Insight into the inhibition ability of <i>Eupatorium adenoprum leaves</i> extract as an efficiency corrosion inhibitor for copper in acid solution

Developing corrosion inhibitors with low toxicity, eco-friendly, favorable water solubility, long-term, and efficiency is essential to inhibit metal corrosion. Herein, Eupatorium adenoprum leaves (EAL) extract is prepared via a pure water extraction method, and its inhibition for copper in 0.5 M H2SO4 is explored for the first time. The EIS and polarization curve results show that EAL extract can enhance the film and charge transfer resistance and reduce the current density of copper. After 48 h immersion, the inhibition efficiency value of 1000 mg/L EAL extract still reaches 97.7%, demonstrating that EAL extract presents long-term and dependable protection for copper in harsh acidic solution. The weight loss, SEM/EDS, and AFM results are consistent with the above conclusion. According to Langmuir adsorption and theoretical calculations, the interaction in EAL extract molecules/copper substrate is discussed in detail. Thanks to the physicochemical adsorption effect, a monolayer EAL extract protective film is formed on copper surface. Furthermore, the crucial active adsorption sites are unsaturated double-bond, aromatic rings, carbonyl groups, and heteroatom in EAL extract molecules. Ultimately, we expect this study to offer theoretical support for developing new eco-friendly inhibitors and facilitate their application in industrial pickling environments.