Abstract
The anatase crystallization behaviors in ionothermal synthesis (sol-gel method containing ionic liquid) of nanostructured TiO 2 were studied in this paper. It was found that the specific physical chemical characteristics of the water/ionic liquid mixture caused the formation path and crystallinity of anatase TiO 2 to depend on the H 2 O/titanium dioxide precursor (titanium tetraisopropoxide, TIP) molar ratio. Hydroxylated titanium compound was a key intermediate for forming anatase TiO 2 . It could be directly formed from hydrolysis of titanium dioxide precursor or ionic liquid-induced water dissolution of the condensation product. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) data indicated that a higher hydroxyl group ratio content of hydroxylated titanium compound was obtained at medium H 2 O/TIP molar ratio and from the system containing hydrophilic ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BuMIm] + [BF 4 ] - ). The self organization ability of ionic liquid drove anatase crystallization through dehydration of the Ti-OH group of hydroxylated titanium compound in the thermal annealing process. As for the particle size of TiO 2 , TEM results indicated smaller particle size of TiO 2 was obtained at medium H 2 O/TIP molar ratio case. © 2009 Springer Science+Business Media, LLC.