Synergistic enhancement of copper corrosion protection using Origanum compactum essential oil and Zn2+ cations

Abstract

Metal corrosion poses a major challenge to the long-term reliability and economic sustainability of metallic structures, especially in the automotive, aerospace, and petrochemical industries. In the present work, we introduce a hybrid corrosion inhibition strategy based on the combination of Origanum compactum essential oil and Zn²⁺ for copper protection in 0.5 M H₂SO₄. The originality of this approach lies in exploiting the synergistic interaction between Zn²⁺ and bioactive constituents of the essential oil to enhance adsorption, surface coverage, and copper passivation. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) demonstrated a high inhibition efficiency of 94.5%, confirming the superior performance of our inhibitor. SEM/EDS, AFM, and contact angle measurements further evidenced the formation of a compact, homogeneous, and hydrophobic protective layer on the copper surface. Importantly, advanced quantum chemical calculations were performed to elucidate the synergistic mechanism in order to understand the molecular-level anticorrosion interactions underlying the system. The Density Functional Theory (DFT) results showed that there was a very strong coordination between Zn²⁺ and the principal constituents of the essential oil (thymol, carvacrol, γ-terpinene, and p-cymene), which enhanced adsorption stability and surface coverage. These results demonstrate that combining Origanum compactum essential oil with Zn²⁺ provides an effective and environmentally attractive strategy for copper corrosion protection in acidic media.