Fujio Okino

Reversible fluorination of graphene: Evidence of a two-dimensional wide bandgap semiconductor

We report the synthesis and evidence of graphene fluoride, a two-dimensional wide bandgap semiconductor derived from graphene. Graphene fluoride exhibits hexagonal crystalline order and strongly insulating behavior with resistance exceeding

Property control of carbon materials by fluorination

10\text{ }\text{G}\ensuremath{\Omega}

Investigation of the ion storage/transfer behavior in an electrical double-layer capacitor by using ordered microporous carbons as model materials.

at room temperature. Electron transport in graphene fluoride is well described by variable range hopping in two dimensions due to the presence of localized states in the band gap. Graphene obtained through the reduction of graphene fluoride is highly conductive, exhibiting a resistivity of less than

Electrochemical Li Insertion in B-Doped Multiwall Carbon Nanotubes

100\text{ }\text{k}\ensuremath{\Omega}

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

at room temperature. Our approach provides a pathway to reversibly engineer the band structure and conductivity of graphene for electronic and optical applications.

Selective Optical Property Modification of Double-Walled Carbon Nanotubes by Fluorination

Abstract Fluorination is one of the most effective chemical methods to modify and control physicochemical properties of carbon materials. The method is rather straightforward, but the interpretation of the results are not necessarily facile. The complication lies in the diversity of carbon materials and the wide-range C–F bond nature. This conversely gives an opportunity to control properties of carbon materials in a wide range, either gradually or drastically. In this review, recent topics in the field of fluorinated carbon materials are covered with an emphasis on the recent research developments in our laboratories and in Japan.

Carbon-alloying of the rear surfaces of nanotubes by direct fluorination

An ordered microporous carbon, which was prepared with zeolite as a template, was used as a model material to understand the ion storage/transfer behavior in electrical double-layer capacitor (EDLC). Several types of such zeolite-templated carbons (ZTCs) with different structures (framework regularity, particle size and pore diameter) were prepared and their EDLC performances were evaluated in an organic electrolyte solution (1 M Et(4)NBF(4)/propylene carbonate). Moreover, a simple method to evaluate a degree of wettability of microporous carbon with propylene carbonate was developed. It was found that the capacitance was almost proportional to the surface area and this linearity was retained even for the carbons with very high surface areas (>2000 m(2) g(-1)). It has often been pointed out that thin pore walls limit capacitance and this usually gives rise to the deviation from linearity, but such a limitation was not observed in ZTCs, despite their very thin pore walls (a single graphene, ca. 0.34 nm). The present study clearly indicates that three-dimensionally connected and regularly arranged micropores were very effective at reducing ion-transfer resistance. Despite relatively small pore diameter ZTCs (ca. 1.2 nm), their power density remained almost unchanged even though the particle size was increased up to several microns. However, when the pore diameter became smaller than 1.2 nm, the power density was decreased due to the difficulty of smooth ion-transfer in such small micropores.

Fluorination of open- and closed-end single-walled carbon nanotubes

Electrochemical Li insertion into boron-doped multiwall carbon nanotubes (B-MWNTs) was investigated in a nonaqueous medium. Transmission electron microscopy observations showed that the walls of the tubes consisted of highly aligned ca. 35-45 graphene layers with good 3D ordering feature. Raman studies revealed that boron doping in multiwall carbon nanotubes (MWNTs) destroyed the local hexagonal symmetry. X-ray photoelectron spectra of B-MWNTs further supported the results of Raman spectra and confirmed the presence of BC 3 nanodomains N 2 adsorption measurements indicated that the Brunauer-Emmett-Teller (BET) surface areas of undoped and doped nanotubes were 10 and 12 cm 2 /g. respectively, with almost similar mesopore volumes. Galvanostatic discharge-charge measurements revealed that the reversible capacity was 156 mAh/g for undoped and 180 mAh/g for B-doped nanotubes in the first cycle with almost equal coulomb efficiencies of 55-58%. The coulomb efficiency increased to more than 90% after the second cycle. Cyclic voltammetry (CV) showed that highly reversible intercalation/deintercalation of Li occurred with some undesirable reduction processes in the initial discharge process. The cycle lives of both undoped and doped samples were quite satisfactory. Slow-scan CV confirmed that the intercalation of lithium in these nanotubes occurred through staging transition, usually observed in Li graphite intercalation compounds.

Direct interaction of elemental fluorine with diamond surfaces

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 fluorination on nano-sized π-electron systems

We found that by fluorination of double-walled carbon nanotubes (DWNTs), it is possible to suppress only the Raman radial breathing mode and absorption peaks from the outer (large diameter) tubes of DWNTs. In contrast, Raman signals from the inner shells showed no difference from the pristine DWNTs. The stability of the inner shells of fluorinated DWNTs was also confirmed from the photoluminescence (PL) map and the optical absorption spectra, which only showed the signals from the inner shells of DWNTs, with no distinct change in the optical properties of the inner tubes after fluorination. Our results indicate that once fluorinated, there exists only a weak, if not none, interaction between the inner tube and the outer fluorinated tube, proving that fluorination can be used to suppress the optical properties of carbon nanotubes without interfering the properties of inner tubes. The present finding can be important in electronic and sensor applications, keeping the inner tube from having unwanted contact with other substances that may distract from the inner tubes own characteristics.