Carica papaya Seeds and Its Active Constituent Benzyl Isothiocyanate against Corrosion of Aluminum

Benzyl isothiocyanate was isolated from an aqueous extract of Carica papaya seeds. Phytochemical screening and isolation of the active components were carried out via high performanvice liquid chromatography and liquid chromatography–mass spectrometry. Both the Carica papaya seed aqueous extract and its most active component were investigated for the ability to inhibit 6061 aluminum alloy corrosion in an acidic medium (pH 3). Electrochemical techniques, scanning electronic microscopy and energy dispersive X-ray spectroscopy were employed to study anti-corrosion activities. The study was carried out by varying the concentrations of the inhibitor to find out its optimum efficiency. Kinetic parameters were evaluated and discussed in detail. Results were fitted into an appropriate adsorption isotherm. By using the data obtained from the adsorption isotherm and the Gibbs–Helmholtz equation, thermodynamic parameters for the adsorption were computed. A suitable mechanism was proposed for the corrosion inhibition process. Surface morphology studies confirmed the adsorption of the inhibitor. The density functional theory in the study of benzyl isothiocyanate also supported the obtained experimental results. To sum up, the active component of Carica papaya seeds is an efficient corrosion inhibitor, being cost effective and not harmful to the environment.