Fabrication of highly permselective mixed matrix graphene oxide/ sodium tripolyphosphate-based cation exchange membranes for monovalent and divalent ion desalination

In this study, graphene oxide (GO) was functionalized by sodium triphosphate (NaTPP) through a physical grafting method and used as a nanofiller to fabricate cation exchange membranes based on polyvinylidene fluoride (PVDF). The influences of the loading percentage of NaTPP in functionalized GO (GON) samples on the hydrophilicity, surface and cross-sectional morphology, permselectivity, and ion transport number of the sodium ion on the fabricated CEMs were explored using different techniques. Adding NaTPP to GO resulted in a more even surface structure, enhanced surface wettability, and decrement of membrane area resistance for the GON-based CEMs compared to GO-containing membranes. The MGON (0.5) membrane showed a high water uptake of 46.2 ± 2.3% and an ion exchange capacity of 3.8 ± 0.1 meq g-1, which facilitated the easier transport of monovalent and divalent ions within the membrane. The results showed that the MGON (0.5) membranes possessed higher permselectivity for monovalent and divalent ions including Na+ (98.3%), K+ (96.4%), Ca2+ (80.2%), and Mg2+(76.3%). Additionally, the membrane area resistance of this optimized membrane was 1.3 ± 0.2 Ω cm2, which was about 87.48% lower than the membrane containing unmodified GO.