Fabrication and characterization of zinc acetylacetonate/Urtica Dioica leaves extract complex as an effective organic/inorganic hybrid corrosion inhibitive pigment for mild steel protection in chloride solution

Zinc acetylacetonate is known as an inorganic anti-corrosive pigment with moderate corrosion inhibition performance in saline solutions due to slight solubility. In this study the zinc acetylacetonate pigment was modified by organic compounds existing in the extract of a green corrosion inhibitor. A series of hybrid organic/inorganic pigments based on zinc acetylacetonate and organic compounds of Urtica Dioica leaves extract (ZnAA-U.D) were synthesized in aqueous solutions. The effect of pH on the morphology and chemistry of the synthesized pigments were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), UV-Vis analysis, thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) techniques. Then, the inhibition effect of pigments in corrosion control of carbon steel in 3.5 wt.% NaCl solutions with pigments extracts were evaluated by visual observations, polarization test and SEM/-EDS analyses. Results revealed that the hybrid zinc acetylacetonate-Urtica Dioica pigment was successfully synthesized through chelation between the organic molecules of U.D extract, such as histamine, serotonin and caffeic acid, and inorganic part of zinc acetylacetonate (Zn2+). The lone pair electrons of heteroatoms existed in the structure of organic compounds of U.D extract could be shared with empty orbital of Zn2+ cations. It was also found that the pH of synthesis media remarkably influenced on the morphology, chemistry and corrosion inhibition properties of the pigment. According to the results the pigment synthesized at pH = 4 showed the highest solubility and corrosion inhibition properties. The hybrid pigment showed mixed corrosion inhibition properties and affected both anodic and cathodic reactions.