Electronic structure-performance relationship in pyridine-based Schiff bases: a dual experimental-DFT study on corrosion inhibition.

Two pyridine-based Schiff bases, N-(4-bromobenzylidene)pyridin-3-amine (BBPA) and N-[4-(dimethylamino)benzylidene]pyridin-3-amine (DBPA), were synthesized and evaluated as corrosion inhibitors for carbon steel in 1.0 M HCl. Their inhibition performance was investigated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM). Both compounds exhibited excellent corrosion protection, achieving inhibition efficiencies above 94% at 10 mM concentration. Adsorption studies revealed that the inhibitors obey the Langmuir isotherm and adsorb on the steel surface through a mixed physisorption-chemisorption mechanism. Density functional theory (DFT), Monte Carlo, molecular dynamics, and DFTB calculations were employed to elucidate the adsorption behavior and electronic properties of the inhibitors. Theoretical results demonstrated that DBPA possesses superior electron-donating ability, stronger adsorption affinity, and enhanced interaction with the Fe (110) surface compared with BBPA, consistent with the experimental findings. SEM analysis confirmed the formation of a protective adsorbed film on the steel surface. The combined experimental and computational results identify DBPA as the more effective inhibitor and highlight the crucial role of electronic substituent effects in governing corrosion inhibition performance.