Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface-enhanced Raman scattering spectroscopy

Two kinds of room-temperature ionic liquids, 1-butyl-3-methylimidazolium bromide ([BMIM]Br) and 1-butyl-3-methylimidazolium tetrafluoroboride ([BMIM]BF4), were used as solvent, and the adsorption of the ionic liquids themselves and of N-methylimidazole (NMIM) were investigated by electrochemical surface-enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the ([BMIM]BF4 liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br-, the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM)(4)Br]Br center dot H2O and [Cu(NMIM)(4)](BF4)(2) were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed. Copyright (C) 2009 John Wiley & Sons, Ltd.