http://www.calutech.com/photocatalytic-oxidation.htm. Retrieved 2006-12-05.
- ^ "Photocatalysis Applications of Titanium Dioxide TiO2". Titanium Information. titaniumart.com. http://www.titaniumart.com/photocatalysis-ti02.html.
- ^ McCullagh C, Robertson JMC, Bahnemann DW, Robertson PKJ (2007). "The application of TiO2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review". Research on Chemical Intermediates 33 (3-5): 359–375. doi:.
- ^ Kostedt IV, William L.; Jack Drwiega; David W. Mazyck; Seung-Woo Lee; Wolfgang Sigmund; Chang-Yu Wu; Paul Chadik (2005). "Magnetically agitated photocatalytic reactor for photocatalytic oxidation of aqueous phase organic pollutants". Environmental Science & Technology (American Chemical Society) 39 (20): 8052-8056. http://pubs.acs.org/doi/abs/10.1021/es0508121.
- ^ Tan, S. S.; L. Zou; E. Hu (2006). "Photocatalytic reduction of carbon dioxide into gaseous hydrocarbon using TiO2 pelllets.". Catalysis Today 115: 269-273.
- ^ "Photoreactive TiO2/Carbon Nanotube Composites: Synthesis and Reactivity". Environmental Science & Technology (American Chemical Society) 42: 4952-4957. 2008.
- ^ Linsebigler, A. L.; G. Lu; J.T. Yates (1995). "Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results". Chemical Review 95: 735-758.
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