Developing a novel amino acid derivative as high-efficient green corrosion inhibitor for mild steel in acidic solution: Experiments and first-principles calculations

Amino acids, which can be derived from many crops, such as soybeans, corns, millets, have the potential as green corrosion inhibitors. However, most amino acids exhibit unsatisfactory corrosion inhibition effect on mild steel. In this work, a novel amino acid derivative, (5-(1 H-Indol-3-ylmethyl)− 3-phenyl-2-thioxo-4-imidazolidinone (IPTI), was synthesized with methyl 2-amino-3-(1 H-indol-3-yl)propanoate (MAIP) as the precursor, and used as the high efficient green corrosion inhibitor for mild steel in HCl medium. Its inhibitive effect was assessed by electrochemical tests and surface analyses. It is confirmed that the inhibitive effect of IPTI is remarkably improved with an inhibition efficiency of 99.34% at 0.5 mM, which is significantly higher than those already reported amino acid derivative inhibitors in the literature. It is also found that IPTI exhibits a good inhibition stability, with the IE% more than 99% after 72 h exposure. After modification by phenyl isothiocyanate with introducing benzene ring and heteroatoms, IPTI has more adsorption sites and better hydrophobicity, which is more effectively block the corrosive substances to steel surface. In addition, theoretical calculations were performed to further investigate the adsorption mechanism of IPTI on MS surface. First principles calculations reveal that IPTI molecule could adsorb on the steel surface through the induced S heteroatom and benzene ring with Fe–S, and Fe–C bonds. Furthermore, compared with MAIP, the S atom of IPTI could form more bonds with iron atoms, which facilitates a stronger interfacial adsorption of IPTI with a more negative adsorption energy.