Reactivity and Toxicity of Imogolite Nanotubes.

Since the discovery of carbon nanotubes (NTs), there has been great interest in the synthesis and characterization of similar shaped structures like inorganic nanotubes, nanorods, or nanowires. Imogolites (Al₂SiO₃(OH)₄) are natural aluminosilicate single wall nanotubes. To date, only Ge-Al imogolite analogues have been successfully synthesized 100 times more  concentrated than Si-Al imogolites.

The growth mechanisms of imogolite-like aluminogermanate nanotubes were examined using a combination of local- (XAS at the Ge-Kedge and 27Al NMR) and semilocal scale techniques (in situ SAXS). 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 final products are most likely obtained by an edge-edge assembly of these short nanotube segments.

Two structures are revealed by SAXS: at 0.25M of Al the Al-Ge imogolite are double-walled NTs whereas at 0.5 M single-walled NTs are obtained.

First tests to reveal cyto  and genotoxicity on various vertebrates cells (human fibroblasts and CHO-K1) are interesting. They show a genotoxicity for concentrations from 8 10^-5 g/L and effects decreasing from proto-imogolite to long tubes