Corrosion inhibitive performance of Kopsia teoi extracts towards mild steel in 0.5 M HCl solution

This study investigates the capacity of Kopsia teoi (K. teoi) to inhibit corrosion, employing its stem extracts to prevent mild steel (MS) corrosion in 0.5 M HCl. In this study, three distinct extracts: dichloromethane alkaloid (KTDAE), dichloromethane non-alkaloid (KTDNAE), and methanol (KTME) were employed to investigate their corrosion mitigation performance, involving electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) techniques. EIS results demonstrated a significant increase in inhibition efficiency with concentration for each extract, reaching 87.04, 90.62, and 93.51 % for KTDAE, KTDNAE, and KTME, respectively. According to PD analysis, Kopsia teoi extracts (KTEs) functioned as mixed-type inhibitors. Surface analysis through scanning electron microscopy-energy dispersive X-ray spectroscopy exhibited notable improvements in the morphology of treated MS plates, revealing the establishment of a protective surface film. Langmuir isotherm confirmed that KTEs formed a monolayer on MS surface, and the calculated free energies of adsorption were −25.924, −26.809, and −27.687 kJ mol−1 for KTDAE, KTDNAE, and KTME, respectively. This suggests effective adsorption through both physisorption and chemisorption mechanisms. Consequently, the results of this study highlight the encouraging effectiveness of KTEs as corrosion inhibitors for MS in acidic environments. [Display omitted] •Kopsia teoi extracts demonstrated effective corrosion inhibition of mild steel in 0.5 M HCl.•Methanol extract of Kopsia teoi yielded the optimum corrosion inhibition efficiency of 93.51 %.•The extracts function as mixed-type inhibitors easing hydrogen evolution and metal dissolution.•Both chemical and physical adsorption govern the adsorption mechanism of Kopsia teoi extracts.•Surface analysis revealed minimal surface damage affirming effective corrosion inhibition.