Titanium oxide, photoexcitation

Furthermore, as we saw in a foregoing section, photoexcitation produces in a semiconductor electrode electron-hole pairs and introduces a photo-potential, which reduces the space charge potential in the semiconductor. With an n-type semiconductor in contact with a corroding metal, photoexcitation raises the Fermi level up to the flat band level of the semiconductor, thus shifting the corrosion potential in the less positive direction toward the flat band potential of the n-type oxide as shown in Figure 22.35c. Photoexcitation therefore will shift the corrosion potential in the less positive (more cathodic) direction and the corrosion will then be suppressed. With some n-type oxides such as titanium oxide, photoexcitation brings the interfacial quasi-Fermi level, peF, down to a level lower than the Fermi level, F(redox> of the oxygen electrode reaction ... 

Figure 4.69 Examples of oxidation reactions of organic molecules at the surface of photoexcited titanium dioxide in polar solvents in the presence of molecular oxygen...

The actions of photoexcited semiconductor particles on organic compounds under oxygen is of significant importance from both practical and basic aspects. Semiconductors like titanium dioxide and cadmium sulfide were shown to induce oxidation of olefins and aromatic hydrocarbons under oxygen, and also to sensitize isomerization of unsaturated systems. The mechanisms of these reactions are discussed. 

This species was proposed to play an important role in the catalytic activation of H202 on TS-1. IR spectroscopic investigations showed that a Ti(t 2-OOH) moiety oxidized small alkenes at room temperature in the dark (propene) or upon photoexcitation (ethene). These data appear to be the first direct detection of the active oxidation site in H202-loaded titanium silicalite (Lin and Frei, 2002). 

Heterogeneous photocatalysis is a process in which illumination of an oxide semiconductor, usually the anatase form of titanium dioxide, produces photoexcited... 

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