Subject photocatalysis

A large variety of organic oxidations, reductions, and rearrangements show photocatalysis at interfaces, usually of a semiconductor. The subject has been reviewed [326,327] some specific examples are the photo-Kolbe reaction (decarboxylation of acetic acid) using Pt supported on anatase [328], the pho-... 

In Part I the fundamental aspects of photocatalysis are described. Photoelectrochemical processes at semiconductors are the most important basics for all photocatalytic reactions (Chapter 2). Design, preparation and characterization of active photocatalysts have been an important research subject,... 

A recent contribution to the chemoselectivity problem is the composite photocatalysis developed by Maldotti et al. [117]. Cyclohexene la was subjected to photo-initiated oxidation in Nation membranes containing Pd(II) porphyrin Pd(4-TMPyP) [4-TMPyP = weso-tetrakis(N-methyl-4-pyridyl)porphyrin] and Fe(III) porphyrin 11 to... 

The earliest example of the semiconductor photocatalysis application as a method of disinfection was published by Matsunaga et al. (1985). This work reveals that Ti02 particles were effective in the inactivation of bacteria, such as Lactobacillus acidophilus, Saccharomyces cerevisiae, and Escherichia coli. To date more than 200 studies are related with this subject and at least three reviews were dedicated to photocatalytic disinfection (Blake et al. 1999 Srinivasan and Somasundaram 2003 Carp et al. 2004). Some general conclusions on Ti02 disinfection are reported below and the literature will be discussed more specifically throughout the chapter. 

When the Ti02 in slurry is used, no regrowth was found after a specific dark period. However, it is not clear whether solar photocatalysis with supported Ti02 avoid the E. coli regrowth once the zero is achieved. The interaction between the catalyst and the bacteria is the determinant factor in addition, the interaction is depending on the chemical matrix of water and geometrical characteristics of the photoreactors. This subject should be studied in more detail. 

It is expected that this strategy can be facilitated by the presence of an appropriate hole scavenger (e.g. ethanol, methanol). Through a competition reaction, the scavenger will disable the hole-driven oxidation processes to Np(VI), U(VI) and Pu(VI), so further limiting the products of the photocatalysis to Pu(III), U(IV) and insoluble Np(IV). Choice of hole scavenger will be the subject of the next section. 

Heterogeneous photocatalysis is a very well-known technology, valuable for purification and remediation of water and air. Several excellent revisions exist on the subject, with different approaches (Bahnemann et al., 1994 Emeline et ak, 2005 Fujishima and Zhang, 2006 Hoffmann et al., 1995 Legrini et al., 1993 Linsebigler et al., 1995 Mills and Le Hunte, 1997 Rajeshwar, 1995 Serpone, 1997). 

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. 

Since photocatalysis was discovered in the early 1970s, more than 6,200 papers related to this process have been published. Most of the work on this subject has focused on showing that organic molecules can be oxidized in PC reactors. So far, more than 800 organic molecules have been tested for oxidation in PC reactions (Blake, 2001). In most cases, the tested organic molecules were converted to CO2, water, and mineral acids. Therefore, it can be definitely concluded that photocatalysis works for oxidation of organic molecules. The rate of oxidation depends on several factors that will be addressed in the upcoming section. 

This review has been written in order to clarify fundamental aspects of photocatalysis, an important subject in inorganic and material chemistry, not to present a list of studies on photocatalysis reported so far, since it seems rather difficult to make a complete review by introducing all or a large part of the reported studies on photocatalysis of relatively long history. This review is based on the author s experience in studies on photocatalysis and topics are limited to so-called semiconductor photocatalysis definition and examples of photocatalysis, its principle and kinetics, visible light-induced photocatalysis, and design of active photocatalysts are discussed in detail. 

Photoreactions on titanium dioxide have been the focus of considerable interest for some time. Titania offers the opportunity to oxidize organic compounds in polluted environments, and has also been exploited to generate titania-supported nanoparticles of metals (e.g., silver) via photoreduction reactions [85]. While there is not enough room here to thoroughly treat photocatalytic processes, a brief introduction to the subject is presented below. Readers seeking detailed treatments of this subject are referred to a recent review by Yates etal. on titania-facilitated photocatalysis [86]. 

Layered compounds provide unique character for electron-transfer processes owing to their low dimensionality. Especially layered materials with ion-exchange and/or intercalation capabilities show behavior that is not seen in so-called bulk-type materials. Layered materials, which have been often used in studies of photoelectron transfer as well as photocatalysis, may be classified into two groups compounds in which the host layers work as an active component for the photoexcitation and electron-transfer reactions, and materials in which the layers are inert for electron-transfer processes. Examples of the former are layered titanates and niobates and of the latter are clays. In the latter case, photoactive materials are intercalated in the interlayer spaces. Recently, the exfoliation of various layered compounds has become possible and artificial assemblies consisting of these exfoliated sheets have been formed. Electron transfer in such assemblies is also an attractive subject in this field. 

Some references of reviews besides the ones already cited are given [1,3, 5-9, 19, 23-25, 28, 31, 33]. Organometallic photochemistry [36] was excellently treated in [37] and may be compared with inorganic photochemistry to gain further inspiration [38-40]. A recent multiauthored book strongly overlaps with the subject matter of the present section, and should certainly be consulted [41]. Electron transfer reactions play a determinant role in many photocatalytic processes several recent reviews and books may be cited on this topic [42-44]. The photochemistry of the M-CO bond [45] and the theme of photocatalysis by transition metal complexes [46] have recently been reviewed. Covalently linked donor-acceptor systems for mimicry of photosynthetic energy transfer have been discussed in [47]. Several special issues of Coordination Chemistry Reviews have been devoted to the photochemistry and photophysics of coordination compounds [48-50], and a special issue to photochemistry [51]. Further developments in photochemistry were the subject of a special issue of Chemical Reviews [52]. Practical considerations useful for designing photochemical experiments may be found in [53]. 

In Section II.C, we described the reactivity of adsorbed dye species at liquid liquid junctions in heterogeneous photoredox reactions. The properties of these systems can be used to catalyze electron-transfer processes. The behavior of dyes at interfaces has been vigorously studied in micelles and microemulsion systems, and many excellent reviews and books are available on this subject [94-97]. In this section, we shall consider some basic aspects of photoprocesses in microheterogeneous systems that are relevant to polarizable ITIES. This is not intended to cover comprehensively the recent developments in the active area of photochemistry at organized assemblies, but to highlight how spatial confinement, hydrophilic hydrophobic forces, and local potentials can affect the course of a photochemical process. We shall also revise some recent developments in photocatalysis and photosynthesis at polarizable liquid liquid interfaces, highlighting advantages and limitations in relation to two-phase catalysis. 

Photocatalysis refers to a process in which light and a catalyst complex bring about or accelerate a chemical reaction. The subject area has been extensively reviewed, and numerous examples of synthetically useful photocatalytic transformations have been cataloged and tabulated. Photocatalysis is also useful for the activation of small... 

The application of (oxy)nitrides in photocatalysis has been the subject of a number of recent reviews, for example, [10, 32]. In this area, the potential of materials for overall water splitting using visible light has been of particular interest. In this regard, Domen and coworkers have discussedthe behavior of d° and d ° electronic... 

At present the scientific literature is lacking in modeling membrane photoreactors because the coupling between photocatalysis and membranes is a relatively new subject of study. 

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