Green Corrosion Inhibition of Mild Steel in an Acidic Medium Using Aglaonema Leaf Extract and Its Synergistic Blends with Orange Peel and Grape Seed Extracts: Electrochemical, Surface, and DFT Studies

The corrosion protection ability of a green inhibitor system derived from Aglaonema leaf extract and its synergistic mixtures with orange peel and grape seed extracts was examined for mild steel in 0.5 M H₂SO₄ acid medium. The inhibition performance was assessed through weight-loss experiments, open-circuit potential monitoring, potentiodynamic polarization, and electrochemical impedance spectroscopy after immersion durations of 24 and 48 h. The findings revealed that inhibition efficiency increased with inhibitor concentration. Among the studied systems, the leaf–peel blend exhibited the highest protection efficiency, reaching 88.2% after 24 h of exposure. Polarization results suggested that the inhibitor behaves as a mixed-type inhibitor, suppressing both anodic metal dissolution and cathodic hydrogen evolution processes. Electrochemical impedance measurements showed a noticeable rise in charge-transfer resistance accompanied by a reduction in double-layer capacitance, indicating the development of a dense protective adsorbed film at the metal–electrolyte interface. Surface characterization by scanning electron microscopy and metallurgical analysis showed substantial reduction in corrosion damage in inhibited systems. FTIR and GC–MS analyses identified oxygen-containing organic compounds responsible for adsorption, while Density Functional Theory calculations correlated molecular electronic properties with adsorption tendency. Overall, the synergistic plant-based formulation provides efficient and eco-friendly corrosion protection, offering a sustainable alternative to conventional synthetic inhibitors for acidic industrial environments.