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Séminaire d’Antoine Thill

Imogolites nanotubes (synthesis and properties).

Antoine Thill

Laboratoire Interdisciplinaire sur l’Organisation Nanométrique et
Supramoléculaire, UMR 3299 CEA/CNRS SIS2M, CEA Saclay, 91191 Gif-sur-Yvette, France

Imogolites are natural aluminosilicates (OH)3Al2O3Si(OH) that were discovered in Japanese volcanic soils in 1962. They consist in 2 nm nanotubes with length up to microns. These tubes have find applications in the photographic industry as a part of anti static layer. More recently many potential applications are explored for these nanomaterials sometimes involving hybrid structures.
Significant progress was recently achieved on aluminosilicate (Al-Si) or aluminogermanates (Al-Ge) nanotubes especially on their formation mechanism. Indeed, it has been discovered that i) the synthesis of Al−Ge imogolite-like nanotubes is possible at high concentration, ii) that imogolite form thanks to an iso volume topological transformation of roof-tile shaped protoimogolite nanoparticles and iii) that double wall Al-Ge imogolite nanotubes can also form.

The growth mechanisms of imogolite-like Al-Ge nanotubes have been examined at various stages of their formation. The accurate determination of the nucleation stage was examined using a combination of local- (XAS at the Ge−K edge and 27Al NMR) and semilocal scale technique (in situ SAXS). For the first time, a model is proposed for the precursors of the nanotubular structure and consist in rooftile-shaped particles, up to 5 nm in size, with ca. 26% of Ge vacancies and varying curvatures. These precursors assemble to form short nanotubes/nanorings observed during the aging process. The transformation of the rooftile-shaped protoimogolite into nanotubes is examined using Atomic Force Microscopy (AFM) and in situ Small Angle X-ray Scattering (SAXS). In particular, in situ SAXS allowed quantifying the transformation of protoimogolite into nanotubes. The size distribution of the final nanotubes was also assessed after growth by AFM. A particular attention was focused on the determination of the single and double walled nanotube length distributions. We observed that the two nanotube types do not grow with the same kinetic and that their final length distribution was different. A model of protoimogolites oriented aggregation was constructed to account for the experimental growth kinetic and the length distribution differences.

Using high resolution cryo-TEM and Small Angle X-ray Scattering, we unravel the mesoscale structure of Al-Ge Imogolite nanotubes in two contrasted situations. On the one hand, Al−Ge imogolite nanotubes synthesized at 0.25 M are double-walled nanotubes of 4.0 ± 0.1 nm with an inner tube of 2.4 ± 0.1 nm. Moreover, SAXS data also suggest that the two concentric tubes have an equal length and identical wall structure. On the other hand, at higher concentration (0.5M), both SAXS and cryo-TEM data confirm the formation of single-walled nanotubes of 3.5 ± 0.15 nm. Infrared spectroscopy confirms the Imogolite structure of the tubes. This is the first evidence of any double-walled imogolite or imogolite-like nanotubes likely to renew interest in these materials and associated potential applications.

Several research area on imogolite are really active. Most importantly, their modification in order to prepared structured hybrid material is a very important direction. Several new results in this direction will be presented. Another direction is the study of the potential toxicity of these material. Preliminary results will also be presented.