A combined experimental and theoretical approach effect of Curcuma. L extract as a corrosion inhibitor on iron in acidic solution

Abstract

ABSTRACT Inhibition performance of the aqueous Curcuma.L extract as a corrosion inhibitor for an iron surface in a 0.1 M HCl solution was investigated using the ac impedance technique. The inhibition efficiency for iron was determined in the presence of the Curcuma.L extract in a 0.1 M HCl solution and reached 81.1% at the optimum concentration. The corrosion inhibitive effect was achieved through the adsorption of Curcuma.L molecules onto the iron surface, which followed the Langmuir adsorption isotherm model. The inhibitive strength of the main compounds in the Curcuma.L extract, namely Curcumin (Inh A), demethoxycurcumin (Inh B), and bis-demethoxycurcumin (Inh C), might have a direct relationship with the electron-donating ability of the molecules, as revealed by quantum chemical parameters. Theoretical investigations were conducted using DFT methods with the B3LYP/6-311G++(d,p) basis set. Mulliken charge and ESP calculations were performed to illustrate the mechanism of inhibition of this extract on the iron surface. The interaction energies derived from Monte Carlo simulations followed the order Inh A > Inh B > Inh C. The aqueous extract of Curcuma.L has been shown to effectively inhibit iron corrosion in acidic environments.