2-Pyridinecarboxaldehyde-based Schiff base as an effective corrosion inhibitor for mild steel in HCl medium: Experimental and computational studies

A new rigid double Schiff base of N,N′-(1,3-phenylene)bis(1-(pyridin-2-yl)methanimine) (PBPM) as a novel corrosion inhibitor was successfully synthesized and characterized in this work. The corrosion inhibition performance of PBPM for mild steel in 1.0 mol L−1 HCl medium was evaluated via weight loss measurements, electrochemical methods, scanning electron microscopy, contact angle measurements and quantum chemical calculations. The inhibition efficiency of PBPM is dependent on the concentration of PBPM and the test temperature. The highest inhibition efficiencies obtained by potentiodynamic and weight loss measurements in the presence of 800 mg L−1 PBPM at 30 °C were 93.93% and 94.04%, respectively. Potentiodynamic polarization tests showed that PBPM acts as an effective mixed-type corrosion inhibitor. The adsorption of PBPM on the surfaces of mild steel was found to obey Langmuir adsorption isotherm, with both physisorption and chemisorption. Scanning electron microscopy analyses affirmed the formation of a protective film on mild steel surfaces. Contact angle measurements revealed the hydrophobic nature of the surface modified by PBPM molecules applied in acidic corrosive solution. Furthermore, the influence of the molecular configuration of PBPM on the corrosion inhibition behaviour was investigated by DFT calculations and Fukui functions, and the protonated behaviour of PBPM in acidic system was also analysed.