Highly b-oriented MFI mixed matrix membrane prepared by detaching twins and junctions

Mixed matrix membranes (MMMs) with aligned microporous sheets offer enhanced molecular transport. Platelike MFI zeolite crystals can form such MMMs with aligned micropores. However, platelike MFI synthesis suffers from twinning and crystal junctions. Here, we present a method to minimize and preferentially detach these twins and junctions to obtain standalone platelike MFI crystals with high aspect ratios (ca. 4.3 mu m by 120 nm). These platelike crystals can be synthesized in kilogram scale and do not aggregate after calcination, exhibiting similar to 100 % dispersion yield, in contrast to the ultrathin nanosheets, which lose similar to 90 % to aggregation. Twins and crystal junctions are eliminated using a preferential detaching strategy by selectively etching the twin boundaries and junctions. Discrete crystals are aligned in a 2.8 mu m thick Pebax matrix to prepare highly b-oriented MFI MMMs with 30 % MFI loading, exhibiting CO2 permeances up to 37 GPU, and CO2/N-2 separation factors up to 16.8 at ambient pressure.