Faster Sorption of Propylene Compared to Propane Using an Elastic Layer-Structured Metal-Organic Framework (ELM-11).

The separation of propane and propylene is the most energy-consuming and difficult separation process in the petrochemical industry because of their extremely similar physical properties. Separating propylene from propane using sorption can considerably reduce the energy consumed by current cryogenic distillation techniques. However, sorption involves several major challenges. An elastic layer-structured metal-organic framework (ELM-11) exhibited a highly efficient propane/propylene sorption separation, owing to its kinetic properties. Under equilibrium conditions, propane and propylene exhibited similar sorption capacities, gate opening pressures, and heats of sorption. Thus, their separation under equilibrium conditions is impractical. However, the sorption rates of the two gases were considerably different, showing different diffusion coefficients, resulting in a high kinetic selectivity (214 at 298 K) of propylene over propane on ELM-11. This kinetic selectivity is considerably higher than those obtained in previous studies. Thus, ELM-11 is a promising sorbent for separation technologies.

Magnetic Supramolecular Spherical Arrays: Direct Formation of Micellar Cubic Mesophase by Lanthanide Metallomesogens with 7-Coordination Geometry.

Here, an unprecedented phenomenon in which 7-coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H2 O molecules, form micellar cubic mesophases at room temperature, creating body-centered cubic (BCC)-type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self-assembling behavior of 6-coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7-coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

Adsorption Properties of Methane, Ethane, and Hexane on Mesoporous Organic Polymers Prepared by the Flash Freezing Method.

Mesoporous organic polymers, including poly(p-phenylene ether-sulfone) (PES), polysulfone (PSF), poly(bisphenol A-carbonate) (PC), and polyvinyl chloride (PVC), were prepared by the previously reported flash freezing method. For the four polymers, the vapor adsorption of water and hydrocarbons (C2H6, C3H8, and C6H14) was examined. PVC showed that the hydrocarbon adsorption was more selective than water adsorption. The isosteric heats of adsorption were determined from the temperature dependence of the vapor adsorption of the hydrocarbons and water. This showed the weak interaction of PVC with water and its stronger (but not too strong) interaction with hydrocarbons. The hydrophobicity and mesoporosity of PVC were determined to be suitable for such selective adsorption of hydrocarbons compared to that of water with low energy consumption during the desorption process of the hydrocarbons. Mesoporous PVC should considered a candidate for the recovery of flammable gases from water/hydrocarbon mixtures.

A flexible two-dimensional layered metal-organic framework functionalized with (trifluoromethyl)trifluoroborate: synthesis, crystal structure, and adsorption/separation properties.

Flexible porous materials have great potential for adsorption/separation of small molecules. In this study, a highly CO2-selective two-dimensional (2D) layered metal-organic framework (MOF) showing gate-type adsorption properties was synthesized and fully characterized by single-crystal X-ray diffraction (XRD), in situ powder XRD, thermogravimetric analysis, inductively coupled plasma atomic emission spectroscopy, and gas adsorption/separation analyses. The MOF named ELM-13 is a 2D layered material functionalized with (trifluoromethyl)trifluoroborate to control interlayer interactions and exhibits dynamic guest accommodation/removal properties. In a gas adsorption study, the MOF showed no adsorption at low pressure followed by abrupt uptake and sudden desorption at a pressure lower than that of adsorption, i.e., gate adsorption, in the N2, O2, Ar, NO, and CO2 isotherms at the boiling/sublimation temperature of each gas. The structure of the MOF in the CO2 adsorption was influenced by both the amount adsorbed and the adsorption process. High-pressure adsorption experiments at 273 K indicated that, out of N2, O2, Ar, and CO2, only CO2 was adsorbed on the MOF below 900 kPa. The CO2 selectivity from an equimolar CO2/N2 mixture with a total gas pressure of 1 MPa at 273 K was experimentally evaluated and compared with the CO2 selectivities of other selected porous materials theoretically, suggesting that ELM-13 is a good candidate for CO2 separation.

Advantaging Synergy Photocatalysis with Graphene-Related Carbon as a Counterpart Player of Titania.

The enhancement of photocatalytic activity of TiO2 can be made either by promoting absorption efficiency of photon energy or by reducing recombination losses of photogenerated charge carriers, for which fabrication of nanocomposite structure with carbon materials is an optional selection. Among various nanocarbons, graphene (G), graphene oxide (GO), and reduced graphene oxide (rGO) are more favorable as the counterpart materials because they can provide availability of both obverse and reverse surface, thus doubling effective sites for adsorption, loading of nanoparticles, and interfacial interaction with the loaded nanoparticles. Composition of G/GO with titania, therefore, is a hopeful strategy for achieving synergy or cooperative effect in photocatalysis. In this personal account, we focus on the background and methodology of several soft chemical approaches that we have utilized up to date to fabricate nanocomposites of G/GO and titania, aiming to shed light on the importance of designing of nanocomposite structure for enhancing photocatalysis. In addition, we emphasize the role of interfacial interaction between carbon and titania by exemplifying a hybridized photocatalyst based on inexpensive biomass-derived carbon sphere (CS), and demonstrate that it is a crucial influential factor underlying an enhanced visible light photocatalysis. CS can be a better selection as a counterpart component than G/GO, whose core-shell composing structure with titania (TiO2 @CS) can efficiently induce charge transfer so as to achieve a much higher photocatalytic performance under visible light illumination as compared to the composite of rGO and titania.

Nanostructured silicon ferromagnet collected by a permanent neodymium magnet.

Nanostructured silicon (N-Si) was prepared by anodic electroetching of p-type silicon wafers. The obtained magnetic particles were separated by a permanent neodymium magnet as a magnetic nanostructured silicon (mN-Si). The N-Si and mN-Si exhibited different magnetic properties: the N-Si exhibited ferromagnetic-like behaviour, whereas the mN-Si exhibited superparamagnetic-like behaviour.

Double-Step Gate Phenomenon in CO2 Sorption of an Elastic Layer-Structured MOF.

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.

Wide Carbon Nanopores as Efficient Sites for the Separation of SF6 from N2.

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.

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.

Energetic contribution to hydration shells in one-dimensional aqueous electrolyte solution by anomalous hydrogen bonds.

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.

Rapid water transportation through narrow one-dimensional channels by restricted hydrogen bonds.

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.

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.

Electron Density Modification of Single Wall Carbon Nanotubes (SWCNT) by Liquid-Phase Molecular Adsorption of Hexaiodobenzene.

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 S11 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 cm­1) 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.

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.

Preparation and characterization of conducting mixed-valence 9,9'-dimethyl-3,3'-bicarbazyl rectangular nanowires.

The facile synthesis of an organic electric conducting nanowire is described. The simple oxidation of 9-methylcarbazole by iron(III) perchlorate in a methanol/acetonitrile mixture under atmospheric pressure and temperature produces abundant nanowires without using a template. The nanowire consists of 9,9'-dimethyl-3,3'-dicarbazyl and has a rectangular nanowire shape with an average diameter of 397 ± 50 nm and length of 17 ± 5 µm. The results of the elemental analysis, (1)H NMR, FT-IR, XPS, and ESR measurements revealed that the chemical composition of the nanowire is (dicarbazyl)(0.12)(dicarbazylium·ClO(4)(-))(0.88)·H(2)O. This result, combined with the UV-vis-NIR measurement, demonstrates that 9,9'-dimethyl-3,3'-dicarbazyl stacks in a mixed valence state. The nanowire is electroactive and has an electric conductivity of 3.0 × 10(-5) S cm(-1).

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 7 MPa at 263, 273, and 303 K 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.

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.

Formation of CO(x)-free H2 and cup-stacked carbon nanotubes over nano-Ni dispersed single wall carbon nanohorns.

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 CH(4) 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/Al(2)O(3), and the former provided CO(x)-free H(2) and cup-stacked carbon nanotubes, while Ni/Al(2)O(3) produced CO(x) in addition to H(2). SWCNH was superior to Al(2)O(3) as the catalyst support of Ni for the CH(4) decomposition reaction.

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.

Marked adsorption irreversibility of graphitic nanoribbons for CO2 and H2O.

Graphene and graphitic nanoribbons possess different types of carbon hybridizations exhibiting different chemical activity. In particular, the basal plane of the honeycomb lattice of nanoribbons consisting of sp(2)-hybridized carbon atoms is chemically inert. Interestingly, their bare edges could be more reactive as a result of the presence of extra unpaired electrons, and for multilayer graphene nanoribbons, the presence of terraces and ripples could introduce additional chemical activity. In this study, a remarkable irreversibility in adsorption of CO(2) and H(2)O on graphitic nanoribbons was observed at ambient temperature, which is distinctly different from the behavior of nanoporous carbon and carbon blacks. We also noted that N(2) molecules strongly interact with the basal planes at 77 K in comparison with edges. The irreversible adsorptions of both CO(2) and H(2)O are due to the large number of sp(3)-hybridized carbon atoms located at the edges. The observed irreversible adsorptivity of the edge surfaces of graphitic nanoribbons for CO(2) and H(2)O indicates a high potential in the fabrication of novel types of catalysts and highly selective gas sensors.