Takahiro Ohkubo

Organized structures of methanol in carbon nanospaces at 303 K studies with in situ X-ray diffraction

Abstract The X-ray diffraction of methanol molecules confined in carbon micropores having different pore widths (micropore widths, 0.7 and 1.1 nm) was measured at 303 K and the structural results were compared with those of ethanol. The methanol molecules confined in micropores of 0.7 nm have a more solid-like ordered structure than in 1.1 nm. The nearest-neighbor peak of the electron radial distribution function of confined methanol did not shift from that of bulk methanol, but the amplitude was much greater than that of bulk methanol. These results were different from those of confined ethanol. Methanol molecules confined in carbon micropores have a rigid organized structure even at 303 K. However, no remarkable orientation effect, as in confined ethanol, was observed.

Oriented structures of alcohol hidden in carbon micropores with ERDF analysis

Abstract The X-ray diffraction (XRD) of alcohol molecules such as methanol, ethanol, and 1-propanol confined in slit-shaped graphitic micropores of activated carbon fibers (ACFs) having different pore widths was measured at 303 K. The effect of the pore width on the molecular assembly structure of alcohol in the micropores was examined. The XRD patterns were analyzed by use of the electron radial distribution function (ERDF) analysis. The adsorbed density of alcohol in micropores of 1.1 nm in width was close to the solid density, while that in micropores of 0.7 nm in width was smaller than the liquid density. The ERDF of alcohol adsorbed in the 0.7 nm micropores showed a highly ordered structure compared with the 1.1 nm micropores, which is completely different from the adsorbed density results. It was presumed that alcohol molecules are hydrogen-bonded to form a layered structure, which is fit for the slit-shaped micropore.

Pore Structures of ZSM-5 Synthesized in the Mesopore Spaces of a Carbon Aerogel

A mesoporous ZSM-5 monolith several millimetres in size has been synthesized employing the template method and using a carbon aerogel with uniform mesopores. Measurement of the pore-size distribution using nitrogen adsorption showed a bimodal pore system of mesopores and micropores whose average pore widths were 8 nm and 0.51 nm, and whose volumes were 0.09 cm3/g and 0.34 cm3/g, respectively.

High-temperature treatment effect of microporous carbon on ordered structure of confined SO2

Abstract The X-ray diffraction (XRD) of SO 2 molecules adsorbed in micropores of activated carbon fiber (ACF) was measured at 303 K. Effect of pore width and high-temperature treatment (HTT) of ACF on the XRD of SO 2 in micropores were examined. The HTT gave rise to a more dipole-oriented structure of SO 2 molecules in micropores of 1.1 nm width, whereas the opposite effect was observed in micropores of 0.7 nm. The intensified image potential of an SO 2 molecule for the heat-treated graphitic pore wall should stabilize the dipole-oriented structure in the case of 1.1 nm micropores, while the heat-treatment provides defective structures in the narrow micropore system. The presence of O 2 stabilized the dipole-oriented structure of SO 2 molecules in the micropore.

Deconvolution and Estimation of Water Diffusion in Sulfonated Polyethersulfone Membranes Using Diffusion-Weighted Inversion Recovery.

An NMR method was applied for the deconvolution of specific water in sulfonated polyether sulfone membranes, where sulfonated polyethersulfone is a proton-conducting polymer in polymer electrolyte membrane fuel cells. The distribution of (1)H longitudinal relaxation times obtained by the inverse Laplace method was utilized to estimate the volume fraction of proton species as a function of relative humidity (RH). The relaxation time distribution clearly revealed two distinguished peaks on the order of 10(-3) and 10(-2) s, which corresponded to water in the larger and smaller channels for proton transports, respectively. We applied a pulse sequence to understand the water species by diffusion-weighted inversion recovery, which led to individual self-diffusion coefficients for deconvoluted water by using the longitudinal relaxation time. At 30% RH, the diffusion coefficient of water in small-sized channels is greater than that in large-sized channels. On the other hand, the diffusion coefficients of protons with smaller and larger water channels are almost the same at 50, 70, and 90% RH.

First-principles molecular dynamics simulation and conductivity measurements of a molten xLi2O-(1- x)B2O3 system.

The electronic properties and atomic structure of a molten xLi2O-(1 - x)B2O3 system were investigated by measuring conductivity and using first-principles molecular dynamics (MD) simulations. The conductivities obtained were converted to a Li self-diffusion coefficient Dσ, using the Nernst-Einstein equation to assess charge transfer mechanisms. Dσ was compared with a Li self-diffusion coefficient, DNMR, which we measured in a previous study using high-temperature pulsed field gradient NMR. The DNMR/Dσ of xLi2O-(1 - x)B2O3 (0.2 ≤ x ≤ 0.5) at 1250 K ranged from 2.5 to 3.2, following the same trend as room temperature ionic liquids. First-principles MD simulations were performed using our own finite element density functional theory code, FEMTECK (finite element method-based total energy calculation) for molten xLi2O-(1 - x)B2O3 systems at 1250 K. We found that the O-B-O angle distribution functions were characterized by a peak at approximately 120°. Although the electron number from the electronic radial distribution function was arbitrary with regard to the cutoff distance, the net Li charge calculated from the integrated electron number surrounding Li was approximately 0.9 at 0.085 nm. The mean square displacement (MSD) of Li as a function of time was evaluated from the atomic configuration. Li self-diffusion coefficients calculated from the MSD were in better agreement with experimental results than they were using classical MD.

Molecular Dynamics Simulation of Water Confinement in Disordered Aluminosilicate Subnanopores

The porous structure and mass transport characteristics of disordered silicate porous media were investigated via a geometry based analysis of water confined in the pores. Disordered silicate porous media were constructed to mimic the dissolution behavior of an alkali aluminoborosilicate glass, i.e., soluble Na and B were removed from the bulk glass, and then water molecules and Na were introduced into the pores to provide a complex porous structure filled with water. This modelling approach revealed large surface areas of disordered porous media. In addition, a number of isolated water molecules were observed in the pores, despite accessible porous connectivity. As the fraction of mobile water was approximately 1%, the main water dynamics corresponded to vibrational motion in a confined space. This significantly reduced water mobility was due to strong hydrogen-bonding water-surface interactions resulting from the large surface area. This original approach provides a method for predicting the porous structure and water transport characteristics of disordered silicate porous media.

Formation of metallic cation-oxygen network for anomalous thermal expansion coefficients in binary phosphate glass

Understanding glass structure is still challenging due to the result of disorder, although novel materials design on the basis of atomistic structure has been strongly demanded. Here we report on the atomic structures of the zinc phosphate glass determined by reverse Monte Carlo modelling based on diffraction and spectroscopic data. The zinc-rich glass exhibits the network formed by ZnOx (averaged x<4) polyhedra. Although the elastic modulus, refractive index and glass transition temperature of the zinc phosphate glass monotonically increase with the amount of ZnO, we find for the first time that the thermal expansion coefficient is very sensitive to the substitution of the phosphate chain network by a network consisting of Zn-O units in zinc-rich glass. Our results imply that the control of the structure of intermediate groups may enable new functionalities in the design of oxide glass materials.

Photoluminescence of Sn 2+ -centre as probe of transient state of supercooled liquid

Physical properties of oxide glasses depend on the cooling process from the super-cooled liquid state. It is demonstrated that the Sn2+ species possessing electrons in the outermost shell can function as a qualitative probe cation to evaluate the randomness of the host glass network. With slower cooling, the formation of a more dense glass network is observed as confirmed by the heat capacity, elastic modulus, 11B NMR, first sharp diffraction peak of X-ray diffraction, and Boson peak results. The optical absorption, photoluminescence (PL), and Sn K-edge X-ray absorption fine structure data strongly suggest that the aggregation of Sn2+ results from the slow-cooling of the melt, and that PL properties of Sn2+ can be affected by the ordering of the transient state of super-cooled liquid. The results highlight that the structure of the transient state of glass is important for the functionalization of optical glasses.

Nanosolution as a New Turn of Nanoconfinement for Fluids

Towards the goal of nanoscale molecular systems, little work has been undertaken on ionic solutions at the nanoscale (‘nanosolution’, NSN). Functional nanoporous materials can be applied to confine, and thereby allow study of molecular assemblies and NSNs; electrically neutral hydrophobic pores reveal a particularly marked confinement effect. This article summarizes the properties and structures of molecules confined within nanospaces and the pioneering work on the distorted and partially dehydrated structures of NSNs.