以碘離子輔助植晶法合成菱形十二面體演繹至八面體的金奈米晶體及探討不同晶面的催化活性

Seed-Mediated and Iodide-Assisted Synthesis of Gold Nanocrystals with Systematic Shape Evolution from Rhombic Dodecahedral to Octahedral Structures and Their Facet-Dependent Catalytic Activity

鍾佩茹(Pei-Ju Chung)

指導教授 ： 黃暄益

國立清華大學/理學院/化學系/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00231

摘要

Until recently, only the morphological evolution for gold nanocrystals from cubic to octahedral structures have been demonstrated. Previously we have developed a facile seed-mediated method for the synthesis of gold nanocrystals from cubic to trisoctahedral and rhombic dodecahedral structures in aqueous solution at room temperature. Cetyltrimethylammonium chloride (CTAC) surfactant, a small amount of NaBr, and varying amounts of reducing agent added were keys to this systematic shape control.
In Chapter 1 we present the development of a seed-mediated and iodide-assisted method to the synthesis of monodisperse gold nanocrystals with systematic shape evolution from rhombic dodecahedral to octahedral structures. Particle growth is complete in 15 min at room temperature, so the process is fast and energy-efficient. By progressively increasing the amount of KI used in a growth solution while keeping the amount of ascorbic acid added constant, nanocrystals with morphologies varying from rhombic dodecahedral to rhombicuboctahedral, edge- and corner-truncated octahedral, corner-truncated octahedral, and octahedral structures were synthesized. The nanocrystals are monodisperse in size and readily form self-assembled structures on substrates. By simply adjusting the volume of gold seed solution added to a growth solution, particle sizes of the octahedral gold nanocrystals can be tuned with average opposite corner-to-corner distances of 42, 48, 54, 60, 68, 93, 107, and 125 nm. In the presence of HAuCl4, iodide may act as a reducing agent. Variation of its amount in the solution may slightly modulate the reduction rate and affect the final crystal morphology. Intermediate structures collected during crystal growth reveal the presence of many twisted structures surrounding a developing nanocrystal core. This nanocrystal growth mechanism and the less important role of surfactant in directing the polyhedral nanocrystal morphology is discussed.
In Chapter 2 we describe the facet-dependent catalytic activity of gold nanocrystals with cubic, rhombic dodecahedral and octahedral structures. Their surfaces are bounded by {100}, {110} and {111} facets respectively, which are the three important low-index planes in a fcc system. We utilized these gold nanocrystals as a catalysts and NaBH4 as a reducing agent to reduce 4-nitroaniline to p-phenylene diamine (benzene-1,4-diamine). We used UV-vis spectroscopy to characterize the rate of reactant consumption and product formation. By carrying out reaction at different temperatires, rate constants (k) and activation energies (Ea) were determined. Surface energies (γ) reported before and the binding energies obtained from density functional theory (DFT) calculations are used to explain the observed catalytic results. We conclude that the rate of catalytic activity is rhombic dodecahedra > cubes > octahedra.

關鍵字

奈米金 ； 自組裝 ； 形狀演譯 ； 晶面催化 ； 八面體 ； 菱形十二面體

並列摘要

無資料

並列關鍵字

gold ； growth mechanism ； nanostructures ； self-assembly ； shape evolution ； facet-dependent

參考文獻

1.6 References

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