以CTEABr為模版試劑的介孔二氧化矽之合成與相變化研究

Synthesis and the Phase Transformation of Mesoporous Silica using CTEABr as the pore-directing agent

劉銘璋(Ming-Chang Liu)

指導教授 ： 鄭淑芬

國立臺灣大學/理學院/化學研究所/博士(2005年)

https://doi.org/10.6342/NTU.2005.10378

摘要

由於介孔二氧化矽在觸媒、光學、感應器、低介電常數材料、薄膜等方面的應用‚吸引了許多研究的熱潮‚介孔材料的結構與穩定性對於相關應用有很大的影響‚因此‚了解控制介孔結構的因素是本研究的目的之一。在酸性條件下使用 cetyltriethylammonium bromide (CTEABr) 當作介孔模版試劑‚以TEOS為矽源‚可合成數種介孔二氧化矽‚我們發現使用不同的酸‚例如硫酸、鹽酸和硝酸‚在不同濃度與不同合成時間下可以合成出四種不同的介孔結構(3D-hexagonal P63/mmc‚ cubic Pm3n‚2D-hexagonal p6mm‚ and cubic Ia3d)。利用in-situ X-光粉末繞射技術研究其形成的機制‚我們發現除了陰離子的種類和濃度可以控制介孔結構‚樣品的乾燥處理亦會引發結構的相變化。
為了進一步了解陰離子對結構的影響‚我們首先進行了陰離子的競爭實驗‚方法是將這三種酸依不同比例混合‚比較何種離子對結構影響較大‚發現是 NO3-> Cl-> HSO4 ‚ 這個序列正好符合Hofmeister series。另外我們做了介面陰離子交換的實驗‚將已形成介孔結構的二氧化矽以不同的鈉鹽溶液(HSO4-, H2PO4-, F-, OAc-, Cl-, Br-, NO3-, SCN-)作後處理‚這些陰離子對介孔結構的影響也符合Hofmeister series‚並且相變化是由堆疊因子(g)較小的結構向較大的結構方向進行。由於陰離子對pyren的環境極性以及放光的半衰期有關係‚藉由放入介孔結構的微包中‚其螢光實驗證實介面陰離子與溶液中的陰離子是會達到交換平衡。
本論文也發展在鹼性條件下合成立方Pm3n結構介孔二氧化矽的方法‚我們將之命名為NTU-1‚用以和酸式合成法之SBA-1作區別‚因為二者的形成機制不同。NTU-1是使用cetyltriethylammonium bromide (CTEABr) 當作介孔模板試劑‚以水玻璃為矽源並加入氯化鈉所合成‚其介孔結構不受陰離子的後處理影響‚在不同陰離子溶液中亦不會發生相變化‚並且具有很好的水熱穩定性以及孔洞性質‚此外我們成功的將鋁、鐵、銅放入二氧化矽的骨架中‚此種材料將是很好的觸媒。

關鍵字

介孔二氧化矽 ； 離子效應 ； 四級銨鹽

並列摘要

Mesopouors silicas have attracted much attention due to their possible applications as catalyst supports, optical materials, sensors, low-k dielectrics, membranes, and selective adsorbents. The porous structure and stability of the material are very important factors for applications. Therefore, the understanding of the factors which control the mesostructures is one of the goals of this study. Mesoporous silica synthesized using cetyltriethylammonium bromide (CTEABr) as the structure-directing agent and tetraethyl orthosilicate (TEOS) as a silica source is of great interest because various mesostructures can be formed by changing the synthesis condition. In the present study, four types of well-ordered mesophases, 3-D hexagonal P63/mmc, cubic Pm3n, 2-D hexagonal p6mm and cubic Ia3d, have been synthesized in the presence of H2SO4, HCl, and HNO3 acids. By using in-situ XRD techniques, the details of formation mechanism were studied. The anions were found to play important roles on the mesophases formed, and drying also led to phase transformation. In the competition of anion experiments, these three acids were mixed at different ratios in order to compare their abilities in affecting the structure formed, which was found to decrease in the order of NO3-> Cl-> HSO4 . This sequence follows the Hofmeister series. The interfacial anions between the template and silica were found to be exchangeable with the anions in the solution. Sodium salts of HSO4-, H2PO4-, F-, OAc-, Cl-, Br-, NO3-, SCN- were utilized to compare their strength of influence. The phase transformation was found toward the mesostructures of increasing the g-value, where g is the packing parameter of surfactants. The influences of anions follow the Hofmeister series of salting-in. Because the polarity and lifetime of pyrene fluorescence are anion-dependent, the anion exchange equilibrium was confirmed by the fluorescence experiments with pyrene seated in the micelle.
A novel synthesis route to prepare SBA-1 in alkaline condition was developed, and the material was termed NTU-1 to distinguish it from that formed in acid. The formation mechanism was different from that in the acidic condition. The cubic mesophase was not affected by post-treatment with other anions. The materials showed high hydrothermal stability and porosity. The alkaline route facilitated the incorporation of Al, Fe, and Cu into the silica framework. It should be a good candidate as a catalyst.

並列關鍵字

Mesoporous silica ； ionic effect ； Hofmeister series

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