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The synthesis of resorcinol–formaldehyde (RF) xerogels is versatile enough to provide materials with custom pore size distributions in the meso-/macroporous range. Specifically, seven xerogels were synthesised by changing the pH of the same RF solution, from pH 3 to pH 6. The resulting materials presented meso-/macroporous size distributions with average pore sizes from < 5 to 510 nm, as determined by Hg intrusion and N2 adsorption. Most of the RF xerogels had very similar geometric densities, except for the gels obtained at the two highest pH values, which were more dense. Both flexural and uniaxial compression tests were carried out to determine the dependence of strength and stiffness on the porosity of the xerogels. The results followed a power-law relationship between the mechanical properties and the density of the materials. However, two series of RF xerogels were found to fit such law independently, with the gels obtained at the three most acidic pH values (pH 3–4) showing unexpectedly high compression moduli. Further characterisation of the xerogels microstructure revealed the existence of rod-like microstructures that would bear most loads during the compression tests. These microstructures would act as struts that, once broken, would cause the catastrophic failure (bursting) of the xerogel. [ABSTRACT FROM AUTHOR]

The present work deals with a new methodology to produce a sustainable carbon material through a simple synthetic route, and its performance as Ni-based electrocatalyst support. Such porous carbon was easily synthesized from the raw Kraft black liquor, a by-product rich in lignin, by chemical polymerization in alkaline medium with a nickel source and subsequent activation by CO2. Nickel nanoparticles were homogeneously distributed in the samples, as revealed by STEM images. XPS analyses and BET method indicated the presence of Ni species in the synthesized material and a micro-mesoporous structure, respectively. The electrochemical characterization in NaOH and NaOH+ ethanol solutions showed that the as-prepared material has the relevant potential to be applied as electrocatalyst for Ethanol Oxidation Reaction (EOR) in alkaline medium. [ABSTRACT FROM AUTHOR]

The air permeability of a number of commercial fibrous carbon materials: soft non-woven felts, rigidised felts and rigid boards, based on either PAN- or Rayon-derived fibres presenting various diameters, graphitised or not, and consolidated by different methods, was measured and investigated. Consistent behaviours were found within families of closely related materials, but the diversity of porous structures prevented any model, including the very popular Tomadakis–Sotirchos equation, to fit all results. The Archie's coefficient and the tortuosity factor for viscous flow were thus calculated. Not only all data were perfectly aligned on one single master curve, but the analysis was extended to many other fibrous materials and the same master curve was found to be relevant. The Archie's coefficient thus appears to be an intrinsic property, purely defined by the material geometry, as it does not depend on the 1D, 2D or 3D type of flow. A fitting equation was proposed, encompassing all fibrous materials in very broad ranges of porosities and porous structures. [ABSTRACT FROM AUTHOR]

Olive stones (OS) were submitted to hydrothermal carbonisation (HTC) in order to evaluate the possibility of producing high added-value products, mainly furfural (FU) and 5-hydroxymethylfurfural (5-HMF) on one hand and hydrochars and carbons on the other hand. Temperature (160-240 °C), residence time (1-8 h), initial pH (1-5.5) and liquid/solid ratio (4-48 w/ w) were systematically varied in order to study the main products and to optimise FU production. FU production yield up to 19.9 %, based on the hemicellulose content, was obtained. Other minor, but valuable, compounds such as 5-methylfurfural (5-MF) and some phenolic compounds were also produced. The hydrochar was carbonised at 900 °C, and the resultant carbon material was highly ultramicroporous with a peak of pore size distribution centred on 0.5 nm and a surface area as high as 1065 m g, typical of most carbon molecular sieves. [ABSTRACT FROM AUTHOR]

The possibility is shown of a directional change of the dielectric permittivity of carbon foam promising for the use in shielding devices in the microwave frequency range. The frequency dependences of the transmission (T) and reflection (R) coefficients in the Ka-band are experimentally analyzed for the foams with the reticular structure. By the methods of 3D-modeling, the effect of the skeleton conductivity and pore and windows size on the value of electromagnetic shielding provided by such a medium is considered. [ABSTRACT FROM AUTHOR]

Roxarsone is included in chicken food as anticoccidial and mainly excreted unchanged in faeces. Microorganisms biotransform roxarsone into toxic compounds that leach and contaminate underground waters used for human consumption. This study evaluated roxarsone biotransformation by underground water microorganisms and the toxicity of the resulting compounds. Underground water from an agricultural field was used to prepare microcosms, containing 0.05 mM roxarsone, and cultured under aerobic or anaerobic conditions. Bacterial communities of microcosms were characterized by PCR-DGGE. Roxarsone degradation was measured by HPLC/HG/AAS. Toxicity was evaluated using HUVEC cells and the Toxi-ChromoTest kit. Roxarsone degradation analysis, after 15 days, showed that microcosms of underground water with nutrients degraded 90 and 83.3 % of roxarsone under anaerobic and aerobic conditions, respectively. Microcosms without nutrients degraded 50 and 33.1 % under anaerobic and aerobic conditions, respectively. Microcosms including nutrients showed more roxarsone conversion into toxic inorganic arsenic species. DGGE analyses showed the presence of Proteobacteria, Firmicutes, Actinobacteria, Planctomycetes and Spirochaetes. Toxicity assays showed that roxarsone biotransformation by underground water microorganisms in all microcosms generated degradation products toxic for eukaryotic and prokaryotic cells. Furthermore, toxicity increased when roxarsone leached though a soil column and was further transformed by the bacterial community present in underground water. Therefore, using underground water from areas where roxarsone containing manure is used as fertilizer might be a health risk. [ABSTRACT FROM AUTHOR]

Roxarsone is an organoarsenical compound used as food additive in the poultry industry. Roxarsone has the potential risk to contaminate the environment, mainly by the use of poultry industry manure as fertilizer, releasing inorganic arsenic to the soil and water. The aim of this work was to isolate and characterize a bacterial consortium capable to degrade roxarsone under aerobic conditions. A bacterial consortium was cultured from a soil sample obtained from a field fertilized with poultry litter containing roxarsone. The consortium was cultured in the presence or absence of roxarsone. Roxarsone degradation and growth kinetics were determined by incubation of the bacterial consortium in the presence of roxarsone at room temperature and under aerobiosis. Both consortiums were characterized molecularly by denaturing gradient gel electrophoresis analysis and metabolically using Biolog Ecoplates. Inorganic arsenic was assessed by precipitation with silver nitrate. The consortium was also analyzed by scanning electron microscopy. The results showed that growth rate of the bacterial consortium was 1.4-fold higher in presence of roxarsone and 81.04 % of the roxarsone was transformed after 7 days of incubation. Molecular characterization revealed the presence of different bacterial groups, being alphaproteobacteria and firmicutes the groups that showed the highest count in both consortiums. The metabolic profile of the consortium did not change in the presence of roxarsone, but it showed a greater ability to oxidize amines, suggesting production of functional amines to decrease the stability of the aromatic ring resonance energy, the principal problem associated with aromatic compounds degradation. [ABSTRACT FROM AUTHOR]

Tannin-based rigid foam is an excellent alternative for other commercial foams due to price advantage, excellent fire resistance and low thermal conductivity. However, expanding its usability is restricted by its corresponding inferior mechanical properties. In the current work, we proposed a novel modification method which markedly improved its mechanical properties with respect to other approaches. The novel modification depends on boosting the foam network structure by adding oligomeric precursors (hydroxyl-terminated) of a hyperbranched poly(amine-ester) together with glutaraldehyde (crosslinker) as parts of the formulation where it was found that the compressive strength elevated remarkably and reached maximum of 37 % with respect to conventional formulation in absence of these additives or in presence of either of these additives alone. The novel modification method may show promise to obtain such materials for lower price under optimized conditions with respect to other reported modifiers due to the huge functionality of a hyperbranched polymer. [ABSTRACT FROM AUTHOR]

In the present study, we present the first steps of the development of a low power consumption GC microsystem for the analysis of benzene in the presence of butadiene, involved in petrochemical industrial applications. This system is made by coupling a low power consumption planar microhotplate based on a preconcentrator with good preconcentration capability and a spiral microchromatographic column that presents a separation capability of both compounds at room temperature, when tested in front of a gas sensor. The first characterization results of the device showed a successful injection of benzene and butadiene when placed in front of the micro-separation module. [ABSTRACT FROM AUTHOR]

New cellular activated carbons mainly derived from tannins and furfuryl alcohol are introduced and suggested as adsorbents and catalyst supports. They present a bimodal porosity, based on a highly porous, reticulated vitreous carbon backbone, whose micro/meso-porosity was developed by steam activation. The macroporosity corresponds to the connected network of cells whose average diameter is close to 250 μm. In contrast, the micro/meso-porosity is located at the inner surface of the cells and is thus fully and easily accessible. Consequently, much higher adsorption kinetics than for usual granular activated carbons are expected. A burn-off close to 30% was shown to be optimal for getting a high proportion of microporosity without complete loss of mechanical resistance. In these conditions, the surface area is close to 850 m g, thus similar to that of many commercial carbonaceous adsorbents. [ABSTRACT FROM AUTHOR]

New comparisons of percolation and effective-medium theories on one hand, and predictions from the crowding factor on the other hand, are described for calculating critical concentrations in suspensions of cellulose fibres. The connectivity threshold from percolation theory appears to correspond to the “gel crowding factor”, which occurs at crowding factor ( N) of N = 16 rather the criterion for fibre collisions, N = 1, postulated in earlier work. The rigidity threshold from percolation theory corresponds to the onset of coherent fibre flocs having mechanical network strength, which occurs at about N = 60. The latter value exceeds the gel crowding factor value by a factor of 3.75. In comparison, percolation theory predicts that flocculation occurs at a rigidity concentration four times higher than the connectivity threshold. These ratios are in good agreement. [ABSTRACT FROM AUTHOR]

The concept of crowding factor applied to the flocculation of cellulose fibres is revisited through the application of percolation and effective medium theories. It is shown that, even if the crowding factor allows predicting the critical concentration of fibre suspension above which flocculation occurs, and indeed leads to acceptable results in most cases, percolation and effective medium theories are most rigorous and much less empirical. Examples of calculation are given for fibres assumed to behave either like rigid rods or like elongated prolate ellipsoids, and compare very correctly with experimental measurements found in the literature. Finally, beyond the purely geometrical aspects, the roles of several physico-chemical parameters on the onset of flocculation are also discussed, and shown to be perfectly explained by percolation predictions. [ABSTRACT FROM AUTHOR]