Synthesis and Characterization of Novel Au(core)-Au/Pt Alloy(shell) Nanostructure
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Synthesis and Characterization of Novel Au(core)-Au/Pt Alloy(shell) Nanostructure Ru-Shi Liu,1 Hau-Ming Chen,1 and Shu-Fen Hu,2 Department of Chemistry, National Taiwan University, Taipei 106, Taiwan 2 National Nano Device Laboratories, Hsinchu 300, Taiwan 1
ABSTRACT A systematic study is reported about the amount-dependent morphology change in a series of Au-Pt bimetallic nanoparticles synthesized using chemical reduction. The amount of Au precursor is kept constant throughout whole series of compounds to obtain fixed Au core size (~7.5 nm). The Au/Pt ratio is varied from 1/1 to 1/4 in order to synthesize Pt shell layer of different thickness. We observed a remarkable shift of surface plasmon band around 410 nm. With the aid of high resolution transmission electron microscope (HRTEM) and energy-dispersive spectrometer (EDS), the composition of shell layer is found to be Pt enriched Au-Pt alloy. As the amount of Pt increases, the Pt clusters formed a string-like shape on the surface of nanoparticles. The average diameter of these Pt clusters is about 2 nm. This special structure may exhibit unique catalytic property. INTRODUCTION The metal nanoparticle catalysts composed of two different metallic elements are of interest from both scientific and technological points of view. Bimetallic catalysts have been considered valuable for investigating the relationship between the catalytic activity and structure of catalysts.[1-4] Furthermore, bimetallic nanoparticles also exhibit different surface plasma band relative to pure metals.[5-6] As the two kinds of metal ions (A and B) formed alloy nanoparticles, both calculated and experimental results suggested that the plasmon absorption band of nanoparticles shifts linearly from the pure A to pure B with increasing B content.[7] Comparatively speaking, the surface plasmon peak of the metal nanoparticles with the core-shell structure would mainly contribute by the surface metal.[8] It is a great challenge to prepare bimetallic nanoparticles with a controlled composition distribution. Here, we report a method to fabricate the core-shell nano structure comprised of Au metal core and Au/Pt alloy shell. EXPERIMENTAL DETAILS Preparation of the Au/Pt Bimetallic Nanoparticles. A solution comprised of 0.2 mM AuCl4and (0–0.8) mM PtCl62- was prepared by dissolving the corresponding salts in water. The reductant was solutions of 4 mL of tannic acid (2%) and 1 mL of citric acid (1%). The colloidal metallic nanoparticles were prepared by adding reductant into solution containing Au and Pt metal salts of various concentration. The reaction mixture was stirred for 15 min at 100℃, followed by 10 min of stirring without heating. Characterization of the Au/Pt Bimetallic Clusters. The surface morphology of the samples was examined by high resolution transmission electron microscope (HRTEM) with energy dispersive spectrometer (EDS) (JEM-2010, 200 kV). The specimens were obtained by placing several drops of the colloidal solution on a Formvar-covered copper grid and evaporating it in air
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