Penetration of Titanium Tetraisopropoxide into Mesoporous Silica Using Supercritical Carbon Dioxide

A penetration of titanium tetraisopropoxide (TTIP) and a reaction with silanol groups to form TiO2 layers on the inner surface of mesoporous silica samples were studied. Influence of the solvent on the penetration behavior was discussed. The TTIP could penetrate into the mesopores with diameters of 2.3 and 2.7 nm and the pore size was decreased by the TTIP coating, only when supercritical CO2 were used as solvent. The pore size change was also observed for mesopores larger than 3.5 nm by using both supercritical CO2 and liquid 2propanol. These behaviors are reasonably discussed not only by the relation between the pore diameter and the solvated TTIP molecular size, but also by the adsorption energy of the solvent molecules on the silica surface. A difference of the penetration behavior of TTIP from that of tetraethoxyorthosilane (TEOS) suggested that the reactivity with silanol groups on the silica surface also affected the penetration behavior