The grafting reaction of tetraneopentyl titanium on the surface of MCM-41 mesoporous molecular sieves dehydroxylated preliminary at 500 ◦C leads to formation of the well-defined bigrafted surface complex (≡Si–O)2Ti(CH2CMe3)2. On reaction with water or alcohol, the neopentyl ligands can be replaced selectively by alcoxy or hydroxy. On calcination at 500 ◦C, a well-dispersed titanium oxide supported on MCM-41 is obtained. In situ FTIR, DRS, and XAFS characterizations suggest that titanium is present as isolated tetrahedral species on the surface of MCM-41. This solid was used for the photocatalytic oxidation of ethylene in oxygen under UV irradiation, and its activity was compared to that of Ti-MCM-41 prepared by direct hydrothermal synthesis. The higher activity of the samples prepared by reaction with the organometallic complex is attributed to the good dispersion of titanium on the surface of MCM-41.

TiO2 films on Al alloy (Al), indium-tin oxide glass (ITO/glass), and glass were prepared by a dip-coating method. ITO is found to have a higher work function, while the work function for Al is lower than that of TiO2 films. An electron transfer is indicated to occur in the interfaces between TiO2 films and conducting substrate Al or ITO, which results in an Ohm contact or Schottky barrier under the transient equilibrium UV radiation conditions. Photocatalytic measurements showed that the TiO2 films on Al have a higher activity for photocatalytic oxidation of C2H4, but the activity for photocatalytic degradation of oleic acid is lower as compared with TiO2 films on glass. Alternatively, TiO2 films on ITO give completely contrary photocatalytic performance to those on Al. These observations could be associated with the electron transfer, in which Al acts as an electron donor and offers electrons to TiO2, allowing photocatalytic oxidation of ethylene to proceed by the photogenerated electrons, while ITO could be an acceptor for the photogenerated electrons, which is beneficial to photocatalytic degradation of oleic acid by the photogenerated holes. This electron-transfer model could be extended to other photocatalytic systems.

Photocatalytic surface sites on SO42−/TiO2 were investigated by pyridine adsorption and in situ Fourier transform infrared (FT-IR) spectroscopy. Results revealed that the sulfate-modification not only increased the number of strong Lewis acidic sites, but also induced a large amount of strong Brønsted acidic sites on the surface of TiO2. Pyridine molecules were chemically captured on Brønsted and Lewis acidic sites on the SO4 2−/TiO2 surface. These pyridine molecules were progressively decomposed to final products of CO2 and H2O under actual photocatalytic conditions. The high photocatalytic performance of SO42−/TiO2 can be explained by the improved surface acidities that favor the adsorption of both oxygen and pyridine molecules. Moreover, the Lewis acidic sites could react with H2O and was then converted to Brønsted acidic sites, leading to the activation of the water. This conversion promoted the formation of hydroxyl groups on the catalyst surface, which could also contribute to the high photocatalytic reactivity of SO42−/TiO2.