Sub-micrometer distribution of Fe oxides and organic matter in Podzol horizons

The spatial distribution of soil constituents at the micrometer scale is of great importance to understand processes controlling the formation of micro-aggregates and the stabilization of organic carbon. Here, the spatial distribution of organic and mineral constituents in Podzol horizons is studied by concerted measurements of (i) the content of various forms of Fe, Al, Si and C determined by selective extraction in the fine earth fraction of soil (f < 2 mm); (ii) the elemental composition of the clay fraction (f < 2 um) with lateral resolution using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and with surface selectivity using X-ray photoelectron spectroscopy (XPS); (iii) the specific surface area (SSA) of fine earth and clay fractions by krypton physisorption. The SSA of the fine earth in illuvial horizons is predominantly due to finely divided Fe oxides, including goethite, characterized by an equivalent particle size of about 10 mu m. Kaolinite platelets of about 2 gm size account for a large volume proportion in the clay fraction but have a minor contribution to SSA. Fe oxides and organic matter (OM) are intimately associated. Heterogeneity at the um scale is created by local variations in the relative amounts of kaolinite and Fe-OM associations. These two kinds of physical entities are in random mixture. Moreover, variation of C/Fe atomic ratios reveals sub-mu m scale heterogeneity. The latter is due to variation in the relative proportion of organic compounds and Fe oxides, indicating that aggregation of nanoparticles, and not only mere adsorption or pore filling, plays a role in these associations. In this regard, our results highlight that OM associated with Fe protects Fe oxides against physical displacement and that part of this associated OM is oxidizable by NaOCl treatment. These findings demonstrate that the concept of OM stabilization through association with Fe must be revisited when considering the sub-mu m scale level because fine Fe oxide particles can be easily dispersed during oxidation of associated carbon. Combination of physical fractionation and microanalysis (e.g. SEM-EDS, vibrational spectroscopy) offer promising perspectives to clarify the relationship between chemical composition and sub-inn scale architecture, and to better understand soil processes

Influence of electrical properties on the evaluation of the surface hydrophobicity of Bacillus subtilis

The surface hydrophobicity of nine Bacillus subtilis strains in different states (spores, vegetative cells, and dead cells) was assessed by water contact angle measurements, hydrophobic interaction chromatography (HIC) and bacterial adhesion to hydrocarbon (BATH). Electrokinetic properties of B, subtilis strains were characterized by zeta potential measurements and found to differ appreciably according to the strain, Correlations between HIC data, BATH data and zeta potential showed that HIC and RATH are influenced by electrostatic interactions. Water contact angle measurements thus provide a better estimate of cell surface hydrophobicity. The water contact angle of B. subtilis varied according to the strain and the state, the spores tending to be more hydrophobic than vegetative cells. (C) 2001 Elsevier Science B.V. All rights reserved

Adhesion of Candida albicans and Candida dubliniensis to acrylic and hydroxyapatite

The aim of this work was to compare the ability of strains of Candida albicans and Candida dubliniensis to adhere to acrylic and hydroxyapatite (HAP). In order to interpret the adhesion results, the surface properties of cells and materials were determined. Surface tension components (polar and apolar) and hydrophobicity were calculated through contact angle measurement and the elemental composition was determined by X-ray photoelectron spectroscopy (XPS). The results showed no significant differences in the number of adhered cells of both species to acrylic and hydroxyapatite. This was corroborated by the similarities in their surface properties and elemental composition. For both species, the adhesion to acrylic increased in the presence of artificial saliva due to the increase in the electron-donor capacity of this material. In the absence of artificial saliva, the number of adhered cells to HAP was greater than to acrylic, on account of the higher number of electron-donor groups of HAP. Hydrophobicity played a minor role in the adhesion process of both candidal species. Conversely, Lewis acid–base interactions seamed to govern this phenomenon.Fundação para a Ciência e a Tecnologia (FCT) - BD3195/2000, Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) POCTI/BIO/42638/2001

Interpretación cuantitativa de las bandas infrarrojas oh de las micas

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La réaction inverse du gaz à l'eau en tant qu'étape intermédiaire de la production de carburant synthétique pour avion : une étude de dimensionnement de réacteur à deux échelles différentes

editorial reviewedIn the context of the energy transition and the growing imperative to develop decarbonised solutions for the transportation sector, our team is investigating the conversion of CO2 to kerosene via a Power-to-kerosene process. Given the high stability of the CO2 molecule, an activation step is essential to convert it into more complex molecules. The reverse water-gas shift (rWGS) reaction is a promising solution to achieve this conversion. A primary objective of this project is to design and construct a small pilot facility that synthesises kerosene from CO2 and H2, calibrated to an available electrolysis capacity of 1.5 Nm³/h. This study focuses on the sizing of the rWGS section for this scale and further compares it to a larger system with an electrolysis capacity 1,000 times greater

La réaction inverse du gaz à l'eau en tant qu'étape intermédiaire de la production de carburant synthétique pour avion : une étude de dimensionnement de réacteur à deux échelles différentes

peer reviewedThis paper presents a reactor model for the reverse water-gas shift reaction (rWGS) implemented in the framework of captured CO2 conversion. Kinetics are included in the model and validated with experimental data from the literature. The model is used to size a reactor at two scales: a small pilot (inlet H2 of 1.5 Nm³/h) and a mature plant (inlet H2 of 1,500 Nm³/h). The designs at both scales differ by the heating configuration; it is assumed that the small-scale unit is isothermal while the industrial-scale unit is adiabatic. For the small-scale unit, it is shown that the equilibrium conversion (65.6 %) can easily be reached within 30 cm at 1 bar. However, this reactor is not optimal for a 20-bar operation as the maximum conversion (65.2 %) is reached in the first centimetres before decreasing to 62.1 %, as methanation occurs, leading to an outlet CH4 selectivity of 17.3 %. In the large-scale adiabatic unit, both operating pressures lead to a sudden temperature drop due to the endothermic reaction followed by a temperature increase, but this latter is more important at high pressure due to methanation accentuation. This difference in the temperature profile results in a CO2 conversion of 64.8 % at 20 bar against 51.1 % at 1 bar. In summary, the equilibrium conversion in an isothermal unit is slightly higher at 1 bar, even in a reactor adequately sized for each pressure. In an adiabatic unit, the equilibrium conversion is reached within the same length for both pressures and is significantly higher at 20 bar, at the extent of an accentuated methanation