Optimized Synthetic Strategies, Structures, Properties & Modification of Open Framework Oxides with High ION Exchange Capacity

This project focuses on microporous and zeolitic materials with negatively charged frameworks, regularly spaced pores and channels of molecular dimension that possess cation-exchange properties that can sometimes discriminate between ions and/or gases based upon size and shape. Apart from formulating strategies for the discovery of new materials with these characteristics, it is important to understand the structural basis for any selectivity. Recent structural results, obtained using synchrotron radiation, suggest strategies to increase ion exchange capacity. It is hypothesized that low valent metals can replace common higher valent ones in framework structures, lithium for silicon for example, thereby producing highly negatively charged frameworks with enhanced ion exchange capacity and selectivity. The crystal chemistry of lithium makes it ideal in this regard and investigations of several new lithosilicates indicate a rich structural chemistry. Syntheses to expand the range of materials with Li in the framework will be pursued, including attempts to tailor the exchange properties of "pure" silica and aluminosilicate molecular sieves. This will be coupled with studies of the relationships between the sorbtive and catalytic properties of these new materials. An extension of Li-substitution into tetrahedral networks is the substitution of Na into octahedral networks. This effectively lowers the cationic charge on the framework and increases the number of extraframework cations and so ion exchange capacity. The structure of the first example of this synthetic philosophy is an Octahedral Molecular Sieves (OMS) based on the chemistry Na4[Na8Nb12.8Ti3.2]O44.8(OH)3.2o8H2O. We are planning to expand the catalogue of such materials and to seek the structural basis for their selectivity toward strontium. These classes of materials are potentially useful in separation, contaminant removal and sequestration applications. They are important to environmental technologies that improve remediation and mitigation, and decrease future cleanup costs by emphasizing pollution avoidance and novel approaches to the measurement, assessment, and feedback for the optimization of pollution avoidance and prevention. It will also impact industrial ecology by providing materials that can be applied to improve manufacturing processes and their environmental impact. Students trained in these areas of high-technology will likely be very competitive in the future job market.