| Research Abstract |
The nanoparticles composed of a silver stearate-shell and a silver-core became metallic bulk silver by heating at temperature (340℃) lower than the melting point of silver metal (960℃). The nanoparticles decreased the mass by 20%, which was equivalent to the amount of the stearate shell. The low temperature metallization resulted from the thermal decomposition of the shell of silver stearate into silvers. It involved two steps. The first, occurring at 250℃, was the decomposition into porous silver particles through the first order reaction with an activation energy of 111 kJ mol^<-1>. The second, occurring at 340℃, was structure change from the porous particles into the silver bulk crystals.
Spectroscopic, chemical, thermal, and voltammetric analyses on six kinds of alkylcarboxylates-stabilized silver nanoparticles 4.7nm in diameter were carried out with an aim to reveal the effect of alkylcarboxylates on the optical, thermal, geometric, and electrochemical properties of the nanoparticl
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es. These nanoparticles are composed of silver atoms and silver alkylcarboxylates having even numbers, m, of carbon atoms from 8 to 18. As a measure of the structure of the nanoparticles, the ratio of the number silver atoms (n_<Ag>) to that of alkylcarboxylates (n_s) per nanoparticle was evaluated by means of titration through chemical oxidation, voltammetric currents, and thermal gravimetric analysis. It increased with an increase in m and ranged from 1.3 to 9.8. Properties of the nanoparticle have been exhibited in absorbance of the UV-vis spectra at the point of the proportionality to n_<Ag>, voltammetric currents of which values were close to the theoretical values at the diffusion of particle itself, and the m-independent kinetic energy of the thermal decomposition and the overpotential of the reduction.
Palladium spherical particles 0.23μm in diameter were synthesized by reducing palladium acetate with hydrazine in the presence of surfactant, aiming at exhibiting both easy separation by filtration and easy dispersion for a catalyst. The particles in the suspension were sedimented slowly but not aggregated. The suspension showed voltammetric redox waves. The anodic wave was ascribed to the oxidation of Pd to Pd^<2+>, whereas the cathodic one was to the reduction of the palladium acetate moiety to Pd. The current ratio of the anodic peak to the cathodic peak, 4:1, was close to the ratios by the partial chemical oxidation with permanganate and by the thermogravimetry, suggesting the composition of 80% palladium metal and 20% palladium acetate in the molar ratio. Heating of the palladium particles yielded palladium metal at 300℃. The particle catalyzed the reduction of methylene blue with hydrazine. The reaction rate was of the first-order with respect to methylene blue. The rate constant was proportional to the geometrical surface area of the palladium particle, suggesting a surface catalysis. Less
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