Green corrosion inhibition of mild steel in HCl medium using leaves extract of Arbutus unedo L. plant: An experimental and computational approach

In this study, leaves extract of Arbutus unedo L. plant was used as a green corrosion inhibitor of mild steel in hydrochloric acid. The aqueous extract is rich in polyphenol and in particular flavonoid compounds as determined by the quantitative aluminum chloride colorimetric method. The n-butanol extract shows the highest concentration of total phenol and total flavonoid contents with 219.46 GAE mg/g extract and 174.66 mg QE/g of dry extract, respectively. Electrochemical impedance spectroscopy and potentiodynamic polarization were used as experimental measurements to confirm the anti-corrosion performances of the extract of plant leaves at different temperatures. The addition of extract plant even at low concentration increases significantly the inhibition efficiency with a maximum of 91.72% at 298 K for 0.5 g/L of leaves extract. Surface analysis was performed to attest the presence of the protected film on the surface of mild steel in HCl solution. The calculated ?G0ads value (-24.441 kJ/mol) confirmed a spontaneous mixed chemical and physical adsorption of leaves extract compounds on the metal surface. The pKa analysis attested that the two leaves extract compounds, quercetin and catechin, exist in the neutral form in an acidic environment. Moreover, density functional theory and molecular dynamic simulation were also conducted to support the high inhibition efficiency results obtained by the experimental tests and to propose the adsorption mechanism.