Gnatyuk Y. Structure and photocatalytic properties of mesoporous titanium dioxide films modified with zirconium dioxide or silver

Template assisted sol-gel method of synthesis of mesoporous zirconium containing titania films with improved stability of porous structure against high temperature sintering has been developed. It was demonstrated that zirconium incorporation (5-10 mol.%) into titania matrix improved thermal stability of mesoporous structure of TiO2/ZrO2 films and led to increase of surface area up to 1000 m2/g and surface roughness of the films. Detailed analysis of XRD spectra of the TiO2/ZrO2 powders proved the formation of solid solution Ti1-xZrxO2 with anatase structure. Both types of acidic sites (Lewis and Bronsted) were identified on the surface of TiO2/ZrO2 samples by means of electronic spectra investigation of adsorbed n-dimethylaminoazobensene. On the basis of ammonia thermodesorption experiments formation of additional types of acidic sites with higher desorption temperatures for the samples with zirconia loading ? 30 mol.% was established that correspond to the appearance of separate phase of highly dispersed amorphous ZrO2. Set of spectrophotometric techniques was used for calculation of optical constants (refractive index, absorption coefficient, thickness) of titanium dioxide films depending on zirconium content. It was observed increase of band gap energy Eg for the new phase of solid solution Ti1-xZrxO2 with increasing zirconium content in the TiO2/ZrO2 films for which indirect allowed band transitions generally prevailed. Taking into account the fact that flat-band potential Efb for TiO2/ZrO2 electrodes measured in direct photoelectrochemical experiment was independent of ZrO2 content it was suggested that increase of Eg mainly occurs due to the anodic shift of the potential of valence band. Energetic diagram for TiO2/ZrO2 system was proposed and discussed. Photocatalytical activity of mesoporous TiO2/ZrO2 films in the process of photoreduction of toxic Cr(VI) ions to the Cr(III) state correlates with increase of specific surface area as well as with oxidation ability of the photogenerated holes of thecatalysts. Mesoporous ТіО2/ZrO2 films with zirconia loading 5-10 mol.% have maximal sorption capacity relatively aliphatic alcohols vapors. Chemosorption of alcohols molecules at the acidic surface sites of ТіО2/ZrO2 films increases selectivity of the process of their photooxidation to CO2 due to the lowering of concentration of toxic gaseous intermediates (acetic aldehyde, acetone). One-step sol-gel method for the preparation of titania films with incorporated Ag nanoparticles (5-15 nm) has been developed. Direct photoelectrochemical investigations proved that Ag nanoparticles improve charge separation process that lead to increase of the photooxidation activity of TiO2/Ag films in comparison with unmodified TiO2.