Density Functional Theory (DFT) Studies on Sulfa Dimedine Azo Derivatives as Green Inhibitors for C-Steel in 0.5 M H3PO4 Solutions

The density function theory (DFT) is used to study the structural properties of two sulfa dimedine azo derivatives in aqueous phase in an attempt to understand their inhibition mechanism. The protection efficiencies of these compounds showed a certain relationship to highest occupied molecular orbital (HOMO) energy, Mulliken atomic charges and Fukui indices. Quantum chemical method was also employed to explore the relationship between the inhibitor molecular properties and its protection efficiency. The protection influence of two sulfa dimedine azo derivatives against C-steel corrosion was studied in 0.5 M H3PO4 solutions at 25oC. Measurements were conducted under various experimental conditions using Weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. These studies have shown that sulfa dimedine azo derivatives are very good ‘‘green”, inhibitors. Corrosion rates obtained from both Tafel extrapolation and EIS methods are comparable with those recorded using Weight loss method, confirming validation of corrosion rates measured by the latter. The inhibitive action of these sulfa dimedine azo derivatives against C-steel corrosion in 0.5 M H3PO4 solutions was discussed in terms of blocking the electrode surface by adsorption of the molecules through the active centers contained in their structures following Temkin adsorption isotherm.