Antioxidant Capacity and Corrosion Inhibition Efficiency of Sambucus nigra L. Extract

I. Martinović, G. Zlatić, Z. Pilić, M. Šušak and F. Falak

Abstract
The cyclic voltammogram recorded in the potential range between 0 V and 800 mV with scan rate of 100 mV s−1 was used to determine the measure of antioxidants content (antioxidant capacity) present in Sambucus nigra L. extract. The antioxidant capacity of the extract was 4.06 mg GAE g −1 fw (mg of gallic acid equivalents per gram of fresh weight of the extract). The corrosion inhibition efficiency of Sambucus nigra L. extract on aluminium, copper, and bronze in 3 % NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. Polarization data showed that extract acted as a mixed-type inhibitor, that the corrosion inhibition process was spontaneous physical adsorption (ΔG ≈ –16 kJ mol–1) of the extract molecules on metals surfaces and followed Freundlich isotherm. Impedance spectroscopy studies revealed that increasing the concentration of extract reduced the double-layer capacitance and increased the charge transfer resistance. The highest inhibition efficiencies (Cu: ~ 57 %, CuSn14: ~74 % and Al: ~58 %) were achieved for an extract concentration of 1.0 g L–1.

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Keywords
antioxidant capacity, corrosion, inhibition, Sambucus Nigra L. extract