Insight into anti-corrosion behavior of Cladanthus mixtus (L.) flower extracts as a biodegradable inhibitor for carbon steel in acid medium: Experimental and theoretical studies

This study conducted a comprehensive investigation into the corrosion inhibition potency of the essential oil of flowers (EOF) and the aqueous extract of flowers (AQEF), a by-product liquid waste derived from the extraction process of Clandanthus mixtus (L.), towards carbon steel in 1 M HCl. Phytochemical screening, gas chromatography (GC), and gas chromatography coupled to mass spectrometry (GC-MS) were employed to explore the chemical composition of the extracts. Flavonoids, tannins, and coumarins were identified as chemical families present in the extracts, while palmitic acid (10 %) and arcurcumene (39.1 %) were found to be the most important constituents, comprising 49.1 % of the total composition of the essential oil. Electrochemical techniques, including Tafel extrapolation methods and electrochemical impedance spectroscopy (EIS), were used to evaluate the inhibition efficiency of the extracts. The inhibition efficiencies reached a maximum of 80 % following a mixed-type inhibition mechanism. The temperature effect was evaluated, revealing a physisorption process followed by desorption at higher temperatures. The synergistic effect between the extract and potassium iodide was assessed at different doses, demonstrating their cooperative role in reducing steel surface deterioration. Surface micrographs were acquired through scanning electron microscopy (SEM) with the Energy Dispersive X-ray (EDX) method in the presence of AQEF, confirming the establishment of a protective barrier that mitigates the corrosive effects of hydrochloric acid. Additionally, this study employed Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations to investigate the behavior of AQEF compounds against corrosion.