Ecofriendly green inhibitor from<i>Hemerocallis fulva</i>against aluminum corrosion in sulphuric acid medium

This research work aims to identify a non-toxic, cheap, and effective greener inhibitor from Hemerocallis fulva (H. fulva) for corrosion of aluminum in a 1 M H2SO4 medium at different concentrations and temperatures. We investigated the inhibitive effect of H. fulva extract in a 1 M H2SO4 solution on aluminum using weight loss measurements with various concentrations and temperatures. Evaluations of the mechanism of corrosion inhibition by potentiodynamic polarization and AC-impedance analysis were also performed. The nature of the adsorption and morphology on the surface of aluminum were performed by atomic force microscopy (AFM) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) studies. The results suggested that the H. fulva extract can be used on aluminum as an efficient eco-friendly corrosion inhibitor in 1 M H2SO4 solution as identified using weight loss because the maximum corrosion inhibition efficiency η (%) was found to be 89% at 600 ppm at 303 ± 1 K. It was found that maximum η (%) was obtained at 303 ± 1 K compared to other temperatures (313, 323, and 333). The activation energy (Ea) was higher in the presence of inhibitor than in the absence of inhibitor, showing the temperature dependency of inhibition. The positive values of enthalpy of activation ΔH° and entropy of activation ΔS° reflect the endothermic and disordered nature of the reaction. Physical adsorption was proposed for the inhibition and the process followed the Langmuir adsorption isotherm. The negative value of ΔGoads indicates spontaneous adsorption. Polarization measurements clearly indicated that the H. fulva acts as a mixed inhibitor and the η (%) increases with inhibitor concentration. SEM-EDX, AFM, and XPS studies confirmed the formation of a protective layer over the surface of the aluminum specimen.