Theoretical and Electrochemical Evaluation of Cannabis Sativa L. Extracts as Corrosion Inhibitors for Mild Steel in Acidic Medium.

Abstract

The corrosion of metals in acidic environments remains a significant challenge, driving the search for sustainable and eco-friendly inhibitors derived from natural sources. This study evaluates the corrosion inhibition potential of three extracts from Cannabis sativa L., namely ethanol extract (EET), hexane extract (EHX), and dichloromethane extract (EDM), for mild steel in a 1 M HCl acidic medium. The investigation employed weight loss (WL) measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) techniques. To understand their inhibitive performance, density functional theory (DFT) was used. For a more comprehensive theoretical analysis, Monte Carlo (MC) and molecular dynamics (MD) simulations were used. The corrosion inhibition efficiency increased with the increase of EET, EHX, and EDM concentrations up to 91 %, 89 %, and 83 %, respectively, obtained at 308 K for a 0.8 g/L concentration. Polarization studies classify EET, EHX, and EDM as mixed-type inhibitors with a predominantly anodic effect, functioning through adsorption on the metal surface. The adsorption of these extracts on mild steel conforms to the Langmuir isotherm model, with adsorption equilibrium constants (K_ads) of 3.0143 M, 5.1245 M, and 2.2009 M for EET, EHX, and EDM, respectively, highlighting their potential as effective corrosion inhibitors. The EET extract exhibits a high activation energy (E_a) of 101.70 kJ/mol, while the EHX and EDM extracts show E_a values of 79.05 kJ/mol and 82.93 kJ/mol, respectively, all significantly higher than the E_a of blank, which is 30.23 kJ/mol, indicating that the extracts effectively inhibit corrosion by increasing the activation energy, with EET being the most potent inhibitor. Theoretical approaches based on DFT, MC, and MD simulations clearly explain the mode of adsorption of the majority of molecules on the metal surface. The inhibition process may result from a synergistic intermolecular effect of the major compounds in the extract, which interact at various active adsorption sites on the metal surface. Simulations indicate that catechin dihydrate in EET (52.42 %), linoleic acid in EHX (42.92 %), and naringenin in EDM (41.92 %) are close to the metal surface, suggesting strong interactions with the material. The results obtained from experimental measurements and theoretical calculations agree, highlighting the potential for developing more sustainable corrosion inhibitors based on plant-derived compounds.