FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behavior of the highly fluorescent anthraquinone dye alizarin on Ag colloids prepared by chemical reduction with hydroxylamine hydrochloride. The SERS spectra were obtained at different conditions of pH, excitation wavelength and pigment concentration in order to deduce the adsorption mechanism of this molecule. On the basis of the results found we propose an adsorption model for alizarin, which has a different acidic behavior on the metal surface to that in solution. On the metal the deprotonation order of the OH groups changes with respect to the aqueous solution, the OH in position 1 being the first to be ionized instead of that in position 2 as occurs in solution. The two main alizarin forms identified on the metal surface correspond to the mono-and dianionic alizarin species.

Trace detection of polycyclic aromatic hydrocarbons is reported in this work on dithiocarbamate calix[4]arene functionalized Ag nanoparticles by using surface-enhanced Raman scattering (SERS). SERS spectra informed about the existence of the pollutant by measuring its characteristic fingerprint vibrational features. In addition, SERS revealed important structural information from both the host and the analyte which was crucial to understand and deduce the host-guest interaction mechanism. The effectiveness of this system was checked for a group of PAHs: pyrene, benzo[c]phenanthrene, triphenylene, and coronene. From the analyzed results, the affinity constants and the limit of detection were deduced for each pollutant.

We report in this work the fabrication, for the first time, of silver nanostars (AgNS) by a simple new method consisting of the chemical reduction of Ag + by neutral hydroxylamine, followed by a capping−reduction process induced by citrate. TEM and SEM were employed to study the morphology of the resulting nanoparticles, which exhibit a star-shaped morphology with a central particle provided with several arms or protuberances with low sharpness in the vertices. Dark field microscopy was employed to study the scattering emission of individual nanostars indicating the increasing presence of nanoparticles with scattering emission toward the red region. AgNS displayed a high performance in surface-enhanced Raman scattering (SERS) applications. The effectiveness of these nanoparticles was probed by using the drug probenecid, leading to intense SERS spectra without the addition of aggregation agents.

The functionalization of silver nanoparticles (Ag NPs) by viologen dications (VGDs) is reported in this work as well as their applications in the surface-enhanced Raman scattering (SERS) detection of polycyclic aromatic hydrocarbons (PAHs). VGDs are able to form intermolecular cavities at interparticle junctions (SERS hot spots) where the analyte can be allocated. This leads to a giant intensification of the Raman emission of the target molecule. This effect was applied in the detection of PAHs, one of the most widespread and dangerous group of pollutants existing in the atmosphere and waters. A comparison between sensing-systems based on different VGDs (lucigenin, diquat, and paraquat) was done for the detection of two PAHs (pyrene and benzo[c]phenanthrene). The functionalization with lucigenin (LG) provided the most powerful and stable VGD-NPs sensor, which allowed the SERS detection of pyrene (PYR) down to 10(-9) M in the macro setup and in the zeptomole range for spectra obtained by single NPs aggregates (micro setup). Besides, SERS spectra afforded important structural information about the interaction mechanism of VGD and PAHs, revealing the formation of a CT complex between the VGD and PYR and changes in the host conformation. The position of the nu(Ag-Cl) band and the plasmon resonance contribution assigned to Ag dimers were also used as spectral markers to monitor the host-guest interaction.

The thermal evolution of amorphous TiO2 powders, consisting of spherical particles and prepared by hydrolysis of a titanium ethoxide aerosol, was studied by using Raman spectroscopy. On calcination at 350°C, the solid crystallized, giving anatase as a major phase. A small amount of rutile was also detected and attributed to small seeds localized at the particle outlayer. The nucleation of rutile at so low a temperature was ascribed to the presence of organic impurities in the powders. The transformation of anatase into rutile was clearly observed after heating at 660°C.