Mechanisms of selective ion transport and salt rejection in carbon nanostructures

Carbon nanostructures, especially carbon nanotubes and graphene nanopores, have been suggested for use in a wide range of purification and separation applications, from the desalination of seawater to the separation of liquids and gases. However, achieving the required high degree of selectivity among the molecules passing through the pores while maintaining rapid transport is a difficult challenge. Here, we examine the physical mechanisms by which nanopores distinguish between small ions and reject salts while passing water, as examples of how selectivity and purification can be achieved. The simple principles described can be utilized to design novel nanoporous materials for the separation of a wide range of gases, liquids, and solutes.