Evolution of iron speciation during hydration of C4 AF

International audienceIt is now well accepted and demonstrated that calcium silicate, calcium aluminate and calcium sulfo aluminate (ettringite, AFm) phases exhibit a good capability to fix metals and metalloids. Unfortunately the role of minor phases and especially calcium-ferric aluminate phase, shorthand C(4)AF is not well defined. In other systems like in soils or sediments iron phases play a key role in the fixation of pollutant. In cement sorption isotherms, indicated that various metals can be retained by the C(4)AF hydrated products. Therefore the capabilities of those phase to retain heavy metal should not be neglected. Previous investigations have shown that the minerals formed during the hydration of C(4)AF are similar to those formed from C3A (pure tri-calcium aluminate) under comparable conditions. Nevertheless no investigation was conducted at the molecular level and there is still a controversy whether Fe substitutes for Al in the hydrated minerals in whole or in part, or if it forms FeOOH clusters scattered throughout the matrix. In this context we have conducted XAS experiments using synchrotron radiation. It was found that the hydration of C(4)AF forms C(3)AH(6) (hydrogarnet) in which Fe randomly substitutes for Al as well as an amorphous FeOOH phase. Intermediate products like AFm (i.e., an ill organized lamellar phase) are also formed but rapidly evolve to C(3)AH(6); iron does not seem to be incorporated in the AFm structure

Modification of the toxicity of Ge-imogolite nanotubes due to tube wall defects

International audienceThe influence of structural modifications on NM toxicity, and in particular structural defects, is poorly studied mainly because of the difficulty to modify the crystallinity of a NM without changing any other morphological parameters. In this study we used a singled-walled alumino-germanate nanotube (Ge-imogolite) as a model, for which this can be achieved. Well crystalized tubes led to moderate toxicity attributed to a direct contact with the bacteria and the generation of reactive oxygen species, whereas lacunar tubes caused more severe toxic effects without any direct contact nor ROS generation. The bacterial growth inhibition in the presence of wall defects was attributed to indirect mechanisms as their higher solubilityleading to Al or Ge ion toxicity and/or to the retention of essential nutrients on the vacancie

Modification of the toxicity of Ge-imogolite nanotubes due to tube wall defects

International audienceThe influence of structural modifications on NM toxicity, and in particular structural defects, is poorly studied mainly because of the difficulty to modify the crystallinity of a NM without changing any other morphological parameters. In this study we used a singled-walled alumino-germanate nanotube (Ge-imogolite) as a model, for which this can be achieved. Well crystalized tubes led to moderate toxicity attributed to a direct contact with the bacteria and the generation of reactive oxygen species, whereas lacunar tubes caused more severe toxic effects without any direct contact nor ROS generation. The bacterial growth inhibition in the presence of wall defects was attributed to indirect mechanisms as their higher solubilityleading to Al or Ge ion toxicity and/or to the retention of essential nutrients on the vacancie

Chemical and Structural Transformation of Aggregated Al 13 Polycations, Promoted by Salicylate Ligand

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Improved nanotube synthesis by the use of micro-waves

International audienceThe synthesis of Imogolites nanotubes is a simple aqueous sol-gel process, consisting in a partial hydrolysis of a mixture of Al and Si (or Ge) monomers followed by a growth step requiring at least 5 days of heating. Here we describe an alternate way of obtaining these nanotubes by substituting convential heating in an oven with micro-wave heating. Tubes were obtained within the hour. When applying micro-waves during 2 hours, the tubes precursors were absent from the suspension and the size distribution of the tubes was shifted by one order of magnitude towards higher aspect ratios. The underlying mechanisms causing this improved synthesis are discusse

Interactions between Fe-doped imogolites nanotubes and the soil bacteria P. Brassecacearum.

International audienceBiogenic silica resulting from the precipitation of dissolved Si through biological processes in plants, often contains small amounts of occluded organic carbon. These phases, called phytoliths, have a long persistence in soils, making them tracers of past conditions. In this context, the knowledge of the carbon speciation associated with phytoliths bears significant importance in examining the carbon dynamics in soils. With carbon concentrations as low as the 0.1% range, examining the nature of organic carbon remains very challenging, and available tools (e.g. pyrolysis) are often prone to serious artifacts. Recent improvements of microwave sources enabled the application of the Dynamic Nuclear Polarization (DNP) technique to NMR, thereby establishing a new non-destructive tool for the qualitative and quantitative determination of the carbon speciation. Applied to the analysis of phytoliths, this method showed the presence of carbons from different sources within the sample: About 20% of the signal correspond to carbohydrates, and are assigned to photosynthetic carbon; the marked alkyl, N-alkyl and carbonyl signals indicate a significant proportion of proteins. This is consistent with the hypothesis that parts of the carbon associated with the phytoliths is imported into the host plant via uptake from the soil. Finally, lignins, glomalin-like and/or humic-like compounds are minor species associated with biogenic silica. This speciation was obtained overnight with a DNP-NMR setup with an excellent sensitivity (few tens of weight ppm); the same spectrum on a standard NMR spectrometer would have required at least 250 days of data acquisition. The considerable gain in sensitivity associated with the use of DNP now makes NMR a relevant technique for the analysis of environmental samples. Session B081 The fate of carbon in plants and terrestrial ecosystems-from respiration to allocation

Improved nanotube synthesis by the use of micro-waves

International audienceThe synthesis of Imogolites nanotubes is a simple aqueous sol-gel process, consisting in a partial hydrolysis of a mixture of Al and Si (or Ge) monomers followed by a growth step requiring at least 5 days of heating. Here we describe an alternate way of obtaining these nanotubes by substituting convential heating in an oven with micro-wave heating. Tubes were obtained within the hour. When applying micro-waves during 2 hours, the tubes precursors were absent from the suspension and the size distribution of the tubes was shifted by one order of magnitude towards higher aspect ratios. The underlying mechanisms causing this improved synthesis are discusse

Interactions between Fe-doped imogolites nanotubes and the soil bacteria P. Brassecacearum.

International audienceBiogenic silica resulting from the precipitation of dissolved Si through biological processes in plants, often contains small amounts of occluded organic carbon. These phases, called phytoliths, have a long persistence in soils, making them tracers of past conditions. In this context, the knowledge of the carbon speciation associated with phytoliths bears significant importance in examining the carbon dynamics in soils. With carbon concentrations as low as the 0.1% range, examining the nature of organic carbon remains very challenging, and available tools (e.g. pyrolysis) are often prone to serious artifacts. Recent improvements of microwave sources enabled the application of the Dynamic Nuclear Polarization (DNP) technique to NMR, thereby establishing a new non-destructive tool for the qualitative and quantitative determination of the carbon speciation. Applied to the analysis of phytoliths, this method showed the presence of carbons from different sources within the sample: About 20% of the signal correspond to carbohydrates, and are assigned to photosynthetic carbon; the marked alkyl, N-alkyl and carbonyl signals indicate a significant proportion of proteins. This is consistent with the hypothesis that parts of the carbon associated with the phytoliths is imported into the host plant via uptake from the soil. Finally, lignins, glomalin-like and/or humic-like compounds are minor species associated with biogenic silica. This speciation was obtained overnight with a DNP-NMR setup with an excellent sensitivity (few tens of weight ppm); the same spectrum on a standard NMR spectrometer would have required at least 250 days of data acquisition. The considerable gain in sensitivity associated with the use of DNP now makes NMR a relevant technique for the analysis of environmental samples. Session B081 The fate of carbon in plants and terrestrial ecosystems-from respiration to allocation

Exposure to Engineered Nanomaterials, seven case studies within the LabEX SERENADE project : a Safer by Design approach

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