PHYSICOCHEMICAL CHARACTERIZATION OF SILICALITE-1 NANOPHASE MATERIAL

A silicalite-1 nanophase material with an elementary particle size of 18-100 nm is synthesized from clear solution and isolated and purified using supercentrifugation. The nanopowder is characterized in detail using scanning electron microscopy, high-resolution transmission elect ron microscopy, attenuated force microscopy, Si-29 magic angle spinnin g NMR, C-13 cross polarization magic angle spinning NMR, X-ray diffrac tion, dinitrogen physisorption, and thermogravimetric analysis and com pared with micrometer-sized silicalite-1. The nanosized and micrometer -sized materials have many common properties including the refined str ucture and the nature and concentrations of tetrapropylammonium specie s incorporated during the synthesis. Unique properties of the nanophas e are a splitting of the characteristic framework vibration at 550 cm( -1) into a doublet at 555 and 570 cm(-1), a high concentration of defe ct sites, and a strain in the crystallites along the ''a'' crystallogr aphic direction. The nanophase exhibits a two-stage dinitrogen physiso rption in the low-pressure region, ascribed to adsorptions in micropor es created by the stacking of the nanoparticles in addition to adsorpt ions in the intracrystalline micropores.