Comparative Corrosion Inhibition Performance of Male, Female and Hermaphrodite Carica papaya Leaf Extracts on Mild Steel in Chloride and Sulphate Acidic Media

This study compared leaf extracts from male, female and hermaphrodite Carica papaya plants as green corrosion inhibitors for mild steel exposed to two acidic media containing 20% marine crude oil: 1.0 M hydrochloric acid (HCl) and 0.5 M tetraoxosulphate(VI) acid (H₂SO₄). The study addresses whether the sex type of the source plant and the identity of the aggressive anion affect inhibition performance. Leaf extracts were prepared using an ethanol–water solvent system and assessed using gravimetric weight-loss measurements, potentiodynamic polarisation and electrochemical impedance spectroscopy. Tests covered inhibitor concentrations, temperatures and immersion times, with surface characterisation used to examine the protective effect. In 1.0 M HCl at 303 K after 24 h, the female extract achieved 85.5% inhibition efficiency, compared with 80.4% for the male extract and 74.7% for the hermaphrodite extract. In 0.5 M H₂SO₄ under the corresponding condition, the reported efficiencies were 79.5%, 74.4% and 68.7%, respectively. Inhibition efficiency increased with concentration and decreased as temperature and exposure time increased; no optimum concentration was established within the tested range. The chloride medium produced higher inhibition efficiencies than the sulphate medium, and the performance penalty associated with sulphate increased with temperature. The results identify female-plant leaf extract as the best-performing of the three materials under the tested conditions and demonstrate that inhibitor performance cannot be transferred uncritically between acid media.