Synthesis of high aspect ratio low-silica zeolite L rods in oil/water/surfactant mixtures

Low-silica zeolite L (zeolite GL) syntheses in the presence of emulsions were investigated. High aspect ratio rods were obtained when zeolite LTL was crystallized in the presence of both cationic and nonionic two-phase emulsions. Conventional syntheses of zeolite L primarily led to low aspect ratio crystals possessing a length/width ratio of approximately 1.5. In the presence of the emulsion aspect ratios were increased with most samples possessing aspect ratios between 5 and 10, although crystals were observed with aspect ratios as high as 42. TEM analysis indicates the LTL pores are parallel to the long axis of the crystals. It is observed that anisotropic crystals are formed when the surfactant (CTAB) to cation ratio is below 3.5. By contrast when the CTAB/(Ba2++K+) is greater than four the LTL phase does not form. Igepal CO-720 was also used to determine if similar high aspect ratio crystals could be formed in nonionic emulsions. While the nonionic emulsions also led to LTL rods, the phase purity of the materials was lower based on SEM and PXRD. This report, to the best of knowledge, is the first of low-silica zeolite L crystals (Si/Al < 1.5) that possess such aspect ratios. Given the ability to exchange at least some of the extraframework cations, the materials reported here are possible candidates for use in applications including microelectronics and sensing.