Iwao Watanabe

Ritsumeikan University, Kioto, Kyōto, Japan

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Publications (100)228.78 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The total reflection X-ray absorption fine structure (TR-XAFS) technique was applied to adsorbed films at the surface of aqueous solutions of surfactant mixtures composed of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium tetrafluoroborate (DTABF(4)). The obtained XAFS spectra were expressed as linear combinations of two specific spectra corresponding to fully hydrated bromide ions (free-Br) and partially dehydrated bromide ions adsorbed to the hydrophilic groups of surfactant ions (bound-Br) at the surface. The ratio of free- and bound-Br ions was determined as a function of surface tension and surface composition of the surfactants. Taking also the results in our previous studies on the DTAB - dodecyltrimethylammonium chloride (DTAC) and 1-hexyl-3-methylimidazolium bromide (HMIMBr) - 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF(4)) mixed systems into consideration, the relation between counterion distribution and miscibility of counterions at the solution surface was deduced for the surfactant mixtures having common surfactant ions but different counterions.
    Journal of Colloid and Interface Science 08/2012; 388(1):219-24. · 3.55 Impact Factor
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    Bunseki kagaku 01/2010; 59(6):447-454. · 0.22 Impact Factor
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    ABSTRACT: The miscibility and distribution of Br(-) and BF(4)(-) ions of imidazolium ionic liquid mixtures, 1-hexyl-3-methylimidazolium bromide (HMIMBr) + 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF(4)), at the air/water surface were investigated by surface tensiometry and the total-reflection XAFS (TRXAFS) method. Tensiometry showed that the surface density of BF(4)(-) was much larger than that of Br(-), the adsorbed films of the HMIMBr-HMIMBF(4) mixture were greatly enriched in BF(4)(-) at all surface tensions, and the excess Gibbs energy of adsorption was positive. However, TRXAFS revealed that the Br ions were all in the free-Br state solvated by six water molecules in the mixed adsorbed film. Entropy-originated nonideal mixing, where a kind of segregation of the counterion distribution takes place in the interfacial region, was suggested in the mixture.
    Langmuir 10/2009; 25(17):9954-9. · 4.38 Impact Factor
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    ABSTRACT: Copper(II) complexes spread on an aqueous solution surface were studied by a polarized total-reflection X-ray absorption fine structure (TR-XAFS) technique. The polarized TR-XAFS spectra at the Cu-K edge for copper(II) porphyrins and copper(II) chlorophyllin in a monolayer were measured in situ at the air-water interface. The polarization dependences of X-ray absorption near-edge structure (XANES) involving a 1s-->4p(z) transition allowed us to estimate the molecular orientation and the local coordination structure around the copper(II) atom in the polarization plane selectively. The extended X-ray absorption fine structure (EXAFS) region of the polarized TR-XAFS spectra for the metal complexes present at the air-water interface was successfully analyzed for the first time. The relative coordination number for the copper center evaluated from the EXAFS analysis indicated larger values in the vertical polarization than in the horizontal one, in agreement with the standing-up molecular orientation at the air-water interface estimated from the XANES region.
    Analytical Sciences 05/2009; 25(4):475-80. · 1.57 Impact Factor
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    ABSTRACT: The adsorbed film of 1-decyl-3-methylimidazolium bromide (DeMIMB) at the air/water interface was investigated employing the surface tension measurement and the x-ray absorption fine structure method under the total reflection condition (TRXAFS). From the surface tension measurement, the surface excess concentrations of ions were determined. From the XAFS measurement, two solvation states of bromide ion were found in the adsorbed film, which were assigned to be "free-Br" and "bound-Br". The hydration number of the former was estimated to be 6 while that of the latter was estimated to be 4. The results based on the XAFS analysis provided significant information on the formation of domains in the adsorbed film; the most conceivable situation is that the adsorbed molecules are definitely not homogeneously dispersed, but domains (islands or clusters) are dispersed in the adsorbed film. A regular and rather tight stacking of immidazolium rings may be formed in the domains.
    Analytical Sciences 11/2008; 24(10):1279-83. · 1.57 Impact Factor
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    ABSTRACT: The total-reflection XAFS measurement possessing bromide ion selectivity at the interfacial region was applied to the adsorbed film of hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium bromide (DTAB) mixture. The surface compositions XjH of individual ions j ( j = HTA+, Cl(-), DTA+, and Br (-)) were evaluated by combining the surface excess concentration of Br(-) estimated from the XAFS with the surface composition of the respective surfactants from the surface tension results. It is clearly shown that HTA+ and Br(-) are preferentially adsorbed to DTA+ and Cl(-) at the air/water interface. The preferential adsorption was estimated numerically in terms of activity coefficient fi+/-(H,p) of component i and excess Gibbs energy of adsorption ĝprH,E. Then, the magnitude of ĝprH,E was compared with that of ĝprH,E attributable to intrinsic interaction between ions.
    Langmuir 08/2008; 24(13):6693-7. · 4.38 Impact Factor
  • Analytical Sciences 01/2008; 24(10):1279-1283. · 1.40 Impact Factor
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    ABSTRACT: Temperature dependence of EXAFS was analyzed for Mo6O192 and W6O192- compounds. The Fourier transform peak for bridging Mo-O bond is quite smaller than that for other Mo-O bonds in Mo6O192-. Such a phenomenon was not observed in W6O192-. That reason of small peak is abnormally large Debye-Waller factor for this bond, which comes from the large static fluctuation of the bridging Mo-O bonds.
    02/2007;
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    ABSTRACT: The total-reflection X-ray absorption fine structure (XAFS) method previously employed for the adsorption of dodecyltrimethylammonium bromide (DTAB) at the air/water interface was applied to that in the presence of NaBr. The surface concentration of the bromide ions Gamma(X)(B) of DTAB and NaBr was evaluated by using the Br K-edge absorption jump values of the total-reflection XAFS spectra and was compared to the corresponding value Gamma(H)(B) estimated from the dependence of surface tension on the bulk concentrations of DTAB m(1) and NaBr m(2). The Gamma(X)(B) values trace almost perfectly the Gamma(X)(B) versus m(1) curve up to a concentration near the critical micelle concentration (cmc) and deviate gradually above the concentration. This behavior is basically similar to that of the single DTAB system and ensures that the XAFS method is also applicable to the DTAB system, even in the presence of NaBr. In addition, this method was extended to the single nonionic amphiphile with covalently bonded bromine, and the surface concentrations of 6-bromo-1-hexanol (BrC6OH), Gamma(X)(1) and Gamma(H)(B), were evaluated and compared with each other. It was found that the Gamma(X)(1) value almost perfectly traces the Gamma(H)(1) versus m(1) curve, even at high surface concentrations. The excellent coincidence confirmed that the total-reflection XAFS method can be applied to the nonionic amphiphile system as well as a cationic surfactant with or without an added salt system. Finally, the difference between the Gamma(X)(B) and Gamma(H)(B) values observed in the DTAB with and without an added salt system is briefly described.
    Langmuir 10/2006; 22(20):8403-8. · 4.38 Impact Factor
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    ABSTRACT: The behavior of monolayer films of free base 5,10,15,20-tetrapyridylporphinato (TPyP) and 5,10,15,20-tetrapyridylporphinato zinc(II) (ZnTPyP) on pure water, 0.1 M CdCl2, and 0.1 M CuCl2 subphases was investigated by surface pressure-area isotherms, specular X-ray reflectometry, and polarized total reflection X-ray absorption spectroscopy (PTRXAS). Surface pressure-area isotherms showed significant differences in the area per molecule on pure water compared to that on salt subphases, with a marked increase in the area observed on the salt solutions. This behavior was noted for both forms of the porphyrin and both salts investigated. Modeling of specular X-ray reflectometry data indicated that thinner and more electron dense layers on salt subphases best fit the observed profiles. These data suggest that the porphyrin macrocycle is oriented parallel to the interface on salt subphases and takes on a tilted conformation on pure water. In the case of ZnTPyP, PTRXAS was used to determine the orientation of the porphyrin moiety relative to the surface and to probe the coordination of the central Zn ion. In agreement with the pressure-area isotherms and reflectometry, the PTRXAS data indicate a change in orientation on the salt subphases.
    Langmuir 02/2006; 22(2):681-6. · 4.38 Impact Factor
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    ABSTRACT: The polarized total-reflection X-ray absorption fine structure method was applied to characterize zinc porphyrins at the air-water interface. The X-ray absorption near edge structure exhibited a significant difference depending on the polarization of the X-ray. A shoulder peak of the Zn K-edge corresponding to the 1s-4p(z) transition for a square planar metal complex without axial coordination(s) was observed at 9662 eV, which indicates that the axial coordination sites of zinc porphyrin molecules examined are not fully hydrated at the air-water interface. The molecular orientation of zinc porphyrins was determined by analyzing the polarization dependence of the transition peak intensity. The meso-substituted porphyrin derivative 5,10,15,20-tetraphenylporphyrinatozinc(II) (ZnTPP) orients rather parallel to the solution surface. In contrast to ZnTPP, the zinc(II) protoporphyrin IX (ZnPP) with hydrophilic carboxyl groups at one side of the molecule stands up with respect to the solution surface, and the average tilting angle of the porphyrin plane to the surface was evaluated to be between 57 degrees and 43 degrees. In addition, the axial coordination of ZnPP is modified depending on the surface concentration, in which the axial hydration to the zinc center is effectively inhibited in the compressed surface layer.
    Langmuir 02/2006; 22(1):209-12. · 4.38 Impact Factor
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    ABSTRACT: The mole fraction of chloride ion of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) mixture in the adsorbed film XHC was estimated not only by the thermodynamic analysis of the surface tension data but also by analyzing the Br K-edge jump of the XAFS spectrum under the total reflection condition (TRXAFS method). The phase diagrams of adsorption (PDA) at several surface tensions from the two methods were in good agreement. On the basis of the PDA obtained, it was clearly shown that the criterion of an ideal mixing for the DTAB-DTAC system is not given by the linear relation between the total molality of surfactant mixture m and XHC, m = m0B + (m0C - m0B)XHC, but by the one between m2 and XHC, m2 = (m0B)2 + [(m0C)2 - (m0B)2]XHC. Furthermore, it was demonstrated that the theoretical approach that provides the latter relation draws a distinction between the criteria for an ionic surfactant mixture without a common ion and that for an ionic surfactant mixture with a common ion.
    Langmuir 09/2005; 21(16):7398-404. · 4.38 Impact Factor
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    ABSTRACT: Changes in the electronic structure of olivine Li(1-x)CoPO(4), 4.8 V positive electrode material for lithium ion batteries, were investigated using the X-ray absorption spectroscopy (XAS) technique. The threshold energy in the Co K-edge increased with electrochemical Li removal, indicating the oxidation of cobalt ions due to charge compensation. Moreover, P and O K-edge XAS showed a slight shift in threshold energy with Li removal. Although it is generally believed that the electrons of PO(4) polyanion do not contribute to the oxidation process, present experimental results indicate changes in the electronic structure around PO(4) units. Such results would be interpreted by the idea of the hybridization effect between the Co 3d and O 2p orbitals and of the polarization effect introduced by Li ions.
    The Journal of Physical Chemistry B 07/2005; 109(22):11197-203. · 3.38 Impact Factor
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    ABSTRACT: We have investigated the local structure of Ag nano-clusters deposited as thin films on silicon substrate by using a total conversion electron yield XAFS (X-ray absorption fine structure) method atAg K-edge. High quality spectra were obtained from samples with thicknesses of 1–10 nm. We have found that these clusters have an fcc structure and that the interatomic distance does not depend on the thickness. The coordination number, N, however, changes with the thickness of the film. The N value for the first nearest shell as a function of the film thickness is compared with the theoretically expected value by taking account of the surface effect. For thinner films, the observed N values are smaller than the expected values. We have observed a correlation between the N value and the electromagnetic field intensity at the surface evaluated from IR measurement. The morphology of Ag nano-cluster particles must affect the local electric field intensity at the surface.
    Physica Scripta 01/2005; · 1.30 Impact Factor
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    ABSTRACT: A detailed investigation of the local structural changes with lithiated perovskite oxides, LixLa1/3NbO3, has been carried out using extended X-ray absorption fine structure (EXAFS) measurements. From Nb K-edge EXAFS measurement, the interatomic distance of first shell Nb−O interaction increased with the composition x by electrochemical Li+ insertion. This behavior ascribed to the expansion of Nb ion due to the reduction of Nb5+ to Nb4+. On the other hand, La K-edge EXAFS measurement showed that the interatomic distance of the first shell La−O interaction decreased with the lithiation reaction. Furthermore, those of second shell Nb−La and third shell Nb−Nb and La−La bonds tended to be unchanged with reaction. Such a complicated behavior in the change of each interatomic distance with lithium insertion can be understood by the model of tilting of NbO6 octahedra in the perovskite structure.
    The Journal of Physical Chemistry B 09/2003; 107(39):10715-10721. · 3.38 Impact Factor
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    ABSTRACT: A new x-ray absorption fine structure (XAFS) method is applied to the air–solution interface. Under the total reflection condition, the XAFS method becomes surface sensitive, enabling the self-assembled monolayer of a metal complex at the solution surface to analyze in situ. Furthermore the introduction of two types of linearly polarized x rays allows us to determine the selective orientation of a planar metal complex at the surface. We obtain spectra for a square planar complex, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato zinc(II) (ZnTPPC) adsorbed on the aqueous solution surface forming a monolayer with two polarized x rays and compared them with spectra of the same compound in a bulk solution and in solid powder. The polarized XAFS spectra exhibit different features leading to the unambiguous conclusion that the plane of the ZnTPPC molecule is oriented parallel to the air–water interface and that there is no coordination to the axial sites of the zinc atom. © 2003 American Institute of Physics.
    The Journal of Chemical Physics 06/2003; 118(23):10369-10371. · 3.12 Impact Factor
  • Makoto Harada, Tetsuo Okada, Iwao Watanabe
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    ABSTRACT: The adsorption isotherms of Zn2+ and Br- on a zwitterionic surface monolayer and their local structures have been studied by total-reflection total-conversion helium ion yield X-ray absorption fine structure (TRTCY-XAFS). The surface monolayer is prepared by spontaneous adsorption of N-dodecyl-N,N-dimethylammonio-butane sulfonic acid (DDABS) on an aqueous solution surface from a bulk solution. The adsorption of Zn2+ on the surface monolayer depends on the nature of coexistent anions; a poorly hydrated large anion such as ClO4- are well partitioned into the DDABS monolayer, and Zn2+ is attracted by generated negative potential. TRTCY-XAFS spectra indicate that Zn2+ attracted by the surface monolayer is mostly hydrated, but is partly bound by the sulfonic acid in DDABS, particularly when the large negative potential is induced by anion-partition. The TRTCY-XAFS spectra of Br- also imply the coexistence of hydrated Br- and that bound by the ammonium group in the surface monolayer. The calculation using FEFF, ver.7.02, suggests that the interaction distance between Br- and water in the surface monolayer (3.15 Å) is shorter than that in bulk water (3.20 Å). In the surface monolayer, the availability of water molecules is limited, and thus the second coordination shell cannot be formed around Br-. This weakens the interaction between water molecules, and results in the shorter coordination distance for Br-.
    The Journal of Physical Chemistry B 02/2003; 107(10). · 3.38 Impact Factor
  • Hajime Tanida, Ken-ichi Kato, Iwao Watanabe
    Bulletin of the Chemical Society of Japan 01/2003; 76(9):1735-1740. · 2.22 Impact Factor
  • Bunseki kagaku 01/2003; 52(6):405-418. · 0.22 Impact Factor
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    ABSTRACT: The compound system, Mn1−xMo2xV2(1−x)O6 (0 ≤ x ≤ 0.4), synthesized by solid state reaction forms the brannerite structure. The electrochemical reaction mechanism as the anode for Li secondary batteries was investigated. X-ray diffraction (XRD) analysis clearly indicated that Mn0.6Mo0.8V1.2O6 anode irreversibly transformed from crystalline brannerite to amorphous phase via a rock-salt type structure during the first lithium insertion/removal reaction. The charge compensation and the change in the local environmental structure during the Li insertion/removal were confirmed by X-ray absorption fine structure (XAFS) of manganese, vanadium and molybdenum.
    Journal of Materials Chemistry 01/2003; 13(4):897-903. · 6.63 Impact Factor

Publication Stats

550 Citations
228.78 Total Impact Points

Institutions

  • 2009–2012
    • Ritsumeikan University
      Kioto, Kyōto, Japan
  • 2006
    • Hyogo University of Teacher Education
      Yashiro, Hyōgo, Japan
    • Kyushu University
      • Faculty of Sciences
      Fukuoka-shi, Fukuoka-ken, Japan
  • 2002–2005
    • Osaka Women's University
      Sakai, Ōsaka, Japan
    • Tokyo Institute of Technology
      • • Department of Applied Chemistry
      • • Chemistry Department
      Tokyo, Tokyo-to, Japan
  • 2001
    • University of Yamanashi
      • Center for Instrumental Analysis
      Kōhu, Yamanashi, Japan
    • Hirosaki University
      • Faculty of Science and Technology
      Khirosaki, Aomori Prefecture, Japan
  • 1973–2000
    • Osaka University
      • Department of Chemistry
      Ōsaka-shi, Osaka-fu, Japan