Abstract

Weight loss and Density Functional Theory (DFT) methods were used to study the corrosion inhibition of 5-methyl-2H-imidazol-4-carboxaldehyde and 1H-Indole-3-carboxaldehyde on mild steel in acid medium. The values of thermodynamic parameters such as free energy of adsorption (ΔGºads), adsorption equilibrium constant (Kads), adsorption entropy (ΔSºads), adsorption enthalpy (ΔHºads) and activation energy (Ea) were calculated and discussed. The adsorption process on mild steel surface showed that 4-methyl imidazol-5-carboxaldehyde and Indole-3-carboxaldehyde obey Freundlich and Temkin adsorption isotherms respectively.Density Functional Theory (DFT) calculations were carried out at B3LYP/6-31+G** level of theory in aqueous medium on the molecular structures to describe electronic parameters. The molecular parameters  associated with inhibition efficiency such as EHOMO, ELUMO, band gap energy (ELUMO- EHOMO), softness (S), electron affinity (EA) and number of electrons transfer were calculated.

Keywords: 4-methyl imidazol-5-carboxaldehyde, Indole-3-carboxaldehyde, Weight loss, DFT