Graphene oxide-polydopamine membranes with controlled interlayer spacing

Stacked graphene oxide membranes (GOMs) show exceptional capabilities for high-throughput sieving of water, ions and molecules, offering transformative potential in environmental and energy sectors^1-5. However, achieving GOMs with subnanometre interlayer spacing and subangstrom tunability while maintaining their structural robustness for rapid and selective ion transport remains a big challenge^6-8. Here we present polydopamine-pillared composite GOMs with tunable and stable interlayer spacing, featuring controllable interlayer spacing down to 5.9 Å in the dry state, and capable of sieving hydrated rubidium (Rb⁺) and potassium (K⁺) ions differing in size by less than 0.1 Å in aqueous environments, achieving an Rb⁺/K⁺ separation factor of 5,320. These composite GOMs were fabricated by using the dopamine assembly and reaction timescale separation method. Specifically, the GOM fabrication capitalizes on the fact that nanoconfined water has a lower freezing temperature than that of bulk water, such that the interlayer spacing is regulated by the rapid assembly of dopamines into nanopillars, driven by nanoconfined liquid water while the surrounding is in bulk ice. The assembly process can be halted anytime by further lowering the temperature to tune and fix the interlayer spacing. Thereafter, the GOM is rigidified through the slower chemical reactions, including polymerization of dopamine molecules and covalent bonding at specific oxygen-containing sites on the graphene oxide surface while retaining ample graphene subnanochannels for high-flux transportation. The GOMs deliver continuous freshwater production for 30 days at a water permeance of 67.9 l m^-2 h^-1 bar^-1, 1-2 orders of magnitude higher than conventional membranes⁹.