Unified Understanding of Water Transport in Graphene Oxide-Modified Membranes for High-Flux and High-Selectivity Desalination Membranes

Understanding the mechanisms governing water transport in graphene oxide (GO) membranes remains a central challenge in the development of next-generation desalination materials. In this work, commercial polyamide reverse osmosis membranes were coated with GO using an in situ dynamic pressurization method, followed by a comprehensive characterization and performance evaluation. Experimentally, GO deposition altered surface morphology, reduced roughness, and increased hydraulic permeability by ∼25% while maintaining salt rejection above 90%. Raman spectroscopy confirmed the incorporation of GO, and AFM and SEM revealed smoothing of the ridge-and-valley structure characteristic of interfacially polymerized polyamide layers. To elucidate the molecular origins of these changes, we performed a systematic series of molecular dynamics (MD) simulations that isolate the effects of slit width, interlayer spacing, and commensurability in stacked GO galleries. The simulations demonstrate that enhanced permeability is linked to the formation of low-friction pathways, reduced hydrogen-bond (HB) structuring, and the emergence of preferential flow routes within GO nanochannels. High commensurability between adjacent slits increases dynamic coupling and suppresses bottlenecks, while geometric expansion of the channels accelerates water mobility without compromising ion exclusion. By integrating experimental observations with molecular-scale analysis, this study provides a unified mechanistic picture of water transport in GO-modified membranes. The synergy between surface smoothing, nanoscale alignment, and reduced interfacial friction explains the observed enhanced permeance and highlights how targeted control of GO morphology can be leveraged to optimize membrane performance. These findings establish a multiscale framework for the rational design of high-flux, high-selectivity desalination membranes based on graphene-derived materials.