Competitive corrosion inhibition performance of alkyl/acyl substituted 2-(2-hydroxybenzylideneamino)phenol protecting mild steel used in adverse acidic medium: A dual approach analysis using FMOs/molecular dynamics simulation corroborated experimental findings

Abstract Competitive corrosion inhibition performances of alkyl and acyl substituted 2-(2-hydroxybenzylideneamino)phenol derivatives as Schiff bases were analysed for protection of mild steels in corrosive 1 molL-1 HCl used in industrial acid-cleansing purposes employing potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The anti-corrosion efficiency of synthesized three different inhibitor molecules, 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 analysed on mild steel sample in the presence of 1 M HCl medium. PDP data reveals that all the three synthesized inhibitor molecules behave as mixed type inhibitor at higher concentration (5 mmol L-1). EIS data reveal that on addition of inhibitor molecules the polarization resistance value increases from 4.76 Ωcm2 to 69.60 Ωcm2, 87.28 Ωcm2 and 115.70 Ωcm2 respectively for Inh-1, Inh-2 and Inh-3 i.e., inhibition efficiency value increases, at 5 mmolL-1 concentration of Inh-1, Inh-2 and Inh-3 reaching a maximum efficiency of 93%, 94% and 95%.. The three synthesized inhibitors are liable towards Langmuir adsorption isotherm by spontaneous adsorption of inhibitors on mild steel surface. FESEM, EDX, AFM and contact angle measurement revealed the adsorption and corrosion inhibiting capability of synthesized inhibitors. Acyl substituent enhances corrosion inhibition performance than methyl substituent on 2-(2-hydroxybenzylideneamino)phenol unit. The electronic properties of the synthesized inhibitor molecules were explored using frontiers molecular orbitals (FMOs) analysis. In order to explore the interactions of inhibitors with the metal surface mimicking the real corrosion inhibition phenomenon, the molecular dynamics and Monte Carlo simulation approach were employed. Furthermore, the electron density distribution and radial distribution function have been used to explain the film formation phenomenon in details.