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Abstract:
Composites incorporating two-dimensional nanostructures within polymeric
matrices have potential as functional components for several
technologies, including gas separation. Prospectively, employing
metal-organic frameworks (MOFs) as versatile nanofillers would notably
broaden the scope of functionalities. However, synthesizing MOFs in the
form of freestanding nanosheets has proved challenging. We present a
bottom-up synthesis strategy for dispersible copper
1,4-benzenedicarboxylate MOF lamellae of micrometre lateral dimensions
and nanometre thickness. Incorporating MOF nanosheets into polymer
matrices endows the resultant composites with outstanding CO2 separation
performance from CO2/CH4 gas mixtures, together with an unusual and
highly desired increase in the separation selectivity with pressure. As
revealed by tomographic focused ion beam scanning electron microscopy,
the unique separation behaviour stems from a superior occupation of the
membrane cross-section by the MOF nanosheets as compared with isotropic
crystals, which improves the efficiency of molecular discrimination and
eliminates unselective permeation pathways. This approach opens the door
to ultrathin MOF-polymer composites for various applications.
