Josué M. Gonçalves

Electrode materials based on α-NiCo(OH)2 and rGO for high performance energy storage devices

Described herein is a composite material based on reduced graphene oxide (rGO) and α-NiCo(OH)2 nanoparticles exhibiting very fast charge/discharge processes, like that in capacitors combined with the high energy density of batteries, suitable for application to high performance energy storage devices. NiCo@rGO showed a superior performance compared to stabilized α-Ni(OH)2 and α-NiCo(OH)2 nanoparticles and Ni@rGO, the analogous composite of the former with rGO. In the nanocomposite, each rGO sheet is decorated with stabilized nickel–cobalt hydroxide nanoparticles conferring specific capacitances as high as 1300 F g−1 and discharge rates superior to 100 A g−1. This nanomaterial is also demonstrated to be remarkably stable, retaining up to 96% of its maximum capacitance after 5000 galvanostatic charge/discharge cycles.

Fast and reliable BIA/amperometric quantification of acetylcysteine using a nanostructured double hydroxide sensor

This study reports the preparation and characterization of nickel/lead hydroxide nanoparticles used to construct electrochemical sensors, which were investigated for amperometric quantification of N-acetylcysteine (NAC). The newly synthesised material presents good uniformity, with the lead (II) ions homogenously incorporated into the alpha nickel hydroxide crystal structure, confirmed by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy analyses. Films of nanoparticles (3 nm in size) were prepared on conductive fluorine-doped tin oxide-coated glass slides and used connected to a specially built batch injection analysis (BIA) cell with a capacity of only 4 mL and the electrode positioned in the bottom. To attain optimal analytical performance, the main parameters for BIA measurements (volume injected, different velocities of injection and best distance of the pipette from the electrode) were evaluated, as was the working potential, to determine the optimal conditions. Linear responses were obtained for the concentration range from 20 to 220 μmol L-1, and the limits of detection (3σ/slope) and quantification (10σ/slope) were calculated as 0.23 μmol L-1 and 0.70 μmol L-1, respectively. The new NAC sensor does not exhibit a memory effect and has enormous potential utility in the quantitative determination of N-acetylcysteine in drugs. The results of the analysis of NAC obtained using BIA presented good concordance with those obtained by chromatography. The analytical frequency attained using BIA (120 analysis h-1) compares very favourably with the one obtained using chromatography (6 analysis h-1).

Thiosemicarbazone@Gold nanoparticle hybrid as selective SERS substrate for Hg 2+ ions

The Raman spectral profile of p-methylcarbohydrazonethioamide (MCHT) is completely changed due to strong SERS effects upon bonding onto gold nanoparticles surface, but some vibrational modes are further enhanced in the presence of Hg(II) ions. The lack of SERS response for most common metal ions indicates that the coordinating groups are interacting with the gold nanoparticles surface and not available for binding metal ions in solution, except for mercury ions. The selective enhancement of some vibrational modes is consistent with significant conformational changes upon binding of Hg(II) ion onto the AuNP@MCHT hybrid, as confirmed by TEM/EDS measurements, demonstrating its potentiality as a highly selective and sensitive SERS substrate.