Dual-function ethoxylated cationic surfactant for pipeline corrosion and sulfate-reducing bacteria control: electrochemical and theoretical studies

Effective corrosion inhibitors are essential for preventing metal degradation. In this study, a novel polyoxyethylene-based cationic surfactant (ECS) was synthesized and its structure was confirmed using various spectroscopic techniques, including FTIR and ¹H NMR. The ECS exhibits both surface-active and antibacterial properties due to the presence of quaternary ammonium, polyoxyethylene, and alkyl chain moieties, which facilitate its adsorption onto bacterial membranes and carbon steel (C-steel) surfaces. Potentiodynamic polarization (PDP) results indicated that ECS effectively suppresses both the anodic and cathodic reactions of C-steel via blocking effect. Corrosion current density (icorr) of C-steel dropped to 48.7µA/cm2 in presence of 175 ppm ECS. Electrochemical impedance spectroscopy (EIS) revealed that corrosion proceeded via a charge transfer-controlled mechanism. 175 ppm of ECS increased the charge transfer resistance (Rct) of C-steel to 497.81 Ω·cm2, compared to 38.6 Ω·cm2 for the blank confirming its effective adsorption. Langmuir adsorption isotherm analysis suggested that ECS is physically adsorbed on the C-steel surface, with a calculated free energy of adsorption (ΔGads) of − 27.314 kJ/mol. Furthermore, the activation energy (Ea) increased from 25.76 to 41.49 kJ/mol in the presence of ECS, indicating the formation of an energy barrier that inhibits the C-steel dissolution process. The ECS achieved a 92% reduction in C-steel degradation. Surface characterization techniques, including scanning electron microscopy (SEM), water contact angle (WCA) measurements, and X-ray photoelectron spectroscopy (XPS), confirmed the formation of a protective ECS layer that effectively shielded the carbon steel from the aggressive attack of the HCl solution. Theoretical studies, including density functional theory (DFT) and Monte Carlo (MC) simulations, were utilized to investigate the adsorption mode of ECS molecules on the C-steel surface and to elucidate how the molecular structure influenced inhibition efficiency.