Waste licorice leaf extract as a sustainable corrosion inhibitor for copper in 0.5 M H2SO4: Intermolecular synergism effect and long-term protection performance

Copper alloys are widely used in industrial applications due to their excellent thermal and electrical conductivity, but they suffer severe corrosion in acidic environments, necessitating the development of efficient and eco-friendly corrosion inhibitors to protect copper alloys from corrosion. This study aims to explore the corrosion inhibition performance and intermolecular synergistic behavior of licorice ( Glycyrrhiza uralensis Fisch.) leaf extract (LE), a waste-derived natural product, for copper alloys in 0.5 mol/L H 2 SO 4 solution. Waste licorice leaves are processed via Soxhlet extraction using pure water as a solvent to prepare LE, which was confirmed to contain glycyrrhizic acid and glabridin as the main active components. Electrochemical measurements, surface characterizations, and theoretical calculations are employed to evaluate the corrosion inhibition efficiency and mechanism. Results show that LE exhibits corrosion inhibition ability, with a maximum efficiency of 91.2 % at 200 mg/L. When compounded with potassium iodide, the optimal efficiency increases to 95.3 % and further reaches 99.3 % after 144 h immersion. The excellent performance is attributed to the formation of complexes between LE components and Cu + , as well as insoluble copper(I) iodide (CuI) generated by I - and Cu + on the metal surface, which together forms a dense protective film to hinder corrosive substance diffusion. Glycyrrhizic acid and glabridin demonstrate intermolecular synergism, with higher glabridin content enhancing the barrier effect of the inhibitor film. Prolonged immersion promotes the formation of a more complete and compact film, significantly improving long-term inhibition performance. This work highlights the potential of waste licorice leaf extract as an efficient, sustainable corrosion inhibitor for copper alloys in acidic media, providing insights into the synergistic mechanisms underlying its performance. • The maximum inhibition efficiency reached to 99.3% after 144 h. • Intermolecular synergistic effect enhanced the corrosion inhibition performance. • The protective film is formed by inhibitor molecules and copper ions .