Photocatalytic Oxidations At Room Temperature in Various Media

Various inorganic compounds, such as CO, SO 2- 3 , l − , Br − and NH 3 , are photocatalytically oxidized at room temperature. The photocatalytic oxidation of hydrocarbons yields aldehydes and ketones, either in the gas phase or in the neat-liquid phase with a selectivity that depends on the molecular structure. For instance, cyclohexane is mainly transformed into cyclohexanone, and alkyltoluenes are selectively converted into the corresponding alkyltolualdehydes. Among various semiconductor oxides (TiO 2 , ZrO 2 , ZnO, CeO 2 , SnO 2 , Sb 2 O 4 , V 2 O 5 ), titania was generally the most active, whereas V 2 O 5 was totally inactive. As expected, for a given oxide, the activity depends on the particular specimen. From photoconductivity and oxygen isotope exchange measurements, it was inferred that the photoactivated oxygen species is atomic in gas phase reactions. In aqueous medium, the photoproduced holes react with OH − groups thus forming strongly oxidizing OH − radicals as shown by the primary products of the oxidation of monochlorophenols. These oxidations could be of interest for the synthesis of fine chemicals or for the removal of pollutants.