Anticorrosive activity of Melothria perpusilla: A renewable and sustainable inhibitor

Abstract

Anticorrosive activity of Melothria perpusilla extract on mild steel in H2SO4 was examined by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy methods. The results revealed that mild steel corrosion was effectively controlled by the extract with 99.4 % efficiency at 3000mg/L concentration. The efficiency was improved with higher extract concentration but decreased as the temperature increased. The Tafel plots and its corrosion potential value (<85 mV) inferred that Melothria perpusilla acts as a mixed type inhibitor. Adsorption of phytochemicals onto the surface of mild steel is the primary factor in reducing corrosion. The increase in activation energy for adsorption from 22.73 kJ mol−1 in acid to 133.74 kJ mol−1 in extract's presence confirms the active role of phytochemicals in adsorption process. The increase in charge transfer resistance from 3.21 Ω cm2 in acid to 369.2 Ω cm2 in extract's presence, coupled with a decrease in double layer capacitance in the EIS investigation, suggests that a charge transfer mechanism is active at the mild steel-solution interface. Gas chromatography-Mass spectroscopy revealed the presence of five major phytochemicals along with other organic compounds in the extract. Fourier transform infrared and UV–visible spectroscopies indicated the active functional moieties (-COOH, –CONH2, -C-O-C-, –C=C- and long chain alkyl groups) are involved in the inhibition. Scanning electron microscopy confirmed the existence of shielding film of phytochemicals on mild steel. Density functional theory validated the inhibitory properties of the constituents. Therefore, it is concluded that Melothria perpusilla is an efficient green inhibitor in acidic condition.