Marcela M. Oliveira

V2O5 nanoparticles obtained from a synthetic bariandite-like vanadium oxide: synthesis, characterization and electrochemical behavior in an ionic liquid.

Highly stable and crystalline V(2)O(5) nanoparticles with an average diameter of 15 nm have been easily prepared by thermal treatment of a bariandite-like vanadium oxide, V(10)O(24) x 9 H(2)O. Their characterization was carried out by powder X-ray diffractometry (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopies, and transmission electron microscopy (TEM). The fibrous and nanostructured film obtained by electrophoretic deposition of the V(2)O(5) nanoparticles showed good electroactivity when submitted to cyclic voltammetry in an ionic liquid-based electrolyte. The use of this film for the preparation of a nanostructured electrode led to an improvement of about 50% in discharge capacity values when compared with similar electrodes obtained by casting of a V(2)O(5) xerogel.

Thin and transparent films of graphene/silver nanoparticles obtained at liquid–liquid interfaces: Preparation, characterization and application as SERS substrates

We report here the synthesis and characterization of transparent and homogeneous thin films of reduced graphene oxide/silver nanoparticles (rGO/AgNPs) nanocomposites, starting from graphene oxide (GO) or reduced graphene oxide (rGO), directly obtained at a water/toluene liquid-liquid interface. Different films (obtained by varying the Ag/rGO or Ag/GO ratio) were prepared, deposited over glass or plastic substrates, and characterized by X-ray diffraction, UV-Vis and Raman spectroscopy, thermal analysis, transmission and scanning electron microscopy. Samples were evaluated as substrates for surface-enhanced Raman spectroscopy (SERS), using dilute solutions (1×10(-7) mol L(-1)) of a common probe molecule, 4-aminothiophenol (4-ATP). These materials exhibit significant high-quality SERS activity, and enhanced modes could be observed for 4-ATP, which suggested that charge transfer occurred between the Ag nanoparticles and 4-ATP molecules.

One material, multiple functions: graphene/Ni(OH)2 thin films applied in batteries, electrochromism and sensors

Different nanocomposites between reduced graphene oxide (rGO) and Ni(OH)2 nanoparticles were synthesized through modifications in the polyol method (starting from graphene oxide (GO) dispersion in ethylene glycol and nickel acetate), processed as thin films through the liquid-liquid interfacial route, homogeneously deposited over transparent electrodes and spectroscopically, microscopically and electrochemically characterized. The thin and transparent nanocomposite films (112 to 513 nm thickness, 62.6 to 19.9% transmittance at 550 nm) consist of α-Ni(OH)2 nanoparticles (mean diameter of 4.9 nm) homogeneously decorating the rGO sheets. As a control sample, neat Ni(OH)2 was prepared in the same way, consisting of porous nanoparticles with diameter ranging from 30 to 80 nm. The nanocomposite thin films present multifunctionality and they were applied as electrodes to alkaline batteries, as electrochromic material and as active component to electrochemical sensor to glycerol. In all the cases the nanocomposite films presented better performances when compared to the neat Ni(OH)2 nanoparticles, showing energy and power of 43.7 W h kg−1 and 4.8 kW kg−1 (8.24 A g−1) respectively, electrochromic efficiency reaching 70 cm2 C−1 and limit of detection as low as 15.4 ± 1.2 μmol L−1.

The effect of different chemical treatments on the structure and stability of aqueous dispersion of iron- and iron oxide-filled multi-walled carbon nanotubes

The effect of five different chemical treatments (HNO3, H2SO4, H2O2, HNO3 + H2SO4 and HNO3 + HCl) on the homogeneity, surface chemistry, structure and dispersibility in water of iron- and iron oxide-filled multi-walled carbon nanotube samples was evaluated by X-ray diffractometry (XRD), Raman, UV-Visible and X-ray photoelectron (XPS) spectroscopies, thermogravimetric analysis (TG) and scanning electron microscopy (SEM). The results indicate that the chemical treatments are generally effective in removing non-nanotube carbonaceous species present in the sample. With the exception of the H2O2 treatment, the chemical treatments also offer good removal of free iron-species. Besides the increase in the sample homogeneity, the chemical treatments promoted an increase in the carboxyl and hydroxyl groups at the carbon nanotube surface, what directly affects the dispersibility of these carbon nanotubes in water. Dispersions of 2.24 × 10-1 g L-1 were obtained for the treated samples with a mixture of nitric and sulfuric acid.

Nickel nanoparticles with hcp structure: Preparation, deposition as thin films and application as electrochemical sensor.

Hexagonal close packed (hcp) nickel nanoparticles stabilized by polyvinylpyrrolidone (PVP) were synthesized through the thermal treatment of face centered cubic (fcc) nickel nanoparticles. Controlling both the temperature of the heat treatment and the amount of PVP was possible the control of the hcp/fcc rate in the samples, where the higher Ni/PVP ratio produces only the hcp-nickel phase (average size of 8.9 nm) highly stable in air. The crystalline structure, the presence of PVP, the size of the nanoparticles and the stability of the hcp-nickel were confirmed using X-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy, Raman spectroscopy, scanning electron microscopy and thermogravimetric analysis. Thin films of hcp and fcc nickel nanoparticles were prepared through a biphasic system and deposited over indium-doped tin oxide (ITO) substrates, which were electrochemically characterized and applied as glycerol amperometric sensors in NaOH medium. Parameters as the number of cycles applied and the scan rate were evaluated and indicate that hcp nickel nanoparticles are more reactive to form Ni(OH)2 and lead to more electroactive Ni(OH)2 structure. The hcp nickel nanoparticles-modified electrode showed the best sensitivity (0.258 μA L μmol(-1)) and detection limit (2.4 μmol L(-1)) toward glycerol.

Nanoestruturas de carbono (nanotubos, grafeno): Quo Vadis?

We describe general considerations about the present and the future standing of carbon nanostructures, mainly carbon nanotubes and graphene. Basic concepts and definitions, select structure/property relationships, and potential applications are reviewed. The analysis of the global market for these nanostructures, the commercial products available currently, the role of the chemistry, the main challenges remaining and a brief view of the field in Brazil are also presented and discussed.