Příprava nanostrukturovaných oxidů kovů na bázi titanu a ceru pomocí přetlakových a superkritických tekutin

Abstract

This diploma thesis deals with preparation of Ti and Ce based oxides by using subcritical (pressurized hot) and supercritical fluids (water, methanol), and their physico-chemical characterization. The thesis is composed of the theoretical part, the experimental part and results with discussion. Within the theoretical part the properties and application of TiO2, Ce and CeO2 are described and the importance of TiO2 doping with cerium is explained. Beside the physico-chemical properties and the phase behavior of supercritical and subcritical fluids and the technologies using supercritical CO2 and other solvents including supercritical water for preparation of nanostructured materials, the summary of the current scientific knowledge about preparation of Ti and Ce based oxides by using subcritical and supercritical fluids and the principles of used characterization techniques are described as well. The experimental part is dedicated to the description of CexTiyOn preparation. In results and discussion, the material properties determined by individual characterization techniques are summarized and the effect of individual parameters of preparation on the purity, textural and structural properties of CexTiyOn is discussed. The gel precursors with different molar ratios of Ti : Ce (0,95:0,05, 0,9:0,1, 0,8:0,2, 0,7:0,3) were prepared by sol-gel method controlled within the reverse micelles environment of nonionic surfactant Triton X-114 in cyclohexane. The gel precursors were subsequently processed by subcritical water and subcritical or supercritical methanol. The effect of the type and the volume of used solvent, temperature and pressure on the purity, textural and structural properties of CexTiyOn was investigated. The physico-chemical properties of prepared materials were determined by using organic elementary analysis, X-ray fluorescence spectroscopy, nitrogen physisorption, X-ray diffraction and Raman spectroscopy. It was revealed that CexTiyOn crystallize in subcritical water, which was not definite in subcritical methanol. Contrary to subcritical water processing, by subcritical methanol processing the complete purification of prepared material is not reached. The increasing Ce amount in CexTiyOn and increased temperature promote the crystallization of monoclinic CeTi2O6 and CeO2 cubic in the mixture with TiO2 anatase, the crystallization of TiO2 brookite is suppressed. The TiO2 anatase crystallite-size slightly decreases with increasing Ce amount. Better purity of CexTiyOn was achieved at lower processing temperature than at higher one. Increased pressure does not affect the material purity, but it affects the crystallization (phase composition). The effect of pressure on the TiO2 anatase crystallite-size was not observed.