再生能源應用已成為全球議題，近年來，半導體光觸媒已可有效的運用太陽能分解有機汙染物，但礙於材料性質限制，尚須研究者不斷改良創新。
為了有效得到理想的半導體光觸媒材料，具有成分梯度變化的試片有利於加快探討合適的參數。本研究為利用旋轉塗佈及水熱法成長具有密度梯度的金紅石相二氧化鈦奈米柱於矽基板上，且結合具有濃度梯度的還原氧化石墨烯成為TiO2-rGO奈米高效能複合材料。此研究所提出的概念有別於以往水熱法製程，僅使用單一參數於一個試片上並需重複製作多組單一參數試片探討。相反的，本實驗所利用的高效能梯度分布可在單一試片中得到多組參數，加快製成條件控制。
XRD, SEM, FTIR, Raman和PL等儀器被使用於研究材料變化的趨勢，包含相、形貌、微結構、光學、成分和化學鍵結的分析，並以光降解亞甲藍水溶液測試光催化性質，最後結果顯示結合大量的還原氧化石墨烯能更加有效的輔助TiO2展現更好的光催化性質。在光電化學中以紫外光照射且加以1V的電位測試光電流密度，TiO2-rGO量測出的光電流為25 μA/cm2，為純TiO2的兩倍之多(約10 μA/cm2)。

The application of renewable energy has become a global issue in recent years. Semiconductor photocatalyst can effectively decompose organic pollutants and split water to harvest hydrogen fuels by solar light. However, researchers keep exploring the novel materials to overcome nature limitations of materials.
In order to efficiently obtain an optimal photocatalyst, a combinatorial composition spread sample was fabricated to facilitate the exploration of appropriate parameters. In this study, density gradient rutile TiO2 was grown on silicon substrate by spin coating and hydrothermal method. Moreover, coupling with density gradient of reduced graphene oxide (rGO) to become a combinatorial density gradient of TiO2-rGO nanorod composites. This novel concept is different from the literature of hydrothermal method which only can produce single parameter on one sample and repeat multiple procedures to explore the best condition. On the contrary, our combinatorial density gradient of TiO2-rGO nanorod composites sample contains a wide range of compositions in a single sample, enabling efficient screening of materials for applications.
Various techniques of XRD, SEM, FTIR, Raman, and PL were employed to determine the various characteristics, including phases, morphologies, microstructures, optical properties, compositions, and chemical bondings. Photodegradation activities were determined by decomposing methylene blue (MB) under UV light. The result shows that coupling with suitable amount of rGO can effectively assist TiO2 to enhance the photocatalytic properties. In photoelectrochemical (PEC) reaction, the cell was measured with a constant 1 V bias under UV light. The measured current of TiO2-rGO nanorod composites was approximately 25 μA/cm2 more than double the value obtained from the pure TiO2 nanorods (approximately 10 μA/cm2).

摘要 I
Abstract II
誌謝 III
Content IV
Table Content VI
Figure Content VII
Chapter 1 Introduction 1
A. Research Objective 1
B. Research Background 1
C. Photocatalysis 2
C.1 Photodegradation 4
C.2 Photoelectrochemical (PEC) reaction 6
D. Titanium Dioxide (TiO2) 9
D.1 Properties and Structure 9
D.2 Fabrication 13
D.3 Applications 21
E. Overview of Graphene and Reduced Graphene Oxide 25
E.1 Graphene 25
E.2 Graphene Oxide (GO) and Reduced Graphene Oxide (rGO) 26
E.3 TiO2-rGO Composites 27
F. Combinatorial Approach 28
F.1 Introduction 28
F.2 Combinatorial Hydrothermal Synthesis 29
Chapter 2 Experiment 32
A.Materials 32
B. Experimental Procedures 33
B.1 Substrate Preparation 33
B.2 Different-Density TiO2 Seed Layer Preparation 33
B.3 Hydrothermal Growth of TiO2 Nanorods 35
B.4 Graphene Oxide Layer 36
C. Characterizations 38
C.1 X-ray Diffraction (XRD) 38
C.2 Scanning Electron Microscope (SEM) 39
C.3 Transmission Electron Microscope (TEM) 40
C.4 Fourier Transform Infrared Spectrometry (FTIR) 41
C.5 Raman Spectroscopy 42
C.6 UV-Visible Spectroscopy 43
C.7 X-ray Photoelectron Spectroscopy (XPS) 44
C.8 Photodegradation 44
C.9 Photoelectrochemical (PEC) Cell 45
Chapter 3 Results and Discussion 47
A. Previous Research 47
B. Manufacturing of a Density Gradient TiO2 Nanorods 49
B.1 Effect of Homemade Stage Angle on the Nanorods Growth 49
B.2 Effect of TBOT Concentration in Precursor Solutions on the Nanorods Growth 50
B.3 The Density Gradient TiO2 Nanorods 51
C. Reduction Analysis of Graphene Oxide 54
C.1 GO Reduced to rGO Using UV Irradiation 55
C.2 rGO Analysis in the TiO2-rGO Nanorods Composite 56
C.3 Reducing Density Gradient of GO in the TiO2-GO Nanorod Composites 58
C.4 Crystal Structure of a Density Gradient of TiO2-rGO Nanorod Composites 58
D. Photodegradation Analysis 59
D.1 Photodegradation Ability of Pure Density Gradient of TiO2 Nanorods 60
D.2 Photodegradation Ability of the Density Gradient of TiO2-rGO Nanorod Composites 62
D.3 Cycling Test for Position 5 of the Density Gradient of TiO2-rGO Nanorod Composites 64
E. Raman Spectroscopy Analysis of Position 5 of the Density Gradient of TiO2-rGO Nanorod Composites 65
F. Optical Properties of Position 5 of the Density Gradient of TiO2-rGO Nanorod Composites 67
G. Performance of Photoelectrochemical (PEC) Cell 68
Chapter 4 Conclusions 72
A.Density Gradient TiO2 Nanorods 72
B.Density Gradient of TiO2-rGO Nanorod Composites 72
C.Photodegradation Analysis 72
D.Photoelectrochemical (PEC) Analysis 73
References 74

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