Mechanistic elucidation of Persicaria maculosa Gray extract as a corrosion inhibitor: Adsorption, electrochemical behavior, and DFT validation

• Introduction • Experimental Methods • Results and Discussion • Conclusion This work reports on the corrosion inhibition performance and mechanistic insight of Persicaria maculosa Gray extract (PMGE) as an ecologically friendly inhibitor for corrosion process in mild steel under acidic conditions. The inhibitory behavior was systematically analyzed using weight-loss (gravimetric) measurements, adsorption studies, electrochemical approach, surface characterization, and density functional theory (DFT) calculations. The extract showed remarkable corrosion inhibition activity at an optimal concentration of 500 mg L -1 , with a paramount inhibition effectiveness of 96.23%. The plant extract functions as a mixed-type inhibitor that significantly reduces the corrosion rate by suppressing both anodic metal dissolution and cathodic hydrogen evolution processes, according to electrochemical experiments. The protective coating formation on the surface of metal substantiated by significant increase in charge transfer resistance during Electrochemical impedance spectroscopy (EIS) analysis with increasing concentration of PGME inhibitor. Adsorption experiments show that the inhibitor molecules bind extensively with the metal surface to form a persistent adsorbed layer, as evidenced by the Langmuir adsorption isotherm. Surface morphology study further demonstrated the presence of a firm protective layer that adequately shields the metal from harmful ions. Additionally, Density functional theory (DFT) simulations subjected to molecular –level insight into the adsorption mechanism, revealing that the active phytochemical constituents had a significant tendency to donate electrons and a high affinity for the metal surface. The combined experimental and theoretical results show that PGME is highly effective and ecologically safe corrosion inhibitor that offers a sustainable alternate for acid corrosion management.