New eco-friendly corrosion inhibitor for zinc based on expired Detralex drug. Adsorption, electrochemical and computational studies

The study addresses the challenge of using outdated pharmaceuticals as anti-corrosion agents for metal substrates in saline environments. While many studies mainly focused on single-component drugs, the present work explores a multi-component drug, highlighting the synergistic effects of its constituents on corrosion inhibition. Expired Detralex, as a novel candidate for green corrosion inhibitor, was tested for zinc substrate in 3 wt % NaCl solution. This eco-friendly drug comprises 90% diosmin and 10% hesperidin, abundant and cost-effective products derived from citrus cultivation. Potentiodynamic polarization (PDP) tests revealed that Detralex inhibited both anodic and cathodic reactions, classifying it as a mixed-type corrosion inhibitor. A high inhibition efficiency, exceeding 90%, was obtained at 7.82 mM drug concentration and corrosion rate of 0.028 mm/year. Electrochemical impedance spectroscopy (EIS) identified distinct equivalent electric circuits in the absence and the presence of inhibitor, respectively, showing the formation of an adsorbed protective layer in the presence of Detralex. Scanning electron microscopy (SEM) confirmed the Detralex adsorption on the Zn surface. Adsorption behavior adhered to the Langmuir isotherm model, with computational studies indicating strong binding interactions between Detralex constituents (diosmin and hesperidin) and the metal surface. FT-IR measurements identified the Zn-hesperidin and Zn-diosmin complex formation. These experimental results confirm the potential of expired Detralex as a cost-effective and sustainable corrosion inhibitor. • Expired Detralex was used as a green corrosion inhibitor for zinc. • Corrosion inhibition efficiency exceeded 90% at 7.82 mM Detralex concentration. • Detralex acted as a mixed-type inhibitor, affecting both anodic and cathodic reactions. • Adsorption followed the Langmuir isotherm model, leading to a protective layer. • Computational studies showed strong binding interactions between Detralex constituents (diosmin and hesperidin) and the zinc surface.