本研究以表面摻雜鎢的二氧化鈦(W-TiO2)進行光催化還原CO2反應，探討材料特性(表面結構、離子價態，元素比例、元素分布、電子轉移)與光催化還原CO2活性，並比較氣相與液相系統的還原特性，最後為了解光催化還原CO2反應機制，而進行光觸媒表面官能基分析。從材料鑑定結果顯示，W均勻分布於TiO2上，並以六價形式存在，在粒徑大小上因W作為不純物在TiO2表面上使鍛燒時顆粒間無法縮合形成大顆粒，並且W能在TiO2表面能隙導入兩個未填滿能階，驅使電子移動至表面並捕捉電子降低電子電洞對再結合機率。以TiO2與W-TiO2進行氣相光催化還原CO2反應，甲烷為主要產物，不同表面摻雜W/Ti比例皆在第一小時有最佳甲烷產率，並且在表面摻雜W/Ti為3.2 at.%W-TiO2時，有最佳產量0.84 μmol/g，是TiO2的2.6倍。液相反應系統中，除主要產物甲烷外，還有次要產物乙烯，另外因CO2水溶解度低、大量水分子阻礙CO2與光觸媒接觸，因此使液相系統總碳量約小於氣相系統的2倍。由EPR與DRIFT的分析中可知，在光催化反應過程中CO2會先形成單牙基與雙牙基碳酸錯合吸附在W-TiO2表面，而光激發電子會從強電負度的W上進行界面轉移至吸附的碳酸根離子，爾後C-O鍵結逐漸被打斷且進行氫化反應，最後因W強電負度的特性使表面C-O斷鍵而生成甲烷。W離子的強電負度促使CO2鍵結於W-TiO2表面上進行電子轉移，並增加表面酸性而益於吸附H2O，而促進光催化還原CO2活性。

In the study, W ion were incorporated into the surface lattice of TiO2 photocatalysts to improve the activity for CO2 reduction. Photocatalytic activity and byproducts in the gaseous and aqueous phases were measured and characterized. Material properties, including microstructures, bandgaps, chemical compositions, chemical states of W ions, and interfacial charge transfer behaviors were characterized. Moreover, photoreduction mechanism of CO2 were proposed based on charge transfer pathways and changes in the surface functional groups during photocatalysis. Sol-gel-derived W-TiO2 contained hexavalent W ions which distributed evenly in surface lattice. The lattice defects retarded crystallization and increased surface areas. In addition, they introduced two unoccupied energy states in the band gap in the surface lattice which promote charge diffusion from the bulk to the surface and trap the charge carriers to suppress recombination. CH4 was the major product in the gas phase reaction system. The W-TiO2 photocatalyst with a surface W/Ti ratio of 0.032 had the highest CH4 yield of 0.84 μmol/g after 4-hour irradiation. The reduction efficiency was 2.6 times higher than that of unmodified TiO2 powders. In the aqueous phase, C2H4 were formed in addition to CH4 as the minor by-product. Due to low solubility of CO2 in water and competitive adsorption of water molecules, total carbon transformation in the aqueous system was 2 times lower than that in the gas phase system. Mechanisms for CO2 reduction were proposed according to EPR and DRIFT analysis. CO2 molecules transformed into m-CO32- and b-CO32- species and then chelated to the W-TiO2 surface for the first step. The carbonate species constantly received electrons through the doped W ions and the H+ ions from water molecules to generate C-H bonds. Due to strong W-O bonding, the last protonation of :CH3 generated CH4. Their high electron negativity not only allows the W6+ ions to strongly bind the carbonate species to facilitate charge transfer, but also increase surface acidity to enhance water adsorption, thus effectively promoting the photocatalytic activity of TiO2 .

第一章、前言 1
1.1研究動機 1
1.2研究目的 2
第二章、文獻回顧 3
2.1二氧化鈦簡介 3
2.1.1光觸媒發展與應用 3
2.1.2二氧化鈦特性 4
2.2光催化還原二氧化碳 6
2.2.1光催化還原CO2原理 6
2.2.2 TiO2光催化還原CO2反應機制 7
2.2.3影響光還原CO2反應因素 9
2.3二氧化鈦修飾 10
2.3.1二氧化鈦摻雜種類與效率 10
2.3.2二氧化鈦摻雜與產物關係 18
2.3.3二氧化鈦摻雜方式 18
2.4鎢摻雜二氧化鈦(W-TiO2) 19
2.4.1鎢摻雜二氧化鈦介紹 19
2.4.2鎢摻雜二氧化鈦特性 20
2.5二氧化鈦表面反應機制 22
2.5.1表面吸附現象 22
2.5.2 FTIR-DRIFT對觸媒表面探討 23
第三章、研究方法 25
3.1實驗架構 25
3.2實驗藥品 26
3.3光觸媒材料合成方法 26
3.4材料鑑定分析 28
3.4.1紫外光可見光分光光譜儀(UV-Vis Spectophotometer) 28
3.4.2 X光粉末繞射儀(X-ray Diffraction, XRD) 29
3.4.3等溫氮氣吸脫附分析(Nitrogen Adsorption-Desorption Isothermal Analysis) 29
3.4.4 X 射線光電子能譜分析(X-ray photoelectron spectroscopy, XPS) 30
3.4.5電子式掃描顯微鏡 ( Scanning Electron Microscopy, SEM) 31
3.4.6穿透式電子顯微鏡元素分析(Transmission Electron Microscopy-Energy Dispersive Spectrum, TEM-EDS) 31
3.4.7電子順磁共振儀(Electron Paramagnetic Resonance, EPR) 31
3.4.8螢光光譜儀分析(Photoluminescence Spectroscopy, PL) 32
3.5光催化二氧化碳還原系統 32
3.5.1氣相人工光催化設備與操作步驟 32
3.5.2液相人工光催化設備與操作步驟 34
3.5.3氣相層析儀定性分析參數設定 35
3.5.4氣相層析儀定量分析參數設定 36
3.6漫反射紅外線傅立葉轉換即時監測(In-situ Diffuse reflectance infrared Fourier transform Analysis, DRIFT) 36
第四章、結果與討論 39
4.1材料特性鑑定 39
4.2光催化還原產物定性分析 49
4.3光催化還原CO2反應 50
4.4光催化還原CO2反應機制 55
4.4.1電子順磁共振(EPR) 55
4.4.2氣相系統光催化還原CO2即時監測 58
第五章、結論 66
參考文獻 67
附錄A.光催化還原CO2產物檢量線 73
附錄B. 不同反應環境下隨時間變化EPR圖譜 74
附錄C. TiO2與W-TiO2不同反應環境下EPR圖譜 76
附錄D. W-TiO2表面殼層計算公式 77
附錄E. 氣相層析儀不同標準品之滯留時間 78

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