Comparative evaluations of antioxidant potentials of Dryobalanops aromatica tree bark extracts as green corrosion inhibitors of mild steel in hydrochloric acid

The antioxidant potential of Dryobalanops aromatica methanolic (ME) and water extracts (WE) tree bark was studied by reducing power and DPPH free radical scavenging capacity assays. Methanolic extract showed better antioxidant capacity than water extract and butylated hydroxytoluene standard. The effective concentration EC₅₀ (362.7 mg DPPH eq/g for ME and 555.4 mg DPPH eq/g for WE) and antiradical power (0.0028 for ME and 0.0018 for WE) suggest that methanolic extract has higher antioxidant properties than water extract. According to potentidynamic polarization, electrochemical impedance spectroscopy, and electrochemical noise, employed to measure the anti-corrosion properties of the D. aromatica tree bark extracts on mild steel in 0.5 M HCl, the water extract seems to perform slightly better than methanol extract. The calculated percentage inhibition efficiencies of the extracts at the optimum concentration (1000 ppm) were; (IE = 93.66% for ME and 92.39% for WE). Adsorption process of D. aromatica ME and WE on mild steel surface in HCl solution followed Langmuir adsorption isotherm. The surface morphology depicts that the surface of the mild steel treated with methanol and water extracts showed improvement compared to mild steel plate treated only with 0.5 M HCl. (paper)