Zeolite crystallization in crosslinked chitosan hydrogels: Crystal size control and chitosan removal

For the purpose of controlling zeolite crystal size, crystallization of zeolite NaA and NaY in glutaraldehyde crosslinked chitosan (GA-CS) hydrogels was studied in this paper. The zeolite crystals were produced by penetration of Na2O–Al2O3–H2O alkaline solution into GA-CS hydrogels filled with colloidal silica, followed by hydrothermal treatment and removal of GA-CS hydrogels. We systematically investigated the effects of the synthesis parameters – including the amounts of silica, chitosan, and glutaraldehyde, and the aging and heating times – on the size, size distribution and crystallinity of the particles. A hydrogen peroxide treatment method was shown to be an effective way for removing GA-CS hydrogels, thereby avoiding the conventional calcination step. X-ray diffraction (XRD), light scattering, scanning electron microscopy (SEM), thermogravimetric analysis (TG), and N2 sorption were used to characterize the zeolite samples. This work showed that GA-CS is a promising space-confinement medium for the synthesis of zeolite nanocrystals with tunable crystal sizes and excellent dispersibility

Organic-functionalized sodalite nanocrystals and their dispersion in solvents

Hydroxy-sodalite nanocrystals with organic functional groups (i.e., double bond; length as m-dashSi–(CH3)(CH2)3NH2, denoted Sod-N, or triple bond; length of mdashSi–CH3, denoted Sod-C) were synthesized by the direct transformation of organic-functionalized silicalite nanocrystals. 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, 19.6 and 19.1 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. Therefore, the organic-functionalized sodalite nanocrystals prepared in this work may be very useful for fabricating zeolite nanostructures and sodalite-polymer nanocomposite membranes