Abstract
New indolium-based ionic liquids (IBILs) of chemical formula 5-methoxy-1,2,3,3-tetramethyl-3H-indolium iodide (IBIL-l), 1-(2-carboxyethyl)-2,3,3-trimethyl-3H-indolium iodide (IBIL-II), 2,3,3-trimethyl-1-(pyren-2-ylmthyl)-3H-indolium iodide (IBIL-III), 1-(3-ethoxy-3-oxopropyl)-2,3,3-trimethyl-3H-indolium bromide (IBIL-IV) and 1-(2-ethoxy-2-oxoethyl)-2,3,3-trimethyl-3H-indolium bromide (IBIL-V) have been synthesized and characterized. The adsorption and corrosion inhibition effect of those IBILs have been studied using polarization measurements and cyclic voltammetry. It has been found that the inhibitive effect of the corrosion of mild steel in 0.5 M H2SO4 is inherently dependent on the structure of the studied IBILs; IBILs with bromide as an anionic head are more efficient than those with iodide. Thermodynamic calculations indicated that the adsorption on steel surface accords with Langmuir adsorption isotherm. Electrochemical measurements showed that the IBIL-IV, with the highest inhibition efficiency, acted mainly as a mixed type inhibitor, albeit the inhibition of the anodic branch is larger than the cathodic one. Cyclic voltammetric measurements at polycrystalline gold electrode gave an insight into the mechanism of corrosion inhibition by the studied ionic liquids. (C) 2019 Elsevier B.V. All rights reserved.