Abstract
Crystalline silicotitanate (CST), HNa3Ti4Si 2O14·4H2O and the Nb-substituted CST (Nb-CST), HNa2Ti3NbSi2O14· 4H2O, are highly selective Cs+ sorbents, which makes them attractive materials for the selective removal of radioactive species from nuclear waste solutions. The structural basis for the improved Cs+ selectivity in the niobium analogs was investigated through a series of solid-state magic angle spinning (MAS) NMR experiments. Changes in the local environment of the Na+ and Cs+ cations in both CST and Nb-CST materials as a function of weight percent cesium exchange were investigated using 23Na and 133Cs MAS NMR. Framework changes induced by Cs+ loading and hydration state were investigated with 29Si MAS NMR. Multiple Cs+ environments were observed in the CST and Nb-CST material. The relative population of these different Cs+ environments varies with the extent of Cs+ loading. Marked changes in the framework Si environment were noted with the initial incorporation of Cs+, however with increased Cs+ loading the impact to the Si environment becomes less pronounced. The Cs+ environment and Si framework structure were influenced by the Nb-substitution and were greatly affected by the amount of water present in the materials. The increased Cs+ selectivity of the Nb-CST materials arises from both the chemistry and geometry of the tunnels and pores.
Original language | English (US) |
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Pages (from-to) | 2079-2093 |
Number of pages | 15 |
Journal | Journal of Solid State Chemistry |
Volume | 177 |
Issue number | 6 |
DOIs | |
State | Published - Jun 2004 |
Keywords
- Cesium
- Ion exchange
- Selectivity
- Silicotitanate
- Solid-state NMR
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry