Mechanically Strengthened Graphene Oxide: Covalent Organic Framework Membranes for Monovalent/Divalent Cation Selectivity via Electrodialysis

Abstract

Electrodialysis is an energy efficient method for water desalination and resource recovery; however, the lack of ion selectivity in conventional ion-exchange membranes limits its performance, particularly in separating monovalent and divalent cations. In this study, we present the design and fabrication of mechanically reinforced graphene oxide (GO)–covalent organic framework (COF) composite membranes with variable selectivity for monovalent over divalent cations, enhancing the performance of electrodialysis processes. The composite membranes, created by stacking GO and sulfonate-functionalized COF nanosheets, exhibit a nacre-inspired “brick-and-mortar” structure that imparts mechanical robustness and high ion selectivity. By adjusting the GO-to- COF ratio, we achieved varying Na+/Ca2+ and Li+/Ca2+ selectivity ratios, reaching up to 15.34 and 6.99, respectively, without compromising the charge efficiency (greater than 75%). The membranes have also shown good stability in synthetic hypersaline brine. These results demonstrate the potential of GO/COF membranes for high-performance, energy-efficient ion separation in electrodialysis, offering a promising solution for desalination, wastewater treatment, and resource recovery.