Nitro substituent effect on the electronic behavior and inhibitory performance of two quinoxaline derivatives in relation to the corrosion of mild steel in 1M HCl

Abstract

Two quinoxaline derivatives, 2-(2,3-dimethoxyphenyl)-1,4-dihydroquinoxaline (HHQ) and 2-(2,3-dimethoxyphenyl)-6-nitro-1,4-dihydroquinoxaline (NHQ) were selected as inhibitors for mild steel corrosion in 1 M HCl using experimental techniques and theoretical approaches (DFT and the simulations of Monte Carlo (MC) and molecular dynamics (MD)). The results obtained by electrochemical polarization measurements show that these two molecules inhibit the corrosion rate of mild steel in the corrosive media. The HHQ and NHQ inhibitors showed a mixed, predominantly anodic character, decreasing the rate of cathodic and anodic corrosion reactions. As reported in electrochemical impedance spectroscopy (EIS) tests, the adsorbed inhibitor molecules built up a pseudo-capacitive response of the interface. The inhibition efficiency is reduced by the effect of the electron attractor group NO2 in the NHQ inhibitor. Adsorption is in accordance with the Langmuir isothermal model. Scanning electron microscopy (SEM) identified that the formation of a protective layer of inhibitor on the surface of mild steel. Analyses inhibited Electrolyte by UV–visible spectroscopy provide concrete evidence on the complexation of iron cation with both quinoxaline molecules in 1 M HCl. The results obtained by the theoretical approaches through the different methods via DFT, MC and MD simulations show a satisfactory concordance with the results of the experimental part.