The structure and textural heterogeneity of single- and double-walled aluminogermanate imogolites
Résumé
This work studies the combined use of XRD, AFM and gas adsorption to determine the structure and textural heterogeneity of two Ge-imogolite nanotubes, one single-walled and another double-walled (<100 nm). In XRD, the indexation of lines is broadened, reflection lines 003, 004, 005 and 006 are identified and the signature of the presence of a double wall is revealed on the diffractogram. Contrary to current assumptions concerning these two products, both AFM and adsorption/desorption of N2 at 77 K and of CO2 at 273 K show that these two imogolites are polydisperse and heterogeneous in terms of length and inner and outer diameter. An analysis of adsorption clearly shows that N2 is limited to the characterization of porosities between 1 and 50 nm and that CO2 is better-suited to the analysis of ultramicropores (<1 nm). The specific surfaces of micropores estimated with N2 are greatly underestimated. The application of the Dubinin–Astakhov model shows that the two imogolites have very extensive microporous specific surfaces whose structure is heterogeneous and accessible to exchanges.