Green production of bioactive components from herbal origins through one-pot oxidation/polymerization reactions and application as a corrosion inhibitor for mild steel in HCl solution

Biopolymers such as polydopamine and polyserotonin are effective corrosion inhibitors for the acidicinduced corrosion of steel. Despite the excellent corrosion inhibition activity of these compounds, they are not cost-effective and readily available in a large scale. In this study, for the first time, a cheap and easy methodology was followed for obtaining the modified Nettle extract including the oxidized/dimerized bio-active products such as serotonin and histamine. The Nettle extract (NTE) and oxidized Nettle extract components (ONTE) were characterized by Fourier transform infrared spectroscopy (FT-1R), scanning electron microscope (SEM), UV-visible spectroscopy, and thermal gravimetric analysis (TGA). The NTE was oxidized under the alkaline condition at an ambient temperature. Finally, 600 ppm NTE and ONTE were separately added to 1 mol L-1 HCI solution to reduce the steel corrosion rate. The corrosion inhibition activity of the utilized inhibitors was assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques. The surface features were examined by SEM, atomic force microscope (AFM), and water contact angle test. The obtained results displayed that the ONTE inhibitor resulted in the higher inhibition efficiency than the NTE. The maximum inhibition efficiency, i.e. 93.40%, was obtained in the case of the acidic solution inhibited by 600 ppm ONTE after 1.5 h. Results of the polarization test and surface analyses proved the ONTE inhibitor components adsorption on the active metal sites, especially on the anodic areas. In studying of effects of temperature on the corrosion rate of mild steel the positive effect of ONTE on the mild steel corrosion mitigation was noticed. It was shown that the adsorption of the inhibitor on the metal surface obeyed the Langmuir isotherm in both physisorption and chemisorption forms. (C) 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.