Adsorption and Quantum Chemical Studies on Cloxacillin and Halides for the Corrosion of Mild Steel in Acidic Medium

The corrosion inhibition of mild steel in H2SO4 by Cloxacillin (CLX) and its synergistic combination with halides (KI, KBr and KCl) was investigated using gravimetric, thermometric, gasometric and quantum chemical methods. The results indicated that CLX is a good adsorption inhibitor for the corrosion of mild steel in H2SO4. Inhibition efficiency of CLX on mild steel increased with increase in concentration but decreased with rise in temperature ranging from 90.40 to 93.98%, 80.85 to 86.43%, 78.41 to 84.07% and 58.61 to 77.57% at 303, 313, 323 and 333 K respectively. The combination of CLX with the halides (KCl, KBr and KI) enhanced the inhibitive and adsorption capability of CLX to a greater extent indicating synergism. The adsorption was spontaneous and the experimental data were also found to fit into the Langmuir (mean R-2 = 0.9978) adsorption isotherm. Physical adsorption mechanism has been proposed from the thermodynamic data obtained in the study and the activation energies of the corrosion inhibition by CLX were higher than the value obtained for the blank which signifies physical adsorption. Some quantum chemical parameters and the Mulliken charge densities on the optimized structure of CLX were calculated using the B3LYP/6-31G (d,p) basis set method to provide further insight into the mechanism of the corrosion inhibition process. The local reactivity was analyzed through the Fukui function and condensed softness indices in order to know the possible sites of nucleophillic and electrophillic attacks.