Search

The present report describes the preparation of lanthanide-doped colorless magnetic materials based on poly-β-ketoester particles. Monodisperse poly(2-acetoacetoxy ethyl methacrylate) (PAAEM) parti...

Here, we have demonstrated the production of colorless and full-color magnetic nanoparticles based on holmium (Ho)-doped polymers, which could not be achieved with conventional dark brown iron oxid...

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.

Potassium carbonate (K2CO3) is recognized as a potential candidate for CO2 capture by flue gas under moist conditions because of its high sorption capacity and low cost. However, undesirable effect...

A Na2CO3–carbon nanocomposite (NaC-NC) was prepared from terephthalic acid and NaOH, and its CO2 capture under moist conditions was examined by thermogravimetric analysis and X-ray diffraction. CO2 capture was repeated twice. The first CO2 capture reaction of bulk Na2CO3 was faster than its second, while the second capture reaction of NaC-NC was faster than its first. This may be because of the nanostructural properties of NaC-NC. The regeneration from NaHCO3 to Na2CO3 of NaC-NC proceeded at a lower temperature than with the bulk NaHCO3. Thus, compared with the bulk Na2CO3, we found that NaC-NC could efficiently capture CO2, increasing the reaction rate and decreasing the regeneration temperature.

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.

The capacity and kinetics of CO2 capture of K2CO3 were studied to determine the mechanism for CO2 sequestration under ambient conditions. Bicarbonate formation 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 XRD results showed that the bicarbonate formation process of K2CO3 could be divided into three reactions, such as the formation of K2CO3·1.5H2O from K2CO3, the subsequent formation of K4H2(CO3)3·1.5H2O from K2CO3·1.5H2O, and the slow formation of KHCO3 from K4H2(CO3)3·1.5H2O...

We investigated the importance of the specific effective surface area through a detailed study on the relationship between electrical conductivity of single-walled carbon nanohorns (SWCNHs) and accessibility of the electrolyte ions in the SWCNH-based supercapacitor. After heat treatment of the SWCNHs, the ratio of sp2/sp3 carbons dramatically increased, suggesting an enhanced electrical conductivity of the SWCNHs. Even though the specific surface area (SSA) slightly decreased by 16% as a result of heat treatment, the specific capacitance per SSA of the SWCNH electrode remarkably increased from 22 to 47 μF cm–2. Such a result indicates an explicit increase in accessible effective surface area by electrolyte ions. Our result clearly showed that a higher degree of utilization for the interstitial pore of SWCNHs by solvated ions is a key factor in achieving a high volumetric capacitance of SWCNH-based supercapacitors.

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.

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.

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.

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.

The quantum molecular sieving effects of pore-structure-controlled single-walled carbon nanotubes (SWCNTs) for H2 and D2 were evaluated at 20, 40, and 77 K. The adsorption amounts of D2 were larger than those of H2. The lower the adsorption temperature, the greater the difference between the D2 and H2 adsorption amounts. Bundled SWCNTs with interstitial pores of diameter 0.6 nm gave the greatest adsorption difference between D2 and H2 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.

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.

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 N2 and H2 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.

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 5A at around ambient temperatures and shows temperature dependence with an anti-Arrhenius trend: higher adsorption rate...

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.

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

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

A two-dimensional flexible porous coordination polymer (2D-PCP) that shows expansion/shrinkage structural transformation accompanied by molecular accommodation was synthesized by control of dimensionality in zero-dimensional and one-dimensional PCPs: The dynamic structural transformation cooperatively proceeds in the solid state with a drastic molecular rearrangement. Kinetics of the structural transformation was investigated.

Single-wall carbon nanotube (SWCNT) bundles were pillared by fullerene (C60) by the cosonication of C60 and SWCNT in toluene to utilize the interstitial pores for hydrogen storage. C60-pillared SWCNTs were confirmed by the shift in the X-ray diffraction peak and the expanded hexagonal and distorted tetragonal bundles revealed by high-resolution transmission electron microscopy. The H2 adsorptivity of the C60-pillared SWCNT bundles was twice that of the original SWCNT bundles, indicating a design route for SWCNT hydrogen storage.

It is important to study the interaction between water molecules and a host structure for understanding the adsorption mechanism of metal-organic framework (MOF) materials. The evolution of the structure of a flexible Cu-MOF, {[Cu(bpy)(H2O)2(BF4)2](bpy)} (bpy=4,4'-bipyridine), upon dehydration and rehydration was studied by thermogravimetric analysis (TGA), infrared (IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and water adsorption. A nearly reversible structural change was observed upon rehydration. More importantly, a unique CO2 "gate adsorption" phenomenon was observed despite the exposure of the Cu-MOF to water. This shows that the Cu-MOF has relatively good stability after exposure to water.

I2 was adsorbed on single-walled carbon nanotube from ethanol solution at 303 K. The I2 adsorption isotherm was Langmuirian, giving 35 (+/-10) mg g(-1) of the saturated adsorption amount (coverage 0.06-0.09). The I2-adsorption treatment of SWCNT bundles reduced the N2 adsorption amount at 77 K by only 3%; the adsorption amount of supercritical H2 at 77 K was decreased by 30% because of the I2-adsorption treatment, indicating the blocking of interstitial pores by adsorbed I2. These adsorption results indicated the adsorption of I2 molecules in the narrow interstitial pores. The I2-adsorption treatment increases the Raman intensity coming from metallic SWCNTs, and the dc electrical conductivity increased by 15% because of the I2-adsorption treatment, strongly suggesting the presence of charge-transfer interaction between I2 and SWCNTs irrespective of small coverage by I2.

Single-wall carbon nanohorns (SWCNHs) and partially oxidized SWCNHs (ox-SWCNHs) were mechanochemically treated for the elucidation of their unique chemical bonding state. The mechanochemical treatment promoted the transformation from sp2 to sp3 bonding from XPS, leading to an increase and decrease in the micropore volume for SWCNHs and ox-SWCNHs, respectively. The changes in the micropore volume and the electrical conductivity responses on CO2 adsorption indicate the occurrence of tubulite-to-tubulite reconstruction in SWCNH through unstable sp3 bonding.

The crystal structure of [Cu(4,4'-bipyridine) 2(CF 3SO 3) 2] n metal-organic framework (CuBOTf) of one-dimensional pore networks after pre-evacuation at 383 K was determined with synchrotron X-ray powder diffraction measurement. Effective nanoporosity of the pre-evacuated CuBOTf was determined with N 2 adsorption at 77 K. The experimental H 2 and D 2 adsorption isotherms of CuBOTf at 40 and 77 K were measured and then compared with GCMC-simulated isotherms using the effective nanoporosity. The quantum-simulated H 2 and D 2 isotherms at 77 K using the Feynman-Hibbs effective potential coincided with the experimental ones, giving a direct evidence on the quantum molecular sieving effect for adsorption of H 2 and D 2 on CuBOTf. However, the selectivity for the 1:1 mixed gas of H 2 and D 2 was 1.2. On the contrary, experimental H 2 and D 2 isotherms at 40 K had an explicit adsorption hysteresis, originating from the marked pore blocking effect on measuring the adsorption branch. The blocking effect for quantum H 2 is more prominent than that for quantum D 2; the selectivity for D 2 over H 2 at 40 K was in the range of 2.6 to 5.8. The possibility of the quantum molecular sieving effect for H 2 and D 2 adsorption on [Cu 3(benzene-1,3,5-tricarboxylate) 2(H 2O) 3] n of three-dimensional pore networks was also shown at 77 K.

Surface-enhanced Raman scattering (SERS) was applied to investigate the fine nanostructure of single-wall carbon nanohorns (SWCNHs) and partially oxidized SWCNHs of which Raman D bands are predominant. SERS of SWCNH samples was measured in vacuo by deposition of SWCNH particles on silver foil with evaporation of SWCNHs-dispersed solvent. New peaks were observed over the wavenumber range of 200 to 1700 cm−1 in addition to peaks observed in normal Raman scattering. The new SERS peaks are tentatively assigned to the vibrational mode due to topological defects such as the pentagon and heptagon.

The experimental adsorption isotherm of N2 molecules on mutually isolated single wall carbon nanotubes at 77 K agreed well with the grand canonical Monte Carlo simulated one. The N2 adsorption isotherm had two steps stemming from monolayer formation on the internal surface and filling of the residual space of the internal tube pore. Although all of radial distribution functions of molecules adsorbed on the internal, external, and flat surfaces indicated a hexagonal packing structure, the radial distribution functions were different from each other. In particular, the radial distribution function of the monolayer on the internal surface showed an additional peak because of the markedly curved surface.

The temperature and magnetic field dependences of magnetic characteristics of an organic radical (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL)) adsorbed on oxidized single-wall carbon nanohorn (ox-NH) were studied with a SQUID magnetometer and an electron spin resonance (ESR) spectrometer. TEMPOL molecules adsorbed on ox-NH do not form any ordered structures, but the formation of disordered clusters was suggested because of intensive restriction by nanoconfinement. Exchange interaction of TEMPOL adsorbed on ox-NH was weaker than that of bulk TEMPOL. Slow relaxation phenomena of magnetization and paramagnetic behaviors were observed by confinement of TEMPOL in nanospace.

The structure of single-wall carbon nanohorn (SWNH) was analyzed with X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The considerably strong peak due to single bonding carbons was observed in C1s XPS spectrum of SWNH. This peak intensity increases with oxidation treatment, coinciding with the decrease in Raman G/D intensity ratio. It is concluded that the presence of a considerable amount of single bonding carbons is the reason for the unique assembly structure accompanying with a strong D-band in Raman spectrum of SWNH.

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

Novel nanostructured carbon material was synthesized by applying zeolite LTA as a template and using methanol as a carbon source. X-ray diffraction (XRD) revealed that the higher the decomposition ...

The supercritical N2, O2, and CH4 adsorption isotherms on a Cu-based metal−organic framework, [Cu(4,4‘-bipyridine)2(BF4)2]n, over the temperature range of 196−303 K were measured by a gravimetric method. The N2 and O2 adsorption isotherms at 196 K showed a vertical adsorption accompanied by a rectangular hysteresis loop. A method of evaluating the absolute adsorption amount of these gases was developed taking into account the intermolecular interactions for the buoyancy-mediated method. The isotherms of the absolute adsorption amount were obviously different from the isotherms of the surface-excess mass adsorption at 196 K. We also obtained isotherms of the absolute adsorption amount of CH4 at different temperatures. The isosteric heat of adsorption from the isotherms of the absolute adsorption amount of CH4 is larger than the liquefaction heat of CH4 at its boiling point by more than 3 kJ mol-1.

Phenanthrene was adsorbed from ethanol solution to the surface of single wall carbon nanotubes, which were previously physically and chemically characterized. Different anionic surfactants were added in the solutions to enhance the phenanthrene solubility and apparently have also improved the dispersion of two respective nanotube samples used. Adsorbed amount was determined through the concentration difference measured by UV-visible spectrophotometry. Results suggest that adsorption of phenanthrene is extremely improved in the case of nanotube purified with higher quality. These findings were confirmed by X-ray photoelectron spectroscopy. The influence of the surfactant on the adsorption kinetics of phenanthrene is suggested to be significant as well.

A new preparation method for porous silica particles was developed using activated silica sols which are called nano-silica solutions in this paper. Several kinds of organic and inorganic acids are employed to neutralize diluted sodium silicate solutions to form the nano-silica solutions: formic acid, acetic acid, propionic acid, oxalic acid, succinic acid, dl-malic acid, citric acid, and tricarballylic acid as carboxylic acids, and sulfuric acid and hydrochloric acid as inorganic acids. The effect of salts in the nano-silica solution is also studied. The products were investigated using a field emission scanning electron microscope, an X-ray diffractometer, the nitrogen adsorption technique, and a mercury porosimeter. Microporous silicas were produced when carboxylic acids were applied; the formation of micropores was influenced by the pH of the nano-silica solutions and molecular sizes of the carboxylic acids. Addition of a salt in a citric acid solution increased the mesopore volume. Macropores were formed when inorganic acids including salts were applied; the salt nanoparticles which were crystallized in silica spheres acted as templates. The anion types and salt concentrations in the nano-silica solutions affected the aggregation condition of silica nanoparticles, following the Schulze-Hardy rule.

Single-wall carbon nanohorn (SWNH), which is a tubular particle with a cone cap, was oxidized in an oxygen flow at various temperatures. N(2) adsorption at 77 K, thermogravimetry (TG), differential thermal analysis (DTA), transmission electron microscopy, and Raman spectroscopy measurements were carried out on the oxidized SWNHs. The specific surface area of the oxidized SWNHs can be controlled by oxidation temperature, giving the maximum value of 1420 m(2)/g. The pore size distribution by the BJH method and the comparison plot of the N(2) adsorption isotherms of SWNH oxidized at different temperatures against that of as-grown SWNH revealed the minimum oxidation temperature for opening internal nanopores. TG-DTA analyses determined the components of as-grown SWNH: amorphous carbon 2.5 wt %, defective carbon at the cone part 15 wt %, tubular carbon 70 wt %, and graphitic carbon 12 wt %. These systematic analyses provided the exact internal nanopore volume of 0.49 mL/g for pure SWNH particles.

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

A mechanochemical intercalation approach which applies a simple mechanical milling to induce intercalation reaction was applied to introduce controlled amount of tetraethoxylsilane (TEOS) into surfactant-preexpanded graphite oxide, and the relationships between the intercalation structure, the porosities of the calcined products, and the Si addition were examined. It was found that a small added amount of TEOS produced a more expanded ordered layer structure with the interlayer distance and silicon content increasing with the amount of TEOS added, although a large amount of added TEOS easily induces layer delamination, resulting in a less ordered structure. The silica structure in the composite is changed from a disordered structure having enhanced bond strain to a condensed silica network when the amount of TEOS added increases. The porosities of the final calcined samples increase with the increase of silicon content but then decrease slightly after reaching a maximum where silicon content starts to become constant, indicating that both silicon content and the composition state of silica particles and carbon layers play important roles in porosity formation.

Mesoporous zeolite A has been synthesized by using a template method with resorcinol-formaldehyde aerogels having three-dimensional mesopores. It was characterized with X-ray powder diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, and nitrogen adsorption/desorption. The pore size distribution calculated from the nitrogen adsorption isotherm is a bimodal distribution with micropores and mesopores. Field emission scanning electron micrograph observations confirm the presence of mesopores.

Resorcinol-formaldehyde aerogels and carbon aerogels of different mesoporosities have been used as templates for preparing bimodal zeolites of mesopores. Samples were thoroughly characterized with X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, N(2) adsorption at 77 K, as well as FT-IR spectroscopy and (29)Si nuclear magnetic resonance spectroscopy. The mesoporous ZSM-5 zeolites have additional mesopores of 9-25 nm in widths and 0.07-0.2 cm(3)/g in volumes, besides their perfect inherent micropores. Experimental results show the mesoporous systems of the finally obtained zeolites can be influenced by proper preparation of resorcinol-formaldehyde aerogels and carbon aerogels through solution chemistry. Consequently, zeolites of tunable mesoporosities can be prepared with this unique methodology.

Hydrogen adsorption isotherms in single-wall carbon nanohorns (SWNHs) have been measured at 20 K. The pore volume from hydrogen adsorption is compared with that from nitrogen adsorption at 77 K to determine the density of confined hydrogen in the internal space of SWNHs; it indicates that the average density of confined hydrogen inside SWNHs at 20 K is higher than that of liquid hydrogen in the bulk and nearly approaches the density of solid hydrogen at the triple point. The surface area from hydrogen adsorption using the BET theory is anomalously large compared with that for nitrogen; however, an alternative method (modified BET theory), in which an assumption is made that the energy of a molecule in the second layer is larger than that in the liquid, gives a reasonable surface area, especially when the adsorbed hydrogen in the first layer is assumed to be in a solid state. In the modified BET model, a packing constraint of the second layer due to the cylindrical geometry of SWNH is also taken into accou...

The stabilities of water molecules in carbon slit-shaped nanospaces have been studied using the potential calculation for possible water clusters (H2O)n of n = 2−12. The adsorption isotherm of water on a graphite slit pore (w = 1.1 nm) with no surface functional groups at 303 K was calculated with GCMC simulation using TIP-5P and 10-4-3 Steele potential functions; this simulated isotherm has a vertical uptake at P/P0 = 0.5. The cluster growth along the vertical adsorption uptake was evidenced through the snapshot of GCMC simulation. The simulated adsorption isotherm agreed well with the experimental isotherm of water on an activated carbon fiber (ACF) having uniform slit pores. Thus, H2O molecules are adsorbed in hydrophobic carbon nanopores without surface functional groups through cluster formation. The isosteric heat of adsorption of clusters of (H2O)n=8-10 obtained from the GCMC simulation coincided well with the experimental value. The radial distribution function of the clusters from the GCMC simula...

A new technique of superwide pressure range adsorption (SWPA) isotherm measurement of N2 from P/P0 = 10-9 to 1 at 77 K was developed. The superwide pressure range adsorption isotherms of N2 on activated carbon fiber, molecular sieve carbon, and carbon black were compared with those of their ordinary pressure range isotherms and the simulated isotherms calculated with grand canonical Monte Carlo technique. The SWPA measurement can show the adsorption uptake below P/P0 = 10-6, which is assigned to the adsorption in ultramicropores of pore width < 0.7 nm. The SWPA method shows the presence of ultramicropores even for nonporous carbon black, which has been believed to be nonporous from the ordinary adsorption measurement. Thus, the SWPA method can elucidate the ultramicropore structures of less-crystalline materials.

The cluster structures of supercritical CH 4 confined in slit-shaped carbon micropores was investigated using in situ small-angle X-ray scattering (SAXS) and the cluster analysis for grand canonical Monte Carlo (GCMC) simulation. The pore size distribution of micropores was determined from the fitting of the GCMC-simulated adsorption isotherm to the experimental one for high-pressure CH 4 ; the pore size distributions of two kinds of activated carbon fibers (ACFs) were very narrow, and their average widths are 0.6 and 1.1 nm. The density fluctuation changes with fractional filling from in situ SAXS and GCMC simulation evidenced explicitly the formation of clusters of high concentration in the micropores. CH 4 molecules in smaller pores of 0.6 nm form highly concentrated clusters even in low fractional filling. Fewer clusters are formed in the case of wider pores of 1.1 nm.

The reduced partition function ratios (RPFRs) of Li + (Solv) n (in which Solv = H 2 O, HAS, and CH 3 OH) clusters with different values were calculated, to investigate the solvent effect of the isotopic effect of the lithium. Structures of three solvated clusters-Li + (H 2 O) n , Li + (H 2 S) n , and Li + (CH 3 OH) n -were optimized by an ab initio molecular orbital method, and their RPFRs were calculated by frequency analysis. The RPFR of the solution was estimated by the extrapolation of the cluster values. The most-stable isomers of all three clusters for n ≥ 4 have four solvent molecules in their first shell. The RPFR is dependent mainly on the number of solvent molecules in the first shell, and the size dependence of the RPFR plateaus at n = 4. The extrapolation of these values can be regarded as the RPFR in the solutions. The RPFRs are ∼1.07 for Li + (H 2 O) n and Li + (CH 3 OH) n and are ∼1.03 for Li + (H 2 S) n . The smaller RPFR of Li + (H 2 S) n is attributed to the smaller binding energy of the Li-S bond, which is weaker than that of the Li-O bond. The present results suggest the possibility of ionophores with S atoms (such as thioether, etc.) for lithium isotopic separation.

A novel nanoporous carbon−silica composite with medium hydrophilicity is synthesized by a series of methods consisting of preexpansion of the interlayer of graphite oxide (GO) by surfactant intercalation, the intercalation of tetraethoxylsilane (TEOS) and its hydrolysis in the interlayer, followed by post carbonization to form a robust bridged/pillared network. High-resolution N2 adsorption results show that carbonization at 823 K gives a composite having the highest specific surface area of more than 1000 m2/g with both microporosity and mesoporosity. Varieties of analytical results using DRIFT, NMR, XPS, and RAMAN spectra indicate that this composite contains small graphene sheets in its structure and its silicon components are silica particles with +4 valence. Morphology observation, thermal desorption, and other properties suggest the important roles of dispersion of GO in aqueous solution, preexpansion of GO interlayer, interlayer hydrolysis of TEOS molecules, and the carbonization condition in the f...

The exact physical adsorption amounts of supercritical hydrogen on the single-wall carbon nanohorn (SWNH) assemblies were determined at 77, 196, and 303 K. There are two physical adsorption sites of interstitial and internal spaces on SWNH assemblies. The interaction potential depths of interstitial and internal spaces are −1000 and −600 K, respectively. However, both hydrogen densities in interstitial and internal spaces were about 70 g L-1 at 77 K at 5 MPa, though the hydrogen densities in interstitial and internal spaces were 15 and 10 g L-1 at 303 K and 6.5 MPa. The similar enhancement in the internal spaces was observed even at 196 K. The additional stabilization by the strong fluid−fluid interaction due to the cluster formation in the internal spaces. On the other hand, hydrogen molecules adsorbed in the interstitial spaces cannot form the stable cluster owing to the space limitation. The enthalpy of adsorption supports the presence of the stable cluster of hydrogen adsorbed in the internal spaces b...

We examined the synthesis and borate uptake of novel chelating resins, named MGR and HMR, derived from the functionalization of macroporous poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate) matrixes with N-methyl-d-glucamine (MG) and 2-amino-2-(hydroxymethyl)-1,3-propanediol (HM), respectively. The structures of free matrixes, resins, and borate-loaded resins were confirmed by infrared spectroscopy. The borate uptake depends significantly on the proton capacity, which is proportional to the GMA fraction in matrixes, but little on the pore structure of macroporous matrixes. The ion-exchange isotherms of borate on MGR and HMR follow the Langmuir equation. MGR shows a larger uptake capacity toward borate than does HMR, comparable to that of Diaion CRB 02, because the tetradentate coordination mode of the former is more stable than the bidentate one of the latter. MGR exhibits a higher rate of borate uptake than does Diaion CRB 02, and the uptake kinetics are explained from a macropore diffusi...

Manganese oxide adsorbent (H1.6Mn1.6O4) was synthesized from precursor Li1.6Mn1.6O4 that was obtained by heating LiMnO2 at 400 °C. LiMnO2 was prepared by two methods: hydrothermal and reflux. The crystallite size of Li1.6Mn1.6O4 and its delithiated product was slightly higher by the hydrothermal method as compared to the reflux method. The adsorbents prepared by the two methods were compared in terms of physical characteristics and lithium adsorption from seawater. The maximum uptake of lithium from seawater by the adsorbent was 40 mg/g, which is the maximum value among the adsorbents studied to date.

The structural and surface properties of a hydrous hollandite-type manganese oxide (H-Hol) were examined by adsorption using different gases with molecular diameters below 0.4 nm. N 2 , O 2 , Ar, CO, and CO 2 with diameters above 0.33 nm are excluded from the tunnel structure of H-Hol, whereas H 2 O and NH 3 with diameters below 0.265 nm can be inserted into the structure. Disagreements were observed for the first and second run adsorption isotherms of H 2 O and NH 3 , indicating that there is a strong interaction contributing to H 2 O and NH 3 adsorption. Insertion of NH 3 into the tunnels of H-Hol is a very slow process; the rate-determining step is that of insertion into the inner H + sites. H + sites on H-Hol play an important role in both NH 3 and H 2 O adsorption. Adsorption and FT-IR results demonstrate that stepwise dehydration decreases the H + sites available for NH 3 adsorption, some but not all of which are recoverable by rehydration.

Silica-pillared layered manganese oxide with high surface area and high thermal stability was first synthesized from birnessite(H)-type manganese oxide by intercalation of octylamine followed by tetraethyl orthosilicate (TEOS) molecules and then by solvothermal treatment in TEOS liquid. Layered phases of manganese oxide with basal spacings of 2.01 and 2.43 nm, respectively, were obtained for each intercalation reaction. The Si/Mn molar ratio increased from 0.63 to 0.84 by the solvothermal treatment, but the basal spacing (2.44 nm) of the layer barely increased. The increase of silica content stabilized the pillared structure against thermal treatment. Porous layered manganese oxides were obtained by heating the silica-pillared material at appropriate temperatures. The manganese oxide sample obtained at 400 °C had a BET surface area of 260 m2/g with a gallery height of about 1.6 nm between layers.