Shape- and Size-Controlled Synthesis of Uniform Anatase TiO2 Nanocuboids Enclosed by Active {100} and {001} Facets

Uniform anatase TiO2 nanocuboids enclosed by active {100} and {001} facets over a wide size range (60-830 nm in length) with controllable aspect ratios were solvothermally synthesized through hydrolysis of titanium tetraisopropoxide (TTIP) using acetic acid (HAc) as the solvent and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as the capping agent. The size and aspect ratio of the anatase TiO2 nanocuboids can be readily adjusted by changing the composition parameters including the contents of [bmim][BF4], water, and HAc in the quaternary solution system. It was revealed that [bmim][BF4] played an important role in stabilizing both the {100} and {001} facets of the anatase TiO2 nanocuboids. On the one hand, [bmim][BF4] acted as a fluoride source to release F-ions for stabilizing the {001} facets; on the other hand, the [bmim](+) ions acted as effective capping ions to preferentially stabilize the {100} facets. The obtained near-monodisperse anatase TiO2 nanocuboids exhibited an interesting self-assembly behavior during deposition. These single-crystalline anatase nanocuboids showed extremely high crystalline phase stability, retaining the pure phase of anatase as well as the morphology even after being calcined at 900 degrees C. Moreover, the anatase nanocuboids exhibited considerably enhanced photocatalytic activity owing the wholly exposed active {100} and {001} facets.