Robust reduced graphene oxide membranes with high water permeance enhanced by K+ modification

Abstract Graphene oxide (GO) lamellar membranes exhibit great potential for application in molecular separation. However, they are still limited by low water permeation and swelling effects. Here, we develop robust K+-crosslinked reduced GO (rGO–K+) membranes for treating wastewater containing multivalent heavy metal ions. The rGO–K+ membranes demonstrated a water permeance of 86.1 L m−2h−1 bar−1 and a rejection rate of 99.8% for FeCl3, which exceed the corresponding values of state-of-the-art nanofiltration (NF) membranes for multivalent metal ion rejection. Further, the rGO–K+ membranes exhibited excellent aqueous stability under a high pressure (up to 9 bar) and acidic, neutral, and alkaline conditions. The improved permeability of the rGO–K+ membranes was attributed to the cation–π interactions between K+ and the rGO sheets, which fixed and enlarged the interlayer spacing, as well as increased the surface hydrophilicity, thus weakening the water transport resistance. The intercalated K+ linked the adjacent layers through the cation–π interactions, which enhanced the membrane stability. The prepared rGO–K+ membranes have potential for use in membrane separation in industrial applications.