Synthesis and assessment of ionic liquid derived from benzalkonium chloride as corrosion inhibitor for carbon steel

Corrosion poses a significant challenge in the materials industry, especially when carbon steel (C-steel) is subjected to highly corrosive environments such as 1 M HCl. In this study, four ionic liquids (ILs)-1-benzyl-1-methylpiperidin-1-ium chloride (ILI), 1-benzyl-2-methylpyridin-1-ium chloride (ILII), 1-benzyl-3-methylpyridin-1-ium chloride (ILIII), and 1-benzyl-4-methylpyridin-1-ium chloride (ILIV) were synthesized and characterized using spectroscopic techniques, including FT-IR and 1HNMR. Electrochemical analyses such as potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) demonstrated excellent protective performance for C-steel in 1 M HCl, reaching a maximum inhibition of 97% at an optimum concentration of 100 ppm. Insights from polarization and impedance analyses confirmed that these compounds act as mixed-type inhibitors by adhering to the steel surface. The adsorption behavior followed the Langmuir isotherm model, with ΔG0 ads values suggesting a combination of physisorption and chemisorption. Quantum chemical assessments validated the experimental results, indicating that ILII–ILIV, due to their two aromatic rings, exhibited superior surface interaction and inhibition efficiency because of their reduced HOMO-LUMO energy gaps. These findings affirm the strong inhibitory potential of the tested ILs in acidic media.