A detailed experimental performance of 4-quinolone derivatives as corrosion inhibitors for mild steel in acid media combined with first-principles DFT simulations of bond breaking upon adsorption

Abstract

Four 4-oxo-1,4-dihydroquinoline-3-carboxylate derivatives were synthesized through the Gould-Jacobs method and evaluated as corrosion inhibitors for 1020 mild steel in 1 mol/L hydrochloric acid. Gravimetric experiments showed that those organic molecules present 84–94 % anticorrosive efficiency at 2.00 mmol/L (298 K). At higher temperatures (318 and 338 K), those values go up to 97.3 % for the methoxy-substituted compound. Electrochemical measurements depicted that the charge-transfer mechanism controlled the corrosive and inhibitive processes and that the presence of the four organic substances in the electrolyte enhanced the polarization resistance and significantly diminished the corrosion density current, acting by adsorption on the metal surface. Polarization curves confirmed that they all are mixed-type corrosion inhibitors. Atomic Force Microscopy illustrated the topography of the metallic surface and suggested to the formation of a protective layer. Atomistic simulations by first-principles Density Functional Theory revealed the formation of covalent bonds between quinolone molecules and the iron surface, with MODC and AODC having the stronger negative interaction energy values compared to NODC and CODC compounds. Electronic analysis of the adsorption geometries of molecules at Fe(110) indicated that chemical coordination is a result of strong charge transfer and charge rearrangement upon adsorption.