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研究生： 吳建寬
Wu, Jian Kuan
論文名稱： 水相中快速合成出由八面體演繹至立方體硫化鉛奈米晶體 以及其不同形狀的排列結構研究
Fast Synthesis of PbS Nanocrystals in Aqueous Solution with Shape Evolution from Cubic to Octahedral Structures and Their Assembled Structures
指導教授： 黃暄益
Huang, Hsuan-Yi
口試委員: 林弘萍
Lin, Hong-Ping
黃哲勳
Huang, Jer-Shing
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： 2012
畢業學年度： 100
語文別： 英文
論文頁數： 54
中文關鍵詞： 硫化鉛 、形狀演變 、形貌 、排列
外文關鍵詞： PbS, shape evolution, morphology, assembly
相關次數： 點閱：3  下載：0 
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    • 半導體奈米粒子時常是在有機相中及高溫下反應。如果能將奈米粒子的合成在水相中進行，則可以減少能量的消耗及能達到綠色化學的效果。根據文獻得知，若想要在水相中合成硫化鉛奈米晶體，則至少需要加熱12小時到24小時，而我們的實驗目的則是要能有效縮短反應時間且達到一系列的形狀變化。
    在本次實驗中，我們在水相的環境中利用植晶方法，經由二次成核的方式長成硫化鉛奈米粒晶體，整個反應時間約2個半小時，合成的奈米粒子其大小範圍則介於30至60奈米之間。除此之外，可藉由硫代乙烯胺濃度從0.05 M至0.025 M的調整，使硫化鉛奈米晶體的形狀從立方體可以逐漸轉變成八面體。至於立方體及八面體的奈米粒子分別是由{100}和{111}晶面所組成的，而立方八面體是{100}和{111}晶面所組成的，經由粉末X-ray繞射的鑑定得知合成出的奈米晶體為硫化鉛，且其不同的形狀可得到具有擇優取向的訊號。此外藉由TEM選區電子繞射鑑定也可以做材料鑑定和得知奈米晶體的晶面。
    除此之外，從SEM上還發現到截角立方體及八面體個別具有不同的單層與多層的排列情形，並藉由粉末X-ray繞射鑑定不同排列情形造成的擇優取向繞射圖。

    Semiconductor nanoparticles are often synthesized in organic solvents with the use of high reaction temperatures. If nanoparticles can be synthesized in aqueous phase, it should reduce the energy cost and the process is more environmentally friendly. According to the literature, PbS nanocrystals are usually synthesized in organic solvents. When they are prepared in aqueous solutions, the reaction mixtures can frequently be heated for 12–24 hours.
    In this study, we have developed a seeding growth method to synthesize PbS nanocrystals in aqueous solution. The method involves addition of a small volume of preheated lead acetate and thioacetamide (TAA) mixture to an aqueous growth solution of lead acetate, thioacetamide, cetyltrimethylammonium bromide, and nitric acid. By varying the amount of thioacetamide added to the growth solution, PbS nanocrystals with different morphologies were generated in 2 h at 90 ºC. The PbS nanocrystals have sizes of 30–60 nm. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) patterns, and scanning electron microscopy (SEM) have been employed to characterize the nanocrystals. Nanocube sizes can also be tuned within a range. UV–vis absorption spectra of PbS cubes, cuboctahedra, and octahedra all show decreasing but continuous absorption from 300 nm to beyond 1000 nm. By monitoring the speed of darkening of solution color, particle growth rate was found to be fastest for nanocubes, followed by truncated cubes, cuboctahedra, and octahedra. The production of different particle morphologies of PbS nanocrystals is linked to their reaction rates. Lowering the concentration of TAA in the reaction mixture can retard the reaction rate, and this favors the formation of octahedra.
    These monodisperse nanocrystals can readily form self-assembled structures. Truncated cubes and octahedra forming monolayer and multilayer packing arrangements have been studied. PXRD was used to confirm these assembled structures. Intensities of certain peaks in the PXRD patterns are enhanced due to preferred orientations of the nanocrystal packing structures.

    TABLE OF CONTENTS Abstract of the Thesis i Table of Contents iv List of Figures vi List of Schemes ix Chapter 1 Introduction to the Synthesis of Lead Chalcogenide Nanocrystals with Shape Evolution 1.1 Introduction to shape–controlled synthesis of nanocrystals 1 1.2 Synthesis of lead chalcogenide nanocrystals with well-defined shapes 8 1.3 Insights from the synthesis of lead sulfide nanocrystals in aqueous solution with systematic shape evolution 14 1.4 References 23 Chapter 2 Fast Synthesis of PbS Nanocrystals in Aqueous Solution with Shape Evolution from Cubic to Octahedral Structures and Their Assembled Structures 2.1 Introduction 26 2.2 Expermental Section 28 2.2.1 Chemicals 28 2.2.2 Synthesis of PbS nanocrystals with shape evolution 28 2.2.3 Synthesis of truncated octahedral PbS nanocrystals 29 2.2.4 Synthesis of PbS nanocubes with size control 30 2.2.5 Formation of ordered PbS nanocrystal assembly 32 2.2.6 Instrumentation 32 2.3 Results and Discussion 33 2.4 Conclusion 53 2.5 References 54 LIST OF FIGURES Chapter 1 Introduction to the Synthesis of Lead Chalcogenide Nanocrystals with Shape Evolution Figure 1.1 SEM images of the gold nanocrystals 2 Figure 1.2 SEM images of the gold nanocrystals by adding KI 3 Figure 1.3 SEM images of the silver nanocrystals 4 Figure 1.4 SEM images of the Ag2O crystals 5 Figure 1.5 SEM images of the Cu2O nanocrystals with morphology evolution from cubes to rhombic dodecahedra 6 Figure 1.6 SEM images of polyhedral palladium nanocrystals 7 Figure 1.7 SEM images of PbSe rods, octahedra and cubes 10 Figure 1.8 TEM images of PbS, PbSe and PbTe nanocrystals 11 Figure 1.9 SEM images of PbSe microcrystals 12 Figure 1.10 TEM image Three different shapes of PbTe nanocrystals 13 Figure 1.11 TEM images of the PbS nanostructures obtained under various reaction temperatures 15 Figure 1.12 SEM images of truncated PbS nanocubes 16 Figure 1.13 TEM images of PbS nanocrystals 17 Figure 1.14 Illustration of the electrode position processes for PbS crystal 19 Figure 1.15 The shape evolution of PbS crystals 20 Figure 1.16 Time-dependent formation of star-shaped PbS crystals 21 Figure 1.17 SEM images of PbS crystals electrodeposited at different currents and PbCl2 concentrations 22 Chapter 2 Fast Synthesis of PbS Nanocrystals in Aqueous Solution with Shape Evolution from Cubic to Octahedral Structures and Their Assembled Structures Figure 2.1 SEM and TEM images of PbS nanoparticles 27 Figure 2.2 SEM images of PbS nanocrystals from cubes to octahedra 35 Figure 2.3 Average PbS nanocrystal sizes and their standard deviations 36 Figure 2.4 XRD patterns of PbS nanocubes, cuboctahedra, and octahedra 38 Figure 2.5 TEM, HRTEM image and SAED patterns of PbS nanocubes 38 Figure 2.6 TEM, HRTEM image and SAED patterns of PbS cubeoctahedra 39 Figure 2.7 TEM, HRTEM image and SAED patterns of PbS octahedra 40 Figure 2.8 UV–vis absorption spectra of PbS nanocrystals 41 Figure 2.9 Photographs of sample A–D after 0.5 and 1 h of reaction 42 Figure 2.10 Photographs of samples A–D after 1.5 and 2 h of reaction 43 Figure 2.11 SEM images of PbS nanocubes with various size 44 Figure 2.12 SEM images of PbS truncated cubes with DI water 46 Figure 2.13 SEM images of the PbS truncated cubes with CTAB solution 47 Figure 2.14 XRD patterns and SEM images of PbS truncated cubes 50 Figure 2.15 From the monolayer to multilayer packing structures for truncated cubic PbS nanocrystals 51 Figure 2.16 XRD patterns and SEM images of PbS octahedra 52 LIST OF SCHEMES Chapter 2 Fast Synthesis of PbS Nanocrystals in Aqueous Solution with Shape Evolution from Cubic to Octahedral Structures and Their Assembled Structures Scheme 2.1 Schematic illustration of the proceudre and exact reaction conditions used in the synthesis of PbS nanocrystals with shape evolution from cubic to octahedral structures 30 Scheme 2.2 Schematic illustration of the experimental procedure and exact reaction conditions used in the synthesis of PbS nanocubes with tunable sizes 31

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