Newly synthesized quercetin derivatives as corrosion inhibitors for mild steel in 1 M HCl: combined experimental and theoretical investigation.

To evaluate the corrosion inhibition efficacy of the derivatives of naturally available organics, mono and di-4-((2-hydroxyethyl)piperazin-1-yl)methyl derivatives of quercetin, a flavonoid, have been synthesized. Their potential as anti-corrosive agents is assessed for mild steel in 1 M HCl employing the weight-loss technique as well as electrochemical methods. Comparing the rate of corrosion in uninhibited and inhibited solutions as a function of temperature, the thermodynamic parameters of adsorption of these derivatives on mild steel surfaces and the kinetic parameters of the corrosion process are evaluated. These parameters together with information derived from electrochemical methods are further used to ascertain the mechanism of corrosion and mode of adsorption of inhibitors with intricate detail. Density functional theory (DFT) calculations were employed to explain the relative corrosion inhibition propensity between the studied mono and di quercetin derivatives. Molecular dynamics (MD) simulations were carried out to obtain the interaction energy between the inhibitor molecules and the metal surface. Results show that both derivatives, acting as mixed-type inhibitors, exert profound anti-corrosive influence (around 95% inhibition efficiency at 1 mM concentration at 313 K). Theoretical studies suggest that the trihydroxy chromone ring and dihydroxy phenyl ring of quercetin maintain a planar orientation with respect to each other and are adsorbed on the metal surface (mostly chemisorption).