Major compounds in Sandoricum koetjape (Burm.f.) Merr. leaf extract and its corrosion inhibition performance for carbon steel in hydrochloric acid solution.

Utilizing renewable resources and gradually replacing toxic inhibitors with plant-based alternatives are significant steps towards environmental sustainability and safeguarding human health. This study focused on isolating key components within the ethanol extract of the leaves of Sandoricum koetjape (Burm.f.) Merr. and studying their corrosion inhibitory properties for carbon steel in a 1 M HCl environment. The component analysis results showed the presence of polyphenols, tannins, alkaloids, flavonoids, sesquiterpene lactones, glucosides, and steroids, responsible for inhibiting chemical activities on the metal surface. Among these, two major flavonoids (quercetin and kaempferol) and one minor flavonoid (kumatakenin) were isolated for the first time from the Sandoricum koetjape leaf extract (SKLE) with high purity by column chromatography, clarifying the corrosion inhibitory mechanism. Electrochemical techniques, including EIS, LPR, and PD, indicated that the inhibitory efficiency increased with a rise in SKLE concentration, reaching the highest value of 88.87 ± 0.91% at 3000 ppm, which was simultaneously confirmed by weight loss measurements. Additionally, surface characterization techniques, such as SEM/EDS, AFM, and XPS, revealed serious corrosion on the unprotected surface and protected surfaces with low SKLE concentrations as well as the presence of a compact and adhesive organic film on the protected surfaces at higher SKLE concentrations. Overall, the SKLE and its major compounds can be considered promising and environmentally friendly corrosion inhibitors for carbon steel in highly acidic environments.