Corrosion inhibition of mild steel in corrosive solution by 2-amino-4-(4-methoxyphenyl)thiazole-5-carboxylic acid ethyl ester: Experimental and DFT investigations

This study investigates the corrosion inhibition performance of 2-amino-4-(4-methoxy-phenyl)thiazole-5-carboxylic acid ethyl ester (AAEE) on mild steel in 1 M HCl solution using weight loss and Scanning Electron Microscopy (SEM) techniques. The inhibitor’s efficiency was evaluated at various concentrations (0.0001 to 0.001 M), immersion times (1, 5, 10, 24, and 48 hours), and temperatures (303, 313, 323, and 333 K). The highest inhibition efficiency of 93% was observed at a concentration of 0.5 mM and a temperature of 303 K after 5 hours of immersion. The inhibitor’s adsorption on mild steel followed the Langmuir adsorption isotherm, and the Gibbs free energy of adsorption (ΔGads) was calculated to be –37 kJ/mol, indicating both physical and chemical adsorption mechanisms. Density Functional Theory (DFT) calculations were performed to understand the electronic properties of the inhibitor, including energy gap (Egap), highest occupied molecular orbital (EHOMO), lowest unoccupied molecular orbital (ELUMO), total hardness (η), electronegativity (χ), and fraction of transferred electrons (ΔN). The experimental results, supported by theoretical insights, show that AAEE forms a stable protective layer on the mild steel surface, effectively inhibiting corrosion. The methodological and theoretical analyses combination offers a comprehensive understanding of the inhibition mechanism, confirming AAEE as an efficient inhibitor for mild steel in hydrochloric acid solution.