Overcoming the permeability-selectivity trade-off of desalination membranes via controlled solvent activation

Abstract

Here, we present a facile solvent activation method for significantly enhancing the desalination performance of reverse osmosis (RO) membranes. Polyamide (PA)-thin film composite (TFC) RO membranes were activated with a dimethyl sulfoxide (DMSO)/water mixture, whose solvency power was carefully controlled by adjusting the DMSO volume fraction. A DMSO/water mixture with a DMSO volume fraction of 0.3 effectively activated the PA selective layer while marginally deforming the polysulfone support of the lab-made PA-TFC membrane, thus considerably enhancing its water permeance by ~43% while maintaining its NaCl rejection (~99.4%). All the commercial membranes activated with the optimized DMSO/water activation protocol also exhibited dramatically enhanced water permeance (26–155%) with unchanged or even higher NaCl rejection, surpassing the conventional permeability–selectivity trade-off. A careful characterization of the structures and properties of the model PA film under various solvent environments revealed the thermodynamics and kinetics associated with the activation-induced structural deformation of the PA network, which governs its structural density, consequently affecting the separation properties of the membrane. Our strategy provides a commercially viable means for the fabrication of high-performance membranes together with shedding light on the underlying the structure-property relationship of polymeric membranes.