Tsuyoshi Kijima

Synthesis and deorganization of an aluminium–based dodecyl sulfate mesophase with a hexagonal structure

An aluminium-based dodecyl sulfate mesophase with a hexagonal structure is synthesized by the homogeneous precipitation method using urea and is thermally deorganized into a hexagonal but less ordered framework structure with a d spacing of 3.4 nm.

Identification of the superconducting phase in the Bi−Ca−Sr−Cu−O system

In order to identify the superconducting phase in the Bi-Ca-Sr-Cu-O system, phase search experiments were performed. The results of power X-ray study, EPMA study, specific gravity measurements and oxygen analysis revealed that the compound having the composition Bi2(Ca, Sr)3Cu2O9 or Bi2(Ca, Sr)3-ΔxCu2O9-Δy is responsible for the high-Tc superconductivity. Two possible structure models, which are closely related to the structure of the bismuth titanate Bi4Ti3O12, are proposed for this compound.

Pillaring and photocatalytic property of partially substituted layered titanates, Na2Ti3−xMxO7 and K2Ti4−xMxO9 (M=Mn, Fe, Co, Ni, Cu)

Abstract Porous pillared materials have been synthesized from substituted tri- and tetratitanates (Na 2 Ti 3− x M x O 7 , K 2 Ti 4− x M x O 9 , M=Mn, Fe, Co, Ni, Cu, x ≤0.3) by a stepwise exchange process. The microstructure of pillared samples was characterized by a number of cleavages running parallel with TiO 6 layers, which produced a waffle-like texture. The pillared samples showed 10–25 times larger BET surface areas (50–120 m 2 /g) as compared to pristine samples. The photocatalytic activity of 1 wt.% Pt/titanates for H 2 evolution from CH 3 OH/H 2 O mixtures was enhanced by pillaring in accord with an increase of the surface area. Partial substitution of various transition elements for the Ti site significantly affected the H 2 evolution rate.

Catalytic properties and surface modification of hexaaluminate microcrystals for combustion catalyst

Abstract Spinel oxide (Mn304) surface layers were produced on hexaaluminate microcrystals by means of the air-oxidation process. The surface layer completely covered the basal plane of hexagonal facets as evident from HREM observation and CO2 chemisorption measurement. The catalytic activity of as prepared Mn304/hexaaluminate composites for methane combustion was evaluated as functions of the Mn304loading and the metal composition of the spinel surface layer. It was revealed that the air oxidationderived composites showed the excellent specific activities superior to those of the corresponding Mn304/hexaaluminates prepared from the conventional evaporation-to-dryness process. Partial substitution of Fe for Mn of the surface layer was effective in enhancing combustion activity in a whole temperature range.

Electronic structure of layered tantalates photocatalysts, RbLnTa2O7 (Ln=La, Pr, Nd, and Sm)

Abstract The correlation of electronic structure with photocatalytic properties of layered perovskite tantalates, RbLnTa 2 O 7 (Ln=La, Pr, Nd, and Sm), containing the partly-occupied Ln4 f shell is studied by means of valence band photoemission (XPS) measurement and first-principles calculations of the band structure based on the all-electron full-potential linear augmented plane-wave (FLAPW) method. The unoccupied La4 f level is located on the bottom of the conduction band, whereas the partially occupied 4 f levels become lowered with an increase of 4 f electrons down to the position above the valence band edge (Ln=Pr) and finally fall into the valence band mainly comprised of O2 p orbitals (Ln=Nd and Sm). It was suggested that unoccupied as well as occupied 4 f orbitals are not completely localized but partly contribute to the hybridization with O2 p and Ta5 d orbitals. The different photocatalytic activity of the present system for the overall water splitting is closely related to the degree of the Ln–O–Ta hybridization, which affect not only the positions, of the conduction band and valence band edges, but also the density of states (DOS) distribution in both bands.

Structure and Composition Analysis of High-Tc Superconducting Bi-Ca-Sr-Cu-O Oxide by High-Resolution Analytical Electron Microscopy

The chemical composition and the crystal structure of the Bi-Ca-Sr-Cu-O oxide with a high-Tc of about 75 K have been studied by the combined techniques of crystal structure imaging and spectroscopic microanalysis using a 400 kV high-resolution analytical electron microscope. The crystal is orthorhombic with lattice parameters a=0.54 nm, b=2.70 nm and c=3.06 nm. The chemical composition is assigned as Bi2CaxSrzCu2Oy, where x and z are approximately 1.0 and 1.5, respectively. The structure image reveals that the structure is comprised of a bismuth oxide layer interleaved with an oxygen deficient perovskite-like layer. It is suggested that a nearly commensurate superstructure based on the perovskite-type structure is formed.

Superconductivity in the Bi-Sr-La-Cu-O System

During the investigation of the Bi-Sr-La-Cu-O system, a family of bismuth oxides with the composition of Bi2Sr2-xLazCuOy (x=0.3–0.6, z=0.2–0.3) has been found to exhibit a superconducting transition with an onset temperature near 27 K and zero resistivity at 5 K. The major phase is an incommensurate one with a composition of Bi2Sr1.5La0.2CuOy and is orthorombic with unit cell dimensions of a=0.538, b=0.542×n and c=2.43 nm where n is a nonintegral number of 4.3.

Efficient photocatalytic decomposition of water with the novel layered tantalate RbNdTa2O7

Under UV irradiation, RbNdTa2O7, the first example of an active photocatalyst containing partially occupied 4f levels, demonstrated efficient evolution of stoichiometric H2/O2 mixtures from pure water even in the absence of loaded metal catalysts.

Synthesis of β-Ni(OH)2 Hexagonal Plates and Electrochemical Behavior as a Positive Electrode Material

β-Ni(OH) 2 hexagonal plates were synthesized from the high specific surface area nickel hydroxide by adopting the solvothermal treatment, i.e., heat-treatment of nickel hydroxide in a closed vessel in the presence of the disperse phase. An aqueous ammonia solution was chosen as the disperse phase, and it was effective for producing unit cell derived hexagonal particles even at a relatively low temperature of around 80°C. A wide variety of sizes and specific surface areas of the hexagonal β-Ni(OH) 2 could be available by choosing the solvothermal conditions such as amount and concentration of ammonia solution as the disperse phase as well as treatment temperature. The solvothermally synthesized hexagonal plates showed stable discharging behavior without serious deterioration in the discharging capacity when relatively high charge/discharge rates were adopted. It was speculated that there is a suitable specific surface area for the hexagonal particles to achieve a higher discharging capacity at high charge/discharge rates.

Uptake of amino-acids by zirconium phosphate. Part 3. Intercalation of L-histidine, L-lysine, and L-aginine by γ-zirconium phosphate

The uptake of L-histidine (His), L-lysine, and L-arginine by γ-zirconium phosphate has been studied. The intercalation of His is initiated by the partial replacement of interlayer water by a monolayer of the guest molecules oriented horizontally to the sheet of the host crystal to form a phase Zr(HPO4)2(His)0.2·1.9H2O with an interlayer spacing of 14.1 A. This is followed by the formation of a phase Zr(HPO4)2(His)0.4·0.8H2O without any appreciable change in interlayer spacing, which is finally converted into a phase Zr(HPO4)2(His)0.9·3H2O with an interlayer spacing of 22.9 A in which the guest molecules are intercalated as a bilayer. Lysine and arginine also form one or two monolayered phases at low uptakes, while at higher loadings the intercalates formed are highly disordered, but with a certain degree of order in the host lattice. The different behaviour of α- and γ-zirconium phosphates in intercalating amino acid molecules is discussed in terms of the structural or functional characteristics of the individual acids and phosphates. A supplementary discussion of the amino acid arrangement in α-zirconium phosphate is also made.