Control of particle size and surface properties of crystals of NaX zeolite

We have successfully synthesized NaX zeolite crystals with controlled sizes from 20 nm to 0.8 mum, using a novel organic-additive-free approach. We show that the NaX crystal size depends on the silicate source and hydrothermal crystallization conditions, especially crystallization temperature and agitation. The physical properties of NaX-nano (20-100 nm) were characterized by X-ray diffraction, high-resolution scanning electron microscopy, FT-IR spectroscopy, Si-29 solid-state NMR spectroscopy, and N-2 adsorption. The results were compared with those for micrometer-sized NaX crystals, NaX-mu. As expected, the external surface area of NaX-nano was found to be significantly enhanced compared with that of NaX-mu. Porosity analysis indicates that NaX-nano has a broad distribution of mesopores from 2 to 20 nm, associated with interparticle voids. Both FT-IR and Si-29 solid-state NMR spectra revealed the presence of Q(3) silicon atoms in NaX-nano. All four Q(3) species were assigned in the Si-29 NMR spectra.