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

Ecotoxicity of manufactured Al nanophases

International audienceWe examined the toxicity of two Al nanophases, viz. nano-boehmite and the Al13 tridecamer, a nano-sized Al polymer. Boehmite is a common Al oxyhydroxide; it is considered as non toxic. In a first approximation, nano-boehmite is also considered as harmless, by analogy with the larger sized counterpart.There are only isolated reports of the occurence of Al13 in natural environments. It is a hydrolysis product of Al3+ and is frequently used in water treatment processes, and may thus enter ecosystems using this route. As a matter of fact, typical Al concentration used in drinking water plants were also used here. The Al13 species is knwon to exhibit severe toxic effects towards crops.Nano-boehmite as well as Al13 exhibit toxic effects toward P. Brassicacearum and E. Coli. Oxidative stress is a likely mechanisms. Indeed, the E Coli sodAsodB double mutant showed increased sensitivity to Al stress compared to the wild strain. A remarkable point is theamplitude of the responses which differs greatly whether AlOOH or Al13 is present in the medium. With P. Brassicacearum, the toxic effects in terms of survival rate observed with nano-boehmite occur also in the presence of Al13 at concentrations lower by 2 orders of magnitude. With E. Coli, the same trend was observed. In this case, the increased sensitivity of the superoxide dismutase deficient strains was evident from the lowest tested concentrations (0.1mM).The evolution of the Al speciation occurred on a timescale incompatible with NMR analyses. Ferron based determinations showed however that the Al13 nanophase becomes undetectable in the growth medium within 90 minutes. Proton NMR based metabolomics suggest thatdistinct metabolic routes are affected by nano-boehmite and Al1

Ecotoxicity of manufactured Al nanophases

International audienceWe examined the toxicity of two Al nanophases, viz. nano-boehmite and the Al13 tridecamer, a nano-sized Al polymer. Boehmite is a common Al oxyhydroxide; it is considered as non toxic. In a first approximation, nano-boehmite is also considered as harmless, by analogy with the larger sized counterpart.There are only isolated reports of the occurence of Al13 in natural environments. It is a hydrolysis product of Al3+ and is frequently used in water treatment processes, and may thus enter ecosystems using this route. As a matter of fact, typical Al concentration used in drinking water plants were also used here. The Al13 species is knwon to exhibit severe toxic effects towards crops.Nano-boehmite as well as Al13 exhibit toxic effects toward P. Brassicacearum and E. Coli. Oxidative stress is a likely mechanisms. Indeed, the E Coli sodAsodB double mutant showed increased sensitivity to Al stress compared to the wild strain. A remarkable point is theamplitude of the responses which differs greatly whether AlOOH or Al13 is present in the medium. With P. Brassicacearum, the toxic effects in terms of survival rate observed with nano-boehmite occur also in the presence of Al13 at concentrations lower by 2 orders of magnitude. With E. Coli, the same trend was observed. In this case, the increased sensitivity of the superoxide dismutase deficient strains was evident from the lowest tested concentrations (0.1mM).The evolution of the Al speciation occurred on a timescale incompatible with NMR analyses. Ferron based determinations showed however that the Al13 nanophase becomes undetectable in the growth medium within 90 minutes. Proton NMR based metabolomics suggest thatdistinct metabolic routes are affected by nano-boehmite and Al1

Speciation of trace amounts of organic carbon with NMR: the example of plant silica particles

International audienceDetermination of the C speciation in natural samples usually involves invasive sample preparation aiming at extracting the organic carbon from its matrix, i.e. a process prone to substantial losses and modification on the nature of the organic compounds. Nuclear magnetic resonance (NMR) is widely used to characterize the nature of natural organic matter, but suffers from an inherent lack of sensitivity, rendering this technique inoperative when the C concentration drops into the single digit % range. Recent advances in the Dynamic Nuclear Polarization (DNP) technique allow however to reconsider this sensitivity issue. Using the example of plant silica particles which occlude C amounts in the sub-percent range, we show that 13C DNP NMR has an improved sensitivity, able to detect 13C spin systems in the 10 ppm range. Binding sites of these organic compounds on the silica matrix are identified with the DNP technique applied to 29Si NMR

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

Speciation of trace amounts of organic carbon with NMR: the example of plant silica particles

International audienceDetermination of the C speciation in natural samples usually involves invasive sample preparation aiming at extracting the organic carbon from its matrix, i.e. a process prone to substantial losses and modification on the nature of the organic compounds. Nuclear magnetic resonance (NMR) is widely used to characterize the nature of natural organic matter, but suffers from an inherent lack of sensitivity, rendering this technique inoperative when the C concentration drops into the single digit % range. Recent advances in the Dynamic Nuclear Polarization (DNP) technique allow however to reconsider this sensitivity issue. Using the example of plant silica particles which occlude C amounts in the sub-percent range, we show that 13C DNP NMR has an improved sensitivity, able to detect 13C spin systems in the 10 ppm range. Binding sites of these organic compounds on the silica matrix are identified with the DNP technique applied to 29Si NMR

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

International audienc

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