Ionic Selectivity Inside Solid-State Nanoscale Channels: Physics and Applications

Abstract

Abstract: Ionic selectivity across nanochannels is of great importance to biological activities as well as for designing novel molecular devices/sensors which has wide potential applications in nanotechnology. With the development of experimental and computational facilities and technologies, it becomes possible to study the ionic selectivity inside and across the nanoscale channels by both experiments and simulations. Because of the confinement effect, there are new physical phenomena in such nanotube that are not observed at macrofluidic or microfluidic size scales, including the anomalous hydration shell order, ionic selectivity based on the surface charge. These novel properties lay the foundation for the selectivity of the various types of ions. Several controlling methods for selecting ions are designed and developed, such as a controllable ion-selective nanopore (for selecting K+ and Na+) based on a single-walled carbon nanotube with specially arranged carbonyl oxygen atoms modified inside the nanopore, which was inspired by the structure of biological ionic channels; Nanopores in graphene sheets with different functional units have been applied to sieve cations of alkali metals or anions of group 17 element, respectively; The pore radius can also be determinant factor for choosing ions. Recently, the separation of the positive and negative ions has appealed more concerns. Inside of nanofluidic nanopores, negative and positive ions are manipulated analogously to semiconductor devices such as metal-oxide-semiconductor field effect transistors, where negative and positive charged carriers are manipulated. In this review, we examine some of the recent advances in the dynamics of the ionic selectivity inside solid state nanoscale channels.