Purification of Zeolite Nanosheets by Density Gradient Centrifugation and Their Assembly On Various Supports

High aspect ratio zeolite nanosheets with thickness of a few nanometers can be obtained from exfoliation of their lamellar precursors (layered zeolites) and can be used as 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 separations¹, low dielectric coatings, corrosion protection, chemical sensors, membrane reactors, etc.

Here we report purification of zeolite nanosheets by density gradient centrifugation (DCG) followed by their assembly on various substrates using filtration and evaporation assisted self assembly. Nanosheets were synthesized by exfoliation of multilamellar MFI by melt compounding with polystyrene. The exfoliated zeolite was extracted by dispersing the nanocomposite in toluene followed by DCG. The so obtained zeolite suspension was free of polymer and unexfoliated zeolite as characterized by transmission electron microscope (TEM). Sub-100 nm thin film of this suspension was deposited on porous supports by filtration and non-porous supports by dip coating. Coating microstructure was characterized by scanning electron microscope (SEM).

[1] K. Varoon, X. Zhang, B. Elyassi, D.D. Brewer, M. Gettel, S. Kumar, J.A. Lee, S. Maheshwari, A. Mittal, C.-Y. Sung, M. Cococcioni, L.F. Francis, A.V. McCormick, K.A. Mkhoyan, M. Tsapatsis, Dispersible exfoliated zeolite nanosheets and their application as a selective membrane, Science, 333 (2011) 72-75.