Transferencia de masa en geles de carbón con porosidad a medida

[EN] Diffusional limitations in carbon gel-supported catalysts are often encountered despite their open structure. However, the analysis of mass transport is rarely taken into account in studies dealing with catalyst preparation and test using these nanostructured carbons as supports. Any catalytic system should be first subject to mass transport analysis before any conclusion can be drawn about relationships between the physico-chemical properties and the measured activity of the catalyst.[ES] Pese a su estructura abierta, a menudo se observan limitaciones difusionales en catalizadores soportados en geles de carbono. Sin embargo, en los diversos estudios de preparación y testeo de catalizadores soportados en estos materiales nanoestructurados, pocas veces se lleva a cabo un análisis de transferencia de masa. Así, antes de obtener cualquier conclusión sobre la relación entre las propiedades fisicoquímicas y la actividad de un catalizador, el sistema debería someterse a un análisis de trasporte de masa.NJ thanks the F.R.S.-FNRS (Belgium), the Fonds de Recherche Fondamentale Collective and the Ministère de la Région Wallonne (project INNOPEM n°1117490) for funding.Peer reviewe

EDLC electrodes from cellulose-based carbon aerogels : influence of the carbon surface chemistry

International audienceThis work investigates the influence of the carbon surface chemistry on the carbon's electrochemical performance if used as EDLC electrode material. Carbon aerogels were synthesized by crosslinking cellulose acetate through a non-toxic isocyanate and subsequent drying in supercritical CO2 and pyrolysis in inert atmosphere (1000°C, nitrogen atmosphere). Subsequently, the surface chemistry of the carbon aerogels was modified by oxidation (in H2O2) or by nitrogen introduction (impregnation with melamine and co-pyrolysis). Thus the carbon material's surface chemistry was modified depending on the modification method, while the morphology remained similar. All carbon samples were analyzed in terms of morphology (by nitrogen adsorption and mercury porosimetry), composition (elemental analysis), and surface chemistry (Boehm titration and pHPZC). For electrochemical analysis, carbon aerogels were tested in the form of EDLC electrodes in a symmetric test assembly in aqueous electrolyte (cyclic voltammetry and galvanostatic cycling). Results show that the carbon's capacitance can be increased by the introduction of heteroatoms. However, the type of functional groups present on the carbon surface seems to really determine capacitance as opposed to the mere presence of oxygen or nitrogen atoms

Life cycle assessment of carbon xerogels

In the framework of the SOMABAT European project, a life cycle assessment applied to the production of 1 kg of carbon xerogels was carried out by comparing three drying technologies (vacuum, microwave and convective drying). These carbon materials with controlled texture are thought to be used as active material at the anode side of Li-polymer battery.Development of novel solid materials for high power Li polymer batteries. Recyclability of components

How do the micropores of carbon xerogels influence their electrochemical behavior as anodes for lithium-ion batteries?

This work aims at shedding light on how the microporous texture of porous carbons influences their electrochemical behavior when used as anodes for Li-ion batteries. To this aim, a synthetic hard carbon (carbon xerogel, CX), prepared from a resorcinol-formaldehyde precursor gel, underwent several post-synthesis treatments in order to modulate its micropore to total pore volume ratio. The micropore volume was either expanded by physical activation or decreased using chemical vapor deposition (CVD) of a carbon layer. Several variables other than the micropore texture of the obtained carbons, which could influence their behavior as anode active materials for Li-ion batteries, such as the particle size or the electrode characteristics, were carefully controlled. The thickness of electrode coatings and the pore texture of the active material-binder composite were analyzed. It was shown that CX-binder composites resulting from water-based slurries preserve the microporosity of the starting materials. Detailed electrochemical characterization of the electrodes prepared with carbon xerogels displaying various defined micropore textures was performed. A clear linear dependency could be evidenced between the Li+ insertion and de-insertion in half-cell configuration with the increase of the volume of supermicropores (0.7 – 2 nm), demonstrating the effect of micropore enlargement by activation on the storage capacity, provided the maximum charge potential value is set at 3.0 V vs. Li+/Li

Structured carbons as supports for hydrogenation hybrid catalysts prepared by the immobilization of a Rh diamine complex

A CNF-monolith sample (carbon nanofibres grown on a ceramic monolith), and a granular carbon xerogel have been used as supports for hybrid catalysts where the active species is an Rh diamine complex. The advantages of these supports are their open porous structure and their morphology, which make catalyst handling easier and avoid difficult separation processes. The obtained catalysts are noticeably more active than the homogeneous Rh complex and are stable against leaching. At first use, partial reduction of the Rh complex takes place and nanometer-sized Rh particles develop, which increases the catalyst activity. Despite the open porous structure, mass transport limitations are present, especially in the case of the carbon xerogel based catalyst. Differences in internal mass transfer limitations are essentially due to the different diffusional path lengths.The authors thank the financial support through public projects of reference: MAT2012-32832 (Spanish Ministry of Economy and Competitiveness and FEDER) and PROMETEO/II/2014/010 (Generalitat Valenciana). C.C.G. thanks her FPU scholarship to the Spanish Ministry of Education

Adsorption process with carbon xerogel cylinders for Refractory Organic Compounds removal in water, coupled with innovative in situ regeneration by H2O2 electrogeneration

peer reviewe

To vaccinate or not to vaccinate? Perspectives on HPV vaccination among girls, boys, and parents in the Netherlands: A Q-methodological study

Background: Despite the introduction of Human papillomavirus (HPV) vaccination in national immunization programs (NIPs), vaccination rates in most countries remain relatively low. An understanding of the reasons underlying decisions about whether to vaccinate is essential in order to promote wider spread of HPV vaccination. This is particularly important in relation to policies seeking to address shortfalls in current HPV campaigns. The aim of this study was to explore prevailing perspectives concerning HPV vaccination among girls, boys, and parents, and so to identify potential determinants of HPV vaccination decisions in these groups. Method: Perspectives were explored using Q-methodology. Forty-seven girls, 39 boys, and 107 parents in the Netherlands were asked to rank a comprehensive set of 35 statements, assembled based on the health belief model (HBM), according to their agreement with them. By-person factor analysis was used to identify common patterns in these rankings, which were interpreted as perspectives on HPV vaccination. These perspectives were further interpreted and described using data collected with interviews and open-ended questions. Results: The analysis revealed four perspectives: "prevention is better than cure," "fear of unknown side effects," "lack of information and awareness," and "my body, my choice." The first two perspectives and corresponding determinants of HPV vaccination decisions were coherent and distinct; the third and fourth perspectives were more ambiguous and, to some extent, incoherent, involving doubt and lack of awareness and information (perspective 3), and overconfidence (perspective 4). Conclusions: Given the aim of publically funded vaccination programs to minimize the spread of HPV infection and HPV-related disease and the concerns about current uptake levels, our results indicate that focus should be placed on increasing awareness and knowledge, in particular among those in a modifiable phase