Takashi Takei

Tokyo Metropolitan University, Edo, Tōkyō, Japan

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Publications (46)82.73 Total impact

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    ABSTRACT: Shape-controlled hollow silica nanoparticles have been successfully synthesized by an inorganic particle template method, which involves sol–gel silica coating over surfaces of the template and followed by acid-dissolution removal of the template. This work demonstrates shape control of the hollow particle using calcium carbonate as the template with a variety of shapes such as cubic, rough-surfaced spherical and rod-like particles. Inner size and shape of hollow silica nanoparticles synthesized were exactly reflected to outer size and shape of template used, and existence of micropores in the silica shell wall was verified by nitrogen gas adsorption analysis.
    No preview · Article · Sep 2012 · Advanced Powder Technology
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    ABSTRACT: A Pt-Ru nanoparticle catalyst was prepared using mesoporous carbon, CMK-3, as a support, and the catalytic activity was compared to that on Ketjen carbon black, KB. The DMFC performances of MEA prepared with these catalysts were also measured and compared with each other. The catalysts deposited on CMK-3, Pt-Ru/CMK-3, had a narrow size distribution around 2.5nm and highly distributed on the surface of the support. Pt-Ru/CMK-3 showed a higher mass activity for methanol oxidation based on a cyclic voltammogram, but a lower DMFC performance than that of Pt-Ru/KB. It was considered that the catalyst layer with CMK-3 had a lower electric conductivity and/or unfavorable microstructure to prepare a large number of active reaction sites in the layer.
    No preview · Article · Feb 2007
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    ABSTRACT: Hollow particles are a newly developing material with the special properties of low density, thermal insulation and distinct optical activity. A number of preparation methods have been proposed in the literature. The polymer bead template method is one of the common processes to synthesize hollow particles, which can easily control particle size. However, byproducts produced during preparation adversely affect the natural environment. We have proposed an inorganic template method which overcomes the above disadvantages and also has some strong points. Although particle surface structure strongly affects wettability and particle dispersability, there are few reports that have discussed hollow particle structure. In this study, the shell wall structure of hollow particles was determined in detail by an analysis adsorption mechanism using the nitrogen adsorption isotherm. The results were compared with those of dense particles. The characteristics of the surface hydroxyl groups which react with surface modification reagents were then evaluated by water vapor adsorption. The modified surface was also characterized by Fourier-transform infrared spectroscopy and thermogravimetry/differential thermal analysis.
    Full-text · Article · Jan 2007 · Advanced Powder Technology
  • Masatoshi Chikazawa · Takashi Takei

    No preview · Chapter · Nov 2006
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    ABSTRACT: Three-dimensionally ordered macroporous carbons were prepared from bimodal polymer-silica colloidal crystals; the resulting carbons had interconnected macropores, and the walls of the macropores were composed of hollow mesosized spheres.
    No preview · Article · Nov 2006 · Chemical Communications
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    ABSTRACT: Thin films of lithium ion conductive ceramic Li4+XAl XSi1-XO4 were fabricated on Au substrate using sol-gel process. The sol of Li-Al-Si-O was spread on Au substrate using a spin coater, and it was gelated at room temperature. The gel was calcinated at 400 °C and heat-treated at high temperatures between 500 °C and 800 °C in air. The addition of poly(vinylpyrrolidone) (PVP) was effective in stabilizing the sol. Furthermore, the morphology of the obtained thin film was changed by the PVP additive. Li4+XAlXSi 1-XO4 thin film prepared at 800 °C exhibited a Li+ ion conductivity of 10-8 S cm-1 at room temperature.
    No preview · Article · Jan 2006 · Key Engineering Materials

  • No preview · Article · Jan 2006
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    ABSTRACT: A new proton-conducting membrane was prepared consisting of uniformly macroporous silica matrix and a proton-conducting gel polymer, 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPS). Three-dimensionally ordered macroporous silica membrane was fabricated by use of a colloidal template method with mono-dispersed polystyrene beads. Surface sulfonation of the pores in the silica matrix was performed by using 1,3-propanesultone. The sulfonated silica matrix exhibited about 400 times higher proton conductivity man unmodified one. The proton conductivity of the composite membrane was also successfully enhanced by using the sulfonated silica matrix.
    No preview · Article · Jan 2006 · Key Engineering Materials
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    ABSTRACT: Silica gel was used as core particles to design a simple preparation for controlled delivery system with a high drug content. Drug loading was carried out by immersing the silica gel in a pre-heated drug solution or suspension. HPLC, SEM, DSC, PXRD analysis and N2 adsorption studies evaluated the drug-loading process. In the next step, the drug-loaded silica gel was coated with hydroxypropyl methylcellulose (HPMC) and an aqueous dispersion of ethylcellulose (Aquacoat) to control the drug release. The release profile was determined using a dissolution test. The results showed that silica gel could adsorb great quantities of the drug, up to about 450 mg/g, by repetition of the loading process. Evaluation of the drug-loading process indicates that drug deposition in the pores occurs during the loading process and the drug-loading efficacy is strongly related to the drug solubility. On the other hand, the dissolution test showed that the drug release could be controlled by polymer coating the drug-loaded silica gel. An HPMC undercoating effectively suppresses the drug release, as it smoothes the drug-loaded core surface and aids in the formation of a continuous Aquacoat coating film. The floating property was also observed during the dissolution test.
    No preview · Article · Oct 2005 · European Journal of Pharmaceutical Sciences
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    ABSTRACT: A new proton conductive membrane was prepared by using three-dimensionally ordered macroporous polyimide and proton conductive gel polymer electrolyte. The polyimide matrix was synthesized by the colloidal template method with mono-dispersed silica beads. The macroporous polyimide membrane with an adequate mechanical strength, flexibility, and porosity was successfully obtained. A gel polymer of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) was injected into pores to prepare a proton conductive composite membrane consisting of macroporous polyimide and gel polymer. The composite membrane exhibited high proton conductivity of 1.2 × 10-1 S -1 at 60°C under 90 % relative humidity, whose value was comparable with that of Nafion®117 membrane. This result indicates that the composite membrane with polyimide matrix can be applied to fuel cells as a new type of proton conductive membrane.
    No preview · Article · Jan 2004
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    ABSTRACT: A series of aluminum-containing kanemite (Al-kanemite) samples with several Si/Al molar ratios were synthesized. The Al-kanemite samples were pillared with silica. X-ray diffractograms showed that the layered structure of the Al-kanemite samples was maintained at Si/Al= infinity approximately 10 but was broken at Si/Al = 5, 2.5, and 1. 29Si MAS NMR spectra of the Al-kanemite samples, except for that of Si/Al = 1, mainly showed peaks of Q(3) sites, which were attributed to Si(OSi)(3)(OH) groups, although peaks assigned to Si(OAl)(OSi)(2)(OH) were also seen. The 27Al MAS NMR spectra indicated that the Al-kanemite samples had only four-coordinate aluminum atoms. The FTIR spectra of pyridine adsorbed on the pillared Al-kanemite derivatives revealed Lewis acid sites on the surface. The nitrogen adsorption isotherms of the derivatives were classified as type I (Langmuir) absorption isotherms. Using the alpha(s) method, the specific surface areas of the derivatives were 572-756 m(2)g(-1), and the pore sizes were calculated as 1.25-1.83 nm. The pillared Al-kanemite derivatives had slit-shaped micropore structures.
    No preview · Article · Jan 2004 · Journal of Colloid and Interface Science

  • No preview · Article · Jan 2004
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    ABSTRACT: Surface modified alumina powder that has photocatalytic activity was studied. To control the amount of Ti introduced on the surface at the molecular level, the powder was prepared by chemical surface modification with a monofunctional titanate-based coupling agent, followed by partial oxidation of the modification group. The surface density of Ti introduced onto the surface was quantitatively increased with the concentration of the modifying reagent, and/or repetition of the modification. Furthermore, the relationship between the surface structure and the occurrence of photocatalytic activity was examined. The surface structure was measured by XPS and UV-Visible absorption spectrometry. The photocatalytic activity was determined by measuring the degradation of Methylene Blue molecules in water solution with UV irradiation. Photocatalytic activity was realized at a Ti surface density of 3.7 nm–2. The optical absorption edge in UV of the sample shifted to longer wavelengths. The ability as a photocatalyst increased with the amount of Ti-O-Ti. Photocatalytic activity was recognized to be related to the amount of Ti-O-Ti on the alumina surface and the ability of UV absorption.† This report was originally printed in J. Soc. Powder Technology, Japan 39, 102-107 (2002) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.
    No preview · Article · Jan 2004 · Powder and particle
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    ABSTRACT: Interlayer hydroxyl groups of layered silicate kanemite have been modified with trimethylsilyl groups by the reaction between the hydroxyl groups and trimethylchlorosilane. Expansion of the interlayer space by intercalation of dimethyldialkylammonium ions into the silicate layers enables the silylating reagent to access the hydroxyl groups. An increase in specific surface areas was observed with increasing concentration of trimethylsilyl groups. This result suggests that the interlayer space of kanemite can be used as an effective molecular adsorption space by weakening the interaction between the interlayer hydrogen bonds of hydroxyl groups. The modification of kanemite with trimethylsilyl groups restricted the adsorption of water below a monolayer capacity and was favorable for benzene adsorption.
    No preview · Article · Oct 2003 · Colloid and Polymer Science
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    ABSTRACT: The aim of this study is to investigate the effect of geometric structure and surface wettability of glidant on tablet hardness. Geometric structure is defined, in this work, as three-dimensional structure such as porosity, particle size and specific surface area. A variety of silica was incorporated in direct compressive fillers as glidant and mixed powder was compressed in single punch tablet machine with and without 0.5 wt.% magnesium stearate. Flowability of mixed powder was evaluated with Carr's index measurement. In the case of unlubricated compression, tablet hardness decreased as a function of additional concentration of silica. Reduction rate directly depended on surface coverage of silica over filler surface and hydrophobicity. Since surface coverage is related to geometric structure, it can be concluded that structural influence plays an important role to determine tablet hardness. While, in the case of lubricated compression, either water adsorption amount or geometric structure effects on tablet hardness. Increase of tablet hardness was observed only when hydrophilic porous and small size nonporous silica were added. All the other silica had deleterious effect on tablet hardness and in particular hydrophobicity strongly reduced tablet hardness.
    No preview · Article · Sep 2003 · International Journal of Pharmaceutics
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    ABSTRACT: The silica-pillared derivatives from kanemite (NaHSi(2)O(5).3H(2)O) were prepared by intercalation of dialkyldimethylammonium (DADMA) ion and pillaring with tetraethylorthosilicate. The formation of silica pillars between the silicate sheets was demonstrated by X-ray diffraction, (29)Si CP/MAS NMR, and TEM observation. The basal spacing depended on the chain length of DADMA. Nitrogen adsorption study showed that the specific surface area was enlarged over 1000 m(2) g(-1) by the pillaring and that the pore size was in the micropore region. Water and benzene adsorption isotherms revealed that the surface properties of the pillared derivatives show hydrophobic character.
    Preview · Article · Dec 2002 · Journal of Colloid and Interface Science
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    ABSTRACT: Properties of sites introduced onto silica surface using surface modification with a monofunctional titanate-based coupling agent were investigated. The surface density of sites introduced onto the surface was quantitatively increased with the repeat times of modification. The photocatalysis appeared before formation of crystalline TiO2. The ability as photocatalyst was increase with the amount of sites. It was recognized that the appearance of photoactivity was related to the existence of Si-O-Ti on surface.
    No preview · Article · Dec 2001 · Studies in surface science and catalysis
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    ABSTRACT: The size-dependent phase transition behavior of carbon tetrachloride confined in silica pores (rp = 5–50 nm) has been investigated by DSC and X-ray measurements. The melting point of CCl4 in the pores linearly decreased with the reciprocal pore size. The solid-to-solid transition temperature of CCl4 in the pores also depended on pore size. Below the pore radius of 16.5 nm, the process of phase transition of CCl4 on cooling was different from that of bulk CCl4. The decrease in the heats of the transitions in the pores suggested the existence of non-transforming phase in the pores. The geometric restriction of small pore contributes to the anomalous transition behavior of CCl4 in the pores.
    Preview · Article · Jul 2000 · Thermochimica Acta
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    ABSTRACT: A new process was proposed to introduce active sites onto calcium carbonate powder. The process consists of three steps: (i) chemical surface modification, (ii) surface oxidation and (iii) surface hydroxylation. Repeating this process can increase the amount of new active sites. IR spectroscopy confirmed the process. The surface density of modifiers was evaluated from measuring the specific surface area and weight loss of the samples caused by the combustion of the modifiers. In one process 1.15 nm-2 modifiers were introduced onto the sample. The process can introduce new active sites quantitatively without influencing the properties of the sample substrate and can also improve its thermostability. Surface acidity increased until four cycles in the repeated modification process; however, it decreased after the fourth cycle. This result was ascribed to a change in the surface binding state by introducing the new active sites and such a conclusion was explained by results of X-ray photoelectron spectroscopy.
    No preview · Article · May 2000 · Advanced Powder Technology
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    ABSTRACT: The relationship between wettability and surface geometric structure of modified silica particles and glass plates was investigated. Surface modification was performed by the autoclave method with 1-dodecanol to control the surface wettability. The preferential dispersion test proved that wettability varied at a surface modification ratio of 20%, which coincided with the changing point of the geometric structure of modifier chains determined by the adsorption method. The geometric structure was also evaluated by atomic force microscopy (AFM), and we could obtain the hexagonal packing of chains of the modifiers both in water and air at high surface modification ratio. Imaging of the surface of the nanosized particles on a glass plate was accomplished in water by taking advantage of the hydrophobic attractive force, which was proved by adhesion force measurements.
    No preview · Article · Feb 2000 · Langmuir