Nanoporous membranes can be used for electrodialysis-based water purification if the ionic selectivity and conductivity of the membrane can be increased. The electrodialysis process uses an applied DC electric field actively transport dissolved ions through the nanoporous membranes, concentrating the ions on one side of the membrane and purifying the water on the other side. Due to the large amount of electrical energy needed, electrodialysis is only used in a small number of water purification plants. One way to increase the efficiency of this process is to increase the ionic selectivity of the membranes. We describe here the use of inexpensive, commercially available polymer supports modified with polyelectrolyte surface chemistries. Specifically, we use a Layer-by-Layer (LbL) assembly to carefully modify nanopore surfaces with polyelectrolyte thin films. We explore how these thin films modify the surface charge influencing the ion selectivity and conductivity of these nanoporous membranes. We can further tailor the properties of the membranes through crosslinking to impact not only the chemical selectivity but also the chemical and mechanical stability of the polyelectrolyte surface modification. using various chemical crosslinking agents to increase not only the chemical selectivity of the membranes, but also their adhesion to the support membrane. We describe the preparation and characterization of these modified nanoporous membranes and evaluated the resulting ionic conductivity. Variations in the structure and composition of the starting nanoporous support membrane, polyelectrolyte deposition parameters and crosslinking chemistries are shown to controllably influence the ionic selectivity and conductivity of the nanoporous membranes as well as adhesion of the polyelectrolyte coating. Continued advances of these engineered nanoporous supports will enable the widespread use of electrodialysis as an economical water purification technology.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.