Non-porous reference carbon for N2 (77.4 K) and Ar (87.3 K) adsorption

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

Negative thermal expansion of water in hydrophobic nanospaces

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.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)journal articl

Configurational evidence for antiferromagnetic interaction in disordered magnetic ionic liquids by X-ray scattering-aided hybrid reverse Monte Carlo simulation

Published online: 11 May 2020Magnetic 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.ArticleJournal of Molecular Liquids.311(1):113321(2020)journal articl

Noticeable Reverse Shift in the Melting Temperatures of Benzene and Carbon Tetrachloride Confined within the Micropores and Mesopores of Hydrophobic Carbons

Carbon aerogels contain both mesopores and micropores. In this study, benzene/CCl4 was adsorbed in the pores of carbon aerogels (both mesopores and micropores) and their phase behaviours were examined using differential scanning calorimetry. The bulk solid benzene melted at 278 K and the melting temperatures of benzene confined inside the mesopores and micropores of carbon aerogels were 258 and 293 K, respectively. Although the melting temperature depression of condensates in mesopores is well known, the observed elevation of the melting temperature for micropores is very limited in the strongly interacted system. Similar melting behaviours were observed for the confined CCl4; depression by 45 K in mesopores and elevation by 48 K in micropores showed about two times the change as compared with that of confined benzene.ArticleADSORPTION SCIENCE & TECHNOLOGY. 31(2-3):145-151 (2013)journal articl

Staggered structural dynamic-mediated selective adsorption of H2O/D2O on flexible graphene oxide nanosheets

Graphene oxide (GO) is the one of the most promising family of materials as atomically thin membranes for water-related molecular separation technologies due to its amphipathic nature and layered structure. Here, we show important aspects of GO on water adsorption from molecular dynamics (MD) simulations, in-situ X-ray diffraction (XRD) measurements, and ex-situ nuclear magnetic resonance (NMR) measurements. Although the MD simulations for GO and the reduced GO models revealed that the flexibility of the interlayer spacing could be attributed to the oxygen-functional groups of GO, the ultra-large GO model cannot well explain the observed swelling of GO from XRD experiments. Our MD simulations propose a realistic GO interlayer structure constructed by staggered stacking of flexible GO sheets, which can explain very well the swelling nature upon water adsorption. The transmission electron microscopic (TEM) observation also supports the non-regular staggered stacking structure of GO. Furthermore, we demonstrate the existence of the two distinct types of adsorbed water molecules in the staggered stacking: water bonded with hydrophilic functional groups and “free” mobile water. Finally, we show that the staggered stacking of GO plays a crucial role in H/D isotopic recognition in water adsorption, as well as the high mobility of water molecules.journal articl

Conducting linear chains of sulphur inside carbon nanotubes

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.ArticleNATURE COMMUNICATIONS. 4:2162 (2013)journal articl

Conducting linear chains of sulphur inside carbon nanotubes

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.ArticleNATURE COMMUNICATIONS. 4:2162 (2013)journal articl

Negative thermal expansion of water in hydrophobic nanospaces

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.ArticlePHYSICAL CHEMISTRY CHEMICAL PHYSICS. 14(2):981-986 (2012)journal articl

Role of the organic linker in the early stages of the templated synthesis of PMOs

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