Dehydration as a Universal Mechanism for Ion Selectivity in Graphene and Other Atomically Thin Pores

Ion channels play a critical role in regulating cell behavior and in electrical signaling. In these settings, polar and charged functional groups -- as well as protein response -- give rise to ion selective transport, allowing the channels to perform specific tasks in the operation of cells. According to recent experiments, graphene nanopores can have both weak to strong selectivity, the origin of which is unclear. Here, we establish that graphene displays an alternative, novel mechanism for selectivity: Dehydration -- the most fundamental physical process in ion transport -- yields selective pores without the presence of charges or structural changes of the pore. This fundamental mechanism -- one that depends only on the geometry and hydration -- is the starting point for selectivity for all channels and pores. Its likely detection in graphene pores resolves the conflicting selectivity results, as well as opens up a new paradigm for engineering molecular/ionic selectivity in filtration and other applications.