Showing papers by "Pedro H. C. Camargo published in 2013"

A Facile Approach to TiO2 Colloidal Spheres Decorated with Au Nanoparticles Displaying Well-Defined Sizes and Uniform Dispersion

Abstract: This paper describes a straightforward approach for the synthesis of hybrid materials composed of titanium dioxide (TiO(2)) colloidal spheres decorated with gold nanoparticles (Au NPs). In the reported method, monodisperse TiO(2) colloidal spheres (∼220 nm in diameter) could be directly employed as templates for the nucleation and growth of Au NPs over their surface using AuCl(4)(-)(aq) as the Au precursor, ascorbic acid as the reducing agent, PVP as the stabilizer, and water as the solvent. The Au NPs presented a uniform distribution over the TiO(2) surface. Interestingly, the size of the Au NPs could be controlled by performing sequential reduction steps with AuCl(4)(-)(aq). This method could also be adapted for the production of TiO(2) colloidal spheres decorated with other metal NPs including silver (Ag), palladium (Pd), and platinum (Pt). The catalytic activities of the TiO(2)-Au materials as a function of composition and NPs size were investigated toward the reduction of 4-nitrophenol to 4-aminophenol under ambient conditions. An increase of up to 10.3-fold was observed for TiO(2)-Au relative to TiO(2). A surface-enhanced Raman scattering application for TiO(2)-Au was also demonstrated employing 4-mercaptopyridine as the probe molecule. The results presented herein indicate that our approach may serve as a platform for the synthesis of hybrid materials containing TiO(2) and metal NPs displaying well-defined morphologies, compositions, and sizes. This can have important implications for the design of TiO(2)-based materials with improved performances for photocatalysis and photovoltaic applications.

Triangular metal nanoprisms of Ag, Au, and Cu: Modeling the influence of size, composition, and excitation wavelength on the optical properties

Abstract: We describe herein a systematic investigation on the optical properties of Ag, Au, and Cu triangular nanoprisms as a function of size and excitation wavelength using the discrete dipole approximation. Specifically, the edge length was varied from 40 to 100 nm while the thickness was kept at 10 nm. In the far field, our results suggest that the in-plane localized surface plasmon resonance (LSPR) peaks red-shifted as the edge length increased. In the near field, the magnitude of the electric fields generated close to the surface of the nanoprisms were calculated considering 514, 633, and 785 nm as the excitation wavelengths. The variation on the magnitude of the electric fields can be understood based on the matching between the excitation wavelength and the position of the in-plane dipole and quadrupole LSPR modes. We believe that these results can have important implications in the design of metal nanoprisms for plasmonic applications.

Emeraldine Salt Form of Polyaniline as a Probe Molecule for Surface Enhanced Raman Scattering Substrates Excited at 1064 nm

Abstract: Associating polyaniline and metallic nanoparticles may result in the combination/synergism of properties, which have been attracting great attention This paper describes an investigation that veri

Size-controlled synthesis of silver micro/nanowires as enabled by HCL oxidative etching

Abstract: The polyol method has been widely employed for the synthesis of uniform silver nanowires (Ag NWs) in high yields. In this article, we describe the utilization of HCl oxidative etching as an effective strategy to control the width of Ag NWs produced by the polyol approach. More specifically, the width of the produced Ag NWs could be tuned from 65 to 765 nm by varying the HCl concentration in the polyol recipe. Our results indicate that the obtained widths displayed a linear and steady increase according to the HCl concentration employed in the reaction. Although the width was also dependent on other experimental parameters such as the AgNO3 and polyvinylpirrolidone (PVP) concentrations and temperature, the HCl oxidative etching enabled the controlled synthesis of Ag NWs over the widest range of widths. The size-dependent optical property investigations revealed that the transverse mode surface plasmon resonance peak for the produced Ag NWs red-shifted from 378 to 467 nm as their width increased from 77 to 584 nm. The application of Ag NWs (77 nm) as SERS substrates for the detection of 4-mercaptopyridine was also demonstrated. As the properties of metal nanostructures are strongly dependent upon size, the results reported herein can have important implications for designing the synthesis of uniform Ag NWs in high yields displaying controlled and/or desired dimensions for applications in areas including plasmonics, electronics, and sensing.

Investigating the influence of the interface in thiol-functionalized silver-gold nanoshells over lipase activity.

Abstract: We employed thiol-funcionalized AgAu nanoshells (AgAu NSs) as supports for the covalent attachment of lipases (BCL, Burkholderia cepacia lipase; PPL, pancreatic porcine lipase). Specifically, we were interested in investigating the effect of the nature/size of the spacer in AgAu NSs-functionalized organic thiols over the covalent attachment of lipases. The catalytic performance of AgAu-lipase systems was measured in the kinetic resolution of (R,S)-1-(phenyl)ethanol via a transesterification reaction. In comparison to free BCL, the lipase attached to AgAu NSs using a small spacer such as cysteamine or mercaptoacetic acid, with the largest spacer mercaptoundecanoic acid, had the fastest conversion rate. The recycling potential for BCL was investigated. After three reaction cycles, the enzyme activity was kept at around 90% of the initial value. The results described herein show that the size of the spacer plays an important role in optimizing lipase activities in metallic nanoshells as solid supports.