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標題: | 利用第一原理計算研究鈦酸鍶水分解光觸媒 First Principles Investigation of the SrTiO3 Based Water Splitting Photocatalysts |
作者: | Hsin-Chieh Chen 陳信杰 |
指導教授: | 林祥泰(Shiang-Tai Lin) |
關鍵字: | 水分解,光觸媒,可見光,鈦酸鍶,氫氣生產,密度泛函法,第一原理計算, water splitting,photocatalyst,visible-light irradiation,srtio3,hydrogen-production,DFT,ab initio, |
出版年 : | 2011 |
學位: | 碩士 |
摘要: | 本研究乃利用第一原理計算來探討加入金屬摻質對鈦酸鍶水分解光觸媒催化效率的影響。於鈦酸鍶中摻雜銠金屬已被證實能夠有效提升其水分解催化活性,但研究也發現,在摻雜釕金屬的鈦酸鍶的可見光吸收效率高出前者許多,但其對於改善水分解能力卻不顯著。我們利用計算出的能態密度(density of state)以及光學吸收光譜來分析影響光催化水分解效率的機制,發現其中主要存在光子吸收效率(自由電子產生量)和電子電洞復合兩個競爭機制,使得金屬摻質方法存在一能使效率最高的最佳濃度。我們也發現,摻雜銠在能隙區所產生的摻質能階距離價帶邊緣很近,摻質不但能縮小激發電子所需跨越的能障,透過摻質積聚效應分析顯示激發後留下的電洞應能有效地由價帶電子補充,進而減少電子電洞復合的機率。另一方面,摻雜釕所產生的摻質能階明顯比價帶邊緣高出許多,使得它們在其上的電子激發後成為強烈的復合中心(recombination center),此外,較高的釕金屬摻質能階也會降低氧化反應的驅動力。我們的研究表明在鈦酸鍶中摻雜銠能夠有效地提升其光催化水分解活性的可能解釋。 The effects of dopant on the photocatalytic activity of SrTiO3-based systems are investigated using first principle DFT calculations. The SrTiO3:Rh(1%) loaded with Pt has been found to give the best efficiency in water splitting; however the same host doped with Ru leads to very low H2 evolution rate even it has a better visible light response. The analysis of the density of state and the calculated absorption spectra were used to illustrate the mechanisms that influence the photocatalytic efficiency. Our calculation results suggested that the two competing factors ─ the free electron generation (via light harvesting) and the charge recombination (due to the presence of recombination centers) process ─ result in the existence of the optimal doping concentration for the transition-metal-doped SrTiO3 lattice. We also found that the energy states introduced by dopant Rh in the bandgap of SrTiO3 were very close to the valence band maximum. These new states thus reduce the bandgap of catalyst and enhance its light absorption capability. The study of dopant clustering showed that the proximity of these states to the valence band allows for efficient electron replenishment and makes them less possible to trap active electrons. In contrast, the energy states introduced by dopant Ru are significantly higher than the valence band, making them an isolated recombination center. These Ru associated states also reduces the driving force for oxidation reaction. As a result, the Rh-doped SrTiO3 catalysts are found to provide a high H2 evolution rate. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/33140 |
全文授權: | 有償授權 |
顯示於系所單位: | 化學工程學系 |
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