Showing papers by "Helena I. S. Nogueira published in 2009"
TL;DR: In this article, the authors show that the presence of oxygen functionalities at the graphene surface provides reactive sites for the nucleation and growth of gold nanoparticles, which are effectively grown at functionalized graphene surfaces using a simple chemical method in aqueous medium.
Abstract: Graphene sheets, which possess unique nanostructure and a variety of fascinating properties, are considered as promising nanoscale building blocks of new nanocomposites, namely as a support material for the dispersion of metal nanoparticles. One of the methodologies used to prepare graphene sheets is the chemical exfoliation of graphite in aqueous medium, which produces oxygen functionalized graphene sheets. Here, we show that the presence of oxygen functionalities at the graphene surface provides reactive sites for the nucleation and growth of gold nanoparticles. Gold nanoparticles are effectively grown at functionalized graphene surfaces using a simple chemical method in aqueous medium. The nucleation and growth mechanism depends on the degree of oxygen functionalization at the graphene surface sheets, no gold nanoparticles are obtained at totally reduced graphene surfaces. Additionally, our studies indicate that the graphene/gold nanocomposites are potential substrates for SERS (surface enhanced Raman ...
838 citations
TL;DR: The findings suggest that a deeper understanding of these mechanisms is critical if the authors want to tackle the obesity epidemic, and that policies aimed at weight control and obesity reduction must address people and places in order to bear fruit.
104 citations
TL;DR: In this paper, a surface enhanced Raman scattering (SERS) spectrum was recorded on a silver colloid and the vibrational wavenumbers were computed by density functional theoretical (DFT) computations at the B3LYP/6-31G* level and they were found to be in good agreement with the experimental values.
Abstract: O acido carboxilico 2-(metoxicarbonilmetilsulfanil)-3,5-dinitrobenzeno foi preparado por substituicao nucleofilica. Seus espectros de infravermelho e Raman com transformada de Fourier foram obtidos e analisados. O espalhamento Raman intensificado pela superficie (SERS) foi obtido sobre prata coloidal. Os numeros de onda vibracionais foram computados pela teoria do funcional de densidade (DFT) com a base hibrida B3LYP/6-31G* e foram comparados com valores experimentais com boa concordância. Interacoes metal-molecula significativas foram substanciadas por um sinal Ag-O intenso nos espectros SERS, indicando a proximidade dos grupos nitro e carbonila a superficie de prata. Estudos SERS sugerem uma orientacao inclinada da molecula sobre a superficie metalica. 2-(Methoxycarbonylmethylsulfanyl)-3,5-dinitrobenzenecarboxylic acid was prepared by nucleophilic substitution. FT-IR and FT-Raman spectra of 2-(methoxycarbonylmethylsulfanyl)-3,5dinitrobenzenecarboxylic acid were recorded and analyzed. Surface enhanced Raman scattering (SERS) spectrum was recorded on a silver colloid. The vibrational wavenumbers were computed by density functional theoretical (DFT) computations at the B3LYP/6-31G* level and they were found to be in good agreement with the experimental values. Significant metal-molecule interaction has been substantiated by the appearance of intense Ag-O mode in the SERS spectrum and this is indicative of the nearness of nitro and carbonyl group to the silver surface. SERS studies suggest a tilted orientation of the molecule at the metal surface.
58 citations
TL;DR: In this article, an organic-inorganic hybrid material was prepared by combining lanthanide(III) substituted Wells-Dawson anions as inorganic building blocks and 3-hydroxypicolinate (picOH) as the organic ligand.
Abstract: Organic–inorganic hybrid materials were prepared by combining lanthanide(III) substituted Wells–Dawson anions as inorganic building blocks and 3-hydroxypicolinate (picOH) as the organic ligand. The organic–inorganic hybrids obtained Kn[Lnx(α2-P2M17O61)(picOH)7]·yH2O (MVI = W and LnIII = La, Ce, Sm, Eu, Tb, Er; or MVI = Mo and LnIII = Eu) were characterized by chemical analysis and spectroscopic methods such as FTIR and FT-Raman, 31P and 13C MAS NMR spectroscopy. Photoluminescence measurements on the prepared hybrid materials were performed showing the intra-4fN emission in the visible (EuIII, TbIII compounds) and in the near-infrared (ErIII compound) spectral regions, being, in all the cases, sensitized by both the picOH ligand and the polyoxometalate moiety. A maximum quantum yield value of 0.18 was found for K11[Eu2(α2-P2Mo17O61)(picOH)7]·10H2O.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
42 citations
TL;DR: The results show that social capital was strongly associated with self-rated health, even after an adjustment for individual attributes, and it is not possible to divorce health planning from urban planning and from the promotion of social capital.
29 citations
TL;DR: In this article, the Fourier transform infrared (FT-IR) and FT-Raman spectra of 4-ethyl-N-(2′-hydroxy-5′-nitrophenyl)benzamide were recorded and analyzed.
Abstract: Fourier transform infrared (FT-IR) and FT-Raman spectra of 4-ethyl-N-(2′-hydroxy-5′-nitrophenyl)benzamide were recorded and analyzed. A surface-enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO stretching mode gives the charge transfer interaction through a π-conjugated path. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported structures. Copyright © 2009 John Wiley & Sons, Ltd.
26 citations
TL;DR: The appearance of the Ag-O stretching mode at 237cm(-1) in the SERS spectrum along with theoretically calculated atomic charge density, leads us to suggest that the molecule is adsorbed through the oxygen atom with the molecular plane tilted on the colloidal silver surface.
16 citations
TL;DR: In this article, a core of lanthanide complexes and shells of amorphous silica using reverse micelles as nanoreactors are synthesized, and optical studies reveal that the luminescence properties of the 3-hydroxypicolinate complexes in the matrices are markedly different from their original features.
Abstract: We have synthesized luminescent nanoparticles comprising a core of lanthanide complexes and shells of amorphous silica using reverse micelles as nanoreactors. 3-Hydroxypicolinate complexes of Eu(III), Tb(III), and the corresponding heteronuclear complexes have been investigated as the photoactive cores. The size of the silica particles is within the nanometer scale, which, together with the ability for surface biofunctionalization, opens up perspectives for their use in bioapplications. Optical studies of the as-prepared nanoparticles reveal that the luminescence properties of the 3-hydroxypicolinate complexes in the matrices are markedly different from their original features.
15 citations