我們提出一個簡易的方法在氧化亞銅立方體、八面體、菱形十二面體的表面上沉積金納米粒子同時不破壞晶面。本研究的目的是測試傳統關於利用金屬助催化劑長在半導體粒子上的方式可提高半導體的光催化活性的認知。如果確實是如此，也必須確定哪些晶面提供了最好的活性，而非不管晶面效應所可能帶來的巨大影響，因為氧化亞銅立方體已被觀察到在甲基橙光催化中是沒有活性的。金修飾的氧化亞銅晶體已用各式各樣的方法鑑定，證實有微量的金粒子沉積在氧化亞銅晶體上。有金修飾的菱形十二面體和八面體的光催化表現優於同樣形貌但沒有金修飾的氧化亞銅晶體，然而金修飾的氧化亞銅立方體還是沒有活性。金修飾於小顆的氧化亞銅立方體上也沒有活性。此外，實驗結果顯示金-氧化亞銅菱形十二面體核殼結構的光催化活性是介於氧化亞銅菱形十二面體和金修飾的氧化亞銅菱形十二面體之間。我們也計算出各種氧化亞銅晶體的個別反應速率常數。EPR測量顯示羥基自由基的產量最高為菱形十二面體，次之為八面體。氧化亞銅立方體在可見光照射下不會產生羥基自由基。EPR的結果與光催化上的觀察相符。根據以上實驗結果，我們可以修正氧化亞銅的能帶圖，使不同晶面在接近表面的能帶彎曲程度有明顯的差異以解釋所觀察到的晶面相關的光催化活性。沒有催化活性的{100}晶面可以被理解為其表面層具有較高的能障阻擋光激發所產生的電子到達立方體表面，所以沒有生成自由基引起光降解。這項工作顯示出傳統認知需要被修改並考慮到半導體的晶面，不然有時候這樣的認知在實驗上可以是完全錯誤的。

We report a simple method for depositing Au nanoparticles on the surfaces of Cu2O cubes, octahedra, and rhombic dodecahedra with preservation of sharp facets. The purpose of this study is to test whether the conventional model of a metal cocatalyst anchored on a semiconductor particle can always enhance photocatalytic activity of the semiconductor. If so, it is also necessary to determine which facet gives the best activity. This is especially interesting for Cu2O cubes, which have been shown to be inactive toward photocatalysis of methyl orange. The Au-decorated Cu2O crystals have been characterized by various techniques. Au-decorated rhombic dodecahedra and octahedra outperformed their pristine counterparts, while Au-deposited cubes remained inactive. Au-decorated small cubes were also inactive. Furthermore, Au‒Cu2O core‒shell rhombic dodecahedra exhibited intermediate photocatalytic activity between those of rhombic dodecahedra and Au-decorated rhombic dodecahedra. Reaction rate constants for the various Cu2O crystals have been determined. EPR measurements showed highest production of hydroxyl radicals for rhombic dodecahedra and a lower level of radical generation for octahedra. Radicals were not produced from Cu2O cubes upon visible light irradiation. The EPR results match perfectly with photocatalysis observations. A modified band diagram has been constructed to account for the observed facet-dependent photocatalytic activity. The inactivity of the {100} face can be understood by considering its surface layer as constituted of a high barrier blocking photoexcited electrons from reaching the cube surface, so no radicals are produced to cause photodegradation. This work firmly shows that the conventional model needs to be modified taking into account of the surface facets of semiconductors, because sometimes this model can fail completely.

論文摘要 ………………………………………………………………………………………………………………..I
ABSTRACT OF THE THESIS III
TABLE OF CONTENTS VI
ACKNOWLEDGEMENTS Ⅴ
LIST OF FIGURES VIII
LIST OF TABLES XIV

CHAPTER 1 Overview of the Dissertation and the Background Knowledge
1.1 The Background Knowledge 1
1.1.1 Photocatalysis 1
1.1.2 The Process for Photocatalytic Degradation of Methyl Orange Dye 6
1.2 Catalytic Properties with Specific Facets 8
1.3 The Method and Principle of Increasing Photocatalytic Activity 11
1.3.1 Metal/Semiconductor Heterostructures 11
1.3.2 Semiconductor/Semiconductor Heterostrutures 17
1.4 References 20

Chapter 2 Highly Facet-Dependent Photocatalytic Properties of Cu2O Established through Formation of Au-Decorated Cu2O Nanocrystals
2.1 Introduction 23
2.2 Experimental Section 25
2.2.1 Chemicals 25
2.2.2 Synthesis of Cu2O Nanocrystals and Au@Cu2O Rhombic Dodecahedra .…26
2.2.3 Synthesis of Au-decorated Cu2O nanocrystals 30
2.2.4 Photocatalysis experiments 33
2.2.5 Hydroxyl radical generation detected using electron paramagnetic resonance spectrometry (EPR) 34
2.2.6 Instrumentation 35
2.3 Results and discussion 37
2.4 Conclusion 68
2.5 References 70

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