Benzimidazole ligands in the corrosion inhibition for carbon steel in acid medium: DFT study of its interaction on Fe30 surface

• Corrosion inhibition by benzimidazole in acid medium.
• DFT study on interaction of benzimdazole with on Fe30.
• Electrochemical impedance and polarization curves of inhibitor on mild steel in acid medium.
• Comparative analysis of amine, pyridine, and benzimidazole ligands.

The corrosion inhibition of N,N′-bis(benzimidazole-2-yl-methyl)amine (L1) and N, N′-bis(benzimidazole-2-yl-methyl)hydroxyethylamine (L2) was analyzed by electrochemical and theoretical methods. The data show that ligands form an adsorption layer over an iron surface, obeying the Langmuir isotherm (ΔGads° of −32.96 kJ mol−1); the value are higher than −20 kJ mol−1 but less than −40 kJ mol−1, belonging to a conversion stage of physical adsorption to chemical adsorption or a comprehensive adsorption. This is consistent with fractal dimension of the electrode surface, estimated by an impedance depression angle of a semicircle that the surface is homogeneously covered by the formation of an inhibitor film. Furthermore, the electronic parameters of the ligands were analyzed by DFT, showing that L1 and L2 possesses corrosion inhibition properties that give up its p orbital electron density through its HOMO orbital to the metal LUMO to form an adsorption layer, and this has been proved theoretically by the interaction of ligands with Fe30. In addition, we have collected corrosion inhibition data for around 70 organic compounds reported in the literature, and the inhibition data plotted against different inhibitors, showing that amine ligands are good corrosion inhibitors.