Electrochemical, Spectrochemical and Quantum Chemical Studies on Dimedone as Corrosion Inhibitor for Copper in Acetonitrile

The inhibition ability of 5,5-Dimethyl-1,3-cyclohexanedione (dimedone, DMD) for copper in acetonitrile at 25°C was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Corrosion resistance increased with inhibitor concentration up to 93.68% inhibition efficiency at 3.00 mM, indicating that DMD molecules can cumulatively adsorb on the copper surface and finally form a protective film on copper-solution interface. This is also supported by the decreasing of copper oxidation in cyclic voltammogram. Polarization curves revealed that DMD is of mixed type inhibitor. The adsorption of DMD on copper surface obeys the Langmuir isotherm and the adsorption mechanism is of physisorption type. The standard energy of adsorption (∆Goads) values was found in good agreement for both polarization and impedance to be -8.17 and -8.43 kJmol-1 respectively. Fourier Transform Infrared spectroscopy (FT-IR) confirmed the interaction of copper with oxygen on DMD. The mole ratio method suggested that the complexation ratio of copper-DMD is 1:2. Scanning electron microscopy (SEM) of copper surface after immersion in DMD solution indicates the presence of a protective layer on the electrode surface. The frontier molecular orbital energy EHOMO (highest occupied molecular orbital), ELUMO (lowest unoccupied molecular orbital) and the Mulliken charge distribution obtained from Quantum chemical calculations revealed (∆E) for DMD 0.2091 hartree, reflecting strong adsorption of the molecules on copper surface. The enhanced corrosion inhibition is possibly due to the compact film structure blocking electron transfer at the electrode surface.