Surface-Enhanced Vibrational Spectroscopy of Tetrafluoroborate 1-n-Butyl-3-methylimidazolium (BMIBF4) Ionic Liquid on Silver Surfaces

The surface-enhanced Raman scattering (SERS) spectra obtained using Ag nanoparticles (NPs) dispersed in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF(4)) ionic liquid and from an Ag island film spin coated with BMIBF(4) are reported. The SERS spectra of the Ag NPs/BMIBF(4) interface do not show enhancement of the BF(4)(-) symmetric stretching signal at 765 cm(-1); however, this vibrational mode is enhanced in the SERS spectra of BMIBF(4) recorded using Ag island films. The results are discussed in terms of the role of water molecules in the structure of the BMIBF(4) adsorbed on the different Ag substrates. Further evidence for the function of water in the structure of the investigated interfaces was obtained by surface-enhanced infrared absorption (SEIRA) spectroscopy. The results support the conclusion that the presence of water in the Ag NPs/BMIBF(4) dispersion promotes the aggregation of the Ag NPs.