Anti-corrosion behaviour of 4(p-tolyldiazenyl)-2-((E)-(p-tolylimino)methyl)phenol on mild steel in 1M H2SO4: Experimental and theoretical studies

The corrosion of mild steel in 1 M H2SO4 solution was significantly inhibited by a new azo Schiff base, 4(p-tolyldiazenyl)-2-((E)-(p-tolylimino)methyl)phenol (ASBm) using both the weight loss and hydrogen evolution methods. The inhibition efficiency increased with increase in ASBm concentration in the temperature range of 30 °C to 50 °C, but decreased at 60 °C. Based on experimental results, chemisorption has been proposed for the inhibition effect of ASBm on mild steel surface at 30 °C – 50 °C while physisorption is proposed to occur at 60 °C. Thermodynamic parameters reveal that the adsorption process was both endothermic and spontaneous. The adsorption of ASBm obeyed Freundlich adsorption isotherm. The protonated species ASBm-H+had proton on N23 atom. Quantum chemical parameters of ASBm and ASBm-H+ were calculated and discussed. Based on Fukui indices, electrophilic centres on ASBm and ASBm-H+were O16 (0.069) and N9 (0.062), respectively. Conversely, nucleophilic sites on ASBm and ASBm-H+, respectively, are N9 (0.131) and C24 (0.159). Molecular dynamics simulation results reveal that ASBm had a higher binding energy on Fe(110) surface at lower temperatures (30° – 40 °C) while the binding energy of ASBm-H+ was higher at higher temperature (50° – 60 °C). The contributions by ASBm fragments to the binding energy on Fe(110) surface have been discussed.