Takashi Takei

Tokyo Metropolitan University, Edo, Tōkyō, Japan

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Publications (45)87.09 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To detect volatile organic compounds (VOCs), optical sensors based on the localized surface-plasmon resonance (LSPR) are widely used because they are simple and inexpensive to fabricate. Although LSPR spectroscopy has been generally applied to biological molecules such as proteins and DNA, small molecular sensing has been difficult because of the very small changes induced in the refractive index. We describe a LSPR gas sensor with high and wide range sensitivity. These characteristics are obtained from the improved peak shift that results from using an Au-dot pattern coated with a porous silica film. The 400-nm-diameter, 800-nm-wide Au dots were patterned by electron beam lithography (EBL) on a quartz glass substrate. The LSPR peak of the isolated Au-dot pattern occurs at 1230 nm in the near isolated area bringing enough refractive index changes. In addition, coating the Au-dot pattern with a thin porous silica film increases the adsorption of VOCs, thereby increasing the refractive-index change. The response of the sensor to VOC vapors was measured in a dynamic-flow system. The relative intensity decreases with toluene vapor exposure but completely recovers to the initial baseline after exposure to clean air. The real-time response allows detection of toluene vapors with concentrations ranging from 1 to 26,000 ppm, and the limit of detection for toluene is calculated to be 0.4 ppm. Eighteen VOC vapors were tested and each type exhibited different calibration curves, but these differences depend on the adsorption characteristics of porous silica rather than on the refractive index of the VOCs.
    Sensors and Actuators B Chemical 01/2014; 196:1–9. · 3.54 Impact Factor
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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.
    Advanced Powder Technology 09/2012; 23(5):562-565. · 1.65 Impact Factor
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    ABSTRACT: Twenty three kinds of metal oxides were screened as supports for Aunanoparticles (Au NPs) in the gas phase oxidation of ethanol. Mild oxidation to acetaldehyde, which is economically preferable, is catalyzed by Au NPs deposited on catalytically inert metal oxides, in particular, strongly acidic MoO3 or weakly basic La2O3. Deep oxidation to acetic acid takes place over Au NPs deposited on n-type semiconductive metal oxides such as ZnO and V2O5, which exhibit a little catalytic activity for ethanol oxidation at 200 °C. Complete oxidation to CO2 and H2O preferentially takes place over p-type semiconductive metal oxides such as MnO2 and Co3O4, and CeO2 which has oxygen-storage and discharge capability. These metal oxides show catalytic activity for ethanol oxidation even at 100 °C producing mainly acetaldehyde, and their catalytic activity is noticeably enhanced in the conversion of ethanol and the selectivity to CO2 by the deposition of Au NPs. The wide range of product tunability can be explained by the adsorption structures of ethanol and by the reactivities of oxygen species on the metal oxide supports.
    New Journal of Chemistry 09/2011; 35(10):2227-2233. · 2.97 Impact Factor
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    Chemistry 01/2011; 17(1):78-81. · 5.93 Impact Factor
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    ABSTRACT: Gold was deposited on alkaline-treated TS-1 (TS-1-Na1) to prepare Au/TS-1-Na1(DP) by deposition–precipitation (DP) and Au/TS-1-Na1(SG) by solid grinding (SG). 129Xe NMR technique has detected that tiny Au clusters have been incorporated into the microporous channels of Au/TS-1-Na1(DP), while they were absent inside the microporous channels of Au/TS-1-Na1(SG). On the other hand, HAADF-STEM observation showed that the amount of Au clusters (1.0–2.0nm) over the exterior surfaces was much larger in Au/TS-1-Na1(SG) than in Au/TS-1-Na1(DP). In propene epoxidation with O2 and H2, Au/TS-1-Na1(SG) exhibited much higher PO formation rate (127gPOkgcat-1h−1) than Au/TS-1-Na1(DP) (74gPOkgcat-1h−1), indicating that Au clusters with diameters of 1.0–2.0nm are more active for PO synthesis than tiny Au clusters incorporated inside the microporous channels.
    Journal of Catalysis - J CATAL. 01/2011; 278(1):8-15.
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    ABSTRACT: A AuLa2(OH)9 coprecipitate calcined in air at temperatures below 450K showed surprisingly high catalytic activity for CO oxidation, 100% conversion at a temperature as low as 193K, when it was reduced in a N2 stream containing H2 or CO at 373K. The reduction treatment transformed Au(OH)3 species interacting with the La(OH)3 support into Au0 clusters smaller than 1.8nm in diameters.
    Chemical Physics Letters 01/2010; 493(4):207-211. · 2.15 Impact Factor
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    ABSTRACT: Gold could be deposited as clusters smaller than 2.0 nm in diameter on TS-1 by solid grinding (SG) of the support with dimethyl Au(III) acetylacetonate after TS-1 was pretreated in aqueous solution of alkaline metal hydroxides. While in C3H6 epoxidation with O2 and H2 mixture Au nanoparticles larger than 2.0 nm deposited on TS-1 without alkaline treatment gave a very low PO formation rate of 11 gPO kgcat.−1 h−1, Au clusters on alkaline treated TS-1 presented a greatly enhanced rate as high as 137 gPO kgcat.−1 h−1, which was comparable to the best data reported so far. In addition, very high H2 efficiency reaching 47% could be obtained by gold clusters on alkaline treated TS-1.
    Applied Catalysis B: Environmental. 01/2010; 95:430-438.
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    ABSTRACT: The influence of the preparation methods (IP:impregnation, DP:deposition-precipitation, SG:solid grinding) for Pt/CeO2 and Au/CeO2 was studied on the size and shape of metal particles and the catalytic activity for CO oxidation. The fine structures of these catalysts were examined by HR-TEM and were correlated to their catalytic properties. The size of metal particles depended on the preparation methods and increased in the order of DP
    Studies in Surface Science and Catalysis - STUD SURF SCI CATAL. 01/2010; 175:843-847.
  • Angewandte Chemie International Edition 09/2009; 48(42):7862-6. · 11.34 Impact Factor
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    ABSTRACT: Heterogeneous catalysts that can work at ambient temperature are useful for in-door air quality control, pure gas production for fuel cells and semiconductors, gas sensing, and so forth. Deposition of gold nanoparticles on base metal oxide is known to provide highly active catalysts for CO oxidation at temperatures below room temperature. Here we report that some select base metal oxides such as Co3O4, MnO2, and NiO are intrinsically active catalysts for CO oxidation below 50°C when pretreated at moderate temperature between 150 and 250°C in a stream of non-reducing dry gases, for example, dry air, CO in air, or N2. These metal oxides are p-type semiconductors and form surface excess oxygen adsorbed at oxygen vacancies which are created by the above pretreatments.
    Journal of Catalysis. 01/2009; 267(2):121-128.
  • Angewandte Chemie International Edition 11/2008; 47(48):9265-8. · 11.34 Impact Factor
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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.
    Advanced Powder Technology 01/2007; 18:81-91. · 1.65 Impact Factor
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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.
    Chemical Communications 11/2006; · 6.38 Impact Factor
  • Key Engineering Materials - KEY ENG MAT. 01/2006; 301:91-94.
  • Key Engineering Materials - KEY ENG MAT. 01/2006; 301:143-146.
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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.
    European Journal of Pharmaceutical Sciences 10/2005; 26(1):87-96. · 2.99 Impact Factor
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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.
    Journal of Colloid and Interface Science 01/2004; 268(2):435-40. · 3.55 Impact Factor
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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.
    Colloid and Polymer Science 10/2003; 281(12):1121-1126. · 2.16 Impact Factor
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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.
    International Journal of Pharmaceutics 09/2003; 262(1-2):75-82. · 3.99 Impact Factor
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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.
    Journal of Colloid and Interface Science 12/2002; 255(1):171-6. · 3.55 Impact Factor