Robson R. Guimarães

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.

How relevant can the SERS effect in isolated nanoparticles be

Gold nanoparticles electrostatically stabilized with negatively charged ruthenium complexes were individually monitored based on their characteristic plasmon bands, by means of hyperspectral dark field microscopy. Very strong SERS enhancements were observed for the isolated gold nanoparticles at exciting wavelengths in resonance with the surface plasmon band, using confocal Raman microscopy, revealing a contrasting behaviour between the agglomerated and non-agglomerated systems. The results highlighted the relevant role played by the surface enhanced resonance Raman mechanisms (SERRS) in isolated nanoparticles, more than compensating for the lack of local hot spots, in relation to the agglomerated systems.

Gold nanoparticles functionalised with Ru–dicarboxybipyridine–trimercaptotriazine: SERS effect and application in plasmonic dye solar cells

A dicarboxybipyridine–trimercaptotriazine ruthenium complex, primarily designed for dye–sensitised solar cells (DSSC), has been successfully employed in the generation of electrostatically stabilised gold colloids, because of its high negative charge and capability of binding to gold nanoparticles via the sulphur groups. Strong SERS enhancements have been obtained for the isolated gold nanoparticles, as monitored by dark field hyperspectral and confocal Raman microscopy. A preliminary design of TiO2 solar cell incorporating the ruthenium dye in association with the gold nanoparticles, has been tested, in the presence of a cobalt complex mediator. The results were considered rather promising, in spite of the slight decay of efficiency in relation to the original dye cell, owing to lixiviation processes and electron recombination effects at the interface.

Investigation of the Photocatalytic Activity of Titanium Dioxide Films Under Visible Light Measured by Electrospray Mass Spectrometry

We report, for the first time, the photocatalytic activity of pure TiO2 P-25 in the form of thin homogeneous mesoporous films under visible light activation. The study was accomplished by analyzing the photodegradation rate of two water contaminant molecules, 2-naphthol and methyl orange, via an electrospray mass spectrometry technique with the use of ammonium hexafluorophosphate as an internal standard. The employed methodology can also be used to run different semiquantitative assays and study other film mediated photocatalytic processes. It was observed that TiO2 films can easily promote photooxidation of 2-naphthol under the incidence of visible light and in the presence of oxygen gas by showing almost complete photodegradation after about 6 hours of reaction. Photooxidation of methyl orange was also observed, yet the decay rate was slower. This process was also confirmed through identification of by-products of the reaction via mass spectrometry and through the decay of the absorbance peak at 468 nm via UV-vis spectrophotometry. This photoactivity of pure TiO2 P-25 films under visible light is attributed to its narrower band gap that occurs because of the thermal treatment that titania undergoes in the process of synthesis of the films. The use of these films as photocatalysts is an advantage since they work as a heterogenous catalyst in the absence of UV radiation.