SERS active Ag–SiO₂ nanoparticles obtained by laser ablation of silver in colloidal silica

Abstract

Highly stable Ag–SiO2 nanoparticle composites were first obtained by laser ablation of a silver target in an aqueous colloidal dispersion of silica and examined by UV–vis absorption spectroscopy, transmission electron microscopy and Raman spectroscopy. The surface enhanced Raman scattering (SERS) activity of these nanocomposites was tested using 2,2’-bipyridine as a molecular reporter and excitation in the visible and near-IR spectral regions. The computational DFT approach provided evidence of ligand adsorption on positively charged adatoms of the silver nanostructured surface, in a very similar way to the metal/molecule interaction occurring in the corresponding Ag(I) coordination compound.

A DFT Approach to the Surface-Enhanced Raman Scattering of 4-Cyanopyridine Adsorbed on Silver Nanoparticles

“…This level of calculation reproduces the red-shifts of the wavenumbers of modes 1 and 6a, recorded at 784 and 468 cm −1 , respectively, in the solution Raman spectrum, with respect to those in pyridine (1005 and 618 cm −1 , respectively), as expected in monosubstituted benzene-like derivatives [47,48]. On the other hand, the presence of chloride in the colloidal solution induces an overall enhancement of the SERS spectrum with well-defined bands, as can be seen when it is compared with the recorded without chloride, as a result of the well-known process of chloride activation [49,50,51]. Actually, chloride anions added to our silver colloids are strongly adsorbed on the metal surface, provoking a marked particle dispersion due to the repulsion between the negative charges (Figure S1), along with the formation of active sites (adatoms) on the silver surface able to give rise to metal/ligand complexes with strong SERS enhancement.…”

Estudio SERS de nanopartículas de Ag-SiO2 sintetizadas mediante fotodeposición y agitación

“…En la figura 2a se muestra el espectro de absorción óptica de las NPs SiO 2 antes de ser decoradas con Ag, donde se observa claramente una banda en 237 nm característico del dióxido de silicio nanoestructurado [26] y ha sido relacionado con la deficiencia de oxígeno en la red amorfa de la sílice [27,28]. En la figura 2b se muestra la absorción óptica de las NPs Ag-SiO 2 después de 30, 60 y 90 minutos de fotodeposición, donde se observa una banda de absorción en 435 nm originado por la resonancia de los plasmónes superficiales de las NPs Ag [21,[29][30][31]. Se observa que la altura de la banda se incrementa conforme el tiempo de fotodeposición aumenta, lo que se explica fácilmente ya que se ha depositado mayor concentración de NPs Ag y eso genera mayor absorción óptica de acuerdo con la ley de Lambert-Beer.…”

Palladium Oxide Nanoparticles: Preparation, Characterization and Catalytic Activity Evaluation

“…All parameters were let free to relax and all calculations converged toward optimized geometries corresponding to energy minima, as revealed by the lack of negative values in the frequency calculation. A scaling factor of 0.98 for the calculated harmonic wavenumbers was employed, as usually performed in calculations at this level of theory [32][33][34][35][36].…”