K. Lobato

Annealed Ti/Zn-TiO2 nanocomposites tested as photoanodes for the degradation of Ibuprofen

Ti/Zn-TiO2 electrodes were successfully prepared by the co-deposition method, on a titanium substrate, using an acidic zinc sulphate solution with TiO2 nanoparticles in suspension. After electrodeposition, samples were heated in air at 450xa0°C for 6xa0h. The X-ray diffraction analysis of the deposits point to the metal matrix modification from Zn to ZnO. In addition, the scanning electron microscopy results indicate that the films have a high surface area with a rich morphology, due to the appearance of ZnO needle-shaped grains. The voltammograms recorded, in Na2SO4 solution, for these electrodes under illumination at λu2009=u2009365xa0nm confirmed the films photoactivity. Photoelectrochemical degradation of Ibuprofen (Ibu) was achieved with the Zn-TiO2 electrodes after thermal treatment. UV–Vis spectrometry, high-performance liquid chromatography (HPLC), chemical oxygen demand (COD) and total organic carbon (TOC) measurements were performed and data demonstrated that Ibuprofen was efficiently degraded. Absorbance at 220xa0nm, COD and TOC removals of 35%, 34% and 23%, respectively, were obtained after a 3 h period.

Comparative study of stress inducing layers to produce kerfless thin wafers by the Slim-cut technique

The decrease in wafer thickness seen as a route to cost reductions has raised a growing interest in techniques that allow the preparation of thin wafers without kerf loss. The Slim-cut process [1] is one of these new techniques and comprises mainly three stages: a stress layer deposition step on the top of a monocrystalline silicon sample, a heating step necessary to induce the stress on the silicon sample and detach a thin silicon layer, and a third step to clean the stress-inducing layer to obtain a silicon foil adapted to the fabrication of solar cells. One of the major problems of this technology consists in finding a stress layer that induces a sufficiently high contraction in order to achieve a rupture of the silicon without contamination of the foil. In this work we present a comparison between thin foils obtained by Slim-cut, using three different stress layers: i) a double screen printed Silver/Aluminum layer, ii) a dispensed epoxy paste, iii) an electrodeposited Nickel metallization. Results on lifetime measurements indicate that some of the stress layers, although capable of inducing large stress, severely degrade lifetime of the foil.

Development of the laser absorption radiation thermometry technique to measure thermal diffusivity in addition to temperature

A comparative technique based on photothermal radiometry has been developed to measure thermal diffusivity of semi-infinite targets with arbitrary geometry. The technique exploits the principle that the frequency response of the temperature modulation induced by a periodic modulated heating source (in this case a laser spot) scales with thermal diffusivity. To demonstrate this technique, a photothermal radiometer has been developed, which detects modulated thermal radiance at a wavelength of 2 μm due to a small temperature modulation induced on the target surface by a modulated erbium fiber laser of power 1 W. Two frequency responses were measured for platinum and oxidized Inconel 600 targets (the frequency response is a scan of the amplitude of the modulated thermal radiance over laser modulation frequency). Scaling the two responses with respect to frequency gives a ratio of thermal diffusivities Dplatinum/DInconel of 4.45(33) which compares with a literature value of 4.46(50). The aim is to combine thi...

The role of ethanol-water solvent mixtures in N719 sensitization of electrodeposited ZnO nanorods

Water plays an important role in N719 sensitization of ZnO films for application as photoanodes in DSC devices. The role of water content in ethanolic N719 sensitization solutions was examined resorting to N719-solvent interaction studies based on Kamlet-Taft solvatochromic parameters. Results show that as the water content increases, solvent’s HBA ability decreases, hindering dye aggregation in solution and increasing the fraction of dye carboxylic groups available for anchorage onto the charged ZnO surface. The impact of dye-dye-solvent equilibria in solution on ZnO nanorod films sensitization and device behavior was evaluated. Devices assembled with films sensitized in N719 solutions containing equal parts of ethanol and water showed a twofold increase in short-circuit current densities when compared to those sensitized in ethanol only, despite exhibiting significantly less stained films. Data indicate that the presence of water in the sensitization solution reduces the amount of dye aggregates in solution and on the ZnO surface.