Effect of Surfactants on the Intensity of Raman Signals of Pyridine Chemisorbed on Gold Clusters and Graphene Oxide Article uri icon

abstract

  • We present density functional theory calculations dedicated to analyze the structure, electronic properties, and Raman spectra of two nanostructures, namely, cetyltrimethylammonium bromide (CTAB)-covered Au13 clusters and graphene oxide (GO) functionalized with CH3(CH2)15N (CH3)3 species, with both of them containing a single co-adsorbed pyridine (Py) as a probe molecule. For gold clusters, we also consider the adsorption of CTAB–propanethiol mixtures to study the stability of mixed overlayers as well as their role played on the intensity and distribution of the Py Raman active modes. The presence of surfactants on Au clusters and GO sheets strongly contributes to notable signal enhancements in the pyridine Raman spectra (when compared with isolated Py). Simulating the use of a 785 nm laser, we find that the C5H5N ring vibrations at ∼630 and 1600 cm–1 increase its activity, presenting enhancement factors (EFs) as large as 264 and 1245, respectively, with the GO substrate (Au cluster) being the most effective in increasing the intensity of the Raman lines at low (high) surfactant coverages. The previous EF values strongly depend on the degree of surface functionalization and surface chemistry, being notably quenched for CTAB–propanethiol mixed overlayers stabilized on gold clusters as well as for GO sheets with high amounts of oxygen-containing functional groups. We also explore the possibility of having charge-transfer resonance Raman effects on our calculated spectra and underline the crucial role played by the laser wavelength for measuring the Raman response of these kinds of samples. We conclude by saying that besides the well-known use of the CTAB surfactant as a phase-transfer catalyst, stabilizer, and shape-directing agent, its presence on gold clusters and GO surfaces should be taken into account in order to better understand the Raman scattering process in more complex CTAB-containing gold-graphene nanostructures. © 2021 American Chemical Society
  • We present density functional theory calculations dedicated to analyze the structure, electronic properties, and Raman spectra of two nanostructures, namely, cetyltrimethylammonium bromide (CTAB)-covered Au13 clusters and graphene oxide (GO) functionalized with CH3(CH2)15N%2b(CH3)3 species, with both of them containing a single co-adsorbed pyridine (Py) as a probe molecule. For gold clusters, we also consider the adsorption of CTAB–propanethiol mixtures to study the stability of mixed overlayers as well as their role played on the intensity and distribution of the Py Raman active modes. The presence of surfactants on Au clusters and GO sheets strongly contributes to notable signal enhancements in the pyridine Raman spectra (when compared with isolated Py). Simulating the use of a 785 nm laser, we find that the C5H5N ring vibrations at ∼630 and 1600 cm–1 increase its activity, presenting enhancement factors (EFs) as large as 264 and 1245, respectively, with the GO substrate (Au cluster) being the most effective in increasing the intensity of the Raman lines at low (high) surfactant coverages. The previous EF values strongly depend on the degree of surface functionalization and surface chemistry, being notably quenched for CTAB–propanethiol mixed overlayers stabilized on gold clusters as well as for GO sheets with high amounts of oxygen-containing functional groups. We also explore the possibility of having charge-transfer resonance Raman effects on our calculated spectra and underline the crucial role played by the laser wavelength for measuring the Raman response of these kinds of samples. We conclude by saying that besides the well-known use of the CTAB surfactant as a phase-transfer catalyst, stabilizer, and shape-directing agent, its presence on gold clusters and GO surfaces should be taken into account in order to better understand the Raman scattering process in more complex CTAB-containing gold-graphene nanostructures. © 2021 American Chemical Society

publication date

  • 2022-01-01