Titanium (IV) Oxide Nanotubes in Design of Active SERS Substrates for High Sensitivity Analytical Applications: Effect of Geometrical Factors in Nanotubes and in Ag-n Deposits

In this chapter, we summarize the results of recent investigations into TiO2 nanotubular oxide layers on Ti metal loaded with Ag nanoparticles, which act as efficient surface plasmon resonators. These Ag-n/TiO2 NT/Ti composite layers appear to be useful as platforms for precise surface analytical investigations of minute amounts of numerous types of organic molecules: pyridine (Py), mercaptobenzoic acid (MBA), 5-(4-dimethylaminobenzylidene) rhodamine (DBRh) and rhodamine (R6G); such investigations are known as surface enhanced Raman Spectroscopy (SERS). Geometrical factors related to the nanotubes and the silver deposit affect the SERS activity of the resulting composite layers. The results presented here show that, for a carefully controlled amount of Ag-n deposit located mainly on the tops of titania nanotubes, it is possible to obtain high-quality, reproducible SERS spectra for probe molecules at an enhancement factor of 105–106. This achievement makes it possible to detect organic molecules at concentrations as low as, e.g., 10−9 M for R6G molecules. SEM investigations suggest that the size of the nanotubes, and both the lateral and perpendicular distribution of Ag-n (on the tube tops and walls), are responsible for the SERS activity. These features of the Ag-n/TiO2 NT/Ti composite layer provide a variety of cavities and slits which function as suitable resonators for the adsorbed molecules

Nanomaterials for Surface Enhanced Raman Spectroscopy

For many decades, Raman spectroscopy has been disregarded as an ineffective analytical tool because of the very low efficiency of “normal” Raman scattering (the typical cross-section for Raman scattering is about 11 and 8 orders of magnitude smaller than the typical cross-sections for absorption in ultraviolet and infrared wavelengths, respectively [...

Raman study on methanol partial oxidation and oxidative steam reforming over copper

In situ Raman spectra of copper surfaces during the catalytic partial oxidation of methanol and methanol oxidative steam reforming have been measured and analysed. Raman measurements reveal that if methanol is present in the surrounding gas phase the ratio of quantities of CuO and Cu2O at the surface of the catalysts decreases at lower temperature. From changes in relative intensity of the band at about 220 cm-1, which is symmetry forbidden and is interpreted as an indicator of poor crystallinity and non-stoichiometry of Cu2O, we noticed that the defect density in crystal lattices of Cu2O at the surfaces of catalysts is significantly different for various reaction conditions. Methoxy species were detected as intermediates via characteristic small nu, Greek(C–O) Raman band at 1070 cm-1

Substrates for Surface-Enhanced Raman Scattering Formed on Nanostructured Non-Metallic Materials: Preparation and Characterization

The efficiency of the generation of Raman spectra by molecules adsorbed on some substrates (or placed at a very close distance to some substrates) may be many orders of magnitude larger than the efficiency of the generation of Raman spectra by molecules that are not adsorbed. This effect is called surface-enhanced Raman scattering (SERS). In the first SERS experiments, nanostructured plasmonic metals have been used as SERS-active materials. Later, other types of SERS-active materials have also been developed. In this review article, various SERS substrates formed on nanostructured non-metallic materials, including non-metallic nanostructured thin films or non-metallic nanoparticles covered by plasmonic metals and SERS-active nanomaterials that do not contain plasmonic metals, are described. Significant advances for many important applications of SERS spectroscopy of substrates based on nanostructured non-metallic materials allow us to predict a large increase in the significance of such nanomaterials in the near future. Some future perspectives on the application of SERS substrates utilizing nanostructured non-metallic materials are also presented