UNSPECIFIED. (2002) Nb-substitution and Cs+ ion-exchange in the titanosilicate sitinakite. MICROPOROUS AND MESOPOROUS MATERIALS, 55 (1). pp. 1-13. ISSN 1387-1811

Abstract

Cesium-133 MAS NMR and X-ray powder diffraction have been used to investigate Cs+ ion-exchange in synthetic samples of the titanosilicate mineral, sitinakite. The effect of incorporating Nb using Nb(V) ethoxide as the Nb source into the sitinakite framework and its influence on Cs+ ion-exchange was also studied. Refinements of X-ray powder data show that substitution of niobium for titanium in the sitinakite framework occurs to a limited extent using the synthetic method employed. Niobium substitution is also supported by Si-29 MAS NMR spectra. Any niobium that was not substituted into the sitinakite structure was present in a distinct Nb-rich oxide/hydroxide phase. NMR studies reveal that in the undoped samples with low Cs loadings, at least four types of Cs+ are present, while at higher levels of Cs+ loadings, an additional two sites are populated. Similar sites appear to be occupied in the Nb-substituted samples but the relative occupancies are strongly modulated relative to the undoped samples. The multiple Cs environments are attributed to Cs+ ions occupying similar structural sites in the titanosilicate channels but experiencing different hydration water coordination environments. (C) 2002 Elsevier Science Inc. All rights reserved.

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