Experimental and theoretical study on corrosion inhibition and adsorption performance of Ipomoea batatas L. leaf extract for mild steel

Recent years have seen a surge in interest in efficient, green, and eco-friendly corrosion inhibitors, leading to extensive research on plant extracts. This study investigates the active phytochemicals in abundant Ipomoea batatas L. leaves, which were extracted with ultrasonics using an ethanol-water solution and applied to mitigate the corrosion of mild steel (MS) in a 1 M HCl pickling solution. The chemical compositions and corrosion inhibition properties of the leaf extract of Ipomoea batatas L. (IBLE) were explored through multiple experiments, and the adsorption thermodynamic and kinetic parameters were analysed. Electrochemical results indicated that the corrosion inhibition mechanism of IBLE is a geometric coverage effect; IBLE acts as a mixed-corrosion inhibitor; and the inhibition efficiency increases with extract concentration and solution temperature, reaching up to 96.4 % at 318 K. X-ray photoelectron spectroscopy (XPS) results showed the adsorption of C=C, C-N, C-N+, C=N, C=N+, C=O, C=O+, C-O, C-O+, Fe-N and other carbonaceous groups on the steel surface. Surface observation confirmed that IBLE can effectively retard steel corrosion. The adsorption analysis revealed that the protective film is a monolayer that follows the Langmuir isotherm, and the oriented adsorption of active ingredients enhances the order of the MS surface. Density functional theory (DFT) and molecular dynamics (MD) simulations were conducted to examine the relationship between inhibition and adsorption of IBLE. The theoretical calculations confirmed that the active compounds in IBLE can adsorb on the Fe (110) surface through physical patterns and by sharing charges with iron to form coordinate bonds. The adsorption abilities of different ingredients vary, but all exhibit synergistic adsorption effects. IBLE can be considered an efficient and renewable corrosion inhibitor for MS in HCl pickling media.