Experimental and computational study of corrosion protection of carbon steel by Lavandula angustifolia extract–Zn(II) hybrid system in saline solution

Steel corrosion is effectively protected using plant-based inhibitors. However, organic inhibitors like plant extracts often show limited performance in neutral environments. To overcome this limitation, this study investigated the corrosion behavior of a combined organic-inorganic inhibitor, consisting of Lavandula angustifolia (LA) plant extract and zinc nitrate, for low-carbon steel in a 3.5% NaCl solution. Electrochemical techniques, including EIS and PDP, along with surface characterization and theoretical modeling, were employed to assess the corrosion inhibition efficiency of this hybrid system. The i corr value for the LA–Zn²⁺ inhibitor at 400 ppm LA and 400 ppm Zn decreased from 11.51 to 0.83 µA/cm², corresponding to an inhibition efficiency of 92%, and showed better performance than the individual inhibitors. This finding was further supported by EIS measurements, where the R ct increased from 862 to 5956 Ω cm². This indicated the formation of a highly protective interfacial layer. FTIR and UV-vis spectroscopy confirmed the interaction between LA’s functional groups and Zn²⁺ ions. CA measurements (19.7° for the blank and 40.12° for the optimal sample) and SEM/EDS analyses further validated the formation of protective surface layers. Additionally, MC, MD, and QM simulations revealed the strong binding affinity and stability of the LA–Zn²⁺ complexes, offering insights into their protective behavior. This study presents LA–Zn²⁺ complexes as eco-friendly, efficient alternatives to traditional corrosion inhibitors.