Dispersible Exfoliated Zeolite Nanosheets and Their Application As Membrane

High aspect ratio zeolite particles with thickness in the 2-3 nanometer range (zeolite nanosheets) can be derived from exfoliation of their lamellar precursors (layered zeolites) and can be used as catalysts and building blocks for fabrication of thin films. Thin zeolite films made using exfoliated zeolite nanosheets could show improved performance and processing advantages as membranes for separations, low dielectric coatings, corrosion protection, chemical sensors, membrane reactors, etc. Here we report exfoliation of a multilamellar zeolite (silicalite-1) and subsequent processing to obtain a dispersible coating suspension of exfoliated silicalite-1 sheets followed by demonstration of its utility as a gas separation membrane. Exfoliation and structure preservation of multilamellar silicalite-1 was confirmed by Transmission electron microscopy (TEM). Scanning probe microscopy (SPM) was used to characterize the thickness of the exfoliated silicalite-1 nanosheets. A thin b-oriented film of exfoliated nanosheets was coated on top of a porous α-alumina support. The coating morphology and cross section was characterized by scanning electron microscopy (SEM) and TEM respectively. The defects in the coating were removed by hydrothermal treatment of the silicalite-1 in presence of a growth solution. The silicalite-1 membrane was characterized by xylene isomer vapor permeance in Wicke-Kallenbach mode at 150°C, where a separation factor of 67 was obtained between p-xylene and o-xylene. The permeance of p-xylene through the membrane (3.1E-07 mol/m²/s/Pa) was close to that of the alumina support (4.2E-07 mol/m²/s/Pa).