Fumihiko Ohashi

Characterization of synthetic imogolite nanotubes as gas storage

Imogolite is a naturally occurring hydrated aluminumsilicate polymer that consists of a tubular structural unit having an external diameter of 2.3–2.7 nm and an inner diameter of ca. 1 nm. The tube length is from about 400 nm to several micrometers. The tube walls are composed of curved gibbsite-like sheets with SiOH groups on the inside and AlOH groups on the outside, having a composition (HO)3Al2O3SiOH [1]. Imogolite is common in the clay fraction of soils derived from glassy volcanic ashes or pumice beds, and it has also been found in many podzols [2, 3]. Several investigations concerning natural imogolite have been published [4–6]. A synthetic route for production of imogolite was described in 1977 from dilute solutions of aluminum chloride and monosilicic acid [7]. Crystallization takes place at a lower concentration of the starting solutions and low pH under the boiling point treatment [8]. However, the above common process does not produce a high yield of well-crystallized imogolite tubes. Recently, nanotubes composed of various materials such as carbon, boron nitride, and oxides have been investigated [9–11], in particular, carbon nanotubes, which have great potential as materials with novel properties that are not found in conventional graphite or carbon fullerene [12]. For instance, since the suggestion of highly efficient storage of a natural gas with single walled carbon nanotubes, experimental determinations of the storage capacity and the mechanism of the storage have been performed extensively [13]. In the present work, the authors attempt to improve a synthetic method and to characterize an aluminosilicate mineral forming such hollow tubular structures for the purpose of gas storage. Imogolite nanotubes were synthesized from a highly concentrated starting solution under hydrothermal conditions. In a typical synthetic procedure, 66.7 ml of Na4SiO4 solution (concn. 100 mmol/l) was mixed with the same amount of 150 mmol/l AlCl3 solution, and then 1 mol/l NaOH was added dropwise (1 ml/min) into the above homogeneous solution under stirring

Solvent free synthesis of polyaniline–clay nanocomposites from mechanochemically intercalated anilinium fluoride

Nanocomposites consisting of conducting polyaniline and clay minerals were successfully synthesized from mechanochemically intercalated anilinium fluoride; the nanocomposites prepared by the mechanochemical intercalation method contained much more polyaniline in the clay layers than those prepared by a conventional solution method.

THE TRAPPING OF B FROM WATER BY EXFOLIATED AND FUNCTIONALIZED VERMICULITE

Micron-grade natural vermiculite was modified by several physical and chemical treatments in order to increase the adsorption capacity of this material for B. A thermal exfoliation (T = 600°C) of pristine material, a chemical exfoliation through reaction with hydrogen peroxide (H2O2 35%), or grafting of a specific B complexant (i.e. N-methyl-D-glucamine: NMDG) led to an increase in the uptake of B at low initial concentrations of the aqueous solutions ([B] ≈ 5 mg L−1). The more efficient material is the NMDG-grafted clay, for which the adsorption uptake is four times greater than that of raw vermiculite, and reaches 0.04 mmol g−1. For all modified materials, the effect of the pH on B adsorption and the adsorption kinetics were studied and compared to raw vermiculite. Adsorption isotherms were also plotted and fitted well with the Freundlich equation.

An application of EGA–MS with skimmer interface to pyrolysis behavior of DHTAM, an antibacterial and antifungal material with thermostability

An application of evolved gas analysis-mass spectrometry (EGA-MS) with skimmer interface was carried out to investigate the pyrolysis mechanism of an antibacterial and antifungal material that is expected with thermostability. The skimmer interface between a furnace and a vacuum chamber with a mass spectrometer transmitted the gaseous species, which were trapped by a general capillary interface. As a result, it became clear that the thermostability of antimicrobial activity was limited by the heat resistance of the coordinate bond between nitrogen and silver in the silver chelate.