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(-2)h(-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-pi 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-pi interactions, which enhanced the membrane stability. The prepared rGO-K+ membranes have potential for use in membrane separation in industrial applications.