Mechanistic insights into the eco-friendly corrosion inhibition of carbon steel in 1 M HCl by Origanum majorana extract: Electrochemical and theoretical study

Abstract

This study explores the efficacy of an acetonic extract derived from Origanum majorana (OM) leaves as an environmentally benign corrosion inhibitor for carbon steel (CS) in acidic medium (1 M HCl). With the increasing demand for environmentally sustainable corrosion mitigation strategies, natural extracts have attracted significant attention. OM leaves were selected as a potential source of bioactive compounds capable of inhibiting CS corrosion. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques were employed to evaluate the inhibition efficiency (IE%) of the OM acetonic extract over concentrations ranging from 0.125 to 1 g·L⁻¹ . The maximum inhibition efficiency reached 94 % at 1 g·L −1 . Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of the functional groups in charge of adsorption, while scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDX) evidenced the formation of a homogeneous organic protective layer on the CS surface and the complete suppression of chloride adsorption. The inhibitor molecules exhibited Langmuir-type adsorption behavior. Thermodynamic parameters indicated a naturally favorable process predominantly governed by physisorption. Density functional theory (DFT) calculations further supported these findings, showing robust adsorption affinity of the inhibitor molecules toward the CS surface through a reduced frontier orbital energy gap (ΔE), consistent with the observed inhibition performance. • Origanum majorana extract was used as a corrosion inhibitor for carbon steel in 1 M HCl . • Maximum inhibition of 94 % at 1 g·L⁻¹ confirmed by PDP and EIS. • Adsorption obeyed Langmuir isotherm behavior. • SEM–EDX showed a compact protective organic film. • DFT identified sakuranetin as the most active compound.