Kulyk K. Synthesis and properties of the silicas modified by cerium compounds

The method of synthesis of nanocomposites CeO2/SiO2 was developed. The process of cerium (III) acetylacetonate chemisorption on the surface of fumed silica and nanocomposites CeO2/SiO2 was studied. The comparative analysis of efficiency of application of methods of molecular layering and impregnation for synthesis of cerium-containing silicas was carried out. It is shown that the method of molecular layering allows to synthesize nanocomposites with a controllable size of cerium dioxide crystallites from 3 to 24 nanometers in a concentration range of 6 24 weights. %. For the first time it was found that process of crystallisation CeO2 in nanocomposites CeO2/SiO2 occurs regularly under the influence of temperature, and that the size of crystallites is exponential function of temperature of treatment and can be presented by the correlation equations with high determination coefficients (R2 = 0,996 0.998). The kinetics was studied and the mechanism of thermal transformations of ceriumacetylacetonate groups grafted on the surface of silica and nanocomposites CeO2/SiO2 was proposed. It is revealed that the increasing in the content of CeO2 nanoparticles in nanocomposites considerably reduces an activation energy of reaction of formation of acetone. The mechanism of formation of acetone as a result of thermal transformation of grafted ceriumacetylacetonate groups was proposed. Kinetic parametres of reaction of formation of acetone was calculated. CeO2 doped xerogels and transparent monolithic quartz sol-gel glasses were synthesized, their structure was studied. New plastic greases was produced with the application of CeO2/SiO2 as highly dispersed fillers. Immobilisation of coumarines on the surface of fumed silica, nanocomposites CeO2/SiO2 and mixed oxides Al2O3/SiO2, TiO2/SiO2 was performed. Thermal transformations of immobilized compounds were studied. It is revealed that a key role in the bonding of investigated coumarines with a surface silanols played by free hydroxyl group in the position 7 or 8 of coumarine ring.