A design concept of amphiphilic molecules for directing hierarchical porous zeolite

Abstract

Aluminosilicate zeolites with hierarchically porous systems have attracted special scientific interest due to their advantages in bulky molecule catalysis. Organic amphiphilic molecules or surfactants are frequently employed in the hydrothermal syntheses of porous zeolites for the construction of enhanced pore systems (mesopores or macropores) beyond sole micropores. This review describes a design concept of novel amphiphilic molecules for a one-step preparation of hierarchically porous zeolites containing mesopores with certain orders. Via a structural-directing mechanism study of the most common surfactant (cetyltrimethyl ammonium bromide, CTAB) in the synthesis of bulk zeolite MFI (zeolite framework code given by the International Zeolite Association), aromatic groups were grafted into the hydrophobic tail of the amphiphilic molecule. Due to the π–π stacking of the aromatic groups and a geometrical match between their arrangement and the zeolitic framework, single-crystalline zeolite nanosheets (SCZNs) were successfully synthesized. Furthermore, following the same idea for the design, bolaform and triply branched amphiphilic molecules with aromatic groups were also prepared and used for the formation of SCZNs with a 90° rotational boundary and single-crystalline mesoporous ZSM-5 with three-dimensional pores, respectively. This design concept will provide a new insight into the molecular factors for governing the simultaneous fabrication of ordered meso- and micro-phases.