Semiconductors photocatalysis using

In most studies, heterogeneous photocatalysis refers to semiconductor photocatalysis or semiconductor-sensitized photoreactions, especially if there is no evidence of a marked loss in semiconductor photoactivity with extended use. It is meant here that the initial photoexcitation takes place in the semiconductor catalyst substrate and the photoexcited catalyst then interacts with the ground state adsorbate molecule [209]. 

Photocatalysis uses semiconductor materials as catalysts. The photoexcitation of semiconductor particles generates electron-hole pairs due to the adsorption of 390 run or UV light of low wavelength (for Ti02). If the exciting energy employed comes from solar radiation, the process is called solar photocatalysis [21],... 

The limiting factors that control photocatalysis efficiency are rapid recombination between photo-generated charge carriers, and the backward reaction leading to recombination of the formed molecular hydrogen and oxygen. To retard these processes efforts have typically focused on surface modification of the semiconductor particles using metals or metal oxides. 

A variety of models have been derived to describe the kinetics of semiconductor photocatalysis, but the most commonly used model is the Langmuir-Hinshel-wood (LH) model [77-79]. The LH model relates the rate of surface-catalyzed reactions to the surface covered by the substrate. The simplest representation of the LH model [Eq. (7)] assumes no competition with reaction by-products and is normally applied to the initial stages of photocatalysis under air- or oxygen-saturated conditions. Assuming that the surface coverage is related to initial concentration of the substrate and to the adsorption equilibrium constant, K, tire initial... 

Titanium dioxide is widely used in the production of plastics, enamels, artificial fibers, electronic materials, and rubber (Hadjiivanov and Klissur-ski, 1996). Its ability to photocatalyze the oxidation of organic materials has been known for years in the paint industry. For this reason, TiOz is used as a white paint pigment (Stafford et al., 1996). TiOz is also known as an excellent catalyst for semiconductor photocatalysis due to its nonselectivity for environmental engineering applications it is nontoxic, insoluble,... 

Semiconductor photocatalysis has been successfully applied in degradation of pollutants e.g. S02 and phenolic waste [69], It is mainly Ti02, which have been used and studied for this purpose, but there are reports where hematite has been used for photodegradation [52-54, 56, 57, 110, 111]. Hematite has also been studied as a gas sensing material [40]. 

This review concentrates on John Albery s work in the field of colloidal semiconductor photoelectrochemistry. John s major contributions to this area, as in so many others, have been through his astounding facility for generating useful asymptotic solutions for highly complex kinetic models of electrochemical systems. So as to put John s work in colloidal photoelectrochemistry into context. Sections 9.1-9.3 of this chapter provide a review of the more salient kinetic models of semiconductor photocatalysis developed over the last 20 years or so. Section 9.4 then concentrates on the Alberian view and presents, for the first time, John s model of the chronoamperometric behaviour of colloidal CdS. 

Vinodgopal, K. and Kamat, P. V. (1995). Electrochemically assisted photocatalysis using nanocrystalline semiconductor thin-films. Solar Energy Mater. Solar Cells 38(1 4), 401 410. 

Abstract The use of semiconductor photocatalysis for treatment of water and air has been a topic of intense research activity over the past 20 years. This chapter provides a review of this highly effective technology. The fundamental processes involved in the technique are initially detailed with a discussion of some recent novel concepts in photocatalysis. A range of applications of water and air treatment are subsequently described with examples of mechanistic description of the major breakdown pathways of some key compounds. Examples of large-scale water treatment applications are also discussed. 

The ability to use fundamental design principles based upon modern experimental and theoretical techniques coupled with the ever-increasing cost of, and demand for energy, means semiconductor photocatalysis is a rich area for both scientific and technological development in the twenty-first century. 

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). 

Pichat, P. Representative Examples of infrared spectroscopy uses in semiconductor photocatalysis. Catal. Today., 2014, 224, 251-257. 

As a whole, these experiments lead to two important points. From the methodology point of view, the work shows that photocatalysis and photochemistry with semiconductors are useful new tools for the investigation of electron-transfer mechanisms. It is felt that in the present stage of this field new experimental evidence is more necessary than a detailed theory. Actually, it has been shown by this method, that the effect of light-produced carriers agrees with the concepts formed on the basis of thermal reactions. 

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