Seawater desalination has been considered a viable approach to quench the increasing demand for clean freshwater in the 21st century. In this ongoing research, molecular dynamic simulations are conducted to simulate salt rejection from seawater by functionalized graphene membranes. For the 2-dimensional numerical experiments, single width membrane pores with uniform structure are first created on the surface of two graphene (GE) sheets. The edges of the pore opening are functionalized with different functional groups (-H, -OH, -COOH, -COO- or -NH2). An external pressure of 100 MPa is applied to the simulation box, which forces water molecules to pass through the GE sheets and be separated from Na+ and Cl- ions. The simulated trajectories of water molecules and ions are analyzed and converted to macroscopic membrane filtration performance parameters, i.e., water permeability and salt rejection efficiency. An intensive computation effort is made by using the Massachusetts Green High Performance Computing Center (MGHPCC) facility. Preliminary results clearly demonstrate that the functional groups at the GE edge should have a significant effect on water permeability but a marginal effect on salt rejection efficiency for GE seawater desalination membranes. Despite similar salt rejections of 93%-100%, the membrane permeability is decreased by 22%-93% for pure water. For seawater, GE-H group increases permeability by 34%, while other groups cause decreases from 17% to 92% compared to the GE membrane without any functional groups at the edge. The decreasing permeability increases in the order of GE-H &lt; GE-OH &lt; GE-NH2 &lt; GE-COOH &lt; GE-COO-. The GE membrane with –OH at its pore edge shows almost 100% salt rejection and the highest water permeability of 6.09×10-6 L/(m2h). Collectively, this study indicates that functionalization of GE membrane pores should be evaluated in developing the next-generation, high water flux membranes for seawater desalination.

Molecular insights into seawater desalination through functionalized nanoporous graphene membranes

2019 Fall National Meeting

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