Morinobu Endo

Shinshu University, Shonai, Nagano, Japan

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Publications (422)1885.55 Total impact

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    ABSTRACT: Here we report the synthesis of cube-like Ag-nanoparticle (Ag-NP) agglomerates using functionalized graphene nanoribbons (GNR) as templates. The morphology and size of the resulting Ag assemblies are carefully controlled by changing the surface activity of the GNR through chemical functionalization. We propose a mechanism explaining the cube-like organization of the Ag-NP. In particular, the functionalized ribbons first organize in a cubic/rectangular shape, and subsequently thiol moieties preferentially anchor on the edges of the ribbons favoring their surface passivation with Ag-NPs. Furthermore, we found these Ag agglomerates serve as efficient substrate for the Raman detection of 4-aminothiophenol (4-ATP) molecules, through a surface enhancement Raman phenomenon. We believe these novel Ag-NP nanocomposites could also find applications as bactericides, catalysts and electrically conducting fillers.
    Carbon 11/2015; 93:800-811. DOI:10.1016/j.carbon.2015.05.098 · 6.16 Impact Factor
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    ABSTRACT: Recently, graphene and carbon nanotube (CNT) composites have attracted great interest of scientists and exhibited fascinating properties even better than they could on their own. Here, we have synthesized the graphenated CNTs (g-CNTs), one of graphene-CNT composites, from waste rice husk (RH) by one-step microwave plasma irradiation (MPI) process. The RH-derived g-CNTs were composed of graphene standing on the sidewalls of CNTs, in which the graphene sheets possessed a large amount of sharp edges, which mainly consisted of 2-6 layers, and the CNTs had several tens of micrometers in length and 50-200 in diameter. They offer great promising in the application of electrochemical electrodes due to their special features including high surface area and specific capacitance. The successful MPI technique can be spread to other waste biomass, in which their components are made of cellulose, hemicellulose, and lignin similar to RHs, to fabricate high-added-value nanocarbons including graphene, CNTs, and g-CNTs, which were dependent of experimental pressure.
    Carbon 11/2015; 94. DOI:10.1016/j.carbon.2015.07.037 · 6.16 Impact Factor
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    ABSTRACT: The present study systematically examined the kinetics of a hydroxyl radical scavenging reaction of various carbon nanotubes (CNTs) including double-walled and multi-walled carbon nanotubes (DWCNTs and MWCNTs), and carbon nano peapods (AuCl3@DWCNT). The theoretical model that we recently proposed based on the redox potential of CNTs was used to analyze the experimental results. The reaction kinetics for DWCNTs and thin MWCNTs agreed well with the theoretical model and was consistent with each other. On the other hand, thin and thick MWCNTs behaved differently, which was consistent with the theory. Additionally, surface morphology of CNTs substantially influenced the reaction kinetics, while the doped particles in the center hollow parts of CNTs (AuCl3@DWCNT) shifted the redox potential in a different direction. These findings make it possible to predict the chemical and biological reactivity of CNTs based on the structural and chemical nature and their influence on the redox potential.
    Carbon 08/2015; 95:302-308. DOI:10.1016/j.carbon.2015.08.048 · 6.16 Impact Factor
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    ABSTRACT: Exploring the potential catalytic applications of boron-doped carbon materials is a fascinating challenge. Here we describe that boron-doped onion-like carbon and carbon nanotubes as metal-free catalysts exhibit excellent catalytic activity and stability in nitroarene reduction under a stoichiometric amount of reductant.
    Chemical Communications 07/2015; DOI:10.1039/c5cc01963j · 6.83 Impact Factor
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    ABSTRACT: Synthesizing 3D carbon nanotube (CNT) networks with multifunctional characteristics has stimulated the interest from the scientific community since the 1990s. Here, the fabrication of a novel composite material consisting of 3D covalently interconnected multiwalled CNT with silicon carbide (SiC) nano and microparticles is reported. The material is synthesized by a two-step process involving the coating of CNT with silicon oxide (SiOx ) via chemical routes, followed by spark plasma sintering (SPS). SPS enables carbothermal reduction of SiOx and subsequent densification of the material into 3D composite blocks. Covalent interconnections of CNT are facilitated by a carbon diffusion process resulting in SiC formation as SiOx coated CNT are subjected to high temperatures. The presence of SiC in the sintered composite has been confirmed by Raman spectroscopy, as well as through energy filtered transmission electron microscopy maps. Interestingly, the 3D CNT composite exhibits high thermal conductivity (16.72 W m−1 K−1); and also a semiconducting behavior with an electron hopping mechanism associated to a 3D variable range hopping model. These findings demonstrate that it is indeed possible to fabricate SiC–CNT composites with enhanced physical properties that can be used as multifunctional materials.
    Advanced Functional Materials 07/2015; 25(31). DOI:10.1002/adfm.201501696 · 11.81 Impact Factor
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    ABSTRACT: High pressure/temperature was applied on samples of pristine multi-walled carbon nanotubes (MWCNT), functionalized nanotubes (f-MWCNT), and nanotubes doped with nitrogen (CNx MWNT). Cylindrical compact pellets of f-MWCNT with diameters of about 6 mm were obtained under pressure of 4.0 GPa at room temperature and at 400 °C, using graphite as pressure transmitting medium. The best pellet samples were produced using nitric and sulfuric acids for the functionalization of MWCNT. The effect of high pressure/temperature on CNT was investigated by several spectroscopy and characterization techniques, such as Raman spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, N2 adsorption/desorption isotherms, and transmission electron microscopy. It was found that MWCNT maintain their main features in the compacted pellets, such as integrity, original morphology, and structure, demonstrating that high-pressure/temperature compaction can indeed be used to fabricate novel CNT self-supported materials. Additionally, the specific surface area and porosity are unchanged, which is important when using bulk CNT in adsorption processes. Raman analysis of the G’-band showed a shift to lower wavenumbers when f-MWCNT were processed under high pressure, suggesting that CNT are under tensile stress.
    Journal of Nanoparticle Research 06/2015; 17(6). DOI:10.1007/s11051-015-3045-y · 2.28 Impact Factor
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    ABSTRACT: Al-based composites incorporating multilayered graphene sheets were developed via a facile approach. The multilayered graphene sheets were fabricated from the expanded graphite via a simple mechanical exfoliation process. The facile extrusion molding process with Al powder and graphene sheets exfoliated from expended graphite afforded Al-based graphene composite rods. These composites showed enhanced thermal conductivity compared to the pristine Al rods. Moreover, the Al-based multilayered graphene sheet composites exhibited lower interfacial contact resistance between graphene-based electrodes than the pristine Al. With increasing degrees of dispersion, the number of exposed graphene sheets increases, thereby significantly decreasing the interfacial contact resistance between the composite and external graphite electrode.
    Nanotechnology 05/2015; 26(21):215603. DOI:10.1088/0957-4484/26/21/215603 · 3.67 Impact Factor
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    ABSTRACT: A high pressure resonance Raman spectroscopy study of linear carbon chains encapsulated inside multi-walled carbon nanotubes (MWCNTs) is reported. While the frequencies of the tangential modes of carbon nanotubes (G band) harden as the pressure increases, the vibrational frequencies of chain modes (around 1850\,cm$^{-1}$) decrease, thus indicating a softening of the Carbon-Carbon bonds in this 1D solid. Pressure-induced irreversible structural changes in the linear carbon chains are unveiled by the redshift in the vibrational modes when the pressure is released. These results have been interpreted as due to a coalescence of carbon chains and this hypothesis is supported by state-of-the-art atomistic reactive molecular dynamics simulations.
    The Journal of Physical Chemistry C 04/2015; 119(19):150423151340002. DOI:10.1021/acs.jpcc.5b00902 · 4.77 Impact Factor
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    ABSTRACT: Nitrogen-doped multi-walled carbon nanotubes (ND-MWCNT) are modified multi-walled carbon nanotubes (MWCNT) with enhanced electrical properties that are used in a variety of applications, including fuel cells and sensors; however, the mode of toxic action of ND-MWCNT has yet to be fully elucidated. In the present study, we compared the interaction of ND-MWCNT or pristine MWCNT-7 with human small airway epithelial cells (SAEC) and evaluated their subsequent bioactive effects. Transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction suggested the presence of N-containing defects in the lattice of the nanotube. The ND-MWCNTs were determined to be 93.3% carbon, 3.8% oxygen, and 2.9% nitrogen. A dose-response cell proliferation assay showed that low doses of ND-MWCNT (1.2μg/ml) or MWCNT-7 (0.12μg/ml) increased cellular proliferation, while the highest dose of 120μg/ml of either material decreased proliferation. ND-MWCNT and MWCNT-7 appeared to interact with SAEC at 6h and were internalized by 24h. ROS were elevated at 6 and 24h in ND-MWCNT exposed cells, but only at 6h in MWCNT-7 exposed cells. Significant alterations to the cell cycle were observed in SAEC exposed to either 1.2μg/ml of ND-MWCNT or MWCNT-7 in a time and material-dependent manner, possibly suggesting potential damage or alterations to cell cycle machinery. Our results indicate that ND-MWCNT induce effects in SAEC over a time and dose-related manner which differ from MWCNT-7. Therefore, the physicochemical characteristics of the materials appear to alter their biological effects. Copyright © 2015. Published by Elsevier Ireland Ltd.
    Toxicology 03/2015; 333. DOI:10.1016/j.tox.2015.03.008 · 3.75 Impact Factor
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    ABSTRACT: Nanosilicas can disperse single wall carbon nanotube (SWCNT) in aqueous solution efficiently; SWCNTs are stably dispersed in aqueous media for more than 6 months. The SWCNT dispersing solution with nanosilica can produce highly conductive transparent films which satisfy the requirements for application to touch panels. Even multiwall carbon nanotube can be dispersed easily in aqueous solution. The highly stable dispersion of SWCNTs in the presence of nanosilica is associated with charge transfer interaction which generates effective charges on the SWCNT particles, giving rise to electrostatic repulsion between the SWCNTs in the aqueous solution. Adhesion of charged nanosilicas on SWCNTs in the aqueous solution and a marked depression of the S11 peak of optical absorption spectrum of the SWCNT with nanosilicas suggest charge transfer interaction of nanosilicas with SWCNT. Thus-formed isolated SWCNTs are fixed on the flexible three dimensional silica jelly structure in the aqueous solution, leading to the uniform and stable dispersion of SWCNTs.
    Langmuir 02/2015; 31(10). DOI:10.1021/la504599b · 4.46 Impact Factor
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    ABSTRACT: Progress in the development of carbon nanotubes (CNTs) has stimulated great interest among industries providing new applications. Meanwhile, toxicological evaluations on nanomaterials are advancing leading to a predictive exposure limit for CNTs, which implies the possibility of designing safer CNTs. To pursue safety by design, the redox potential in reactions with CNTs has been contemplated recently. However, the chemical reactivity of CNTs has not been explored kinetically, so that there is no scheme to express a redox reaction with CNTs, though it has been investigated and reported. In addition, the reactivity of CNTs is discussed with regard to impurities that consist of transition metals in CNTs, which obfuscates the contribution of CNTs to the reaction. The present work aimed at modeling CNT scavenging in aqueous solution using a kinetic approach and a simple first-order reaction scheme. The results show that CNTs follow the redox reaction assumption in a simple chemical system. As a result, the reaction with multiwalled CNTs is semi-quantitatively denoted as redox potential, which suggests that their biological reactions may also be evaluated using a redox potential scheme.
    Carbon 11/2014; 83. DOI:10.1016/j.carbon.2014.10.009 · 6.16 Impact Factor
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    ABSTRACT: Changes in the optical properties of single walled carbon nanotubes (SWNTs) caused by the encapsulation of molybdenum (Mo) clusters were investigated in the current research. Detailed transmission electron microscope observations showed that the encased Mo clusters within the hollow core of SWNTs exhibited in the form of short rod-like structure, indicating the growth of the clusters within the confined nano space. The upshifted G-band frequency as well as the quenched photoluminescence and absorption signals signified the modulation in the electronic properties of SWNTs caused by a strong coupling interaction between the nanotube and the Mo clusters.
    RSC Advances 10/2014; 4(97). DOI:10.1039/C4RA07745H · 3.84 Impact Factor
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    ABSTRACT: We report on the use of pulsed KrF-laser irradiation for the in situ reduction of graphene oxide (GO) films under both vacuum and partial hydrogen pressure. By exposing GO films to 500 pulses of a KrF-laser, at a fluence of 10 mJ/cm2, their sheet resistance (Rs) is dramatically reduced from highly insulating (∼1010 Ω/sq) to conductive values of ∼3 kΩ/sq. By increasing the laser fluence, from 10 to 75 mJ/cm2, we were able to identify an optimal fluence around 35 mJ/cm2 that leads to highly conductive films with Rs values as low as 250 Ω/sq and 190 Ω/sq, under vacuum (10−5 Torr) and 50 mTorr of H2, respectively. Raman spectroscopy analyses confirmed the effective reduction of the KrF-laser irradiated GO films through the progressive recovery of the characteristic 2D band of graphene. Furthermore, systematic Fourier-transform infrared spectroscopy analysis has revealed that KrF-laser induced reduction of GO preferentially occurs through photodissociation and removal of carboxyl (COOH) and alcohol (OH) groups. A direct correlation is established between the electrical resistance of photoreduced GO films and their COOH and OH bond densities. The KrF-laser induced reduction of GO films is found to be more efficient under H2 background than under vacuum. It is concluded that our KrF-laser reduced GO films mainly consist of turbostratic graphite built from randomly organized few-layers-graphene building blocks, which contains some residual oxygen atoms and defects. Finally, by monitoring the KrF-laser fluence, it is shown that reduced GO films combining optical transmission as high as ∼80% along with sheet resistance as low as ∼500 Ω/sq can be achieved with this room-temperature and on-substrate process. This makes the laser-based reduction process developed here particularly attractive for photovoltaic hybrid devices using silicon substrates.
    Carbon 10/2014; 77:857-867. DOI:10.1016/j.carbon.2014.05.090 · 6.16 Impact Factor
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    ABSTRACT: Graphene monoliths made from graphene oxide colloids by unidirectional freeze-drying method were activated by typical activation processes of CO2 activation, chemical activation using ZnCl2 or H3PO4, and KOH activation. The porosity development of graphene monolith markedly depends on the activation method. The monoliths with highest surface area are obtained by the KOH activation method; only the KOH activation is effective for production of the graphene monolith of which surface area is in the range of 1760–2150 m2 g−1. The mechanism of the porosity development by KOH activation method is proposed. This work provides a promising route for the bottom-up design of pore width-tunable nanoporous carbons.
    Carbon 09/2014; 76:220–231. DOI:10.1016/j.carbon.2014.04.071 · 6.16 Impact Factor
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    ABSTRACT: In order to improve interfacial bonding strength between carbon nanofibers (CNFs) and SiC matrix in CNFs/SiC composites and to disperse CNFs uniformly in the matrix, SiC coating on surface of CNFs was performed in argon atmosphere in the temperature range of 1400 to 1800 degrees C using SiO2, SiO, and mixture of Si and SiO2 powders (Si/SiO2 powder) as silicon sources, and the modification and dispersibility of the treated CNFs were investigated. beta-SiC particles were deposited on the surface of the CNFs in all the specimens at 1600-1800 C. So more SiC was formed by heating CNFs with SiO powder at 1600 C. However, the formed SiC was oxidized at higher temperature, practically, at 1800 C. This oxidation was advanced more by using SiO2 and Si/SiO2 powders as silicon sources and very fine carbon fibers were observed on the surface of CNFs. The dispersibilities of CNFs heated with Si/SiO2 and SiO powders were superior to those of as-received CNFs, CNFs treated with NaClO3 solution and CNFs heated with SiO2 powder, which resulted from the advanced oxidation of CNFs and the silanol group (-SiOH) on surface of formed SiC.
    Journal- Ceramic Society Japan 09/2014; 122(1429):822-828. DOI:10.2109/jcersj2.122.822 · 0.85 Impact Factor
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    ABSTRACT: Naphthalene (N) or naphthalene-derivative (ND) adsorption-treatment evidently varies the electrical conductivity of single wall carbon nanotube (SWCNT) bundles over a wide temperature range due to a charge-transfer interaction. The adsorption treatment of SWCNTs with dinitronaphthalene molecules enhances the electrical conductivity of the SWCNT bundles by 50 times. The temperature dependence of the electrical conductivity of N- or ND-adsorbed SWCNT bundles having a superlattice structure suggests metal-semiconductor transition like behavior near 260 K. The ND-adsorbed SWCNT gives a maximum in the logarithm of electrical conductivity vs. T(-1) plot, which may occur after the change to a metallic state and be associated with a partial unravelling of the SWCNT bundle due to an evoked librational motion of the moieties of ND with elevation of the temperature.
    Faraday Discussions 08/2014; 173:145-56. DOI:10.1039/c4fd00119b · 4.61 Impact Factor
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    ABSTRACT: A new synthetic method is demonstrated for transforming rice husks into bulk amounts of graphene through its calcination and chemical activation. The bulk sample consists of crystalline nano-sized graphene and corrugated individual graphene sheets; the material generally contains one, two, or a few layers, and corrugated graphene domains are typically observed in monolayers containing topological defects within the hexagonal lattice and edges. Both types of graphenes exhibit atomically smooth surfaces and edges.
    Small 07/2014; 10(14). DOI:10.1002/smll.201400017 · 8.37 Impact Factor
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    ABSTRACT: Chemically doped graphene has been actively investigated as an electrode material for achieving high-performance electrochemical systems. However, the stability of pure-carbon-rich edges and/or heteroatom-decorated edges, and their effect on the electrochemical performance remain largely unexplored. We found that in a high temperature thermal doping process, the functionalized graphene edges were structurally stable at 1200 °C, whereas the edges at 1500 °C were unstable and coalesced into loops through covalent bond formation between adjacent graphene edges. Interestingly, boron and nitrogen co-doped graphene prepared at 1200 °C showed the largest capacitance in both acidic and alkaline media due to the presence of the BNO moieties along the edge sites. The doped material also showed the best rate capability due to the largely enhanced electrical conductivity originating from the substitutionally doped boron and nitrogen atoms. Our findings regarding the stability of heteroatom-decorated edges without loop formation can now be utilized as a guideline for maximizing the electrochemical activity of graphene in various electrochemical systems.
    06/2014; 2(25). DOI:10.1039/C4TA00936C
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    ABSTRACT: Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 degrees C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 degrees C that gave the stoichiometry of CF0.20. CF0.30, and CF0 43, respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 degrees C, the strong radial breathing modes (ABMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 degrees C were thermally treated at 1000 degrees C in argon. However, in the case of the DWCNTs fluorinated at 400 degrees C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.
    Chinese Journal of Catalysis 06/2014; 35(6):864–868. DOI:10.1016/S1872-2067(14)60107-8 · 1.55 Impact Factor
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    ABSTRACT: Vertically-aligned carbon nanosheets (CNSs) have been fabricated on the Cu substrate from Kapton polyimide (PI) film under Ar/H2 plasma irradiation. The high purity CNSs possess petal-like structures with many sharp edges, which are composed of few-layer graphene sheets. In addition, the irradiated Kapton PI film was covered by a layer of urchin-like carbon particles with about 4 μm in diameter, which also consist of few-layer graphene sheets along radial directions. Except for the morphologies, both the CNSs and urchin-like carbon particles demonstrate similar microstructures and chemical compositions.
    Carbon 06/2014; 72:421–424. DOI:10.1016/j.carbon.2014.02.021 · 6.16 Impact Factor

Publication Stats

7k Citations
1,885.55 Total Impact Points

Institutions

  • 1703–2015
    • Shinshu University
      • • Institute of Carbon Science and Technology
      • • Faculty of Engineering
      • • Division of Electrical and Electronic Engineering
      Shonai, Nagano, Japan
  • 2011
    • Rice University
      • Department of Mechanical Engineering and Materials Science
      Houston, Texas, United States
  • 2004
    • Chuo University
      • Department of Physics
      Edo, Tōkyō, Japan