Tailoring interlayer/interedge ion channels of graphene oxide membranes via a reduction-assisted alkali/alkaline earth cation-anchored strategy

Membrane-based mono/divalent ions sieving is pivotal for enhancing sustainable development across various fields related to resource extraction, environmental preservation and energy conversion. Two-dimensional (2D) laminar membranes are emerging as promising candidates for high-precision ion separation, where selective ion transport occurs either along the plane (interlayer) or through the plane (interedge). Herein, we propose a reduction-assisted cation-anchored strategy for tailoring both interlayer and interedge ion channels in 2D graphene oxide (GO) membranes. By rational immobilization of a series of semi-dehydrated cations, the GO interplanar interactions and architectures are elaborately manipulated. Characterizations and simulations unveil that alkali cations (K + , Na + , Li + ) and alkaline earth cations (Mg 2+ , Ca 2+ , Ba 2+ ) tend to anchor at interlayer and interedge regions of GO through cation-π and coordination interactions, enabling the angstrom-level size control over the GO interlayer spacings (from 4.4 to 4.6 Å) and the edge-to-edge distances (from 4.1 to 5.8 Å), respectively. By leveraging the synergy of dual-channel co-regulation, the Li + &Ca 2+ -co-anchored reduced GO (Li + &Ca 2+ -rGO) membrane exhibited an extraordinary discrimination ability towards mono/divalent ions. Our findings elucidate the semi-dehydration binding mechanisms of alkali and alkaline earth cations within GO membranes, and highlight their critical roles in angstrom-scale fine-tuning of interlayer and interedge ion channels, paving the way for the development of 2D laminar membranes for precise ion separation applications.