Elucidating Ionic Liquid Environments That Affect the Morphology of TiO₂ Nanocrystals: A DFT+<i>D</i> Study

Using ionic liquids as controlling agents is known to effectively affect the morphologies of TiO₂ crystals. To obtain a profound understanding of this observation, density functional theory calculations with inclusion of Grimme treatment of the dispersion forces (DFT+<i>D</i>) have been performed to study a typical ionic liquid 1-ethyl-3-methylimidazolium bromide ([Emim]­Br) adsorption on the low-index TiO₂ facets, and the equilibrium crystal shape of TiO₂ has been predicted using Wulff’s rule. [Emim]Br is found to adsorb most strongly on (110) for rutile and (100) for anatase. The gap of surface energy shows an obvious increase after [Emim]Br adsorption, especially, between (101) and (001) for anatase and also between (110) and (001) for rutile. This gap variation results in increasing the (100) facet exposure of anatase, and an increase in the length-to-diameter ratio of rutile nanocrystals, which is verified by our experiments. This study is meaningful to gain further understanding of how ionic liquids achieve shape-controlled nanocrystals synthesis by turning surface chemistry, which will push a valuable step toward the ultimate goal, controlling synthesis of inorganic nanomaterials