Engineering Selective Desalination Membranes via Molecular Control of Polymer Functional Groups

Abstract

Membrane-based desalination processes are used widely to address increasing global demand for purified water. To continue to meet increasing demand, advanced and highly selective desalination membranes are needed to effectively and efficiently purify water that is increasingly contaminated and saline. A general lack of fundamental structure-property relationships frustrates the development of these membranes. Advanced polymer synthesis capabilities that enable increasingly precise molecular control over the position of functional groups on a polymer backbone could be instrumental in engineering advanced desalination membranes, but little is known about how the position of functional groups influences water and salt transport properties. In this study, we prepared and characterized a series of equivalent water content copolymers to determine how the functional group configuration along the polymer backbone influences desalination-relevant transport properties. Shifting the copolymer composition from one rich in vicinal diol groups to one rich in side chains with a single hydroxyl group drove an increase in the water/salt permeability selectivity, which is directly related to desalination-critical salt rejection. The results suggest that controlled placement of functional groups within a polymer could be a viable strategy for preparing advanced and highly selective desalination membrane materials.