The Interfacial activity of Vitex doniana (VD) leaves extract as inhibitor has been studied on carbon steel corrosion in hydrochloric acid solution using weight loss, gasometry, electrochemical techniques and quantum chemical calculations. Increase in inhibition efficiency with increased inhibitor concentration which indicate that VD molecules acted by accumulating at metal/electrolyte interface. Weight loss results show that inhibition efficiency increased with increase in inhibitor concentration but decreased with increase in temperature indicating a physical adsorption. Data obtained from the potentiodynamic polarization scan revealed that the corrosion inhibitor shifted corrosion potentials to more negative potential indicating prominent cathodic protection. The impedance data showed a decrease in double layer capacitance and an increase in charge transfer resistance which suggests that electron migration was retarded in the bulk solution. The Nyquist and Bode plots of the test solutions were similar in both inhibited and free medium but contained capacitive and inductive loops. To assess the interaction of VD molecules with Fe(110) surface, quantum chemical calculations were performed to elucidate the molecular reactivity parameters of inhibitor molecules while molecular dynamics studied the binding properties of inhibitor molecules on metal surface. Local reactivity was estimated and discussed through condensed Fukui indices. Theoretical calculations were carried out using Dmol3 basis set for all atoms.
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