Comparison of two Schiff bases containing O-methyl and nitro substitutes for corrosion inhibiting of mild steel in 1 M HCl solution

Two new Schiff bases, N-(4-methoxybenzylidene)-2-[2-((E)-2-(4-methoxybenzylideneamino)phenyl)disulfanyl]benzenamine (Sb1)) and N-(4nitrobenzylidene)-2-[2-((E)-2-(4-nitrobenzylideneamino)phenyl)disulfanyl]benzenamine (Sb2)), were investigated as corrosion inhibitors for mild steel in 1 M HCl solution using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The results revealed that the Schiff bases act as effective corrosion inhibitors and the inhibition efficiency was increased by increasing inhibitors concentration. The adsorption of these compounds obeyed the Langmuir adsorption isotherm. The Sb1 molecule possessing an electron-donating O-methyl substitute showed a better inhibition performance in comparison with the Sb2 with nitro substitute, because of the positive effect of its electron–donating substitute. The molecular dynamics simulation, in agreement with experimental outcomes and quantum chemical data, showed higher inhibition efficiency for Sb1. It also showed that the Sb2 molecules oriented not beneficially on metal surface which provided a low surface coverage, and thus, a lower inhibition performance.