Metal-organic framework confined nanochannels in layered graphene oxide membranes for enhanced ion sieving

Selective separation of monovalent and divalent ions remains a significant challenge due to their comparable hydrated sizes. In this work, a GC/ZIF-8 composite membrane was fabricated by regulating the surface charge characteristics of graphene oxide (GO) with chitosan (CS) and tailoring the interlayer structure through the in-situ growth of ZIF-8 nanocrystals. Benefiting from the synergistic effects of surface charge regulation and size-sieving, the GC/ZIF-8 membrane exhibited outstanding mono−/di-valent ion separation performance. Under a concentration-gradient-driven process, the ion permeation rates followed the order of K + > Na + > Li + > Mg 2+ , indicating the preferential transport of monovalent ions and effective exclusion of Mg 2+ . The K + /Mg 2+ Na + /Mg 2+ , and Li + /Mg 2+ selectivities of the GC/ZIF-8 membrane reached 280.3, 150.8, and 52.5, respectively, while maintaining a high K + permeation rate of 0.209 mol‧m −2 ‧h −1 . As a result, an excellent balance between ion permeability and selectivity was achieved. This work provides an effective strategy for enhancing ion separation performance of two-dimensional membranes through the synergistic regulation of surface charge and interlayer structure, offering new insights into the design of high-performance ion-selective membranes for salt-lake resource recovery and water treatment applications.