Evaluation of the corrosion inhibition behaviour of mild steel using Harumanis mango peel extract as a green inhibitor in hydrochloric and sodium chloride media

Organic plant extracts are increasingly used as green corrosion inhibitors. However, their practical application is limited by factors such as corrosion dependence, sensitivity to temperature variations, competition with aggressive ions, and the instability of the protective inhibitor film. Thus, this study aims to explore the potential of a local mango peel as a green corrosion inhibitor for mild steel. The Harumanis mango peel extract (HMPE) was obtained through solvent extraction with 60:40 (ethanol-water) system. The chemical characterization has shown that the appearance of vital functional groups such as aromatic rings, hydroxyl groups, and carbonyl groups proves that HPME is a good corrosion inhibitor. The effectiveness of HMPE corrosion inhibitors in different concentrations investigated in mitigating mild steel corrosion in acidic (0.5 M HCl) and near-neutral (0.6 M NaCl) media. The corrosion inhibition performance was evaluated using several corrosion tests, such as weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The surface of the mild steel also was analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and x-ray photoelectron microscopy (XPS). Mild steel samples were immersed in both acidic and near-neutral media in the presence of different concentrations of HMPE ranging from 0 to 350 ppm. The immersion tests found the highest inhibition efficiency at 350 and 250 ppm in acidic and near-neutral media, respectively. The polarization studies demonstrated a decrease in corrosion current density (icorr) after the addition of HMPE, thus confirming the inhibitor effect for both mediums. The lowest icorr obtained were 35.99 μA cm-2 at 350 ppm and 1.76 μA cm-2 at 250 ppm in both 0.5 M HCl and 0.6 M NaCl, respectively. Furthermore, the Tafel analysis also identified the HMPE corrosion inhibitor as a mixed-type inhibitor in both 0.5 M HCl and 0.6 M NaCl solutions but predominantly anodic in 0.6 M NaCl. The EIS result indicated increased in charge transfer resistance (Rct) as the HMPE inhibitor was added, which signified higher inhibition efficiency with the highest at 76% and 90% in 0.5 M HCl and 0.6 M NaCl, respectively. The OM observations revealed that the mild steel samples treated with HMPE exhibited smoother surfaces compared to the sample in blank, indicating reduced in corrosion damage. SEM analysis also supported these findings by showing significant improvements on the surface with HMPE in both 0.5 M HCl and 0.6 M NaCl. In addition, XPS analysis confirmed the adsorption of HMPE components on the mild steel surface, forming protective film rich in carbon, oxygen, and nitrogen-containing species. Peaks corresponding to C–C, C=O, Fe₂O₃, and FeOOH indicated the formation of a stable organic–inorganic layer that reduced further metal dissolution. Moreover, adsorption studies also show that the inhibition mechanism followed the Langmuir adsorption isotherm. Hence, these findings highlight the potential of Harumanis mango peel extract as a green corrosion inhibitor for mild steel in acidic and near-neutral media.