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

由硬脂酸银壳和银核组成的纳米粒子在低于金属银熔点(960℃)的温度(340℃)下加热，得到金属块状银。纳米颗粒的质量降低了20%，相当于硬脂酸盐壳的数量。低温金属化是硬脂酸银壳热分解成银的结果。它包括两个步骤。第一个反应发生在2 5 0℃，分解为多孔银粒子的反应为一级反应，反应活化能为111kJ mol-1~(-1)。对6种直径4.7 nm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，揭示了烷基羧酸盐对纳米…的光学、热、几何和电化学性能的影响更多的ES。这些纳米粒子由碳原子数为8到18的偶数m的银原子和烷基羧酸银组成。通过化学氧化、伏安电流和热重分析，用滴定的方法计算了每个纳米粒子中银原子(n_lt；Ag&gt；)和烷基羧酸盐(N_S)的数量之比，以衡量纳米粒子的结构。随m的增加而增加，变化范围为1.3~9.8。纳米粒子的紫外-可见吸收光谱的吸光度与n_t；Ag&gt；成正比，其伏安电流值与粒子本身扩散时的理论值接近，并具有m-独立的热分解动能和还原过电位。在表面活性剂存在下，用肼还原醋酸钯制备了直径0.23μm的球形钯粒子，其目的是既易于过滤分离，又易于作为催化剂分散。悬浮液中的颗粒是缓慢沉淀的，但没有聚集。悬浮液呈现伏安氧化还原波峰。阳极波归因于Pd氧化为Pd^-lt；2+-gt；，而阴极波归因于Pd的醋酸钯部分还原为Pd。阳极峰与阴极峰的电流比为4：1，接近高锰酸盐部分化学氧化法和热重法的值，表明金属钯的摩尔比为80%，醋酸钯的摩尔比为20%。加热钯颗粒得到300℃的金属钯。该粒子催化联氨还原亚甲基蓝。亚甲基蓝的反应速率为一级反应。反应速率常数与钯颗粒的几何表面积成正比，表明该催化剂具有表面催化作用。较少

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