Corrosion Inhibition Potential of Benue Propolis Extracts on Carbon Steel in 1.0 M Hydrochloric Acid Medium: Experimental and Computational Studies

Cycloeucalenol (CEU) was the major composition of the Benue Propolis extracts identified via proton NMR. The corrosion inhibition behaviour of this extracts on carbon steel in 1.0 M HCl was investigated by using weight loss, electrochemical impedance spectroscopy, and computational methods. The results obtained revealed that the inhibition efficiency increased with an increase in inhibitor concentration, but decreased with increase in temperature. Impedance measurement showed that charge transfer was responsible for the corrosion process. The charge transfer resistance (R2) increased with concentration of the inhibitor as opposed to the double layer capacitance (Cdl) which decreased. The values of the Gibbs free energy (ΔG°) indicated a spontaneous adsorption of the extract components on the metal surface. The physically adsorbed propolis extract onto the carbon steel surface followed Langmuir adsorption isotherm model. The HOMO map shows the electron cloud situated in the C=C sp2 group, and then spread across the three consecutive cyclohexane rings and their substituents. From the Fukui function indices calculations, CEU is discovered to have its site for nucleophilic and electrophilic attacks each at one of carbon atoms of the alkene group in the molecule. The results have demonstrated that the composition of Benue propolis is active inhibitor of corrosion of carbon steel surface in HCl acidic medium.