Coupling transport of water and ions through a carbon nanotube: A novel desalination phenomenon induced by tuning the pressure direction

Abstract We find a surprising desalination phenomenon when tuning the pressure direction for the ionic transport through a carbon nanotube (CNT). A series of molecular dynamics (MD) simulations manifest that under a given longitudinal pressure, the water flux exhibits interesting maximum behaviors with the increase of lateral pressure; while the ion flux shows an excellent linear reduction even to nearly zero. This indicates an optimized pressure choice for not only the permeability but also the desalination performance, which can be attributed to the competition between the enhanced water motion and reduced water occupancy inside the CNT. The ion translocation time has a linear decay that follows the water, and their values are quite close to each other, suggesting the strong coupling motion of them inside the CNT. Furthermore, with the increase of ionic concentration, the flux of water and ions exhibit an opposite change, indicating their transport competition. Although the lateral pressure promotes the motion of water and ions inside the CNT, the higher concentration can always slow down the motion, since the ion clusters can have significant blockage effect. Our results imply a new method for controlling the transport of water and ions, and should have great implication for the desalination technology.