Photocatalytic surfaces for cleaning urban air using semi-conductor nanomaterials
Photocatalytic oxidation has shown to be a promising and effective technology for pollution control (Yu et al. 2002; Fujishima et al. 2000; Obuchi et al. 1999.). Unlike traditional pollution control methods such as adsorption which merely transfers pollutants from gas phase to solid phase 1 photocatalytic oxidation actually oxidises pollutants to CO2 and H2O.1 Photocatalysis emerged as a promising technology in 1972 when Fujishima and Honda split water into oxygen and hydrogen with a TiO2 i- Pt element.4 In addition to water splitting for fuel cell applications photocatalysis is attractive in air and water pollution control due to its potential to use solar energy. 2 In order to allow practical and economical implementation of photocatalysts in the chemical fields of pollutant elimination 3 researchers must produce visible light activated photocatalysts. Titanium dioxide (TiO2) has been leading the photocatalytic research field for a number of years. It exists in three different crystal forms: anatase rutile and brookite (Figure 1). It is widely acknowledged that anatase is the most photoactive of the three.456 but this can be attributed with the decrease in surface area associated with rutile crystal formation. Degussa P25 is a well-known and widely investigated photocatalyst due to its high activity for many kinds of photocatalytic reaction. It has been found that there is a positive interaction between anatase and rutile TiO2 particles in Degussa P25 powders which enhances the electron-hole separation and increases the total photocatalytic activity. The mixing of an active oxidizing phase (anatase 75%) with a comparatively inactive phase (rutile 25%) can produce a kind of photocatalyst with unusually high activity. The intimate contact between two phases might be sufficient to enhance the separation of photogenerated electrons and holes and result in the highphotocatalytic activity of TiO2.7.
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Environmental Protection Agency 2006-S-ET-8
Keywords: Photocatylitic oxidation; Air Pollution Control; Water Pollution Control; Solar Energy