Phytochemical profile and corrosion inhibitive behaviour of Culcasia scandens leaf extract as organic inhibitor of mild steel in Trioxonitrate V acid solution

The effect of Culcasia scandens leaf extract on the corrosion of mild steel in 2 M HNO3 solution was studied using weight loss or gravimetric technique at 303K, 323K and 343K for 30 minutes. The Culcasia scandens leaf extract inhibited the corrosion of mild steel in 2 M HNO3 solution. The inhibition efficiency increased with the concentration of the extract and temperature rise. The inhibition is attributed to the adsorption of the extract on the surface of the mild steel coupon. The corrosion rate, degree of surface coverage θ increased with increase in the inhibitor concentration and temperature. The increase in the degree of surface coverage with rise in temperature suggests that strong chemical bond exist between the extracts and the adsorbent. The highest degree of surface coverage was 0.9729 at 343 K and 350 g/L concentration of the adsorbate. The adsorption characteristics of the Culcasia scandens leaf extract obey Langmuir isotherm. Negative values were obtained for the free energy of adsorption (Go ads) from the isotherm parameters indicating that the inhibition is through spontaneous adsorption of inhibitors onto the metal surface supporting physical adsorption mechanism. The heat of adsorption(Qads) values were all positive implying that the accumulation of the adsorbate on the coupon surface was endothermic. The values of activation energy, Ea ranged from 3.341- 15.71 further supporting physisorption. The preliminary phytochemical screening, FTIR of the Culcasia scandens leaf extract was carried out to determine the phytoconstiuents and the functional groups responsible for the inhibition of mild steel.

Author(s): Ekpeno J. Nkop, Adewoyin M. Ogunmolasuyi, Kelvin O. Osezua and Idorenyin. A. Essien

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