Ryusuke Futamura

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 (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~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 ~90 GPa to become metallic.

Partial breaking of the Coulombic ordering of ionic liquids confined in carbon nanopores

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 the widely used ionic liquid (EMI-TFSI) when it is confined inside nanoporous carbons. We show that Coulombic ordering reduces when the pores can only accommodate 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.

High electrical conductivity of double-walled carbon nanotube fibers by hydrogen peroxide treatments

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.

Water adsorption property of hierarchically nanoporous detonation nanodiamonds

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.

Structures and energetics of organosilanes in the gaseous phase: a computational study

The gas-phase conformations and stabilities of neutral and anionic organosilanes with structure ((HO)3Si-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.

Nanoporosity Change on Elastic Relaxation of Partially Folded Graphene Monoliths

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 compression for 25 h unfolds double-bent-like structures, relaxing the unstable nanographene stacked structure formed on the initial compression without nanographene sheets collapse. This behavior stems from the highly elastic nature of the nanographenes.

Essential Role of Viscosity of SWCNT Inks in Homogeneous Conducting Film Formation

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.

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.

Adsorption-desorption mediated separation of low concentrated D2O from water with hydrophobic activated carbon fiber

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.

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.