Photoinduced reactivity of titanium dioxide

The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors investigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5. The products at the initial stage of the reaction were hydroquinone, pyrocatechol, 1,2,4-benzenetriol, pyrogallol, and 2-hydroxy-1,4-benzoquinone. These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O. A reaction scheme involving hydroxyl radicals as real reactive species has been proposed. Although H2O2 was formed via O2\ewdot produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction. About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction. These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2\ew...

Heterogeneous Photocatalytic Decomposition of Phenol over TiO2 Powder

Electron-transfer mediated reactions may be initiated by long-wavelength ultraviolet or visible light irradiation of semiconductor particles. The application of this field of photoelectrochemistry to sensitized organic photo-transformations is reviewed. The method has the potential to modify functional groups and to assist in studying heterogeneous photocatalysis and radical ion intermediates.

Organic heterogeneous photocatalysis: chemical conversions sensitized by irradiated semiconductors

TiO2-Photocatalyzed epoxidation of 1-decene by H2O2 under visible light

Colloidal semiconductors as photocatalysts for solar energy conversion

Semiconductor-catalyzed photooxygenation of aromatic olefins

Careful examination of the effects of oxygen and water on titanium dioxide photocatalyzed oxidation of benzene and toluene has revealed that electron transfers from water and toluene to the photogenerated positive holes, synchronized with electron transfer from the photoexcited titanium dioxide to oxygen, result, respectively, in aromatic nuclear hydroxylation giving phenolic products and in oxidation of the side chain of toluene affording benzyl alcohol and benzaldehyde.

Titanium dioxide photocatalyzed oxidation of aromatic hydrocarbons: the role of water and oxygen to induce aromatic hydroxylation

cis-β-Alkoxystyrenes such as cis-β-methoxy-, cis-β-ethoxy-, and cis-β-isopropoxystyrene were autoxidized as neat at room temperature in the dark even in the absence of any radical generator. UV-irradiation and the use of a radical generator facilitated the oxygenation of these olefins. These oxidations afforded the corresponding epoxides or their derivatives in considerable yields as well as carbonyl compounds resulting from oxidative cleavage of the double bonds. The mechanisms for these oxidations are proposed to involve free-radical chain pathways and charge-transfer complexes between the olefins and oxygen which play an important role in the initiation steps.

Oxygenation of Aromatic Vinyl Ethers. A Noticeable Formation of Epoxides and Reaction Mechanism

The Chemistry of Superoxide

On montre que TiO 2 et CdS induisent l'oxydation d'olefines et d'hydrocarbures aromatiques, et sensibilisent l'isomerisation de systemes insatures

Tatsuya Kanno

Papers

Semiconductor-catalyzed photooxygenation of aromatic olefins

Titanium dioxide photocatalyzed oxidation of aromatic hydrocarbons: the role of water and oxygen to induce aromatic hydroxylation

Oxygenation of Aromatic Vinyl Ethers. A Noticeable Formation of Epoxides and Reaction Mechanism

The Chemistry of Superoxide

Semiconductor-catalyzed Photoreactions of Organic Compounds