Atomic insight into water and ion transport in 2D interlayer nanochannels of graphene oxide membranes: Implication for desalination

Abstract

Currently, graphene oxide (GO) membrane is becoming a new-generation material for desalination application with high water permeability and ion rejection rate. The unusual 2D interlayer nanostructure in GO membrane provides a reliable and precise molecular sieving function for fast water transport and ion rejection. However, the studies on molecular mechanisms for water and ion transport in the 2D interlayer nanochannels of GO membrane are far from adequate, and the trade-off between selectivity and permeability is another problem significantly restraining the further development of GO membrane for desalination. In this work, molecular dynamics simulations were conducted to investigate the atomic mechanism of water and ion transport in 2D nanochannels of GO membrane, and the influences of interlayer space and nanostructure on water and ion transport were also revealed. We find that there are strong electrostatic, vdW and hydrogen bond interactions between water/ion and the oxygen-containing groups in GO nanosheets, which largely impedes their transport. The hydration interaction also plays an important role in ion adsorption in the 2D nanochannels. The fast water and ion transport in GO membrane mainly occurs in the non-oxidized region of neighboring GO nanosheets. By combing the influences of interlayer space and nanostructure on water and ion transport, a new design principle for high-efficient GO desalination membrane is proposed. The findings in this work expand our understanding of water and ion transport in GO membrane and may also greatly promote the development of desalination membrane prepared by other 2D materials.