Pichichio extracts ( <i>Solanum mammosum</i> ) as a corrosion inhibitor of low carbon steel in an acidic environment

Abstract Pichichio ( Solanum mammosum ) is a tropical plant known for its pharmacological properties, primarily associated with its fruit and leaves. Ethanolic extracts of its fruit and leaves are being studied for the first time as a green corrosion inhibitor due to their effectiveness on low carbon steel in acidic medium (1.0 M HCl) based on ASTM G 31. The extracts Fourier Transform Infrared (FTIR) spectra and High Performance Thin Layer Chromatography had identified coumarins, polyphenolic compounds, and possible anthraquinones. Pichichio leaf extract (PLE) exhibiting higher antioxidant capacity compared to pichichio fruit extract (PFE) but this property does not show a clear correlation with inhibition efficiency. Gravimetric analysis indicated that both extracts provide significant corrosion inhibition (greater than 90 %) at concentrations of 1000 mg L −1 , though the inhibition efficiency decreases with lower concentrations, higher temperatures, and extended application times. Electrochemical analysis revealed Randles-type behavior with deviations at low frequencies, as well as slight variations in the open circuit potential ( E oc ) and Tafel slopes. Both extracts (PLE and PFE) act as mixed-type inhibitors, with a predominant barrier effect, displaying Langmuir-type adsorption curves for PFE and Flory-Huggins-type for PLE. The variations in the thermodynamic adsorption energies are significant only for PFE, suggesting better surface interaction. Surface visualization through physical methods suggests that the extracts reduce overall surface roughness, which correlates well with their barrier effect.