Photocatalytic hydrogen evolution over mesoporous TiO2/metal nanocomposites

Na+ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130-140 m(2)/g, pore diameter 5-9 nm and anatase content 70-90%. The mesoporous TiO2 samples prepared were found to have photocatalytic activity in Cu-II, Ni-II and Ag-1 reduction by aliphatic alcohols. The resulting metal-semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water-alcohol mixtures, their efficiency being 50-60% greater than that of the metal-containing nano-composites based on TiO2 Degussa P25. The effects of the thermal treatment of mesoporous TiO2 upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO2/Ag-0 to TiO2/Ni-0 to TiO2/Cu-0 was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal-semiconductor nanocomposites. (C) 2008 Published by Elsevier B.V.