Ionic covalent organic nanosheet (iCON)–quaternized polybenzimidazole nanocomposite anion-exchange membranes to enhance the performance of membrane capacitive deionization

Abstract

Membrane capacitive deionization (MCDI) is a promising technique to achieve desalination of low-salinity water resources. The primary requirements for developing and designing materials for MCDI applications are large surface area, high wettability to water, high conductivity, and efficient ion-transport pathways. Herein, we synthesized ionic covalent organic nanosheets (iCONs) containing guanidinium units that carry a positive charge. A series of quaternized polybenzimidazole (QPBI)/iCON (iCON@QPBI) nanocomposite membranes was fabricated using solution casting. The surface, thermal, wettability, and electrochemical properties of the iCON@QPBI nanocomposite membranes were evaluated. The iCON@QPBI anion-exchange membranes achieved a salt adsorption capacity as high as 15.6 mg g−1 and charge efficiency of up to 90%, which are 50% and 20% higher than those of the pristine QPBI membrane, respectively. The performance improvement was attributed to the increased ion-exchange capacity (2.4 mmol g−1), reduced area resistance (5.4 Ω cm2), and enhanced hydrophilicity (water uptake = 32%) of the iCON@QPBI nanocomposite membranes. This was due to the additional quaternary ammonium groups and conductive ion transport networks donated by the iCON materials. The excellent desalination performance of the iCON@polymer nanocomposite membranes demonstrated their potential for use in MCDI applications and alternative electromembrane processes.