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

Background: Due to the growing concern about environmental pollution caused by commercial corrosion hibitors, the anticorrosive properties of several natural products have been studied. Methods: 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 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. Significant findings: 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 Lang-muir 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 obtain electronic properties of the chief compounds of the natural extract and explained the inhibitor/metal surface interactions and adsorptions modes.

Automated summary

This study evaluated the inhibition performance of Randia monantha pulp and seed extract on the corrosion of A36 mild steel in 1M HCl solution. The results showed that the extract had a good inhibition effect, achieving an inhibition efficiency of 91% at a concentration of 1000 ppm. Electrochemical measurements indicated that the molecules of the extract acted as a mixed-type inhibitor and their adsorption process obeyed the Langmuir isotherm primarily through a physisorption mechanism. Surface analysis confirmed the adsorption of compounds from the extract, and chemical quantum calculations provided insights into the electronic properties and interactions between the inhibitor and metal surface.