二氧化矽空心球包覆金奈米粒子的材料合成與催化應用

Abstract

奈米尺度的空心材料，在近幾年受到廣泛的研究與開發，主要原因在於此材料在形態上的特殊構造，可做為物質分離、藥物輸送以及附載金屬粒子作催化反應等相關應用。在傳統的合成方式中，主要以聚苯乙烯或是二氧化矽球等材料當作內層模板，之後藉由鍛燒、鹼/酸液浸泡的方式移除內層模板，但其製備過程繁雜、瑣碎，而且所製備出的二氧化矽空心球，其尺度無法小於100奈米，因而限制了材料的應用性。 在本篇論文中，利用反微乳液(reverse microemulsion)當作合成模板，一步合成出二氧化矽空心球，並加以調控及應用。藉由加入有機矽烷(3-aminopropyltrimethoxysilane, APTS)，導致矽氧鍵結的程度不足，使縮和不完全的二氧化矽在去離子水洗滌的過程當中，藉著球殼上的微孔洞流出，形成二氧化矽空心球。在本實驗中，藉此方式合成二氧化矽空心球，調整不同的溶劑、助界面活性劑(co-surfactant)，及界面活性劑的比例，去控制二氧化矽空心球的大小，可從25奈米調整到170奈米。所以我們可以視其附載物的大小，依所需二氧化矽空心球的大小來進行合成。此奈米尺度的二氧化矽空心球，在生醫方面研究與應用上均具有相當的潛力，是一個值得我們去深入探討的議題。 另一方面，將二氧化矽空心球附載金奈米粒子，探討其材料在催化方面的應用。在對位硝基酚(p-nitrophenol)的還原實驗中，二氧化矽空心球提供了一個抑制二硫基琥珀酸(meso-2,3-dimercaptosuccinic acid, DMSA)毒化金奈米粒子的功能；同時在一氧化碳的氧化反應中，二氧化矽空心球可以阻止金奈米粒子在高溫反應過程中聚集的發生；不僅如此二氧化矽空心球亦可當作一個微反應器，藉由水氣的調控作為啟動反應是否進行的開關。由上述說明可以知道二氧化矽空心球不論在催化上或是在生醫方面的應用均具有相當高的潛力。

In recent years, hollow nanostructures have been reported of their unique properties such as high surface-to-volume ratio and the large fraction of void space in hollow structure. Those materials could be used in various applications including catalysis, drug delivery, hydrogen storage, and rechargeable batteries. In general, the as-synthesized materials are prepared through coating the target materials on the templates. Then, hollow structures are obtained by removal of the templates. However, the synthetic procedures were complicated and involved numerous steps. It was difficult to reduce the particle size to 100 nm. Thus, those methods restricted the development of hollow nanostructure in the biomedical applications. Herein, we synthesized hollow silica nanospheres (HSNs) with tunable sizes from 25 nm to 170 nm by a one-step water in oil reverse microemulsion (W/O) method. The size of HSNs could be adjusted via three approaches: (1) changing the oil phase in the reverse microemulsion, (2) adjusting the volume of co-surfactant, and (3) varying the ratio of surfactant CA-520 to Triton X-100. The compositions and structures were characterized by different characterization techniques, such as transmission electron microscope (TEM), and nitrogen adsorption-desorption isotherms. Furthermore, the functional materials such as metal, metal oxide, drug, and protein could be encapsulated in the hollow silica nanospheres through this novel method. Hollow silica nanospheres have potential applications in catalysis, cell-labeling and drug delivery. Herein, we demonstrate its application in catalysis. The gold nanoparticle encapsulated in hollow silica nanospheres (Au@HSNs) were examined on p-nitrophenol reduction and CO oxidation reaction. The silica shell of hollow silica sphere protected the gold nanoparticle from sintering during calcination and reaction. In p-nitrophenol reduction, the Au@HSNs displayed high catalytic activity and resistance to DMSA (meso-2,3-dimercaptosuccinic acid) poisoning. In CO oxidation reaction, the catalyst performed amazingly at low-temperature CO oxidation even at -20℃, and displayed high stability after many catalytic cycles. Furthermore, the water vapor could not only enhance the catalytic activity but also be a switch to turn on/off the nanoreactor.