酸性溶液下中孔徑分子篩的反應機構之探討

Formation mechanism of mesoporous sieves in acid solution

張正明(Cheng-Ming Chang)

指導教授 ： 鄭吉豐

中原大學/理學院/化學研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200519

摘要

本篇研究主要以中孔徑分子篩的形成機構為題，利用動態光散射儀測量中孔徑分子篩在合成過程中粒子與粒徑分佈的變化，藉由顆粒成長趨勢與路徑來推測其形成機制。
整體合成反應過程以粒徑的動態變化來進行觀察，反應過程中涉及了界面活性劑在水溶液中的微胞(圓形與棒狀形微胞)形成，矽源在酸性溶液之催化下，在初期時(約5~20分鐘)形成矽酸鹽，而當加入界面活性劑於溶液中經反應20分鐘後使微胞粒徑增加了3~5 nm，證明是矽酸鹽之寡聚體確實吸附在微胞表面的親水性區域，而微胞外圍則為含有高電荷密度的區域，經由粒徑分析圖來觀察顆粒發現彼此仍穩定存在而得到證實。經過一段潛伏時間，矽酸鹽繼續進行水解與縮合反應而改變了微胞外圍的電荷平衡，此時粒子開始進行聚集，因此粒徑的大小也開始增加。由於外圍電荷之改變將受制於界面活性劑本身的性質並且會造成不同的聚集方式。對MCM-41而言，粒徑會呈跳躍式成長突然增至1000 nm以上，而SBA-15的粒徑則是由20 nm逐漸變化至500 nm後才與MCM-41呈相同的發展趨勢，兩者同樣在反應後期的溶液外觀呈現白色不透明狀，並且開始慢慢沉澱析出進一步形成hexaganol結構的固體，我們發現這兩者之間的差異性。
透過動態光散射分析儀的觀察，我們可發覺中孔徑分子篩的粒徑成長機構與趨勢的差異性，釐清在合成過程中之諸多現象，這有助於更了解中孔徑分子篩的形成機制，進而利用合成條件的變更對粒徑之變化做觀察與調控以合成出我們所須要性質的材料。

關鍵字

中孔徑分子篩 ； 動態光散射儀

並列摘要

The formation mechanism has been studied in this work through dynamic light scattering method which can get information about growth and distribution curve of particle size in a period of process.
Some conclusions were drawn through the observation of variation at particle size distribution during the formation of MCM-41 and SBA-15 mesoporous molecular sieves. The micelle of surfactants was formed by molecular aggregates above the CMC. The micelle species grew by 3~5 nm during the TEOS dosage. This step in acid synthesis most likely involved the fast incorporation of protonated silicate oligomer into the hydrophilic region of micelle. The silicated micelles were little change of size in induction time. Further process involved two different ways of particle growth. In MCM-41 system, there was a rapid increase in size of the particle species corresponding to a jump growth process. In SBA-15 system, there was another transition state which particle size increased slowly, but viscosity increased very fast. Beyond the transition, The particle size in SBA-15 grew very fast like the formation of MCM-41 system.
Finally, the solution appearance became white milk emulsion and particle grew up to 10 μm. The product of inorganic network structure was transformed into solid state by sedimentation force.

並列關鍵字

mesoporous sieves ； dynamic light scattering

參考文獻

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