Benzimidazole derivatives: Design, synthesis, and electrochemical assessment as efficient mild steel corrosion inhibitors in acidic environments

Using electrochemical methods, quantum chemical analysis, Monte Carlo simulations, and surface characterization, the corrosion inhibition performances of two novel organic compounds, ethyl BOU-Et and BOU-Be, on mild steel in 1.0 M HCl were comprehensively examined. Both inhibitors significantly improve corrosion resistance, according to potentiodynamic polarization and electrochemical impedance spectroscopy, with inhibition efficiencies of 98 % for BOU-Et and 97 % for BOU-Be at the ideal concentration (10-3 M). The durability of the protection is also demonstrated by immersion time tests, which show that after 12 h, BOU-Et and BOU-Be retain 98 % and 93 % effectiveness, respectively. The negative Gibbs adsorption free energy values confirm that the adsorption of the inhibitors on the mild steel surface follows the Langmuir isotherm, indicating uniform monolayer formation with strong and spontaneous chemisorption. Calculations using density functional theory highlight how global reactivity descriptors and frontier molecular orbitals contribute to explaining the electronic interactions of the inhibitors with the metal surface. Compared to BOU-Be, BOU-Et exhibits a slightly lower HOMO-LUMO band gap and higher adsorption energy, indicating stronger electron donation and adsorption affinity. Morphological analysis by scanning electron microscopy shows that the steel surface is smoother and better protected in the presence of inhibitors, especially BOU-Et, indicating better film-forming qualities.