Multilayer Graphene Oxide Membrane in Forward Osmosis: Molecular Insights

We investigate the performance of layered graphene oxide (GO) membrane in forward osmosis (FO) process for seawater desalination via nonequilibrium molecular dynamics (MD) simulations. A 0.56 M NaCl solution is used as the feed solution and a mixture of 1.0 M MgCl2 and 0.05 M Al2(SO4)3 solution is used as a draw solution. The effect of internal structure of the layered GO membrane on its performance as a FO membrane is investigated by considering three different membrane configurations which differ in their pore offset distance W. The dynamics of the permeating water and ions through the layered GO membrane is also investigated. Increase in W reduces the water permeability of the layered GO membrane and increases its salt rejection. One of the reason for this could be the blockage of permeate pathways through the layered GO membrane due to the movement of the GO nanosheets. This becomes more prominent with increasing W. Increasing W also leads to increase in distance traversed by the permeating water molecule through the layered GO membrane while it decreases velocity of the same. This study also reveals that ion permeability is affected by the parameter W, type and magnitude of charge the ion possesses and the intensity of interaction between water molecules and the ion.