Preparation of Mesoporous Titanium Oxides by Template Synthesis and Phase Transition of TiO2 inside Mesoporous Silica

To prepare mesoporous TiO2 (meso-TiO2) with anatase and rutile crystal structures, hydrothermal and template synthesis were used. Meso-TiO2 with anatase structure was obtained by hydrothermal synthesis. The crystal structure of meso-TiO2 by hydrothermal synthesis converted from anatase to rutile by simple heating at 600 degrees C and above. However, their mesopore structure collapsed due to phase transition. To prepare meso-TiO2 with rutile structure, template synthesis method was applied using mesoporous silica KIT-6 as a template. Once we incorporated anatase TiO2 inside mesopores of silica, the phase transition temperature of TiO2 confined inside KIT-6 was much higher (900 degrees C) than that of free-standing TiO2 (600 degrees C). The suppression of TiO2 phase transition inside mesopores of KIT-6 is closely related with the interaction between TiO2 surface and silica walls in KIT-6 because oxygen vacancy in TiO2 is regarded as the starting point for phase transition. After removal of silica template by NaOH solution washing, meso-TiO2 with mixed phase between anatase and rutile was obtained.