Carbon-based black pigments are a wide group of dark-colored materials, which are classified according to the starting material used and their method of manufacture. Raman spectroscopy is an ideal technique for the characterization of carbonaceous matter: crystalline carbon materials present well-defined peaks, which can be easily assigned; amorphous carbon materials, on the other hand, show broad bands between 1300 and 1600 cm À1 . The aim of this work was the discrimination between carbon-based pigments by micro-Raman spectroscopy. Five carbon-based pigments provided by Zecchi (lampblack, ivory black, bistre, bitumen, and graphite), two humic-earth materials [Van Dyck (Kremer) and Earth of Kassel (Zecchi)], and a commercial wood charcoal were studied. Raman spectra of all the samples showed the characteristic bands at approximately 1580 and 1350 cm À1 ; however, a clear difference in position, width, and relative intensity could be observed for most of the samples. The resulting analysis showed that micro-Raman spectroscopy allowed the discrimination of most of the reference pigments and allowed the identification of carbon-based black pigments in two South American colonial paintings dated from the early 18th century.
The combination of plasmonic nanoparticles and mesoporous materials is of much interest in applications such as sensing or catalysis. The production of such hybrid materials can be done in various ways, leading to different architectures. We present a comparative study of the SERS performance of different nanocomposite architectures comprising mesoporous TiO 2 thin films and Au nanoparticles (NPs). The selection of TiO 2 as mesoporous support material was based on its high chemical and mechanical stability. Au NPs of different sizes and shapes were placed at different locations of the composite and used as a plasmonic material compatible with the synthesis conditions of the mesoporous films, displaying a high chemical stability. Using pnitrothiophenol as a molecular probe, we evaluated the performance toward surface-enhanced Raman scattering (SERS) sensing, on the basis of minimum acquisition time, spot-to-spot reproducibility and limit of detection. The obtained results indicate that each platform features different sensing capabilities. While systems comprising Au NPs within the mesopores allow working with low acquisition times and present high signal uniformity, only a detection limit of μM was achieved. On the other hand, those systems made of branched Au NPs covered with mesoporous films require low acquisition times and can achieve detection limits as low as 10 pM, but signal uniformity is compromised. We propose that careful comparison of different SERS platforms based on Au NPs and mesoporous thin films will facilitate selecting an appropriate configuration for any desired application.
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