Adsorption and anticorrosion studies of newly designed Schiff bases for the protection of EN3B mild steel in 3.5% NaCl solution: A combined experimental and theoretical approach

Abstract

Three newly synthesized Schiff bases; 5-(diethylamino)-2-[(n-undecylimino)methyl]phenol (NS11), 5-(diethylamino)-2-[(n-tetradecylimino)methyl]phenol (NS14) and 5-(diethylamino)-2-[(n-hexadecylimino)methyl]phenol (NS16) have been presented as efficient corrosion inhibitors for the protection of EN3B mild steel in 3.5% NaCl solution at acidic pH 1.5. The inhibitors were characterized by multitude techniques i.e., Fourier transform-infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry and single crystal X-ray diffraction (XRD) analysis. An anti-corrosive film of the inhibitors was generated on EN3B mild steel surface by dip-coating method and the presence of adsorbed molecules in a monolayer was detected via reflection absorption infrared spectroscopy (RAIRS). Electrochemical measurements revealed a strong inhibition potential of the inhibitors with the maximum inhibition efficiency of 99.8% achieved by NS16. These results were further complemented by morphological examinations and density functional theoretical (DFT) calculations revealing that the electron donating power of substituents is directly related to the inhibition potential of the inhibitors.