Experimental and DFT analysis of the concentration dependency of corrosion inhibition by a pyridine Schiff base for mild steel in HCl solution

In the present article, we studied the corrosion inhibition of the pyridine Schiff base N, N´-bis(4-dimethylaminobenzaldehyde)-2, 6-pyridinediamine (4-DMBPy) during the corrosion of mild steel AISI 1020 in a 0.1 M HCl solution. The electrochemical analysis by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) revealed that the Schiff base promotes a protective efficiency up to 81 % at 25 ppm, followed by a decrease at higher concentrations. The Schiff base – surface interactions follow a Freundlich isotherm, indicating a physical adsorption mechanism. The theoretical calculus by Fukui function and dual reactivity descriptors confirmed the physical interaction with mild steel and the low reactivity of the adsorbed species that led to corrosion protection affecting the cathodic and anodic reactions. The quantum calculations by density functional theory (DFT) indicated that protective efficiency decreases due to the tendency to interact with each other. These interactions led to the formation of molecular aggregates and a desorption process. Molecular dynamics (MD) simulations exhibited that the 4-DMBPy molecule preferred to arrange parallel to the Fe (110) surface through physical adsorption. The results were complemented by the scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and atomic force microscopy (AFM) analyses to reveal the further information about the corrosion process and the effect of the 4-DMBPy Schiff base as a corrosion inhibitor.