Understanding corrosion inhibition of mild steel in acid medium by new benzonitriles: Insights from experimental and computational studies

Two benzonitrile derivatives, namely 4-(isopentylamino)-3-nitrobenzonitrile (PANB) and 3-amino-4-(isopentylamino)benzonitrile(APAB) have been synthesized and evaluated as corrosion inhibitors for mild steel (MS) in 1 M HCl solution at 303 K by gravimetric, potentiodynamic polarization (PDP) curves, and electrochemical impedance spectroscopy (EIS) methods, as well as Density Functional Theory (DFT) and molecular dynamics (MD) simulations. The results suggest that tested compounds are excellent corrosion inhibitors for mild steel with PANB showing superior performance. Polarization measurements revealed that PANB and APAB behaved as mixed type inhibitors. The polarization resistance, according to EIS studies, found to be dependent on the inhibitor's concentration. The adsorption of PANB and APAB on mild steel surface obeyed Langmuir's adsorption isotherm. On the one hand, DFT and MD simulations are being used to explain the effect of the molecular structure on the corrosion inhibition efficiency and on the other hand to simulate the adsorption of benzonitrile derivatives on mild steel surface. The protection of carbon steel in 1 M HCl was confirmed by using scanning electron microscope (SEM) and Atomic Force Microscopy (AFM). Electrochemical, DFT and MD simulations results are in good agreement.