SWNTs have been efficiently grown on patterned substrates, for its subsequent application to the development of ionizing radiation sensors. SWNTs before and after exposure to X-rays were characterized by Raman and XPS spectroscopy, revealing the appearance of alterations that have been justified as possibly due to the presence of adsorbed oxygen species. These materials have been used for the fabrication of a sensor prototype that has shown a quasi-linear behavior as a function of the time of exposure to X-ray radiation.

No abstract

Photocatalytic water splitting with generation of hydrogen is a green process that concerns activity of a semiconductor material under sunlight irradiation and ambient pressure and temperature. This process has been regarded as a promising solution to resolve the global energy and environmental problems. In this research, photocatalytic hydrogen generation by water splitting, H2O (l) → H2 (g) + 1/2 O2(g), has been studied on photocatalysts based on mixed oxide solid solutions (ZnCdFeCuS), synthesized by coprecipitation of different metal precursors.  Iron and copper nanoparticles were incorporated as cocatalysts to enhance the photocatalytic activity of the ZnCd solid solution. The effect of the different synthesis parameters, including temperature, elemental atomic ratios, amount of S, Cu and Fe incorporated in the catalyst, and calcination temperature, on the photocatalytic production of hydrogen has been studied in order to determine the best experimental synthesis conditions. The catalysts have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and BET. The experiments of photocatalytic water splitting were performed in aqueous solution of the photocatalysts. Before use, the catalysts were either activated under a nitrogen flow of 300 mL min-1 at different temperatures (400, 700 and 900°C) for 2 hours. In all cases, the photocatalytic activity was measured by dispersing 50 mg of the catalyst in deionized water in an ultrasound bath at room temperature and atmospheric pressure containing 0.5 M Na2S and 0.03 M Na2SO3 as sacrificial reagents. The catalytic peak for the overall water splitting reaction occurs in a short pH range, typically 4-5.2 and for this reason, solutions were pH-adjusted. The reaction mixture was purged with N2(g) for 30 min and after that evacuated several times to completely remove the air prior the irradiation process. The water splitting reaction was conducted in a quartz reactor equipped with a water-cooling jacket. The reaction mixtures were irradiated at different light wavelengths (from 220 to 700 nm) using a solar simulator and appropriate cutoff filters in a static air atmosphere. The evolved gases were analyzed by GC-TCD, using N2 as carrying gas.