Hirofumi Kanoh

Super Flexibility of a 2D Cu-Based Porous Coordination Framework on Gas Adsorption in Comparison with a 3D Framework of Identical Composition: Framework Dimensionality-Dependent Gas Adsorptivities

Selective synthetic routes to coordination polymers [Cu(bpy)(2)(OTf)(2)](n) (bpy = 4,4-bipyridine, OTf = trifluoromethanesulfonate) with 2- and 3-dimensionalities of the frameworks were established by properly choosing each different solvent-solution system. They show a quite similar local coordination environment around the Cu(II) centers, but these assemble in a different way leading to the 2D and 3D building-up structures. Although the two kinds of porous coordination polymers (PCPs) both have flexible frameworks, the 2D shows more marked flexibility than the 3D, giving rise to different flexibility-associated gas adsorption behaviors. All adsorption isotherms for N(2), CO(2), and Ar on the 3D PCP are of type I, whereas the 2D PCP has stepwise gas adsorption isotherms, also for CH(4) and water, in addition to these gases. The 3D structure, having hydrophilic and hydrophobic pores, shows the size-selective and quadrupole-surface electrical field interaction dependent adsorption. Remarkably, the 2D structure can accommodate greater amounts of gas molecules than that corresponding to the inherent crystallographic void volume through framework structural changes. In alcohol adsorption isotherms, however, the 2D PCP changes its framework structure through the guest accommodation, leading to no stepwise adsorption isotherms. The structural diversity of the 2D PCP stems from the breathing phenomenon and expansion/shrinkage modulation.

Cadmium(II) adsorption using functional mesoporous silica and activated carbon.

The role of surface functionality on silica and carbonaceous materials for adsorption of cadmium(II) was examined using various mesoporous silica and activated carbon. Silica surfaces were principally functionalized by mono-amino- and mercapto-groups, while carboxylic group was introduced to the activated carbons by oxidation. Functional groups on silica surface were formed using grafting and co-condensation techniques in their preparation. Mono-amino group was found more effective than di- and tri-amino groups for cadmium(II) adsorption on the grafted silica. Mono-amino groups prepared by co-condensation adsorbed cadmium(II) as much as 0.25mmol/g compared to mercapto- and carboxyl-groups which adsorbed around 0.12mmol/g, whereas Langmuir adsorption affinities were as strong as 50-60L/mmol for all of the three functions. The working pH range was wider for mercapto- and carboxyl-functions than for amino-group. Basic site could be an adsorption center for amino-functional groups while ion exchange sites were found to work for the mercapto- and carboxyl-functions to adsorb cadmium(II) from aqueous phase. Based on the experimental results, surface functional groups rather than structure of silica and carbon seemed to play a decisive role for cadmium(II) adsorption.

Confinement in Carbon Nanospace-Induced Production of KI Nanocrystals of High-Pressure Phase

An outstanding compression function for materials preparation exhibited by nanospaces of single-walled carbon nanohorns (SWCNHs) was studied using the B1-to-B2 solid phase transition of KI crystals at 1.9 GPa. High-resolution transmission electron microscopy and synchrotron X-ray diffraction examinations provided evidence that KI nanocrystals doped in the nanotube spaces of SWCNHs at pressures below 0.1 MPa had the super-high-pressure B2 phase structure, which is induced at pressures above 1.9 GPa in bulk KI crystals. This finding of the supercompression function of the carbon nanotubular spaces can lead to the development of a new compression-free route to precious materials whose syntheses require the application of high pressure.

Tuning of Gate Opening of an Elastic Layered Structure MOF in CO2 Sorption with a Trace of Alcohol Molecules

It is important to tune the sorption behavior of metal-organic framework (MOF) materials. Ethanol treatment on the hydrated form of [Cu(bpy)(2)(BF(4))(2)], which is a representative flexible MOF showing the fascinating gate phenomenon on CO(2) sorption, induces an easier dehydration and a significant decrease in the CO(2) gate pressure. The results of IR, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) measurements indicated that water molecules in the lattice of the hydrated form can be removed even at room temperature after the ethanol treatment and the basic 2D layered structure remains with a slight interlayer expansion. The results of thermogravimetric (TG) and gas chromatograph/mass spectrometry (GC/MS) analyses and of CO(2) sorptions indicated that the change of the gate phenomenon was caused by a trace of residual ethanol molecules included in the structure. Similar phenomena were observed on alcohols with different polarity and molecular size.

Intensive Edge Effects of Nanographenes in Molecular Adsorptions

Graphene has become a primary material in nanotechnology and has a wide range of potential applications in electronics. Fabricated graphenes are generally nanosized and composed of stacked graphene layers. The edges of nanographenes predominantly influence the chemical and physical properties because nanographene layers have a large number of edges. We demonstrated the edge effects of nanographenes and discrimination against basal planes in molecular adsorption using grand canonical Monte Carlo simulations. The edge sites of nanographene layers have relatively strong Coulombic interactions as a result of the partial charges at the edges, but the basal planes rarely have Coulombic interactions. CO2 and N2 prefer to be adsorbed on the edge sites and basal planes, respectively. As a result of these different preferences, the separation ability of CO2 is higher than that of N2 in the low-pressure region, thereby offering selective adsorptions, reactions, and separations on nanographene edges.

Significant hydration shell formation instead of hydrogen bonds in nanoconfined aqueous electrolyte solutions.

Nanoscale confined electrolyte solutions are frequently observed, specifically in electrochemistry and biochemistry. However, the mechanism and structure of such electrolyte solutions are not well understood. We investigated the structure of aqueous electrolyte solutions in the internal nanospaces of single-walled carbon nanotubes, using synchrotron X-ray diffraction. The intermolecular distance between the water molecules in the electrolyte solution was increased because of anomalously strong hydration shell formation. Water correlation was further weakened at second-neighbor or longer distances. The anomalous hydrogen-bonding structure improves our understanding of electrolyte solutions in nanoenvironments.

Mechanism of Sequential Water Transportation by Water Loading and Release in Single-Walled Carbon Nanotubes.

Water in carbon nanotubes (CNTs) displays unique behaviors such as ring-like structure formation, anomalous hydrogen bonds, and fast transportation. We demonstrated the structures and stability of water in loading and release processes using a combination of X-ray diffraction analysis and hybrid reverse Monte Carlo simulations. Water formed nanoclusters in water loading, whereas layered structures were formed in water release. The water nanoclusters formed in water loading were well stabilized in CNTs. In contrast, in water release, the water layers were less stable than the water nanoclusters. The significant stabilization of nanoclusters in water loading and the relatively low stability of water layers in water release suggest easy water loading and release through CNTs, providing sequential water transportation through CNTs.

Adsorption properties of an activated carbon for 18 cytokines and HMGB1 from inflammatory model plasma

The ability of an activated carbon (AC) to adsorb 18 different cytokines with molecular weights ranging from 8 kDa to 70 kDa and high mobility group box-1 (HMGB1) from inflammatory model plasma at 310 K and the mechanisms of adsorption were examined. Porosity analysis using N2 gas adsorption at 77K showed that the AC had micropores with diameters of 1-2 nm and mesopores with diameters of 5-20 nm. All 18 cytokines and HMGB1 were adsorbed on the AC; however, the shapes of the adsorption isotherms changed depending on the molecular weight. The adsorption isotherms for molecules of 8-10 kDa, 10-20 kDa, 20-30 kDa, and higher molecular weights were classified as H-2, L-3, S-3, and S-1 types, respectively. These results suggested that the adsorption mechanism for the cytokines and HMGB1 in the mesopores and on the surface of the AC differed as a function of the molecular weight. On the basis of these results, it can be concluded that AC should be efficient for cytokine adsorption.

Predominant nanoice growth in single-walled carbon nanotubes by water-vapor loading

Water in single-walled carbon nanotubes was found to form nanosized ice-like structures (nanoice) above a water density of 0.5 g mL−1 in SWCNTs, but nanosized liquid water-like structures (nanowater) formed below that density, i.e., nanoice grows predominantly from nanowater at a low water density of around 0.5 g mL−1 and room temperature.

Diffusion‐Barrier‐Free Porous Carbon Monoliths as a New Form of Activated Carbon

For the practical use of activated carbon (AC) as an adsorbent of CH(4) , tightly packed monoliths with high microporosity are supposed to be one of the best morphologies in terms of storage capacity per apparent volume of the adsorbent material. However, monolith-type ACs may cause diffusion obstacles in adsorption processes owing to their necked pore structures among the densely packed particles, which result in a lower adsorption performance than that of the corresponding powder ACs. To clarify the relationship between the pore structure and CH₄ adsorptivity, microscopic observations, structural studies on the nanoscale, and conductivity measurements (thermal and electrical) were performed on recently developed binder-free, self-sinterable ACs in both powder and monolithic forms. The monolith samples exhibited higher surface areas and electrical conductivities than the corresponding powder samples. Supercritical CH₄ adsorption isotherms were measured for each powder and monolith sample at up to 7u2005MPa at 263, 273, and 303u2005K to elucidate their isosteric heats of adsorption and adsorption rate constants, which revealed that the morphologies of the monolith samples did not cause serious drawbacks for the adsorption and desorption processes. This will further facilitate the availability of diffusion-barrier-free microporous carbon monoliths as practical CH₄ storage adsorbents.