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Rapid exfoliation of a layered titanate by ultrasonic processing

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Abstract

The application of ultrasound dramatically increases the rate of exfoliation of H(x)Ti(2-x 4)O(4)(.)gammaH(2)O (H-Ti) in the presence of aqueous tetrabutylammonium (TBA) hydroxide. The effect of ultra sonication power and processing time on particle size distributions are evaluated. Applied powers of 60-300 W and reaction times of 2-30 min effectively reduce the H-Ti particle size to < 100 nm. Both particle size distribution analysis and UV-Vis spectroscopy were used to study the effect of ratio of TBA ion to exchangeable protons in H-Ti; a minimum ratio of TBA/H greater than or equal to 0.5 is required for rapid exfoliation.

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... The detailed crystal structure of Sasaki's nanosheets is presented in Figure 2.3. Lepidocrocite-like potassium-lithium titanate is different with lepidocrocite-like caesium titanate in terms of structural arrangement of interlayer ions (blue dot in Figure 2.3) due to the size of potassium ion is smaller than caesium 44 (see Figure 2 Other methods of exfoliation such as supercritical fluid exfoliation 48 and combination of bulky molecules exfoliation and ultrasonication 49 have been investigated. By applying ultrasonic wave in a solvent, cavitation bubbles are generated and collapse into high energy jets thus breaking up layered nanosheets. ...
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Layered nanocomposites with poly(ethylene oxide), PEO, and poly(vinylpyrrolidone), PVP, incorporated between HxTi2-x/4□x/4O4 (□ = Ti vacancy) titanate layers, are synthesized from a colloidal titanate suspension obtained by exfoliation in aqueous tetrabutylammonium hydroxide and subsequent acidification. Products are characterized by powder X-ray diffraction, thermal analyses, FTIR spectroscopy, scanning electron microscopy, and elemental analysis. Interlayer expansions for the vacuum-dried nanocomposites are 0.81 and 2.2 nm for the PEO- and PVP-containing products, respectively. Both nanocomposites are comprised of 10−100-μm diameter platelets, much larger than those of 0.1−1 μm for the starting titanate. FTIR spectra indicate the presence of the polymers and suggest decreased water interaction with titanate sheet surfaces for the polymer-containing products. Thermal analyses of nanocomposites show intercalate water loss below 200 °C, polymer degradation and structure decomposition between 200 and 450 °C, and a titanate phase change above 450 °C. Elemental analyses give empirical formulas of H0.7Ti1.83O4(C2H4O)1.54(H2O)1.28 and H0.7Ti1.83O4(C16H36N)0.05(C6H9NO)1.22(H2O)0.92 for the PEO and PVP nanocomposites, respectively. These results are compared with those obtained for other layered nanocomposites.
Article
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.