Water and air detoxification

Application of heterogeneous photocatalysis to water and air purification appears a particularly convenient method in the cases of easily accessible UV light (mainly solar, but also artificial) and diluted pollutants. H02-based photocatalysis offers unique possibilities of mineralization of most organic compounds and, in addition, sterilization. This type of AOP useful for water and air purification has been studied and developed extensively over the last few decades. UV light, especially as a part of solar radiation, must be used to activate this process. In addition oxygen and water are indispensable. 

Photocatalytic systems became a subject of many detailed studies and improvements. A need to compare photocatalytic activity of various materials enforced selection of a model pollutant . Perhaps the most commonly chosen is 4-chloroph-enol (4-CP) [56, 57]. The route of 4-CP oxidation in the presence of excited Ti02 was described in many original and review papers [58-64], The oxidative pathway includes attack of hydroxyl radicals or direct oxidation with a hole leading to 

Up to now hundreds of organic and inorganic compounds have been successfully degraded in the photomineralization process [60,65], Photodegradation processes may be useful for either water or air purification. There are several reports also on photocatalyzed removal of selected inorganic ions such as CN [66], NO3 

Although the dye sensitization method can be very efficient, its application in photocatalytic water purification is usually very limited due to a low stability of such systems. 

Photocatalytic C02 reduction over simple oxide semiconductors, although characterized by low efficiencies, might contribute to natural processes occurring in atmosphere of young Earth (see section 10.3, Chapter 10). More sophisticated systems developedi in future may be useful for C02 utilization as a substrate for production of chemicals. Until now yields of these processes, usually allowing formation of micromoles of products, are still not sufficient. Selected examples of C02 reduction in heterogeneous photocatalytic systems are described below. 

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