Seiichi Tahara

Single- and double-layered organically modified nanosheets by selective interlayer grafting and exfoliation of layered potassium hexaniobate.

Organically modified niobate nanosheets are promising building blocks for the design of advanced hybrid materials. Nanosheets with controlled thickness and surface composition are important for precise structural design of the nanosheet-based materials. In this work, single-layered and double-layered niobate nanosheets functionalized by phenylphosphonate moieties were selectively prepared by interlayer grafting of A-type and B-type intercalation derivatives of potassium hexaniobate (K4Nb6O17·3H2O) with phenylphosphonic acid (PPA), followed by exfoliation by ultrasonication in acetonitrile. The interlayer grafting of PPA was monitored using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and solid-state NMR spectroscopy, and the thicknesses of the exfoliated nanosheets were measured by atomic force microscopy (AFM). Transparent hybrid films were obtained by incorporating the single- and double-layered nanosheets into an epoxy matrix.

Preparation of a nanocomposite consisting of a siloxane network and perovskite-related nanosheets via a sol–gel process

Abstract A nanocomposite possessing perovskite-related nanosheets dispersed in a siloxane network was prepared by cohydrolysis of the n-decoxy derivative of an ion-exchangeable layered perovskite, HCa2Nb3O10 xH2O (HCaNb), and tetramethoxysilane (TMOS) via a sol–gel process involving exfoliation. In the X-ray diffraction (XRD) pattern of the product after drying for 1 d, the (0 0 l) reflections disappeared. The transmission electron microscopy (TEM) image of the product after drying for 1 d showed dark lines with a thickness of 1.5 nm, which was consistent with the thickness of an individual nanosheet, indicating exfoliation of HCaNb. In the XRD patterns of the reaction products of the n-decoxy derivative of HCaNb and TMOS before drying and after drying for 60 min, (0 0 l) reflections were detected. After drying for 80 min, the intensity of the (0 0 l) reflections decreased. The intensity decreased with an increase in the drying time, indicating that the exfoliation of HCaNb occurred during the drying process.

Preparation of a Reduced Layered Tungstic Acid H x W 2 O 7 via Acid Treatment of Bi 2 W 2 O 9 in the Presence of Sn 2+ Ions

A reduced layered tungstic acid with a double-octahedral structure was prepared by acid treatment of an Aurivillius-type Bi 2 W 2 O 9 in the presence of Sn 2+ ions. While the color of the product formed by acid treatment with no Sn 2+ ions present, H 2 W 2 O 7 , was yellow, a blue powder was obtained after the acid treatment in the presence of Sn 2+ ions. No notable change in the morphology was observed after acid treatment. The X-ray diffraction pattern of the product acid-treated in the presence of Sn 2+ ions was very similar to that of H 2 W 2 O 7 . Essentially all the Bi 3+ ions were lost upon acid treatment, indicating the occurrence of selective leaching of bismuth oxide sheets in Bi 2 W 2 O 9 . A UV-visible absorption spectrum and XPS analysis demonstrated that the W 6+ ions were partially reduced to W 5+ ions, and the number of protons in the product was correspondingly 2.4 per [W 2 O 7 ]. These results suggest the successful formation of a reduced layered tungstic acid, H 2.4 W 2 O 7 .