A graphene-like membrane with an ultrahigh water flux for desalination

Abstract

An ultrathin nanoporous membrane which combines high water permeability and high salt rejection is the core of ultrafiltration technology. Recently, we reported the synthesis of a chemically robust and nanoporous two-dimensional conjugated aromatic polymer (2D-CAP) membrane. Due to its array of highly regular sub-nanometer pores and channels, the ultrathin 2D-CAP membrane can be potentially used in desalination. Herein, we used molecular dynamics simulations to analyze the transmembrane hydrodynamics of mono- and multi-layer 2D-CAP membranes as a function of layer number. The energy barriers to water and ions across these membranes were calculated to evaluate the potential of 2D-CAP to function as the ultimate RO membrane. Our simulation results show that the bilayer CAP membrane exhibits superior ion rejection (100%) and a water flux (1172 L m⁻² h⁻¹ bar⁻¹) with a performance that is three orders of magnitude higher than the commercial reverse osmosis membrane, which is three times higher than the theoretically reported monolayer nanoporous MoS₂ membrane (the state-of-the-art membrane reported for desalination). In addition, the 2D-CAP bilayer membrane is highly resistant to swelling even at a high water flux. The monolayer 2D-CAP membrane shows good ion selectivity between monovalent and divalent ions.