Abstract
Carbon steel is a fundamental material used across numerous industries; however, it is highly susceptible to corrosion when exposed to various media, particularly mineral acids that are widely employed in industrial processes. Surfactants capable of adsorbing into metal surfaces act as effective organic corrosion inhibitors. Owing to their inherent surface activity in aqueous environments, these compounds can provide efficient and simultaneous protection of metal substrates. In this study, three novels cationic gemini inhibitor surfactants (CGIS) were synthesized through a multi-step procedure involving Schiff base formation followed by quaternization reactions. The synthesized compounds IIIa, IIIb and IIIc were obtained in high purity with good yields. Structural characterization of the surfactants was carried out using Fourier Transform Infrared (FTIR) spectroscopy and Proton Nuclear Magnetic Resonance ((1)H NMR) spectroscopy. The corrosion inhibition performance of CGIS for carbon steel was evaluated in 1.0 M HCl acidic medium was systematically investigated. The evaluation employed a combination of gravimetric (weight loss) measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization techniques. The results of this study indicate that increasing the CGIS concentration and temperature leads to enhanced inhibition efficiency. The improved performance is attributed to the adsorption of CGIS molecules into the carbon steel (CS) surface, forming a protective barrier against corrosion. Potentiodynamic polarization measurements revealed that CGIS acts as a mixed-type inhibitor. Changes observed in electrochemical impedance spectra confirmed the formation of a protective layer resulting from inhibitor adsorption on the CS surface. The adsorption behavior of CGIS on carbon steel was found to follow the Langmuir adsorption isotherm. Furthermore, kinetic and thermodynamic parameters were calculated and analyzed to elucidate the inhibition mechanism. Scanning electron microscopy (SEM) images further demonstrated the improved surface morphology of carbon steel in the presence of CGIS. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-44281-2.