Influence of the N-3 alkyl chain length on improving inhibition properties of imidazolium-based ionic liquids on copper corrosion

1-butyl-3-ethylimidazolium bromide ionic liquid, [beim]Br, was studied experimentally and theoretically as a potential inhibitor of copper corrosion in acidic media (pH = 3) by dc polarization, quartz crystal microbalance (QCM), scanning electron microscopy (SEM) and density functional theory (DFT). This ionic liquid is selected to study an effect of the alkyl chain length at the position N-3, since so far only ionic liquids with different alkyl substituents at the position N-1 are investigated. Improved inhibitory properties of the investigated ionic liquid against corrosion of copper in acidic solution at the given conditions are confirmed comparing to corresponding 1-butyl-3-methylimidazolium bromide ionic liquid. It is found that [beim]Br acts as a cathodic corrosion inhibitor, whereby its effectiveness depends on the applied concentration. The inhibitory effect of the studied ionic liquid (IL) was achieved through quick and spontaneous adsorption on the copper surface following the Langmuir's adsorption isotherm. Results obtained by SEM showed that copper protection is achieved through the less damaged copper surface in the presence of inhibitor. Applying DFT calculations, it is found that interactions with the metal surface occur by donating electron from the Br− anion to the copper. Based on the obtained Fukui functions influence of the inductive effect of ethyl/methyl group on the inhibitory activity is also discussed.