Synthesis, characterization, and studies of the interfacial and anticorrosion properties of a ternary cationic ionic liquid on carbon steel in a molar concentration of hydrochloric acid: Experimental and computational insights

Corrosion in acidic environments is a serious industrial challenge that must be addressed and cationic ionic liquid play a critical role in tackling the wet corrosion menace for the metal industry. For this purpose, a novel ternary cationic ionic liquid namely N¹-(3-(11-(octadecyldimethylammonio)undecanamido)propyl)-N¹,N¹,N²,N²,N²-pentamethylethane-1,2-diaminium tribromide (Mono-18–11-di-N) is synthesized and elucidated for anticorrosion activity on St37–2 grade steel in a molar concentration of hydrochloric acid medium. The structural elucidation of Mono-18–11-di-N was achieved by FT-IR, ¹H NMR, and ¹³C NMR methods while the electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), dynamic-EIS, density functional theory (DFT) calculations, and Monte Carlo (MC) simulation techniques were adopted in the anticorrosion evaluation. The Critical Micelle Concentration (CMC) of Mono-18–11-di-N is 0.000491 M and at CMC, the surface tension is 21.86 dyn cm⁻¹ inferring good surface activity properties. Mono-18–11-di-N is effective against the wet corrosion of St37–2 steel. It can, at 20 mg/L decrease the corrosion rate of the metal from 0.57 mm/y to 0.11 mm/y and enhance the polarization resistance from 363 Ω cm² to 1908 Ω cm². A corrosion rate of 0.03 mm/y and an inhibition efficiency of 93% is achievable after 24 h of immersion at 25 °C. Additionally, surface morphological examination using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), optical profilometer (OP), and atomic force microscope (AFM) methods prove the adsorption of Mono-18–11-di-N molecules on the substrate surface. Moreover, DFT and MC simulations revealed that Mono-18–11-di-N relies on lone pairs of electrons in bromide anion, oxygen, and nitrogen atoms to adsorb parallel to the St37–2 surface and protect it against corrosion.