A pH-Induced Size Controlled Deposition of Colloidal Ag Nanoparticles on Alumina Support for Catalytic Application
A pH-Induced Size Controlled Deposition of Colloidal Ag Nanoparticles on Alumina Support for Catalytic Application
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DOI：
10.1021/jp907277g
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发表时间：
2009-10-01
影响因子：
3.7
通讯作者：
Yamashita, Hiromi
中科院分区：
文献类型：
--
作者：
Mori, Kohsuke;Kumami, Akihito;Yamashita, Hiromi
提出了一种合理的负载型金属催化剂的合成方法。高度分散的银纳米粒子（NPs）的平均直径约为。以3-巯基丙酸（3-MPA）为保护剂，制备了粒径为10 nm、粒径分布窄的纳米级超细粉体。在pH高于5的区域内，Ag纳米粒子的zeta电位带负电荷，这是由于解离的羧酸根离子（-COO-）的存在，导致Ag纳米粒子之间的电排斥。另一方面，电荷逐渐增加的区域中的pH值小于5由于形成质子化的羧基（-COOH），这诱导了银纳米粒子之间的氢键。这种pH触发的组装分散控制使得能够通过静电吸引在带正电荷的Al 2 O3载体上沉积具有不同直径的存款Ag NP的强方案。采用紫外-可见光谱和透射电镜对所制备的Ag/Al 2 O3材料进行了表征，并考察了其在水中还原对硝基苯酚反应中的催化活性。反应速率随着制备的胶体溶液的pH的增加而增加，这与Ag纳米颗粒的尺寸减小有关。4-硝基苯酚的还原被认为是结构不敏感的反应，并且通过对Ag微晶进行计算，Ag纳米颗粒的所有表面原子在该尺寸范围内作为相同的活性物质起催化作用。
A rational synthetic method of supported metal catalysts has been proposed. Highly dispersed Ag nanoparticles (NPs) with a mean diameter of ca. 10 nm and a narrow size distribution have been prepared in the presence of 3-mercaptopropionic acid (3-MPA) as a protective reagent. The zeta electric potential of the Ag NPs was negatively charged in the region of pH higher than 5 due to the presence of dissociated carboxylate ion (-COO-), which led to the electric repulsion between Ag NPs. On the other hand, the electric charge gradually increased in the region of pH less than 5 owing to the formation of a protonated carboxyl group (-COOH), which induced the hydrogen bonding between Ag NPs. Such pH-triggered assembly dispersion control enables a strong protocol to deposit Ag NPs with different diameters on the positively charged Al2O3 support by electrostatic attraction. The obtained Ag/Al2O3 materials were characterized by means of UV-vis spectra and transmission electron microscopy (TEM), and the catalytic activities were evaluated in the reduction of 4-nitrophenol in water. The reaction rate increased with increasing pH of the prepared colloidal solution, which is correlated with the decreasing size of the Ag NPs. The reduction of 4-nitrophenol is considered as a structure-insensitive reaction, and all surface atoms of the Ag NPs act catalytically as the same active species in this size range by performing calculations on the Ag crystallites.