Tuneable ion transport by electrically responsive membranes under electrical assistance

The conventional membrane technology provides an effective solution for ion separation. However, the traditional membrane is not able to tune the permselectivity during operation, and has inherent drawbacks of permeance and selectivity trade-off. In view of this, the purpose of this project is to realize controllable ion transport without impeding water filtration through electrically responsive membrane (ERMs) under electrical assistance. To achieve this, we developed electrically responsive membranes with different electrical conductivities and surface charge properties by incorporating multi-walled carbon nanotubes (CNTs) and different acids doped polyaniline (PANI). The external potential was supplied to create tuneable electrostatic interactions between surface charged ERMs and ions, which was expected to regulate and control ion transport. It was found that the developed ERMs exhibited improved rejection without decreasing the water permeance under applied potential. The responsiveness of ion rejection to the electrical potential was affected by the combined effect of charge density and electrical conductivity. The calculations based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory suggested that imposing an external voltage increased the surface potential of ERMs and thus improved the electrostatic repulsive force between ERMs and ions, resulting in improved ion rejection. It is believed that this simple and feasible strategy for fabrication of ERMs has a potential for practical applications in tunable ion separation.