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

• Published in: Journal of materials chemistry 2003-04, Vol.13 (5), p.1145-1148
• Main Authors: De Stefanis, A., Tomlinson, A. A. G., Steriotis, Th. A., Stefanopoulos, K. L., Keiderling, U.
• Format: Article
• Language: English
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/b300292f

Small angle neutron scattering (SANS) of the montmorillonite (MO)-derived acid-restructured clays K10, HMO and the Mg2+ exchanged congener of the latter, Mg-HMO, has been investigated. K10 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 Mg2+ exchanged derivative; the scattering curve of the latter exhibits a peak at Q = 5.46 nm-1 ascribed to intra-layer Mg2-Mg2+ distances. Analysis of the mid-Q region (0.2-2.6 nm -1) of the curves demonstrates that K10 and HMO differ in nanostructure. In particular, the solid matrix of K10 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 Mg2+N between aluminosifcate sheets and enhanced correlation between platelets due to surface Mg2+ cations acting to bind clay platelet packets together face to face in agreement with the high Mg2+ loading level of HMO (10% w/w). The presence of the Mg2+ cations reduces the surface roughness and results in an increase of the length of the platelet packets in line with this enhanced ordering.