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Structural resolution of nanotubes with complex stoichiometry


Nanotube and butanone, small and malls, atom and moat : these anagrams illustrate how meaning comes from the association of the letters of the alphabet. In the same way, the properties of matter derive from its structure at the atomic scale, that is, the nature of the constituent atoms and their organisation.

Single-walled inorganic nanotubes are hollow cylinders of nanometric diameter with exceptional properties in fields as diverse as nano-electronics, nano-fluidics, nano-catalysis and molecular sieving. Yet, the structure of the nanotubes formed of at least three types of atoms remains elusive, which hinders the understanding and control of their properties. How are the atoms organized within these nanotubes ?

X-ray scattering is a technique of choice for studying the organization of matter but the nanometric lateral size of the objects considered here is a strong limitation. Indeed, it implies that scattering diagrams are mainly composed of broad peaks, giving access to a very limited number of structural parameters. Researchers from Laboratoire de Physique des Solides have thus proposed a methodology based on the use of helicoidal symmetries and the minimization of a semi-empirical energy to reduce the determination of the structure to a small number of geometrical parameters.

This methodology is applied to nanotubes of the ‘imogolite’ type, which can be synthesized with adjusted functionalities. These nanotubes are considered in a geological context for the storage of carbon, metal cations or radionuclides in soils, where they are naturally present, or even as markers of the evolution of the Martian climate. Our methodology allowed us to determine the positions of the atoms of such nanotubes. An original rolling mode has been demonstrated for methylated imogolite nanotubes of nominal composition (OH)3Al2O3Si(Ge)CH3. The elementary cell formed of (OH)3AlO3 octahedrons and of a O3Si (CH3) -or O3Ge(CH3) tetrahedron - rolls on a cylinder forming an ‘armchair’ structure, while the rolling mode is ‘zig-zag’ for hydroxylated nanotubes.

Structure and rolling mode of a hydroxylated imogolite nanotube with nominal composition (OH)3Al2O3GeOH and of its methylated counterpart (OH)3Al2O3GeCH3. Comparison between experimental and simulated X-ray scattering diagrams of a powder of methylated alumino-germanate nanotubes.

Reference

Structural resolution of inorganic nanotubes with complex stoichiometry
Geoffrey Monet, Mohamed S. Amara, Stéphan Rouzière, Erwan Paineau, Ziwei Chai, Joshua D. Elliott, Emiliano Poli, Li-Min Liu, Gilberto Teobaldi and Pascale Launois
Nature Communications 9, 2033 (2018)
doi:10.1038/s41467-018-04360-z

Contact

Pascale Launois
Geoffrey Monet