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

The corrosion inhibition of N,N'-bis(benzimidazole-2-yl-methyl)amine (L-1) and N, N'-bis(benzimidazole-2-yl-methyl)hydroxyethylamine (L-2) was analyzed by electrochemical and theoretical methods. The data show that ligands form an adsorption layer over an iron surface, obeying the Langmuir isotherm (Delta G(ads)degrees 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 L-1 and L-2 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 Fe-30. 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. (C) 2016 Elsevier B.V. All rights reserved.