Corrosion inhibitory potential of selected flavonoid derivatives: Electrochemical, molecular⋅⋅⋅Zn surface interactions and quantum chemical approaches

Abstract

Zinc metal corrosion inhibitor potential of some flavonoid derivatives, namely, naringenin (NRNG), morin hydrate (MNHD), and 6-hydroxyflavone (6-HFN), was investigated by measuring their inhibitory activities, determining their thermodynamic and kinetic adsorption mechanistic properties as well as comparing their molecular⋅⋅⋅Zn metal surface interaction strengths. The inhibition efficiencies were evaluated in 1.5 M hydrochloric acid (HCl) environment and different concentrations of the inhibitors (from 2.0 × 10−4 – 1.8 × 10−3 M) using gravimetric and various electrochemical methods at 30–60 °C. The molecular···metal surface interactions were determined using the density functional theory method by using the GGA/RPBE/DNP approach. Electrochemical studies show that 6-HFN and NRNG are the most and least effective corrosion inhibitors, with 77.54 and 70.46 maximum percentage inhibition efficiency, respectively. Atomic Absorption Spectroscopy technique was used to compare the concentration of the zinc ions that remained in the solution after gravimetric analysis in the absence and presence of the inhibitors at 30 °C; it was found that the inhibited solution contained less concentrations of zinc ions as compared to the uninhibited solution. Surface morphology techniques (e.g., 3D microscope) suggest that a localised type of corrosion took place on the metals, and the corrosion damage was minimal in the presence of the inhibitors. FT-IR showed a strong adsorption of the functional groups found in the inhibitor compounds, with CC functional group being strongly retained by all three inhibitors. The flavonoid inhibitor compounds were found to absorb chemically at low temperatures and physically at high temperatures. Langmuir adsorption isotherm was obeyed. The trend for molecular···metal surface interaction strengths follows the trend obtained from experimental findings on inhibition efficiency. Overall, the results suggest that all the molecules investigated are good corrosion inhibitors with a preference for those compounds in which there exists extended electron delocalization through the aromatic rings and in which there are minimal electron-withdrawing groups on the aromatic rings.