Center for Functional Nanomaterials, Department of Chemistry, Graduate School of EEWS (WCU), Graduate School of Nanoscience and Technology (WCU), KAIST, Daejeon 305-701, Korea.
J Am Chem Soc. 2010 Mar 31;132(12):4169-77. doi: 10.1021/ja908382n.
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.
2 纳米厚的 MFI 沸石纳米片是通过二氧化硅和一种有机表面活性剂之间的协同组装合成的，该表面活性剂带有双季铵基团。沸石纳米片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进一步组装成其有序的多层介孔结构。该组装过程涉及从最初的六方介相到无定形的多层介相，然后到具有结晶沸石骨架的层状介相的连续转变。通过用二氧化硅柱支撑沸石纳米片（如在层柱粘土中），可以保留层间空间中的中孔体积，即使在通过煅烧去除表面活性剂后也是如此。中孔直径可以根据表面活性剂尾部长度进行控制。由于层间结构的连贯性，分级介孔/微孔沸石可以显示出小角度 X 射线衍射峰，直到对应于层间距的第四阶反射。此外，Ar 吸附分析和透射电子显微镜研究表明，这些支柱极有可能是用 MFI 结构构建的。未来，使用包含在表面活性剂中的沸石结构导向官能团的这种方法将适用于其他相关纳米形态沸石的合成。
