Evaluation of the antioxidant and corrosion-inhibiting properties of Syzygium guineense, Bridelia retusa, and Erucastrum arabicum extracts

Abstract

This study examined the phytochemical composition, antioxidant, and corrosion-inhibiting capability of Syzygium guineense (SG), Bridelia retusa (BR), and Erucastrum arabicum (EA) leaves. The maceration realized with methanol-dichloromethane (1:1, v/v) extracted active compounds from dried leaves. Phytochemical screening indicated flavonoids, phenols, terpenoids, saponins, coumarins, and tannins from the plants’ extracts. FTIR analysis before corrosion showed absorption bands corresponding to O-H, C=C, C-O, and C-H bonds. All extracts exhibited pronounced concentration-dependent antioxidant activity, with the highest radical scavenging activity from SG extract (92.22 ± 0.55%) at 0.6 mg/L, followed by BR (69.67 ± 0.86%) and EA (20.45 ± 0.66%). All extracts inhibited corrosion of a 55% Al-Zn alloy in HCl (0.5 M) with positive and negative impacts of concentration and exposure time, respectively.  The activation energy, enthalpy, and entropy increased with extract concentrations; addition of 0.2 g/L of the extracts increased Ea from 36.06 to 85.23 kJ mol^-1; 25.29 to 34.92 J mol^-1, and 18.3 to 35.8 J mol^-1K^-1 for SG, BR, and EA extracts, respectively. Negative Gibbs free energy (-14.09 to -26.61 kJ mol^-1) and Langmuir R2 values (0.9592-1.0) indicated favorable adsorption of extracts following the Langmuir model. The observed anti-corrosion was predominantly through physisorption, with chemisorption contributions for EA extracts.

KEY WORDS: Extract, Phytochemical, Adsorption, Antioxidant, Corrosion

Bull. Chem. Soc. Ethiop. 2026, 40(10), 2115-2130.                              

DOI: https://dx.doi.org/10.4314/bcse.v40i10.5