Persian Liquorice extract as a highly efficient sustainable corrosion inhibitor for mild steel in sodium chloride solution

Abstract

The Persian Liquorice was introduced as a sustainable corrosion inhibitor with excellent inhibition action for mild steel in sodium chloride solution. Persian Liquorice is a root of Glycyrrhiza glabra including many active compounds like Glycyrrhizin (GL), 18β- Glycyrrhetinic acid (GA), Liquritigenin (LTG), Licochalcone A (LCA), Licochalcone E (LCE), and Glabridin (GLD). The Fourier transform infrared (FT-IR) spectroscopy was utilized to track various active components exist in the Persian Liquorice extract. Electrochemical impedance spectroscopy, potentiodynamic polarization and electrochemical current noise measurements were conducted to investigate the corrosion inhibition role of various concentrations of Persian Liquorice extract toward mild steel corrosion in sodium chloride solutions. Surface analysis, molecular dynamics and quantum mechanics simulation methods were combined to get insights of inhibitor molecules adsorption on the mild steel surface. The electrochemical investigations revealed that in the presence of 600 ppm Persian Liquorice extract the maximum inhibition efficiency of 98.8% was obtained, which is connected to the build-up of a protecting layer over the mild steel surface, blocking the pathway of harsh ions diffusion. There is no report on use of any sustainable corrosion inhibitor for mild steel in chloride solution with this high level of inhibition power even after long immersion time (72 h). The formation of protecting layer on the mild steel surface was proved by scanning electron microscope and atomic force microscope results. The results derived from MD simulations and QM calculations revealed the adsorption of Persian Liquorice components on the steel substrate via donor-acceptor interactions.