Corrosion inhibition of two imidazole–pyridine derivatives on Q235 steel in HCl: Experimental and theoretical studies

This study aims to clarify the influence mechanism of pyridine ring substitution position on the performance of imidazolinyl pyridine-based preservatives, linking molecular structure with anti-corrosion performance. Two preservatives, MB2 and MB4, were designed. Their anti-corrosion performance and mechanism in 1 mol/L HCl were investigated via weight loss method, electrochemical tests, surface analysis: scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and theoretical calculations. Results show that at room temperature with 2.00 mmol/L dosage, MB4 achieves 99.08% anti-corrosion efficiency, surpassing MB2's 98.38%. At 313–333 K, MB4's efficiencies (93.96%–86.98%) far exceed MB2's (66.43%–51.82%), proving better temperature stability. SEM/EDS/XPS reveal both form protective films, but MB4's stronger adsorption enhances performance. Quantum chemical calculations show MB4's pyridine-4-aldehyde optimises nitrogen (N) atom electron cloud density for stronger metal interaction. Molecular dynamics (MD) simulations, mean square displacement (MSD) and free volume fraction (FFV) calculations indicate that imidazole rings adsorb on iron first, with carbon chains as hydrophobic barriers. MB4 has lower adsorption energy (−234.223 vs. −209.702 kcal·mol −1 ) and smaller free volume (13.61% vs. 14.24%), inhibiting ion diffusion. The study innovatively demonstrates para-substituted structures enhance efficiency via electronic effects and film compactness, guiding the development of temperature-resistant pickling preservatives.