Ionic Liquid-Assisted Synthesis of Large-Scale TiO2 Nanoparticles with Controllable Phase by Hydrolysis of TiCl4

Pure rutile and rutile-anatase composite TiO2 nanoparticles have been successfully synthesized via an ionic liquid-assisted method by hydrolysis of titanium tetrachloride in hydrochloric acid. It is found that the phase composition (ratio of rutile to anatase) of the products increases with increasing the content of ionic liquid [Emim]Br (1-ethyl-3-methyl-imidazolium bromide), therefore, TiO2 nanoparticles with controlled phase compositions can be obtained in high yields. The structural and morphological characterizations of the resulting samples are investigated by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Brunauer−Emmett−Teller (BET) analysis, and the results indicate that the diameters of the anatase nanoparticles are in the range of 4−6 nm and the well-defined rutile nanorods are about 3−6 nm in diameter and 20−60 nm in length. More importantly, we find that the [Emim]+ ions can serve as capping agents based on their strong interactions with the (110) facets of rutile, and the [Emim]Br favors the formation of the rutile structure with a rod-like shape due to the mutual π-stacking interactions of imidazole rings. We believe that this method can be developed into a general way to synthesize other metal oxide nanoparticles on a large scale.