大場 友則

Graphene is a fundamental unit of carbon materials and, thus, primary sp2-bonded carbon material. Graphene is, however, easily broken macroscopically despite high mechanical strength, although its natural degradation has rarely been considered. In this work, we evaluate the natural degradation of two-layer graphene in vacuo, in low-humidity air, and in high-humidity air at 300, 400, 450, and 500 K. Over 1000 days of degradation at 300 K, the graphene structure was highly maintained in vacuo, whereas the layer number of graphene tended to decrease in high- and low-humidity air. Water was slightly reacted/chemisorbed on graphene to form surface oxygen groups at 300 K. At 450 and 500 K, graphene was moderately volatilized in vacuo and was obviously oxidized in high- and low-humidity air. Surprisingly, the oxidation of graphene was more suppressed in the high-humidity air than in the low-humidity air, indicating that water worked as an anti-oxidizer of graphene by preventing the chemisorption of oxygen on the graphene surface.

BaTiO₃ nanocatalysts chemisorb and reduce CO₂ efficiently at 700 K and 0.1–1.0 MPa.

TiO2 anatase, which exhibits the highest catalytic performance, transforms to rutile at 800 K. To inhibit the transition of anatase to rutile, several strategies, such as metal and/or non-metal doping, oxygen enrichment, and surface coating, have been studied, resulting in stable anatase within 773-1273 K. However, highly stable anatase without dopants is still required. Here, a new approach, which involves the synthesis of anatase nanocatalysts in carbon nanotubes (CNTs), was proposed to inhibit the anatase-to-rutile transition. The nanocatalysts exhibited high thermal anatase stability along with a suppression of the crystal growth up to 1200 K. The highly stable anatase in CNTs also exhibited high photocatalytic activity, which was evaluated based on methylene blue decomposition under visible- and UV-light irradiation. This was attributed to the maintenance of the small crystal size of the nanocatalysts in addition to a synergetic effect between the TiO2 nanocatalysts and CNTs.

Low temperature CO₂ reduction and mechanism on BaTiO₃ nanocatalysts from 500 K, CO₂ physical adsorption at 300–500 K, CO₂ chemisorption above 450 K, CO₂ reduction at 500–850 K, and CO₂ and CO release above 800 K.

Investigating the interfacial properties between water and graphene is important, as the water–carbon interface influences various applications. Graphene is the fundamental unit of various carbon allotropes and composed of a single atomic species, although slight oxygen groups are normally attached on it. Therefore, adsorption properties on graphene is inevitable to advance fundamental understating on surface sciences. However, the detection of water adsorption on graphene is considerably hard, because amount of water is tiny and mass production of graphene to a detectable level using a standard adsorption apparatus is extremely difficult. We succeeded to detect water vapor adsorption on several layer graphene using lab-made adsorption apparatus with a quartz crystal microbalance technique. This study derives the properties of water on single-, triple-, and six-layer graphene from the contact angles of water droplets and the water vapor adsorption isotherms. The surface hydrophobicity evaluated from the contact angles and water vapor adsorption isotherms decreased in the following order: single-layer graphene &gt triple-layer graphene &gt six-layer graphene. At a relative pressure of 0.4 and water surface densities of 0.5–1.5 mg m−2 (corresponding to 2–5 water layers), the water stability was 1.0 kJ mol−1 smaller on single-layer graphene than on triple- and six-layer graphene. The weak interaction between water molecules and single-layer graphene induced slight water adsorption on graphene. As the water amount increased, the water–graphene interaction energy increased with steps of 0.17–0.18 mg m−2 (corresponding to nearly 50% of a water monolayer), and the water structure correspondingly transformed from cluster to layer. The structure transformation of adsorbed water induced the affinity change from hydrophobic to hydrophilic on graphene interfaces. The mechanism of water–graphene interfaces can be exploited in applications of graphene-based carbon nanomaterials.

Defects are widely present in nanomaterials, and they are recognized as the active sites that tune surface properties in the local region for catalysis. Recently, the theory linking defect structures and catalytic properties of nanocatalysts has been most commonly described. In this study, we prepared boron-doped carbon nano-onions (B-CNOs) by applying an annealing treatment of ultradispersed nanodiamond particles and amorphous boron. These experimental conditions guarantee doping of CNOs with boron atoms in the entire carbon nanostructure, thereby ensuring structural homogeneity. In our research, we discuss the correlations between defective structures of B-CNOs with their catalytic properties toward SO2 and tert-butanol dehydration. We show that there is a close relationship between the catalytic properties of the B-CNOs and the experimental conditions for their formation. It is not only the mass of the substrates used for the formation of B-CNOs that is crucial, that is, the mass ratio of NDs to amorphous B, but also the process, including temperature and gas atmosphere. As it was expected, all B-CNOs demonstrated significant catalytic activity in HSO3- oxidation. However, the subsequent annealing in an air atmosphere diminished their catalytic activity. Unfortunately, no direct relationship between the catalytic activity and the presence of heteroatoms on the B-CNO surface was observed. There was a linear dependence between catalytic activity and Raman reactivity factors for each of the B-CNO materials. In contrast to SO2 oxidation, the B-CNO-a samples showed higher catalytic activity in tert-butanol dehydration due to the presence of Brønsted and Lewis acid sites. The occurence of three types of boron-Lewis sites differing in electron donor properties was confirmed using quantitative infrared spectroscopic measurements of pyridine adsorption.

Catalytic thermal reduction of CO2 has the potential to minimize the energy requirement in carbon capture and utilization. However, this process necessitates high energy with a reactant gas, heating, and pressurization. High-performance catalysts are thus needed to transform CO2 into value-added carbon products at low energy consumption. We here demonstrate the thermal reduction of CO2 to carbon products at 700 K and ambient pressure using nanoscale perovskite-type titanium nanocatalysts. The reactivity of CO2 was exponentially increased by decreasing the particle size until 10 nm. The reaction yields calculated from the weight changes of nanocatalysts under CO(2 )flow were very high, i.e., between 1600 and 3300 mu mol g(-1) h(-1) for nanocatalysts smaller than 20 nm, which were similar to those of CO2 reductions with a reactant gas into lower hydrocarbons and alcohols. A CO2 reductant was evaluated by transmission electron microscopy, chemical mapping using energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy. Graphitic carbons were coated on 9-12 nm nanocatalysts after CO2 reduction. Graphitic carbons were mainly observed on the 12 nm nanocatalyst. A nanodiamond-like structure was partly observed on the 9 nm nanocatalyst, as well as a graphitic structure. Nanodiamond was hardly produced in the mild condition at 700 K and ambient pressure, which was normally produced above 2 GPa and 1600 K. A nanodiamond was produced by quasi-high-pressure effect in graphene and amorphous carbons, which were previously produced on nanocatalysts. The low-temperature CO2 thermal reduction using perovskite-type titanium nanocatalysts at 700 K is thus a promising approach to CO2 reduction and novel way to produce nanodiamond-like structure.

The freezing point of water is lower in an aqueous solution than in pure water. Although this freezing point depression is well-known, it remains poorly understood in the nanoenvironment. Observing the freezing property in a nanoaqueous solution is demonstrated by the structure analyses of water and the aqueous solution in the carbon nanotubes (CNTs) at 213-303 K. The 1 nm spaces of the CNTs obstructed ice formation of both the aqueous solution and water in the studied temperature range, although the bulk aqueous solution and water were frozen between 213 and 243 K by supercooling. Contrarily, aqueous solutions in the 3 nm spaces facilitated ice formation at higher temperatures of 243-273 K than the water-freezing temperature of 213-243 K, consistent with the freezing temperature in bulk. The elevation of freezing temperature in the aqueous solution is first observed in the 3 nm diameter CNTs, indicating facilitation of ice formation in the nanoenvironment.

We fabricated single-layer graphene as an ideal two-dimensional electrode for evaluating fundamental mechanism of ion transfer into a capacitance system and conducted cyclic voltammetry and molecular dynamics simulations to evaluate its capacitive performances in different aqueous electrolytes solutions of KCl, NaBr, NaCl, NaF, and LiCl. The system of KCl electrolyte had the highest areal capacitance at various scan rates and the fast ion diffusion coefficient. The highest capacitance and the fast ion diffusion were also observed from the molecular dynamics simulations. Cationic mobility especially influenced capacitance performance, whereas those capacitance performances were inactive for anionic mobility. Those are the result of direct contact of K+ ions with graphene interfaces by dehydration. The comparison analyses indicated the guides for efficient capacitance by ion dynamics during charging cycles. These results therefore improve our understanding of ion dynamics during charging and will contribute to the development of energy storage applications of electric double-layer capacitors.

Various carbon materials have been fabricated for use as catalyst supports, carriers, adsorbents, and electrodes as well as in other advanced applications. The performances of carbon materials in such applications can be improved by adjusting their physical properties, especially their nanostructures. The determination of the carbon nanostructure is thus considerably important. Reverse Monte Carlo and hybrid reverse Monte Carlo simulations, which are used to analyze the diffraction patterns of carbon materials, can be used to obtain nanostructure images. Here, we describe a new approach to carbon nanostructure investigation, namely, hybrid reverse molecular dynamics (HRMD) simulation. This approach has the advantage that all of the carbon atoms move toward probable carbon structures by force fields to adapt a simulated diffraction pattern to an experimental one, in contrast to the random movements in reverse Monte Carlo and hybrid reverse Monte Carlo simulations. HRMD simulation also prevents the formation of inappropriate structures.

Graphene is an ideal candidate to use in various applications as a component in semiconductor devices with excellent properties, such as its atomic thickness, optical transparency, chemical stability, and high electrical and thermal conductivities. The high gas sensitivities of graphene functionalized with metal, metal oxides, and other groups have been improved through intensive research. However, the development of a metal-free graphene gas sensor and clarification of its mechanism still remain a challenge. In this study, H2, CO2, NH3, and He gas sensing performances are demonstrated using two- to multilayered graphene, directly fabricated on a quartz substrate. The sheet resistances of more than 100 graphene layers were considerably changed from 3% to 6% by He gas injection, caused by its piezoresistive property. The anomalous resistance changes by piezoresistivity is a result of electron transfer path changes associated with graphene assemble structure changes by insertion of He gas between graphene crystal units and pressing graphene units. The sheet resistances of the synthesized graphene were found to dramatically change through physical adsorption and chemisorption. The chemisorption of NH3 gas on functional oxygen groups at graphene edges was responsible for the chemiresistive behavior of the material. The gas sensing and piezoresistive mechanisms of graphene determined in this work sheds light on the development of a graphene gas sensor.

Hydroxyapatite [Ca10(PO4)6(OH)2, HAP] has P-OH Brønsted acidic sites, Ca2+ Lewis acidic sites, and OH- and O2- basic sites on which acidic and basic gas molecules can be selectively adsorbed, and has no micropore onto which various molecules adsorb regardless of the chemical properties of gas molecules. The interaction between the surface sites and acidic and basic gas and water molecules has been investigated by evaluating the adsorption properties of various molecules on the surfaces of calcium-deficient HAP. The specific adsorption sites were assessed by examining the reversible and irreversible adsorption of NH3, CO2, aldehydes, and water vapor on HAP at the temperature of 298 K, using two HAP samples with different Ca/P ratios, but similar structures and surface areas: Ca-deficient HAP with an extreme lower Ca/P ratio (named P-HAP) and one with a higher Ca/P ratio (named C-HAP). Irreversible adsorption of NH3 on C-HAP is attributed to the adsorption on both Ca2+ Lewis acidic and P-OH Brønsted acidic sites. Irreversible adsorption on P-HAP is attributed to the adsorption on P-OH Brønsted acidic sites only. Irreversible adsorption of CO2 occurred on C-HAP only, and preferentially on OH- basic sites. Acetaldehyde undergoes a catalytic reaction over both OH- basic sites and surface P-OH Brønsted acidic sites at 298 K. Water irreversible adsorption was extensively observed for P-HAP, and water was barely desorbed at low pressures. In situ powder X-ray diffraction showed an asymmetric expansion of the lattice in the [100] direction, indicating that water was incorporated into P-HAP crystals, especially on structural OH- sites. Irreversible adsorption of acidic and basic molecules was therefore less observed on P-HAP than on C-HAP, but P-HAP had considerable irreversible adsorption of water vapor with associated asymmetric lattice expansion. The incorporation of water vapor was first observed and could be useful to improve adsorption or catalytic performance with the mediation of water vapor and/or hydration.

Supramolecular polymers have emerged in the last decade as highly accessible polymeric nanomaterials. An important step toward finely designed nanomaterials with versatile functions, such as those of natural proteins, is intricate topological control over their main chains. Herein, we report the facile one-shot preparation of supramolecular copolymers involving segregated secondary structures. By cooling non-polar solutions containing two monomers that individually afford helically folded and linearly extended secondary structures, we obtain unique nanofibers with coexisting distinct secondary structures. A spectroscopic analysis of the formation process of such topologically chimeric fibers reveals that the monomer composition varies gradually during the polymerization due to the formation of heteromeric hydrogen-bonded intermediates. We further demonstrate the folding of these chimeric fibers by light-induced deformation of the linearly extended segments.

Abstract: Structures of NaCl and LiCl aqueous solutions in pores of carbon nanotubes with diameter 1 and 2 nm were evaluated by using X-ray diffraction and molecular dynamics simulations. Water intermolecular distances in carbon nanotubes with 1 and 2 nm pore diameters were more elongated and shortened than bulk water, respectively. Those were results of weakened and strengthened hydrogen bonds. The structures of aqueous solutions in carbon nanotubes were considerably different from water despite tiny amounts of ions in the pores. The nearest neighbour distances in aqueous solutions were rarely changed from that in water system in 1 nm carbon nanotubes pore, while those were longer than water in 2 nm carbon nanotubes pore. On the other hand, the second nearest neighbour distances in aqueous solutions in 1 and 2 nm pore diameter carbon nanotubes were both decreased from those in water in carbon nanotubes. Significant hydration formation and cleavage of hydrogen bonds were thus observed in 2 nm carbon nanotubes pore, because the elongated nearest neighbour and shortened second nearest neighbour distances were observed. Anomalous feature of the unchanged nearest neighbour and shortened second neighbour distances in 1 nm carbon nanotubes pore is the result that water intermolecular distance was much longer than bulk and hydrogen bonds were thus severely separated. Ions might play dominant role to connect hydrogen bonds and of course form hydration shell. Those anomalous structure changes from water to aqueous solution were observed only in extremely narrow carbon nanotubes. [Figure not available: see fulltext.].

Activated carbons have been well-used for separation, removal, and storage for various gases. Pore width and surface functional groups are primal factors of interactions with adsorbed molecules. Surface functional groups especially influence adsorptions of acidic and basic molecules, although all molecules are considerably influenced by pore width. Controlling optimal pore width and surface functional group is however very difficult, because both factors of pore width and surface functional groups are simultaneously changed in preparation process. We here attempted to prepare oxygen-introduced activated carbon with different surface oxides into activated carbons and with the similar pore structure. NH 3 , CO 2 , acetaldehyde, isoprene, and water were used for evaluating the influence of surface oxides in carbon pores. As the surface oxides increased, NH 3 adsorbed amounts were considerably increased accompanying an irreversible adsorption and a threshold pressure of water adsorption was shifted to lower relative pressure, while adsorption isotherms of the other molecules were rarely changed. A comparison of interaction between any surface oxides and adsorbed molecules indicated that NH 3 and water molecules having the electron donor were strongly adsorbed on the acid surface oxides. The oxygen-introduced activated carbons without any destruction of the pore structure exhibited a considerable adsorption potential for molecules having the electron donor, and maintained an adsorption potential for molecules having the nonpolar and electron acceptor, proposing effective removal and separation with high adsorption capacity. [Figure not available: see fulltext.].

High-pressure adsorption measurement of supercritical gas needs accurate particle density which should be obtained by high-pressure He buoyancy measurement. As the surface excess mass adsorption is not greatly larger than the bulk gas contribution in the adsorbed layer, the absolute adsorption amount containing the bulk gas contribution in the adsorbed layer must be used for thermodynamic analysis and evaluation of the storage amount. The plot of the compression factor of adsorbed layer against the inverse of the average adsorbed layer density provides the Henry, virial, and cooperative types, giving information on the strength of the gas-solid interaction. The nanoporous material showing the cooperative type is promising for the storage of the target gas. Two factors of the strength of the gas-solid interaction and the surface area predict that nanopores consisting of narrow belt walls are promising for gas storage. Molecular simulation of methane in the graphitic pore over the wide temperature range from 120 to 300 K indicates an upward shift of the critical temperature of methane adsorbed in the graphitic pore. The heat of adsorption of methane in the graphitic pore without the heat-releasing mechanism elevates the temperature of the graphitic carbon by 70 K, decreasing the adsorption amount of methane by 30% an efficient heat releasing mechanism must be installed in the storage device.

Understanding of the explicit difference between supercritical gas and vapor is necessary for a better design of nanoporous materials for gas storage we show the difference between supercritical gas and vapor with the van der Waals equation which leads to the critical point and the second virial coefficient. Detailed explanation on intermolecular interactions such as dispersion interaction and electrostatic interaction and the gas-solid interaction is given for enhancing the physical adsorption of supercritical gas by nanoporous materials. Plausible routes of quasi-vaporization for enhancement of supercritical gas adsorption on nanoporous materials are suggested. The effectiveness of the quasi-vaporization of supercritical gas with the strong interaction potential field of nanopores and the specific surface interaction is shown for supercritical nitric oxide, nitrogen and methane. The simple analytical method of supercritical gas adsorption isotherms with the aid of the quasi-vaporization can provide the quasi-saturated vapor pressure and isosteric heat of adsorption, being useful to design the better nanoporous materials for gas storage.

© 2018 American Chemical Society. CO2 removal and sensing, especially by amine groups, are necessary to prevent global warming. However, understanding the dynamic mechanism of CO2 capture on nitrogen sites remains challenging. We fabricated a nitrogen-doped polymer and compared the mechanism of CO2 adsorption with that of a similar polymer without nitrogen atoms by evaluating the CO2 adsorption at 243, 273, and 303 K; electrical resistance changes due to CO2 adsorption at 297 K; and molecular dynamics simulations. The CO2 adsorption of the nitrogen-doped polymer was significantly improved owing to the negative partial charges on nitrogen sites. In addition, the electrical response of the nitrogen-doped polymer to CO2 showed adequate reversibility. These results originated from the stronger adsorption of CO2 on nitrogen sites than on ring and vinyl sites. Our findings contribute to the understanding of CO2-nitrogen attraction and will be beneficial for the development of efficient CO2 capture and sensing.

Perovskites have been attracting attention because of their considerable luminescence properties. A conventional perovskite such as BaTiO3 has no intrinsic photoluminescence. Doping with rare metals, nanocrystallization, and addition of organometallic halides induce significant photoluminescence and photovoltages. Here, we report anomalous light reflection and photoluminescence of BaTiO3 on heating. Light absorption shifted from the near-ultraviolet region to the visible region on heating. The small emission peaks at around 400-500 nm disappeared and new peaks appeared above 800 nm; the quantum yields of these peaks were less than 1% and more than 7%, respectively.

Folding one-dimensional polymer chains into well-defined topologies represents an important organization process for proteins, but replicating this process for supramolecular polymers remains a challenging task. We report supramolecular polymers that can fold into protein-like topologies. Our approach is based on curvature-forming supramolecular rosettes, which affords kinetic control over the extent of helical folding in the resulting supramolecular fibers by changing the cooling rate for polymerization. When using a slow cooling rate, we obtained misfolded fibers containing a minor amount of helical domains that folded on a time scale of days into unique topologies reminiscent of the protein tertiary structures. Thermodynamic analysis of fibers with varying degrees of folding revealed that the folding is accompanied by a large enthalpic gain. The self-folding proceeds via ordering of misfolded domains in the main chain using helical domains as templates, as fully misfolded fibers prepared by a fast cooling rate do not self-fold.

In this study fully atomistic grand canonical Monte Carlo (GCMC) simulations have been employed to study the behaviour of an electrolyte salt (NaPF6) and different non-aqueous (organic) solvents in carbon nanopores, to reveal the structure and storage mechanism. Organic solutions of Na+ and PF6- ions at 1 M concentration were considered, based on the conditions in operational sodium ion batteries and supercapacitors. Three organic solvents with different properties were selected: ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC). The effects of solvents, pore size and surface charge were quantified by calculating the radial distribution functions and ionic density profiles. It is shown that the organic solvent properties and nanopore confinement can affect the structure of the organic electrolyte solution. For the pore size range (1-5 nm) investigated in this paper, the surface charge used in this study can alter the sodium ions but not the solvent structure inside the pore.

Separation of CO2 based on adsorption, absorption, and membrane techniques is a crucial technology necessary to address current global warming issues. Porous media are essential for all these approaches and understanding the nature of the porous structure is important for achieving highly efficient CO2 adsorption. Porous carbon is considered to be a suitable porous media for investigating the fundamental mechanisms of CO2 adsorption, because of its simple morphology and its availability in a wide range of well-defined pore sizes. In this study, we investigated the dependence of CO2 adsorption on pore structures such as pore size, volume, and specific surface area. We also studied slit-shaped and cylindrical pore morphologies based on activated carbon fibers of 0.6–1.7 nm and carbon nanotubes of 1–5 nm, respectively, with relatively uniform structures. Porous media with larger specific surface areas gave higher CO2 adsorption densities than those of media having larger pore volumes. Narrower pores gave higher adsorption densities because of deep adsorption potential wells. However, at a higher pressure CO2 adsorption densities increased again in nanopores including micropores and small mesopores. The optimal pore size ranges of CO2 adsorption in the slit-shaped and cylindrical carbon pores were 0.4–1.2 and 1.0–2.0 nm, respectively, although a high adsorption density was only expected for the narrow carbon nanopores from adsorption potentials. The wider nanopore ranges than expected nanopore ranges are reasonable when considering intermolecular interactions in addition to CO2–carbon pore interactions. Therefore, cooperative adsorption among CO2 in relatively narrow nanopores can allow for high density and high capacity adsorption.

Graphene and graphite are of great interest in materials science. Using chemical vapor deposition at various CH4:H-2 ratios, we synthesized materials with graphene-laminated architectures, ranging from graphene to graphite. A lower proportion of CH4 and lower synthesis temperature produced fewer graphene layers. The transparent properties changed from transparent to semi-transparent, black, and silver as the number of graphene layers was increased. The sheet electrical resistivity ranged from 10(6) to 0.2 Omega rectangle(-1), and the smaller resistivity was nearly equaled as the values of highly orientated pyrolytic graphite and glassy carbon. The graphene-laminated materials featured a wide range of transmittance, reflectance, and electrical conductance properties. (C) 2017 Elsevier B.V. All rights reserved.

We present the structures of NaCl aqueous solution in carbon nanotubes with diameters of 1, 2, and 3 nm based on an analysis performed using X-ray diffraction and canonical ensemble Monte Carlo simulations. Anomalously longer nearest-neighbor distances were observed in the electrolyte for the 1-nm-diameter carbon nanotubes; in contrast, in the 2 and 3 nm carbon nanotubes, the nearest-neighbor distances were shorter than those in the bulk electrolyte. We also observed similar properties for water in carbon nanotubes, which was expected because the main component of the electrolyte was water. However, the nearest-neighbor distances of the electrolyte were longer than those of water in all of the carbon nanotubes; the difference was especially pronounced in the 2-nm-diameter carbon nanotubes. Thus, small numbers of ions affected the entire structure of the electrolyte in the nanopores of the carbon nanotubes. The formation of strong hydration shells between ions and water molecules considerably interrupted the hydrogen bonding between water molecules in the nanopores of the carbon nanotubes. The hydration shell had a diameter of approximately 1 nm, and hydration shells were thus adopted for the nanopores of the 2-nm-diameter carbon nanotubes, providing an explanation for the large difference in the nearest-neighbor distances between the electrolyte and water in these nanopores.

Edges of carbon materials have been known to work as active sites for various applications such as catalysts, adsorbent, and electrodes, but selecting precursors for carbon materials with controlled edges in the absence of metallic substrate is challenging. This work developed a method to select the superior precursors instantaneously using molecular dynamic simulation. This simulation predicted that hydrogen in precursors gasified and the hydrogen attacked the active sites in precursors upon carbonization, causing the decrement of active sites. Thus, it is essential to reduce the concentration of hydrogen in precursors and it is also necessary to introduce reactive functional groups near the active site to protect the active sites. We indeed synthesized the selected precursors such as diethynyl anthracene, diethynyl chrysene, divinyl naphthyridine, and divinyl phenanthroline and proved that edges in those precursors were maintained even after carbonization at 773 K using diffuse reflectance infrared Fourier transform and X-ray photoelectron spectroscopy with the aid of spectra simulated by density functional theory calculation. Especially, ca. 100% of edge structures of zigzag edges and armchair edges in diethynyl anthracene and diethynyl chrysene was maintained even after carbonization at 773 K. (C) 2017 Elsevier Ltd. All rights reserved.

Fabrication of a graphene separation sheet is difficult because of the necessity for leakage-free graphene transfer onto a substrate. In this study, porous graphene sheets with thicknesses of one, two, and four layers were directly fabricated on stainless-steel mesh substrates and demonstrated to display high separation ability for H-2, CO2, and CH4. The single-layer graphene sample exhibited higher permeance for these molecules than double-and four-layer graphene and displayed similar high selectivity to that of other porous materials. Permeance was proportional to molecular velocity and inversely proportional to interaction strength with graphene; molecular size-dependent permeance was not seen. Molecules that interacted strongly with graphene were attracted to the graphene surface, which hindered permeation. Such graphene surface rejection allowed graphene containing larger pores than the molecular size to provide both high molecular permeance and selectivity. The relationship between the permeance of porous graphene for H-2 and H-2/CO2 with selectivity suggested that its permeance was higher than that of other materials with high separation performance. Therefore, the porous graphene samples separated molecules with extremely high permeance by graphene surface rejection.

Unlike classical covalent polymers, one-dimensionally (1D) elongated supramolecular polymers (SPs) can be encoded with high degrees of internal order by the cooperative aggregation of molecular subunits, which endows these SPs with extraordinary properties and functions. However, this internal order has not yet been exploited to generate and dynamically control well-defined higher-order (secondary) conformations of the SP backbone, which may induce functionality that is comparable to protein folding/unfolding. Herein, we report light-induced conformational changes of SPs based on the 1D exotic stacking of hydrogen-bonded azobenzene hexamers. The stacking causes a unique internal order that leads to spontaneous curvature, which allows accessing conformations that range from randomly folded to helically folded coils. The reversible photoisomerization of the azobenzene moiety destroys or recovers the curvature of the main chain, which demonstrates external control over the SP conformation that may ultimately lead to biological functions.

Electric double-layer capacitors using nanoporous carbons store electricity efficiently, with high power density and a long life. Smooth ion adsorption and a high concentration of carbon nanopores are crucial factors for achieving high capacitance performance in such devices. Previous studies have investigated the static properties of nanoelectrolytes using experiments and simulations. An analysis of the dynamic properties performed here sheds new light on the mechanism of ion transportation between electrodes. In this study, the dynamics of a nanoelectrolyte under switching between plus and minus partial charges in conical carbon electrodes were investigated using molecular dynamics simulations. Fast ion transportation between the conical carbon electrodes was observed during charging and discharging cycles, behavior that was associated with increasing hydration numbers and decreasing hydrogen bonding numbers. Smooth ion transportation was thus, made possible by the breaking of hydrogen bonding networks that resulted from the recovery of the hydration shell.

Intricately designed π-conjugated molecules containing interactive groups can be used to generate supramolecular polymers with outstanding structural and functional properties. To construct such supramolecular polymers, the non-covalent synthesis of supermacrocyclic monomers from relatively simple molecules represents an attractive strategy, although this has been rarely exploited. Here, we report the supramolecular polymerization of two barbiturate-naphthalene derivatives that circularly hexamerize by hydrogen bonding. The two molecules contain an aliphatic "wedge" unit with either an ether or ester linkage. This subtle difference is amplified into distinct features both in terms of the morphology of the supramolecular polymers and the polymerization process. The degrees of conformational freedom of the wedge unit determine the stacking of the supermacrocycles, as is evident from 2D X-ray diffraction analyses on the aligned fibers. The differences in stacking impart the supramolecular polymer fibers with different morphological features (cylindrical or helical), which are reflected in the properties of concentrated solutions (suspension or gel). The degrees of conformational freedom of the wedge unit also affect the polymerization kinetics, in which the more flexible ether linkage induces pathway complexity by the formation of off-pathway aggregates.

The Adsorption heat pump is a technology for cooling and heating by using hot water as a driving heat source. It will largely contribute to energy savings when it is driven by solar thermal energy or waste heat. The system is available in the market worldwide, and there are many examples of application to heat recovery in factories and to solar cooling systems. In the present system, silica gel and zeolite are popular adsorbents in combination with water refrigerant. Our study focused on activated carbon-ethanol pair for adsorption cooling system because of the potential to compete with conventional systems in terms of coefficient of performance. In addition, activated-ethanol pair can generally produce larger cooling effect by an adsorption-desorption cycle compared with that of the conventional pairs in terms of cooling effect per unit adsorbent mass. After the potential of a commercially available activated carbon with highest level specific surface area was evaluated, we developed a new activated carbon that has the optimum pore characteristics for the purpose of solar or waste heat driven cooling systems. In this paper, comparison of refrigerants for adsorption heat pump application is presented, and a newly developed activated carbon for ethanol adsorption heat pump is introduced.

An alkylene-tethered perylene bisimide (PBI) dyad with hydrophilic substituents forms helical supramolecular polymers that can be visualized by AFM in THF-water mixtures. The supramolecular polymers also form thixotropic gel-like lyotropic mesophases in the mixtures.

Water in carbon nanotubes is surrounded by hydrophobic carbon surfaces and shows anomalous structural and fast transport properties. However, the dynamics of water in hydrophobic nanospaces is only phenomenologically understood. In this study, water dynamics in hydrophobic carbon nanotubes is evaluated based on water relaxation using nuclear magnetic resonance spectroscopy and molecular dynamics simulations. Extremely fast relaxation (0.001 s) of water confined in carbon nanotubes of 1 nm in diameter on average is observed; the relaxation times of water confined in carbon nanotubes with an average diameter of 2 nm (0.40 s) is similar to that of bulk water (0.44 s). The extremely fast relaxation time of water confined in carbon nanotubes with an average diameter of 1 nm is a result of frequent energy transfer between water and carbon surfaces. Water relaxation in carbon nanotubes of average diameter 2 nm is slow because of the limited number of collisions between water molecules. The dynamics of interfacial water can therefore be controlled by varying the size of the hydrophobic nanospace.

A double-step CO2 sorption by [Cu(4,4'-bpy)2(BF4)2] (ELM-11) was observed during isothermal measurements at 195, 253, 273, and 298 K and was accompanied by interlayer expansion in the layered structure of ELM-11. The first step occurred in the range of the relative pressure (P/P0) from 10(-3) to 10(-2). The second step was observed at P/P0 ≈ 0.3 at the four temperatures. Structural changes in ELM-11 during the CO2 sorption process were examined by X-ray diffraction (XRD) measurements. The structural change for the first step was well understood from a detailed structural analysis, as reported previously. The XRD results showed further expansion of the layers during the second step as compared to the already expanded structure in the first step, and both steps were found to be caused by the gate phenomenon. The energy for the expansion of the layer structure was estimated from experimental and simulated data.

Helium at low temperatures has unique quantum properties such as superfluidity, which causes it to behave differently from a classical fluid. Despite our deep understanding of quantum mechanics, there are many open questions concerning the properties of quantum fluids in nanoscale systems. Herein, the quantum behavior of helium transportation through one-dimensional nanopores was evaluated by measuring the adsorption of quantum helium in the nanopores of single-walled carbon nanohorns and AlPO4-5 at 2-5 K. Quantum helium was transported unimpeded through nanopores larger than 0.7 nm in diameter, whereas quantum helium transportation was significantly restricted through 0.4-nm and 0.6-nm nanopores. Conversely, nitrogen molecules diffused through the 0.4-nm nanopores at 77 K. Therefore, quantum helium behaved as a fluid comprising atoms larger than 0.4-0.6 nm. This phenomenon was remarkable, considering that helium is the smallest existing element with a (classical) size of approximately 0.27 nm. This finding revealed the presence of significant quantum fluctuations. Quantum fluctuation determined the behaviors of quantum flux and is essential to understanding unique quantum behaviors in nanoscale systems.

Carbon nanotubes and graphene are among the major nanomaterials in nanoscience and technology. Despite having pi electrons, these nanocarbon allotropes have been simply considered as neutral in classical calculations. In this study, the effects of partial charges on graphene and curved interfaces on molecular adsorption were investigated using Monte Carlo simulations of N-2 and NaCl aqueous solutions on graphene and carbon nanotubes. The simulated N-2 adsorption behavior and adsorption potential on partially charged and non-charged graphene coincided with each other. The adsorption potentials suggested that partially charged graphene attracted Na ions and repelled Cl ions. However, those tendencies were not present in NaCl aqueous solutions on graphene. Conversely, in partially charged carbon nanotube models, a preference for Na ions and repulsion of Cl ions in the internal nanospaces were observed in the adsorption potentials using Monte Carlo simulations. Curved interfaces in the internal nanospaces of carbon nanotubes enhanced these properties, suggesting significant electrostatic interactions in a curved pi-conjugated system.

We have developed a laser-induced chemical vapor deposition (LCVD) method for preparing nanocarbons with the aid of SF6. This method would offer advantages for the production of aggregates of nanoscale foams (nanofoams) at high rates. Pyrolysis of the as-grown nanofoams induced the high surface area (1120 m(2) g (1)) and significantly enhanced the adsorption of supercritical H-2 (16.6 mg g (1) at 77 K and 0.1 MPa). We also showed that the pyrolized nanofoams have highly ultramicroporous structures. The pyrolized nanofoams would be superior to highly microporous nanocarbons for the adsorption of supercritical gases. (C) 2016 Elsevier B.V. All rights reserved.

The unique water transport properties in nanospaces are essential for control of various chemical reactions, biochemical activities, and electrochemical systems. Fast water transport has been observed in one-dimensional nanospaces. However, water transport via zero-dimensional nanospaces has not yet been observed. Zero-dimensional nanospaces were obtained by extremely small and thin gate (zero-dimensional gate) insertion on graphene walls of single walled carbon nanohorns. The water transport properties were examined by water vapor loading and release via the zero dimensional gates, and molecular dynamics simulation. Although relatively large gates provided considerable adsorption hysteresis by long-term equilibrium, water vapor loading and release via the extremely small gates showed consecutive water loading and release. The molecular dynamics simulation showed consecutive water transport via the gates, probably because of lower energy barriers to water transport in the vicinity of the gates. The zero-dimensional gates rejected water vapor transfer, but admitted condensed water for transfer.

Single-walled carbon nanotubes (SWCNTs) have been recognized as promising nanocarriers by many researchers from around the world through hundreds of articles published in the last decade pertaining to SWCNTs-based drug delivery applications. In line with this issue, systematic studies of non-covalent interaction between camptothecin (CPT) and the oxidized SWCNTs (Ox-SWCNTs) have been done in this work. Through the developed process of purification and acid oxidation, we obtained the Ox-SWCNTs that were essentially free of metals and well dispersed in aqueous solutions. A quenching phenomenon, which is indicative of the interactions between CPT and the Ox-SWCNTs, was observed and used as the basis of analysis for monitoring the adsorption of CPT. A comparison of the kinetic models and the overall adsorption capacity was best described by the pseudo second-order kinetic model and Weber-Morris kinetic model. Langmuir and Freundlich models were introduced to fit the adsorption isotherms data. The adsorption of CPT was found to be dependent on concentration and adsorption temperature. The thermodynamic analysis exhibited that the adsorption of CPT on the Ox-SWCNTs was exothermic and spontaneous. (C) 2015 Elsevier B.V. All rights reserved.

Incoherent neutron scattering by water confined in carbon nanohorns was measured with the backscattering spectrometer SPHERES and analyzed in exemplary breadth and depth. Quasielastic spectra admit δ-plus-Kohlrausch fits over a wide q and T range. From the q and T dependence of fitted amplitudes and relaxation times, however, it becomes clear that the fits do not represent a uniform physical process, but that there is a crossover from localized motion at low T to diffusive α relaxation at high T. The crossover temperature of about 210 to 230 K increases with decreasing wave number, which is incompatible with a thermodynamic strong-fragile transition. Extrapolated diffusion coefficients D(T) indicate that water motion is at room temperature about 2.5 times slower than in the bulk; in the supercooled state this factor becomes smaller. At even higher temperatures, where the α spectrum is essentially flat, a few percentages of the total scattering go into a Lorentzian with a width of about 1.6μeV, probably due to functional groups on the surface of the nanohorns.

Recently, various composites for reducing CO2 emissions have been extensively studied. Because of their high sorption capacity and low cost, alkali metal carbonates are recognized as a potential candidate to capture CO2 from flue gas under moist conditions. However, undesirable effects and characteristics such as high regeneration temperatures or the formation of byproducts lead to high energy costs associated with the desorption process and impede the application of these materials. In this study, we focused on the regeneration temperature of carbon aerogel-potassium carbonate (CA-KC) nanocomposites, where KC nanocrystals were formed in the mesopores of the CAs. We observed that the nanopore size of the original CA plays an important role in decreasing the regeneration temperature and in enhancing the CO2 capture capacity. In particular, 7CA-KC, which was prepared from a CA with 7 nm pores, exhibited excellent performance, reducing the desorption temperature to 380 K and exhibiting a high CO2 capture capacity of 13.0 mmol/g-K2CO3, which is higher than the theoretical value for K2CO3 under moist conditions.

Room-temperature ionic liquids (IL) have been of considerable worldwide interest as universal solvents, reaction media, gas scavengers, and electrolytes, particularly in supercapacitors. The behavior of ILs confined in nanoscale cavities is essential for high-performance capacitors, yet it is not well understood.. Here, the structural properties of the 1-ethyl-3-methylimidazolium chloride IL confined in small diameter carbon nanotubes (CNTs) are characterized by experimental structural and vibrational analyses, complemented by molecular simulations. The IL poorly fills the 1 nm CNTs and the included IL possesses a similar local structure to that seen in the bat: For 2 and 3 nm diameter CNTs, highly ordered cationic networks associated with restricted vibrational motion are observed. Anions are relatively mobile in the ordered cationic network within. the CNTs. Rigid crystalline cationic networks and mobile chloride anions distinguish the unique properties of the confined IL.

The supramolecular design of photochromic molecules has produced various smart molecular assemblies that can switch their structures and/or functions in response to light stimuli. However, most of these assemblies require large structural changes of the photochromic molecules for an efficient conversion of assembled states, which often suppresses the photoreactivity within the self-assemblies. Here we report molecular assemblies, based on a photo-cross-linkable chromophoric dyad, in which a small amount of ultraviolet-generated photochemical product can guide the entire system into different assembly processes. In apolar solution, the intact dyad self-assembles into right-handed superhelical fibrils. On ultraviolet-irradiation of these fibrils, an effective photoreaction affords a sole photo-cross-linked product. When right-handed helical fibrils, containing a minor amount of the photoproduct, are thermally reconstructed, the intact molecule and the photoproduct undergo a co-assembly process that furnishes superhelical fibrils with different molecular packing structures. This molecular design principle should afford new paradigms for smart molecular assemblies.