Electrochemical and DFT theoretical evaluation of the Randia monantha Benth extract as an eco-friendly corrosion inhibitor for mild steel in 1 M HCl solution

Due to the growing concern about environmental pollution caused by commercial corrosion inhibitors, the anticorrosive properties of several natural products have been studied. The present work assessed the inhibition performance of Randia monantha pulp and seed (RMPS) extract on corrosion of A36 mild steel in 1M HCl solution through weight loss and electrochemical measurements such as potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS). Surface analysis was carried out using scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). Chemical characterization of RMPS extract and theoretical studies of its chief compounds were performed by spectroscopic studies and density functional theory (DFT) calculations, respectively. Electrochemical measurements results showed that corrosion inhibition increased as inhibitor concentration increased, achieving an acceptable inhibition efficiency of 91% at 1000 ppm. Polarization curves indicated that molecules of RMPS acted as a mixed-type inhibitor and their adsorption process obey the Langmuir isotherm manly by physisorption mechanism. Examination of corroded steel surface by SEM and EDS confirmed the adsorption of compounds presented in the extract. The chemical quantum calculations allowed to obtain electronic properties of the chief compounds of the natural extract and explained the inhibitor/metal surface interactions and adsorptions modes.