Experimental and theoretical evaluation of the corrosion inhibition performance of two benzimidazole derivatives for low carbon steel in acidic solution

In this study, two benzimidazole derivatives, <i>i.e.</i> 2-(2-aminophenyl)-1<i>H</i>-benzimidazole (APhBI) and 2-(2-hydroxophenyl)-1<i>H</i>-benzimidazole (HPhBI) were tested as corrosion inhibitors for S235 steel in 1 M HCl solution, at 298-318 K. Weight loss, electrochemical impedance spectroscopy, and potentiodynamic polarization measurements were performed to evaluate the corrosion inhibition efficiency of these derivatives and the possible synergistic effect of five common intensifiers. The optimum corrosion inhibition concentration was found to be 3 mM for both derivatives, leading to corrosion inhibition efficiencies of 87.09% and 85.06% for APhBI and HPhBI, respectively. Electrochemical measurements revealed that after 24 h immersion both derivatives behaved mainly as cathodic-type inhibitors, following kinetically controlled processes. Attenuated total reflectance Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy measurements confirmed the adsorption of the compounds on the S235 steel samples, thus altering their morphology as observed by scanning electron microscopy measurements. Both physisorption and chemisorption are involved in the adsorption process, which obeys the Langmuir isotherm. Density Functional Theory (DFT), Monte Carlo (MC), and Molecular Dynamics (MD) simulations confirmed the formation of a stable protective layer on the Fe(110) surface, with inhibitors aligning to maximize interactions with Fe atoms. Mulliken charge analysis and electrostatic potential (ESP) mapping revealed that heteroatoms (N and O) serve as primary adsorption sites, facilitating strong molecular interactions with the metal surface.