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Abstract: Two phosphoric acid activation procedures; Activation after Hydrothermal Impregnation (recently published) and Activation after Incipient Wetness Impregnation instead of conventional impregnation are analyzed in two natural bio-fiber precursors: banana pseudostem and coconut fiber matting. Both procedures are compared analyzing, in both precursors, the influence that variables such as H3PO4/precursor ratio, activation temperature and impregnation time have on the resulting activated carbons (ACs) properties. The work also pays special attention to the mesoporosity development and the application of these ACs to adsorb gasoline vapors. Both H3PO4 activation procedures develop activated carbons having suitable activation yields and porosity developments, giving the Activation after Incipient Wetness Impregnation method better results than the Activation after Hydrothermal Impregnation. Both natural bio-fibers are good precursors, rendering the coconut fiber matting better results than the banana pseudostem. The variables studied affect the porosity development, being precursor and H3PO4/precursor ratio the variables that most affect. By a suitable selection of these variables, activated carbons having high adsorption capacities (BET above 2500m2 g−1 and micropore volume above 1.00cm3 g−1) and well developed mesoporosity (reaching 1.41cm3 g−1), can be prepared. Most of the samples prepared perform very well for adsorbing gasoline vapors, showing a linear relationship with their resulting volumes. [Copyright &y& Elsevier]

Abstract: Hydrogen sorption properties were investigated for selected mixtures of MgH2 and carbon materials, including graphite, activated carbon, multi-walled carbon nanotubes (MWCNTs), carbon nanofibres (CNFs) and activated carbon fibres. The introduction of such carbon materials decreases the decomposition temperature of MgH2. The best results were achieved in the mixtures involving CNFs and MWCNTs, with metallic impurities, particularly nickel and iron, inherited from the original synthesis. The peak temperatures of MgH2 decomposition were reduced to 322 and 341°C, respectively, compared with 360°C for simply milled MgH2. Substantial improvement in the decomposition kinetics of MgH2 was achieved, particularly with CNF additions. The MgH2 decomposition was completed within 20min at 300°C with a 5wt.% CNF addition, compared to 240min for simply milled MgH2. The improved kinetics was maintained even after several hydriding–dehydriding cycles. X-ray diffraction and transmission electron microscopy reveal that some structural changes occur after cycling: there is an increase in particle size of the MgH2 phase, with separation between the magnesium and carbon phases, indicating a clear relationship between the decomposition temperature of MgH2 and its structure. It has also been shown that the presence of carbon materials prevents MgH2 particle growth which, in turn, enhances its decomposition. [Copyright &y& Elsevier]

Abstract: Titanium dioxide nanoparticles prepared in situ by sol–gel method were supported on a spherical activated carbon to prepare TiO2/AC hybrid photocatalysts for the oxidation of gaseous organic compounds. Additionally, a granular activated carbon was studied for comparison purposes. In both types of TiO2/AC composites the effect of different variables (i.e., the thermal treatment conditions used during the preparation of these materials) and the UV-light wavelength used during photocatalytic oxidation were analyzed. The prepared materials were deeply characterized (by gas adsorption, TGA, XRD, SEM and photocatalytic propene oxidation). The obtained results show that the carbon support has an important effect on the properties of the deposited TiO2 and, therefore, on the photocatalytic activity of the resulting TiO2/AC composites. Thus, the hybrid materials prepared over the spherical activated carbon show better results than those prepared over the granular one; a good TiO2 coverage with a high crystallinity of the deposited titanium dioxide, which just needs an air oxidation treatment at low-moderate temperature (350–375°C) to present high photoactivity, without the need of additional inert atmosphere treatments. Additionally, these materials are more active at 365nm than at 257.7nm UV radiation, opening the possibility of using solar light for this application. [Copyright &y& Elsevier]