Revealing the confinement effects of graphitic carbon nitride nanochannels on the water desalination performance

Abstract

The lamellar graphitic carbon nitride (g-C3N4) membranes with controllable interlayer thickness could have promising separation performance for desalination. Understanding the molecular basis of the transport behavior of water and ions through well-defined g-C3N4 nanochannels is essential for the design of novel desalination membranes. Herein, we performed non-equilibrium molecular dynamics (MD) simulations to investigate the transport mechanisms of water molecules and ions through g-C3N4 nanochannels with various thicknesses. The confinement effect of the nanochannel could impact the water density distribution between the g-C3N4 nanosheets. Meanwhile, owing to the strong adsorption effect of g-C3N4 nanosheets, the interfacial water layer and the middle water layer in nanochannels featured with distinct transport behaviors. This water conduction behavior is different from that of graphene nanochannels. For desalination, the MD simulations showed that the g-C3N4 nanochannel could entirely reject the ions when the channel thickness was smaller than 1.0 nm. Additionally, the migration behavior of hydrated ions was correlated with the water structures in g-C3N4 nanochannels. This work not only improved the understanding of the molecular transport mechanism of water molecules and ions in the g-C3N4 nanochannel, but also provided useful guidelines for designing next-generation desalination membranes.