Chemically modified expired Dapsone drug as environmentally benign corrosion inhibitor for mild steel in sulphuric acid useful for industrial pickling process

Expired drug Dapsone was chemically modified by reacting with benzaldehyde; salicylaldehyde and the resulting product (Schiff bases) were investigated as corrosion inhibitor for mild steel in sulphuric acid solution. Schiff base 1 (Dapsone-benzaldehyde) and Schiff base 2 (Dapsone-salicylaldehyde) gave maximum inhibition efficiency of 95.67% and 94.23% at a concentration of 0.219 mM respectively. Addition of very small amount of KI (0.602 mM) further increased their efficiency up to 99.03% and 97.98% respectively. The observed results indicate increase in corrosion inhibition efficiency with raising the concentration of the inhibitors. The corrosion inhibition behavior was afforded by the adsorption of Schiff bases onto the mild steel following the Langmuir adsorption isotherm model via mixed physical and chemical adsorption. The synergistic influence of KI at various concentrations of the inhibitors was determined by the calculation of the synergism parameters which suggested a co-operative mechanism. DFT calculations were carried out to elucidate the mechanism of corrosion inhibition process. It was found that the protonated inhibitors are strongly adsorbed on the steel surface than the neutral inhibitors. The results suggest that the developed formulations can be used as corrosion inhibitors during industrial pickling process.