Molecular simulation of reverse osmosis for heavy metal ions using functionalized nanoporous graphenes

Currently, elimination of heavy metal ions from contaminated water resource is an important issue in environmental protection. In this study, we simulated the separation performance of heavy metal ions using nanoporous graphene surfaces as reverse osmosis membranes with functionalized groups (boron, nitrogen and hydroxyl groups). We show these nanoporous graphenes could realize high water permeation and ion rejection for various conditions. The simulated water permeability is 2-5 orders of magnitude greater than that of currently commercial membranes. The interfacial water structures and flow velocity of water molecules within the nanopores were characterized. The calculations of the potential of mean force reveal water molecules generally face lower free energy barrier than ions when passing through graphene pores. The free energy barriers for ions can be explained as the combining contributions from the ion dehydration effect and the surface electrostatic interaction. Overall, the functionalized nanoporous graphene membranes exhibit potential application in the removal of heavy metal ions, and meanwhile our simulation results provide new insights into the ion rejection mechanism. (C) 2017 Elsevier B.V. All rights reserved.