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Activated carbons for the complete removal of CHCl3 from indoor atmosphere and drinking water are in high demand for human health. We must understand the structural adsorption mechanism of CHCl3 on activated carbon to design the optimum pore structures for the removal of even trace amounts of CHCl3. CHCl3 adsorption on well-characterized pitch-based activated carbon fibres (ACFs) can provide a clear guideline on adsorption sites for CHCl3 and the adsorbed structure of CHCl3. We measured the N2 adsorption isotherms of ACF with different fractional fillings of preadsorbed CHCl3 (ϕ, up to 0.8). The difference in pore size distribution of the CHCl3-preadsorbed ACF indicates preferential CHCl3 adsorption sites in smaller micropores that are not situated in the deepest pore sites. The N2 adsorption of the CHCl3-preadsorbed ACF provides information on the position of adsorbed CHCl3 relative to pore entrances. CHCl3 molecules form small clusters to adapt to the narrow micropores in the initial stage of adsorption according to the electron radial distribution function analysis of X-ray diffraction. The number of CHCl3 clusters increased and the clusters grew with increasing ϕ. The CHCl3 clusters merge with each other in the final stage of CHCl3 adsorption, giving a liquid-like structure.

Customized micro- and mesoporous carbons are in high demand for ecofriendly technologies. Reactivation of the well-characterized pitch-based activated carbon fiber (ACF) can provide a clear understanding of the structural mechanism of steam activation, which would be helpful for designing better micro- and mesoporous carbons. ACFs were reactivated with steam at 973–1173 K. X-ray diffraction and Raman spectroscopy indicated that the stacking number of graphene-like layers of the pore wall decreased with an increase in the reactivation temperature. The average fiber diameter of the ACFs, which was measured via scanning electron microscopy, decreased with the increase in the reactivation temperature. The relationship between the decrease in the fiber diameter and the burn-off suggested that reactivation above 1023 K produced micropores inside the fiber. A deconvolution analysis of the pore-size distribution revealed the variation of the distribution. The peak difference was approximately 0.3 nm, depending on the reactivation temperature. These results indicate that reactivation with steam proceeds via the preferential one-by-one gasification of less-crystalline graphene-like units.

The fractional filling dependence of corrected diffusivity of H2O and D2O confined in activated carbon fiber (ACF) determined using newly developed pressure feedback analysis clearly shows that the adsorption kinetics of H2O and D2O on ACF are governed by cluster growth associated with molecular hopping and cluster aggregation. The isotope effect provides an essential influence on the strength of hydrogen bonding, leading to an explicit difference in the adsorption diffusivity during the aggregation process of water molecular clusters at high fractional filling. These results show that the collective dynamic behavior of water molecules in hydrophobic nanospace is governed by the fine balance of hydrogen bonds.

Quinone-based aromatic compounds have been studied as electrode materials for various energy-storage devices. However, the relatively large activation barrier of the charge-transfer process of these redox-active molecules causes sluggish reactions and a decrease in energy efficiency. To lower the activation barrier, aromatic compounds must be strongly adsorbed on the electrode surface, preferably via π-π stacking interactions. Molecules in slit-shaped micropores strongly adsorb on the graphitic walls, thus experiencing unique micropore-confinement properties. In this study, the micropore-confinement effect is extended to the adsorption of quinone-based redox-active molecules in 0.8 nm slit-shaped micropores of activated carbon, which produces a drastic reduction in the activation barrier of the charge-transfer process and creates a zero-overpotential redox reaction. The property originates from the short distance (approximately 0.3 nm) between the quinone molecules and the graphitic wall due to the strong adsorption of the aromatic compound. Our results provide the first demonstration that the micropore-confinement effect can reduce and nearly eliminate the activation barrier of an electrochemical reaction. We also demonstrate the applicability of this approach via the charge/discharge performance of a two-electrode cell. Cells comprising the aromatic compound/activated carbon material as positive and negative electrodes exhibit a greater retention capacity than those without activated carbon. The technique described herein can guide the development of high-performance, rapid charging/discharging electrodes for energy-storage devices such as batteries, supercapacitors, and hybrid devices using organic materials.

We studied X-ray absorption of multiwall carbon nanotube (MWCNT) produced by the chemical vapor deposition method using ethanol and benzene precursors at 1473 K with X-ray absorption fine structure in order to obtain a new designing direction for X-ray shielding fabrics. Acid oxidation and thermal annealing further treated the MWCNTs. The energy dependence of X-ray absorptivity of MWCNTs was efficiently used to remove the effect of the metallic impurity contribution, to elucidate the relationship between X-ray mass attenuation coefficient and the structure of MWCNT. The thermal annealing treatment at 2773 K was the most effective method to increase the crystallinity and to remove the impurities of MWCNTs. The acid and oxidation treated MWCNT induced not only the surface structure difference between MWCNT and highly oriented pyrolytic graphite (HOPG) but also the addition of surface oxygen related functional groups from those treatments, which influence the mass attenuation coefficient (μ/ρ). The X-ray absorptivity of heat treated E-MWCNT and B-MWCNT at 2773 K was close to that of HOPG indicating that those MWCNTs have a well-ordered crystal structure, quite similar to HOPG. On the other hand, E-MWCNT having a less-crystalline surface structure showed larger X-ray absorptivity than HOPG by about 9%.

The permeable single wall carbon nanotube (SWCNT) film electrodes of high electrical conductivity for filtration of ions are promising for future water treatment technology. The permeable SWCNT film electrodes were obtained by the use of the Zn/Al-based dispersant-aided SWCNT ink. The G band peak position and ID/IG value of Raman spectra do not change before and after the polarization of the SWCNT electrodes, showing the robustness of permeable SWCNT film electrodes. The analysis of N2 adsorption isotherms showed that microporosity and specific surface area of the SWCNT electrodes were larger than those of the pristine SWCNT, due to the debundling of SWCNTs and removal of the caps of SWCNT on the dispersion treatment. Application of the electric voltage above − 3 V to the SWCNT electrodes enhanced markedly the adsorption-mediated permeability of K+ ions, reaching the removability of 90%. The removability dependence of Na+ ions on the initial ion concentration showed that the SWCNT permeation electrodes filter was efficient for diluted Na+ ionic solution. The ions of smaller Stokes radius were adsorbed for the mixed ionic solution of Li+, Na+, K+, Rb+, and Cs+, suggesting that the inner tube space of SWCNT electrodes is important for adsorption of ions.

Nanodiamond particles form aggregates having porosity in the range of micropores to mesopores with an average pore diameter of 4.5 nm. The measured porosity depends on the removal of pre-occupied water and gases from the nanodiamond aggregates, which is sensitive to thermal treatments. We heated hydrogel nanodiamonds at 423–623 K in vacuo in order to understand the relationship between water adsorptivity and pore structure evaluated from nitrogen and argon adsorption isotherms at 77 K and 87 K, respectively. Temperature-programmed evolved gas analysis showed the evolution of water and CO2 on heating nanodiamonds in vacuo up to 700 K. The surface functional groups of nanodiamonds were not affected by the thermal treatments, as shown by FTIR and XPS analyses. However, the water adsorptivity was enhanced by heating at 623 K due to the removal of the pore blocking effect originated from water molecules selectively adsorbed. Water molecules adsorbed on these selective sites should cause the intensive hygroscopic property of nanodiamonds.

Electrically-conductive graphene colloids with tuned nanoporosity are promising materials for numerous applications. As charge-transfer interaction enhances electrical conductivity of polyaromatic hydrocarbon crystals, we intercalated water-soluble pyrene derivatives such as pyrene-boronic acid in nanoporous graphene by reduction of a mixture of graphene oxides and pyrene derivatives. The pyrene derivative intercalation increases more than twice both microporosity and mesoporosity. The N2 adsorption isotherms at 77 K of all samples have low-pressure adsorption hysteresis due to inaccessible small microporosity; the total porosity evaluated by water adsorption at 298 K is almost twice that of N2 adsorption. These adsorption measurements together with X-ray diffraction suggest the presence of a pore mouth structure whose width is about 0.4 nm. The charge-transfer interaction between the pyrene derivative and porous graphene is evidenced by a high frequency shift of the G band of Raman spectrum, appearance of a new optical absorption band, and the increase in electrical conductivity. The intercalation of pyrene-boronic acid through charge-transfer interaction increases the voltammetric charge of cyclic voltammogram for nanoporous graphene owing to an enhanced ion-accessibility from 3% to 54%, which indicates their high application potential for electrochemical studies.

Hexagonal ferrite Ba(Fe1−xScx)12O19 is an important magnetic oxide material in both science and engineering because it exhibits helimagnetism around room temperature (300 K). In this study, the magnetic phase diagram of Ba(Fe1−xScx)12O19 consisting of ferri-, heli-, antiferro-, and paramagnetic phases has been completed through magnetization and neutron diffraction measurements. The magnetic phase transition temperature to paramagnetism decreases with the increase in x, and the temperature at which the magnetization reaches a maximum, which corresponds to the magnetic phase transition from heli- to ferrimagnetism, is determined for low x crystals. The temperatures at which helimagnetism appears are precisely determined by observing the magnetic satellite reflection peaks in neutron diffraction at various temperatures, which characterize helimagnetism. Based on these results, the magnetic phase diagram of the Ba(Fe1−xScx)12O19 system is constructed in the T-x plane. Helimagnetism appears at x ≳ 0.06, and magnetism with antiferromagnetic components appears as the extension phase of helimagnetism at x ≳ 0.19 through the coexistence region. The turn angle ϕ0 of the helix for each x crystal is calculated from the relationship, ϕ0 = 2πδ, where δ is the incommensurability. The turn angle ϕ0 decreases with the increase in temperature for the same x crystal, and increases with the increase in x at the same temperature. Furthermore, it is found that there are clear thresholds at which ϕ0 cannot take values between 0°

Fabrication of nanographene shows a promising route for production of designed porous carbons, which is indispensable for highly efficient molecular separation and energy storage applications. This process requires a better understanding of the mechanical properties of nanographene in their aggregated structure. We studied the structural and mechanical properties of nanographene monoliths compressed at 43 MPa over different times from 3 to 25 h. While in monoliths compressed over shorter time adsorption isotherms of Ar at 87 K or N2 at 77 K exhibited a prominent hysteresis due to presence of predominant mesopores, compression for long time induces a low pressure hysteresis. On the other hand, compression for 25 h increases the microporosity evaluated by Ar adsorption, not by N2 adsorption, indicating that 25 h compression rearranges the nanographene stacking structure to produce ultramicropores that can be accessible only for Ar. TEM, X-ray diffraction, and Raman spectroscopic studies indicated that the c...

The adsorption and desorption of D2O on hydrophobic activated carbon fiber (ACF) occurs at a smaller pressure than the adsorption and desorption of H2O. The behavior of the critical desorption pressure difference between D2O and H2O in the pressure range of 1.25-1.80kPa is applied to separate low concentrated D2O from water using the hydrophobic ACF, because the desorption branches of D2O and H2O drop almost vertically. The deuterium concentration of all desorbed water in the above pressure range is lower than that of water without adsorption-treatment on ACF. The single adsorption-desorption procedure on ACF at 1.66kPa corresponding to the maximum difference of adsorption amount between D2O and H2O reduced the deuterium concentration of desorbed water to 130.6ppm from 143.0ppm. Thus, the adsorption-desorption procedure of water on ACF is a promising separation and concentration method of low concentrated D2O from water.

The adsorption isotherms of H2O and D2O on pitch-based activated carbon fibers (ACFs) of different pore widths from 0.6 to 1.5 nm were measured at 298 K. Briefly speaking, the D2O adsorption isotherms are close to the H2O adsorption isotherms. However, we observed an evident difference in the rising and desorption relative pressures for the H2O and D2O adsorption isotherms. The D2O adsorption rises at a higher relative pressure than the H2O adsorption. Correspondingly the D2O desorption occurs at a higher relative pressure than the H2O desorption. Detailed comparison of the H2O and D2O adsorption isotherms confirmed a reproducible difference over the whole relative pressure range. The different adsorption behavior of H2O and D2O in the hydrophobic micropores is discussed with the relevance to the difference in the hydrogen bonding of H2O and D2O.

The highly microporous graphene aerogel monolith of unidirectional textures is obtained from reduction and KOH activation of colloidal graphene oxide prepared with an ice-templating route. The free-standing geometry and well-aligned textures of graphene monolith are persevered even after an intensive KOH activation at 973 K, although the frame structure is slightly disordered. The non-overestimated surface area of the KOH activated graphene monolith is 990 m2 g−1. The free-standing graphene aerogel monolith has predominant microporosity with appropriate macroporosity and a low bulk density of 8 ± 0.5 mg cm−3, being one of the lightest materials of the reported porous graphene materials.

Detonation nanodiamonds (DND) form fractal-like aggregates composed of polydisperse DND particles. We present a novel methodology for the visualisation and characterisation of fractal clusters of DND from one-dimensional small-angle X-ray scattering (SAXS) intensity. The fractal nature and polydispersity of DND are modelled by combining a diffusion-limited aggregation (DLA) process implemented in Monte Carlo simulations with the distribution of DND sizes measured from high-resolution transmission electron microscopy. The radius of gyration (42–44 nm), aggregation number (850–1150), and the maximum dimension (226–242 nm) of DND fractal clusters were obtained from the fitting of the synchrotron-based SAXS data (q∼0.11–4.75 1/nm) measured for two samples of commercialized DND powders by the developed theoretical model.

Detonation nanodiamonds hard-hydrogels are aggregates of polyhedral particles of sp3-hybridized-carbon coated by atomically thin sp2-hybridized carbon. Electronic properties of diamond are sensitive to water in the surrounding environment. The effect of adsorbed water on the electrical conductivity of detonation nanodiamonds was studied by exposure to humid air after thermal treatment in vacuo. The electrical conductivity increases with heating and decreases during the isothermal treatment at 393 K due to release of strongly adsorbed water, and gradually increases on exposing to humid air, indicating adsorption of water molecules on micropores and mesopores in the nanodiamond aggregates. Keywords: Nanodiamonds, Electrical conductivity, Adsorbed water, Micropore, Graphene-like carbon

Newly developed inorganic single-wall carbon nanotube (SWCNT) inks of the Zn/Al complex and colloidal silica give a quite homogeneous SWCNT film on the polyethylene terephthalate (PET) substrate by the bar-coating method, whereas the surfactant-based SWCNT inks of sodium dodecyl sulfonate (SDS) and sodium dodecyl benzene sulfonate (SDBS) cannot give a homogeneous film. The key properties of SWCNT inks were studied for the production of homogeneous SWCNT films. The contact angle and surface tension of the inorganic dispersant-based SWCNT inks were 70° and 72 mN m(-1), respectively, being close to those of water (71.5° and 71 mN m(-1)). The viscosity was significantly higher than that of water (0.90 mPa·s), consequently, providing sufficient wettability, spreadability, and slow drying of the ink on the substrate, leading to homogeneous film formation. On the other hand, the surfactant dispersant-aided SWCNT inks have the contact angle and surface tension twice lower than the inorganic dispersant-based SWCNT inks, guaranteeing better wettability and spreadability than the inorganic dispersant-based inks. However, the small viscosity close to that of water induces a heterogeneous flow of SWCNT ink on rapid drying, leading to inhomogeneous film formation.

Graphene monoliths were prepared through unidirectional freeze-drying method of graphene oxide colloids-KOH mixed solution and successive reduction by heating at 573 K in Ar. The porosity- and crystallinity-controlled graphene monoliths were prepared by the KOH activation at different temperature and the post-heating in Ar. These activated graphene monoliths were characterized by N2 adsorption at 77 K, X-ray diffraction and Raman spectroscopy. Water adsorption isotherms show a typical hydrophobicity below P/P 0 = 0.5 and a marked hydrophilicity above P/P 0 = 0.6, which depends on the pore width. In the water adsorption isotherms of porous graphene monoliths activated at different temperature, the higher the activation temperature, the larger the rising P/P 0. No essential change in the shape of the water adsorption isotherm for the post-heated nanoporous graphene monoliths is observed except for the decrease in water adsorption amount with higher post-heating temperature. The linear relationship between the saturated water adsorption and pore volume whose width is smaller than 4 nm indicates clearly that water molecules are adsorbed in small mesopores by the cluster-associated filling mechanism.

It is shown that the viscosity of SWCNT inks is essential to produce highly homogeneous SWCNT films on the PET substrate with bar coating method. The Zn/Al complex-aided SWCNT ink has a viscosity threshold of 1.30 mPa s for the preparation of homogeneous films. The local flows of the film are suppressed above this viscosity, allowing homogeneous film formation. The Zn/Al complex dispersant can be easily removed from SWCNTs coated on PET by 1 M HNO3, giving a pure SWCNT film with the sheet resistance of 150 ohm/sq and transmittance of 90% at 550 nm immediately after HNO3 treatment.

Structural changes with temperature of CCl4 confined in a 1.1 nm slit-shaped carbon nanospace were investigated by neutron diffraction (ND) measurements and radial distribution function fdrdf analy...

Published online: 11 May 2020, Magnetic ionic liquids (MIL) are a new type of ionic liquids that show paramagnetic response to magnetic fields. Here, we elucidate a plausible 3D liquid structure of the 1-ethyl-3-methyl-imidazolium tetrachloroferate (Emim[FeCl4]) and 1-butyl-3-methyl-imidazolium tetrachloroferate (Bmim[FeCl4]) MILs by X-ray scattering-aided hybrid reverse Monte Carlo simulations. Bmim[FeCl4] showed anomalously continuous structural changes over a wide temperature range (90–523 K) without crystallization, while Emim[FeCl4] displayed a melting point at 291 K with no glass transition.Conventional electron radial distribution function (ERDF) analysis provides misleading information about the structures of these MILs due to the mutual cancelation of the partial anion-anion and anion-cation ERDFs. Subsequent hybrid reverse Monte Carlo (HRMC) analysis revealed the precise coordination structures of both ionic liquids, and the alternating periodic arrangement of the anions and cations was visualized based on the HRMC simulation results. The results clearly revealed that the 1st coordination structure of the FeCl4 anion around the Bmim cation was widespread compared to that of the Emim cation, resulting in the absence of crystallization. In addition, we obtained new insights into the antiferromagnetic interaction between the FeCl4− ions of Bmim[FeCl4] even in the absence of the crystallization at low temperatures. Our results shed new light on the development of MILs not only for practical applications but also for the advancing the basic science of pure liquids with a high magnetic response., Article, Journal of Molecular Liquids.311(1):113321(2020)

Monitoring structural integrity during and after extreme events such as an earthquake or a tsunami is a mundane yet important task that still awaits a workable solution. Currently available stress sensors are not sufficiently robust and are affected by humidity. Insufficient information about crack formation preceding structural failure increases risk during rescue operations significantly. Designing durable stress sensors that are not affected by harsh and changing environment and do not fail under catastrophic conditions is a fundamental challenge. To address this problem, we developed a stress sensor based on creased single-walled carbon nanotubes (SWCNTs) encapsulated in a non-fluorinated superhydrophobic coating. The creased SWCNT film was fabricated and integrated in polydimethylsiloxane (PDMS) to provide a highly linear response under elastic deformation. The non-fluorinated water-repellent coating was fabricated by spray-coating the film with nanosilica particles, providing water resistance during elastic deformation. The compact design and superior water resistance of the sensor, along with its appealing linearity and large stretchability, demonstrates the scalability of this approach for fabricating efficient strain sensors for applications in infrastructure and robotic safety management as well as advanced wearable sensors.

Nanodiamond aggregates have interparticle pores of 4.5 nm on average, exhibiting porous nature involved in their water storage. This work studies the hygroscopic nature of porous nanodiamond aggregates by water absorption based on liquid water droplets. Nanodiamond aggregates show hydrophobicity from the water vapor adsorption. Surprisingly, porous nanodiamond aggregates quickly absorb water droplets at the bulk scale. The volume of absorbed liquid water is comparable to that of the water-absorbing clay Montmorillonite and higher than those of zeolites ZSM-5 and molecular sieve 5A. This hygroscopic nature of nanodiamonds is ascribed to the micro- and mesoporous structure of their aggregates and the special core-shell structure of each nanodiamond particle (wrapped by graphene-like carbon). The absorption rate of liquid water in the porous nanodiamonds is influenced by the surface wettability, while the hygroscopic capacity depends mainly on the hierarchical porosity.

Double-walled carbon nanotube (DWNT) fibers are of great interest due to their electrical properties and light weight, making them attractive for industrial applications including their potential use in power transmission lines. We present here a detailed study of the mechanism by which hydrogen peroxide (H2O2) treatment improves the electrical transport of DWNT fibers. These fibers were immersed and sonicated in H2O2 for several hours. Experimental results suggest that residual H2O2 could be intercalated within intertube channels inside the bundles of DWNTs, and the oxidation treatment could also result in the removal of small diameter carbon nanotubes (CNTs). In addition, an increase in the fiber density resulted in a decrease of the electrical resistivity. The H2O2 treatment of the DWNT fibers resulted in a metallic-like temperature dependent resistivity behavior with a transition to a semiconducting-like behavior below 30 K. We compared the effects of H2O2 with other well-known solvents and additives commonly used to reduce the carbon nanotube fiber electrical resistivity and found that the electrical conductivity values observed in our study are as good as those obtained with thionyl chloride and iodine additives. The H2O2 method was also used to treat other forms of carbon, where only the multi-walled carbon nanotubes doped with nitrogen exhibited a decrease in electrical resistivity. The fabrication method presented here is simple, efficient and low cost, thus making it an ideal process to be applied in the fabrication of electrically conducting carbon nanotube fibers.

The adsorption of methane and water, and their coexisting state in carbon micropores were investigated by X-ray scattering measurements. The mechanisms of single-component adsorption of water and methane in the carbon micropores proceeded by cluster formation and micropore filling, respectively. The X-ray scattering of the coexisting state reveals that a mesoscopic phase separation occurred in the carbon micropores at 111 K because of the weak interaction between water and methane. At this low temperature, water molecules could not reform hydrogen bonds even with further adsorption of methane molecules. The X-ray scattering measurements provided detailed information on the coexisting state and can be used to study the temperature dependence of the phase behavior of the methane–water system during methane hydration formation in nanospaces.

The detonation nanodiamonds form the aggregate having interparticle voids, giving a marked hygroscopic property. As the relationship between pore structure and water adsorption of aggregated nanodiamonds is not well understood yet, adsorption isotherms of N2 at 77 K and of water vapor at 298 K of the well-characterized aggregated nanodiamonds were measured. HR-TEM and X-ray diffraction showed that the nanodiamonds were highly crystalline and their average crystallite size was 4.5 nm. The presence of the graphitic layers on the nanodiamond particle surface was confirmed by the EELS examination. The pore size distribution analysis showed that nanodiamonds had a few ultramicropores with predominant mesopores of 4.5 nm in average size. The water vapor adsorption isotherm of IUPAC Type V indicates the hydrophobicity of the nanodiamond aggregates, with the presence of hydrophilic sites. Then the hygroscopic nature of nanodiamonds should be associated with the surface functionalities of the graphitic shell and the ultramicropores on the mesopore walls.

The adsorption and desorption of D

We fabricated mesoscopic cage-like structured Single-Wall Carbon Nanotube (SWCNT) cryogels having ultramicroporous necks using highly concentrated SWCNT-water inks with the aid of Zn–Al sol-gel dispersant. High-resolution transmission electron microscopy (TEM) image shows the presence of three-dimensional cage-like structures in the SWCNT cryogels, which are quite different from the bundle structures of pristine SWCNTs. Average bundle size of the SWCNT cryogels is 30% smaller than that of pristine SWCNTs according to the TEM observation. Adsorption isotherms of N2 at 77 K and Ar at 87 K for SWCNT cryogels and pristine SWCNTs have explicit adsorption hysteresis in low and high relative pressure regions, indicating the presence of necked ultramicropores and mesopores. Ar adsorption isotherms show that the SWCNT cryogels have predominant low and high relative pressure hysteresis, suggesting the presence of mesopores with necked entrances of ultramicropores. Surface areas of SWCNT cryogels by Ar and N2 adsorption are about two times larger than those of pristine SWCNTs which is in agreement with the geometrically evaluated surface area from SWCNT bundles. Mesopore volumes evaluated by adsorption of N2 and Ar are 3 and 2.3 times larger than those of pristine SWCNTs in the mesopore range above 15 nm. The marked increase in the mesoporosity of the SWCNT assemblies by freeze-drying supports the mesoscopic three-dimensional cage-like structures observed by TEM.

A new non-porous carbon material from granular olive stones has been prepared to be used as a reference material for the characterization of the pore structure of activated carbons. The high precision adsorption isotherms of nitrogen at 77.4 K and argon at 87.3 K on the newly developed sample have been measured, providing the standard data for a more accurate comparative analysis to characterize disordered porous carbons using comparative methods such as t- and αS-methods. Financial support from a Strategic Japanese–Spanish Cooperative Program: Nanotechnologies and New Materials for Environmental Challenges (PLE2009-0052). K.K. was supported by Exotic Nanocarbons, Japan Regional Innovation Strategy Program by the Excellent, JST.

International audience; Ionic liquids are composed of equal quantities of positive and negative ions. In the bulk, electrical neutrality occurs in these liquids due to Coulombic ordering, in which ion shells of alternating charge form around a central ion. Their structure under confinement is far less well understood. This hinders the widespread application of ionic liquids in technological applications. Here we use scattering experiments to resolve the structure of a widely used ionic liquid (EMI–TFSI) when it is confined inside nanoporous carbons. We show that Coulombic ordering reduces when the pores can accommodate only a single layer of ions. Instead, equally charged ion pairs are formed due to the induction of an electric potential of opposite sign in the carbon pore walls. This non-Coulombic ordering is further enhanced in the presence of an applied external electric potential. This finding opens the door for the design of better materials for electrochemical applications.

The structure of the hydrogen-bonding network of water in carbon micropores was investigated by X-ray diffraction (XRD) and neutron diffraction (ND). ND provided positional information about both o...

The structure of nanometer-order sulfuric acid solution in carbon micropores is investigated by large- and small-angle X-ray scattering experiments. The electron radial distribution function of the...

Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (similar to 800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at similar to 450-650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding similar to 90 GPa to become metallic., Article, NATURE COMMUNICATIONS. 4:2162 (2013)

The gas-phase conformations and stabilities of neutral and anionic organosilanes with structure ((HO)(3)Si-organic linker-Si(OH)(3)), where the organic linker is benzene, ethene, or ethane, were studied using density functional theory. The calculations were performed at the B3LYP/6-311+G(2d,2p) level of theory and show that the cis-bis(trihydroxysilyl)-ethene and gauche-bis(trihydroxysilyl)-ethane species are more stable than their trans and anti-counterparts, respectively. The local geometries of the organic and inorganic fragments in these hybrid compounds are similar to those found in the case of pure silicate compounds or in the parent organic molecules. The calculated enthalpies of deprotonation for these species suggest an acid-base behavior for 1,4-bis(trihydroxysilyl)benzene species that is intermediate of those calculated for the silicate monomer and for the silicate dimer, while for the cis-bis(trihydroxysilyl)-ethene and gauche-bis(trihydroxysilyl)-ethane, an acid-base behavior that is intermediate of those calculated for small and for large pure silicates. It was also found that the calculated charges of the Si atoms are almost independent of the type of carbon atom to which they are bonded and that the charge localized on the organic moiety is always negative, even for the neutral species. This information is valuable for the development of molecular force fields for simulating systems involving organosilicates.

The density and intermolecular structure of water in carbon micropores (w = 1.36 nm) are investigated by small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) measurements between 20 K and 298 K. The SAXS results suggest that the density of the water in the micropores increased with increasing temperature over a wide temperature range (20-277 K). The density changed by 10%, which is comparable to the density change of 7% between bulk ice (I(c)) at 20 K and water at 277 K. The results of XRD at low temperatures (less than 200 K) show that the water forms the cubic ice (I(c)) structure, although its peak shape and radial distribution functions changed continuously to those of a liquid-like structure with increasing temperature. The SAXS and XRD results both showed that the water in the hydrophobic nanospaces had no phase transition point. The continuous structural change from ice I(c) to liquid with increasing temperature suggests that water shows negative thermal expansion over a wide temperature range in hydrophobic nanospaces. The combination of XRD and SAXS measurements makes it possible to describe confined systems in nanospaces with intermolecular structure and density of adsorbed molecular assemblies., Article, PHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)

Classical MD simulations for surfactant-bromide-water solutions containing several organosilicate precursors show that the presence or absence of molecular-scale periodicity in the pore walls of PMOs is dictated by the strength of the surfactant micelle-organosilica interaction and by the relative flexibility and orientation of the organic linker.