Photocatalytic oxidations organic compounds

The Adsorption Integrated Reaction (AlR-11) process is a destructive photocatalytic oxidation (PCO) process for the treatment of gas-phase waste streams that can operate successfully at low concentrations of contaminants and at a low energy cost. In the process, ultraviolet (UV) light illuminates a proprietary catalyst at room temperature, and produces hydroxyl radicals, which destroy organic compounds by oxidation. Very few by-products are created by the process, and many contaminants are broken down into harmless carbon dioxide and water. 

Photocatalytic oxidation can be an effective way of removing pollutants in the gas phase, such as NOx, SOx, and volatile organic compounds (VOCs). 

At present, several stable photocatalytic systems for production of hydrogen from water and organic compounds are made of semiconducting oxides and suitable proton reducing catalyzer. An efficient electron transfer between inorganic semiconductor and bacterial hydrogenase was shown to result in hydrogen photoproduction. 

Usually, the most typical processes that are covered by photocatalysis are the photocatalytic oxidation (PCO) and the photocatalytic decomposition (PCD) of substrates, which most often belong to the organic class of compounds. The former process employs the use of gas-phase oxygen as direct participant to the reaction, while the latter takes place in the absence of Oz. 

Studies carried out by Cermenati et al. [60] also gave evidence about the contribution of radical species in the photocatalytic oxidation of organic compounds. The addition of superoxide dismutase,... 

In these photocatalytic oxidation processes the organic compound is either directly oxidized by the valence band holes ... 

The photocatalytic oxidation of organic and inorganic compounds and the photo-catalytic production of H202 occurs also at the surface of iron(III)(hydr)oxides. It has been proposed (e.g., Hoffmann, 1990 Faust and Hoffmann, 1986) that the oxidation of S(IV) by 02 in atmospheric water is catalyzed by iron(III)(hydr)oxide particles. It is assumed that the reductant (HSO3) is specifically adsorbed at the surface of an iron(III)(hydr)oxide, forming either a monodentate or a bidentate surface complex ... 

The photocatalyzed oxidation of gas-phase contaminants in air has been demonstrated for a wide variety of organic compounds, including common aromatics like benzene, toluene, and xylenes. For gas-phase aromatic concentrations in the sub-lOO-ppm range, typical of common air contaminants in enclosed spaces (office buildings, factories, aircraft, and automobiles), photocatalytic treatment leads typically to complete oxidation to CO2 and H2O. This generality of total destruction of aromatic contaminants at ambient temperatures is attractive as a potential air purification and remediation technology. 

A. Photocatalytic Conversion of Chlorine-Containing Organic Compounds ON Titanium Oxide... 

Effect of platinum content. Since a beneficial role of platinum deposited on titania had been reported for the photocatalytic oxidation of some organic compounds (refs 6, 7), several catalysts, from 0.5 to 10 wt % Pt with a constant particle size, were prepared and studied. The variations of the initial rate of formation of cyclohexanone as a function of Pt contents are shown in Fig. 2. There is not only no beneficial effect of Pt as mentioned in refs.(6, 7) but a... 

Many dyes are decolorized and ultimately mineralized by photocatalysis. In the degradation of azo dye,18 21) the degradation rate decreases in the order monoazo > diazo > triazo.1819) Three processes including oxidation and reduction are considered to occur simultaneously in the photocatalytic degradation of dye. These are illustrated in Fig. 9.9. Process 1 is the common photocatalytic degradation process of organic compounds. Process 2 is spectral sensitization as observed in a wet-type solar cell. In process 3 one moiety of dye molecule serves as the electron acceptor, suppressing recombination between electron and positive hole. 

At the end of 1970 s we attempted an investigation of the action of semiconductor particles on medium sized organic compounds. In this article, we would like to describe some of the work done in our laboratory on the photocatalytic action of semiconductors on the oxidation of olefins and hydrocarbons, and on the isomerization of unsaturated systems. 

Photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated (Sun and Pignatello, 1995). In addition to the dominant hydroxyl radical mechanism, Sun and Pignatello found evidence that direct hole oxidation may be the mechanism for the photocatalytic degradation of some organic compounds. The assumed mechanism for this oxidation is H+ acting as an electron-transfer oxidant, while O behaves like a free OH and abstracts H or adds to C=C multiple bonds. Hole oxidation has been used to explain the oxidation of oxalate and trichloroacetate ions, which lack abstractable hydrogens or unsaturated C-C bonds. Whether the reaction... 

Polychlorobiphenyls (PCBs) have been studied under the UV/Ti02 photo-catalytic process to assess the use of photocatalytic oxidation in the treatment of PCBs. These organic microcontaminants are biologically refractory therefore, AOPs were studied for the remediation of PCBs. Haloaliphatic and haloaromatic compounds have been found to be mineralized to C02 and HC1 by UV/Ti02 process (Mathews, 1988). 

---