The silica species contained in an aged clear suspension, which upon heating gives rise to the crystallization
of Silicalite-1, were extracted with 80% efficiency using a sequence of acidification, salting out, phase transfer
into organic solvent, and freeze-drying methods. This silica powder was characterized by X-ray scattering,
transmission electron microscopy, atomic force microscopy, and 29Si magic angle spinning nuclear magnetic
resonance. These techniques gave evidence for the presence of a very specific morphology, corresponding to
slab shaped particles, with dimensions of 1.3 × 4.0 × 4.0 nm. The nanoslabs have the MFI structure with
nine channel intersections per particle, each containing a TPA cation. The identity of the extracted nanoslabs
with the species in suspension is evidenced with in situ and ex situ X-ray scattering.
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 electron microscopy, attenuated force microscopy, 29 Si magic angle spinning NMR, 13 C cross polarization magic angle spinning NMR, X-ray diffraction, dinitrogen physisorption, and thermogravimetric analysis and compared with micrometer-sized silicalite-1. The nanosized and micrometer-sized materials have many common properties including the refined structure and the nature and concentrations of tetrapropylammonium species incorporated during the synthesis. Unique properties of the nanophase 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 defect sites, and a strain in the crystallites along the "a" crystallographic direction. The nanophase exhibits a two-stage dinitrogen physisorption in the low-pressure region, ascribed to adsorptions in micropores created by the stacking of the nanoparticles in addition to adsorptions in the intracrystalline micropores.
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