Experimental and computational studies on the corrosion inhibition of Bisbenzimidazole diamide derivative on mild steel in acidic media

A new bis-benzimidazole diamide derivative, namely N 1 , N 4 -bis((1H-benzo[d]imidazol-2-yl)methyl)cyclohexane-1,4-dicarboxamide (BCHDA), was synthesized, characterized, and evaluated as a corrosion inhibitor for mild steel in 0.5 M H 2 SO 4 solution. The inhibition performance of BCHDA was investigated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), surface morphology analysis (SEM–EDX), density functional theory (DFT), and molecular dynamics (MD) simulations. Potentiodynamic polarisation measurements were carried out at temperatures ranging from 298 to 328 K and inhibitor concentrations between 10 −4 and 10 −3 M. Potentiodynamic polarisation results indicated that BCHDA acts as a mixed-type inhibitor by suppressing both anodic metal dissolution and cathodic hydrogen evolution reactions. As per electrochemical impedance studies, a maximum corrosion inhibition efficiency of 94.32% at 10 −3 M at 298 K was shown by BCHDA. The adsorption behavior followed the Langmuir adsorption isotherm model. SEM–EDX analysis confirmed the formation of a compact and protective inhibitor layer on the steel surface. To gain molecular-level insight into the inhibition mechanism, DFT calculations were performed for both neutral BCHDA and protonated BCHDAH + species. while the MD simulations further confirmed a strong adsorption behavior, with highly negative interaction energies of − 185 kcal mol −1 for neutral BCHDA and − 160 kcal mol −1 for protonated BCHDAH + . The combined experimental and theoretical results demonstrate that BCHDA is an efficient corrosion inhibitor for mild steel in acidic medium due to its strong adsorption ability, multiple active adsorption centers, and stable protective film formation.