Hexagonalization of Aluminogermanate Imogolite Nanotubes Organized into Closed-Packed Bundles

Imogolite nanotubes are promising building blocks for nanotechnologies with potential applications in molecular separation, molecular storage, or catalysis. We present an experimental study of the structure of germanium-based imogolite nanotubes Al2O3Ge(OH)(4) arranged in bundles. It combines cryo-transmission electron microscopy, infrared spectroscopy, thermogravimetric measurements, and X-ray scattering experiments. Thanks to a systematic method developed to analyze X-ray scattering diagrams as a function of the nanotube shape, single-walled germanium-based imogolite nanotubes, known as cylindrical for more than 30 years, are shown to take an hexagonal base shape when arranged in bundles. Physical and chemical properties of hexagonal imogolite nanotubes should markedly differ from those of cylindrical ones, making hexagonal basis nanotubes a "new" member, of particular interest, of the rich family of imogolites.