Novel eco-friendly quinolinone derivative as a water-soluble corrosion inhibitor for low carbon steel: Synthesis, inhibitive efficacy, and DFT analysis

A novel and rapid synthetic route for producing 4-imino-3-(2-phenylhydrazono)-3,4-dihydroquinolin-2(1H)-one (IQ) from 3-(2-phenylhydrazono)quinoline-2,4(1H,3H)‑dione 1 is introduced. The inhibitory effectiveness of IQ in mitigating the corrosion of low carbon steel (LCS) in acidic environments was evaluated using weight loss (Wt-L) and electrochemical methods, such as potentiodynamic polarization (Pd-P) and electrochemical impedance spectroscopy (EIS). The optimum concentration of IQ was determined to be 30×10⁻³ Mm, at which it exhibited the highest inhibition efficiency of approximately 93.2 %. The nature of IQ as a mixed-type inhibitor was demonstrated by its ability to inhibit both anodic and cathodic reactions, primarily acting as an anodic inhibitor.

The adsorption of IQ onto the LCS surface followed the Langmuir adsorption model, indicating a monolayer adsorption mechanism. Moreover, EIS findings suggest that IQ forms a protective layer on the LCS surface at the metal/electrolyte interface, preventing its dissolution in the acidic medium. Further analysis of the corrosive solution containing IQ after two days of LCS immersion showed the formation of Fe-IQ complex, confirmed by ultraviolet/visible spectroscopy. Using atomic force microscopy (AFM), we confirmed that a protective layer of IQ forms on the surface of LCS. Additionally, in silico studies of IQ revealed the active sites responsible for its interaction with the LCS surface under acidic conditions. These findings underscore the potential of IQ as an effective corrosion inhibitor for LCS in acidic environments, providing significant protection by forming a stable, protective film on the metal surface.