Abstract
In this paper, we investigate the selection rule for desalinating seawater using functionalized graphene sheet as a semi-permissible membrane. Both the applied mathematical modeling and MD simulations will be used to determine the acceptance conditions for water molecule or sodium ion permeating into the functionalized graphene. Both the Lennard-Jones potential and Coulomb forces are considered by taking into accounts the major molecular and ionic interactions between molecules, ions and functionalized graphene sheet. The continuous approximation will then be used to coarse grain most significant molecular and ionic interactions so that the multi-body problems could be simplified into several two-body problems and the 3D motions are reduced into degenerated 1D motion. Our mathematical model and simulations show that the negatively charged graphene always accepts sodium ions and water; however the permeability of water molecules and sodium ions becomes very sensitive to the presence of positive charges on the graphene.
Highlights
Graphene oxide comprises graphene sheets which are decorated by certain functional groups such as hydrophilic oxygen [1]
We investigate the possibilities and limitations of using functionalized graphene sheet for the saltwater desalination
The total force between the sodium ion and the functionalized graphene sheet can be deduced in a similar way, i.e. Ftot = FI – ΔΦ + Fext, where FI denotes the ionic forces between the ion and the functionalized graphene
Summary
Graphene oxide comprises graphene sheets which are decorated by certain functional groups such as hydrophilic oxygen [1]. Numerous computational simulations have been performed on the ultra-filtration using nanotubes [2]-[9], zeolite [10] and graphene [11] [12]. All these theoretical investigations reveal a rapid and effective ultra-filtration using nanomaterials in comparison to conventional membrane. We adopt the continuous approximation introduced by Cox et al [14] [15], where the pairwise interactions between ions, molecules and functional groups are coarse grained so that the time-consuming calculations could be fasten by performing certain line integrals, and single and double surface integrals. The resulting force fields could be incorporated into the MD algorithm to determine the time evolution of the physical system numerically
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