Study of Alkane Thiols as a Blocking Mechanism for Specific Adsorption for Application of Charge Selective Membrane Transport

Abstract

Electrodialysis (ED) is an electrochemical process used for separation of ions across perm-selective membranes. ED uses a DC bias to selectively transport ions across membranes for applications ranging from desalination of water to demineralization of fruit juice. The energy cost of ED is due to accumulation of hydroxide and hydronium ions from the electrochemical process of water; additionally there is the cost of using platinum electrodes. This paper addresses the idea of using polycarbonate track etched membrane (PCTE) coated with gold between the membranes to reduce the energy cost and to explore a wider selection of electrode materials. This paper aims to show how thiol monolayers on gold can be used as ideal polarizable electrodes (electrode behaves like a capacitor with only charging current and no faradaic current) for application of potential to the membrane surface double layer. We report the characterization of such monolayers on gold-coated microscope slides. The goal is to control the diffuse layer potential at each membrane-solution interface while at the same time prevent adsorption on the electrode surface and minimize Faradaic activity due to electrolyte and redox species in solution. This lays the groundwork for the application of thiol-modified polycarbonate track-etched membranes for ion-selective transport. The paper proposes the use of electrochemical impedance spectroscopy (EIS) to measure characteristics of gold (Au)-coated membranes and their inherent limitations. In this work, the fabrication of a membrane permeate flow cell is described with the aim of subsequently studying the transport of ions through conductive polycarbonate track etched membrane (PCTE) by interrogating the system using EIS and CV measurements. In particular, we would like to ascertain the voltage range that can be applied to the Au-coated membrane without getting a considerable faradaic activity; the difference between platinum and Au electrode; the effects of different electrolyte concentrations and various applied DC potentials.