Nanomorphogenesis of template-induced crumpled polyamide nanofiltration membranes

Abstract

Tailored thin-film composite (TFC) nanofiltration (NF) membranes can potentially achieve high permeance and effective salt separation during wastewater reclamation and water reuse. Recently, customized polyamide (PA) nanofilms with crumpled structures have received considerable attention owing to their outstanding separation performance; however, the underlying mechanism of the formation of crumpled features at the nanoscale remains poorly understood. Herein, we report the use of a particulate polydopamine (PDA) interlayer as a regulator for modulating chemical inhomogeneity (i.e., the diffusion and distribution of amine monomers) during the interfacial polymerization (IP) process, in which the characteristic spatial patterns of PA nanostructures are formed following a diffusion–reaction dynamics model in the Turing theory. Furthermore, the nanomorphologies and separation performance of PA membranes can be effectively controlled by tuning the physical inhomogeneity (i.e., the roughness of the organic–aqueous reaction interface) of the particulate interlayer. The interlayer-mediated TFC NF membrane exhibits crumpled nanosized stripes with three times higher permeance and four times higher Cl−/SO42− selectivity (up to 82.1) than those of pristine PA membranes. We have also identified an array of topographical parameters for both the PDA interlayer and PA nanostructures based on experimental observations and multiscale simulations (i.e., molecular dynamics and dissipative particle dynamics) to establish quantitative relationships between the interlayer morphology, PA morphology, and performance characteristics of NF membranes. Our work provides molecular insights into the nanomorphogenesis of crumpled PA nanofilms and interlayer effects on the IP reaction and final separation performance.