大場 友則

A nano-structured alloy of Ni and Fe was prepared using poly(vinyl alcohol) (PVA) as a polymer precursor, followed by the reduction of Ni2+ and Fe3+ ions to the corresponding metals by heat treatment of the PVA film containing the metal ions under an inert atmosphere. The alloy obtained was characterized by nitrogen adsorption studies, X-ray diffraction and electron microscopy measurements, and by X-ray photoelectron spectroscopy. The nano-structured alloy had the same crystal structure as that of metallic Ni although metallic Fe formed a different structure. The introduction of Fe atoms caused disorder and less crystallinity in the crystal structure of the alloy, whereas Ni atoms tended to maintain the original crystal Structure. Nitrogen adsorption measurements at 77 K showed that the nano-structured Ni-Fe alloy contained mesopores of 4-10 nm in diameter.

We synthesized a discrete type of organic-inorganic hybrid crystal [Cu(ina)(2)(NH3)(2)(H2O)(2)] (ina = isonicotinate). The monomer units connect to each other with hydrogen bonds and pi-pi interactions, forming a three-dimensional network. Removal of ammonia and water molecules by vacuum heating treatment induced a substantial change from nonporous to porous crystals. The resultant porous crystals can predominantly adsorb supercritical hydrogen rather than nitrogen vapor at 77 K.

Single wall carbon nanotube (SWCNT), which has bundle structure and entangled structure, was untangled and cut by sonication in hydrogen peroxide (H(2)O(2)) solution. The untangled state of SWCNT was examined by SEM, TEM, Raman spectroscopy and N(2) adsorption. It was confirmed that the surface area of sonicated nanotubes strongly depended on the sonication time. The BET specific surface area (SSA) of nanotubes sonicated for 3 h was maximum. The SSA decreased at 6 h or more of sonication time. These results indicated that the bundle structure was untangled and the cap of SWCNT was opened. Thus, N(2) molecules can access the most efficiently inside of the SWCNT sonicated for 3 h. On the contrary, the sonication treatment for 6 h or more decomposed the nanotubes to produce amorphous carbon, evidenced by TEM and SEM observation; the amorphous carbon blocked the open pore sites such as the internal pore spaces and interstitial pores.

The experimental adsorption isotherm of N-2 Molecules on mutually isolated single wall carbon nanotubes at 77 K agreed well with the grand canonical Monte Carlo simulated one. The N-2 adsorption isotherm had two steps stemming from monolayer formation on the internal surface and filling of the residual space of the internal tube pore. Although all of radial distribution functions of molecules adsorbed on the internal, external, and flat surfaces indicated a hexagonal packing structure, the radial distribution functions were different from each other. In particular, the radial distribution function of the monolayer on the internal surface showed an additional peak because of the markedly curved surface.

The synthesis, structural changes, and nitrogen gas sorption isotherm of a porous metal-organic framework (PMOF) comprising stacked two-dimensional sheets are reported. This compound easily loses guest molecules and shrinks its interlayer distance. The guest-free species show a unique double-step sorption isotherm. Sorption and X-ray structural analyses have clarified that the first uptake is a micropore filling, while the second uptake originates from a clathrate formation. This explains the total sorption amount corresponding to about the double of the original void volume of the crystals.

We showed water adsorption isotherms at 303 K on water-resistant three-dimensional (3-D) pillared-layer metal organic frameworks (MOFs) with I -D semi -rectangular pores, of which size depends on the length of ligand. The shapes of all three adsorption isotherms are type I by IUPAC classification showing strong water-MOFs interaction. The adsorbed amount of water molecules on the hydrophilic site of carboxylic group in 2-D sheets coincided with the crystal water amount. The adsorption on the hydrophilic sites occurs at similar relative pressure even if the used ligand is different. (c) 2007 Elsevier Inc. All rights reserved.

The surface oxygen concentration of pitch-based activated carbon fibers (ACF) was controlled by heat treatment in Ar and H-2. The surface oxygen-to-carbon ratio was determined by X-ray photoelectron spectroscopy; the O/C ratios of the as-received ACF, the ACF treated in Ar, and the ACF treated in H-2 were 0.07, 0.03, and 0.02, respectively. The adsorbed states of water in the nanopores of the three ACFs were investigated by density fluctuation analysis from small-angle X-ray scattering and grand canonical Monte Carlo (GCMC) simulation. Although the adsorption isotherms of the three ACFs at 303 K have almost similar features, their density fluctuation profiles with filling differ. The density fluctuations in the course of adsorption showed that the cluster size of the adsorbed water increased with the decrease in the number of surface oxygens. Radial distributions calculated from the snapshots of the GCMC simulation suggested that the water structure has a short-range order with hydrogen bonding. The island type growth of clusters on the surface oxygens served as evidence for the ACF with surface oxygen.

The radial breathing mode (RBM) frequency in Raman spectra of single-wall carbon nanotubes (SWNTs) is upshifted (3-9 cm(-1)) by immersion of the SWNTs in various alcohols and water. However, the immersion in the solvents does not cause any visible variation in the tangential mode frequency. The degree of this RBM frequency upshift induced by the solvent adsorption corresponds to that caused by applying a high pressure of 1 GPa (6-10 cm(-1)/GPa) in the literature. The degree of the RBM frequency upshift increases with increases in the molecular weight of the solvents. RBM frequency upshift caused by immersion of SWNTs in water is much larger than that by the molecular weight of alcohols, indicating the cluster formation of water molecules.

Novel nanostructured carbon material was synthesized by applying zeolite LTA as a template and using methanol as a carbon source. X-ray diffraction (XRD) revealed that the higher the decomposition temperature, the more graphitic and ordered the structure. The optimum pyrolytic temperature for addition of microporosity was below 1273 K by analysis of N-2 adsorption isotherm. The resultant carbons have the long-range periodic structure of a nanoscale curvature according to XRD and Raman spectroscopic examinations. The morphological similarity between zeolite LTA and synthesized carbon was evidenced by scanning electron microscopic observation. Grand canonical Monte Carlo simulation of N-2 adsorption isotherm indicates that synthesized nanoporous carbon has a hollow hemispherical structure of which diameter is less than 0.7 nm.

Water adsorption isotherms of hydrophobic activated carbon fibres (ACFs) having average pore widths, w, of 0.7 and 1.1 nm at 303 K were greatly different from each other; the adsorption isotherm of ACF with w 0.7 nm had no clear hysteresis loop, while that of ACF with w 1.1 nm had an explicit hysteresis loop. The structures of water adsorbed in both nanopores were studied using adsorption measurement, grand canonical Monte Carlo (GCMC) simulation, and in situ small angle X-ray scattering (SAXS). The in situ SAXS study of water in the 1.1 nm pores with the aid of GCMC simulation showed that adsorption proceeds through isolated cluster formation, whereas a mixed structure of a partial monolayer array and isolated clusters are formed on the desorption near the fractional filling, phi = 0.4. This adsorbed structure difference is the origin of the adsorption hysteresis. In contrast, both adsorption and desorption processes have the isolated cluster structure near phi = 0.4 in the case of 0.7 nm pores, agreeing with the absence of a clear hysteresis loop.

New nanoporous materials and fundamental concepts on molecule solid interaction are introduced. The nanopore structures of single wall carbon nanotube (SWCNT), single wall carbon nanohorn (SWCNH), double wall carbon nanotube (DWCNT), and highly flexible Cu-complex crystals as a representative of metal organic frameworks (MOFs) are explained. Adsorption properties of SWCNT, SWCNH, and DWCNT for supercritical CH4, and H-2, and Cu-complex crystals for supercritical CH4, are shown. DWCNT has a better adsorption potential for supercritical H-2, than SWCNT. The Cu-complex crystals form very quickly a new clathrate compound with CH4, molecules on adsorption of CH4, the reproducible clathrate formation is sensitive to temperature.

Interfacial importance and nanopore structures of single wall nanocarbons such as single wall carbon nanotube (SWCNT) and single wall carbon nanohorn (SWCNH) are described in terms of intermolecular interaction theory. The relationships between the nanopore structure and nanoconfinement effect for molecules and ions are shown using examples on supercritical H2 adsorption on SWCNT, quantum molecular sieving effect of SWCNT for H2 and D2 below 77 K, water structure and hydration structure of Rb, Cs, and Sr ions in nanopores of activated carbon fiber and SWCNH, and capacitance storage of SWCNH. The SWCNT produced by laser ablation shows upward-curved adsorption isotherm of H2 at 77 K, suggesting the presence of the strong sites. The adsorption amount of D2 on this SWCNT at 77 K was clearly larger than that of H2 by about 20% at 77 K due to quantum effect. The hydration number around Cs and Sr ions in 1.1 nm slit pores of ACF reduced by more than 20 %. The capacitance depended on the opening of SWCNH and charging time for organic electrolyte (C2H 5)4NBF4 in propyrene carbonate. ©The Electrochemical Society.

Lithium ions of perovskite-type lithium ion conductor La0.55Li0.35TiO3 were replaced by divalent Mg2+ Zn2+, and Mn2+ ions in an ion exchange reaction using molten chlorides. The polycrystalline Mg-exchanged and Zn-exchanged samples are solid electrolytes for divalent Mg2+ and Zn2+ ions, whose dc ionic conductivities (sigma = 2.0 x 10(-6) S cm(-1) at 558 K for the Mg-exchanged sample, La-0.56(2)Li0.02(1)Mg0.16(1)TiO3.01(2) and sigma = 1.7 x 10(-6) S cm(-1) at 708 K for the Zn-exchanged samples, La0.55(1)Li0.0037(2)Zn0.15(1)TiO2.98(2)) were compared to those of the known highest Mg2+ and Zn2+ inorganic solid electrolytes. The Mn-exchanged sample, then, showed paramagnetic behavior in the temperature range of 2 to 300 K. The Mn ions in the exchanged sample are divalent and the spin configuration is in high spin state (S=5/2). (c) 2006 Elsevier B.V. All rights reserved.

N-2 adsorption on Cu-organic crystals [Cu(bpy)(2)( BF4)(2)] (bpy=bipyridine) at 77K begins suddenly at P/P-0=0.1. This unique adsorption is named gate adsorption. Gate adsorption is associated with the change of crystal structure from GCMC and dynamic GCMC simulations. An expansion of 10% opens internal pore spaces in the crystal, giving rise to gate adsorption. The complete filling of the internal spaces with N-2 molecules induces an expansion of 30%.

The growth mechanism of water clusters in carbon nanopores is clearly elucidated by in situ small-angle X-ray scattering (SAXS) studies and grand canonical Monte Carlo (GCMC) simulations at 293-313 K. Water molecules are isolated from each other in hydrophobic nanopores below relative pressures (P/P-0) of 0.5. Water molecules associate with each other to form clusters of about 0.6 nm in size at P/P-0= 0.6, accompanied by a remarkable aggregation of these clusters. The complete filling of carbon nanopores finishes at about P/P-0=0.8. The correlation length analysis of SAXS profiles leads to the proposal of a growth mechanism for these water clusters and the presence of the critical cluster size of 0.6 nm leads to extremely stable clusters of water molecules in hydrophobic nanopores. Once a cluster of the critical size is formed in hydrophobic nanopores, the predominant water adsorption begins to fill carbon nanopores.

The average interstitial nanopore structure of single-wall carbon nanohorn (SWNH) assemblies was determined using X-ray diffraction and grand canonical Monte Carlo (GCMC) simulation aided N-2 adsorption at 77 K. The interstitial nanopores of SWNH assemblies can be regarded as quasi one-dimensional pores due to the partial orientation of the SWNH particles; the average pore width of the interstitial pores is 0.6 run. Good agreement between the GCMC simulation of a structural model with one-dimensional interstitial nanopores and an experimental adsorption isotherm below P/P-0 = 10(-4) is evidence of the quasi one-dimensionality of the interstitial nanopores. A snapshot from the GCMC simulation showed one-dimensional growth of adsorbed N-2 molecules.

The temperature dependencies of in situ small-angle X-ray scattering (SAXS) of water adsorbed and of adsorption isotherm of water in hydrophobic carbon nanopores were measured over the temperature range of 293 to 328 K. The structures of water nanoclusters adsorbed in the nanopores were determined with the density fluctuation analysis of in situ SAXS data. The difference of the density fluctuations between adsorption and desorption was ascribed to the water structural difference. The structural transitions of the water nanoclusters were observed around 318 K for adsorption and 308 K for desorption.

The relationships between the enhanced interaction potential and intensive confinement effect of slit-shaped and cylindrical nanospaces are shown. The structures of water molecules and aqueous ions confined in nanospaces of activated carbon fiber (ACF) and single wall carbon nanohorn (SWNH)s were studied by adsorption, in situ small angle X-ray scattering(SAXS), GCMC simulation, and EXAFS spectroscopy. Water molecules are associated with each other to form the clusters, being stabilized in the carbon nanospaces. This stabilization mechanism of water in carbon nanospaces were evidenced by the interaction potential calculation, GCMC simulation, and the density fluctuation analysis of in situ SAXS. The Ornstein-Zernike analysis of in situ SAXS profiles lead to the conclusion that the critical size of water clusters for predominant water adsorption in hydrophobic carbon nanospaces is about 0.5 nm corresponding to the octomer to decamer. The adsorption hysteresis of water adsorption isotherm of nanoporous carbon was interpreted by the cluster growth, which is confirmed by the density fluctuation analysis. The Rb and Br ions confined in the carbon nanospaces were examined by EXAFS spectroscopy. The remarkable decreases in the hydration number and the water-Rb ion distance of the solution confined in the nanospaces were observed. In particular, the hydration number of the Rb ion in the nanospaces of SWNH is less than 3, being much smaller than the hydration number (6) of the bulk solution. The electrical double layer structure in the nanospaces should be quite different from that in the bulk solution.

The stabilities of water molecules in carbon slit-shaped nanospaces have been studied using the potential calculation for possible water clusters (H2O)n) of n = 2-12. The adsorption isotherm of water on a graphite slit pore (w = 1.1 nm) with no surface functional groups at 303 K was calculated with GCMC simulation using TIP-5P and 10-4-3 Steele potential functions; this simulated isotherm has a vertical uptake at P/P-0 = 0.5. The cluster growth along the vertical adsorption uptake was evidenced through the snapshot of GCMC simulation. The simulated adsorption isotherm agreed well with the experimental isotherm of water on an activated carbon fiber (ACF) having uniform slit pores. Thus, H2O molecules are adsorbed in hydrophobic carbon nanopores without surface functional groups through cluster formation. The isosteric heat of adsorption of clusters of (H2O)(n=8-10) obtained from the GCMC simulation coincided well with the experimental value. The radial distribution function of the clusters from the GCMC simulation is close to the structure of ice I-h. Therefore water molecules can gain an explicit hydrophobicity through clusterization in nanopores.

A new technique of superwide pressure range adsorption (SWPA) isotherm measurement of N-2 from P/P-0 = 10(-9) to 1 at 77 K was developed. The superwide pressure range adsorption isotherms of N-2 on activated carbon fiber, molecular sieve carbon, and carbon black were compared with those of their ordinary pressure range isotherms and the simulated isotherms calculated with grand canonical Monte Carlo technique. The SWPA measurement can show the adsorption uptake below P/P-0 = 10(-6), which is assigned to the adsorption in ultramicropores of pore width < 0.7 nm. The SWPA method shows the presence of ultramicropores even for nonporous carbon black, which has been believed to be nonporous from the ordinary adsorption measurement. Thus, the SWPA method can elucidate the ultramicropore structures of less-crystalline materials.

Single wall carbon nanohorns (SWNHs) were treated in vacuum at different temperatures of 473 to 1073 K. The nanostructural change due to the heat-treatment vas studied by adsorption of N-2 at 77 K and H2O at 303 K. The determined particle density showed that gas is not adsorbed in internal pores, but in interstitial pores. The high temperature treatment (HTT) in vacuo changed water adsorption, but it gave almost no influence on N-2 adsorption. The maximum nanopore volume from H2O adsorption was observed at 673 K, indicating the interstitial nanopore change due to a local orientational change of SWNH particles. (C) 2004 Elsevier B.V. All rights reserved.

The interaction of water with hydrophobic surfaces is quite important in a variety of chemical and biochemical phenomena. The coexistence of water and oil can be realized by introduction of surfactants. In the case of water vapor adsorption on graphitic nanopores, plenty of water can be adsorbed in graphitic nanopores without surfactants, although the graphitic surface is not hydrophilic. Why are water molecules adsorbed in hydrophobic nanopores remarkably? This work can give an explicit insight to water adsorption in hydrophobic graphite nanopores using experimental and theoretical approaches. Water molecules are associated with each other to form the cluster of 1 nm in size, leading to a significant stabilization of the cluster in the graphitic nanopores. This mechanism can be widely applied to interfacial phenomena relating to coexistence of water and nanostructural materials of hydrophobicity.

The cluster structures of supercritical CH4 confined in slit-shaped carbon micropores was investigated using in situ small-angle X-ray scattering (SAXS) and the cluster analysis for grand canonical Monte Carlo (GCMC) simulation. The pore size distribution of micropores was determined from the fitting of the GCMC-simulated adsorption isotherm to the experimental one for high-pressure CH4; the pore size distributions of two kinds of activated carbon fibers (ACFs) were very narrow, and their average widths are 0.6 and 1.1 nm. The density fluctuation changes with fractional filling from in situ SAXS and GCMC simulation evidenced explicitly the formation of clusters of high concentration in the micropores. CH4 molecules in smaller pores of 0.6 nm form highly concentrated clusters even in low fractional filling. Fewer clusters are formed in the case of wider pores of 1.1 run.

The temperature dependence of N-2 adsorption isotherms on carbon micropores having different pore widths was measured in the temperature range 77-207 K and was simulated using the grand canonical Monte Carlo (GCMC) technique. The adsorbed amount decreased with increasing temperature, irrespective of the difference in the pore width. However, the adsorption decrease depended on both pore width and temperature. The narrower the pore width, the less the adsorption decrease. A slight increase in the measuring temperature from 77 to 82 K gave rise to a large decrease in the adsorption for activated carbon fiber having an average pore width of 1.1 nm, whereas carbon samples with 0.6-0.7 nm average pore width did not show such a remarkable difference. Molecular fluctuation in pores of width 1.2 nm increased as the temperature was increased in the GCMC simulation.

Direct measurements of the kinetic energy of Ne atoms adsorbed on activated carbon (AC) at submonolayer coverage, is reported. The electronvolt spectrometer of the ISIS neutron source that utilizes the neutron Compton scattering technique, was employed. The specific adsorption area of the AC was similar to3000 m(2)/g. The momentum distribution of adsorbed Neon was measured at 12 K. The kinetic energy of Ne was found to be 66.3 +/- 6.2 K, and is much higher than that of solid neon, at the same temperature, being 45.8 +/- 4.8 K. This result is considered to be an evidence for the occurrence of a confinement effect of Ne atoms within the pores of the AC. The result was also used for deducing the average pore size of the AC adsorber assumed to have slit shaped pores. (C) 2002 Elsevier Science B.V. All rights reserved.

The N2 adsorption on the internal and external surfaces of single-walled carbon nanotubes of the continuous model at 77 K was compared with that on the structureless graphite surface with grand canonical Monte Carlo (GCMC) simulation. The inapplicability of the BET analysis for evaluation of the surface area of the internal and external surfaces of the nanotube was explicitly shown and the reason was explained with the monolayer structure difference. The ordinary αs-plot analysis using the standard isotherm of the flat graphite surface did not provide a reasonable method for the internal surface area. However, if we adopt the adsorption isotherm of the internal surface of the pore width being large enough to remove the enhanced potential effect, the subtracting pore effect method (SPE-IC method) using its αs-plot gave an accurate surface area for the internal surface except for the pore width = 2 nm. The cause for the inapplicability of BET analysis was discussed with the radial distribution function of the monolayer.

The N-2 adsorption on the internal and external surfaces of single-walled carbon nanotubes of the continuous model at 77 K was compared with that on the structureless graphite surface with grand canonical Monte Carlo (GCMC) simulation. The inapplicability of the BET analysis for evaluation of the surface area of the internal and external surfaces of the nanombe was explicitly shown and the reason was explained with the monolayer structure difference. The ordinary alpha(s)-plot analysis using the standard isotherm of the flat graphite surface did not provide a reasonable method for the internal surface area. However, if we adopt the adsorption isotherm of the internal surface of the pore width being large enough to remove the enhanced potential effect, the subtracting pore effect method (SPE-IC method) using its alpha(s)-plot gave an accurate surface area for the internal surface except for the pore width = 2 nm. The cause for the inapplicability of BET analysis was discussed with the radial distribution function of the monolayer.

N-2 adsorption isotherms in internal and ineterstitial nanopores of single wall carbon nanohorn (SWNH) were calculated by GCMC simulation and is compared with experimental one. Fitting of the GCMC-simulated isotherm to experimental one in internal nanopores gave the average pore width w = 2.9 nm. The N-2 adsorption isotherm in the interstitial nanopores of the bundled SWNH particles well coincided with the observed one.

Characterization of nanopores must be carried out with integrated information from different levels and angles. It is shown that gas adsorption can provide a key information in the integrated characterization of nanopores. In particular, further understanding of pore filling is necessary; an evidence on quantum effect in pore filling and a new method of adsorption isotherm from P/Po = 10(-9) are introduced with the relevance to the nanopore characterization.

N-2 adsorption in the internal nanospace and on the external suface of the single SWNH particle is studied by grand canonical Monte Carlo simulation and is compared with the experimental result. The detailed comparison of the simulated adsorption isotherm with the experimental isotherm in the internal nanospaces provides 2.9 nm of the average pore width of the internal nanospaces.

The morphological change of Dubinin-Radushkevich (DR) plots of the N-2 adsorption isotherm for graphite slit pores was examined with relevance to the pore size distribution (PSD) and the temperature dependence using grand canonical Monte Carlo (GCMC) simulation. The simulated DR plots with different half-widths of PSD having Gaussian and Gaussian-like distributions of average pore width = 1.2 nm were almost the same as each other below [ln(P-0/P)](2) = 60; the Linearity depending on the half-width of PSD was observed over the [ln(P-0/P)](2) range of 10-60. On the other hand, the DR plot deviated downward from the linear relation seriously above [ln(Po/P)](2) = 60. This is caused by adsorption in the pore for pore widths less than 1.0 nm. The micropore volume calculated from the DR plot for pore widths more than 1.6 nm is underestimated considerably, but that for pore widths less than 1.4 nm is reasonable. The higher the adsorption temperature, the narrower the linear region of the DR plot. The limitation of the Dubinin-Astakov plot is appointed.

The effect of the preformed monolayer on second layer adsorption of N-2 molecules in a graphite slit micropore of pore width = 1.04 - 1.24 nm at 77 K was studied using GCMC simulation. The predominant potential comes from the interaction of a molecule with the preformed monolayer and is more than 70% of the total molecular potential. Therefore, the second stage filling after monolayer adsorption on the micropore walls should he called cooperative filling which was suggested experimentally by Sing et al. (C) 2000 Elsevier Science B.V. All rights reserved.