Electrochemical Investigations of Ionic Transport through Synthetic Nanopore Membranes

Multiporous membrane systems have created a way for scientists to efficiently separate unwanted contaminates from wastewater and drinking water. In ion-exchange membranes the selectivity is typically governed by the surface charge. The ability for a membrane to reject ions of the same sign while simultaneously transporting ions of opposite sign is called permselectivity. In this work, 30 nm polycarbonate membranes are gold-plated using a well-known template synthesis method. The gold-plating time can be precisely controlled to give nanopores as small as 1 nm. By exposing this membrane to a chloride containing salt, a layer of adsorbed chloride will form along the pore walls and membrane faces. The adsorbed chloride gives this membrane a net negative surface charge which will reject anions and transport cations. Using a varying concentration cell, the permselectivity of these membranes can be obtained potentiometrically. The membrane is exposed to various chloride salt solutions to determine how the chemical identity of the cation affects permselectivity. The diameter of these nanopores is also changed to probe how the pore radius affects the permselectivity of these cations. These membranes show ideal cation permselectivity so long as the pore radius is smaller than the thickness of the electrical double layer. Membranes investigated in this work have effective diameters smaller than 10 nm.