Towards Understanding the Anticorrosive Mechanism of Novel Surfactant Based on Mentha pulegium Oil as Eco-friendly Bio-source of Mild Steel in Acid Medium: a Combined DFT and Molecular Dynamics Investigation

Today, due to the increasingly stringent European directives concerning the use of molecules with certain toxicities towards the environment or their users, the essential oils, extracts, and molecules derived from plants exhibiting the characteristic of being biodegradable can be considered as a source of green corrosion inhibitors instead of harmful synthetic chemicals. The present work was devoted to testing the essential oil extracted from Mentha pulegium leaves(M1) as a corrosion inhibitor for C-steel in 1 mol/L HCl solution using both electrochemical techniques and gravimetric measurements for the evaluation of the inhibition efficiencies at different temperatures. The results obtained showed that the inhibition efficiency increased with an increase in M1 concentration to reach a maximum value of 92.21%. We sought to determine the molecule responsible for this high efficiency, starting with the analysis of oil chemical composition by gas chromatography coupled with mass spectrometry. This analysis revealed that menthol(M2) and isomenthol(M3) were the principal constituents. In order to identify the molecule responsible for the inhibition and explain the protection mechanism involved, quantum chemical calculations and Monte Carlo simulations were used to explain the interaction of menthol, the major constituent of M1 with the Fe-surface. To practically confirm these results, we studied the action of 1 mol/L HCl on steel with and without the addition of M2 by both methods(gravimetric and electrochemical study). A very high efficiency was obtained, an efficiency of 94.90% at 10‒3 mol/L, which was retained for a long exposure time, and slightly decreased in function of temperature. Finally, a good correlation between the experimental data, theoretical calculations, and SEM studies was obtained, which denied that the M1 efficiency was only a result of a synergy effect and confirmed the high efficiency of Mentha oil and its main component(menthol) as a strong ecological inhibitor of corrosion.