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Preparation of Gold Nanocrystals of Different Morphology and Study on Their Electrocatalytic Performance

Author: RanYan
Tutor: XiaHaiBing
School: Shandong University
Course: Materials Engineering
Keywords: morphology control gold nanocrystals seeded-mediated growthmethod electrocatalytic properties
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 124
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Abstract


Owing to their special properties, gold nanocrystals (Au NCs) have been widely used in the fields of optoelectronics, biomedicine and catalysis. Although the remarkable progress has been achieved in the research of controlled sythesis of shape and size, and physicochemical properties of Au NCs, there is few systematic and detailed studies on the growth kinetics, especial the effect of the growth kinetics on the Miller index and morphology of as-prepared nanocrystals. In this thesis, Au NCs of different sizes and various shapes via seeded-mediated method were synthesized. The size, morphology and crystal structure, as well as the optical properties of Au NCs were characterized systematically by transmission electron microscopy (TEM). scanning electron microscopy (SEM) and UV-vis spectroscopy. respectively. Furthermore, the electrocatalytic properties of Au NCs with high miller index were also studied.In this thesis, the following subjects are included:1. The size of the spherical Au NCs is modulated by varying the amount of the seeds. When the amount of seeds decrease, the peak positions in the UV-vis absorption spectra exhibit a red-shift, indicating the size of the NCs increases. On the other hand, larger spherical Au NCs are obtainded by expanding the amount of the growth solution.2. The size of the trisoctahedral Au NCs can be controlled just by changing the amount of the seeds. In our research, we focus on the effect of ascorbic acid (AA) on the Miller indices of as-prepared Au NCs. To verify the change of the crystal plane index, the cyclic voltammetry curves under acidic conditions are obtained. Meanwhile, the catalysis of different Miller index of the trisoctahedral Au NCs on methanol oxidation under alkaline conditions were tested and further compared. These results indicate that the increasing of AA promotes the growth kinetics, and leads to the change of Miller index. The electrocatalytic properties were related to the plane index of nanocrystals. 3. When the ratio of oxidizer to reducing agent is fixed, hyperbranched Au NCs of controlled sizes are obtained by changing the amount of the oxidizer and reducing agent. In this case, the amount of reducing agent, AA, and the congcentration of CTAC is crucial to the morphology of the obtained Au NCs. And the possible formation mechanism of the hyperbranched Au NCs is discussed. Moreover, the electrocatalytic properties of as-obtained hyperbranched Au NCs are different from those of the trisoctahedral Au NCs.

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