Cyanthillium cinerium(L.) extract as green corrosion inhibitor for mild steel in acidic medium: Electrochemical and computational study

The present study aims to elucidate the corrosion inhibition efficacy of Cyanthillium cinerium(L.) H.Rob. as a green inhibitor on 5LX70 mild steel (MS) in 1 M HCl medium by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), scanning electron microscopy (SEM), and density functional theory (DFT). The EIS results yielded 88.12 % inhibition efficiency at 600 ppm of inhibitor concentration with a uniform corrosion mechanism while the polarization results achieved 85.73 % of efficiency. The shift of corrosion potential from blank to the highest inhibitor concentration was found to be less than 85 mV suggesting mixed type behavior of the inhibitor. The addition of inhibitor to the aggressive solution produced an increase of 374.1 Ωcm² charge transfer resistance at the electrolyte/electrode interface and a decrease of 17.78 µAcm⁻² corrosion current in polarization studies; this confirmed the protective ability of the inhibitor on MS surface. The SEM results confirmed the surface coverage by the inhibitor on the metal surface. Quantum chemical parameters obtained by DFT simulations suggested that the inhibitor molecules could chelate with metal atoms and further Mulliken charges and Fukui indices indicated the local reactive descriptors. Monte Carlo simulations provided energy profiles that are indicative of chemical adsorption on the Fe (1 1 0) surface. This study demonstrates that Cyanthillium cinereum is a promising green corrosion inhibitor for mild steel, offering an eco-friendly and sustainable solution.