Mesoporous MFI Zeolite with a 2D Square Structure Directed by Surfactants with an Azobenzene Tail Group

Mesoporous MFI zeolites (MMZs) have been constructed by using the surfactant-containing azobenzene segment in the hydrophobic tail. The cylindrical pi-pi stacking of azeobenzene groups is considered to be the key factor to form the ordered mesostructure through cooperative structural matching and the rearrangement of MFI frameworks. The mesostructure has been tuned from a disordered hierarchical arrangement into an ordered 2D square p4mm structure by changing the length of the alkyl chain between the diquaternary ammonium head group and azobenzene group. The geometric matching between the MFI zeolitic framework and the alkyl chain length plays an important role in the construction of the crystallographically correlated mesostructure with 2D square ordering. A combination of X-ray diffraction patterns and electron microscopy studies provides visible evidence for the mesostructural transformation from a short-range hexagonal or lamellar ordering to 2D square mesostructure.