Synthesis and Characterization of Composite Photocatalyst

利用水熱法製程在120 ~ 180 ℃的溫度範圍之間以過氧化鋅為前驅物來製備氧化鋅/過氧化鋅的複合材料。氧化鋅/過氧化鋅複合材料所呈現出的形態為在稜柱形氧化鋅結晶體的表面上有小顆粒狀的過氧化鋅「融合」在其上。此外，以溶膠-凝膠法以及初濕含浸法，利用二氧化鈦作為母相，並在不同鍛燒溫度下來製備鈦酸鍶/二氧化鈦之複合材料。另一方面，在光觸媒活性分析上，以波長300 nm的光源照射甲基橙以及亞甲基藍溶液以進行降解反應，發現氧化鋅/過氧化鋅與鈦酸鍶/二氧化鈦複合材料有最佳的光反應活性。如此反應活性的提高是由於在組成複合材料的兩相在表面存在著緊密鍵結的異相結構鍵結且兩種不同相的氧化物之間其結構上以及其能帶上的差異，因而有助於光激發電子電洞對的分離。 本研究同時也提出一種製備緊密接合雙成份半導體光觸媒組合物的製程，該製程是以該組合物內之其中一成份半導體光觸媒相為起始相，經由一個以上的化學反應將此起始相部份轉化合成出具不同化學組成之另一成份半導體光觸媒相，以形成最終之雙成份組合物物件以該製程所獲得之雙成份半導體光觸媒呈現較其任一組成的單一相材料有著更佳的光觸媒活性。ZnO/ZnO2 composite photocatalysts were synthesized by hydrothermal treatment at 120 ~ 180 ℃ of ZnO2, which in turn was obtained from an aqueous solution of ZnSO4 and H2O2. The composite particles showed morphology of ZnO prismatic crystallites with small ZnO2 granules “fused” at surface. Besides, SrTiO3/TiO2 composite photocatalysts were prepared by sol-gel and incipient wetness impregnation method and proceeded to calcine at high temperature, with TiO2 as the main phase of the composite. Photocatalytic activity was characterized based on photocatalytic degradation of methyl orange and methylene blue under UV-light (300 nm) illumination, and the maximum activity was both observed for the composite photocatalysts synthesized based on pre-formed main phase, ZnO/ZnO2 and SrTiO3/TiO2. The enhanced activity has been attributed to the presence of the intimate hetero-structure on the surface of composites and the effective way for the separation of excitons. This study also points out a new approach to synthesize a coupled composite photocatalyst containing strongly coupled constituents by phase transformation among the constituents through one or more than one chemical reaction(s).Table of Contents 摘要 I Abstract II List of Figures VI List of Tables XI Introduction 1 Chapter 1 Background 3 1-1 Composite photocatalysts 3 1-2 ZnO2 8 1-3 ZnO 8 1-3-1 Properties and synthetic methods of ZnO 9 1-3-2 Applications of ZnO 12 1-4 TiO2 14 1-4-1 Properties and synthetic methods of TiO2 14 1-4-2 Applications of TiO2 24 1-5 SrTiO3 25 1-5-1 Properties and synthetic methods of SrTiO3 26 1-5-2 Applications of SrTiO3 28 1-6 Synthetic methods 29 1-6-1 Hydrothermal process 29 1-6-2 Sol-gel process 30 Chapter 2 Experimental 35 2-1 Synthesis of composite photocatalyst 35 2-1-1 ZnO/ZnO2 composite photocatalyst 35 2-1-2 SrTiO3/TiO2 composite photocatalyst 38 2-2 Experimental Instruments and Chemical Reagents 41 2-2-1 Experimental Instruments 41 2-2-2 Chemical Reagents 42 2-3 Analyses 42 2-3-1 X-ray Diffraction 42 2-3-2 UV-Vis spectrum 44 2-3-3 Scanning Electron Microscopy 45 2-3-4 Brunauer-Emmett-Teller (BET) surface area 47 2-3-5 X-ray Photoelectron Spectroscopy 48 2-4 Kinetic analyses 50 Chapter 3 Result and Discussion 55 3-1 ZnO/ZnO2 composite photocatalyst 55 3-1-1 XRD analyses 55 3-1-2 UV-vis spectrum analyses 59 3-1-3 SEM analyses 63 3-1-4 BET surface area analyses 68 3-1-5 Kinetic analyses 69 3-2 SrTiO3/TiO2 composite photocatalyst 76 3-2-1 SrTiO3/TiO2 with molar ratio Sr/Ti=0.1 calcined at different temperatures 76 3-2-1-1 XRD analyses 76 3-2-1-2 UV-vis spectra analyses 83 3-2-1-3 BET surface area analyses 87 3-2-1-4 XPS analyses 89 3-2-1-5 Kinetic analyses 94 3-2-2 SrTiO3/TiO2 calcined at 600 and 700 ℃ with different molar ratios 114 3-2-2-1 XRD analyses 114 3-2-2-2 Kinetic analyses 117 3-2-3 Effect of amount of composite photocatalyst 122 Chapter 4 Conclusions 126 References 12