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

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. [Display omitted] •rGO-K+ membranes are prepared for multivalent metal ions rejection.•The permeance of rGO-K+ was up to 86.1 L m−2 h−1 bar−1 with a high FeCl3 rejection.•rGO-K+ exhibited structural stability under high pressure and different pH solutions.•The improved performances of rGO-K+ are attributed to K+ modification.