Asymmetric Membrane Capacitive Deionization Using Anion-Exchange Membranes Based on Quaternized Polymer Blends

Robert McNair; Levente Cseri; Gyorgy Szekely; Robert Dryfe

doi:10.1021/acsapm.0c00432

Asymmetric Membrane Capacitive Deionization Using Anion-Exchange Membranes Based on Quaternized Polymer Blends

ACS Appl Polym Mater. 2020 Jul 10;2(7):2946-2956. doi: 10.1021/acsapm.0c00432. Epub 2020 Jun 1.

Authors

Robert McNair^{1

2}, Levente Cseri¹, Gyorgy Szekely^{1

3}, Robert Dryfe^{2

4

5}

Affiliations

¹ Department of Chemical Engineering & Analytical Science, University of Manchester, The Mill, Sackville Street, Manchester, M1 3BB, U.K.
² Department of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, U.K.
³ Advanced Membranes and Porous Materials Center (AMPMC), King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
⁴ National Graphene Institute, University of Manchester, Booth Street East, Manchester, M13 9PL, U.K.
⁵ Henry Royce Institute for Advanced Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, U.K.

Abstract

Membrane capacitive deionization (MCDI) for water desalination is an innovative technique that could help to solve the global water scarcity problem. However, the development of the MCDI field is hindered by the limited choice of ion-exchange membranes. Desalination by MCDI removes the salt (solute) from the water (solvent); this can drastically reduce energy consumption compared to traditional desalination practices such as distillation. Herein, we outline the fabrication and characterization of quaternized anion-exchange membranes (AEMs) based on polymer blends of polyethylenimine (PEI) and polybenzimidazole (PBI) that provides an efficient membrane for MCDI. Flat sheet polymer membranes were prepared by solution casting, heat treatment, and phase inversion, followed by modification to impart anion-exchange character. Scanning electron microscopy (SEM), atomic force microscopy (AFM), nuclear magnetic resonance (NMR), and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the morphology and chemical composition of the membranes. The as-prepared membranes displayed high ion-exchange capacity (IEC), hydrophilicity, permselectivity and low area resistance. Due to the addition of PEI, the high density of quaternary ammonium groups increased the IEC and permselectivity of the membranes, while reducing the area resistance relative to pristine PBI AEMs. Our PEI/PBI membranes were successfully employed in asymmetric MCDI for brackish water desalination and exhibited an increase in both salt adsorption capacity (>3×) and charge efficiency (>2×) relative to membrane-free CDI. The use of quaternized polymer blend membranes could help to achieve greater realization of industrial scale MCDI.