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A comparative investigation of electrocatalytic and adsorption properties of platinum microparticles electrodeposited onto a glassy carbon surface (Pt/GC) and within a thin Nafion® film formed on a GC electrode (Pt/Nf/GC) is described. As test reaction the methanol oxidation in sulfuric acid solutions is used. Dependences of the steady-state specific reaction rates upon potential and methanol concentration were established, as well as those of the platinum surface coverage with methanol chemisorption products upon concentration. It was shown that at higher platinum loadings (above 60 μg cm−2) the specific activities of Pt/GC and Pt/Nf/GC are nearly the same and close to that of smooth platinum. At such loadings the surface coverage of the platinum deposit surface with organic particles does not differ from that of smooth platinum. At very low platinum loadings in the polymeric matrix (10–30 μg cm−2) a considerable decrease in the adsorption of strongly chemisorbed methanol particles is observed. These deposits are characterized by a low specific activity, which may be caused by the decrease of the platinum particle’s size, leading to a decrease in the amount of weakly bound methanol particles participating in the limiting reaction step. 相似文献
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Y. Mikhaylova E. Pigorsch K. Grundke K.-J. Eichhorn B. Voit 《Macromolecular Symposia》2004,210(1):271-280
Thin films of hydroxyl (POH) and carboxyl (PCOOH) terminated aromatic hyperbranched polyesters (HBPs) were prepared by spin coating on silicon wafers and subsequently annealed above their glass transition temperature (Tg). The surface properties and the swelling behaviour of these films in aqueous buffer solutions were studied as a function of annealing time using contact angle measurements and ellipsometry. Non-annealed films were hydrophilic with surface free energies of 51 mJ/m2 for POH and 49 mJ/m2 for PCOOH, respectively. The swelling behaviour of the polymer films in buffer solution with pH 7.4 was described in terms of changes of the thickness and effective refractive index of the swollen layer. Under identical conditions a lower water uptake was found for hydroxyl terminated HBPs (POH) which were annealed more then 2 h. The lower water uptake correlates with the surface properties of the films. The annealed films were less hydrophilic. Their surface free energy was 38 mJ/m2 independent of the annealing. Films of carboxyl terminated HBPs (PCOOH) showed similar surface properties after annealing. However, these films were unstable under the same conditions in aqueous solutions. Stable PCOOH films were obtained by additional covalent binding to the substrate using an epoxy silane as a coupling agent. 相似文献
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Mikhaylova M. Jo Y. S. Kim D. K. Bobrysheva N. Andersson Y. Eriksson T. Osmolowsky M. Semenov V. Muhammed M. 《Hyperfine Interactions》2004,159(1-4):257-260
The g-factor of the exteremely proton-rich nucleus 23Al(T
1 / 2 = 0.47 s) has been measured for the first time, applying β-NMR technique on this nucleus implanted in Si. The obtained ∣g∣ = (1.58 ± 0.2) suggests that the spin of the ground state of 23Al is 5 / 2. The magnetic moment is determined as ∣μ∣ = (3.95 ± 0.55) μ
N
. 相似文献
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Tusseeva E. K. Mikhaylova A. A. Khazova O. A. Kourtakis K.-D. 《Russian Journal of Electrochemistry》2004,40(11):1146-1151
Possibilities for production of active Pt–Ru electrodes for the direct methanol fuel cell with a decreased content of platinum-group metals in them are studied. Platinum and ruthenium are electrodeposited on a thin layer of carbon black applied to a Nafion 117 membrane. The deposition potential effect on the specific surface area of the catalyst and its electrochemical activity in the methanol oxidation is studied. The oxidation currents are related to unit true surface area or unit catalyst mass. The dependence of activity on the Pt : Ru ratio in the plating solution and in the deposit is studied. The effect of the catalyst amount deposited and the particle size on the activity is studied. It is shown that the catalytic activity decreases at the average diameter of Pt–Ru particles less than 4 nm. The results are compared with the size effects observed earlier. 相似文献
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Vikulova E. S. Sukhikh A. S. Mikhaylova M. A. Nazarova A. A. Zherikova K. V. Morozova N. B. 《Journal of Structural Chemistry》2022,63(8):1323-1332
Journal of Structural Chemistry - Structures of volatile mixed-ligand complexes of magnesium with N,N,N′,N′-tetramethylethylenediamine (tmeda) and fluorinated β-diketonate ligands... 相似文献
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Mikhaylova M Kim DK Bobrysheva N Osmolowsky M Semenov V Tsakalakos T Muhammed M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(6):2472-2477
Superparamagnetic iron oxide nanoparticles (SPION) with an average particle diameter of 6 nm are prepared by controlled chemical coprecipitations. Colloidal suspensions of noninteracting SPION, where the surface has been modified with three different types of biocompatible substances, namely, starch, gold (Au), and methoxypoly(ethylene glycol) (MPEG) have been fabricated via three different techniques. Starch-coated SPION are prepared by coprecipitation in a polymeric matrix, Au-coated SPION are fabricated by the microemulsion method, and MPEG-coated SPION are prepared using the self-assembly approach. The magnetic nanoparticles form a core-shell structure, and the magnetic dipole-dipole interactions are screened by a layer of coating agents. The amounts of coating agents and SPION are indirectly calculated from the thermogravimetric analysis and superconducting quantum interference device measurements by assuming passive oxidation on the surface of the SPION, and the other conditions do not influence the measurements. The dependency of the spectral characteristics of M?ssbauer spectroscopy as a function of an external magnetic field Hext is measured to investigate the effect of dipole-dipole screening of the different coating layers on the SPION. Uncoated SPION show a stable magnetic moment under Hext, and the superparamagnetic (SPM) fraction transforms to a ferrimagnetic state. Starch and Au-coated SPION retain the SPM fraction according to M?ssbauer spectroscopy and magnetization measurements. MPEG-coated SPION show hyperfine magnetic structure without the quadrupole effect with increasing the value of the blocking temperature. 相似文献
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A. A. Mikhaylova E. K. Tusseeva A. Yu. Rychagov Yu. M. Vol’fkovich A. V. Krestinin O. A. Khazova 《Russian Journal of Electrochemistry》2010,46(11):1280-1288
Composites of functionalized single-wall carbon nanotubes and polyaniline are deposited onto electrodes by in situ electrochemical
polymerization. Their electrochemical behavior and differential capacitance are studied by cyclic voltammetry, electrochemical
impedance spectroscopy, and chronovoltamperometry. The differential capacitance of the composite electrode exceeds that of
pure polyaniline film deposited onto electrode, which can be explained by the nanotubes’ loosening effect on the polyaniline
structure. The composite-electrode capacitance is as large as 1000 F g−1 or higher. Thus obtained composite films were used as a support for deposited platinum-ruthenium catalyst. The Pt-Ru structure
and catalytic properties in the methanol oxidation reaction are studied. It is shown that the specific current of methanol
oxidation at Pt-Ru is larger by a factor of 7–15 than those measured when pure polyaniline, pure carbon nanotubes, or standard
Vulcan XC-72 carbon black are used as supports. It is found that the catalytic activity is the same for all studied supports,
provided the current is reduced to the unit of Pt-Ru true surface area. Thus, the observed large catalytic effect is associated
with the structure and high dispersivity of the electrodeposited metals incorporated to the single-wall carbon nanotubes-polyaniline
composite. 相似文献
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Salazar-Alvarez G Qin J Sepelák V Bergmann I Vasilakaki M Trohidou KN Ardisson JD Macedo WA Mikhaylova M Muhammed M Baró MD Nogués J 《Journal of the American Chemical Society》2008,130(40):13234-13239
The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, T(B), of the nanoparticles depends on their shape, with the spherical ones exhibiting larger T(B). Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects. 相似文献
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