Slit-width-controlled H2Ti4O9/TiO2 nanocomposites were fabricated by stirring with (CnH2n+1NH3)2Ti4O9 and a titanyl acylate complex at 20 °C for 48 h followed by UV light irradiation from a 450 W high-pressure mercury lamp. (CnH2n+1NH3)2Ti4O9 was synthesized by an intercalation reaction with H2Ti4O9 and CnH2n+1NH2 in aqueous or heptane solution for 48 h. The remaining CnH2n+1NH2 and acylate after titania incorporation was completely decomposed into CO2, H2O, and NH3 by UV light irradiation. A slit in the obtained nanocomposites was produced, and its width could be controlled by changing the carbon length of CnH2n+1NH2. Furthermore, the slit expansion and the transformation of the layer structure to fiberlike TiO2 were successfully confirmed by scanning electron microscopy photographs for the first time.

Synthesis of titania-pillared hydrogen tetratitanate nanocomposites and control of slit width

This chapter makes a comprehensive and critical overview on the preparation of hectorite-like solids, pillaring, properties and catalytic applications of pillared interlayered synthetic hectorite clays (PILCs). Hectorite, with some specific properties, is a natural mineral among the most common smectite group of clay minerals. However, hectorite in natural occurrence is scarce. The general synthesis of hectorite-like solids is by means of hydrothermal process or solid-state reaction. The synthesis variables, crystallization, structure of synthetic hectorite along with their characteristics are discussed. Using synthetic hectorite clays with tuneable composition and high purity as layered host precursors is much conducive to designed features and specific applications of PILCs, in contrast to using natural clay minerals with impurities plus other uncertain factors arising from natural deposits. The various intercalation methods and intercalated species in PILC products have been reported with an objective to improve the porous structure and properties of the resultant PILCs. Among many potential uses of pillared synthetic hectorite, the important applications concerning catalysis are emphasized. Finally, the prospects of synthetic hectorite-based materials are briefly remarked.

Synthetic Hectorite: Preparation, Pillaring and Applications in Catalysis

A novel interstratified lizardite/saponite which has never been found in nature is hydrothermally synthesized from uniform Si-Al-Mg gels at 300°C. The stacking ratios of lizardite layer to saponite layer in the structure are designed between 3/1 and 1/3. These materials give partially ordered X-ray diffraction patterns depending on the layer composition. The lattice-fringe image of the L/S= 1/1 sample shows that platelet particles have a thickness of 17.5 A consisting of a lizardite layer (7.5 A) and a dehydrated saponite layer (10.0 A). They can disperse in water like smectite.

Hydrothermal Synthesis of Interstratified Lizardite/Saponite

We have performed torsional oscillator and ultrasonic measurements for 4He confined in 2D nano-porous substrate, hectorite. For 4He films, the resonance frequency of the torsional oscillator increases rapidly just below a superfluid transition temperature (TC), and then becomes constant at the lower temperature. In contrast, the sound velocity below TC increases monotonically with decreasing temperature. For liquid 4He the sound velocity has a small bend at Tb of about 0.9 K. Its increase below Tb is enhanced as the pressure is increased.

Comparison between Torsional Oscillator and Ultrasonic Measurements of 4 He Confined in Nano-Porous Media

The mechanical responses of physisorbed films to the vibration of a substrate were investigated by measuring the sound velocity and attenuation of a two-dimensional mesoporous hectorite. The sound velocity of a hectorite pellet adsorbed by both 4 He and 3 He submonolayer films increased drastically at low temperatures accompanied by the attenuation. The most plausible explanation for this behavior is that helium films decouple from the vibrating substrate at low temperatures.

Mechanical responses of helium films adsorbed on two-dimensional mesoporous hectorite

Novel mesoporous materials having exceptionally large pores were produced from hydrothermally synthesized silicate-bearing hectorites. Experiments suggest that interlayer anisotropic silicates act as larger pillars. Method of preparing such materials is described, together with their porous properties. The mesoporous material from a precursory hectorite synthesized at 150°C has a total specific surface area of 848 m 2 g −1 , a pore volume of 0.98 cm 3 g −1 and an pore average diameter of 46 A, values which are significantly higher than those of conventional pillared clays.

Y. Onodera

Papers

Mesoporous Materials Produced from Hydrothermally Synthesized Hectorites