以一鍋合成鈀奈米晶體─由八面體演繹至立方體

One-Pot Synthesis of Palladium Nanocrystals with Systematic Shape Evolution from Octahedral to Cubic Structures

沈圓婷(Yuan-Ting Shen)

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.2011.00237

摘要

本篇論文是利用一鍋合成具系統性形狀演化的鈀奈米晶體，形狀變化可從八面體演繹至立方體。 八面體、截半六面體及立方體在此可利用氯化十六烷基三甲基銨鹽做為保護劑、維生素C作為還原劑及添加少量的溴化鉀來合成。而形狀演化是藉由微量地調控溴化鉀溶液的量來達成。
從結構鑑定證明八面體是由{111}的面所組成的，而立方體則是有{100}的面所組成，在此不同形狀的鈀奈米晶體是由於其<100>方向和<111>方向成長速率不同所造成。我們成功地利用一個系統性的方法合成出全為{111}面及全為{100}面的鈀奈米晶體，並解釋這些形狀之間的關聯性。這些鈀奈米晶體可用來檢驗其不同形狀及表面所產生的不同性質。
根據為了探討鈀奈米晶體的成長機制所做的相關實驗，我們發現溴離子的添加會大大地影響鈀的還原速率及晶體不同面的相對成長速率。隨著增加溴化鉀的量可使整體的反應速率增加。而且晶體在<111>方向加速成長的速率會勝過在<100>方向的，進而促使{100}面的比例增加。
將來，我們會將這些具特定晶面的奈米粒子做為催化劑應用在有機反應中，並探討其晶面特性對於有機反應的影響。

關鍵字

奈米晶體 ； 鈀 ； 形狀控制

並列摘要

We have prepared Pd nanocrystals with systematic shape evolution from octahedral to cubic structures through a one-pot synthesis approach. Octahedral, cuboctahedral, and cubic structures can be synthesized by using cetyltrimethylammonium chloride (CTAC) surfactant as capping agent, H2PdCl4, ascorbic acid as reducing agent and a very small amount of KBr. Fine tuning in the amount of KBr added to the growth solution enabled the fine control of nanocrystal morphology.
Structural characterization confirmed that octahedra are bounded by {111} facets, whereas the cubes are bounded by {100} facets. The final shapes of Pd nanocrystals resulted from the different growth rates in the <100> direction to that of <111> direction. We have successfully used a systematic method to synthesize Pd nanocrystals with entirely {111} and {100} facets and found the relationships among these shapes. These nanocrystals should allow the examination of their various properties as a function of particles shapes and surfaces.

According to our experiments regarding the study of growth mechanism of the Pd nanocrystals, we found that bromide ions play a critical role to influence the reduction kinetics of Pd precursors and relative rates of Pd addition on the surfaces of nanoparticles. With the increase of KBr added to the growth solution, the whole reaction rate was increased. Furthermore, the accelerated growth rate in the <111> direction suppressed that of <100> direction to increase the proportion of {100} facets of Pd nanocrystals. In the future, we will apply these nanoparticles with specific facets as catalysts for the facet-dependent organic reactions.

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