A detailed study on the synergistic corrosion inhibition impact of the Quercetin molecules and trivalent europium salt on mild steel; electrochemical/surface studies, DFT modeling, and MC/MD computer simulation

Abstract

For the first time, Quercetin (3,3′,4′5,7-Pentahydroxyflavone) and Eu ions were used in 3.5 wt% NaCl solution for mild steel (MS) corrosion mitigation. Tafel outcomes demonstrated the effectiveness of Quercetin:Eu compounds in the corrosion inhibition of the steel samples via mixed-type mechanism. The EIS and Tafel results showed about 98% and 90% efficiencies during 48 h of MS exposure to 3.5 wt% NaCl solution containing 200:600 ppm Quercetin:Eu, respectively. Also, EIS measurements displayed that in the presence of 200:600 ppm Quercetin:Eu inhibitor, the total resistance reached 69,751 Ω·cm2 after 48 h of immersion. The Tafel curves indicated that the icorr diminished to 0.71 μA·cm−2 after 48 h of MS subjection to the electrolyte. The FE-SEM micrographs proved that after introducing 200:600 ppm Quercetin:Eu complex, a compact and almost smooth inhibitive layer covered the MS surface. Based on the AFM test results, the average roughness reached 96 nm after 200:600 ppm Quercetin:Eu complexes adsorption on the MS surface. Detection of 17 wt% Eu element on the protected metal surface clarified the successful Quercetin:Eu complex adsorption. The theoretical (i.e., DFT and MC/MD) results further ensured the Quercetin:Eu complexes adsorption on the metallic surface.