Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper

Abstract

5-Methoxy-2-(octadecylthio)benzimidazole (MOTBI) monolayer was self-assembled on fresh copper surface obtained after etching with nitric acid at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM) were established using impedance studies. The optimum conditions are methanol as solvent, 10mM concentration of the organic molecule and an immersion period of 24h. The MOTBI SAM on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy and reflection absorption FTIR spectroscopy and it is inferred that chemisorption of MOTBI on copper surface is through nitrogen. Corrosion protection ability of MOTBI SAMwasevaluated in aqueous NaCl solution using impedance, electrochemical quartz crystal nanobalance,potentiodynamicpolarizationandweight-lossstudies.Whilebarecoppershowedacharge-transfer resistance (Rct) value of 1.89k cm2 in 0.20MNaClaqueousenvironment,theRct value for SAMcovered copper surface is 123.4k cm2. The MOTBI SAM on copper afforded corrosion inhibition efficiency of 98–99%inNaClsolutionintheconcentrationrangeandinthetemperaturerangestudied.TheSAMfunctions as a cathodic inhibitor. Quantum chemical calculations showed that MOTBI has relatively small E betweenHOMOandLUMOandlargenegativechargeinitsbenzimidazolering,whichfacilitateformation of a polymeric [Cu+-MOTBI] complex on copper surface.