Exploiting the Alkaloid Extract from Waste material of Nicotiana tabacum as efficient Biomass Inhibitor for Mild Steel Corrosion in Acidic Media

Background Extracts rich in alkaloid and derived from agricultural waste represent a scalable route to environmentally friendly corrosion inhibitors. In this study, a total alkaloid extract from discarded Nicotiana tabacum leaves (NTLE) was prepared and evaluated as a green inhibitor for mild steel corrosion in 0.5 M HCl. Results Chemical profiling confirmed selective enrichment in alkaloids, with nicotine amounting to 91%, and consistent with FT-IR signatures of heteroaromatic amine functionalities. Electrochemical measurements show that NTLE markedly reduces corrosion kinetics: potentiodynamic polarization indicates mixed-type inhibition with suppression of both anodic dissolution and cathodic hydrogen evolution, achieving up to 95% inhibition at 0.115 g·L⁻¹. EIS reveals increased charge-transfer resistance and decreased double-layer capacitance with concentration, consistent with interfacial film formation. Langmuir, kinetic–thermodynamic, and Flory–Huggins adsorption isotherms, and the Temkin model were used to investigate the mode of inhibition of NTLE extract. The free energy of adsorption showed that the corrosion inhibition takes place by spontaneous physical adsorption of NTLE molecules on the mild steel surface. Surface characterization using SEM shows mitigated acid attack in the presence of NTLE, contact-angle measurements indicate restoration of surface hydrophobicity, and four-point probe measurements evidence substantial recovery of electrical continuity relative to the corroded substrate. Conclusions Overall, alkaloid extracts obtained from unused biomass material of Nicotiana tabacum provides an effective, low-dose, and ecologically safer strategy for protecting mild steel in acidic media.