Carbon steel inhibition in 1.0 M HCl by using Walnut Green Husk (Juglans regia) extract: Practical and theoretical studies

In this study, Walnut Green Husk (WGH) extract is introduced as a sustainable, low-cost, and eco-friendly corrosion inhibitor for carbon steel (C-steel) in 1.0 M HCl. The application of agricultural waste-derived extracts, with combined experimental and theoretical validation, remains underexplored despite growing interest in green corrosion inhibitors, especially for achieving high-efficiency inhibition under varied operating conditions. The inhibition efficiency ( IE% ) was assessed at various concentrations (0–25 g L −1 ) and temperatures (298–318 K) over immersion times (3–12 h). The corrosion rate ( W corr ) was evaluated under inhibited and uninhibited conditions. The inhibition efficiency ( IE% ) increased with inhibitor concentration and immersion time, reaching 91.35%, 92.36%, and 95.49% at 25 g L −1 over 3, 6, and 12 h, respectively. With increasing temperature, the corrosion rate ( W corr ) increased, while the inhibition efficiency ( IE% ) decreased, indicating reduced adsorption stability at elevated temperatures and confirming a predominantly physisorption-controlled inhibition mechanism. The adsorption data fitted well with the Langmuir adsorption model, while the negative ΔG° ads values of −14.90 to −16.85 kJ mol −1 indicate that adsorption is thermodynamically spontaneous. However, these ΔG° ads values were considered only as supportive thermodynamic evidence and not as definitive proof of the adsorption mechanism. The results for surface coverage θ corroborated earlier findings, indicating that the inhibitory effect is due to physical adsorption of the additive components on the C-steel surface, thereby enhancing inhibition. The findings of the theoretical search revealed efficient adsorption of organic components from WGH extract onto the surface of C-steel, including heteroatoms and π-electron systems. This adsorption creates a persistent protective layer that effectively blocks active corrosion sites while enhancing overall inhibition. These results highlight the strong potential of WGH extract as an efficient, scalable, and environmentally benign alternative to conventional toxic corrosion inhibitors for industrial applications.