  Nanopore desalination technology hinges on high water-permeable membranes
which, at the same time, block ions efficiently. In this study, we consider a
recently synthesized [Science 363, 151-155 (2019)] phenine nanotube (PNT) for
water desalination applications. Using both equilibrium and non-equilibrium
molecular dynamics simulations, we show that the PNT membrane completely
rejects salts, but permeates water at a rate which is an order-of-magnitude
higher than that of all the membranes used for water filtration. We provide the
microscopic mechanisms of salt rejection and fast water-transport by
calculating the free-energy landscapes and electrostatic potential profiles. A
collective diffusion model accurately predicts the water permeability obtained
from the simulations over a wide range of pressure gradients. We propose a
method to calculate the osmotic water permeability from the equilibrium
simulation data and find that it is very high for the PNT membrane. These
remarkable properties of PNT can be applied in various nanofluidic
applications, such as ion-selective channels, ionic transistors, sensing,
molecular sieving, and blue energy harvesting.
