Aqueous fraction of Alternanthera philoxeroides as a biodegradable corrosion inhibitor of mild steel in sulphuric acid solution.

The aqueous extract of Alternanthera philoxeroides effectively inhibited the corrosion of mild steel in 1.0 M H2SO4, as tested using gravimetric and electrochemical methods. Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) analysis identified phytochemical components with functional groups that interact with the metal surface. The aqueous extract showed very good anticorrosive inhibition activity. Inhibition efficiency increased with inhibitor concentration and reached its optimum at 3 h immersion time. The decrease in inhibition efficiency at higher temperatures suggested partial desorption of adsorbed inhibitor molecules. The Langmuir isotherm model described the adsorption of the inhibitor on the mild steel surface, and the free energy of adsorption (ΔG ads° = -33.18 kJ mol-1) indicated mixed-mode adsorption, involving both physical and chemical adsorption. The formation of an efficient protective layer that minimized damage and roughness on the metal surface was observed during surface characterization using field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM/EDX) and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) analysis indicated the adsorption of C-, O-, and N-containing species that formed bonds with iron atoms, thereby confirming the interaction of inhibitors with the metal surface. Consequently, this study demonstrated the effectiveness of the aqueous fraction of Alternanthera philoxeroides as an eco-friendly inhibitor for mild steel in an acidic environment.