Synergistic effect between Anemone coronaria and Quercus robur leaf extracts on mild steel corrosion in HCl 1 M solution: electrochemical and computational study

Abstract

The leaves of Anemone coronaria (AC) and Quercus robur (QR) were evaluated as ecological corrosion inhibitors for mild steel (MS) in 1 M HCl. Individual extracts (AC and QR) and a mixture of the two were tested at concentrations ranging from 0.1 to 0.5 g L⁻¹ to investigate potential synergistic effects. The corrosion inhibition performance was assessed using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The results showed that corrosion resistance increased with inhibitor concentration, with individual efficiencies of 93.66% (AC) and 92% (QR), while the mixture achieved a maximum inhibition efficiency of 95%, indicating a synergistic effect. Fourier-transform infrared (FT-IR) spectroscopy revealed characteristic functional groups within the extracts, while scanning electron microscopy (SEM) confirmed the formation of a protective barrier on the steel surface. The adsorption process followed the Langmuir isotherm, and thermodynamic analysis revealed a spontaneous, mixed physisorption–chemisorption mechanism. DFT calculations revealed a strong interaction between the inhibitor molecules and the mild steel surface, characterized by a low energy gap (ΔE), supporting excellent anticorrosion performance at the molecular level. These findings demonstrate that the combined use of AC and QR extracts represents a novel, eco-friendly approach to corrosion inhibition, offering high efficiency, biodegradability, and minimal environmental impact.