Morinobu Endo

Shinshu University, Shonai, Nagano, Japan

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Publications (405)1732.97 Total impact

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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.
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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; 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 · 3.71 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: 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
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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 · 7.51 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 · 1.30 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
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    ABSTRACT: Thin carbon nanotubes (CNTs) were heated at 2800°C to heighten the crystallinity of the CNTs. The microstructures and fracture toughness of the thin CNTs and the heat-treated thin CNTs/alumina composites were investigated. Using such thin CNTs was effective for obtaining finer microstructures of the composites but the heat-treatment made the uniform dispersion of the CNTs difficult. The composites containing the heat-treated thin CNTs showed higher fracture toughness than those containing the thin CNTs and the thick CNTs used in previous study when their content was the same.
    Key Engineering Materials 06/2014; 617:205-208. DOI:10.4028/www.scientific.net/KEM.617.205 · 0.19 Impact Factor
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    ABSTRACT: Graphene oxide (GO) has recently become an attractive building block for fabricating graphene-based functional materials. GO films and fibers have been prepared mainly by vacuum filtration and wet spinning. These materials exhibit relatively high Young's moduli but low toughness and a high tendency to tear or break. Here, we report an alternative method, using bar coating and drying of water/GO dispersions, for preparing large area GO thin films (e.g. 800-1200 cm(2) or larger) with an outstanding mechanical behavior and excellent tear resistance. These dried films were subsequently scrolled to prepare GO fibers with extremely large elongation to fracture (up to 76 %), high toughness (up to 17 J/m(3)) and attractive macroscopic properties, such as uniform circular cross section, smooth surface, and great knotability. This method is simple and after thermal reduction of the GO material, it can render highly electrically conducting graphene-based fibers with values up to 416 S/cm at room temperature. In this context, GO fibers annealed at 2000 °C were also successfully used as electron field emitters operating at low turn on voltages of ca. 0.48 V/μm and high current densities (5.3 A/cm(2)). Robust GO fibers and large-area films with fascinating architectures and outstanding mechanical and electrical properties were prepared bar coating followed by dry film scrolling.
    ACS Nano 05/2014; 8(6). DOI:10.1021/nn501098d · 12.03 Impact Factor
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    ABSTRACT: Nitrogen‐doped carbon inverse opals are synthesized by M. Terrones and co‐workers using an impregnated ordered opal template with a sucrose solution containing an organic compound with nitrogen. The materials are then subjected to thermal treatments and the opal removed by HF. The resulting pores preserve the ordering of the silica nanoparticles in the opal. Interestingly, the optical, electrical, and chemical properties significantly vary as a function of the nitrogen content within the porous carbon structure, and the size of the silica spheres used in the opal template.
    Advanced Functional Materials 05/2014; 24(18). DOI:10.1002/adfm.201470115 · 10.44 Impact Factor
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    ABSTRACT: Nitrogen-doped carbon inverse opal (CIO-N) is synthesized by a two-step process involving the infiltration of carbon-nitrogen precursors within opals followed by the thermolysis and removal of the opal structure in hydrofluoric acid (HF). Undoped samples exhibit a reflection peak in the red region of the spectrum whereas N-doped samples display shifts to the blue region of the spectrum as the nitrogen content is increased. The degree of crystallinity of CIO-N strongly depends upon the nitrogen content and on the size of the precursor silica particles used to prepare the inverted opals. In addition, the introduction of nitrogen into the samples is able to increase the electrical conductivity by one order of magnitude from 2 to 30 S cm-1 (at room temperature). All samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-Vis) spectroscopy, and electrical conductivity measurements. It is envisaged that CIO-N could have important applications in the fabrication of photonic crystals, photoconducting materials, molecular sensors, field emission devices, capacitors, batteries, among many others.
    Advanced Functional Materials 05/2014; 24(18). DOI:10.1002/adfm.201303391 · 10.44 Impact Factor
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    Chemical Reviews 04/2014; 114(11). DOI:10.1021/cr400341h · 45.66 Impact Factor
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    ABSTRACT: Vertically-aligned carbon nanosheets (CNSs), which were fabricated by microwave plasma-enhanced chemical vapor deposition in Ar and CH4 system, have been annealed at high temperatures in the range of 1200–3000 °C. The morphologies and microstructures of the treated CNSs were analyzed by scanning and transmission electron microscopes, and Raman spectroscopy. High temperature treatment process efficiently removed the amorphous carbon and some defects and improved the graphitization of the CNSs. The graphitized grains increase and the interlayer spacing decreases with increasing heat temperatures. Heat treatment of the CNSs at temperatures from 1500 to 2000 °C was found to achieve the edges consisting of many single-layer graphene sheets. Annealing at temperatures above 2100 °C, the edges of nanosheets consist of 2–5 layer graphene with many zigzag junctions. The mechanism of reconstruction for the edges in the CNSs ascribes possibly to the carbon atom vaporization at high temperatures.
    Carbon 03/2014; 68:360–368. DOI:10.1016/j.carbon.2013.11.012 · 6.16 Impact Factor
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    ABSTRACT: To enhance the fracture toughness of silicon carbide (SiC) ceramics and prevent the generation of cracks and chippings in the SiC ceramics during machining process, carbon nanofibres (CNFs) were compounded with SiC. The densification and microstructure development of the CNFs/SiC composites pressureless sintered in Ar atmosphere were investigated. The fracture toughness of SiC ceramics was enhanced by the addition of 1–3 wt% CNFs, which resulted from the pullout and/or bridging effect of CNFs bonded much more closely with SiC. The addition of 3 wt% CNFs prevented the chippings from generating in the composite during precision machining process.
    International Journal of Applied Ceramic Technology 03/2014; 11(2). DOI:10.1111/ijac.12131 · 1.22 Impact Factor
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    03/2014; 5:60–65. DOI:10.1016/j.jcou.2014.01.001
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    ABSTRACT: Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremely important.
    The Journal of Physical Chemistry C 02/2014; 118(8):4454–4459. DOI:10.1021/jp410732r · 4.84 Impact Factor
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    ABSTRACT: Engineered carbon nanotubes are currently used in many consumer and industrial products such as paints, sunscreens, cosmetics, toiletries, electronic processes and industrial lubricants. Carbon nanotubes are among the more widely used nanoparticles and come in two major commercial forms, single-walled carbon nanotubes (SWCNT) and the more rigid, multi-walled carbon nanotubes (MWCNT). The low density and small size of these particles makes respiratory exposures likely. Many of the potential health hazards have not been investigated, including their potential for carcinogenicity. We, therefore, utilized a two stage initiation/promotion protocol to determine whether inhaled MWCNT act as a complete carcinogen and/or promote the growth of cells with existing DNA damage. Six week old, male, B6C3F1 mice received a single intraperitoneal (ip) injection of either the initiator methylcholanthrene(MCA, 10 mug/g BW, i.p.), or vehicle (corn oil). One week after i.p. injections, mice were exposed by inhalation to MWCNT (5 mg/m3, 5 hours/day, 5 days/week) or filtered air (controls) for a total of 15 days. At 17 months post-exposure, mice were euthanized and examined for lung tumor formation. Twenty-three percent of the filtered air controls, 26.5% of the MWCNT-exposed, and 51.9% of the MCA-exposed mice, had lung bronchiolo-alveolar adenomas and lung adenocarcinomas. The average number of tumors per mouse was 0.25, 0.81 and 0.38 respectively. By contrast, 90.5% of the mice which received MCA followed by MWCNT had bronchiolo-alveolar adenomas and adenocarcinomas with an average of 2.9 tumors per mouse 17months after exposure. Indeed, 62% of the mice exposed to MCA followed by MWCNT had bronchiolo-alveolar adenocarcinomas compared to 13% of the mice that received filtered air, 22% of the MCA-exposed, or 14% of the MWCNT-exposed. Mice with early morbidity resulting in euthanasia had the highest rate of metastatic disease. Three mice exposed to both MCA and MWCNT that were euthanized early had lung adenocarcinoma with evidence of metastasis (5.5%). Five mice (9%) exposed to MCA and MWCNT and 1 (1.6%) exposed to MCA developed serosal tumors morphologically consistent with sarcomatous mesotheliomas, whereas mice administered MWCNT or air alone did not develop similar neoplasms. These data demonstrate that some MWCNT exposures promote the growth and neoplastic progression of initiated lung cells in B6C3F1 mice. In this study, the mouse MWCNT lung burden of 31.2 mug/mouse approximates feasible human occupational exposures. Therefore, the results of this study indicate that caution should be used to limit human exposures to MWCNT.
    Particle and Fibre Toxicology 01/2014; 11(1):3. DOI:10.1186/1743-8977-11-3 · 6.99 Impact Factor

Publication Stats

6k Citations
1,732.97 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
  • 2013
    • Nagano University
      長野, Nagano, Japan
  • 2012
    • Michigan State University
      • Department of Physics and Astronomy
      East Lansing, Michigan, United States
  • 2011
    • Rice University
      • Department of Mechanical Engineering and Materials Science
      Houston, Texas, United States
  • 2007
    • Universidade Federal do Ceará
      • Departamento de Física
      Fortaleza, Estado do Ceara, Brazil
  • 2004
    • Chuo University
      • Department of Physics
      Edo, Tōkyō, Japan