The corrosion inhibition and adsorption behavior of mercaptobenzimidazole and bis-mercaptobenzimidazole on carbon steel in 1.0 M HCl: Experimental and computational insights

Mercaptobenzimidazoles are an important class of biologically active compounds and one of the most frequently encountered heterocycles in industrial and medicinal chemistry. Herein, bis-mercaptobenzimidazole (bis-MBI) has been synthesized and characterized, in the aim to investigate and compare its corrosion inhibition performance with mercaptobenzimidazole (MBI) for carbon steel (CS) in 1.0 M HCl. Investigations were carried out by combining electrochemical and surface characterization techniques with computational calculations. Experimental results revealed that tested molecules have good inhibition effects against CS corrosion with bis-MBI showing the highest inhibition efficiency (92% at 1 mM). Potentiodynamic polarization measurements displayed that both inhibitors showed high cathodic effects, adsorbed on steel surface through physical and chemical interactions following a Langmuir isotherm model. Natural bond orbitals (NBO) analysis was conducted to evaluate donor-acceptor (D-A) interactions and nature of bonding in tested molecules. In addition, the adsorption of inhibitors' molecules on steel surface was simulated by molecular dynamics (MD) in a simulation cell that includes all corrosive species. Results from this work showed that bis-mercaptobenzimidazole can be used as effective corrosion inhibitor for carbon steel.