Multistage Filtration Desalination via Ion Self-Rejection Effect in Cation-Controlled Graphene Oxide Membrane under 1 Bar Operating Pressure.

By building a thin graphene oxide membrane with Na self-rejection ability, high permeability, and multistage filtration strategy, we obtained fresh water from a saline solution under 1 bar of operating pressure. After five and 11 cycles of the multistage filtration, the Na concentration decreased from 0.6 to 0.123 mol/L (below physiological concentration) and 0.015 mol/L (fresh water), respectively. In comparison with the performance of commercial reverse osmosis membranes, energy consumption was only 10% and water flux was higher by a factor of 10. Interestingly, the energy consumption of this multistage filtration strategy is close to the theoretical lowest energy consumption. Theoretical calculations showed that such Na self-rejection is attributed to the lower transportation rate of the Na than that of water within the graphene oxide membrane for the hydrated cation-π interaction. Our findings present a viable desalination strategy for graphene-based membranes and improve the mechanistic understanding of water/ion transportation behaviors in confined spaces.