Effects of pH on the Structure of Titania Prepared via Ionic Liquid-assisted Hydrothermal Method

The mesoporous anatase TiO2 material was prepared by ionic liquid-assisted hydrothermal method using tetrabutyl titanate as titanium source and ionic liquid 1-butyl-3-methylimida-zolium tetrafluoroborate ((C4MIM)BF4) as template. The pH values of the starting suspensions were adjusted from 1 to 11 using HCl or NH3·H2O solution. The influence of pH on the ionic liquid-water system for the preparation of titanium dioxide was investigated. The obtained TiO2 samples were characterized with X-ray diffraction (XRD) and N2 adsorption-desorption measure- ments, respectively. The results showed that the addition of ionic liquid inhibited the formation of the brookite TiO2, and increasing pH values enhanced the crystallization. When the pH was changed at a wide range (pH=1~9), the pore size distributions of the samples were relatively narrow, and the average pore diameter was reduced from 6.6 nm to 5.0 nm by increasing pH value. At the same time, the average size of the TiO2 nanoparticles in the samples was controlled at about 9 nm by using ionic liquid-assisted hydrothermal method. This is consistent with the results of the transmission electron microscopy (TEM) analyses.