Green inhibitor compound of Vanillin and L-Cysteine for acid-driven corrosion of carbon steel

Bio-based Vanillin (VA) possesses promising corrosion inhibitive potentiability due to its aromatic framework together with oxygen-containing functional groups. In this work, L -cysteine ( L -Cys) is firstly utilized as the co-inhibitor to enhance the corrosion inhibition capability of Vanillin through the compound-inhibitor strategy. The electrochemical measurements, multi-scale surface analyses and molecular dynamics (MD) simulations are conducted to systematically investigate the corrosion inhibitive behavior and elucidate the synergistic mechanism for Q235 carbon steel in sulfuric acid (H 2 SO 4 ) solution. Results indicated that the novel compound green inhibitor provided the superior inhibition efficiency and outperformed either component alone. The strongest synergistic effect and the best overall performance occurred at a VA: L -Cys molar ratio of 2:1. At VA and L -Cys concentrations of 30 and 15 mM, the inhibition efficiencies reached 96.19% at 25 °C and 90.66% at 50 °C, and it remained 93.18% after 24 h of immersion at 25 °C. This compound corrosion inhibitor belonged to the mixed-type corrosion inhibitor. The MD simulations revealed that some VA and L -Cys molecules adopted flat-lying configurations, whereas other VA molecules interacted with Fe atoms in vertical or inclined configurations and oriented their hydrophobic groups toward the solution, filling residual gaps. This adsorption arrangement maximized the surface coverage, forming a denser and more hydrophobic inhibitor film. The adsorption film was effectively anchored to steel through chemical bonding and exhibited pronounced hydrophobicity, thereby impeding contact between the corrosive medium and metal and suppressing the corrosion reaction.