Local structure analysis of Ti species stabilized in ion exchangeable layer solids by X-ray absorption spectroscopy

Nano-sized titanium dioxides are incorporated into the interlayer spaces of ion-exchangeable layered perovskites, H_1-xCa_2-xLa_xNb₃O₁₀ (x=0.0~0.75), by replacing the interlayer protons with positively charged TiO₂ nano-sol particles or basic titanium glycolate complex (titanatrane). Powder X-ray diffraction analysis, UV-Vis absorption spectroscopy, thermogravimetric analysis, and N₂ adsorption-desorption isotherm measurements show that quantum sized TiO₂ particles are stabilized inbetween perovskite lattices to form micropores (SBET= 37~110 m²/g). X-ray absorption spectroscopy at the Ti K-edge was used for investigating the local environment around Ti atoms constituting the interlayer pillars. According to the XANES spectra, the 'as-pillared' Ti species have the same local environments with those of precursory species, which subsequently converted into TiO₂ clusters with rutile and anatase-like local structures when TiO₂ nano-sol particles and titanatrane are used as pillaring species, respectively. It is also found that the local environment of TiO₂ remains almost constant irrespective of the layer charge density, while the TiO₂ pillar content and the microporosity increase with the latter.