Pressure-Driven Solvent Transport and Complex Ion Permeation through Graphene Oxide Membranes

In this paper, an in-depth investigation of three graphene oxide (GO) based membranes—pure GO, Al ³⁺ intercalated GO (Al-GO), and poly(ethylene glycol) (PEG) modified GO (PEG-GO)—is presented. Both Al-GO and PEG-GO membranes have wider interlayer d-spacing compared to pure GO, and the d-spacing size correlates well to the cross-membrane water flux with J _PEG-GO > J _Al-GO > J _GO . Pressure-driven transport of water/ethanol mixtures across all three types of GO membranes is dominated by solvent viscosity—not solvent polarity showing distinctively semi-hydrophilic membrane characteristics. Interestingly, the results suggest that both ethanol cluster size and molecular geometry contribute to preferential ethanol rejection, indicating that both GO and Al-GO membranes possess superior size sieving capability. Further, the lower permeation of tris(1,10-phenanthroline)ruthenium(II) (Ru(phen) ₃ ²⁺ ) compared to the charge-equivalent smaller-sized tris(bipyridine)ruthenium(II) (Ru(bpy) ₃ ²⁺ ) demonstrates the excellent steric selectivity of GO membranes. Compared to pure GO, the widened d-spacing in PEG-GO allows ≈100% higher ion permeation while ion flux through Al-GO is an order of magnitude lower, suggesting the significant role of electrostatic interaction in ion transport. In conclusion, these findings ought to enrich the understanding of the GO-based membranes and enable future rational designs for a wide range of applications, including water purification and solvent separation.