Adsorption and anticorrosion behavior of 1-((pyridin-2-ylamino)(pyridin-4-yl)methyl)pyrrolidine-2,5-dione on mild steel surface in hydrochloric acid solution

New Mannich base 1-((pyridin-2-ylamino)(pyridin-4-yl)methyl)pyrrolidine-2,5-dione (SAP) was synthesized, characterized, and investigated as a corrosion inhibitor on mild steel (MS) in 1.0 M HCl using weight loss, electrochemical experiments, and theoretical calculations. Impedance spectra validated the decrease in the double-layer capacitance ( C dl ) and increase in the charge-transfer resistance ( R CT ) of the corrosion process due to the addition of the inhibitor. Tafel polarization studies proved that the inhibitor has a mixed type inhibitive nature with predominant control of cathodic reaction. A maximum inhibition efficiency of 88.7% from weight loss measurements and above 94.5% from electrochemical analysis were observed in the presence of 200 ppm of SAP, and the adsorption of SAP on MS surface in 1.0 M HCl was found to follow Langmuir’s adsorption isotherm. The calculated values of thermodynamic parameters predict the adsorption of SAP molecules on the MS surface was physical adsorption. FTIR, SEM–EDX, and AFM were used to characterize the surface morphology of the mild steel samples in the presence and absence of inhibitor. Density functional theory based quantum chemical calculations also fortifies the experimental inferences revealing SAP as good inhibitor. Graphical Abstract