The potential-dependent adsorption behavior of water and ionic liquid was probed by surface-enhanced Raman spectroscopy （SERS） at the Ag electrode surface in the ionic liquids containing water with different concentrations. The configuration of water at the ionic liquid/electrode interface and the relationship between the potential of zero charge （pzc） and the molar frac- tion of water were deduced through the changes in the vibrational frequency of OH stretching mode. A small Stark effect value was determined in the system with lower molar fraction of water. With the increase of the water concentration, the OH stretching vibrational frequency gradually shifted to the high wavenumber region, the pzc was also moved positively, and the Stark effect value of OH stretching vibrational mode increased. It reached about 76 cm-1 V-I in the 1 tool L-1 [BMIM]Br aqueous solution. These differences were mainly contributed by hydrogen bonding and the configuration of water in the ionic liquid solution. In the solution with lower water content, water molecules existed at the interface layer through hydrogen bond- ing with cations, while in the higher content solution, the intermolecular hydrogen bonding between water molecules was strengthened and the possibility of the direct interaction between the water molecule and electrode surface increased.
The fabrication and characteristics of spindle Fe2O3@Au core/shell particle were investigated, and the effect of the core/shell nanoparticles as the surface enhanced Raman spectroscopy (SERS)-active substrates was studied. By using the seed-catalyzed reduction technique, anisotropic Fe2O3@Au core/shell particles with spindle morphology were successfully prepared. The Fe2O3 particles with spindle morphology were initially prepared as original cores. The Au nanoparticles of 2 nm were attached onto the Fe2O3 particles through organosilane molecules. Uniform Au shell formed onto Fe2O3 core modified by Au nanoparticles through the in-situ reduction of HAuCl4. The shell thickness was controlled through regulating the concentration of HAuCl4 solution. The results of TEM, XRD and UV-vis characterization show that the core/shell particles with the original shape of the Fe2O3 particles are obtained and these surfaces are covered by Au shell completely. The surface enhanced Raman spectrum of the probe molecules adsorbed on these core/shell substrates is strong and the intensity is enhanced with the increase of the thickness of Au shell or the aspect ratio of particles. The spindle Fe2O3@Au core/shell particles exhibit optimum (SERS) activity.
