Unraveling the inhibitive performance and adsorption behavior of expired compound glycyrrhizin tablets as an eco-friendly corrosion inhibitor for copper in acidic medium

Background: Developing effectively and eco-friendly corrosion inhibitor is of great significance in copper corrosion protection. The expired compound glycyrrhizin tablets (ECGT) shown huge potential, which was firstly investigated in this work. Methods: Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP) were employed to evaluate the corrosion inhibition performance. Surface characterization methods, including Optical Microscope (OM), Water Contact Angle (WCA), Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and X-ray photoelectron spectroscopy (XPS) were conducted to clarify the corrosion inhibition mechanism. Furthermore, the interfacial adsorption process of ECGT molecules on copper surface was studied using theoretical calculations, including quantum chemical calculation and molecular dynamics simulation. Significant findings: Results illustrated that ECGT molecules could dramatically delay the corrosion rate of copper in 0.5 M H2SO4 solution as a mixed-type corrosion inhibitor. The maximum corrosion inhibition efficiency reached 93.55 % at 500 ppm and could increase to 94.17 % after 24-hour immersion. The adsorption characteristics of ECGT molecules aligned well with the Langmuir isotherm model, and a hydrophobic protective film with excellent corrosion resistance formed on copper surface through surface topography and XPS analysis. Theoretical calculations at molecular scale illustrated the both chemisorption and physisorption behaviors of ECGT molecules, and visualized the cooperative behavior between main molecules, effectively inhibiting the invasion process of corrosive media to copper surface. This article demonstrated the potential of ECGT as an ecofriendly corrosion inhibitor for copper, which could provide a new strategy for the recycle and reutilization of ECGT.