Abstract
The corrosion efficiency on mild steel in 1 M HCl of three imines obtained from the condensation of tribulin with aniline derivatives, namely 3-(phenylimino) indolin-2-one (TANH), 3-(4hydroxyphenylimino) indolin-2-one (TANO) and 3-(4-chlorophenylimino) indolin-2-one (TANC) are investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique. TANO exhibited the highest corrosion inhibition efficiency followed by TANC and TANH at optimum concentration of 1.0 mM. Langmuir's adsorption isotherm and X-ray photoelectron spectroscopy (XPS) showed that the adsorption mechanism is a prominent chemisorption phenomenon than physisorption. Based on XPS analysis, the highest inhibition efficiency of TANO was contributed by C-O and C-N molecules presented in the compound. The active binding sites of TANH, TANO, and TANC on the mild steel surface were determined by calculating Mulliken atomic charges and analysis of the electrostatic potential surface (ESP) at the B3LYP/6-311+G(d,p) level of theory. The correlation of imines inhibition efficiencies with its electronic parameters was investigated and the result showed that the corrosion inhibition efficiency of imines was governed mainly by the frontier orbital energy gap, the chemical softness, and chemical hardness properties. (C) 2021 Elsevier B.V. All rights reserved.