Photocatalytic oxidation of aromatic alcohols to aldehydes in aqueous suspension of home prepared titanium dioxide. 2: Intrinsic and surface features of catalysts

In this paper some intrinsic electronic properties of home-prepared (HP) TiO2 catalysts were investigated by diffuse reflectance spectroscopy and quasi-Fermi level measurements. These powders were used for carrying out the photocatalytic oxidation of benzyl alcohol to benzaldehyde and CO2 in water; the selectivity for aldehyde formation was enhanced by the addition of small amounts of ethanol, a typical hole trap. The values of band gap, valence band and conduction band edges are almost identical for all the HP samples in which anatase phase is predominant, whereas appreciable differences can be noticed for an HP sample containing high amount of rutile phase. A comparative ATR-FTIR study of the HP catalyst showing the highest selectivity and the commercial titania showing the highest activity towards benzyl alcohol oxidation (Degussa P25 TiO2) was carried out. The ATR-FTIR results indicate that HP and Degussa P25 surfaces show a very dissimilar hydrophilicity and different ability for adsorbing the organic compounds deriving from benzyl alcohol photocatalytic oxidation. Results show moreover that the improved selectivity to aldehyde by adding ethanol is due to competition between the substrate and the hole trap for adsorption on reactive sites.