Nanostructures of the montmorillonite-derived restructured clays K10®, HMO and the Mg2+ exchanged analogue Mg-HMO. A SANS, N2 sorption and XRPD study

Small angle neutron scattering (SANS) of the montmorillonite (MO)-derived acid-restructured clays K101, HMO and the Mg21 exchanged congener of the latter, Mg-HMO, has been investigated. K101 is a strong acid-treated clay, HMO a new, mild-acid treated material with different X-ray powder diffraction (XRPD) characteristics and Mg-HMO a Mg21 exchanged derivative; the scattering curve of the latter exhibits a peak at Q ~ 5.46 nm21 ascribed to intra-layer Mg21-Mg21 distances. Analysis of the mid-Q region (0.2-2.6 nm21) of the curves demonstrates that K101 and HMO differ in nanostructure. In particular, the solid matrix of K101 exhibits a mass fractal dimension, Dm ~ 2.53 which is absent from HMO but which is characteristic for sepiolites prepared via prolonged acid treatment. For Mg-HMO, recently found to be an efficient base catalyst for fine chemicals production, both XRPD and SANS point to a more ordered ''parallel-plate in primary particle'' shape. This is ascribed to both intercalation of Mg21 between aluminosilicate sheets and enhanced correlation between platelets due to surface Mg21 cations acting to bind clay platelet packets together face to face in agreement with the high Mg21 loading level of HMO (10% w/w). The presence of the Mg21 cations reduces the surface roughness and results in an increase of the length of the platelet packets in line with this enhanced ordering.