Inhibition performance of extract reinforcement corrosion inhibitor from waste Platanus acerifolia leaves in simulated concrete pore solution

In our previous study, the ultrasound-assisted enzymatic extract of Platanus acerifolia leaves (PAL) was confirmed as an efficient corrosion inhibitor of steel. In this study, a new strategy-ultrafiltration-was proposed to further enhance the corrosion inhibition effect of this green steel corrosion inhibitor. To pinpoint the main players in the corrosion-inhibiting performance, the active compounds of the treated PAL extract were further quantitatively characterized via high performance liquid chromatography (HPLC). Electrochemical approaches were employed to investigate the anti-corrosion behavior. The adsorption film and surface morphology of the steel surface were characterized via X-ray photoelectron spectroscopy (XPS) and scanning electron microscope with energy dispersive spectrometer (SEM-EDS), respectively. Furthermore, simulations were carried out to further explore the inhibition mechanisms of the active molecules. The results showed that ultrafiltration significantly removed the polysaccharide impurities, thereby further concentrating the inhibition constituents. Twelve flavonoids and their derivatives were quantitatively traced, among which the procyanidins was the most pronounced ingredient (220 ppm). Ultrafiltration can effectively improve the inhibition performance of the extract. In the presence of chloride ions, the inhibition efficiency of the 1.5 wt.% two-step processed extract was equivalent to that of the 5 wt.% primary extract. Plus, SEM-EDS observations confirmed that the two-step processed extract was able to effectively mitigate the corrosion degree. XPS and simulation analyses revealed that the flavonoids and their derivatives executed the corrosion inhibition performance by forming a protective carbon-containing organic film on the steel surface via chelation and surface physical adsorption.