Synthesis and Organic-Functionalization of Sodalite Nanocrystals
Sodalite is a small-pore zeolite whose framework consists of a six-membered ring aperture with a pore size of 2.8 Å. Because of its small pore size, sodalite has been considered as a good candidate material for hydrogen storage, and hydrogen separation. To develop high-selectivity, high-flux sodalite-polymer nanocomposite membranes for hydrogen separation and purification, template-free sodalite nanocrystals with good interfacial compatibility with the chosen polymer are needed. This presentation focuses on the synthesis of template-free sodalite nanocrystals with suitably tailored surface properties.
Hydroxy-sodalite nanocrystals with organic functional groups (i.e.,–(CH3)(CH2)3NH2, denoted Sod-N, or ≡Si-CH3, denoted Soc-C) were synthesized by the direct transformation of organic-functionalized silicalite nanocrystals. In the transformation process, silicalite with organic functional groups became amorphous first and then re-crystallized, yielding a sodalite structure; in contrast, the zeolite A structure was observed as an intermediate product in the transformation of silicalite nanocrystals without organic functional groups. The chemical structure of organic-functionalized sodalite nanocrystals was confirmed by 29Si MAS NMR spectroscopy. Gas sorption results showed that the sodalite nanocrystals contained uniform pore channels that were accessible to hydrogen, but inaccessible to nitrogen, as expected. The BET surface areas are calculated to be 22.8, 19.1 and 19.6 m2/g for plain sodalite nanocrystals (Sod), Sod-N, and Sod-C, respectively; similarly, Sod-N and Sod-C exhibited slightly lower hydrogen adsorption than Sod. The dispersion of Sod-N and Sod-C in organic solvents was favored by the presence of organic functional groups.