Preparation and characterization of mesoporous TiO₂ particles by modified sol-gel method using ionic liquids

Synthesis of mesoporous TiO₂ particles using ionic liquid (IL)-assisted sol-gel method was investigated. The prepared TiO₂ particles using water immiscible room temperature ionic liquid, [Bmim][PF ₆], as an effective templating material had good structural properties including high surface area, stable crystal structure, controlled porosity and tailor-designed pore size distribution. Due to the unique properties of the ionic liquid, including zero vapor pressure and water-immiscibility, TiO₂ particles with the anatase crystal phase were formed after the extraction of organic solvents without further heat treatment at high temperature. Especially, it was found that the strength of the hydrogen bonds on the anion part of ionic liquid with water was essential factor to form this mesoporous structure of TiO₂ particles. The mechanism for the formation of these nanostructured TiO₂ particles is an effective aggregation of the TiO₂ particles with a self-assembled ionic liquid. Moreover, the length of alkyl group on the cation part of ionic liquid could determine the pore size and volume of TiO ₂ particles. Among the ionic liquids, it was found that 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF₆]) was the most effective ionic liquid to prepare mesoporous TiO₂ particles.