Environmental Cleaning by Molecular Photocatalysts

Visible light absorbing organic photosensitizers and photocatalysts active in photodegradation of pollutants were described in this chapter. An important reactive is singlet oxygen obtained by energy transfer from the photoexcited sensitizer to triplet oxygen (photosensitized oxidative degradation). The other possibility when the photosensitizer is on the surface of inorganic semiconductors like TiO is formation of superoxide radicals (photocatalytic oxidative degradations). The degree of degradation depending on the reactivity of the pollutants was discussed against these reactive species. It was shown that visible light photons have sufficient energy which can be transformed into highly reactive species of oxygen for degradation of pollutants. Technical applications were shown. In general the use of solar visible light is relatively open field for oxidative degradation of pollutants. In the Sect. 11.2 oxidative methods for photodegradation of pollutants were described. At first a short overview on UV processes for water cleaning was given in the Sect. 11.2.1. More details of photodegradation of pollutants with oxygen by the visible light were described in the Sect. 11.2.2. Visible light decomposition of ammonia to dinitrogen in the presence of a photosensitizer based on electron relay (photo-induced electron transfer) was shown in the Sect. 11.3. The photodecomposition of aqueous ammonia with visible light into N was achieved by a photocatalytic system consisting of a sensitizer, an electron mediator, and an electron acceptor (O) as an artificial nitrogen cycle. Finally, in the Sect. 11.4 the use of thin films of visible light absorbing organic semiconductors for the photodecomposition of pollutants was described. Thin films of an organic p-conductor and an organic n-conductor on Nafion were active by irradiation with visible light in the photocatalytic oxidation of amines.