Structural control on crystal growth of titanate in aqueous system: Selective production of nanostructures of layered titanate and anatase-type titania

Layered titanate nanosheets and anatase-type titania nanospines were selectively grown from a molecular titanium precursor, TiF₄, by a reaction with various cationic species in an agar gel matrix. A layered structure of the titanate was fundamentally produced by the assembly of anionic titanate species with a certain amount of specific cations under a basic condition. Nanoscale flaky and rodlike forms were constructed from the titanate monolayers with sodium and ammonium ions, respectively. On the other hand, anatase-type crystalline titania was formed from TiF₄ under an acidic condition or in the absence of a sufficient amount of the cationic species. Especially, a spherical architecture of anatase nanospines was produced through a moderate reaction with ammonia provided by decomposition of urea. The role of the counter cations was essential for the selection of the crystal structures and the construction of the particular rodlike and flaky forms of the layered titanates.