Synthesis and Characterization of a New N4S2 Schiff base and Investigation of its Adsorption and Corrosion Inhibition Effect by Experimental and Theoretical Methods

In this study, a new N4S2 Schiff base compound based on [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl] amine and pyridine-2-carboxaldehyde was synthesized for the first time and its corrosion inhibition performance against mild steel corrosion in 1 M HCl was studied by several experimental and theoretical techniques. Potentiodynamic polarization examinations indicated that the synthesized N4S2 Schiff base performs as mixed-type inhibitor and its corrosion inhibition performance promoted at higher concentrations. Electrochemical Impedance Spectroscopy (EIS) examinations demonstrated that the polarization resistance of the mild steel increases by adding the synthesized compound while the capacitance values of the electrical double layer decreases indicating inhibitor adsorption at metal/electrolyte interface. The EIS experiments also revealed that the corrosion inhibition performance does not alter by increasing the temperature of the corrosive media from 30°C to 35°C but then slowly reduces with the subsequent increment in temperature since thermal agitation of the adsorbed inhibitor species accelerates. The inhibitor’s adsorption process is found to obey the Langmuir isotherm may be predominantly via chemisorption. However, possibility of the inhibitor physisorption was confirmed by calculation of potential of zero charge (EPZC) for the electrode surface in the blank and inhibitor-containing test electrolytes. Density Functional Theory (DFT) was also utilized to optimize the structure of the neutral N4S2 ligand and its protonated form along with their possible complex compounds with ferrous ions. Also, the relationship between structure of the N4S2 Schiff base and the corrosion inhibition performance was discussed by computing some quantum chemical parameters. Scanning Electron Microscopy (SEM) images approved the corrosion inhibition capacity of the Schiff base compound.