大場 友則

We report XRD and IR measurements of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) adsorbed in activated carbons, molecular sieving carbon, and single wall carbon nanohorn, where we specifically chose a wide range of pore sizes from 0.5 nm to 2.5 nm. Electron radial distribution function analysis reveals denser packing upon adsorption in two steps, for pore widths larger and comparable to the ion size. Average ion-distance was decreased by 0.05 nm in the latter case. With support of DFT calculations we identify a suppression of specific vibrational modes, which are interpreted as constrainment by the pore walls. Possible consequences for supercapacitor application are discussed. (C) 2015 Elsevier B.V. All rights reserved.

SF6 and SF6-N2 mixed gases are used widely as insulators, but such gases have high greenhouse gas potential. The separation of SF6 from SF6-N2 mixed gases is an inevitable result of their use. Single-walled carbon nanohorns (CNHs) were used here for a fundamental study of the separation of SF6 and N2. The diameters of the interstitial and internal nanopores of the CNHs were 0.7 and 2.9 nm, respectively. The high selectivity of SF6 over N2 was observed only in the low-pressure regime in the interstitial 0.7 nm nanopores; the selectively was significantly decreased at higher pressures. In contrast, the high selectivity was maintained over the entire pressure range in the internal 2.9-nm nanopores. These results showed that the wide carbon nanopores were efficient for the separation of SF6 from the mixed gas.

Nanopores (pores between 1 and 5 nm) have been the object of a great deal of attention because they can selectively adsorb relatively large molecules such as macromolecules and polymer molecules. Conventional methods for analyzing porous structures-such as N-2 adsorption measurements at 77 K can be used to investigate microporous and mesoporous structures, but there is a lack of investigation of nanopores or the boundary between micropores (<2 nm) and mesopores (2-50 nm). Here, we propose the evaluation method of nanopores using a large probe molecule, SF6. Grand canonical Monte Carlo simulations for N-2 and SF6 suggested that SF6 was adsorbed in 1.5-5 nm nanopores, while there was N-2 adsorption for the wide range of pore sizes. The SF6 adsorption could therefore be used to confirm existence of the nanopores. To test this, we used single-walled carbon nanohorns as porous carbons with widely distributed pore size. SF6 was well adsorbed only in the nanopores at 195 K, whereas N-2 adsorption was observed in all micropores and mesopores. This structural analysis of nanopores using a large-molecule probing method complements structural analyses using N-2 adsorption, as well as other techniques. (c) 2015 Elsevier Ltd. All rights reserved.

Knowledge of the dynamic properties of electrolyte solutions during charge and discharge cycles is crucial for understanding and developing electric energy devices. Molecular dynamics simulations of aqueous NaCl solution in nanopores between charged graphene layers were performed to assess the dynamical mechanism of ion transfer. Ions moved to the oppositely charged graphene layer according to the strength of their partial charges. The ion hydration numbers increased during ion transfer, suggesting quick rearrangement of water molecules around the ions to form a hydration shell. The extent of hydrogen bonding also increased during ion transfer. Water molecules participating in ion transfer hydrated the ion and simultaneously maintained hydrogen bonding, supporting a quick ion transfer mechanism during charge and discharge cycles.

The capacity and kinetics of CO2 capture of K2CO3 were studied to determine the mechanism for CO2 sequestration under ambient conditions. Bicarbonate formatioft of K2CO3 was examined by thermogravimetric analysis under various CO2 concentrations in the presence of water vapor, and the accompanying structural changes of K2CO3 were demonstrated by X-ray diffraction (XRD). Morphological variations were observed during the reaction in the presence of different CO2 concentrations through scanning electron microscopy (SEM). Structural changes and morphological variations, which occurred during the course of the reaction, were then connected to the kinetic and exothermic properties of the CO2 capture process from XRD and SEM measurements. The MID results showed that the bicarbonate formation process of K2CO3 could be divided into three reactions, such as the formation of K2CO3 center dot 1.5H(2)O from K2CO3, the subsequent formation of K4H2(CO3)(3)center dot 1.5H(2)O from K2CO3 center dot 1.5H(2)O, and the slow formation of KHCO3 from K4H2(CO3)(3)center dot 1.5H(2)O. The SEM observations showed that the morphology of the particles at all three stages played a crucial role in the kinetic behavior for CO2 sorptivity of K2CO3. CO2 capture of K2CO3 was inhibited under a concentrated CO, atmosphere during the initial stage, consisting of the first and second reactions, but the formation of KHCO3 from K4H2(CO3)(3)center dot 1.5H(2)O was thermodynamically favorable upon the increase of the CO2 concentration.

In this study, CO2 occlusion of K2CO3 was examined at different temperatures under moist conditions. The CO2 occlusion rate increased with increasing temperatures, whereas the saturated occlusion amount decreased. The highest occlusion amount (i.e. 6.48 mmol.g(-1)) was obtained at 313 K. Results of X-ray powder diffraction analysis showed that the formation of bicarbonate as a result of the K2CO3 decomposition with CO2 and H2O involved two reactions with K4H2(CO3)(3)center dot 1.5H(2)O as an intermediate. It was determined that the lower saturated occlusion amount at higher temperatures originated from the exothermic property of the second reaction. Because the equilibrium constant for the bicarbonate formation is smaller at higher temperatures, the reaction does not proceed as quickly or efficiently according to Le Chatelier's principle. Therefore, the CO2 occlusion of K2CO3 is suitable for the saturated occlusion amount at lower temperatures.

The behavior of water at hydrophobic interfaces can play a significant role in determining chemical reaction outcomes and physical properties. Carbon nanotubes and aluminophosphate materials have one-dimensional hydrophobic channels, which are entirely surrounded by hydrophobic interfaces. Unique water behavior was observed in such hydrophobic channels. In this article, changes in the water affinity in one-dimensional hydrophobic channels were assessed using water vapor adsorption isotherms at 303 K and grand canonical Monte Carlo simulations. Hydrophobic behavior of water adsorbed in channels wider than 3 nm was observed for both adsorption and desorption processes, owing to the hydrophobic environment. However, water showed hydrophilic properties in both adsorption and desorption processes in channels narrower than 1 nm. In intermediate-sized channels, the hydrophobic properties of water during the adsorption process were seen to transition to hydrophilic behavior during the desorption process. Hydrophilic properties in the narrow channels for both adsorption and desorption processes are a result of the relatively strong water-channel interactions (10-15 kJ mol(-1)). In the 2-3 nm channels, the water-channel interaction energy of 4-5 kJ mol(-1) was comparable to the thermal translational energy. The cohesive water interaction was approximately 35 kJ mol(-1), which was larger than the others. Thus, the water affinity change in the 2-3 nm channels for the adsorption and desorption processes was attributed to weak water-channel interactions and strong cohesive interactions. These results are inherently important to control the properties of water in hydrophobic environments.

Wave functions of quantum helium in narrow slit pores are strongly restricted; as such, quantum helium condensed in narrow slit pores displays different behaviors from that in bulk. Herein, we report the densities of helium adsorbed on carbon surfaces and in carbon slit pores with average pore widths of 0.7, 0.9, and 1.1 nm at 2-5 K. The density of adsorbed quantum helium in the 0.7-nm slit pores was significantly higher than those in the larger slit pores and bulk. The average layer density of helium in the 0.7-nm pores was also significantly higher than those in the larger slit pores, suggesting solid-like structure formation even under helium vapor condition. The highly dense state of helium in narrow slit pores is due to strong attractive potential effects in such slit pores.

Graphene is possibly the thinnest membrane that could be used as a molecular separation gate. Several techniques including absorption, cryogenic distillation, adsorption, and membrane separation have been adopted for constructing separation systems. Molecular separation using graphene as the membrane has been studied because large area synthesis of graphene is possible by chemical vapor deposition. Control of the gate sizes is necessary to achieve high separation performances in graphene membranes. The separation of molecules and ions using graphene and graphene oxide layers could be achieved by the intrinsic defects and defect donation of graphene. However, the controllability of the graphene gates is still under debate because gate size control at the picometer level is inevitable for the fabrication of the thinnest graphene membranes. In this paper, the controlled gate size in the graphene sheets in single-walled carbon nanohorns (NHs) is studied and the molecular separation ability of the graphene sheets is assessed by molecular probing with CO2, O2, N2, CH4, and SF6. Graphene sheets in NHs with different sized gates of 310, 370, and >500 pm were prepared and assessed by molecular probing. The 310 pm-gates in the graphene sheets could separate the molecules tested, whereas weak separation properties were observed for 370 pm-gates. The amount of CO2 that penetrated the 310 pm-gates was more than 35 times larger than that of CH4. These results were supported by molecular dynamics simulations of the penetration of molecules through 300, 400, and 700 pm-gates in graphene sheets. Therefore, a gas separation membrane using a 340-pm-thick graphene sheet has high potential. These findings provide unambiguous evidence of the importance of graphene gates on the picometer level. Control of the gates is the primary challenge for high-performance separation membranes made of graphene.

To develop high-performance activated carbons (ACs) for adsorption heat pumps (AHPs), it is important to characterize the adsorption behaviors of the refrigerant molecules in the pores of ACs. Not only pore structures, such as pore size and shape, but also surface functionalities strongly influences the adsorption behaviors, especially for polar molecules, such as water and ethanol, which are typical refrigerants for AHP. In this study, we examined the influence of surface functional groups on the adsorption behaviors of ethanol molecules in carbon micropores using model ACs with different amounts of oxygen-containing surface functional groups but comparable porosities. For the AC with an increased amount of surface functional groups, ethanol adsorption/desorption isotherms showed significant decreases in the adsorption amounts and shortened adsorption equilibrium times compared to those with less surface functional groups throughout the entire relative pressure region. This suggests diffusional hindrance of ethanol molecules in micropores with abundant surface functional groups. To verify our hypothesis, we examined the influence of surface functional groups on the adsorption behavior of ethanol molecules using a solid-state NMR technique. The NMR results revealed that the hydroxyl group of ethanol molecules strongly interacts with the surface functional groups, giving rise to an oriented adsorption of ethanol molecules in the micropores with oxygen-containing surface functional groups. Furthermore, electrochemical analyses confirmed that diffusion resistance of electrolyte ions in the micropores increases after the introduction of oxygen-containing surface functional groups, which supports our hypothesis. (C) 2014 Elsevier Ltd. All rights reserved.

Water surrounded by hydrophobic interfaces affects a variety of chemical reactions and biological activities. Carbon nanotubes (CNTs) can be used to investigate the behavior of water at hydrophobic interfaces. Here, we determined the fundamental unit of water by evaluating the ice-like cluster formation of water in the limited hydrophobic nanospaces of CNTs, using X-ray diffraction and molecular simulation analysis. The water in CNTs with a diameter of 1 nm had fewer hydrogen bonds than bulk water under ambient conditions. In CNTs with diameters of 2 and 3 nm, water formed nanoclusters even under ambient conditions, because of prolific hydrogen bonding; predominant ice-like cluster formation was induced in the 2-3 nm nanospaces. The results confirming the cluster formation in the CNTs also demonstrated that the critical cluster size was 0.8-3.4 nm. The fundamental cluster size was 0.8 nm; these results indicated that 0.8 nm clusters are the fundamental units of water assemblies.

We report a combined experimental (X-ray diffraction) and theoretical (molecular dynamics, hybrid density functional theory) study of 1-ethyl-3-methylimidazolium chloride, [C2C1MIM][Cl], inside carbon nanotubes (CNTs). We show that despite its huge viscosity [C2C1MIM][Cl] readily penetrates into 1-3 nm wide CNTs at slightly elevated temperatures (323-363 K). Molecular simulations were used to assign atom-atom peaks. Experimental and simulated structures of RTIL inside CNT and in bulk phase are in good agreement. We emphasize a special role of the CNT-chloride interactions in the successful adsorption of [C2C1MIM][Cl] on the inner sidewalls of 1-3 nm carbon nanotubes.

Using the first realistic model of single walled carbon nanohorn and molecular simulation data we show the 3D graphs relating the selectivity of CO2/CH4 separation with a surface to volume ratio of a nanohorn, the total mixture pressure and the mole fraction of CO2 in the bulk phase. It is proved that surface to volume ratio is a crucial parameter determining the selectivity. Finally, the equation is proposed, making possible to predict the selectivity of a nanohorn for separation of CO2/CH4 mixture. (C) 2014 Elsevier B.V. All rights reserved.

An understanding of the structure and behavior of electrolyte solutions in nanoenvironements is crucial not only for a wide variety of applications, but also for the development of physical, chemical, and biological processes. We demonstrate the structure and stability of electrolyte in carbon nanotubes using hybrid reverse Monte Carlo simulations of X-ray diffraction patterns. Hydrogen bonds between water are adequately formed in carbon nanotubes, although some hydrogen bonds are restricted by the interfaces of carbon nanotubes. The hydrogen bonding network of water in electrolyte in the carbon nanotubes is further weakened. On the other hand, formation of the ion hydration shell is significantly enhanced in the electrolyte in the carbon nanotubes in comparison to ion hydration in bulk electrolyte. The significant hydrogen bond and hydration shell formation are a result of gaining stability in the hydrophobic nanoenvironment.

Water has unique properties in the nanopores of activated carbons and carbon nanotubes, which are apparently different from those of typical adsorbed molecules such as N₂ and Ar. Here the mechanism of water vapor adsorption in carbon nanopores and the adsorbed structures are reviewed using adsorption isotherms, X-ray scattering, and molecular simulations. Water cluster formation in hydrophobic carbon nanopores promoted self-adsorption of water by gaining stability. Water stabilization is a result of anomalously strong hydrogen bonding between water molecules in such carbon nanopores. On the other hand, in the case of an aqueous electrolyte solution, the formation of a hydration shell around ions is dominant in carbon nanopores. These findings promote our understanding of water nanoscience and nanotechnology as well as electrochemical nanoscience.

We fabricated nanoscale BaTiO3 and its asymmetric crystal structure was obtained using an asymmetric reaction field in carbon nanospaces. The nano-crystal phases changed from symmetric to asymmetric crystals with decreasing crystallite size. The fabrication of an asymmetric crystal in a nanospace can be adapted for various ceramic fabrications.

Fabrication of monolayer graphene is a challenge and many processes yield few-layer or multi-layer graphene materials instead. The layer number is an important property of those materials and a quality control variable in graphene manufacture. We demonstrated that N2 adsorption on graphene materials was used to distinguish its layer number. We performed grand canonical Monte Carlo simulation of N2 adsorption on graphene materials with 1-10 layers to indicate the possibility of distinction of layer number by evaluating the dependence of N2 adsorption characteristics on the layer number of graphene materials as well as the adsorption mechanism. The threshold relative pressures of monolayer adsorption of N2 on monolayer and two-layer graphene were 1 × 10-3 and 2 × 10-4, respectively, while those of the others were 1 × 10 -4. In contrast, the threshold pressures of second layer adsorption of N2 were similar to each other. The difference of threshold pressures is attributed to stabilized energies induced by interactions with graphene materials. Therefore, the layer number of graphene materials could be evaluated from the threshold pressures of adsorption, providing a guide to aid fabrication of graphene materials. © 2013 Elsevier Ltd. All rights reserved.

Organic electrolytes are widely used for electric double-layer capacitors. However, the molecular mechanism involved is far from being understood. We demonstrate the structures and stabilities of tetraethylammonium and tetrafluoroborate ions in propylene carbonate solution in carbon nanopores using Monte Carlo simulations. These ions were significantly desolvated at nanopore widths below 1.0 nm. The nanopore potential compensated for the loss of stability of the ions as a result of desolvation for nanopore widths of 0.7-1.2 nm for Et4N+ and 0.6-0.9 nm for BF4-. High-capacitance electrodes can therefore be obtained using such nanoporous carbons.

Adsorption-related concepts are explained together with important intermolecular interactions in physical adsorption. The vapor adsorption isotherms on flat surfaces or macropores, mesopores, and micropores are interpreted by multilayer adsorption, capillary condensation, and micropore filling, respectively. Recent studies on capillary condensation in small mesopores are described. The difference between vapor adsorption and supercritical gas adsorption is discussed in terms of surface excess adsorption and absolute adsorption. New aspects of physical adsorption are shown on water vapor adsorption in hydrophobic micropores, quantum molecular sieving effect, and gate adsorption and breathing phenomena on porous coordination polymers. © 2013 Elsevier Ltd. All rights reserved.

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.

We report the vertical alignment of propylene carbonate (PC) molecules interacting with Et4N+ and BF4- which are confined in extremely narrow slit pores (w similar to 0.7 nm) of carbide-derived carbon and pitch-based activated carbon fiber. On the basis of X-ray diffraction (XRD), electron radial distribution function analysis reveals that the nearest PC-PC distance is 0.05-0.06 nm shorter than that in the bulk solution, indicating dense packing of PC molecules in the pores. This confinement effect results from the vertically aligned PC molecules, which are indicated by the reverse Monte Carlo analysis. The ensemble structure of PC molecules in the subnanometer carbon pores will provide better understanding the supercapacitor function.

Electron density of single wall carbon nanotubes (SWCNT) is effectively modified by hexaiodobenzene (HIB) molecules using liquid-phase adsorption. UV-Vis-NIR absorption spectra of the HIB-adsorbed SWCNT, especially in the NIR region, showed a disappearance of S-11 transitions between the V1 valance band and the C1 conduction band of van Hove singularities which can be attributed to the effective charge transfer between HIB and the SWCNT. The adsorption of HIB also caused significant peak-shifts (lower frequency shift around 170 cm(-1) and higher shift around 186 cm(-1)) and an intensity change (around 100-150 cm(-1) and 270-290 cm(-1)) in the radial breathing mode of Raman spectra. The charge transfer from SWCNT to HIB was further confirmed by the change in the C1s peak of X-ray photoelectron spectrum, revealing the oxidation of carbon in SWCNT upon HIB adsorption.

Water vapor adsorption on porous carbons has been actively studied because of its importance in various applications and basic science. However, the unique behavior and structure of water in carbon nanospaces have still been remained unclear. Carbon nanotubes inherently have rather restricted one-dimensional nanospaces and thus, force the adsorbed water to be aligned in them. The structure of water adsorbed in those nanospaces is ice-like even at ambient temperature. In this paper, we show the water structures in two-different single wall carbon nanotubes (CNTs) with average CNT diameters of 1.1 (narrow) and 2.5 (wide) nm at 260-300 K, which were evaluated by using in situ synchrotron X-ray diffraction (XRD). The water structures in the both CNTs were nano-ice-like forms at 300 K rather than a liquid-like. The ice-like structure in the wide CNTs was developed with decreasing temperature, although even at 260 K, sharp ice peaks were not observed in the XRD pattern. On the other hand, in the narrow CNTs, the water structure was gradually transformed from an ice-like form to a liquid-like form with decreasing temperature to 260 K. The structure transformation of solid-to-liquid with decreasing temperature is due to the fact that the highly restricted nanospaces obstruct the formation of ice-like clusters and/or hydrogen bonds. The anomalous structure transformation in both CNTs could be a clue to reveal one-dimensional water behavior in CNTs.

The hydration structure of NaCl aqueous solution was elucidated in carbon nanotubes (CNTs) on the basis of canonical ensemble Monte Carlo simulations. Hydration shells were preferentially formed even in narrow CNTs to gain stabilization energy, whereas hydrogen bonding between water molecules in such CNTs was sacrificed. Nanoscale-confined aqueous electrolyte solutions therefore prioritize hydration shell formation between ions and water rather than hydrogen-bond formation between water molecules.

Water plays an important role in controlling chemical reactions and bioactivities. For example, water transportation through water channels in a biomembrane is a key factor in bioactivities. However, molecular-level mechanisms of water transportation are as yet unknown. Here, we investigate water transportation through narrow and wide one-dimensional (1D) channels on the basis of water-vapor adsorption rates and those determined by molecular dynamics simulations. We observed that water in narrow 1D channels was transported 3-5 times faster than that in wide 1D channels, although the narrow 1D channels provide fewer free nanospaces for water transportation. This rapid transportation is attributed to the formation of fewer hydrogen bonds between water molecules adsorbed in narrow 1D channels. The water-transportation mechanism provides the possibility of rapid communication through 1D channels and will be useful in controlling reactions and activities in water systems.

We report a precise control over the hierarchy levels in the outstanding self-organization process shown by chiral azobenzene dimer 1. This compound forms uniform toroidal nanostructures that can hierarchically organize into chiral nanotubes under the control by temperature, concentration, or light. The nanotubes further organized into supercoiled fibrils, which finally intertwined to form double helices with one-handed helical sense.

High-density CH4 storage using adsorption techniques is an important issue in the use of CH4 as a clean energy source. The CH4 adsorption mechanism has to be understood to enable innovative improvements in CH4 adsorption storage. Here, we describe the adsorption mechanism, based on CH4 structure, and stabilities in the internal and external nanopores of single-walled carbon nanohorns, which have wide and narrow diameters, respectively. The adsorption of larger amounts of CH4 in the narrow nanopores at pressures lower than 3 MPa was the result of strong adsorption potential fields; in contrast, the wider nanopores achieve higher-density adsorption above 3 MPa, despite the relatively weak adsorption potential fields. In the wider nanopores, CH4 molecules were stabilized by trimer formation. Formation of CH4 clusters therefore compensates for the weak potential fields in the wider nanopores and enables high-density adsorption and adsorption of large amounts of CH4.

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.

The quantum molecular sieving effects of pore-structure-controlled single-walled carbon nanotubes (SWCNTs) for H-2 and D-2 were evaluated at 20, 40, and 77 K. The adsorption amounts of D-2 were larger than those of H-2. The lower the adsorption temperature, the greater the difference between the D-2 and H-2 adsorption amounts. Bundled SWCNTs with interstitial pores of diameter 0.6 nm gave the greatest adsorption difference between D-2 and H-2 per unit pore volume. Diffusion-dominated behavior was observed in the low-pressure region at 20 and 40 K as a result of lower mobility. Bundled SWCNTs with only interstitial pores provided a significant quantum molecular sieving as a result of strongly interacting potential wells.

In this study, we investigated the possibilities of using activated carbon fibre (ACF) as a carbon capture and storage (CCS) technology. The CO2 adsorption isotherms of ACFs with different porosities were systematically examined at 273 and 298 K under ambient pressure conditions. The porosities of the ACFs were characterized by the adsorption of nitrogen at 77 K. We analyzed the adsorption capabilities of three types of ACFs (A5, A10 and A20) having different slit-shaped pore widths, specific surface areas and micropore volumes. Our results reveal that A5 had ultramicropores and achieved a higher adsorption of CO2 at low relative pressure (<0.015) at 273 K. However, A10, which had an average pore width of 0.9 nm, exhibited the highest adsorption capacity of 195 mg g(-1) at a higher pressure of about 100 kPa, which is a relatively high value compared with that of conventional activated carbon. By establishing the temperature dependence of CO2 adsorptivity and using Dubinin-Radushkevich analysis, we characterized the interaction energy between pores and CO2 molecules. Our results shed light on the fundamental aspects of CO2 adsorption of ACFs, moving them towards being a viable CCS.

We demonstrate a water penetration mechanism through zero-dimensional nanogates of a single-walled carbon nanohorn. Water vapor adsorption via the nanogates is delayed in the initial adsorption stage but then proceeds at a certain rate. The mechanism is proposed to be a water cluster-chain-cluster transformation via the nanogates. The growth of water clusters in internal nanospaces facilitates water penetration into these nanospaces, providing an intrinsic mechanism for zero-dimensional water.

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 0.25 mmol/g compared to mercapto- and carboxyl-groups which adsorbed around 0.12 mmol/g, whereas Langmuir adsorption affinities were as strong as 50-60 L/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. (C) 2012 Elsevier B.V. All rights reserved.

Transitional metals (M) were dispersed on single. wall carbon nanohorns (M/SWCNHs, M = Fe, Co, Ni, Cu) by simple thermal treatment of the deposited metal nitrate without H-2 reduction. Nanometallic Ni particles on SWCNH were evidenced by high-resolution transmission electron microscopic observation and X-ray photoelectron spectroscopy. The nano-Ni dispersed on SWCNH showed the highest CH4 decomposition activity; the activity of used transitional metals decreases in the order Ni >> Co > Fe >> Cu. On the other hand, the reaction rate over Ni/SWCNH was much larger than that over Ni/Al2O3, and the former provided COx-free H-2 and cup-stacked carbon nanotubes, while Ni/Al2O3 produced COx in addition to H-2. SWCNH was superior to Al2O3 as the catalyst support of Ni for the CH4 decomposition reaction.

We prepared a partially charged single walled carbon nanotube (SWCNT) by charge transfer-mediated encapsulation of methylene blue (MB) molecules, which enhances the CO2 adsorptivity. The liquid phase adsorption of MB molecules on SWCNT could give the MB-encapsulated SWCNT, which was evidenced by the remarkable depression of the X-ray diffraction intensity from the ordered bundle structure, the decrease of N-2 and H-2 adsorption in the internal tube spaces of SWCNT, and the high-resolution transmission electron microscopic observation. The molecular spectroscopic examination revealed the charge transfer interaction between the encapsulated MB molecules and SWCNT. The electrical conductivity increased by the encapsulation of MB suggested the electron transfer from SWCNT to MB molecules, giving rise to positively charged SWCNT. The enhancement of CO2 adsorption by the MB-encapsulation coincided with the positively charged SWCNT.

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 N-2 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 N-2 in the low-pressure region, thereby offering selective adsorptions, reactions, and separations on nanographene edges.

The gate adsorption mechanism and kinetics of an elastic layer-structured metal organic framework (ELM), [Cu(bpy)(2)(BF4)(2)](n) (ELM-11), that shows typical single-step CO2 gate adsorption/desorption isotherms accompanied with dynamic structural transformation in a wide temperature range were investigated. Adsorption of quite a small amount of CO2 on the external surface of ELM-11 crystals was observed at the pressure just below a gate adsorption pressure and induced a slight structural change in ELM-11. The structural change should start occurring at the outer parts of ELM-11 and transmit to more inner parts with rising pressure. The adsorption provides the stabilization of the framework through the interaction between fluid solid and fluid fluid and enables the framework to expand largely along the stacking direction. The CO2 adsorption rate of ELM-11 is almost comparable to that of Zeolite SA at around ambient temperatures and shows temperature dependence with an anti-Arrhenius trend: higher adsorption rate with lower temperature.

We introduce a way to selectively probe local vibration modes at nanostructured asperities such as tips of carbon nanohorns. Our observations benefit from signal amplification in surface-enhanced Raman scattering (SERS) at sites near a silver surface. We observe nanohorn tip vibration modes in the range 200-500 cm(-1), which are obscured in regular Raman spectra. Ab initio density functional calculations assign modes in this frequency range to local vibrations at the nanohorn cap resembling the radial breathing mode of fullerenes. Careful interpretation of our SERS spectra indicates presence of caps with 5 or 6 pentagons, which are chemically the most active sites. Changes in the peak intensities and frequencies with time indicate that exposure to laser irradiation may cause structural rearrangements at the cap. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682771]

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.