Structural collapse of Al-13-intercalated montmorillonite by Na-salicylatesolutions

The chemical, textural and structural transformations of Al-13-intercalated montmorillonite, resulting from the depolymerization of the interlamellar Al-13 polycations by Na salicylate solutions, were studied. Nitrogen gas ad sorption shows a dramatic decrease in specific surface area from 493 to 39 m(2)g(-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 Angstrom) phase accounting for 60% of the clay. T he Al remaining in the clay galleries (45% of the initial Al) is composed o f 13% Al-13 and 87% hexacoordinated At, probably Al(OH)(3)(0) and oligomeri c Al-salicylate complexes, as shown by 27 Al NMR. The instability of Al-13- intercalated montmorillonite towards organic ligands is related to the hydr ation 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 Al-13-intercalated clays.