萬本儒臺灣大學：化學工程學研究所楊捷超Yang, Chieh-ChaoChieh-ChaoYang2007-11-262018-06-282007-11-262018-06-282004http://ntur.lib.ntu.edu.tw//handle/246246/52183先前的研究顯示，在可見光源下，載負Au於高能隙半導體光觸媒K2La2Ti3O10光催化水分解的產氫活性(固定時距內累積產氫量與瞬時產氫速率)，優於載負Ni於K2La2Ti3O10的光催化活性，以此為出發點，本研究設計了兩部份的實驗來尋求Au影響光催化水分解活性的機制。 實驗結果發現，Au即具有光催化水分解的能力，由UV-Vis吸收光譜，判定為具有半導體性質的奈米金，能隙值小，能被可見光源激發產生電子、電洞，因此能夠氧化、還原水產生氫氣與氧氣。但其所產生的氫氣量卻是相當有限，若載負Au於半導體型光觸媒(如TiO2或K2La2Ti3O10)上，其光催化水分解累積產氫量與瞬時產氫速率將大幅提高，遠超過擔體觸媒與Au本身的活性表現。推測是半導體型光觸媒減低了電子、電洞再結合的發生，由奈米金受可見光源激發產生電子、電洞，電子傳遞至半導體型光觸媒上還原水產生氫氣，而奈米金價帶上的電洞則氧化水產生氧氣。 表面電漿共振吸收為主的Ag/TiO2與d-d transition吸收為主的Ni/TiO2之可見光源光反應結果，兩者對於光催化水分解都有促進水分解產生氫氣與氧氣的表現，但是Ag/TiO2的催化活性還是優於Ni/TiO2，除了表面電漿共振吸收影響光催化水分解高過d-d transition吸收的影響之可能性外，Ag、Ni與TiO2間的接觸模式也可能影響其催化活性。由表面電漿共振吸收所趨動的導電電子，與d-d transition吸收之價電子，能量都足以還原水產生氫氣，但Ag與TiO2間為歐姆式接觸(Ohmic contact)，TiO2價帶上電子可以移往Ag而不需要消耗額外的能量，所留下的電洞將可氧化水產生氧化；而Ni與TiO2間為肖基勢接觸(Schottky contact)，TiO2價帶上電子會受限於肖基勢接觸而需消耗額外的能量才可傳遞至Ni，因此其光催化水分解活性較Ag/TiO2(LTR’)活性更低。 另一方面，利用以Maxwell Equation為基礎描述球型金屬粒子在介質中反射、穿透與吸收行為的Mie Theory，嘗試去模擬Au、Ag與Ni載負於固態介質的吸收光譜，瞭解到隨著介質介電常數(dielectric constant)的增加，金屬的特徵吸收會有紅位移(往高波長移動)的現象，包括Au、Ag的表面電漿共振吸收與Ni的d-d transition吸收，這與UV-Vis吸收光譜的實驗結果相吻合，然而擔體介質本身的吸收行為卻無法呈現，原因是Mie Theory的基本假設是介質的吸收低而忽略其影響。Based on the research results in the past years, photo-catalytic activity of Au/K2La2Ti3O10 for water decomposition under visible light irradiation was better than that of Ni/K2La2Ti3O10. In order to explore the reasons, two experiments were designed. It was found that Au itself can catalyze water decomposition under visible light irradiation. From its UV-Vis spectrum, it is likely that nano-size gold possesses the character of semiconductor. Owing to small band gap, e--h+ pairs can be excited to reduce and oxidize water into hydrogen and oxygen. Even so, the amount of hydrogen evolved was limited. Loaded Au on high energy gaps semiconductors, TiO2 or K2La2Ti3O10, can tremendously improve photo-catalytic activity in water decomposition under visible light irradiation. High energy gap semiconductors, TiO2 or K2La2Ti3O10, prevent the recombination of e--h+ pairs originated in nano-gold. The catalytic activities of Ag/TiO2 and Ni/TiO2 were compared in this research. It was found that the activity of Ag/TiO2 was higher than that of Ni/TiO2 for photodecomposition of water. In visible light region, there was mainly surface plasmon resonance for Ag and primarily d-d orbital interband transition for Ni. Thereby, it suggests that the enhancement of photo-catalytic activity by surface plasmon resonance may be superior to that by d-d orbital interband transition. The excited conduction band electrons (SPR) and valence band electrons (d-d transition) possessed enough energy to reduce water into hydrogen. Nevertheless, there may be another reason for better activity of Ag/TiO2. It takes excess energy to transfer electrons from TiO2 to Ni due to the Schottky barrier between Ni and TiO2. Ag/TiO2 showed higher photo-catalytic activity as a result of Ohmic contact between Ag and TiO2. The modeling of absorption spectra of Au, Ag, and Ni loaded on solid mediums were attempted in this research based on Mie Theory. It was found that the SPR and d-d transition band of Au, Ag, and Ni shifted to longer wavelength (red-shift) in higher dielectric constant medium. The shifts are consistent with the experimental results. However, the intrinsic absorption of medium could not be shown from the model. This is because the basic assumption of Mie Theory does not consider the absorption of the medium.目錄 I 摘要 III Abstract IV 表索引 VI 圖索引 VII 第一章 緒論 1 1.1前言 1 1.2金屬吸收及其模擬之文獻回顧 5 1.3動機 11 1.4研究主題 13 第二章 研究設計與實驗方法 14 2.1研究設計 14 2.2實驗方法 22 2.3基本參數運算 30 2.4藥品與氣體記錄 33 第三章 實驗結果與討論 34 3.1確認Au/K2La2Ti3O10在可見光源(419nm)下 光催化水分解主要產氫來源 34 3.2求證表面電漿共振在可見光源下(419nm)下 影響光催化水分解的可能性 47 3.3以Mie Theory模擬載負Au、Ag與Ni於固態 觸媒之吸收光譜 66 第四章 結論 79 第五章 參考文獻 82 附錄一 能帶位置決定方式 85 附錄二 Mie Theory模擬計算 894075781 bytesapplication/pdfen-US表面電漿共振水分解光催化金goldphoto-catalyticsurface plasmon resonancewater decompositionthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/52183/1/ntu-93-R91524015-1.pdf