Ce L(III)-edge X-ray absorption spectroscopic studies on the tetrameric Ce-polyoxyhydroxy cation intercalated aluminosilicate

The cerium ion intercalated aluminosilicate was prepared by ion exchange reaction between Na⁺ in montmorillonite and Ce⁴⁺ in aqueous solution. The X-ray absorption near edge structure (XANES) analyses indicate that the Ce⁴⁺ ions are partially reduced to the Ce³⁺ ones during the intercalation into layered aluminosilicate due to a charge transfer between host and intercalant. From the EXAFS analysis, two different (Ce-O) bonding pairs could be characterized with the distances and coordination numbers of 2.31 (±0.02) Å x 8.2 (±1.5) and 2.66 (±0.02) Å x 2.7 (±1.0), respectively, with the oxygen atoms as the first nearest neighbor, and two (Ce-Ce) pairs at 3.78 Å as the second neighbor. It is therefore concluded that the most probable Ce-species stabilized in the interlayer space of aluminosilicate after the intercalation is the tetrameric Ce-polyoxy/hydroxy cations with the mixed valent state of 0.75 Ce⁴⁺/0.25 Ce³⁺.