Corrosion Inhibition of Mild Steel by <i>Plumeria rubra</i> Flower Extract: Electrochemical and Computational Study

Abstract The corrosion inhibition efficiency of Plumeria rubra flower extract (PRFE) on 5LX70 mild steel in 4% NaCl aqueous medium was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and density functional theory (DFT). The PRFE was analyzed by FTIR for the confirmation of functional groups in the extract molecules. EIS and PDP methods indicated that the corrosion inhibition was increased with an increase in the concentration of inhibitor, with a surface area coverage of 90.12%. Polarization results revealed that PRFE is a mixed‐type inhibitor. A maximum corrosion inhibition of 90.98% was achieved at 120 ppm of extract concentration. Quantum chemical parameters of the inhibitor molecules were calculated using the DFT method to ascertain the relation between the parameters and inhibition efficiency. Molecular descriptors like HOMO, LUMO, energy gap, absolute electronegativity, electrostatic surface potential, and so on, were determined, and found that the inhibitor molecules favorably formed a protective layer on the metal surface. The Mulliken charge analysis of the constituent atoms of selected PRFE molecules further supported in identifying the active sites for binding with the mild steel surface. Experimental results have confirmed that PRFE is a good corrosion inhibitor for mild steel which was further affirmed by the computational study.