Twin-free, directly synthesized MFI nanosheets with improved thickness uniformity and their use in membrane fabrication

Zeolite nanosheets can be used for the fabrication of low- defect-density, thin, and oriented zeolite separation membranes. However, methods for manipulating their morphology are limited, hindering progress toward improved performance. We report the direct synthesis ( i.e., without using exfoliation, etching, or other top-down processing) of thin, flat MFI nanosheets and demonstrate their use as high-performance membranes for xylene isomer separations. Our MFI nanosheets were synthesized using nanosheet fragments as seeds instead of the previously used MFI nanoparticles. The obtained MFI nanosheets exhibit improved thickness uniformity and are free of rotational and MEL intergrowths as shown by transmission electron microscopy (TEM) imaging. The nanosheets can form well-packed nanosheet coatings. Upon gel-free secondary growth, the obtained zeolite MFI membranes show high separation performance for xylene isomers at elevated temperature (e.g., p-xylene flux up to 1.5 x 10(-3) mol m(-2) s(-1) and p-/o-xylene separation factor of similar to 600 at 250 degrees C).

Automated summary

In this study, a new method for direct synthesis of low-defect-density, thin, and flat zeolite nanosheets was reported, and their application as high-performance membranes was demonstrated. These nanosheets showed improved thickness uniformity and absence of rotational and intergrowth defects, making them promising for various separation applications.