Inhibitive properties, thermodynamic, kinetics and quantum chemical calculations of polydentate Schiff base compounds as corrosion inhibitors for iron in acidic and alkaline media

Abstract

Quantum chemical calculations based on the density functional theory (DFT) method were performed on five polydentate Schiff base compounds (PSCs), act as corrosion inhibitors for iron in aerated 2.0 M HNO3 and 2.0 M NaOH, aiming to analyze the characteristics of the inhibitor/surface mechanism as well as to analyze the experimental data and to describe the structural nature of the inhibitor on the corrosion process. The relationship between molecular structure of PSC and their inhibition efficiencies was discussed. The inhibition effect has been investigated using weight loss, thermometric, potentiodynamic polarization measurements and quantum chemical study. Among the compounds studied, 4-(2-hydroxynaphthylideneamino) antipyrine (PSC_1) exhibited the best inhibition efficiency IE (%) 78.4 % at 10−4 M at 303 K. The high IE of (PSCs) was attributed to the blocking of active sites by adsorption of inhibitor molecules on the iron surface. Adsorption of (PSCs) inhibitors is spontaneous, exothermic, obeyed Temkin isotherm and is regarded as physiochemical mechanism. Polarization measurements indicate that all the examined Schiff bases are of mixed-type inhibitor in HNO3; causing only inhibition of the cathode process in NaOH. The results showed that the inhibition efficiency of PSCs increased with the increase in EHOMO and decrease in E LUMO − E HOMO; and the areas containing N and O atoms are most possible sites for bonding the metal iron surface by donating electrons to the metal.