Adsorption behavior of some green corrosion inhibitors on Fe (110) surface: The critical role of d- interactions in binding strength

Wise selection and application of a green corrosion inhibitor requires a careful study of its adsorption mechanism at the metal surface. Herein, density functional theory calculations were carried out to investigate the adsorption behavior of six green corrosion inhibitor molecules on Fe(110) surface, i.e. serotonin, tyrosine, coumaric acid, histamine, vanillic acid, and lysine. Different adsorption configurations through the functional groups and aromatic rings were carefully examined for each molecule. The projected density of states, Bader charge values, charge density difference, and the ELF analysis were calculated For the energetically preferred adsorption configurations. Ab-initio molecular dynamics simulations were also performed to obtain the equilibrium structure for the adsorption of the molecules on the Fe(110) at 300 K in an acidic solution. The analyses reveal the critical role of pi-d interactions, in the form of pi-back donation, in determining the preferred adsorption configuration of the inhibitor molecules on the Fe(110). The adsorption energies were found to be in the range of -154.376 kJ/mol for lysine to -371.275 kJ/mol for coumaric acid. The adsorption energy data reveals that the molecules with larger pi-networks have greater adsorption energies at the Fe (110) surface, and thus better corrosion protection efficiency.