Amide Substituted Zinc Centered Macrocyclic Phthalocyanines for Corrosion Inhibition of Mild Steel in Hydrochloric Acid Medium

The present work describes the corrosion inhibition of mild steel—one of the metals widely utilized in industrial processes, in 0.25 M hydrochloric acid, using an amide substituted macrocyclic zinc phthalocyanine (TAZnPc). The corrosion inhibition efficiency was studied via potentiodynamic polarization technique and electrochemical impedance spectroscopy in a temperature range of 303 to 323 K, with the concentration of the inhibitor of 0.625–2.5 mM. The electrochemical study reveals that TAZnPc acts as mixed inhibitor, and the inhibition efficiency was found to increase with increasing the inhibitor concentration and decreasing temperature. The studied inhibitor showed the utmost inhibition efficiency of 86.48% at its optimum concentration of 5 mM. The excellent inhibitory performance is attributed to both the physisorption and chemisorption processes of adsorption of TAZnPc on the surface of mild steel. It was found that it followed the Langmuir adsorption isotherm. The results obtained by both potentiodynamic polarization technique and electrochemical impedance spectroscopy methods were in good agreement with each other. The surface morphology of the mild steel surface was studied by taking scanning electron microscope images, energy-dispersive X-ray spectroscopy and atomic force spectroscopy images without and with TAZnPc in 0.25 M HCl.