The ever increasing demand for freshwater is a concurrent global issue and seawater desalination is being looked upon as a solution to this problem. Reverse osmosis (RO), a highly efficient membrane-based separation technique, is widely used for seawater desalination across the globe.
The efficiency of RO depends on the water permeation and the ion rejection capacity of the RO membrane. Carbon-based nanoporous materials such as carbon nanotubes (CNTs), graphene nanopores, and graphene oxide (GO) hold the potential to become next-generation RO membranes as they permit unparalleled water permeation through them. The development of RO membranes from these materials requires an in-depth understanding of fluid and ion transport through these materials. Here, the mechanism of water and ion transport through nanoporous graphene and hourglass-shaped nanopores were studied using molecular dynamics simulations. Water desalination through graphene nanopores was investigated using different water models and under different operating temperatures. Moreover, water and ion permeation across hourglass-shaped nanoporous membranes of varying inlet and outlet angles were studied. Calculations based on principles of physicochemical hydrodynamics were employed to analyze the nanoscale transport phenomena. The permeation rates through graphene nanopores were found to be correlated with the bulk transport properties of the simulated water. The results had further pointed towards a kinetic relationship between the permeation rates and the nanopore characteristics. A possible mechanism of water transport across the hourglass-shaped nanopores was also deduced.