Quantum chemical calculations, molecular dynamic (MD) simulations and experimental studies of using some azo dyes as corrosion inhibitors for iron. Part 2: Bis-azo dye derivatives

Abstract

The adsorption behavior and inhibition mechanism of five synthesized bis-azo dye (BAD) derivatives on the corrosion of iron in aerated HNO3 and NaOH were investigated by performing potentiostatic polarization, weight loss (WL), thermometric and UV-visible spectra measurements. DFT calculations is applied to study the correlation between corrosion inhibition and global reactivity descriptors such as: E-HOMO, E-LUMO, molecular gap (Delta E), the dipole moment (mu), the global hardness (eta), softness(S), electro-negativity (chi) (k), proton affinity (PA), electrophilicity (omega), nucleophilicity (epsilon), electrons transferred from inhibitors to metal surface (Delta N), initial molecule-metal interaction energy (Delta psi), total electronic energy (E) and the energy change during electronic back-donation process (Delta E (b-d)). To mimic the real environment of corrosion inhibition, molecular dynamic (MD) simulations in aqueous phase have also been modelled consisting of all concerned species (inhibitor molecule, H2O, H3O+ ion, NO3- ion, OH- and Fe surface). The results confirmed that BAD molecules inhibit iron by adsorption behavior through donating and accepting electrons together with the formation of [Fe (II) and Fe (III)-BAD] chelate complex compounds. BAD's behavior is mainly chemisorption with some physisorption obeyed Frumkin and that of El-Awady adsorption isotherm. Kinetic parameters such as: (K-b, 1/y, K-ads. f, Delta G degrees (ads)) have been determined and discussed. Binding energies of BAD molecules on Fe (110) surface followed the order: BAD_2 > BAD_1 > BAD_3 > BAD_4> BAD_5. Theoretical results were found to be consistent with the experimental data reported. Our results provide important atomic/molecular insights into the anticorrosive mechanism of inhibitor molecules, which could help in understanding the organic-metal interface and designing more appropriate organic corrosion inhibitors. (C) 2018 Elsevier B.V. All rights reserved.