Facile performance enhancement of reverse osmosis membranes via solvent activation with benzyl alcohol

Abstract

We present a facile method to enhance separation performance of polyamide (PA) reverse osmosis (RO) membranes via solvent activation with a new type of organic solvent, benzyl alcohol (BA). Activation with BA remarkably improved water permeance (up to similar to 140% increase) while maintaining high NaCl rejection (similar to 99.6%) of the pristine RO membrane, thereby overcoming the flux-rejection trade-off limitation. Thus, the water permeance and permselectivity of the BA-activated RO membrane significantly exceeded those of commercial RO membranes. This significant performance enhancement was attributed to the appropriate solvency power of BA (determined based on Hansen solubility parameters), which led to the balanced structural deformation of the PA selective layer; BA activation produced a less dense and highly permeable PA structure by greatly swelling PA, while simultaneously healing loosened sites via structural compaction of the PA network with a sufficiently reduced modulus. Based on the activation results with various organic solvents ranging from mild to strong solvents, we propose a more reliable predictor of the solvent activation effect. Our strategy is a simple, effective and commercially viable method to enhance RO membrane performance. Additionally, our study highlights on the underlying solvent activating mechanism of PA RO membranes.