Molecular dynamics investigation of functional group effects on water transport and ion rejection in multilayer graphene oxide membranes

Non-equilibrium molecular dynamics simulations are employed to investigate how oxygen-containing functional groups influence water transport and ion rejection in multilayer graphene oxide (GO) membranes. To isolate chemical effects from steric confinement, all membrane models share an identical geometry with fixed interlayer spacing and pore dimensions. The results reveal a non-linear dependence of desalination performance on surface chemistry. The rGO membrane exhibits the highest water permeability ( 〈 P 〉 ≈ 1553 L m −2 h −1 bar −1 ), approximately 2.5 times higher than that of pristine GO, due to low-friction slip flow over graphitic domains, whereas selective removal of hydroxyl or epoxy groups reduces water flux, highlighting their role in maintaining hydrogen-bond connectivity within confined water networks. Ion rejection mechanisms are species-dependent: chloride exclusion is governed by steric confinement and hydration preservation, while sodium retention is controlled by interactions with oxygen-containing functional groups. Partial reduction of carboxyl density leads to an “ion-trap” regime characterized by increased intra-membrane ion accumulation despite enhanced permeability. These findings provide molecular-level insight into the role of surface chemistry in nanoconfined transport and offer design guidelines for optimizing GO membranes by balancing hydrophilic connectivity and interfacial friction.