Impacts of pyridinium gemini surfactants on corrosion inhibition of carbon steel

Pyridinium gemini surfactants (PGS-n) are an important class of amphiphiles with antibacterial properties and hence, are usually preferred in industrial and medicinal applications. In this work, three PGS-n with different alkyl chain lengths having two amide spacers, 3,3′-(Malonylbis(azanediyl))bis(1-dodecylpyridin-1-ium) dibromide (PGS-12), 3,3′-(Malonylbis(azanediyl))bis(1-tetradecylpyridin-1-ium) dibromide (PGS-14), and 3,3′-(Malonylbis(azanediyl))bis(1-octadecylpyridin-1-ium) dibromide (PGS-18), were synthesized, characterized and tested as corrosion inhibitor on carbon steel in HCl for the first time. The corrosion inhibition efficiency was examined by weight loss measurement, electrochemical impedance spectroscopy (EIS), and potentiodynamic measurements at 30 °C. Furthermore, micellization parameters such as critical micelle concentration (cmc), degree of counter ion dissociation, and Gibb's energy of micellization of these PGS-n were determined. The inhibition efficiency of the studied PGS-n was found to be maximum near their cmc values and found to follow the order: PGS-18 > PGS-14 > PGS-12. The PGS-n with the longest alkyl chain could achieve a maximum inhibition efficiency of 99.2 %. The adsorption of PGS-n on the surface of carbon steel was found to follow the Langmuir adsorption isotherm. The results obtained from EIS measurements agreed well with those of polarization and weight loss studies. Field emission scanning electron microscopic analysis revealed that the corrosion of the carbon steel surface is not severe, especially in the presence of PGS -18. Density functional theory was employed to calculate various quantum chemical parameters of the PGS-n. The results suggest PGS-n as an effective inhibitor for corrosion inhibition of carbon steel.