Highly permeable nanofilms with asymmetric multilayered structure engineered via amine-decorated interlayered interfacial polymerization

Abstract

Tailormade polyamide (PA) membrane structures for ultrafast water transportation that possess excellent selectivity are promising for efficient water reclamation. In this study, an ultrathin (8 nm) and asymmetric PA nanofilm with a multilayer structure, where the back surface is a porous layer containing a spherically porous structure and the upper surface is a dense selective layer having nodular wrinkles, is engineered via amine-decorated interlayer-mediated interfacial polymerization (IP). The self-assembled network of strongly charged and highly hydrophilic ionomers exhibits strong attraction toward aqueous amine monomers, and temporally disrupts their diffusion by imposing a heterogeneous energy barrier toward the organic phase to be polymerized with acyl chloride monomers. This triggers a diffusion-driven instability that enables the formation of internal voids at the back surface of the PA nanofilm. The asymmetric PA membrane exhibits an improved water permeance of up to 12.5 L m−2 h−1 bar−1; this is 3-fold larger than that of the traditional PA membrane (4.4 L m−2 h−1 bar−1). Further, it has a high divalent salt rejection ratio of 98.9%, thus overcoming the trade-off among state-of-the-art nanofiltration membranes. The formation mechanism of such asymmetric PA nanofilms was clarified through multiscale theoretical simulations. These findings represent advances toward developing ultrapermeable membranes for highly efficient ion/molecular separation.