Marine Octocoral Phyllogorgia dilatata: Identification of Sesquiterpenes and Activity as a Natural and Renewable Corrosion Inhibitor

In the context of highly efficient, non-toxic and natural organic corrosion inhibitors, Phyllogorgia dilatata was studied as an anticorrosive for mild steel in acid medium. The marine octocoral crude extract (PDCE) was characterized and analyzed by LC-HRMS, revealing the presence of 16 different organic molecules. The corrosion inhibition was evaluated via weight loss study and electrochemical techniques. The obtained polarization curves showed that PDCE acts as a mixed-type inhibitor and gravimetric, Electrochemical Impedance Spectroscopy and Linear Polarization Resistance analyses reached an average maximum anticorrosive efficiency of 93.4% at 1 g L-1. The data crossing between gravimetric and electrochemical measurements indicated that the protection mechanism is due to adsorption, blocking electro-active sites. The adsorption data followed the Freundlich theory and SEM/EDX images confirmed the formation of a protective multilayer film.