Green corrosion inhibition of carbon steel in 10% (v/v) HCl solution using cagaita (Eugenia dysenterica) extract

Corrosion of carbon steel in acidic environments is a major industrial problem with significant economic and environmental impacts. In this study, an innovative and sustainable corrosion inhibition strategy is proposed using an aqueous extract of cagaita (Eugenia dysenterica), a native fruit from the Brazilian Cerrado—one of the largest and most biodiverse biomes worldwide. Electrochemical measurements in 10 wt% HCl showed that the cagaita extract reduces the corrosion current density from 8.51 × 10⁻⁴ to 0.68 × 10⁻⁴ A·cm⁻² at 0.3 g·L⁻¹, corresponding to an inhibition efficiency of 80–92%. Minor displacement of the corrosion potential (≈ 7 mV), together with reductions in both anodic and cathodic Tafel slopes, indicates a mixed-type inhibition mechanism governed by adsorption. Adsorption behavior followed the Freundlich isotherm (R² = 0.9973), while the Langmuir model yielded a high affinity constant (K _L = 21.99 L·g⁻¹) and near-unity surface coverage. The estimated adsorption free energy (ΔG°_ads ≈ − 31.6 kJ·mol⁻¹) and the decrease in activation energy from 53.8 to 48.6 kJ·mol⁻¹ confirm strong adsorption and surface-blocking effects. Spectroscopic analyses confirmed the predominance of phenolic compounds, mainly epicatechin and quercetin, supporting the use of biodiversity-rich biomes such as the Brazilian Cerrado as valuable sources of green and effective corrosion inhibitors.