The recent developments of single crystalline zeolite nanosheets (ZNs) have enabled the fabrication of ultrathin zeolite membranes. These ZN based membranes can realize preferable crystal orientations to shorten the diffusion length and reduced intercrystalline spaces that simultaneously improve the mass transport rate and molecular selectivity. Most of the existing ZN-based membranes are either multilayered-ZN films deposited from ZN suspensions or monolayered intergrown ZN films obtained via secondary growth of sparsely coated small-size ZN seeds. In literature, the MFI-type ZN membranes of such structures have been demonstrated with extraordinary selectivity and permeation rates in separation of hydrocarbon isomers and pervaporation (PV) desalination of concentrated brines. However, current ZN-based membranes require rigid ceramic substrates to allow high temperature calcination for structure directing agents (SDA) removal and prevent the ZN layers from bending and cracking. The development of more practical polymer-supported ZN membranes has been so far very limited. A major challenge to developing ZN membranes on polymer supports is the lack of efficient methods for preparing well-dispersed suspensions of preactivated ZNs. Preactivated ZNs are necessary in this case because post-coating activation of zeolitic pores is difficult for polymer supported membranes. In this presentation, we report the efficient synthesis of an ultrathin silicalite ZN membrane by directly tiling the porous polyvinylidene fluoride (PVDF) films with preactivated large plates of multilayered ZNs. The ZN plate-tiled (ZNPT) membrane on PVDF support (ZNPT-PVDF) have been studied for application as an ion separator for vanadium redox flow battery (RFB). This research demonstrates that the new ZNPT-PVDF could be an environmentally and economically favorable alternative RFB ion separator to the fully perfluorinated Nafion ® membanes.

Zeolite nanosheet – polymer layered composite membranes as alternative ion separators for aqueous redox flow batteries

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