Active Nanoporous Membranes for Desalination

Current water desalination technologies such as reverse osmosis (RO) and nanofiltration (NF) use tortuous structures and cylindrical nanopores to reject salts by size exclusion. The selective rejection of salts dissolved in water using nanopores requires large pressure gradients across the membranes to produce reasonable flow rates. The electrical power required for generating large pressure gradients increases the operational cost for desalination and limits its application as portable units in small communities and in third-world countries. Further, recently proposed desalination methods using carbon nanotubes and nanofluidic diodes have limited lifetime due to clogging and fouling from contaminants in feed water. Thus, existing or evolving technologies are expensive, bulky and not practical where it is needed the most. In order to develop a desalination system that is not limited by the disadvantages of existing systems, this article investigates the feasibility of a novel active nanopore membrane with superior ion rejection and water transport properties. An active nanopore is a shape-changing hyperboloidal pore that is formed in a rugged electroactive composite membrane and utilizes coupled electrostatic, hydrodynamic and mechanical interactions due to reversible mechanical oscillations between the charged pore walls and dissolved ions in water for desalination. This novel approach takes advantage of the shape of the pore to create a pumping action in the hyperboloidal channel to selectively transport water molecules. In order to demonstrate the applicability of this novel concept for water desalination, the paper will use a theoretical model to model the ion rejection properties and flow rate of salt-free water through an active nanoporous membrane.