RESUMO

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.

Assuntos

Ouro/química , Nanopartículas Metálicas/química , Titânio/química , Coloides/síntese química , Coloides/química , Tamanho da Partícula , Povidona/química , Propriedades de Superfície

RESUMO

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 AgNO(3) 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.