Studying the Urtica dioica leaves extract inhibition effect on the mild steel corrosion in 1 M HCl solution: Complementary experimental, ab initio quantum mechanics, Monte Carlo and molecular dynamics studies

Finding a cheap and green source of corrosion inhibitor has become an attractive area of research in recent years. Although there are a large number of reports on the application of plant extracts as a powerful source of corrosion inhibitors for metals in acidic media but most of them are not readily available and cost-effective. Thus, it would not be economically acceptable to use them in industrial applications. The second is that ethanol should be frequently used during the inhibitors extraction process, making the process environmentally unacceptable. In addition, the organic molecules present in the extracts of most of the plants only include oxygen containing groups that cannot be easily protonated in acidic media. In this study, Urtica dioica leaves have been introduced as a unique source of invaluable and unique chemical compounds like histamine and serotonin, which are known as important biocompatible and biologically active molecules. Urtica dioica is a wildflower type of plant that growths in large scale, therefore, it is a low cost source of green inhibitors. The extract of Urtica dioica includes nitrogen containing groups that can be easily protonated in the acidic media and shows high inhibition action. The effectiveness of the Urtica dioica leaves toward mild steel corrosion inhibition in 1 M HCl solution was studied by electrochemical impedance spectroscopy (EIS), polarization test, scanning electron microscope (SEM), atomic force microscope (AFM) and computational approaches. Results revealed that the extract of Urtica dioica showed mixed inhibition effect and its adsorption on the mild steel surface obeyed a Langmuir adsorption isotherm. In addition, a high corrosion inhibition efficiency of 92% was obtained for this inhibitor after 2 h immersion. This inhibitor also yielded high inhibition power even after a long immersion time (24 h), indicating the higher effectiveness of Urtica dioica compared with those reported in literature. It was observed that the corrosion rate of steel in 1 M HCl solution remarkably decreased in the presence of Urtica dioica extract. The computational results elucidated from the Monte Carlo and molecular dynamics simulations evidenced the adsorption of green inhibitors on the steel substrate. Furthermore, the density functional theory calculations suggested the inhibitors adsorption via electronic donor-acceptor interactions. (C) 2018 Elsevier B.V. All rights reserved.