臺灣博碩士論文加值系統

二氧化鈦(TiO2)是一種廣為人知的光觸媒，這幾年因為能源以及環境相關議題崛起，其應用和研究更備受重視。一般來說，研究TiO2多以粉末樣品為題，討論其催化活性，但若要清楚了解反應機制，單晶(single crystal)樣品的單純結構較能清楚呈現活性位點所在。本論文以rutile TiO2(110)單晶作為研究材料，在超高真空系統中，以程溫脫附、反射吸收式紅外光譜、歐傑電子能譜配合密度泛涵理論計算等技術與方法，研究氧、水和甲醇分子的表面吸附與反應現象。
氧與單晶表面的作用顯示，270 K才出現O2分子脫附，實驗證明單晶表面的oxygen vacancy (Ov)，使O2分子吸附其上而形成oxygen adatom (Oa)。水分子在單晶表面的熱脫附實驗顯示，在157 K、180 K與190 K分別觀察到多層、第二層以及單層分子脫附峰，而於400-500 K看見來自Ov位點的水分子脫附訊號。光化學部分是以365 nm的UV光照射樣品，證實吸附在rutile TiO2(110)上的水分子並不會發生反應。甲醇分子吸附在rutile TiO2(110)的反應顯示照光會形成甲醛並在209 K脫附。若將氧氣與甲醇分子共吸附於表面，則因氧裂解生成Oa與甲醇反應形成methoxy中間體，在照光後分別於較低溫看見甲醛(216 K)和甲醇(260 K)生成；若不照光則在500-600 K看見因自身氧化還原(disproportionation)而同時生成的甲醛和甲醇。

In consideration of recent trend in environmental and economical issues of green-process chemistry, the eco-friendly and recyclable titanium oxide has received much attention with the aim of establishing greener, more sustainable photocatalysts. However, the quality of commercial or bench-made TiO2 is somewhat uncontrollable, and thus frequently affects the reproducibility of TiO2-mediated reactions. In order to understand the reaction mechanisms of TiO2-catalyzed interactions of oxygen, water, and methanol, as well as their cross interactions, a single crystal rutile TiO2(110) was selected in this study in order to exclude the complexity caused by powder samples. Ultrahigh vacuum in combination with temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), auger electron spectroscopy (AES), LED UV source and density function theory (DFT) calculations were used to study the TiO2 thermal and photo-chemistry.
O2 desorbs molecularly at 270 K and oxygen vacancies (Ov) are responsible for the dissociative adsorption of O2 molecules to form O adatoms (Oa). In the study of water molecules, the multilayer, the second layer and the monolayer molecular desorption peaks were found at 157 K, 180 K and 190 K, respectively. Under 365 nm UV light irradiation, water remained inactive. Methanol was found to turn into formaldehyde which desorbed at 209 K in TPD, once adsorbed on surface and followed by UV irradiation. Coadsorbed O2 and methanol can create methoxy intermediates by OH bond breaking with Oa. Under UV irradiation, formaldehyde and methanol were observed to desorb at 216 K and 260 K. Without UV irradiation, disproportionation of methoxy affords formaldehyde and methanol simultaneously at 500-600 K.

論文審定書 i
謝誌 ii
摘要 iii
Abstract iv
目錄 v
圖次 viii
表次 xi
第壹章、介紹 1
第貳章、實驗設備與方法 6
2-1 超高真空系統與實驗裝置 6
2-1-1程溫脫附實驗 (TPD) 8
2-1-2反射式吸收紅外光譜 (RAIRS) 10
2-1-3歐傑電子光譜(AES) 13
2-2 rutile TiO2 (110)單晶與實驗藥品 13
2-2-1 rutile TiO2(110)試片 13
2-2-2實驗藥品 14
2-3 密度泛涵理論計算(Density Functional Theory Calculations，DFT) 15
第參章、實驗結果與詮釋 16
3-1 瞭解rutile TiO2(110)表面性質 16
3-1-1 利用Auger電子能譜鑑定rutile TiO2(110)表面 16
3-1-2 rutile TiO2(110)氧化態不同導致顏色改變 18
3-2 氧氣在單晶表面之熱化學研究 20
3-2-1 氧氣在rutile TiO2(110)表面之TPD實驗 20
3-2-2 anneal溫度及時間對氧在rutile TiO2(110)表面上吸附行為的影響 23
3-2-3 比較sputter 與anneal對O2吸附的影響 26
3-2-4 比較不同吸附溫度的影響 28
3-2-5 O2與oxygen vacancy在rutile TiO2 (110)表面的重要性 30
3-3 水分子在rutile TiO2(110)表面之研究 31
3-3-1 水分子在rutile TiO2(110)表面之熱化學 31
3-3-2 水分子在rutile TiO2(110)表面之光化學 34
3-4 甲醇在rutile TiO2(110)表面之研究 36
3-4-1甲醇在rutile TiO2(110)表面之熱化學 36
3-4-2甲醇在rutile TiO2(110)表面之光化學 39
3-4-3 甲醇與氧在rutile TiO2(110)表面共吸附 42
3-5 甲醇與乙醛在rutile TiO2(110)上RAIR光譜之研究 45
3-5-1甲醇在rutile TiO2(110)上RAIR光譜之研究 45
3-5-2乙醛在rutile TiO2(110)上RAIR光譜之研究 48
3-5-3 RAIR光譜在rutile TiO2(110)的應用及討論 50
3-6 密度泛涵理論計算(DFT)：優化分子結構與模擬IR振動光譜 51
3-6-1 利用DFT計算甲醇在TiO2(110)的優化結構與光譜 51
3-6-2 利用DFT 模擬計算methoxy優化結構與光譜 54
3-6-3 利用DFT模擬計算乙醛優化結構與光譜 57
第肆章、討論與結論 59
4-1 單晶基本性質 59
4-2 各種不同形式氧分子與其反應性 60
4-3 甲醇的氧化反應 60
4-4 結論 62
第伍章、參考文獻 64

圖次
圖1-1 rutile TiO2(110)與 anatase TiO2(101)模型 2
圖1-2 rutile TiO2(110)表面結構 3
圖1-3 Oxygen vacancy 和 Interstitial Ti 4
圖2-1 完整系統裝置示意圖 7
圖2-2 LED-UV點光源 9
圖2-3 分子在金屬表面產生鏡像偶極矩 10
圖2-4 s-與p-polarized偏極光 11
圖2-5 RAIR裝置示意圖 12
圖2-6 單晶規格與實體樣品 13
圖3-1 rutile TiO2(110)經過(a) 0 (b) 1 次清潔步驟後所測得之AES能譜 17
圖3-2 rutile TiO2(110)經過 (a) 0 (b) 3 (c) 40次清潔步驟所呈現顏色變化 (d) 單晶於500 K所呈現的顏色 19
圖3-3 (a) 40 L O2於130 K 在單晶表面不同離子碎片峰之TPD譜 (b) 不同曝氣量(0.1 L、0.5 L、1.0 L、2.0 L、10 L、40 L) m/z = 32之TPD譜 22
圖3-4 (a) 單晶於不同溫度(470 K、510 K、600 K、790 K) anneal 10分鐘 (b) 單晶於不同溫度(340 K、750 K、780 K) anneal 10分鐘及30分鐘之TPD譜 24
圖3-5 單晶分別經過300 K sputter 10分鐘、750 K anneal 10分鐘、300 K sputter 10 分鐘接著750 K anneal 10分鐘之TPD譜 27
圖3-6單晶分別在130 K、200 K、300 K下吸附O2 40 L之TPD譜 (a) m/z = 32 (b) m/z = 16 29
圖3-7 不同D2O (m/z = 20)曝氣量(0.05 L、0.1 L、0.2 L、0.5 L、0.8 L)之TPD圖譜 32
圖3-8 0.1 L D2O於130 K吸附在單晶表面，照射365 nm UV光1小時前後(a) m/z = 20 (b) m/z = 4 TPD比較 35
圖3-9 (a) 0.1 L CH3OD 於130 K吸附在單晶表面不同離子脫附峰之TPD譜 (b) 不同曝氣量(0.02 L、0.05 L、0.1 L、0.2 L、0.3 L、0.8 L)之TPD譜 38
圖3-10 0.1 L CH3OD 於130 K吸附在單晶表面經不同照光時間之TPD譜 (a) m/z = 29 (b) m/z = 33 40
圖3-11 (a) 0.1 L CH3OD與40 L O2共吸附表面後經anneal以及照光之TPD比較 (b) 新單晶上0.08 L CH3OD與40 L O2 共吸附經anneal以及照光之TPD比較 44
圖3-12 (a) 不同CH3OD曝氣量(0.1 L、0.3 L、0.8 L、1.3 L)之RAIR光譜 (b) 1.3 L CH3OD經不同照光時間(dark、0.5 hr、1 hr、1.5 hr)之RAIR光譜 (c) 照射0分鐘及30分鐘UV光後以s-polarized 偏極光偵測所得RAIR光譜 47
圖3-13 (a) 以p-polarized 偏極光偵測acetaldehyde於不同曝氣量(0.5 L、1.5 L、5.5 L)之RAIR光譜 (b) 固定acetaldehyde曝氣量為5.5 L比較s-和p-polarized偏極光所得RAIR光譜 49
圖3-14 (a) CH3OH分子在rutile TiO2(110)表面優化後的結構 (b) CH3OD自由分子優化後的結構 52
圖3-15 (a) 自由CH3OD分子計算光譜 (b) 曝氣量1.3 L CH3OD之RAIR光譜 (c) CH3OH分子在rutile TiO2(110)模型上計算光譜 (d) CH3OH分子計算光譜 (e) NIST標準光譜-氣相CH3OH分子 53
圖3-16 (a) CH2O分子在rutile TiO2(110)模型上計算光譜 (b) 自由CH2O分子計算光譜 (c) NIST標準光譜-氣相CH2O分子 56
圖3-17 acetaldehyde分子在rutile TiO2(110)模型上優化後的結構 57
圖3-18 (a) 自由 CH3CHO分子計算光譜 (b) CH3CHO分子在rutile TiO2(110)模型上計算光譜 (c) 曝氣量5.5 L CH3CHO之RAIR光譜 (d) NIST標準質譜-氣相CH3CHO分子 58

表次
表2-1 14

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