Surfactants with Aromatic-Group Tail and Single Quaternary Ammonium Head for Directing Single-Crystalline Mesostructured Zeolite Nanosheets

Single-crystalline mesostructured zeolite nanosheets (SCZN) are synthesized by using designed surfactants with an aromatic group and only single quaternary ammonium head. Both the number of benzene rings and the length of the carbon chain play important roles in the ordered self-assembly of these alternating MFI (mordenite framework inverted) nanosheets. The surfactants, only with two benzene rings and a carbon chain larger than 4, lead to the formation of SCZN because of their highly ordered orientation through it pi-pi stacking; the interlamellar spacing of SCZN could be controlled in the range of 1.7-2.1 nm through variation of the carbon chain length from 6 to 10. A combination of X-ray diffraction patterns and electron microscopy provides visible evidence for the mesostructural transformation from two amorphous aluminosilicate layers to one MFI sheet. The highly ordered orientation of the aromatic groups through pi-pi stacking geometrically matches the MFI framework to form the crystallographically correlated mesostructure. The low binding energies for the self-assembly of this synthesis system, obtained by molecular mechanics calculations, provide theoretical evidence of the feasibility of our strategy. In addition, this strategy is successfully verified using bolaform cationic surfactants, which also result in the crystallographically ordered MFI nanosheets owning to the similar pi-pi stacking interactions.