以一鍋合成鈀奈米晶體─由八面體演繹至立方體

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研究生：	沈圓婷 Shen, Yuan-Ting
論文名稱：	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
指導教授：	黃暄益 Huang, Hsuan-Yi
口試委員:	黃暄益呂世源李積琛
學位類別：	碩士 Master
系所名稱：	理學院 - 化學系 Department of Chemistry
論文出版年：	2011
畢業學年度：	99
語文別：	英文
論文頁數：	57
中文關鍵詞：	奈米晶體、鈀、形狀控制
相關次數：	點閱：1 下載：0
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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。

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.

TABLE OF CONTENTS

Abstract of the Thesis ………………………………………………………….    i
Acknowledgements …………………………………………………………….    iv
Table of Contents ………………………………………………………………    vi
List of Figures ………………………………………………………………….    viii
List of Schemes ………………………………………………………………...    xi

ONE–POT SYNTHESIS OF PALLADIUM NANOCRYSTALS
WITH SYSTEMATIC SHAPE EVOLUTION
FROM OCTAHEDRAL TO CUBIC STRUCTURES
1.1    Introduction    1
1.2    Studies of Palladium Nanocrystals    2
1.3    Insights of the Growth Mechanism from the Synthesis of Nanocrystals with Systematic Shape Evolution    8
1.4    Facet-Dependent Properties of Nanocrystals    16
1.5    Introduction of the Thesis Study    20
2    Experimental Section    23
2.1    Chemicals    23
2.2    Synthesis of Pd Nanocrystals by Adjusting the Amount of KBr    23
2.2.1    Synthesis of Octahedral Pd Nanocrystals    23
2.2.2    Synthesis of Truncated Octahedral Pd Nanocrystals    23
2.2.3    Synthesis of Cuboctahedral Pd Nanocrystals    24
2.2.4    Synthesis of Truncated Cubic Pd Nanocrystals    24
2.2.5    Synthesis of Cubic Pd Nanocrystals    25
2.3    Synthesis of Pd Nanocrystals by Introducing KBr into the Reaction Solution at Different Timings    27
2.4    Synthesis of Pd Nanocrystals by Varying the Amount of AA    27
2.4.1    Varying the Amount of AA in the Presence of 25 μL KBr    27
2.4.2    Varying the Amount of AA in the Presence of 30 μL KBr    28
2.5    Time-Dependent UV–vis Absorption Spectroscopy at a Fixed Wavelength    28
2.6    Instrumentation    29
3    Results and Discussion    30
4    Conclusion    54
5    References    55



LIST OF FIGURES
Figure 1.1    A table summarizing the reaction conditions and the shapes of Pd nanocrystals obtained under each condition.    4
Figure 1.2    SEM and TEM images of Pd octahedral.    5
Figure 1.3    TEM images of samples prepared at different concentrations of citric acid.    6
Figure 1.4    SEM images and UV–vis extinction spectra of Pd nanocubes of different sizes.    7
Figure 1.5    Geometrical models of Pd nanocrystals and SEM images of polyhedral Pd nanocrystal samples.    8
Figure 1.6    TEM images of Pd nanostructures with different concentrations of KBr.    10
Figure 1.7    TEM images of Pd nanostructures by controlling the volume percent of ethylene glycol (EG) in reaction.    11
Figure 1.8    Reaction pathway that leads to Pd nanocrystals with different shapes.    11
Figure 1.9    SEM image of Pd nanocubes, nanodendrites, Pd-CTAB complexes. EDX spectrum of Pd-CTAB complexes.    13
Figure 1.10    Reaction pathway that leads to cubic, multi-armed, and dendritic Pd nanoparticles
15
Figure 1.11    SEM and TEM images of the cubic, multi-armed, and dendritic Pd nanoparticles    15
Figure 1.12    TEM images of cubic and cuboctahedral Pt particles and their use for benzene hydrogenation.    17
Figure 1.13    SEM, TEM, and HAADF–STEM images of THH.
Schematic drawings of a THH nanocrystal viewed from different angles.    18
Figure 1.14    Cyclic voltammograms of different Au-Pd nanocrystal
-modified electrodes.    19
Figure 1.15    Polyhedral metal nanocrystals bound by the fcc {100} and {111} planes for silver, gold, and platinum.    22
Figure 3.1    SEM images of Pd nanocrystals with shape evolution from octahedral to cubic structures and the by-products.    32
Figure 3.2    SEM image of Pd nanoparticles with 100 μL of 10–3 M KBr added into the reaction solution.    32
Figure 3.3    SEM images of Pd nanocrystals over large areas.
Respective size distribution plots    33
Figure 3.4    Polyhedral structures of Pd nanocrystals with respect to the amount of KBr added to the reaction solution.
34
Figure 3.5    Illustration of the effects of face-selective growth.
Various morphologies of a cubic crystal by tuning the ratio of growth rates.    37
Figure 3.6    TEM images, SAED patterns and geometric models of their corresponding Pd nanocrystals.    38
Figure 3.7    SEM images of Pd nanoparticles with the addition of KBr at different timings.    40
Figure 3.8    SEM images of Pd nanoparticles with the addition of KBr at 6 min.    40
Figure 3.9    SEM images of shape evolution of Pd nanocrystals by varying the amount of AA.    42
Figure 3.10    UV–vis absorption spectra of Pd nanoparticles with different shapes.    47
Figure 3.11    The UV–vis absorption spectra at different stages of the synthesis process.    48
Figure 3.12    UV–vis absorption spectra of aqueous H2PdCl4 solution with different amounts of KBr.    49
Figure 3.13    UV–vis absorption spectra of mixture of H2PdCl4 with CTAC and different amounts of KBr.    49
Figure 3.14    UV–vis spectra of solutions taken at different reaction stages at KBr/H2PdCl4 molar ratios of 0 and 0.007.    50
Figure 3.15    Time-dependent absorbance at the peak positions including 226 nm and 286 nm.    51
Figure 3.16    Time-dependent absorbance at the peak position at KBr/H2PdCl4 molar ratios of 0, 0.007, 0.14, and 12.    52
Figure 3.17    Photographs of solutions taken at different reaction stages at KBr/H2PdCl4 molar ratios of 0 and 0.007.    53


LIST OF SCHEMES
Scheme 2.1    Schematic illustration of the synthetic procedure for preparing Pd nanocrystals with systematic shape evolution.    26

                                

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