Quantum chemical calculations, molecular dynamics simulation and experimental studies of using some azo dyes as corrosion inhibitors for iron. Part 1: Mono-azo dye derivatives

Abstract

This study consists of two parts. In the first part, the inhibitive performance of six mono-azo dye (MAD_ 1 6 ) derivatives was investigated experimentally (gravimetric, thermometric, UVvisible spec-trophotometric and electrochemical potentiostatic methods) and computationally against corrosion of Fe metal in 2 M HNO3 and 2 M NaOH solutions. Density functional theory (DFT) calculations and molec-ular dynamics simulation (MDS) approach were performed. Quantum chemical parameters such as the highest occupied molecular orbital energy (E-HOMO ), lowest unoccupied molecular orbital energy (E-LUMO), the energy gap between E-LUMO and E-HOMO (Delta E ), dipole moment (D ), chemical hardness (eta), softness (sigma), electronegativity (chi), proton affinity, global electrophilicity (omega), global nucleophilicity (epsilon) and total energy (sum of electronic and zero-point energies) were calculated and discussed with the help of HF/SDD, HF/6-311 G, HF/6-31++G, B3LYP/SDD, B3LYP/6-311 G and B3LYP/6-31++G methods. Polarization measurements indicate that (MAD) compounds are of mixed-type inhibitor in acidic, act mainly as cathodic in alkaline solution. Kinetic model involving binding constant (K-b ), active sites (1/y) and standard free energy values of adsorption (Delta G degrees) were compared with the parameters of equilibrium constant (K-ads ), lateral interac-tion (f ) and (Delta G degrees), that obtained from Frumkin adsorption isotherm model. Then, we calculated binding energies on Fe (110) surface of the inhibitors. The theoretical data obtained are in good agreement with the experimental inhibition efficiency results.