Electrochemical and theoretical insights on the adsorption and corrosion inhibition of novel pyridinium-derived ionic liquids for mild steel in 1 M HCl

The corrosion protection performance of new synthesized ionic liquids derived from pyridine namely: 1-ethyl-4-(2-(4-fluorobenzylidene)hydrazinecarbonyl)pyridin-1-ium iodide (IPyrC₂H₅), and 1-butyl-4-(2-(4-fluorobenzylidene)hydrazinecarbonyl)pyridin-1-ium iodide (IPyr-C₄H₉) was investigated against mild steel corrosion in 1 M HCl by using electrochemical methods. PDP experiments revealed that the IPyr-C₂H₅ and IPyr-C₄H₉ behaved as anodic type inhibitors. Electrochemical impedance spectroscopy (EIS) measurements indicated that both compounds could inhibit the corrosion of mild steel with an inhibition efficiency of 88.8% for IPyr-C₂H₅ and 92.3% for IPyr-C₄H₉ at optimum concentration after 30 min of immersion. These compounds can be adsorbed on the mild steel surface through physical and chemical bonds, according to Langmuir isotherm model. DFT method was employed to correlate the molecular structure of pyridinium-derived ionic liquids and their experimental inhibition efficiencies. Molecular dynamics (MD) studies revealed higher interaction energy for inhibitor IPyr-C₄H₉ compared to IPyr-C₂H₅. The radial distribution function (RDF) indicated chemical adsorption of the inhibitors on the metallic surface.