Exploration of Metaplexis hemsleyana leaves extract as an eco-friendly corrosion inhibitor for Q420-steel in HCl media

Effective prevention of metal corrosion has become an urgent and significant issue, which necessitates the development of innovative inhibitors with environmental benignity, cost-effectiveness, highly efficient, and high aqueous solubility. Herein, metaplexis hemsleyana leaves extract (MHE) was prepared by a simple water-based extraction method and employed as an eco-friendly inhibitor with high inhibition efficiency for Q420 steel in 1 M HCl solutions. Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-vis) spectroscopies were conducted to explore the active inhibitory components existing in MHE. Systematic electrochemical tests and morphological examinations were carried out to investigate the anti-corrosion performance of MHE, and the results indicate that MHE is a mixed-type inhibitor with an inhibition efficiency of 92.86% at the concentration of 0.8 g/ L. This high efficiency is attributed to the formation of a protective layer on the mild steel surface, which blocking the diffusion pathways of aggressive ions, thereby reducing corrosion. The Langmuir adsorption isotherm reveals that the Gibbs free energy is -20.96 kJ/mol, which suggests that MHE can adsorb spontaneously onto the steel surfaces. Furthermore, quantum chemical calculations and molecular dynamics simulations were performed to establish the relationship between the electronic structures of MHE and corrosion inhibition effectiveness and explore the detailed corrosion inhibitive behavior of MHE.