Adsorption and corrosion inhibition performance of two planar rigid pyridinecarboxaldehyde-based double Schiff bases for mild steel in HCl solution: Experimental and computational investigations

Abstract

Two planar rigid double Schiff bases, (1E,1′E)-N,N’-(1,4-phenylene)bis(1-(pyridin-2- yl)methanimine) (PBPM2) and (1E,1′E)-N,N’-(1,4-phenylene)bis(1-(pyridin-3-yl)methan- imine) (PBPM3), were investigated as corrosion inhibitors for mild steel in HCl solution. The experimental resultspresented that the inhibition efficiencies in 1.0 mol L−1 HCl slightly negatively correlate with temperature, while positively correlate with inhibitor concentration and soaking time, respectively. The maximum inhibition rates of PBPM2 and PBPM3 obtained by weight loss measurement at 30 °C reach up to 91.88 % and 92.18 %, respectively. The fitting analysis indicated that PBPM2 and PBPM3 conform to Langmuir adsorption isotherm, and physicochemical adsorption mechanism occurred onthe surface of mild steel. Potentiodynamic polarization measurement showed that PBPM2 and PBPM3 are mixed-type inhibitors with anodic characteristics. The contact angle and energy dispersive spectroscopy data indicated that the hydrophobicity for mild steel surface is modified by PBPM2 and PBPM3 applied in HCl solution, which causes the formation of the compact protective film on the metallic surface. The structure–activity relationship and protonation behavior were investigated by density functional theory and Fukui indexes. The computational results conformed PBPM3 has higher inhibition performance the PBPM2. Furthermore, molecular dynamics simulation revealed real adsorption configuration of PBPM2 and PBPM3 molecules on mild steel surface and certified that PBPM3 has stronger adsorption capacity and better inhibition performance than PBPM2, which agree with the experimental results.