New insights into anatase crystallization behavior in ionothermal synthesis of nanostructured TiO2
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The anatase crystallization behaviors in ionothermal synthesis (sol–gel method containing ionic liquid) of nanostructured TiO2 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 TiO2 to depend on the H2O/titanium dioxide precursor (titanium tetraisopropoxide, TIP) molar ratio. Hydroxylated titanium compound was a key intermediate for forming anatase TiO2. 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 H2O/TIP molar ratio and from the system containing hydrophilic ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BuMIm]+[BF4]−). 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 TiO2, TEM results indicated smaller particle size of TiO2 was obtained at medium H2O/TIP molar ratio case.
KeywordsTiO2 Ionic Liquid Anatase TiO2 TiO2 Sample Nanostructured TiO2
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