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Ferrites of the type M II Fe 2 O 4 (M ) Fe and Co) have been prepared by the traditional coprecipitation method. These ferrites were modified by the adsorption of fatty acids derived from soybean and castor oil and were then dispersed in cyclohexane, providing very stable magnetic fluids, readily usable in nonpolar media. The structural properties of the ferrites and modified ferrites as well as the magnetic fluids were characterized by XRD (X-ray powder diffraction), TEM (transmission electron microscopy), DRIFTS (diffusion reflectance infrared Fourier transform spectroscopy), FTNIR (Fourier transform near-infrared), UV-vis, normal Raman spectroscopy, and surface-enhanced Raman scattering (SERS). XRD and TEM analysis have shown that the magnetic nanoparticles (nonmodified and modified) present diameters in the range of 10-15 nm. DRIFTS measurements have shown that the carboxylate groups of soybean and castor oil fatty acids adsorb on the ferrite surface, forming three different structures: a bridging bidentate, a bridging monodentate, and a bidentate chelate structure. The FTIR and Raman spectra of nonmodified Fe 3 O 4 and CoFe 2 O 4 nanoparticles have shown that the number of observed phonons is not compatible with the expected O h 7 symmetry, since IR-only active phonons were observed in the Raman spectra and vice versa. SERS measurements of a CoFe 2 O 4 thin film on a SERS-active gold electrode at different applied potentials made possible the assignment of the signals near 550 and 630 cm -1 to Co-O motions and the signals near 470 and 680 cm -1 to Fe-O motions.

This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than -0.4 V vs a Pt quasireference electrode (PQRE). In the -0.4 to -1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than -1.0 V some imidazolium ring vibrational modes and N-CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <-2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than -0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag-N bond. In the -0.9 to -1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <-1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near -2.4 V. The Ag electrode has presented SERS activity from 0.0 to -3.0 V.

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The SERS and SERSS effects of methylene blue (MB) adsorbed on a silver electrode have been investigated. SER and SERR spectra at monolayer and multilayer conditions have shown experimental evidences for the monomer adsorption. Contrary to previous reports, the in situ SERR spectra of MB adsorbed on a silver electrode with MB in solution were observed using confocal Raman microscopy, which avoids the strong fluorescence background from MB in solution. It has been observed that the relative Raman intensities of the adsorbed species (monomer and dimer/aggregates) are wavelength dependent and also dependent on the characteristics of the film, multi-or monolayer film, and on the applied potential. The monolayer condition and exciting at resonance or close to it cause the enhancement of the monomer signal, characterized by the feature at ∼481 cm -1 . Models for monomer, dimer, or MB aggregates as adsorbed on the electrode surface have also been presented and used to discuss the effect of laser excitation on the monomer/dimer (or aggregates) equilibrium at the electrode surface.

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