Koki Urita

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.

Confinement in Carbon Nanospace-Induced Production of KI Nanocrystals of High-Pressure Phase

An outstanding compression function for materials preparation exhibited by nanospaces of single-walled carbon nanohorns (SWCNHs) was studied using the B1-to-B2 solid phase transition of KI crystals at 1.9 GPa. High-resolution transmission electron microscopy and synchrotron X-ray diffraction examinations provided evidence that KI nanocrystals doped in the nanotube spaces of SWCNHs at pressures below 0.1 MPa had the super-high-pressure B2 phase structure, which is induced at pressures above 1.9 GPa in bulk KI crystals. This finding of the supercompression function of the carbon nanotubular spaces can lead to the development of a new compression-free route to precious materials whose syntheses require the application of high pressure.

Effect of a quaternary ammonium salt on propylene carbonate structure in slit-shape carbon nanopores.

The effect of addition of tetraethylammonium tetrafluoroborate (Et(4)NBF(4)) on the structure of propylene carbonate (PC) confined in slit-shaped carbon nanopores of activated carbon fiber (pore width = 1.0 nm) was studied by synchrotron X-ray diffraction and reverse Monte Carlo simulation. PC molecules are randomly packed in the slit carbon nanopores of 1 nm in the absence of Et(4)NBF(4). Addition of Et(4)N(+) and BF(4)(-) ions promotes formation of considerably ordered double layers of PC molecules even in the highly restricted slit pore space. PC molecules can accept these ions efficiently. This structural modulation function of PC molecular assemblies should contribute to the evolution of supercapacitance in carbon nanopores.

Evidence of Dynamic Pentagon−Heptagon Pairs in Single-Wall Carbon Nanotubes using Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) was applied to detecting pentagon-heptagon pairs, the so-called Stone-Wales defect, in single-wall carbon nanotubes (SWCNTs). When a probing laser light was scanned over a SWCNT-dispersed silver surface, two distinct SERS spectra were obtained: (1) temporally stable spectra similar to that of resonance Raman spectra of bulk SWCNTs and (2) temporally fluctuating spectra with additional peaks which were not observed in the non-SERS spectra. The fluctuations in the SERS spectra are discussed in association with dynamic reconstruction of defective structures of SWCNTs (nonhexagonal arrangements of carbon atoms) in the vicinity of SERS-active sites under irradiation of the laser light.

Enhanced hydrogen adsorptivity of single-wall carbon nanotube bundles by one-step c60-pillaring method.

Single-wall carbon nanotube (SWCNT) bundles were pillared by fullerene (C60) by the cosonication of C60 and SWCNT in toluene to utilize the interstitial pores for hydrogen storage. C60-pillared SWCNTs were confirmed by the shift in the X-ray diffraction peak and the expanded hexagonal and distorted tetragonal bundles revealed by high-resolution transmission electron microscopy. The H2 adsorptivity of the C60-pillared SWCNT bundles was twice that of the original SWCNT bundles, indicating a design route for SWCNT hydrogen storage.

Direct synthesis of novel homogeneous nanocomposites of Li2MnSiO4 and carbon as a potential Li-ion battery cathode material

Homogeneous nanocomposites of nanocrystalline Li2MnSiO4 and carbon as well as a carbon nanotubes-embedded nanocomposite are synthesized directly by a novel method using organic-inorganic hybrid polymers which consist of covalently bonded phenolic oligomer and siloxane parts. The nanocomposites show superior charge-discharge performance at room temperature in spite of low carbon contents.

Anomaly of CH4 Molecular Assembly Confined in Single-Wall Carbon Nanohorn Spaces

Vibrational-rotational properties of CH(4) adsorbed on the nanopores of single-wall carbon nanohorns (SWCNHs) at 105-140 K were investigated using IR spectroscopy. The difference vibrational-rotational bands of the ν(3) and ν(4) modes below 130 K show suppression of the P and R branches, while the Q branches remain. The widths of the Q branches are much narrower than in the bulk gas phase due to suppression of the Doppler effect. These results indicate that the rotation of CH(4) confined in the nanospaces of SWCNHs is highly restricted, resulting in a rigid assembly structure, which is an anomaly in contrast to that in the bulk liquid phase.

Selective D2 adsorption enhanced by the quantum sieving effect on entangled single-wall carbon nanotubes

The quantum sieving effect of D(2) over H(2) is examined at 40 and 77 K by means of experiments and GCMC simulations, for two types of single-wall carbon nanotubes that are distinguishable by their unique entangled structures; (1) a well-bundled SWCNT and (2) loosely-assembled SWCNT produced by the super growth method (SG-SWCNT). Oxidized SWCNT samples of which the so-called internal sites are accessible for H(2) and D(2), are also studied. Experimental H(2) and D(2) adsorption properties on the well-bundled SWCNTs are compared with the simulated ones, revealing that pore-blocking and restricted diffusion of the molecules suppress the high selectivity of D(2) over H(2). The non-oxidized SG-SWCNT assembly shows the highest selectivity among the SWCNT samples, both at 40 and 77 K. The high selectivity of the SG-SWCNT assembly, which is pronounced even at 77 K, is ascribed to their unique assembly structure.

Enhanced electric double-layer capacitance by desolvation of lithium ions in confined nanospaces of microporous carbon.

Carbon electrodes with specific microporous structures are strongly desired to improve the performance of electric double-layer capacitors (EDLCs). We report solvated states of Li ions in confined carbon micropores affecting specific capacitance. The average Li(+) solvation number of 1 M LiClO4/propylene carbonate (PC) electrolyte introduced into porous carbon electrodes was determined using Raman spectroscopy and (7)Li NMR. Micropores with slightly larger pore size against the solvated molecules and the narrow two-dimensional spaces decreased the solvation number, enhancing specific capacitance. Hence, specific carbon morphology may be related to high EDL capacitance, and micropore structure is important in obtaining highly capacitive EDLC materials.

Physico-Chemical Properties of Iodine-Adsorbed Single-Walled Carbon Nanotubes

I2 was adsorbed on single-walled carbon nanotube from ethanol solution at 303 K. The I2 adsorption isotherm was Langmuirian, giving 35 (+/-10) mg g(-1) of the saturated adsorption amount (coverage 0.06-0.09). The I2-adsorption treatment of SWCNT bundles reduced the N2 adsorption amount at 77 K by only 3%; the adsorption amount of supercritical H2 at 77 K was decreased by 30% because of the I2-adsorption treatment, indicating the blocking of interstitial pores by adsorbed I2. These adsorption results indicated the adsorption of I2 molecules in the narrow interstitial pores. The I2-adsorption treatment increases the Raman intensity coming from metallic SWCNTs, and the dc electrical conductivity increased by 15% because of the I2-adsorption treatment, strongly suggesting the presence of charge-transfer interaction between I2 and SWCNTs irrespective of small coverage by I2.