Cysteine as an Eco-Friendly Anticorrosion Inhibitor for Mild Steel in Various Acidic Solutions: Electrochemical, Adsorption, Surface Analysis, and Quantum Chemical Calculations

Abstract

The corrosion of iron in acidic environments has a negative impact on global industry. Herewith, the inhibitory effect of cysteine (Cys.) on mild steel (MSL) corrosion in different acidic solutions (1 M HCl, 1 M H 2 SO 4 , and 1 M H 3 PO 4 ) was investigated through weight loss, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy, scanning electron microscopy (SEM), and theoretical calculations. The measurement results indicated that the adsorption of Cys. molecules on the metal surface caused corrosion inhibition. As a result, a protective layer or insoluble compound, or both, is obtained, blocking the active sites, preventing corrosion. The effectiveness (IE %) of the Cys. was enhanced by increasing concentration and lowering temperature. The maximum IE % of inhibition at 1 × 10 −2 M of Cys. obtained are 97.3, 89.7, and 84.4% in HCl, H 3 PO 4 , and H 2 SO 4 solutions, respectively. At the same inhibitor concentration, the double-layer capacity decreased, and the charge-transfer resistance increased from 17.17 to 188.5, 3.564 to 31.91, and 1.325 to 8.715 Ω cm 2 in HCl, H 3 PO 4 , and H 2 SO 4 solutions, respectively. Adsorption and PDP studies confirmed that it obeys the Langmuir adsorption isotherm and acts as a mixed-type inhibitor of physicochemical nature. The corresponding thermodynamic and kinetic parameters were also calculated and discussed. Moreover, the inhibitory effect on the surface was inspected by SEM. The findings demonstrated that the order of IE % using Cys as anticorrosion agent for MSL is HCl > H 3 PO 4 > H 2 SO 4 solutions.

Amphiphilic Janus Graphene Oxide Acts as a Corrosion Inhibitor to Mitigate the Corrosion Caused by a 1 M HCl Solution on Mild Steel

“…Toghan et al discussed the relationship between corrosion potential and zero-charge potential (ZCP) to further explore the adsorption mechanism of corrosion inhibitors. , It has been reported that the ZCP of iron in a HCl solution is equal to −530 mV versus SCE . Clearly, in this study, the corrosion potential is more positive than the ZCP ( E coor – Eq > 0), indicating that the electrode surface is positively charged.…”

“…In the presence of the inhibitor within the corrosive medium, it competes with H + , H 2 O, and C1 – for adsorption sites and establishes the protective barrier, thereby impeding both mass and charge transfer processes and effectively retarding metal corrosion. , …”