Substituted Schiff Bases for Mild Steel Protection: Corrosion Inhibition Performance, Antibacterial Activity, and Quantum Chemical Analysis

ABSTRACT In this study, four substituted Schiff bases (L1a, L1b, L2a, and L2b) were synthesized and evaluated as corrosion inhibitors for mild steel in 1 M HCl solution using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and quantum chemical calculations. The results revealed that all compounds exhibited remarkable inhibition efficiency, with L1b and L2b achieving up to 92%, whereas L2a showed 83%–85%. The inhibition efficiency slightly decreased with increasing temperature, indicating physisorption as the predominant mechanism. EIS data confirmed the formation of a protective adsorbed film, and the polarization parameters demonstrated that all Schiff bases behaved as mixed‐type inhibitors with cathodic predominance. Adsorption followed the Langmuir isotherm model, suggesting monolayer coverage on the metal surface. Density functional theory (DFT) analysis further supported the experimental findings, where higher E HOMO values and lower E LUMO gaps correlated with stronger adsorption tendencies. Moreover, antibacterial screening revealed inhibition zones ranging from 22 to 27 mm, with L1a (27 mm) showing the strongest activity against Escherichia coli . The theoretical parameters, combined with these antimicrobial assessments, highlight the dual functionality of the synthesized Schiff bases in both corrosion mitigation and bacterial inhibition underacidic conditions.