LAUSR

In this paper, an in‐depth investigation of three graphene oxide (GO) based membranes—pure GO, Al3+ 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 JPEG‐GO > JAl‐GO > JGO. 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)32+) compared to the charge‐equivalent smaller‐sized tris(bipyridine)ruthenium(II) (Ru(bpy)32+) 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.