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Properties of shells and cores of fatty metal nanoparticles by means of electrochemical analysis

通过电化学分析研究脂肪金属纳米粒子的壳和核的性质

基本信息

批准号：
16550070
负责人：
CHEN Jingyuan
金额：
$ 2.37万
依托单位：
University of Fukui
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

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 … More 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

由硬脂酸银壳和银核组成的纳米粒子在低于银金属熔点（960℃）的温度（340℃）下加热成为金属块状银。纳米颗粒的质量减少了 20%，相当于硬脂酸盐壳的质量。低温金属化是由于硬脂酸银壳热分解成银的结果。它涉及两个步骤。第一个发生在250℃，通过一级反应分解成多孔银颗粒，活化能为111 kJ mol^-1。第二个是在340℃下发生的，从多孔颗粒到银块状晶体的结构变化。对六种直径为4.7nm的烷基羧酸盐稳定的银纳米粒子进行了光谱、化学、热和伏安分析，旨在揭示烷基羧酸盐对银纳米粒子的光学、热学、几何和光学性能的影响。纳米颗粒的电化学特性……更多 es。这些纳米粒子由银原子和具有8至18个碳原子的偶数m的烷基羧酸银组成。作为纳米粒子结构的量度，通过化学氧化、伏安电流和热滴定来评估每个纳米粒子的银原子数(n_<Ag>)与烷基羧酸盐数(n_s)的比率。重量分析。它随着m的增加而增加，范围为1.3至9.8。纳米粒子的性质表现在与n_<Ag>成正比的点处的紫外-可见光谱吸光度、接近粒子本身扩散理论值的伏安电流、热分解的m独立动能和还原过电势。直径为0.23μm的钯球形粒子通过在表面活性剂存在下用肼还原乙酸钯来合成，旨在表现出易于过滤分离和催化剂易于分散的特点。悬浮液中的颗粒缓慢沉降但不聚集。悬浮液显示伏安氧化还原波。阳极波归因于Pd氧化成Pd 2+ ，而阴极波归因于乙酸钯部分还原成Pd。阳极峰与阴极峰的电流比为4:1，与高锰酸盐部分化学氧化和热重分析的比值接近，表明摩尔比为80%金属钯和20%乙酸钯的组成。将钯颗粒加热至300℃产生钯金属。该颗粒催化亚甲基蓝与肼的还原。相对于亚甲基蓝，反应速率为一级。速率常数与钯颗粒的几何表面积成正比，表明存在表面催化作用。较少的