Pillared MFI Zeolite Nanosheets of a Single-Unit-Cell Thickness
Pillared MFI Zeolite Nanosheets of a Single-Unit-Cell Thickness
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DOI：
10.1021/ja908382n
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发表时间：
2010-03-31
影响因子：
15
通讯作者：
Ryoo, Ryong
中科院分区：
文献类型：
--
作者：
Na, Kyungsu;Choi, Minkee;Ryoo, Ryong
沸石MFI纳米片的2 nm厚的水热合成通过二氧化硅和有机表面活性剂，这是官能化的双季铵基团之间的合作组装。通过位于沸石纳米片外部的表面活性剂尾部之间的疏水相互作用，沸石纳米片进一步组装成其有序的多层介观结构。该组装过程涉及从最初的六方中间相到没有结晶度的多层中间相，然后到具有结晶沸石框架的层状中间相的连续转变。层间空间中的中孔体积可以通过用二氧化硅柱支撑沸石纳米片来保留，如在柱撑粘土中，即使在通过煅烧除去表面活性剂之后。中孔孔径可以根据表面活性剂尾长进行控制。由于层间结构的一致性，分级介孔/微孔沸石可以表现出小角度的X射线衍射峰高达对应于层间距离的四阶反射。此外，Ar吸附分析和透射电子显微镜研究表明，柱是非常可能的MFI结构。本方法利用表面活性剂中含有的沸石结构导向官能团，将适用于未来其他相关纳米晶沸石的合成。
Zeolite MFI nanosheets of 2-nm thickness have been hydrothermally synthesized via cooperative assembly between silica and an organic surfactant, which is functionalized with a diquaternary ammonium group. The zeolite nanosheets have been further assembled into their ordered multilamellar mesostructure through hydrophobic interactions between the surfactant tails located outside the zeolite nanosheet. This assembly process involves successive transformations from an initially hexagonal mesophase to a multilamellar mesophase without crystallinity and then to a lamellar mesophase with a crystalline zeolite framework. The mesopore volume in the interlamellar space could be retained by supporting the zeolite nanosheets with silica pillars, as in pillared clays, even after surfactant removal by calcination. The mesopore diameters could be controlled according to the surfactant tail lengths. Due to the interlamellar structural coherence, the hierarchically mesoporous/microporous zeolite could exhibit small-angle X-ray diffraction peaks up to the fourth-order reflections corresponding to the interlayer distance. In addition, an Ar adsorption analysis and transmission electron microscopic investigation indicated that the pillars were highly likely to be built with an MFI structure. The present approach using a zeolite structure-directing functional group contained in a surfactant would be suitable for the synthesis of other related nanomorphous zeolites in the future.