How the Diameter and Structure of (OH)₃Al₂O₃Si_<i>x</i>Ge_1–<i>x</i>OH Imogolite Nanotubes Are Controlled by an Adhesion versus Curvature Competition

Imogolites are natural aluminosilicate nanotubes displaying an astonishing monodispersity in diameter. The diameter is controlled by the structure and composition of the nanotube wall and can be tuned by several chemical manipulations. It has recently been discovered that the structure of imogolite nanotubes can change from single-walled (SW) to double-walled (DW) when Si is replaced by Ge during synthesis. Starting from the pure Ge composition, we show that the transition between DW and SW structures can be induced by the incorporation of a small quantity of Si in the synthesis. At that point, the suspension contains a mixture of structures with a nearly constant average diameter. In particular, we found evidence for the presence of a few nanoscrolls. Above 25% Si, SW nanotubes become more stable and present a continuously decreasing diameter with increasing Si. A model is proposed to explain the stability of these different nanotubes and, more generally, the structures of other organic or inorganic nanotubes as a balance between rigidity, surface tension, and adhesion competitive energies

The Challenge of Studying TiO₂ Nanoparticle Bioaccumulation at Environmental Concentrations: Crucial Use of a Stable Isotope Tracer

The ecotoxicity of nanoparticles (NPs) is a growing area of research with many challenges ahead. To be relevant, laboratory experiments must be performed with well-controlled and environmentally realistic (i.e., low) exposure doses. Moreover, when focusing on the intensively manufactured titanium dioxide (TiO₂) NPs, sample preparations and chemical analysis are critical steps to meaningfully assay NP’s bioaccumulation. To deal with these imperatives, we synthesized for the first time TiO₂ NPs labeled with the stable isotope ⁴⁷Ti. Thanks to the ⁴⁷Ti labeling, we could detect the bioaccumulation of NPs in zebra mussels (D<i>reissena polymorpha</i>) exposed for 1 h at environmental concentrations via water (7–120 μg/L of ⁴⁷TiO₂ NPs) and via their food (4–830 μg/L of ⁴⁷TiO₂ NPs mixed with 1 × 10⁶ cells/mL of cyanobacteria) despite the high natural Ti background, which varied in individual mussels. The assimilation efficiency (AE) of TiO₂ NPs by mussels from their diet was very low (AE = 3.0 ± 2.7%) suggesting that NPs are mainly captured in mussel gut, with little penetration in their internal organs. Thus, our methodology is particularly relevant in predicting NP’s bioaccumulation and investigating the factors influencing their toxicokinetics in conditions mimicking real environments