Improving water desalination via inhomogeneous distribution of [BMIM][BF4] in 2D carbon nanotube networks: Nonequilibrium molecular dynamics simulation

Abstract Improving water desalination performance by rational design of nanoporous membrane is a promising alternative to solve global freshwater shortage. Herein, 2D carbon nanotube (CNT) networks with various pore sizes were constructed and their water desalination performances were systematically evaluated by nonequilibrium molecular dynamics simulations. Compared with the conventional reverse osmosis membranes, the 2D CNT network with smaller pores can effectively promote water permeability with 100% salt rejection. In addition, the water permeability of 2D CNT network can be further adjusted through incorporation of 1-n-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) molecules by taking advantage of its hollow structure. Interestingly, the [BMIM][BF4] molecules tended to form a cluster and inhomogeneously distributed around pores when its content was low, which exert an asymmetric force on water molecules near the pores, thus facilitates to tune their dipole orientation. As a result, compared to the hollow and full-filled 2D CNT networks, the water permeability of the one with half-filled [BMIM][BF4] increased by over 22.14%. Therefore, providing asymmetric forces for water molecules around membrane pores is an effective approach to improve water permeability, which provides a clear vision for the design of next-generation desalination membranes.