Nobuyuki Nishimiya

Preparation and characterization of TiO2 incorporated Y-zeolite

Abstract A preparation of TiO 2 -dispersed Y-zeolite has been attempted by a method comprising a substantial ion-exchange of ammonium titanyl oxalate (NH 4 ) 2 TiO(C 2 O 4 ) 2 and its decomposition. The modification of Y-zeolite was well controlled from the viewpoint of the incorporated amount of TiO 2 . The framework of Y-zeolite was retained through the modification and TiO 2 was incorporated in the form of anatase microcrystals. Titanium species bound to the framework through Ti–O–Si bonds were also observed by IR analysis. The porosity change of Y-zeolite by the TiO 2 modification was analyzed by N 2 adsorption at 77 K, and the pore size of TiO 2 modified Y-zeolite proved to increase with the amount of incorporated TiO 2 . Photolysis of ethanol to give methane was enhanced by the TiO 2 -dispersed Y-zeolite; the rate of reaction in the Pt–TiO 2 –zeolite system of an appropriate amount of TiO 2 was more than five times that in a conventional Pt–TiO 2 system.

Hydrogen sorption by single-walled carbon nanotubes prepared by a torch arc method

Single-walled carbon nanotubes (SWCNTs) were prepared by a novel torch arc method operated in open air and isotherms of hydrogen sorption were volumetrically measured at 295 and 77 K under pressures below 110 kPa. The averaged diameter of SWCNTs was 1.32 nm, as measured by high-resolution transmission electron microscopy, and the dominant presence of the (9,9) armchair nanotubes accompanied by the (10,10) armchair nanotubes was suggested by the breathing mode Raman scattering. The maximum hydrogen concentrations reached 0.932 wt.% at 295 K under 106.7 kPa and 2.37 wt.% at 77 K under 107.9 kPa with the hydrogen uptakes not yet saturated. It is likely that the sorbed hydrogen molecules resided on the exterior surfaces of SWCNTs. The higher surface area of SWCNTs by a factor of 10 as compared to the graphitic raw material would play a dominant role for hydrogen sorption to bring about the higher hydrogen wt.% by a factor of 10. The high graphitic nature of SWCNTs would also play an important role, but the observed surface H/C ratio, 0.680 at 77 K under 100 kPa, exceeded the expected value, 0.333, for the commensurate adsorption structure, and the uppermost value, 0.49, for the densest monolayer, which suggested the presence of unknown sorption mechanism(s) other than physisorption on carbon hexagons.

Effect of amplitude and frequency of ultrasonic irradiation on morphological characteristics control of calcium carbonate

We have previously reported on the morphological control of calcium carbonate by changing synthetic conditions such as temperature, pH and degree of supersaturation in liquid reaction. The present study reports the effect of amplitude and frequency of ultrasonic irradiation on the particle size of calcium carbonate using a horn type ultrasonic apparatus at two different frequencies. The calcium carbonate precipitated by mechanical stirring had a particle size of about 20mum. By contrast, the particle size of vaterite formed under ultrasonic irradiation was about 2mum, with a specific surface area of 25-30m(2)/g. The major polymorph of calcium carbonate formed by ultrasonic irradiation was vaterite with some calcite present. For 40kHz ultrasonic irradiation, the specific surface area of the calcium carbonate increased with increasing amplitude. The particle size of vaterite formed at this frequency was about 2mum, and its distribution was sharper than that obtained at 20kHz. The mode diameter of the synthesized vaterite was found to decrease with increasing amplitude at 40kHz.

Hyperstoichiometric hydrogen occlusion by palladium nanoparticles included in NaY zeolite

Abstract Amounts of occluded hydrogen in palladium-containing NaY zeolites increased with the palladium content. Allocation of mols of hydrogen atoms to palladium gave large H/Pd ratios higher than unity at 298 K under 100 kPa of hydrogen. As the palladium content increased, the proportion of the external palladium increased and the H/Pd value decreased to approach that for powdery palladium. The hyperstoichiometric occlusion of hydrogen can be attributed to palladium nanoparticles or clusters inside the pores of zeolite. Whereas the interstitial site per palladium atom was unity for powdery palladium, for the internal palladium species it seemed to be two or more. Before reaching the stoichiometric composition, PdH, the palladium species released substantial heat on hydriding similarly to powdery palladium. After the hydrogen content exceeded the stoichiometry, the heat on hydriding was as low as 1 kJ/mol H 2 .

Thermal stability and hydrophobicity of mesoporous silica FSM-16

Thermal stability and hydrophobic property of mesoporous silica, FSM-16, has been studied. The mesoporous structure of FSM-16 was stable against calcination up to 1073 K in vacuo, but collapsed at 1273 K. Adsorption isotherm and differential heat of adsorption measurements showed that the calcination temperature affected the hydrophobic nature of FSM-16, and that the surface changed to hydrophilic by hydroxylation of surface siloxane during water adsorption. Once the surface became hydrophilic, the hydrophobic character was never restored even after evacuation at 823 K.

Oxygen sorptivity of mesoporous aluminosilicate modified by Co-salen complex

Mesoporous aluminosilicate, FSM-16 (Al-FSM-16(n)), was functionalized by Co-salen modification. The Si/Al ratio, n, was varied from 12.8 to 60.0, and inclusion of Co-salen (N,N 0 -bis(salicylidene)ethylenediaminocobalt(II)) was carried out by a novel preparative method comprising Co 2a ion exchange in a nonaqueous solution of cobalt(II) acetate and chelation with salen-H2 (N,N 0 -bis(salicylidene)ethylenediamine). Prominent O2 sorptivity was imparted to this mesoporous material and the amount of O2 sorbed on Co-salen-Al-FSM-16(60.0) was 0.275 mmol g ˇ1 at 298 K, significantly larger than that on Al-FSM-16(60.0) itself (0.085 mmol g ˇ1 ). The O2 sorption on Co-salen-Al-FSM-16(60.0) remarkably proceeded under a pressure around 20 kPa at 298 K, which was similar to powdery, free Co-salen. The maximum O2/Co-salen ratio for Co-salen included in mesopores was seven times as large as that for neat Co-salen. The pore structure of Al-FSM-16(n) with a high n value was retained through the modification as evidenced by XRD, TEM and N2 adsorption measurements, but that of Al-FSM-16(12.8) was partly collapsed. ” 2000 Elsevier Science B.V. All rights reserved.

Hydriding characteristics of zirconium-substituted FeTi

Abstract Hydriding of FeTi 1− a Zr a alloys ( a =0.1, 0.2 and 0.5) proceeded without any activation treatments. Zirconium substitution lowered the equilibrium pressure in the β phase region and narrowed the width of the plateau. The hydrogen capacity increased with the zirconium content, but the reversible amount of hydrogen, conveniently defined as the difference in the hydrogen contents under 4 MPa and 0.05 MPa of hydrogen, decreased with the a value owing to the increased hydrogen content under 0.05 MPa. When the value a was equal to 0.5, the isotherm showed no plateau and major parts of observed data obeyed the general solid solution model, wherein the number of interstitial sites was equal to the number of metal atoms. A new ternary phase Fe 2 TiZr would substantially be present and hydrogen atoms occupy the interstitial sites to form Fe 2 TiZrH 4 . At lower temperatures, the hydrogen capacity x (Fe 2 TiZrH x ) exceeded 4 under high pressures of hydrogen.

Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing

Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm(3), had a specific surface area of 65 m(2)/g and a composition of CaCO(3)•0.5H(2)O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature.

Hydriding–dehydriding characteristics of aged Mg–10%Ni alloy hydride and water resistance of sol–gel encapsulated composite

Abstract Thermodynamic assessments of a 20-year-old Mg–10%Ni alloy hydride, which had been stored under a dry atmosphere, was carried out. More than 80 mol% of the magnesium in the aged sample was reactive to hydrogen. After a further two-year aging in an ambient atmosphere, formation of magnesium hydroxide proved to be significant. The hydrogen absorbing ability was diminished through consumption of magnesium, and the rate of deterioration was accelerated due to the increased surface area brought by decomposition of magnesium hydroxide on dehydriding at elevated temperatures. The presence of water would favor the formation of magnesium hydroxide. Encapsulation of the hydride with the siliceous shell prepared by the sol–gel method provided a water resistant composite which had fair hydriding–dehydriding characteristics.

Surface free energy predominates in cell adhesion to hydroxyapatite through wettability.

The initial adhesion of cells to biomaterials is critical in the regulation of subsequent cell behaviors. The purpose of this study was to investigate a mechanism through which the surface wettability of biomaterials can be improved and determine the effects of biomaterial surface characteristics on cellular behaviors. We investigated the surface characteristics of various types of hydroxyapatite after sintering in different atmospheres and examined the effects of various surface characteristics on cell adhesion to study cell-biomaterial interactions. Sintering atmosphere affects the polarization capacity of hydroxyapatite by changing hydroxide ion content and grain size. Compared with hydroxyapatite sintered in air, hydroxyapatite sintered in saturated water vapor had a higher polarization capacity that increased surface free energy and improved wettability, which in turn accelerated cell adhesion. We determined the optimal conditions of hydroxyapatite polarization for the improvement of surface wettability and acceleration of cell adhesion.