Rapid Preparation of Room Temperature Ionic Liquids with Low Water Content as Characterized with a ta-C:N Electrode

Abstract

Room temperature ionic liquids (RTILs) provide an ionic, solvent-free medium for electrochemical reactions. RTILs are appreciated for their many unique properties; nevertheless, it is precisely these qualities that can be very easily debased by water and organic impurities. Water, as a major contaminant in hygroscopic RTILs, has a strong effect on the physical and electrochemical properties (e.g., viscosity and dielectric constant, hence the background voltammetric current, diffusion coefficient of redox analytes and electron-transfer kinetics). In this work, a simple and relatively rapid purification process was investigated that involves sparging ultrahigh purity Ar through the RTIL while being heated at 70°C (so-called sweeping). A more conventional vacuum drying method at 80°C was used for comparison. The electrochemical properties of two RTILs, [BMIM][BF4] and [EMIM][BF4], were assessed voltammetrically using a nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) thin-film electrode. We found the sweeping purification method to be superior to vacuum drying in terms of more timely and effective removal of water. In addition, we present for the first time some of the basic electrochemical properties of novel ta-C:N electrode in contact with a RTIL.