| Summary: | 博士 === 國立成功大學 === 化學工程學系 === 89 === Abstract
In this dissertation, the synthesis of Au/Pt、Au/Pd and Pt/Pd bimetallic nanoparticles at various molar ratios by the coreduction of their corresponding pairs of metal salts (i.e. HAuCl4/H2PtCl6、HAuCl4/H2PdCl4 and H2PtCl6/H2PdCl4) with hydrazine in the reverse micelles of water/AOT/isooctane at 25℃ was investigated. The size, structure, optical properties, and composition distribution of the resultant nanoparticles were characterized by employing TEM, UV/VIS, XRD, EDX, and XPS. TEM photographs showed that the obtained Au/Pt、Au/Pd and Pt/Pd bimetallic nanoparticles were essentially monodispersed, with a mean diameter of about 3~4.5 nm、2.5~3 nm and 7~11 nm, respectively. It was found that the mean diameters of all three bimetallic nanoparticles depended on the compositions of feeding solution and exhibited a negative deviation for the Au/Pd and Au/Pt systems, while a positive deviation for Pd/Pt systems. The monodispersion of bimetallic systems as well as the different sizes between the bimetallic nanoparticles and their corresponding individual nanoparticles implied that they were not the physical mixtures of individual metallic nanoparticles and bimetallic nanoparticles were really formed.
For the Au/Pd and Au/Pt systems, both the UV/VIS absorption spectra and the XRD patterns of the bimetallic systems and the physical mixtures of individual metallic nanoparticles also suggested the formation of bimetallic nanoparticles. The EDX analysis on the single particle showed that the composition for each particle was roughly consistent with that of feeding solution. The XPS measurement revealed that the Pt and Pd atoms were significantly enriched in the outer part of Au/Pt and Au/Pd bimetallic nanoparticles respectively. This indicated the formation of a structure of Aucore-Ptshell and Aucore-Pdshell. It was also noticed that the surface composition of bimetallic nanoparticles varied linearly with the composition in the feeding solution within the molar ratios range of [HAuCl4]/[H2PtCl6] = 9/1~1/9 and [HAuCl4]/[H2PdCl4] = 3/1~1/9.
For the Pt/Pd bimetallic systems, the EDX analysis and XPS measurement suggested a structure of homogeneous alloy except that the molar ratio of Pt/Pd = 9/1 with Pt atoms slightly concentrated on the particle surface. Also, the composition for each particle is roughly consistent with that of feeding solution.
Furthermore, the characterization and formation kinetics of particles suggested the following viewpoint. For the Au/Pt bimetallic systems, (1) the reduction of AuCl4- and PtCl6-2 ions was almost finished before the formation of nuclei, (2) the nucleation rate of Au was much faster than that of Pt, (3) the size of bimetallic nanoparticles was determined by the number of the nuclei formed at the very beginning of reaction, and (4) the nuclei for bimetallic system might be composed of Au and Pt. For the Au/Pd bimetallic systems, (1) the reduction of AuCl4- and PdCl4-2 ions was almost finished before the formation of nuclei, (2) the nucleation rate of Au was much faster than that of Pd, (3) the size of bimetallic nanoparticles was determined by the number of the nuclei formed at the very beginning of reaction, and (4) the nuclei for bimetallic system might be composed of Au and Pd. For the Pt/Pd bimetallic systems, (1) the reduction of PtCl6-2 and PdCl4-2 ions was almost finished before the formation of nuclei, (2) the nucleation rate of Pd was much faster than that of Pt, (3) the size of bimetallic nanoparticles was determined by the number of the nuclei formed at the very beginning of reaction, and (4) the nuclei for bimetallic system might be composed of Pt and Pd. According to these suggestions, the formation process of Au/Pt、Au/Pd and Pt/Pd bimetallic nanoparticles were proposed.
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