Gravimetric, Electrochemical, Surface Morphology, DFT, and Monte Carlo Simulation Studies on Three N-Substituted 2-Aminopyridine Derivatives as Corrosion Inhibitors of Mild Steel in Acidic Medium

Abstract

Three N-substituted 2-aminopyridine derivatives, namely, 6-(2,4-dihydroxyphenyl)-4-phenyl-2-(phenylamino)nicotinonitrile (DPPN), 6-(2,4-dihydroxyphenyl)-2-((4-hydroxyphenyl)amino)-4-phenylnicotinonitrile (DHPN), and 6-(2,4-dihydroxyphenyl)-2-((4-methoxyphenyl)amino)-4-phenylnicotinonitrile (DMPN) were investigated for their inhibitive effects on mild steel corrosion in 1 M HCl solution using electrochemical, surface, chemical, and theoretical studies. Results showed that the protection capabilities of inhibitors used in the study increase with increase in their concentrations and attained the maximum numerical values of 95.81, 96.24, and 96.63% for DPPN, DHPN, and DMPN, respectively, at the 20.20 × 10–5 mol L–1 concentration. The results of the electrochemical impedance spectroscopy studies revealed that DPPN, DHPN, and DMPN molecules retard corrosion by adsorbing at the metal/electrolyte interface. Adsorption of the DPPN, DHPN, and DMPN molecules on the surface was found to obey the Langmuir adsorption i...