W0297

Maximizing Ion Exchange Capacity in Zeolites: Structure Solution of Some Novel Compounds Using Synchrotron X-Ray Sources. Akhilesh Tripathi and John B. Parise¹, ¹Department of Chemistry & Geosciences, State University of New York, Stony Brook, New York 11794-3400, USA.

The containment, handling and long-term storage of radioactive strontium-90, cesium-137 and actinides in waste streams produced by defense-related and power generation activities pose substantial engineering, scientific, and societal challenges. We recently reported a new class of material based on NaNbTi (SOMS) which function to both sequester and immobilize hazardous divalent metals by selective ion exchange and subsequent thermal alteration to stable perovskite-type phases¹. In continuation of this project, preparation of several other octahedral molecular sieve based up on transition elements has been carried out using hydrothermal methods. The guiding principle behind choosing these transition elements is similar to that which explains framework topology of zeolites. Substitution of Al^III into a Si^IVO₂^4- tetrahedron in a zeolite framework imparts a net negative change, requiring a metal cation to charge-balance and simultaneously promote open-framework growth. For example, substitution of Mo^iv/Zr^iv for Nb^V in the NaNbO₃ structure, charge-balanced by a sodium, can produce tunnel structures. Some new cluster compound and framework compounds obtained are reported. Some of these compounds crystallize as extremely small crystals. In-house X-ray sources have too weak intensities for their characterization. We have carried out their structural studies using various synchrotron facilities such as the one at Brookhaven National laboratories, NY, USA.

1. M. Nyman, Akhilesh Tripathi, J. B. Parise, R. S. Maxwell, W. T. A. Harrison & T. M. Nenoff; A New Family of Octahedral Molecular Sieves: Sodium Ti/Zr^IV Niobates; J. Am. Chem. Soc. 123, 1529-1530, 2001.