Solution-processable exfoliated zeolite nanosheets purified by density gradient centrifugation

Highly crystalline exfoliated MFI-nanosheets can pave the way for large-scale deployment of sub-500-nm zeolite membranes due to their processing and packing advantages. Exfoliated MFI-nanosheets prepared by melt compounding contain a large amount of polymer and unexfoliated particles which are detrimental to the fabrication of ultrathin zeolite membranes. Complete removal of polystyrene from the nanosheet suspension in toluene is demonstrated by centrifugation of the suspension across chlorobenzene as confirmed by thermogravimetric analysis (TGA) data and transmission electron microscopy (TEM) images. Rate-zonal centrifugation in a nonlinear density gradient fractionated exfoliated MFI-nanosheets from unexfoliated particles. The purified nanosheets were highly crystalline as indicated by high-resolution TEM (HRTEM) and electron diffraction (ED). Coating of purified MFI-nanosheets on a smooth -alumina support, fabricated by filtration of -alumina suspension, led to a compact, b-oriented, 80-nm-thick film. A mild hydrothermal treatment of the film led to a 200-nm-thick membrane, which demonstrated molecular sieving properties. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 3458-3467, 2013