Metals heterogeneous photocatalysis

Heterogeneous Photocatalysis. Heterogeneous photocatalysis is a technology based on the irradiation of a semiconductor (SC) photocatalyst, for example, titanium dioxide [13463-67-7] Ti02, zinc oxide [1314-13-2] ZnO, or cadmium sulfide [1306-23-6] CdS. Semiconductor materials have electrical conductivity properties between those of metals and insulators, and have narrow energy gaps (band gap) between the filled valence band and the conduction band (see Electronic materials Semiconductors). 

Litter, M.I. 1999. Heterogeneous photocatalysis transition metal ions in photocatalytic systems. Appl Catal B Environ 23 89-114. 

Litter MI. Heterogeneous photocatalysis. Transition metal ions in photo-catalytic systems. Appl Catal B Environ 1999 23 89-114. 

Serpone, N. Lawless, D. Terzian, R. Minero, C. Pelizzetti, E. Heterogeneous photocatalysis Photochemical conversion of inorganic substances in the environment Hydrogen sulfide, cyanides, and metals. In Photochemical Conversion and Storage of Solar Energy, E. Pelizzetti, M. Schiavello, eds., Kluwer Acad. Publ. Dordrecht, The Netherlands, 1991. 

Photo-initiated AOPs are subdivided into VUV and UV oxidation that are operated in a homogeneous phase, and in photocatalysis (Fig. 5-15). The latter can be conducted in a homogeneous aqueous phase (photo-enhanced Fenton reaction) or in a heterogeneous aqueous or gaseous phase (titanium dioxide and certain other metal oxide catalysts). These techniques apply UV-A lamps or solar UV/VIS radiation and they are in pre-pilot or pilot status. According to Mukhetjee and Ray (1999) the development of a viable and practical reactor system for water treatment with heterogeneous photocatalysis on industrial scales has not yet been successfully achieved. This is mainly related to difficulties with the efficient distribution of electromagnetic radiation (UV/VIS) to the phase of the nominal catalyst. 

Treatment of Heavy Metals and Metalloids in Water by Heterogeneous Photocatalysis... 

In view of the enormous literature published on the subject, only the cases of chromium, mercury, lead, uranium, and arsenic are reviewed here. In 1999, we published an extensive review on metal treatment by heterogeneous photocatalysis in which the early literature is mentioned (Litter, 1999). In this chapter, we will remind the most important issues and update the most recent information. 

Heterogeneous photocatalysis on semiconductor particles has been shown to be an effective means of removing toxic organic pollutants as well as toxic metal ions from water. In the first part of this chapter, systematic kinetic... 

There has been recent interest in a somewhat different aspect of adsorption and reaction on metal oxides photocatalysis. The interest stems partially from that role that some transition-metal oxides can play in photochemical reactions in the atmosphere. Atmospheric aerosol particles can act as substrates to catalyze heterogeneous photochemical reactions in the troposphere. Most tropospheric aerosols are silicates, aluminosilicates and salts whose bandgaps are larger than the cutoff of solar radiation in the troposphere (about 4.3 eV) they are thus unable to participate directly in photoexcited reactions. However, transition-metal oxides that have much smaller bandgaps also occur as aerosols — the most prevalent ones are the oxides of iron and manganese — and these materials may thus undergo charge-transfer excitations (discussed above) in the pres-... 

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