| Abstrakt: |
Anomalous small-angle X-ray scattering (ASAXS) has been exploited to monitor the solvation behavior of transition metal and lanthanide ions within the interlayers of the natural aluminosilicate clay mineral montmorillonite. The ASAXS technique can reveal the distribution of specific metallic species within a multicomponent and disordered matrix, which is typical of the semicrystalline smectite clays. The variations of scattering signal intensity as a function of absorption energy were monitored for Cu(II)−, Er(III)−, and Yb(III)−clays as a function of hydration. Two different hydration levels were probed: as prepared at ambient conditions, or so-called dry powders, and wet pastes. ASAXS intensities increase as the energy of the probing X-rays approaches the absorption energy of a given metal ion if it is associated with the interlayer solvent (water in this case) and decrease if the metal ion is associated with the solid matrix. The results show that (1) the ions are always associated with the clay in some fashion (they do not wash out into solution upon hydration, for example), (2) Cu(II) is well solvated within the interlayers of the clay, especially the wet sample, as expected, and (3) the lanthanide ions Er(III) and Yb(III) have associated with the clay interlayer surface, most likely as small hydrolyzed species even though the pH is well below the pKh values. The latter ASAXS measurements provide the first direct evidence of this lanthanide hydrolysis phenomenon within clay interlayers, which has previously been inferred from elemental analysis and IR information. |
