Graphene Oxide Membranes for Water Isotope Filtration: Insight at the Nano- and Microscale

Recent experimental studies have revealed the selective permeation properties of lamellar graphene oxide (GO) membranes as applied to filtration of water isotopes. In this work, we explore the molecular structures and diffusive dynamics of water isotopes in GO membrane nanochannels by employing ReaxFF reactive molecular dynamics simulations. The significance of isotope effects and their role in the interactions between light/heavy water and the functional groups of GO membranes are identified, and it is found that isotope separation is driven by a combination of phase change from liquid to vapor and kinetic fractionation due to the difference in isotope diffusivity. Our phenomenological model reveals that pervaporation mode and monolayer surface diffusion of water result in efficient isotope separation, while liquid-phase pressure-driven permeation is not an effective mass transport mode for isotope filtration. These observations suggest that there is great promise for GO membranes as a means for isotope filtration, expanding the application space of GO membranes beyond the established scope of filtration by size-exclusion and preferential adsorption mechanisms.