奈米粒子陣列自組裝於中孔洞氧化矽材料

Abstract

金屬奈米粒子陣列 (metallic nanoparticle arrays, MNAs) 在催化、偵測器、磁學、光學和電學等研究領域極有應用性，因此受到相當廣泛的討論。其物理、化學性質隨奈米粒子的顆粒大小、形狀以及排列而有所改變。為了得到高品質的金屬奈米粒子，經常使用奈米中孔洞氧化矽材料做為生長模板，以達到有效控制奈米粒子生長的目的。本研究中利用中孔洞氧化矽奈米粒子 (mesoporous silica nanoparticles, MSNs) 以及中孔洞氧化矽薄膜 (mesoporous silica thin films, MSTFs) 作為生長大面積MNAs的模板，這兩種材料擁有孔徑約5 nm規則排列的垂直孔道以及高度表面積，因此非常有潛力製作出高度規則排列的MNAs材料。 本篇論文第一部分中，我們在規則排列的垂直孔道模板中還原出六角形週期排列金奈米粒子。利用簡易的還原法還原AuCl4-，在孔道還原出高密度六角形週期排列的金奈米粒子陣列。同時，在大面積垂直孔道的MSTFs也還原出高密度的金奈米粒子，並藉由金奈米粒子陣列間的熱點 (hot-spots) 造成表面增強拉曼光譜 (surface-enhanced Raman spectroscopy, SERS)。我們以4-mercaptobenzoic acid (4-MBA) 作為偵測拉曼光譜的試劑，均勻分布在此研究的金奈米粒子陣列，偵測極限可至10 nM，表面增強拉曼散射增強因子 (SERS enhancement factor) 達107。論文第二部份在中孔洞氧化矽奈米材料孔道中附載磷鎢酸 (phosphotungstic acid, PTA)。PTA是一種擁有氧化還原能力的超強酸，同時有質子轉移能力。藉由中孔洞氧化矽奈米材料當作模板探討不同附載PTA的方法，利用高解析度穿透式電子顯微鏡 (HRTEM) 以及X光能量散佈光譜儀 (EDX) 分析高附載量的磷鎢酸。在照射紫外光後材料能夠還原出金奈米粒子。金結合附載強酸的中孔洞氧化矽材料可應用於甘油氧化並具有催化活性。

Highly ordered metallic nanoparticle arrays (MNAs) have received tremendous attention because of various applications in catalysis, sensors, magnetism, optics and electronics. The physicochemical properties of MNAs are highly dependent on their size, shape and arrangement. In order to obtain high quality MNAs, mesoporous silica materials were used as template to effectively control the formation of nanoparticles. Herein, we utilized mesoporous silica nanoparticles (MSNs) and mesoporous silica thin films (MSTFs) as growth templates for fabricating MNAs materials. The templates have uniform pore diameters (~5nm), well-ordered vertical mesochannels, and high surface area, thus providing great opportunities to prepare highly ordered periodical MNAs materials. In the first part of this thesis, hexagonal packing of gold nanoparticles grew on periodic mesochannels were achieved using MSNs and MSTFs as templates. Disc-like monodispersed MSNs with highly ordered mesopores were synthesized and coated on silicon wafer. Ultrahigh number density and hexagonal close-packed gold nanoarrays were obtained via a facile reduction of AuCl4- on the mesostructures of MSNs, leading to densely deployed hot-spots along and across the mesochannels of MSNs, as a potential platform for surface-enhanced Raman spectroscopy (SERS). Meanwhile, we also applied the same reduction process on large area MSTFs with perpendicular mesochannels. Hexagonal gold nanoarrays deployed on the periodic mesochannels were obtained and further examined by scanning electron microscopy (SEM). Experiments of prominent SERS were demonstrated on both of Au-decorated thin film materials by using 4-mercaptobenzoic acid (4-MBA) as a molecular probe. The detection limit of 4-MBA is as low as 10 nM, with a corresponding SERS enhancement factor above 107. In the second part, phosphotungstic acid (PTA), a kind of heteropoly acid (HPA) with Keggin structure, was introduced into the mesochannels of mesoporous silica. PTA shows the characteristics such as strong acidity, redox capacity, and ability of proton transfer. We employed mesoporous silica to confine the growth dimensions of PTA by means of various loading methods. High-loaded PTA in the individual mesochannel was identified by high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDX) analyses. After exposure to UV light, it is able to induce gold nanoparticles via photo-assisted reduction. The Au-decorated mesoporous silica with strong acid provided a new application in oxidation of glycerol.