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  • 學位論文

Facet-Dependent Organocatalytic Activities of Au and Cu2O Nanocrystals and Facet-Dependent Optical Properties of Pd-Cu2O Core-Shell Nanocrystals

晶面對金和氧化亞銅奈米晶體在有機催化反應上的影響及鈀和氧化亞銅的核殼結構的晶面相關光學性質

指導教授 : 黃暄益
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摘要


Nanomaterials possess very distinct properties from their bulk counterpart. By controlling particularly their shape, size and composition of the nanoparticles their catalytic and optical properties can be modified significantly. Though the shape controlled synthesis of Cu2O and Au nanoparticles have been well developed but characterization of their facet dependent catalytic activity and product selectivity has not been studied before. Similarly for the first time facet-dependent optical properties have been observed for Pd-Cu2O core‒shell nanocrystals. In chapter 1, we have reported the highly facet-dependent catalytic activity of Cu2O nanocubes, octahedra and rhombic dodecahedra for the multi-component direct synthesis of 1,2,3-triazoles from the reaction of alkynes, organic halides, and NaN3. Cleanly surfactant-removed Cu2O nanocrystals with the same total surface area were used for their catalytic activity comparison. Rhombic dodecahedral Cu2O nanocrystals bounded by the {110} facets were much more catalytically active than Cu2O octahedra exposing the {111} facets, whereas Cu2O nanocubes displayed the slowest catalytic activity. The superior catalytic activity of Cu2O rhombic dodecahedra is attributed to the fully exposed surface Cu atoms on the {110} facet. A large series of 1,4-disubstituted 1,2,3-triazoles have been synthesized in excellent yields with high regioselectivity under green condition using these rhombic dodecahedral Cu2O catalysts, including the synthesis of rufinamide, an antiepileptic drug, demonstrating the potential of these nanocrystals as promising heterogeneous catalysts for other important coupling reactions. In Chapter 2, we have synthesized Au nanocubes, octahedra, and rhombic dodecahedra were examined for facet-dependent catalytic activity in the formation of triazole. Rhombic dodecahedra gave 100% regioselective 1,4-triazole. The product yield increases by decreasing the particle size. However, a mixture of 1,4- and 1,5-triazoles was obtained with lower yields when cubes and octahedra of similar sizes were used. The lowest Au atom density on the {110} surface and largest unsaturated coordination number of surface Au atoms may explain thier best catalytic efficiency and product regioselectivity. Various spectroscopic techniques were employed to verify the formation of the Au–acetylide intermediate, and establish the reaction mechanism in which phenyl acetylene binds to the Au {110} surface via the terminal binding mode to result in the exclusive formation of 1,4-triazole. The smallest rhombic dodecahedra can give diverse 1,4-disubstituted triazoles in good yields by coupling a wide variety of alkynes and organic halides. In chapter 3, we have developed Pd‒Cu2O core‒shell nanocubes and truncated octahedra with six average sizes for each particle shape have been synthesized from 29-nm Pd nanocubes. The nanocubes have average edge lengths of 64‒124 nm, while the truncated octahedra are 107‒183 nm in opposite tip distance. The core and shell composition and lattice orientation have been determined, showing the formation of single-crystalline Cu2O shells. The surface plasmon resonance (SPR) band from the Pd nanocrystal cores is barely visible. However, the Cu2O shells display facet-dependent optical properties. The Cu2O absorption band for smaller Pd‒Cu2O cubes is consistently more red-shifted than somewhat larger Pd‒Cu2O truncated octahedra. This work again shows that the observed facet-dependent optical phenomenon in metal‒Cu2O core‒shell nanocrystals is derived from the Cu2O shells. Use of 40-nm Pd cubes as cores gave uniform and size-tunable Pd‒Cu2O nanocubes and truncated octahedra that display the Pd SPR band. The Pd SPR band is consistently located at 650 nm for Pd‒Cu2O truncated octahedra, and 670 nm for the cubes despite large variation in the shell thickness. Both the Cu2O absorption and the Pd plasmonic band exhibit facet-dependent optical properties.

並列摘要


材料從塊材縮小至奈米尺度時,其性質會有明顯的不同。藉由控制奈米粒子的形狀、 大小和組成它們的催化效果和光學性質上會有顯著的改變。雖然合成氧化亞銅和金奈 米粒子的形狀控制已經有很好的發展,但對於晶面催化活性和產物選擇性在之前尚未 被探討。在本篇論文中,也是第一次探討鈀-氧化亞銅核殼奈米晶體的晶面光學性質。 在第一部分,我們報導了氧化亞銅奈米立方體,八面體及菱形十二面體的晶面催化活 性,反應中加入炔類、有機鹵素和疊氮鈉直接合成1,2,3-triazoles。清除氧化亞銅奈米 晶體上的界面活性劑後,將不同形狀的氧化亞銅奈米晶體定相同表面積並探討它們之 間的催化活性。菱形十二面體的{110}晶面有最好的催化活性,八面體的{111}晶面次 之,立方體的{100}晶面之催化活性則最差。由於菱形十二面體最表層的銅原子是最完 全暴露的,故其有最佳之催化活性。使用菱形十二面體氧化亞銅奈米粒子可以合成一 系列具良好產物選擇性的1,4-disubstituted 1,2,3-triazoles,其中包括抗癲癇藥物 rufinamide,這也表示這些具有異相催化潛力的奈米粒子應可進形其他重要的偶聯反應。 在第二部分,我們合成金奈米立方體、八面體和菱形十二面體並以用於催化反應形成 triazoles 並探討它們之間的催化活性。使用菱形十二面體的金奈米晶體當作催化劑時, 可以得到100%區域選擇的1,4-triazole。隨著奈米粒子的尺寸減小,產率則會增加。然而,使用金奈米立方體和八面體當作催化劑時,會合成低產率的1,4- and 1,5-triazoles 的混合物。{110}晶面具有最低的金原子密度和最大未飽和配位數,這可以用來解釋它 具有最佳的催化活性和高的產物選擇性。利用各種光譜技術可用來驗證金-乙炔中間體 的形成,並建立苯基乙炔終端鍵結Au{110}表面以產生1,4-triazoles 的反應機制。藉由 最小的菱形十二面體作為催化劑可以耦合多種炔烴和有機鹵化物合成高產率1,4- disubstituted triazoles。 在第三部分,利用29 nm 的鈀立方體合成六種鈀-氧化亞銅尺寸大小的核殼立方體及截 角八面體。奈米立方體的平均邊常為64 至124 nm,截角八面體的兩頂點之間距離為 107 至183 nm,分析核與殼的組成及晶格方向可確認氧化亞銅殼層為單晶結構。雖然 鈀核的表面電漿共振的峰不易觀察,氧化亞銅殼層之光學性質則呈現明顯的晶面效應。 較小顆的氧化亞銅立方體其吸收峰比較大顆的截角八面體略為紅移,因此再次證明金 屬氧化亞銅核殼奈米晶體其氧化亞銅殼層確實具有光學晶面效應。我們並利用40 nm 的鈀立方體作為核合成均一及尺寸可控之鈀-氧化亞銅立方體及截角八面體以呈現出鈀 核的表面電漿共振峰。鈀表面電漿共振峰在截角八面體時為650 nm,立方體則為670 nm。氧化亞銅及鈀兩者的表面電漿共振峰皆具有光學晶面效應。

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