Exploring the Adsorption Mechanism of Novel Biscoumarin Derivatives as Corrosion Inhibitors for Stainless Steel in 2 M H₂SO₄ Medium: An Integrated Approach Combining Electrochemical and Theoretical Studies

This study investigates the inhibition effect of two newly synthesized biscoumarin compounds, (Z)-4-hydroxy-3-((4-hydroxy-2-oxo-2H-chromen-3(8aH)-ylidene)(phenyl)methyl)-2H-chromen-2-one (P1) and (Z)-3-((4-chlorophenyl)(4-hydroxy-2-oxo-2H-chromen-3(8aH)-ylidene)methyl)-4-hydroxy-2H-chromen-2-one (P2), on the corrosion behavior of stainless steel in a 2M H₂SO₄ solution. Various methods, including potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM–EDX), as well as density functional theory (DFT), Monte Carlo simulation (MC) and molecular dynamics (MD), were used in this investigation. The electrochemical findings revealed that P1 and P2 exhibit mixed inhibition behavior. Higher inhibition efficiencies are achieved at higher concentrations of these compounds. Indeed, at a concentration of 10⁻³ M, the inhibition efficiency reached 99 and 99.5% for P2 and P1 respectively, although it decreased slightly with increasing temperatures. The adsorption of studied inhibitors followed the Langmuir adsorption isotherm model. In addition, SEM–EDX analysis of the steel surface revealed a protective layer formed by the adsorbed inhibitors. Furthermore, the theoretical methods (MC and MD) were consistent with the experimental data, confirming the obtained results.