PROTONATED PENTATITANATE - PREPARATION, CHARACTERIZATIONS, AND CATION INTERCALATION

A protonated pentatitanate with a monoclinic layer structure, H2Ti5O11.3H2O, has been prepared by treating its parent compound, Cs2Ti5O11, with a hydrochloric acid solution. The hydration water, as well as protons, is introduced upon interlayer Cs ion removal, expanding the separation between lost lamellae, [Ti5O112-]infinity. Half of the substituting protons exist as oxonium ions and the other half as hydroxyl groups, both of which are reversibly exchangeable with cations. The material lost free interlayer water up to 100-degrees-C yielding a less hydrated phase, H2Ti5O11.H2O, with a smaller interlayer distance. Subsequent dehydration resulted in the metastable form of titanium dioxide TiO2(B) around 500-degrees-C, which was transformed into anatase and then rutile at elevated temperatures. The material H2Ti5O11.3H2O underwent a stepwise intercalation reaction with K and Cs ions, replacing oxonium ions and hydroxylated protons in this order. This reaction gave rise to half- and fully-loaded phases with different degrees of swelling. The structural characterizations of the phases indicate that the reaction proceeds topochemically, accompanied by a lateral gliding of adjacent host lamellae along the c axis as well as a swelling/contraction of the interlayer spacing.