Surface enhanced Raman scattering of TNT and DNT on colloidal nanoparticles of Ag/TiO2

Metallic silver nanoparticles coated with titanium dioxide were synthesized via a simple route. The chemical reduction of Ag+ to Ag-o was followed with the controlled polymerization of TiO2 to produce very small size and narrow distribution of nanoparticles produced the desired TiO2/Ag colloidal suspensions. The prepared nanoparticles were characterized by UV-VIS absorption and by Energy Dispersive X-ray Spectroscopy. The spectrum of the suspension of normal Ag nanoparticles had a surface plasmon resonance peaked at 420 mn arising from particles characteristic of Ag colloidal dispersions. Similar surface plasmon absorptions due to Ag nanoparticles were observed for the suspension of Titania coated Ag nanoparticles, but at longer wavelength than for the suspension of Ag nanoparticles. This absorption shift ( +15 to +20 nm) is caused by refractive index of Titania and suggests coverage of Ag nanoparticles with Titania. TiO2/Ag colloids were used to measure Raman spectra in capillary tubes at different excitation sources to observe the enhancement of the Raman signatures of solution of TNT and DNT at different pH values. At pH = 10.3 TNT showed an increase of the NO2 stretching mode at the 1365 cm(-1) in comparison with the other pHs and the solution without colloids. In addition, the band ca. 1213 cm-1 and NO2 (1370 cm(-1)) band were shifted from their normal positions.