Surface-Enhanced Raman Scattering and Electrochemical Investigations on the Adsorption of Imidazole: Imidazolium Couple and Its Implications on Copper Corrosion Inhibition

Abstract

The adsorption dynamics of Imidazol (Imid) and Imidazolium (ImidH + ) on copper was investigated by Surface-Enhanced Raman Scattering (SERS) as a function of the applied potential and pH. Although both species adsorb on metal surfaces the neutral molecule changes the orientation from tilted to perpendicular as the potential is made more negative. On the other hand, the cation remains parallel over the whole studied potential window. Imid is the major species on copper electrode, although ImidH + can be identified even in alkaline solutions. Cyclic voltammetry and chronoamperometry measurements show good correlation with SERS data in terms of CuCl (CuCl 2 − as well) and Cu 2 O formation. Initially, a chemisorption mechanism is proposed at cathodic potentials, which changes to physisorption near the copper corrosion potential and finally a soluble complex is formed at more positive potentials. Such findings indicate that Imid is a good cathodic inhibitor, but its inhibition efficiency is very low at anodic potentials.

On the 4‐methylimidazole behavior at a copper electrode: A view from surface‐enhanced Raman scattering

“…At E = −0.4 V, the overlapped bands at 625 and 530 cm −1 besides the 410 cm −1 one correspond to Cu 2 O, which is formed at a less cathodic potential due to the presence of atmosphere air. The 276 cm −1 band is typically assigned to the ν Cu‐Cl vibration and its appearance is fully justified by the chloride medium . The region characteristic of the ν C4C5 vibration shows a band at 1,560 cm −1 , but a closer look allows us identifying again the 1,599 cm −1 band, whose intensity is even smaller as compared with the spectrum at E = −1.0 V (Figure c).…”

“…We have recently reported that Imid cannot be considered an efficient inhibitor at its natural pH (around 8.0) because it physically adsorbs on the oxidized copper surface at the corrosion potential and further reacts with corrosion products providing a soluble complex, in contrast to benzotriazole behavior in which an insoluble passive film is formed . Furthermore, our SERS data clearly show that imidazolium (ImidH + ) is the major species in extremely acidic medium (pH = 2.0) and near the corrosion potential, but its interaction to the metal surface is even weaker as compared with the neutral species.…”

“…In the present study, SERS spectra of 4‐MeImid at a copper electrode are reported for the first time in the literature, and undoubtedly, the motivation for the choice of this system is very well justified by the aforementioned information. In other words, it is fundamental to investigate its adsorption mode in order to compare it to the one recently proposed for Imid and to explain in a molecular level its better performance in acidic medium . The solution pH and potential dependences on the spectra are here shown, and the aspects related to the effective participation of the adsorbing azole species, molecular orientation, and surface bond in the presence of chloride and atmospheric air are discussed in detail.…”

“…A circular platinum grid and the saturated calomel electrode were used as counter and reference electrodes, respectively, and all potentials were quoted to this latter. The cleaning and activation of the working electrode were made according to the previously described method …”

“…Cyclic voltammetry measurements were performed at the same aforementioned temperature, but an IVIUM Vertex model potentiostat (IVIUM Technologies) was used at this case. The voltammograms of the 0.001 mol L −1 (pH = 8.8) and 0.1 mol L −1 (pH = 2.0) 4‐MeImid solutions are illustrated in Figure S1 and detailed information on the adopted procedure may be found in our recent work …”