Elucidating the adsorption mechanism and corrosion inhibition performance of benzothiazolium salts on carbon steel in acidic solution.

This study evaluates the corrosion inhibition performance of two benzothiazolium salts, (E)-2-(4-bromostyryl)-3-ethylbenzo[d]thiazol-3-ium iodide (BBEI) and (E)-2-(2-chlorostyryl)-3-ethylbenzo[d]thiazol-3-ium iodide (BCEI), on carbon steel (CS) in 1 M HCl solution. The inhibitory action was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). Results indicated that the inhibition efficiency of both compounds increased with concentration but decreased with temperature, reaching maximum values of 98.6% for BBEI and 96.9% for BCEI at 10-3 M and 303 K. PDP analyses revealed that both molecules act as mixed-type inhibitors, suppressing anodic dissolution and cathodic hydrogen evolution. Adsorption studies showed good agreement with the Langmuir isotherm, suggesting the formation of stable monolayer coverage on the CS surface. Surface characterization techniques, including UV-Vis, SEM/EDS, AFM, XRD, contact angle measurement, XPS and FTIR, confirmed the development of a protective inhibitor film that significantly reduced metal dissolution. The observed protective layers correlated with the high inhibition efficiencies recorded electrochemically. To complement the experimental findings, theoretical investigations were performed using density functional theory (DFT) and molecular dynamics (MD) simulations. Theoretical descriptors, adsorption energies, and electronic parameters highlighted the strong affinity of BBEI and BCEI towards the steel surface, corroborating the experimental results. Overall, the combined experimental and theoretical approach provides a comprehensive understanding of the inhibition mechanism of benzothiazolium salts on carbon steel in acidic medium, demonstrating their potential as effective corrosion inhibitors for practical applications.