The optimization of the poor heat transfer characteristics of fluids conventionally employed in solar devices are at present one of the main topics for system efficiency and compactness. In the present work we investigated the optical and thermal properties of nanofluids consisting in aqueous suspensions of single wall carbon nanohorns. The characteristics of these nanofluids were evaluated in view of their use as sunlight absorber fluids in a solar device. The observed nanoparticle-induced differences in optical properties appeared promising, leading to a considerably higher sunlight absorption. We found that the thermal conductivity of the nanofluids was higher than pure water. Both these effects, together with the possible chemical functionalization of carbon nanohorns, make this new kind of nanofluids very interesting for increasing the overall efficiency of the sunlight exploiting device.

Several antimony-and antimony-platinum-doped tin dioxide electrodes supported on titanium have been characterized by X-ray photoelectron spectroscopy (XPS) for surface analysis and secondary-ion mass spectrometry (SIMS) for in-depth profile analysis. The surface analysis of the freshly prepared electrodes indicates that the Sb/Sn ratio in the electrode surface is similar to the nominal composition in the precursor solution, but the amount of Pt is higher than this nominal composition. The presence of platinum also produces the segregation of Sb near the electrode surface. The anodic polarization treatment of the electrode produces changes in its chemical state. The growth of a passivating hydroxide in the outer layer is the main cause of the deactivation of Ti/SnO 2 -Sb electrodes. The introduction of platinum in the layer prevents the hydroxide formation and modifies the deactivation mechanism of the electrode. The growth of an isolating TiO 2 between the support and the active oxide produces the deactivation of Ti/SnO 2 -Sb-Pt electrodes.

In the recent years, great interest has been devoted to the unique properties of nanofluids. The dispersion process and the nanoparticle suspension stability have been found to be critical points in the development of these new fluids. For this reason, an experimental study on the stability of water-based dispersions containing different nanoparticles, i.e. single wall carbon nanohorns (SWCNHs), titanium dioxide (TiO2) and copper oxide (CuO), has been developed in this study. The aim of this study is to provide stable nanofluids for selecting suitable fluids with enhanced thermal characteristics. Different dispersion techniques were considered in this study, including sonication, ball milling and high-pressure homogenization. Both the dispersion process and the use of some dispersants were investigated as a function of the nanoparticle concentration. The high-pressure homogenization was found to be the best method, and the addition of n-dodecyl sulphate and polyethylene glycol as dispersants, respectively in SWCNHs-water and TiO2-water nanofluids, improved the nanofluid stability.

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