Search

Physisorption of methane in porous solids has been actively studied to achieve high methane storage capacity, but it requires heavy vessels due to the high pressures involved. In addition, physisorption of methane is quite sensitive to temperature elevation, even near ambient conditions. We developed a method for high-density methane storage at ambient pressure by installing pore-entrance locks controlled by waste heat at 473 K. Under ambient conditions, the entrance locks are stable enough to store a large amount of highly pressurized methane in the carbon nanopores at 19.9 MPa and can be unlocked at 473 K for encapsulation and release of methane. This novel ambient pressure storage method for pressurized methane enables storage of more methane than any other adsorbent at 3.5 MPa and 298 K. The waste-heat open/close pore-entrance locking mechanism supports long-term storage of a renewable energy source and provides a stationary energy supply.

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...

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.

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.

Capacity and kinetics of CO2 capture of Na2CO3 were studied to determine the mechanism for CO2 sequestration under ambient conditions. Bicarbonate formation of Na2CO3 was examined by a thermogravimetric analysis (TGA) under various CO2 and water vapor concentrations and the accompanying structural changes of Na2CO3 were demonstrated by X-ray diffraction (XRD). Morphological variations were observed during the reaction of CO2 capture through scanning electron microscope (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 the XRD and SEM measurements. The results showed that the bicarbonate formation of Na2CO3 has two different pathways. For higher CO2 and H2O concentrations, the bicarbonate formation proceeded effectively. However, for lower CO2 and H2O concentrations, the reactions were more complicated. The formation of Na2CO3•H2O from Na2CO3 as the first step, followed by the subsequent formation of Na5H3(CO3)4, and then the bicarbonate formation proceeds. To understand such fundamental properties in CO2 capture of Na2CO3 is very important for utilization of Na2CO3 as a sorbent for CO2 capture.

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.

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.

We have developed a laser-induced chemical vapor deposition (LCVD) method for preparing nanocarbons with the aid of SF 6 . 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.

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.

The capacity and kinetics of CO2 sorption for Na2CO3 and K2CO3 under moist conditions were studied to determine the mechanism for CO2 capture under ambient conditions. Bicarbonate formations of Na2CO3 and K2CO3 were examined by thermogravimetric analysis under various CO2 concentrations and humidity, and the accompanying structural changes of Na2CO3 and K2CO3 were exhibited by X-ray diffraction (XRD). Also, morphological changes were observed during the reaction by scanning electron microscopy (SEM). The structural and morphological changes during the reactions were then related to the kinetic and exothermic properties of the CO2 sorption of Na2CO3 and K2CO3 together with H2O from XRD and SEM measurements. The modification of Na2CO3 and K2CO3 for improvement in regeneration temperature and CO2 occlusion kinetics were also examined by substitution of different metal ions or formation of nanostructured materials.

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.

On the basis of the structure of the unimolecular Zn3(OAc)4–3,3′-bis(aminoimino)binaphthoxide complex, a poly-Zn3(OAc)4–3,3′-bis(aminoimino)binaphthoxide (poly-Zn) complex was prepared from 3,3′-diformylbinaphthol, tetramine, and Zn(OAc)2. The first-generation poly-Zn catalyst (poly-Zn1) was prepared from poly(aminoiminobinaphthol) and Zn(OAc)2. Although poly-Zn1 showed high catalytic activity for iodolactonization, the catalyst could not be reused. The second-generation poly-Zn catalyst (poly-Zn2) was prepared by the self-organization of 3,3′-diformylbinaphthol, tetramine, and Zn(OAc)2. This produced a stable and active poly-Zn2 catalyst for asymmetric iodolactonization that was reused over five cycles.

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

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...

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

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.

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.

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

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

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.

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

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 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 cm‑1) and an intensity change (around 100–150 cm−1 and 270–290 cm−1) in the radial breathing mode of Raman spectra. The charge transfer from SWCNT to HIB was further confirmed by the change in the C1s peak of X-ray photoelectron spectrum, revealing the oxidation of carbon in SWCNT upon HIB adsorption.

Water 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.

On the basis of the structure of the unimolecular Zn3(OAc)4–3,3′-bis(aminoimino)binaphthoxide complex, a poly-Zn3(OAc)4–3,3′-bis(aminoimino)binaphthoxide (poly-Zn) complex was prepared from 3,3′-diformylbinaphthol, tetramine, and Zn(OAc)2. The first-generation poly-Zn catalyst (poly-Zn1) was prepared from poly(aminoiminobinaphthol) and Zn(OAc)2. Although poly-Zn1 showed high catalytic activity for iodolactonization, the catalyst could not be reused. The second-generation poly-Zn catalyst (poly-Zn2) was prepared by the self-organization of 3,3′-diformylbinaphthol, tetramine, and Zn(OAc)2. This produced a stable and active poly-Zn2 catalyst for asymmetric iodolactonization that was reused over five cycles.

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.