含金屬介孔材料的合成與鑑定

Synthesis and Characterization of Metal-incorporated Mesoporous Materials

陳仕元(Shih-Yuan Chen)

指導教授 ： 鄭淑芬

國立臺灣大學/理學院/化學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.01649

摘要

本研究的重點是含金屬介孔材料的合成與鑑定，包含了氧化矽SBA-15與氧化鋯材料。在實驗初步測試方面，發現在中性條件下即可合成出純的氧化矽介孔材料，其孔洞性質與母液中的共聚合物界面活性劑，鹽類，共溶劑與氨基酸的濃度有關。當NaCl/Si的莫耳比固定，改變共聚合物濃度由0.5到1.25wt%時，孔洞結構由不規則的介孔孔洞轉變為類似泡棉的大孔。當加入醇類為共溶劑時，則產物具有規則排列的蟲洞。若使用氨基酸Glutamic acid取代鹽類時，母液的pH值約為3.2，則可合成出二維六角堆積的孔洞。形成不同介孔結構的原因，可能是母液中的共聚合物、鹽類、共溶劑與氨基酸的濃度改變，使得共聚合物微胞的疏水端與親水端之體積比與介面性質改變，而得到不同的孔洞結構。
基於上述結果，我們發展了一套新的合成方法，在不加其他酸的條件下，利用金屬前驅物的酸性來合成含金屬的二氧化矽介孔材料(SBA-15)。與傳統方法比較，新的合成方法可以引入大量的金屬到氧化矽骨架中，金屬引入量的排序如下：Zr(IV)＞Fe(III)＞Al(III)＞Cr(III)，其最大引入量為11，7，5與2 mol％。根據金屬前驅物的酸性與氧化矽的等電荷點，我們推測合成含鋯與含鐵的SBA-15材料是經由I+X-S+反應機制，而含鋁與含鉻的SBA-15材料是經由I+S-反應機制。
在氧化鋯介孔材料方面，當合成時加入鹽類，可大幅提升材料的結晶性，但對熱穩定性幫助並不顯著。我們發現若將部份界面活性劑從材料中萃取出來，再鍛燒，則可穩定介孔結構達600℃。當完全移除界面活性劑，所得到的氧化鋯材料為多孔性，具有高表面積與高孔洞體積。使用部分界面活性劑移除的介孔氧化鋯進行含浸法，可成功製備出含鉬、鑭與釔金屬氧化物的氧化鋯介孔材料，且可以保持高表面積與孔洞體積。

關鍵字

金屬 ； 介孔洞材料

並列摘要

This study is focused on the synthesis and characterization of metal-incorporated mesoporous materials with high crystallinity, including siliceous SBA-15 and zirconia. In the preliminary experiment, it was found that the mesostructured silica materials could be prepared in the acid-free condition. The pore structures were dependent on the concentration of P123 triblock copolymer, salt, co-solvent and amino acid in the mother solution. When the NaCl/Si ratio was fixed, the mesopore was transferred from disordered pore to mesostructured cellular foam by increasing the concentration of P123 from 0.5 to 1.25wt%. When the alcohol was added in the synthesis solution, the mesoporous silica with well-ordered worm pore was obtained. Interestingly, hexagonal P6mm structure of SBA-15 like material could be obtained by using glutamic acid instead of salt in a self-generated acidic condition (pH=3.2). The transformation of pore structures was probably attributed to the change of the hydrophobic to hydrophilic volume and the PPO/PEO interface by varying the concentration of P123, salt, cosolvent and amino acid.
Based on above results, we developed a new method for synthesizing metal-incorporated SBA-15 including Al, Cr, Fe and Zr in a self-generated acidic environment and without the addition of other mineral acids. It was found that the amounts of incorporated metals in SBA-15 were greater than those prepared by traditional acid-synthesis condition. Among the metal species studied, the incorporated amount decreased in the order of Zr(IV) > Fe(III) > Al(III) > Cr(III). The maximum loadings of Zr, Fe, Al and Cr in SBA-15 were 11, 7, 5 and 2 mol%, respectively. The crystallinity of the products was greatly enhanced by the addition of salts in the synthesis gel. Based on the pH value of mother solution and the isoelectric point of silica, synthesis of Zr- and Fe-SBA-15 was likely through the I+X-S+ pathway, whereas Al- and Cr-SBA-15 were through the I+S- pathway.
For the mesoporous zirconia materials, the addition of salts in the synthesis gel was found to increase the crystallinity of the product, but only slightly improve the thermal stability. Partial extraction of the surfactant from the as-made zirconia material before calcination was found to be a key step to maintain the mesostructure of the material up to 600℃ calcination. Impregnation of other metal species on the above material, such as La, Y, and Mo, on mesoporous zirconia was also successfully achieved without significantly losing the mesostructure and the surface area a lot.

並列關鍵字

mesoporous materials ； metal

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