A comparative UV-vis-diffuse reflectance study on the location and interaction of cerium ions in Al- and Zr-pillared montmorillonite clays

The environment, location and interaction of the Ce3+ ions in the micropores of Al- and Zr-pillared clays have been studied by UV-vis-diffuse reflectance spectroscopy (UV-vis-DRS). The DRS spectra show that the chemical environment of the Ce3+ ions in cerium exchanged clay is different from that of the Al- and Zr-pillared clays. The Al-Ce pillared clays (Al-Ce-PM) show four distinct absorption bands at 224, 263, 294 and 342 nm in the UV region which are attributed to 4f --> 5d interconfigurational transitions of Ce3+ ions associated with alumina pillars. The O-2 --> C3+ charge transfer band observed at 263 nm for Ce-exchanged and Al-Ce-PM clays is blue shifted by 10 nm for Ce-Zr-pillared clays (Ce-Zr-PM) due to fully hydrated Ce3+ ions. The Ce3+ ions are incorporated in the Al- and Zr-pillars possibly as AlCeO3 and CexZr1-xO2 particles upon heat treatment. (C) 2004 Elsevier B.V. All rights reserved.