Experimental and Computational Aspects of Green Corrosion Inhibition for Low Carbon Steel in HCl Environment Using Extract of Chamaerops Humilis Fruit Waste

The inhibition effect of a methanolic extract of Chamaerops humilis (CHFE) on the corrosion of low-carbon steel in 1 M HCl solution was evaluated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy. The extract was obtained from the fruit seeds by the Soxhlet extraction method. The CHFE demonstrated promising anticorrosive performance, and the inhibition efficiency increased with increasing the concentration of the extract, peaking at 93% at only 500 ppm. Importantly, the inhibitor exhibited a remarkable stability after 48 h of immersion, reaching an efficiency of 94%. The extract revealed a mixed-type inhibitive behavior. In addition, elevating the solution temperature showed a negative influence on the inhibition efficacy. Thermodynamic parameters suggested that the steel dissolution is an endothermic, spontaneous process. In addition, the experimental findings match well with the Langmuir adsorption isotherm and physisorption of the extract prevails. Furthermore, SEM/EDX and UV-Vis analyses demonstrated that the steel surface is protected by the extract molecules, confirming the electrochemical results. Density functional theory (DFT), Fukui function and molecular dynamics (MD) calculations unraveled the nature of inhibitor—metal surface interactions and provided insights into the most favorable electrophilic and nucleophilic active sites of oleic acid, a major constituent of the extract, helping to elucidate the mechanism of corrosion inhibition at the molecular level.