Hydrothermal synthesis of nanocrystalline NaX zeolite at room temperature.

NaX zeolites were prepared by hydrothermal synthesis under room-temperature conditions. Some influence parameters such as crystallization time, Al2O3/SiO2, Na2O/SiO2 and H2O/SiO2 molar ratios on the crystalline end products were studied, the products were characterized by XRD, SEM, TEM, particle size analysis and N2 adsorption-desorption techniques. The results indicated that although 28 days product was fully crystalline according to the XRD investigation, the crystals were able to continue to grow. The TEM revealed that the samples were composed of highly crystalline NaX zeolite nanocrystals with the average size of around 30 nm. Long crystallization time favored the aggregation of individual nanocrystals, which led to the formation of large congregated agglomerates. Furthermore, mild alkalinity circumstance was favorable for the crystallization of FAU zeolite. However, higher water quantity resulted in the formation of larger steady congregated agglomerates. The samples obtained with H2O/SiO2 molar ratios of 100, 150, 250, 300 and 400 showed the mean particle sizes of 42, 108, 359, 551 and 962 nm, with the particle size distribution ranges of 30-63, 62-140, 215-602, 345-746 and 498-1395 nm, respectively.