Toward a Low-Temperature Sol-Gel Synthesis of TiO2(B) Using Mixtures of Surfactants and Ionic Liquids

An approach toward the synthesis of nanocrystalline TiO2(B) in surfactant/ionic liquid systems at low temperature (100 degrees C) by means of sol-gel chemistry is presented. As reaction medium, a solution of imidazolium- and ammonium-based surfactants in ionic liquids was applied. Interestingly, TiO2(B), in coexistence with anatase, was observed only in cases where the ionic liquid is based on imidazolium moieties. The final product contained up to 60 wt % TiO2(B), depending on the initial amount of surfactant. X-ray powder diffraction measurements and transmission electron microscopy revealed small particle sizes (ca. 2 nm for TiO2(B), around 6 nm for anatase) as well as a high crystallinity of the material. The materials possessed surface areas up to 300 m(2)/g. Electrochemical studies further confirmed the presence of the two titania polymorphs anatase and TiO2(B) in similar proportions. Small-angle X-ray scattering experiments gave insight into the phase behavior of the surfactant in the ionic liquid under reaction conditions. The formation of TiO2(B) is discussed based on systematic variation of diverse parameters.