The Transport Properties of Water and Ions Confined in the Highly Aligned Graphene Aerogels: A Molecular Dynamics Simulation

Highly aligned graphene aerogels (HAGA) with three-dimensional (3D) porous structures, excellent photothermal conversion ability and spectral absorption rate are considered to be a potential material to develop efficient and clean water production by utilizing solar energy solar energy. In this study, we employed molecular dynamics (MD) simulations to investigate the mechanisms of water and salt ion transport within HAGA. We also explored how the nanopore size of the network structure affects the movement behavior of water and salt ions. Improved water transport and salt ion blocking abilities were observed when the nanopore size of HAGA was smaller. Specifically, when the nanopore size was 0.83 nm, both the mobility of water and salt ions were significantly enhanced due to the single-chain phenomenon. In addition, the effects of the external temperature field on the transport process of water and salt ions within the nanoscale HAGA are also considered. It is found that the abilities of water and salt ions transport became drastic with the increase of temperature. Under the same temperature gradient, the water molecules flowed toward the heat temperature direction, however, the salt ions moved toward the cold temperature direction. These special phenomena can be explained by the thermal creep effect and the thermophoretic effect, respectively. Overall, these findings provide a more thorough understanding of the water and salt ions transport mechanisms of HAGA, which are significant for providing useful guidelines of HAGA design.