Eco-friendly impact of a novel green Melilotus officinalis extract as a sustainable inhibitor to reduce acid corrosion of copper

Abstract

In this study, we deployed green Melilotus officinalis extract (MOE) as a corrosion inhibitor for copper. The anticorrosion properties of MOE for Cu in 1 M HNO₃ were investigated by various experimental and numerical techniques, including potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and a weight loss (WL) method at different temperatures. Additionally, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis (EDX) and atomic force microscopy (AFM) were utilized to examine the surface morphology of Cu with and without the extract. By contrasting the inhibition effectiveness with and without the extract, the inhibition efficiency (% IE) was observed. The WL method revealed that 300 ppm of the extract had an IE of 93.8% for Cu immersed in one molar HNO₃ solution. The MOE was classified as a mixed type according to the PDP study since it delayed both cathodic and anodic processes, with a cathodic predominance. At 25–45 °C, MOE's free adsorption energies were 23.1–21.5 kJ mol⁻¹, showing that mixed-type adsorption occurred on the Cu surface. Additionally, the Langmuir adsorption isotherm and the adsorption data from the WL tests of MOE showed a good match. The extract could adsorb spontaneously onto the metal surface, according to the thermodynamic conditions. Analysis of the corrosion product using different techniques revealed that a protective layer had formed on the metal's surface. Hence, MOE had a good corrosive inhibitive effect on Cu in HNO₃ solution. It turned out that all the methods used gave consistent results.