The inhibiting action of 2-oxo-1,2-dihydroquinoline-4-carboxylic acid (Q1) on the corrosion of carbon steel in hydrochloric acid has been studied using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increases with increase in inhibitor concentration. Impedance measurements showed that the double-layer capacitance decreased and charge-transfer resistance increased with increase in the inhibitor concentration and hence increasing in inhibition efficiency. Polarization curves show that Q1 is a mixed-type inhibitor. The adsorption of Q1 onto the carbon steel surface was found to follow the Langmuir adsorption isotherm. Quantum chemical parameters such as highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), energy gap (ΔE) and dipole moment (μ) were calculated. Quantum chemical calculations also supported experimental data and the adsorption of inhibitor molecules onto the metal surface.
