Adsorption of redox-active Schiff bases and corrosion inhibiting property for mild steel in 1 molL−1 H2SO4: Experimental analysis supported by ab initio DFT, DFTB and molecular dynamics simulation approach

Abstract An alkyl and acyl substituted redox-active Schiff bases, namely, 2-(2-hydroxybenzylideneamino)phenol (Inh-1), 2-((2-hydroxyphenylimino)methyl)-4-methylphenol (Inh-2) and 2-((2-hydroxyphenylimino)methyl)4-methoxyphenol (Inh-3) were synthesized and characterised. Afterwards, its anticorrosion aspect for mild steels dipped into 1 molL−1 H2SO4 solution was explored by potentiodynamic polarization as well as electrochemical impedance spectroscopy. These molecules act as excellent corrosion inhibitors to protect mild steels immersed in 1 molL−1 H2SO4 solution. Surface studies were performed by employing FESEM and AFM; while the elemental characterization of mild steels that were exposed in corrosive medium with and without containing the synthesized Schiff base molecules was performed using EDX study. All these studies established the formation of corrosion protecting layer developed over metal surfaces. Adsorption competency of the synthesized inhibitors were studied and explained in details. The spontaneity and nature of adsorption of the synthesized inhibitors were explained based on free energy determined from experimental findings. Additionally, the experimentally obtained corrosion inhibition property as well as adsorption capability were furthermore insightfully explained and correlated with density functional theory and Fukui indices analysis. Also, density functional based tight binding calculation was carried out for visualizing interactions of inhibitors occurring with metal surface atoms favouring its adsorption. Finally, molecular dynamics simulation was employed to envisage the interactions of synthesized inhibitors with metal surface atoms along with corrosive species as it happens in real corrosive environment. Furthermore, the analysis of radial distribution function have been used to elucidate experimentally predicted adsorption behaviour of studied molecules.