Tuning the Water Desalination Performance of Graphenic Layered Nanomaterials by Element Doping and Inter-Layer Spacing

Through atomic molecular dynamics simulations, we investigate the performance of two graphenic materials, boron (BC_3) and nitrogen doped graphene (C_3N), for seawater desalination and salt rejection, and take pristine graphene as a control. Effects of inter-layer separation have been explored. When water is filtered along the transverse directions of three-layered nanomaterials, the optimal inter-layer separation is 0.7–0.9 nm, which results in high water permeability and salt obstruction capability. The water permeability is considerably higher than porous graphene filter, and is about two orders of magnitude higher than commercial reverse osmosis (RO) membrane. By changing the inter-layer spacing, the water permeability of three graphenic layered nanomaterials follows an order of C_3N \ge GRA > BC_3 under the same working conditions. Amongst three nanomaterials, BC_3 is more sensitive to inter-layer separation which offers a possibility to control the water desalination speed by mechanically changing the membrane thickness. This is caused by the intrinsic charge transfer inside BC_3 that results in periodic distributed water clusters around the layer surface. Our present results reveal the high potentiality of multi-layered graphenic materials for controlled water desalination. It is hopeful that the present work can guide design and fabrication of highly efficient and tunable desalination architectures.