Photocatalysis composite semiconductors

Chapters 12 and 13 cover two of the most important novel catalytic applications of carbon materials, electrocatalysis and photocatalysis. In the first case, carbons are used mostly as supports for metal catalysts in fuel cells, while the synergistic effects of carbon-based composite semiconductor materials, such as C-TiOi, make them particularly effective in photocatalytic degradation reactions. 

K. Vinodgopal, I. Bedja, P.V. Kamat, Nanostructured semiconductor films for photocatalysis. Photoelectrochemical behavior of Sn02/Ti02 composite systems and its role in photocatalytic degradation of a textile azo dye, Chem. Mater. 8 (1996) 2180-2187. 

Titanium dioxide (Ti02) is one of the most widely used semiconductors for heterogeneous photocatalysis. This is mainly due to its activity, photostabihty, non-toxicity and commercial availability. It is found in nature and can exist in three crystal modifications rutile, anatase and brookite (Kirk-Othmer, 1996). Its composition is temperature dependent at calcination temperatures above 900 K, the anatase modification is transformed into rutile. Ti02 is insoluble in water and in diluted acids, but it dissolves slowly in hot sulfuric acid (Remy, 1973). It has a high surface activity and corrosion stabihty. The commercial production of this white pigment has been known since the early 1900s. 

For example, certain soil components can act as adsorption sites for organic materials and facilitate their photodecomposition upon exposure to sunlight. In the case that the soil component is a semiconductor, this process can occur through the formation of electron-hole pairs (i.e., photocatalysis, see Chapter 10). Photochemical processes may then affect soil components and composition. 

Titanium oxide Titanium dioxide with the nominal composition Ti02 is a semiconductor with a band gap of 3.2 e V it exists in three different crystalline modifications, two of which (anatase and rutile) are commonly employed in photocatalysis. 

Perovskite semiconductors and related materials, among a large number of other applications, are widely used in photocatalysis, especially in the photogeneration of hydrogen. Their adaptation includes new preparation strategies, supporting the active phase, development of composite materials, doping with anions and cations to induce lattice defects, and the exploitation of the surface plasmon resonance of the noble metals. 

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