Supercritical CO2 intercalation of layered silicates

In this study, we use supercritical CO2 as the processing medium for intercalating the structure of natural clay, Cloisite Na+, and depositing CO2-philic sugar acetate, P-D-galactose pentaacetate, between the layers of the clay. Based on our measurements of the phase behavior of the P-D-galactose pentaacetate-CO2 system, we select two processing conditions: a dense gas solution (DGS) at 40 degrees C and 11.7 MPa with 2.4 wt.% sugar acetate in CO2 and a gas-expanded liquid (GEL) at 40 degrees C and 7.9 MPa with 6.1 wt.% sugar acetate in CO2. The morphology of the as-received natural clay and clay samples processed under the DGS and the GEL conditions is determined by wide-angle X-ray diffraction (XRD), transmission electron microscopy (TEM) and low-energy electron diffraction (LEED) methods. The XRD results indicate intercalation of the clay layers. While the ordered structure remains, the gallery spacing between Cloisite Ne layers is doubled, from 0.3 1 to 0.52 and 0.59 nm for DGS- and GEL-processing conditions, respectively. The LEED patterns of the processed clays show bright spots characteristic of the highly crystalline sugar acetate superimposed on the halo pattern of the clay, confirming the deposition of the sugar acetate in the intercalated structure of the clay after scCO(2) processing. (c) 2006 Elsevier B.V. All rights reserved.