Efficient isotropic water desalination in anisotropic lamellar nano-channels formed by layered black phosphorus membrane

Abstract Recent developments in nanomaterials have greatly advanced the design and fabrication of water filtration membranes and hopefully alleviate the deteriorating freshwater scarcity. In this work, we demonstrated that lamellar stacking of layered black phosphorus (BP) can serve as an efficient membrane for seawater desalination. Using molecular dynamics simulations, we show that the nano-channels inside BP membranes can effectively block ionic passage while maintaining high water flux (~ 30 L/cm2/day/MPa) at a large range of interlayer spacing (9 A to 12 A). Despite the in-plane anisotropy of the BP membrane, the filtration performance of the nano-channels is barely affected by the orientation of the adjacent BP layers. Quantitative potential of mean force analysis indicates that the excellent water filtration performance is attributed to the high energy barriers (>15 kJ/mol) for ions versus the low energy barrier (~ 2 kJ/mol) for water to enter the nano-channels. Moreover, the effect of defects presented in the BP membrane to water filtration has been addressed which is found to hardly affect the filtration performance, indicating the robustness of the BP-based nano-channels. Therefore, the results presented in this study offer a competitive membrane for seawater desalination which is also expected to guide the future design of membrane materials.