Zhukovskiy M. Synthesis and photocatalytic properties of nanocomposites based on titanium dioxide films.

The thesis is devoted to development of novel heterogeneous photocatalyst. Mesoporous TiO2 films were prepared by template assisted sol-gel method and used as support for deposition of metal sulfides particles on its surface to produce visible light sensitive nanocomposites. Optimal component ratio and condition of the temperature treatment of mesoporous titania films for active photocatalyst and superhydrophilic surfaces production were established. The TiO2/CdS, TiO2/PbS, and TiO2/CuxS nanocomposites were synthesized via the photocatalytic reduction of sulfur on the surface of nanocrystalline TiO2 films. The photocatalytic synthesis produced smaller CdS nanoparticles in comparison with conventional chemical deposition of cadmium sulfide. The mean size of CdS nanoparticles can be varied by changing the illumination intensity and the TiO2 film calcination temperature. AFM study of the surface structure of TiO2/CdS and TiO2/PbS nanocomposites showed that the photocatalytic deposition results in formation of the polycrystalline 7-80 nm (CdS) or 20-30 nm (PbS) long nanorods. Spatial separation of the photogenerated charge carriers in TiO2/CdS and TiO2/PbS nanocomposites was assumed to be the driving force of the formation of such elongated metal sulfide nanoparticle agglomerates. It has been shown by laser flash photolysis and photoelectrochemical studies that in the case of photocatalytically produced TiO2/CdS nanocomposites one order of magnityude more efficient spatial separation of the photogenerated charge carriers between components of the heterostructure (with formation of the intermediates of photochemical reactions - the TiIII centres in TiO2 nanoparticles and S" anion-radicals in CdS nanoparticles) is achieved leading to its higher quantum efficiency in redox phototransformation of organic (xanthene dye - Bengal Rose) as well as inorganic (Na2S) substances under illumination with UV and visible light. Effective retarding of photocorrosion has been observed in the presence of S2- ions. The photocatalytic hydrogen formation in water-alkohol mixtures with participation of TiO2/М0 nanocomposites produced in situ by photoreduction of copper (II) and nikel (II) chlorides and silver nitrate on the surface of mesoporous titania films have been studied. The growth of the quantum yield of hydrogen evolution from TiO2/Ag0 to TiO2/Ni0 to TiO2/Cu0 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. Decrease in the photoreaction rate at further increase in metal content was supposed to be connected with light filtration by deposited metal particles, enlargement of metal nanoparticles and deterioration of the intimate electron interaction between components of the metal-semiconductor nanocomposites.