Plasmonic properties of bimetallic nanostructures and their applications in hydrogen sensing and chemical reactions.

• Other Authors: Jiang, Ruibin.
• Format: Others
• Language: English; Chinese
• Published: 2013
• Subjects: Nanostructured materials > Electric properties; Nanotechnology; Plasmons (Physics)
• Online Access: http://library.cuhk.edu.hk/record=b5549790; http://repository.lib.cuhk.edu.hk/en/item/cuhk-328573

表面等離子體基元共振是自由電子在納米尺寸的集體共振效應，該效應會產生一系列新奇的性質。貴金屬納米結構由於可以產生表面等離子體基元共振而受到各個領域廣泛的關注。在共振激發的情況下，貴金屬納米結構具有極大的散射和吸收截面積以及極強的進場放大效應。這些奇特的性質可以應用於傳感、成像、光學調製、光熱療、光催化和太陽能電池等領域。金和銀納米結構由於其表面等離子體基元共振波長處在可見和近紅外波段而受到廣泛研究。然而，在某些應用中純金或純銀納米結構不能起到很好的作用。例如，金和銀對很多化學反應的催化活性很弱或者沒有催化活性。如果把金和銀與其他金屬複合在一起就可以同時獲得表面等離子基元共振和其他效應。在我的博士研究期間，我製備了Au/Ag 和Au/Pd 複合雙金屬納米結構和研究了該複合結構的表面等離子體基元共振的性質和在氫氣傳感和光催化中的應用。 === 由於在金屬納米結構的製備中晶種起著至關重要的作用，所以我首先研究了晶種的晶體結構和形狀對雙金屬納米結構合成的影響。我研究了銀和鈀分別在相同條件下在單晶金納米棒、多晶金納米棒和納米雙錐種子上的生長過程。研究發現當晶種是單晶金納米棒時，銀和鈀的生長形成長方體雙金屬納米結構。然而，當晶種是多晶的金納米棒和納米雙錐時，銀和鈀的生長生成納米棒雙金屬結構。銀和鈀在多晶金納米棒上的生長由兩端開始，而在多晶金納米雙錐上的生長由臺階面開始。這表明在雙金屬納米結構的生長過程中納米晶種的晶體結構對最終納米結構的形貌具有決定性的作用，而納米晶種的形狀對生長動力學有明顯的影響。 === 在Au/Ag納米晶製備過程中，我發現Au/Ag納米晶具有四個表面等離子體基元共振峰。於是我對這四個共振峰的演變和共振模式進行了實驗和理論研究。電動力學模擬表明能量最低的共振峰是縱向的電偶極共振，能量次低的共振峰是沿橫向的電偶極共振，兩個高能量的共振峰是沿著橫向的電八極共振。遲滯效應和兩個垂直橫向激發的干涉是導致形成兩個電八極共振的關鍵因素。研究發現隨著銀殼厚度的增加，縱向電偶極共振峰藍移，橫向電偶極共振峰先藍移后稍微紅移，兩個電八極共振沒有明顯的峰位移動。四個表面等離子體基元共振的強度都隨著銀殼厚度的增加而增強。 === 鈀被廣泛地應用於氫氣傳感和催化反應中。於是我研究了Au/Pd 雙金屬納米結構的氫氣傳感和光催化性能。在氫氣傳感研究中，我製備了兩種不同結構的Au/Pd 納米結構。一種具有連續的鈀殼層，另一種鈀殼層不連續。對於具有連續鈀殼層的納米結構，氫氣的傳感性能隨著鈀殼層厚度的增加而增加。實驗發現當納米結構暴露在4%的氫氣中時表面等離子體基元共振峰移動高達56 nm。不連續鈀殼層的納米結構的氫氣傳感性能不如連續鈀層的納米結構。我進一步對Au/Pd 雙金屬納米結構的光催化性能進行了研究。所選取的催化反應是Suzuki 偶聯反應。研究結果表明Au/Pd 納米結構可以有效地捕獲光能來促進化學反應。由於Au/Pd 納米結構使表面等離子體基元共振功能和催化功能緊密集成在一個納米結構中，因此表面等離子基元共振部份所捕獲的光能可以有效地傳遞到催化功能部份而實現光催化。研究發現熱電子效應和光熱轉化效應同時加速化學反應。其中光熱轉化在我的實驗中體現為非局部加熱效應，熱電子對化學反應的促進作用依賴于環境溫度。因此，光熱轉化效應可以促進熱電子轉移效應。 === 本論文的研究結果有助於人們瞭解具有表面等離子體基元共振性質的雙金屬納米機構的設計和應用。對Au/Ag雙金屬納米結構表面等離子體基元共振性質的研究不僅加深了人們對雙金屬表面等離子體基元共振的瞭解而且對利用不同共振模式實現特定功能有著指導意義。對Au/Pd雙金屬納米結構在氫氣傳感和催化反應應用中的研究明確表面雙金屬表面等離子體納米結構可以實現單一組成不具備的功能，這在一定程度上有助於擴展表面等離子基元共振在生命科學、能源和環境領域的應用。 === Noble metal nanocrystals have attracted great interest from a wide range of research fields because of their intriguing properties endowed by their localized surface plasmon resonances, which are the collective oscillations of free electrons. Under resonant excitation, metal nanostructures exhibit very large scattering and absorption cross sections and large near-field enhancement. These extraordinary properties can be used in different applications, such as plasmonic sensing and imaging, plasmon-controlled optics, photothermal therapy, photocatalysis, solar cells, and so on. Gold and Silver nanocrystals have plasmon resonances in the visible and near-infrared regions. However, gold and silver are not suitable for some applications. For example, they are generally inactive for catalyzing chemical reactions. The integration of plasmonic metals with other metals can offer superior or new physical/chemical properties. In this thesis, I prepared Au/Ag and Au/Pd bimetallic nanostructures and studied their lasmonic properties and applications in hydrogen sensing and photocatalysis. === Seeds have a crucial importance in the synthesis of bimetallic nanostructures. I therefore first studied the roles of the crystalline structure and shape of seeds on the overgrowth of bimetallic nanostructures. The overgrowth of silver and palladium on single crystalline Au nanorods, multicrystalline Au nanorods, and nanobipyramids were studied under the same conditions for each metal. The growths of silver and palladium on single crystalline Au nanorods gave cuboidal nanostructures, while rod-shaped nanostructures were obtained from the growths of silver and palladium on multicrystalline Au nanorods and nanobipyramids. Moreover, the growths of silver and palladium on multicrystalline Au nanobipyramids started at the stepped side facets, while the growths started at the twin boundaries on multicrystalline Au nanorods. These results unambiguously indicate that the crystalline structure of seeds plays a significant role on the final morphologies of multimetallic nanostructures, while the seed shape has a prominent effect on the growth kinetics. === Four plasmon resonance bands were observed in Au/Ag bimetallic nanocrystals. I then studied the evolution and nature of the four plasmon bands during the silver coating on Au nanorods both experimentally and theoretically. Electrodynamic simulations revealed that the lowest-energy peak belongs to the longitudinal dipolar plasmon mode, the second-lowest-energy peak is the transverse dipolar plasmon mode, and the two highest-energy peaks can be attributed to octupolar plasmon modes. The retardation effect and the interference between two perpendicularly polarized excitations along the edge directions are important for the formation of the distinct highest-energy and second-highest-energy octupolar plasmon modes, respectively. As the Ag shell thickness is increased, the longitudinal plasmon mode blue-shifts, the transverse plasmon mode first blue-shifts and then red-shifts slightly, and the two octupolar plasmon modes stay at nearly constant wavelengths. The extinction intensities of all the four plasmon bands increase with the increase of the overall particle size. === Palladium is widely used in hydrogen sensing and catalysis. I therefore studied the applications of Au/Pd bimetallic nanostructures in hydrogen sensing and photocatalysis. Two types of Au/Pd bimetallic nanostructures, nanostructures with continuous and discontinuous Pd shells, were employed to study their hydrogen sensing performances. For the nanostructures with continuous Pd shell, the hydrogen sensing performances were improved with the increase in the Pd shell thickness. A plasmon shift of 56 nm was observed when the hydrogen concentration was 4%. The nanostructures with discontinuous Pd shell exhibited smaller plasmon shifts compared with those with continuous Pd shell. For the photocatalytic application of Au/Pd bimetallic nanostructures, I studied their photocatalytic performance for Suzuki coupling reactions. The results indicate that plasmonic Au/Pd bimetallic nanostructures can efficiently harvest light energy for chemical reactions. The intimate integration of plasmonic and catalytic components in one nanostructure enables the light energy absorbed by the plasmonic component to be directly transferred to the catalytic component. Both hot electron transfer and photothermal heating contribute to the plasmon-enhanced chemical reactions. The photothermal effect is a nonlocal heating and the contribution of the hot electron transfer effect is dependent on the environmental temperature. Therefore, the photothermal heating effect can promote the hot electron transfer effect. === I believe that my research work will be very helpful for the design and application of plasmonic bimetallic nanostructures. My study on the plasmonic properties of Au/Ag bimetallic nanocrystals has deepened the understanding of the plasmons of Au/Ag nanorods and will be helpful for utilizing the different modes to achieve specific functions. The hydrogen sensing and photocatalysis of Au/Pd bimetallic nanostructures have shown that the integration of functional components with plasmonic nanostructures can achieve unconventional properties, which will flourish the applications of plasmons in life sciences, energy, and environmental areas. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Jiang, Ruibin = 雙金屬納米結構表面等離子體基元共振的研究及其在氫氣傳感和化學反應中的應用 / 江瑞斌. === Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. === Includes bibliographical references. === Abstracts also in Chinese. === Jiang, Ruibin = Shuang jin shu na mi jie gou biao mian deng li zi ti ji yuan gong zhen de yan jiu ji qi zai qing qi chuan gan he hua xue fan ying zhong de ying yong / Jiang Ruibin. === Abstract --- p.I === Acknowledgements --- p.VI === Table of Contents --- p.VIII === List of Figures --- p.X === List of Tables --- p.XIII === Chapter 1 --- Introduction --- p.1 === Chapter 1.1 --- Localized surface plasmon resonances --- p.1 === Chapter 1.2 --- Applications of localized surface plasmon resonances --- p.3 === Chapter 1.3 --- Overview of this thesis --- p.13 === Chapter 2 --- Theory, Simulation, and Experimental Methods for the Investigation of LSPRs --- p.20 === Chapter 2.1 --- Theoretical methods --- p.20 === Chapter 2.2 --- Simulation methods --- p.30 === Chapter 2.3 --- Experimental methods --- p.35 === Chapter 3 --- Preparation of Metal Nanostructures --- p.43 === Chapter 3.1 --- Preparation methods for Au nanocrystals --- p.43 === Chapter 3.2 --- Seed-mediated growth method --- p.46 === Chapter 3.3 --- Metal nanostructure preparations --- p.54 === Chapter 4 --- Crystalline Structure-Determined Growth of Bimetallic Nanocrystals --- p.62 === Chapter 4.1 --- Au nanocrystal seed preparation --- p.64 === Chapter 4.2 --- Au/Ag bimetallic nanocrystals --- p.66 === Chapter 4.3 --- Au/Pd bimetallic nanocrystals --- p.71 === Chapter 4.4 --- Summary --- p.77 === Chapter 5 --- Plasmons of Au/Ag Core/Shell Bimetallic Nanocrystals --- p.83 === Chapter 5.1 --- Variations of plasmons with Ag shell thickness --- p.86 === Chapter 5.2 --- Nature of the different plasmon modes --- p.94 === Chapter 5.3 --- Summary --- p.99 === Chapter 6 --- Au/Pd Bimetallic Nanostructures for Hydrogen Sensing --- p.105 === Chapter 6.1 --- Au nanorods with continuous Pd shell for hydrogen sensing --- p.107 === Chapter 6.2 --- Au nanorods with discontinuous Pd shell for hydrogen sensing --- p.114 === Chapter 6.3 --- Theoretical simulations --- p.117 === Chapter 6.4 --- Summary --- p.119 === Chapter 7 --- Plasmon-Enhanced Chemical Reactions --- p.124 === Chapter 7.1 --- Mechanisms of plasmon enhancement in chemical reactions --- p.125 === Chapter 7.2 --- Plasmon-enhanced Suzuki coupling reactions --- p.129 === Chapter 7.3 --- Summary --- p.149 === Chapter 8 --- Conclusions --- p.156 === Curriculum Vita --- p.160