Ion flocculation in water: From bulk to nanoporous membrane desalination

Abstract

In this work, we employed molecular dynamics simulations of a mixture of 1:1 and 3:1 salts in order to explore the flocculation as a prominent factor in desalination through nanoporous membranes. The NaCl rejection by the nanomembranes is enhanced due to the addition of the multivalent cation from ~70% to 100%. Our findings indicate that the mechanism behind this effect is the ionic clustering due to the presence of the multivalent ion combined with the dielectric discontinuity at the nanopore. We show that the confinement increases the sodium‑sodium aggregation and that the clusters are able to support the high pressures applied in the non-equilibrium simulations. Our results indicate that a simple flocculant can enhance ion rejection rate of the nanomembrane, which is consistent with recent experimental findings that the rejection sharply increases with the particle size.