Evaluation of Bitter Kola Leaf Extract as an Anticorrosion Additive for Mild Steel in 1.2 M H₂SO₄ Electrolyte

Abstract

Plant-based material, namely bitter kola leaf, as an additive for surface modification of mild steel in H₂SO₄ solution was thoroughly scrutinized using  electrochemical, theoretical and optimization techniques. The functional groups, of the biomolecules of the bitter kola leaf extract, were examined using  Fourier transform infrared spectrometry (FTIR) and gas chromatography-mass spectrophotometry (GC-MS). For clarification purpose, scanning electron  microscopy (SEM) was used to inspect the texture of the degraded and inhibited steel after 21 h of immersion. For the response surface methodology  (RSM), central composite design of Design-Expert Software was used to optimize the inhibition efficiency as a function of acid concentration, inhibitor  concentration, temperature and time. The optimum inhibition efficiency of 93 % was obtained at 0.9 g L^–1 bitter kola leaf. The mutual correlation between  the considered variables and expected response was adequately interpreted by a quadratic model. The fitness of the model was justified by the  following standards which include P-value (<0.0001), adjusted R² (0.9843), R² (0.991), adequate precision (43.14) and coefficient of variation (2.59). Bitter  kola leaf extract behaved as a mixed-type inhibitor and adequately satisfied Langmuir adsorption isotherm. Furthermore, the theoretical modelling  revealed the most active molecule of bitter kola leaf responsible for the overall inhibition. The experimental and theoretical results are in agreement that   bitter kola leaf extract is a viable corrosion inhibitor of mild steel in H₂SO₄ solution.