The Molecular Dynamics Simulation Of Layered Nanomaterials For Seawater Desalination

Seawater desalination technology is an effective mean to deal with the global fresh water crisis.Reverse osmosis(RO)membrane based on polyamide(PA)has been a research hotspot in the field of seawater desalination for a long time,but its shortcomings such as low filtration efficiency and easy to be polluted restrict its further development.In recent years,two-dimensional nanomaterials with pores,typically represented by graphene and its derivatives,molybdenum disulfide(MoS2)and graphite acetylene,have been widely studied due to their excellent stability,high water transport rate and efficient salt resistance ability.However,the mechanism of interlayer movement and separation of water molecules and salt ions is still unclear.With the rapid development of high-performance computers,people could use molecular dynamics simulation and other methods to explore the desalination mechanism of interlayer nanomaterials from the atomic level and to find out factors that affect the water filtration performance,which could provide theoretical guides for experiments.In this paper,by nonequilibrium molecular dynamics simulation,we explore the transport performance of water molecules and salt ions in different layer spacing of stacked nanomaterials(graphene,BC3,C3N,Au),and analyze the influence of layer spacing,charge,lattice arrangement and other factors on desalination performance.the water molecules and salt ions penetration performance under different layer stack nanomaterials(graphene,BC3,C3N,Au)with different layer spacing and analyze the influence of layer spacing,charge,lattice configuration to desalination performance.The transport and separation mechanisms of salt ions and water molecules in different layered nanomaterials were obtained.The main conclusions are as follows:(1)For graphene(GRA),boron and nitrogen doped graphene(BC3 and C3N),when water is filtered laterally along the doped graphene layers,the optimal interlayer distance is 0.7nm?0.9nm,and they have high water permeability and salt resistance ability.Compared to porous graphene filters,they are far more permeable and their permeability is about two orders of magnitude higher than that of commercial reverse osmosis membranes.By changing layer spacing,the order of water permeability of three graphene layered nanomaterials is C3N?GRA?BC3.Under the same conditions,BC3 is more sensitive to the interlayer distance,which could provide the possibility of controlling the desalination speed by adjusting the film thickness.This is mainly due to the charge transfer of BC3 itself,which leads to the periodic distribution of water clusters on the material surface,thus affecting the interlayer transport of water molecules.(2)The 111 crystal plane of gold has excellent water permeability,which is about three orders of magnitude higher compared to the commercial reverse osmosis membrane,but its salt resistance rate decreases at layer spacing with 0.7nm,and the water flux is not satisfactory.The water flux of 100 crystal plane is lower than that of 111 crystal water filter,but the salt resistance rate still reaches 100%under 0.9 nm layer spacing.It is notable that at 0.65 nm layer spacing,100 crystal plane has the high water flux,and water flux is almost zero at the layer spacing of 0.7nm-1nm.Its water flux is almost zero.This might be attributed to configuration changes of waters molecules,disturbing the stable hydrogen bonding network and reducing the degree of order of water molecules,eventually speeding up the water transport rate.