Corrosion inhibition of carbon steel in 1 M H2SO4 using new Azo Schiff compound: Electrochemical, gravimetric, adsorption, surface and DFT studies

New Azo Schiff compound namely 4-((4-hydroxy-3-((pyridine-2-ylimino)methyl)phenyl)diazenyl)benzonitrile (5) which is denoted as AS was synthesized and characterized using FT-IR, 13C NMR and 1H NMR spectroscopy. The new compound was evaluated as corrosion inhibitor for carbon steel in 1 M H2SO4, using electrochemical and gravimetric techniques. Tween-80 surfactant was added to enhance the solubility of AS in the acidic medium. The inhibition efficiency was found to be dependent on the concentration of AS and temperature, the highest inhibition efficiency values (91.32% and 90.30% by potentiodynamic and weight loss measurements respectively) were recorded in the presence of relatively low concentration of AS (0.08 mM) at 303 K, and it acts as anodic inhibitor. To understand the mechanism of the corrosion inhibition, the adsorption of AS onto carbon steel surface was studied, the results indicated that the adsorption process obeys Langmuir adsorption isotherm, the calculated ΔGads values were found to be around −37 kJ mol−1 which indicates that AS is adsorbed on the carbon steel surface by chemical and physical interactions. For further investigations DFT studies were employed to explain the nature of interaction between the AS molecules (neutral and protonated) and metal surface. Finally, the morphology of both corroded and inhibited surfaces were studies by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques which confirmed the high inhibition efficiency of AS at the optimum conditions, a significant reduction in the distortion and roughness of the surface were observed (the surface roughness was reduced from 17.10 nm to 2.15 nm as measured by AFM).