Thermodynamic and density functional theory investigation of sulphathiazole as green corrosion inhibitor at mild steel/Hydrochloric acid interface

The corrosion inhibition efficiency of sulphathiazole (STZ) on mild steel in 0.5 M HCl at 303-333 K was studied using gravimetric and quantum chemical methods. Results show that STZ acts as inhibitor for steel corrosion even at very low concentration. The adsorption of STZ on steel surface obeyed the Temkin adsorption isotherm. The kinetic and thermodynamic parameters for mild steel corrosion and inhibition adsorption, respectively, were determined and discussed. The calculated activation and Gibbs free energy values confirm the chemical nature of the adsorption process. It is most probable that the inhibition property of STZ was due to charge sharing between the inhibitor molecules and the metal surface. Attempt were made to correlate the structural and electronic properties such as EHOMO, ELUMO, Energy gap, Mulliken charges, HOMO and LUMO orbitals using density functional theory (DFT) at the BLYP/6-31G(d) basis set with the inhibitive action of STZ.