Structural collapse of Al13-intercalated montmorillonite by Na-salicylate solutions
Abstract:The chemical, textural and structural transformations of Al13-intercalated montmorillonite, resulting from the depolymerization of the interlamellar Al13 polycations by Na salicylate solutions, were studied. Nitrogen gas adsorption shows a dramatic decrease in specific surface area from 493 to 39 m2g-1, due to the loss of microporosity. Modelling of small-angle X-ray scattering (SAXS) curves shows that the final product contains two phases: a Na-exchanged swelling phase accounting for 40% of the clay, and a fixed interlayer distance (20.8 Å) phase accounting for 60% of the clay. The Al remaining in the clay galleries (45% of the initial Al) is composed of 13% Al13 and 87% hexacoordinated Al, probably Al(OH)03 and oligomeric Al-salicylate complexes, as shown by 27Al NMR. The instability of Al13-intercalated montmorillonite towards organic ligands is related to the hydration shell of the tridecamer, revealed by SAXS. These results focus on the necessity to take into account the presence of organic ligands in natural media when using materials such as Al13-intercalated clays.
Document Type: Research Article
Publication date: 2001-09-01