Corrosion inhibition and adsorption properties of pharmaceutically active compound esomeprazole on mild steel in hydrochloric acid solution

The effect of a pharmaceutically active compound esomeprazole (IUPAC name: [S]-5-methoxy-2-[(4-methoxy-3,5-dimethylpyridin-2-yl)methylsulfinyl]-3H-benzoimidazole) on the corrosion of mild steel in 0.5 M HCl solution has been investigated using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy, adsorption isotherm, and scanning electron microscope (SEM). Inhibition efficiencies of esomeprazole increased as the concentration of esomeprazole increases, but decreased with increases in temperature, immersion period, and acid concentration. The inhibition was assumed to occur via adsorption of the inhibitor molecule on the metal surface. The Langmuir adsorption isotherm was found to be the best isotherm that described the adsorption characteristics of the inhibitor. Also, the activation and thermodynamic parameters of dissolution and adsorption were calculated and discussed. Further, the SEM analysis confirms the formation of an adsorbed protective film on the mild steel surface. Based on all these results, esomeprazole is found to inhibit the corrosion of mild steel in 0.5 M HCl solution, and a plausible mechanism of corrosion inhibition is proposed.