Water photocatalysis

For the treatment of air and water, photocatalysis over Ti02 is a technique that is simple, robust, easily automated, and flexible. It is versatile because organic pollutants, some inorganic pollutants, and microorganisms can be eliminated or inactivated, respectively. In water, some ions can also be transformed. Its operating cost arises mainly from the UV lamps and the corresponding electrical consumption. Provided that the needs and location of the treatment allow it, this cost can be reduced substantially by the use of solar irradiation instead of UV lamps. For these reasons, photocatalytic water purification appears well adapted to isolated communities, in particular if no competent labor force is available. 

Water Treatment. Several components must be treated simultaneously in a multicomponent mixture as available in wastewaters to prove the technology of heterogeneous photocatalysis. The formation and subsequent elimination of intermediates in the photooxidative process must be monitored, identifying all intermediates and final products. 

Studies have appeared where photolysis in natural bodies of water under normal sunlight conditions has been examined. For example, metolachlor was slowly photodegraded by sunlight in lake water, with a half-life of 22 days in summer and 205 days in winter (28). Addition of a 5% solution of dissolved organic matter to the water extended the half-Hves two to three times longer, depending on the season (see PHOTOCHEMICAL TECHNOLOGY, photocatalysis). ... 

Nonbiological methods for removal of trichloroethylene from water are also being studied. These include the use of a hollow fiber membrane contactor (Dr. A.K. Zander, Clarkson University), photocatalysis by solar or artificially irradiated semiconductor powders (Dr. G. Cooper, Photo-catalytics, Inc.), and micellar-enhanced ultrafiltration (Dr. B.L. Roberts, Surfactant Associates, Inc.). 

Recently, we have shown that the combination of barium tetratitanate, BaTi40g and sodium hexatitanate, NagTigOis, with ruthenium oxides leads to active photocatalysts for water decomposition[1,2]. The unique feature of these photocatalysts is that no reduction of the titanates is required to be activated this is intrinsically different from conventional photocatalysts using TIO2 which are often heat-treated in a reducing atmosphere. Such different photocatalytic characteristics suggest that efficiency for the separation of photoexcited charges (a pair of electrons and holes) which is the most important step in photocatalysis is... 

Like water, the interaction of 02 with Ti02 also has implications for photocatalysis. As with water again, reactions of 02 with Ti02 are also important because 02 will form part of the environment in many Ti02 applications. 

High-resolution STM and NC-AFM images have appeared both at elevated pressures and in liquids, and one would expect a great deal of attention to be focused in this direction over the coming years. An area of particular topical interest is the interface between light harvesting surfaces (e.g., Ti02) and liquid water in connection with photocatalysis. 

Matthews RW, McEvoy SR (1992) Destruction of phenol in water with sun, sand and photocatalysis. Sol Energy 49(6) 507-513... 

The problem of wastewater treatment is one of the issues where photocatalysis plays a major role. Some model molecules are used to mimic the most common water pollutants, and among these, dyes and phenols are the most commonly used. 

Oxidation reactions are the most studied processes owing to the well-known ability of illuminated Ti02 in water to produce reactive oxygen species. In this context, heterogeneous photocatalysis could contribute to the replacement of hazardous compounds such as KMn04 and K2Cr20 [13]. 

Mills, A., Davies, R.H. and Worsley, D. (1993) Water purification bysemiconductor photocatalysis. Chemical Society Reviews, 22 (6), 417-425. 

Fernandez, P., Blanco, J., Sichel, C., and Malato, S. (2005) Water disinfection by solar photocatalysis using compound parabolic collectors. Catalysis Today,... 

Note Catalyst, 1 g (Ti02 0.3 g) water, 350 mL Na2C03, optimum quantity. An inner irradiation-type quartz cell, high-pressure Hg lamp (400 W) from Arakawa, H. and Sayama, K., Photocatalysis, Science and Technology, Kodansha/Springer, Berlin, 2002. 

Domen, K. and Hara, M., Water photolysis by layered compounds, in Photocatalysis, Science and Technology, Kaneko, M. and Okura, I. (Eds), Kodansha/Springer, Berlin, 2002, Chap. 16. 

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