Electrochemical, Surface, and Molecular-Level Investigation of 2-Mercaptopyrimidine as a Green Corrosion Inhibitor for Steel in Chloride-Contaminated Concrete Pore Solution

The exploration of environmentally friendly inhibitors for mitigating corrosion of steel embedded in concrete has emerged as a focal point in research. This paper investigates the use of 2-mercaptopyrimidine (2-MP) as a relatively low-toxicity organic corrosion inhibitor for steel immersed in simulated concrete pore (SCP) solutions having high alkalinity and contaminated with chloride. The inhibitory effectiveness of 2-MP was examined at various dosages (100–800 ppm) through electrochemical experiments, including open circuit potential (OCP), linear polarization resistance (LPR), and potentiodynamic polarization (PDP) tests. A comprehensive examination of the steel coupons immersed in the inhibited SCP solution was also conducted, employing techniques such as scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and an optical 3D profilometer. Additionally, an in-depth computational study was performed integrating density functional theory (DFT) and molecular dynamic (MD) simulations. The electrochemical measurements showed the remarkable inhibitory efficiency of 2-MP, reaching as high as 89–91% at a concentration of 800 ppm. The electrochemical test results indicate that the 2-MP works as a cathodic-type corrosion inhibitor. Furthermore, it was found that the molecule followed the Langmuir isothermal adsorption model. Surface analysis confirmed the superior inhibitive characteristics of 2-MP, evident by enhanced surface quality, minimized damage, and reduced roughness indices. The computational results demonstrated the atomistic mechanism detailing the molecule's active sites and adsorption behavior onto the iron surfaces within the SCP solution.