Suchergebnisse

A bottom-up approach based on hydrothermal carbonization of organic molecules has been used to prepare carbon materials doped with either nitrogen or sulfur or both. To generate mesopores, ZnCl2 has been used as removable structure-directing agent. The final mean pore size depended on the type of dopant element. The doped materials exhibited remarkable activity as electrocatalyst in oxygen reduction reaction with nearly complete selectivity to H2O2 synthesis. N-doped catalyst with an intermediate nitrogen content (4 wt%) and around 80% of pore volume in the mesopore range provided significantly better performance than a catalyst of comparable composition but differing in the porous structure, i.e. 70 % of pore volume in the microporous range. ; The financial support of European Commission (FREECATS project, FP7 Grant agreement nº 280658), from Spanish Ministry MINECO and the European Regional Development Fund (project ENE2013-48816-C5-5-R), and Regional Government of Aragon (DGA-ESF-T66 Grupo Consolidado) are gratefully acknowledged. ; Peer reviewed

2 figures.-- Work presented at the HeteroNanoCarb Conference 2017, 11th-15th December, Benasque (Spain). ; It is of fundamental and practical significance to translate the novel physical and chemical properties of individual graphene nanosheets into the macroscale by the assembly of graphene building blocks into macroscopic architectures with control over the porous structure and functionalities. 3D graphene aerogels have some interesting properties such as high specific surface area, open porous network for ion transport, supra-flexibility, tough mechanical strength and conductive framework which lend them high potential for wide application fields such as supercapacitors, oil-water separations, sorbents, chemical reactor platforms and solar cells.[1-2] One way to prepare 3D aerogels is starting from GO sols and its gelation under hydrothermal conditions [2]. The functional groups of GO nanosheets are removed by reduction resulting in a decrease of hydrophilicity and loss of surface charges, which leads to the crosslinking of RGO nanosheets and ultimate phase separation. Herein, we have varied the hydrothermal synthesis conditions (pH, time, and freezing method) to achieve a control over the pore orientation and size of graphene aerogels. The mechanical properties of the aerogels varied from more rigid to flexible materials. In addition, we have been able to synthetize graphene aerogels with aligned channels resembling honeycomb structures (Figure 1). As a proof of concept, the materials have been tested as hydrophobic absorbents of organic compound and as support for nanodiamonds (Figure 2). The nanodiamonds supported on graphene aerogels have been tested for the selective dehydrogenation of propane providing an excellent performance. ; The financial support from Spanish Ministry MINECO and the European Regional Development Fund (project ENE2016-79282-C5-1-R) and Government of Aragon (Consolidated Group DGAT66).

6 pages, 2 tables.--Available online 7 March 2013 ; The aim of this work is to study the activity of new Pd catalysts, supported on two different nano structured carbon materials, for bromate catalytic hydrogenation. The influence of the support has been studied, obtaining the best results with a palladium catalyst supported on carbon nanofibers (CNF) grown in sintered metal fibers (SMF). The results have shown the importance of the catalyst support in order to minimize the mass-transfer limitations ensuring an efficient catalyst use. In this way the most active catalysts are those with a mesoporous structure containing high dispersed Pd nanoparticles. The activity of this catalyst for bromate reduction has been tested in different types of water, namely, distilled water, natural water and industrial wastewater. It has been shown that the catalyst activity depends on the water matrix and bromate reduction rate depends on the hydrogen partial pressure. The potential use of the catalyst has been studied in a continuous reactor. It has been observed that the catalyst is active without any important deactivation at least during 100. h of reaction, but is necessary to avoid salt precipitation and plugging problems. © 2013 Elsevier B.V. ; The authors thank the European Union (European Community's Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 226347 Project) for financial support. ; Peer Reviewed

5 Tablas, 7 Figuras.-- Material suplementario disponible en línea en la página web del editor. ; Controlling the physicochemical properties of nanoparticles in fluids directly impacts on their liquid phase processing and applications in nanofluidics, thermal engineering, biomedicine and printed electronics. In this work, the temperature dependent viscosity of various aqueous nanofluids containing carbon nanotubes (CNTs) or graphene oxide (GO), i.e. 1D and 2D nanoparticles with extreme aspect ratios, is analyzed by empirical and predictive physical models. The focus is to understand how the nanoparticle shape, concentration, motion degrees and surface chemistry affect the viscosity of diluted dispersions. To this end, experimental results from capillary viscosimeters are first examined in terms of the energy of viscous flow and the maximum packing fraction applying the Maron-Pierce model. Next, a comparison of the experimental data with predictive physical models is carried out in terms of nanoparticle characteristics that affect the viscosity of the fluid, mostly their aspect ratio. The analysis of intrinsic viscosity data leads to a general understanding of motion modes for carbon nanoparticles, including those with extreme aspect ratios, in a flowing liquid. The resulting universal curve might be extended to the prediction of the viscosity for any kind of 1D and 2D nanoparticles in dilute suspensions. ; This work has been funded by the Spanish MINEICO under the project ENE 2016-79282-C5-1-R (AEI/FEDER, UE), the Government of Aragón (Grupo reconocido T03-20R) and associated EU Regional Development Funds (DGA/FEDER, UE). SVR thanks Spanish MINEICO for her PhD grant (BES2014-068727 and associated EU Social Funds). J.M.G.-D. greatly acknowledges Spanish Ministry of Science, Innovation and Universities (MICINN, formerly MINEICO) for his "Juan de la Cierva – incorporación" grant (Ref. JCI-2016-27789). We also acknowledge institutional support from the Unit of Information Resources for Research at the "Consejo Superior de Investigaciones Científicas" (CSIC) for the article-processing charges contribution. ; Peer reviewed