Semiconductor-catalyzed

Karunakaran C, Dhanalakshmi R (2008) Semiconductor-catalyzed degradation of phenols with sunlight. Sol Energy Mater Sol Cells 92 1315-1321... 

Therefore, it seems reasonable to suppose that in the semiconductor catalyzed oxidation of DPE, the resulting radical cation of the olefin could react with the superoxide anion to give a peroxy-ethy1-1,4-diradical which subsequently reacts with the olefin and oxygen through the free radical chain processes. 

Hydrazone cyclization and hydroalkylation [138-140] are rare examples of reactions conducted on a preparative scale, since the products were isolated in milligram amounts and not just identified in solution. As already mentioned in Section 6.2.5, photocorrosion of the semiconductor photocatalyst often prevents its use in preparative chemistry. This is very true also for colloidal semiconductors although the pseudo-homogeneous nature of their solutions allows one to conduct classical mechanistic investigations, until now they were too labile to be used in preparative chemistry [107, 141, 142]. In contrast to the above-mentioned reactions, in recent years we have isolated novel compounds on a gram-scale employing photostable zinc and cadmium sulfide powders as photocatalysts [97, 107, 143-145]. During this work we found also a new reaction type which was classified as semiconductor photocatalysis type B [45]. In contrast to type A reactions, where at least one oxidized and one reduced product is formed, type B reactions afford only one unique product, i.e., the semiconductor catalyzes a photoaddition reaction (see below). 

In the case of Ti02, ranged from 0.5 to 300. Quantum yields in excess of one provide strong evidence for a free-radical chain mechanism. These quantum yields are relatively high compared to tther photoassisted semiconductor-catalyzed redox reactions thus some contribution to the overall rate may, in fact, he due to a homogeneous free-radical chain pathway with a very low concentra-lion of freely diffusing initiator radicals (i.e., SOj, SO4, OH). 

K. Tokumaru, H. Sakuragi, T. Kanno, T. Oguchi, H. Misawa, Y. Shimamura and Y. Kuriyama, in Semiconductor-Catalyzed Photoreactions of Organic Compounds, M.A. Fox ed., ACS Symposium Series No. 278, American Chemical Society, Washington, D.C. (1985), p. 43. 

The potential applications of semiconductor-catalyzed organic functional group transformations for organic synthesis have been studied actively with two... 

Products of Semiconductor-catalyzed Molinate emd Thiobencarb Oxidation. Examination of the photooxid tion products of molinate by GC-MS provided evidence of seven substemces sufficiently stable 2uid concentrated to be chromatographed and detected by mass spectrometry (molinate sulfoxide und sulfone decomposed). 

Thus, application of ZnO to a rice field after herbicide treatment can be shown to provide an economical and agronomically-feasible means of degrading persistent pesticide residues before they reach public waterways. Intentional semiconductor-catalyzed photodegradation may, in fact, have much more general utility and might also be used to degrade many hazardous wastes under other circumstances. 

In this chapter, we examine the proposed model in more detail and develop quantitative solutions for the concentrations of constituents as a function of time in a hypothetical system similar to that examined in the laboratory. The insights developed from the results of such modeling should assist in developing a firmer understanding of the relative importance of processes such as adsorption, sensitization as well as competition effects in the semiconductor-catalyzed degradation of contaminants in complex aqueous environments. 

Approach to Quantitative Modeling of Semiconductor-Catalyzed Contaminant Photodegradation... 

Carbon dioxide is catalytically reduced to the formate ion by a suspension of zinc sulfide when the reaction mixture is irradiated at wavelengths longer than 290 nm. The reaction is carried out in a mixture of water and 2,5-dihydrofuran, with the latter acting as the reducing agent. 2-Propanol cannot be substituted for 2,5-dihydrofuran. The pathway of this semiconductor-catalyzed reaction likely... 

Fox, M. A. Chen, C. C. Mechanistic features of the semiconductor catalyzed olefin-to-carbonyl oxidative cleavage. Journal of the American Chemical Society 1981,17, 6757-6759. 

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