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研究生： 黃瀞儀
Huang, Jing-Yi
論文名稱： 氧化亞銅奈米粒子之光學性質與能帶結構探討與氧化亞銅與硫化鎘之異質介面所造成的光催化活性的抑制
Modified Semiconductor Band Diagrams Constructed from Optical Characterization of Size-Tunable Cu2O Cubes, Octahedra and Rhombic Dodecahedra and Photocatalytic Activity Suppression at the Cu2O-CdS Heterojunctions
指導教授： 黃暄益
Huang, Michael H.
口試委員: 劉學儒
Liu, Hsueh-Ju
段興宇
Tuan, Hsing-Yu
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： 2017
畢業學年度： 105
語文別： 英文
論文頁數： 82
中文關鍵詞： 氧化亞銅 、晶面效應 、光學性質 、能帶結構 、硫化鎘 、光催化 、異質結構
外文關鍵詞： cuprous oxide, facet-dependent, optical property, band diagram, cadmium sulfide, photocatalysis, heterojunctions
相關次數： 點閱：2  下載：0 
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    • 第一章 氧化亞銅奈米粒子之光學性質與能帶結構探討
    藉由量測可調控尺寸之氧化亞銅立方體、八面體及菱型十二面體之奈米粒子的吸收及放光光譜，發現其吸收及放光波長隨著奈米粒子的尺寸增加而紅位移，此研究中我們所合成的奈米粒子從10奈米到大於250奈米。其中放光光譜帶位移超過130奈米，而10奈米之立方體的放光強度最強。以相同體積之立方體、八面體及菱型十二面體奈米粒子做比較，菱型十二面體之吸光波長最短，而立方體吸光波長最長，其能隙差距為0.17電子伏特 (51.5奈米)，我們可以由肉眼明顯分辨出三種形狀的顏色差異。此篇論文中，我們可以藉由調控遠大於量子點的奈米粒子之尺寸以及晶面來改變其吸收以及放光波長，同時由實驗結果可以畫出考慮尺寸及晶面所造成能帶彎曲之修正過後的能帶圖。除此之外，藉由此實驗我們可以更全面性的理解氧化亞銅{100}, {111}及{110}三種晶面在光催化、電性量測以及吸收光三種情況下能帶彎曲的程度差異。

    第二章 氧化亞銅與硫化鎘之異質介面所造成的光催化活性的抑制

    過去我們已經成功合成出金修飾在氧化亞銅表面以及氧化亞銅-氧化鋅異質結構之奈米粒子，本實驗中我們以簡單的合成方法合成出氧化亞銅-硫化鎘之異質結構。過去兩個例子中，修飾上金和氧化鋅的立方體奈米粒子皆無光催化活性，在此我們藉由對甲基澄做為染料對立方體之氧化亞銅-硫化鎘之異質結構進行光催化降解實驗，其結果如果們預期，仍然無光催化活性，再次證明了立方體始終無活性是來自於電子無法到達表面而造成的，與上面的修飾物無關。過去我們認為半導體-半導體異質結構的表面可以促使電子、電洞有效的分離，並減少兩者之間的再結合，因而提升光降解效果。但在深入研究氧化亞銅-氧化鋅異質結構後，推翻我們過去的想法，我們必須考慮兩者相接的晶面，其可能造成光催化效果變好亦可能變差。本實驗中也發現相似的情形，不管是八面體或是菱形十二面體，接上硫化鎘後，其光催化效率階變差，甚至無光催化活性。經HR-TEM鑑定，硫化鎘以(110)晶面與氧化亞銅{111}表面相接，而硫化鎘以的(101)晶面與氧化亞銅{110}表面相接。此結果讓我們認為不管是氧化亞銅或者硫化鎘的晶面皆會影響結果，在不同晶面相連接的情況下，可能抑制了光催化效果，並顛覆過去人們認為半導體異質結構的電子與電洞分離可提升光催化效果的結果。

    ABSTRACT of CHAPTER 1

    Modified Semiconductor Band Diagrams Constructed from Optical Characterization of Size-Tunable Cu2O Cubes, Octahedra and Rhombic Dodecahedra

    By making Cu2O nanocubes, octahedra, and rhombic dodecahedra with tunable sizes and recording their light absorption and emission spectra, their absorption and emission bands shift steadily to longer wavelengths with increasing particle sizes from 10 nm to beyond 250 nm. Emission intensities are highest for the smallest nanocubes. Photoluminescence band shifts exceed 130 nm over this size range. For particles having the same volume, rhombic dodecahedra absorb light of shortest wavelength, while cubes show most red-shifted absorption with their band gaps differ by 0.17 eV (or 51.5 nm). They show obviously different colors. The presence of optical size and facet effects in semiconductors means their emission wavelengths are tunable through facet control and use of nanocrystals much larger than quantum dots. A modified and general band diagram for Cu2O crystals has been constructed incorporating their optical size and facet effects with surface band bending. In addition, a more complete understanding of the different orders of surface band bending for the {100}, {111}, and {110} facets used in explaining the facet-dependent photocatalytic activity, electrical conductivity, and light absorption properties of Cu2O crystals is presented.

    ABSTRACT of CHAPTER 2

    Photocatalytic Activity Suppression at the Cu2O-CdS Heterojunctions

    We have previously synthesized Au-decorated Cu2O and ZnO‒Cu2O heterostructures. In both cases, Cu2O cubes were found to remain photocatalytically inactive toward photodegradation of methyl orange (MO). From the Cu2O‒ZnO heterostructure study, we found the initially active Cu2O octahedra also became inactive after ZnO deposition. Unfavorable interfacial band banding is believed to give this dramatic outcome. To demonstrate another example of interfacial facet effects on photocatalysis, we have prepared heterostructured Cu2O‒CdS using Cu2O cubes, octahedra, and rhombic dodecahedra. Surprisingly, with sufficient growth of CdS nanoparticles on the surfaces of Cu2O cubes, octahedra, and rhombic dodecahedra, all samples show complete suppression of photocatalytic activity in degrading MO. Obviously, semiconductor-semiconductor heterostructures do not always lead to enhanced photocatalytic activity from better electron-hole pair separation. Sometimes formation of bad heterojunctions can completely inhibit interfacial charge transport. Through extensive analysis of interfacial HR-TEM images, we found that the (110) planes of CdS are grown over the {111} faces of Cu2O, while (101) planes of CdS are grown on the {110} faces of Cu2O. We assume the (110) and (101) planes have a large upward surface band bending preventing photoexcited electrons from migrating to the CdS side. The band alignment of Cu2O and CdS drive the photoexcited charge carriers to move toward the interfaces instead of migrating to individual surfaces, so all charge carriers are stopped at the interface and recombine. These unexpected situations explain the sharp decline in photocatalytic activity for Cu2O octahedra and rhombic dodecahedra decorated with CdS.

    第一章 論文摘要 I ABSTRACT of CHAPTER 1 II 第二章 論文摘要 IV ABSTRACT of CHAPTER 2 V ACKNOWLEDGEMENT VII TABLE OF CONTENTS VIII LIST OF FIGURES XI LIST OF SCHEMES XX LIST OF TABLES XXII CHAPTER 1 Modified Semiconductor Band Diagrams Constructed from Optical Characterization of Size-Tunable Cu2O Cubes, Octahedra and Rhombic Dodecahedra 1.1 Introduction 1 1.2 Research Summary 11 1.3 Experimental Section 12 1.3.1 Chemicals 12 1.3.2 Synthesis of small Cu2O nanocubes with tunable sizes 13 1.3.3 Synthesis of small Cu2O octahedra with tunable sizes 14 1.3.4 Synthesis of different sizes of rhombic dodecahedra 15 1.3.5 Synthesis of 220 nm Cu2O cubes and 400 nm Cu2O octahedra 17 1.3.6 Consideration of particle volumes 19 1.3.7 Instrumentation 20 1.4 Results and discussion 21 1.5 Conclusion 40 1.6 References 42 CHAPTER2 Photocatalytic Activity Suppression at the Cu2O‒CdS Heterojunctions 2.1 Introduction 45 2.2 Motivation and research summary 57 2.3 Experimental Section 58 2.3.1 Chemicals 58 2.3.2 Synthesis of Cu2O nanocrystals 59 2.3.3 Synthesis of Cu2O‒CdS heterostructures 60 2.3.4 Photocatalytic experiments 63 2.3.5 Instrumentation 63 2.4 Results and discussion 64 2.5 Conclusion 79 2.6 References 81

    CHAPTER 1

    Modified Semiconductor Band Diagrams Constructed from Optical Characterization of Size-Tunable Cu2O Cubes, Octahedra and Rhombic Dodecahedra

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    CHAPTER 2

    Photocatalytic Activity Suppression at the Cu2O‒CdS Heterojunctions

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