The structure and textural heterogeneity of single- and double-walled aluminogermanate imogolites

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 N-2 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 N-2 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 N-2 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.