Investigation of cation environment and framework changes in silicotitanate exchange materials using solid-state 23Na, 29Si, and 133Cs MAS NMR

Brian R. Cherry, May Nyman, Todd M. Alam

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37 Scopus citations

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 languageEnglish (US)
Pages (from-to)2079-2093
Number of pages15
JournalJournal of Solid State Chemistry
Volume177
Issue number6
DOIs
StatePublished - Jun 1 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

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