Titanium oxide based mesoporous powders and gels: Doping effects and photogenerated charge transfer

Titanium oxide based mesoporous structures and gels are synthesized and investigated by means of advanced X-ray techniques and EPR spectroscopy. In these systems, annealing treatments were performed up to 500 °C in order to improve the crystalline structure of the titanium dioxide with a stable polytype and to incorporate the nitrogen ions inside the crystal sites. EPR experiments were performed to analyze the involved paramagnetic centres and their evolution with respect to the synthesis conditions and the performed treatments.For the gel based titanium oxide, three characteristic molar ratios in the ternary phase diagram (TiOCl2, H2O, DMF) have been chosen for representative gels with good optical transparency. Photo-induced phenomena were investigated by using UV-irradiation of the gels which leads to charge transfer on the titanium ions. The kinetics of the photoinduced reactions are investigated by EPR which contributes also to analyze and to assign the local environments around titanium as function of the material composition, the carried out thermal treatment and UV-irradiation. The kinetic features and their correlation with the microstructure of the gels are discussed as well as the properties of the electronic active centres.