PREPARATION AND ACID-BASE PROPERTIES OF A PROTONATED TITANATE WITH THE LEPIDOCROCITE-LIKE LAYER STRUCTURE

A layered solid acid, H(x)Ti(2-x/4)square(x/4)O(4) . H2O (square: vacancy, x similar to 0.7), has been prepared by acid exchange of a cesium titanate, Cs(x)Ti(2-x/4)square(x/4)O(4). The body-centered orthorhombic structure comprises host layers of lepidocrocite-type and interlayer H2O molecules, 70% of which are protonated to be H3O+. The material undergoes ion-exchange and intercalation reactions at ambient temperature. Alkali metal ions were taken up continuously via solid solution up to similar to 70% substitution of exchangeable protons, forming monolayer hydrates with the interlayer separation of similar to 9 Angstrom. The reaction beyond the loading proceeded only for Na and Li ions, which yielded bilayer hydrates. The distinctive threshold loading of 70% dominating two defined hydrate structures corresponds to the half-occupation of interlayer pseudocubic cavities by guest cations. Rietveld refinements for the cation-loaded phases formed at the threshold supported the monolayer arrangement in which cations and water molecules alternate.