Ion-Exchange Synthesis and Structural Characterization of Complex Niobium and Tantalum Oxides

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CONFERENCE: Celebration of Undergraduate Research

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Nunes, Claudia
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Complex niobium and tantalum oxides are of interest for their potential applications as photocatalysts for reactions including water-splitting. Photocatalysis is a chemical process in which a light-activated catalyst is used to facilitate a chemical reaction that would normally occur very slowly or not at all. The compounds that are the focus of research in our laboratory are niobium and tantalum oxides with the defect pyrochlore structure. This structure has the general formula A2M2O6O′ (M = Nb, Ta), with variable occupancy possible in both the A and O′ sites and strong potential for ion exchange at the A site. The starting compounds were synthesized hydrothermally with potassium in the A site and then ion-exchange reactions were carried out under relatively mild aqueous conditions. Extensive work has been done using both Zn2+ and Ag+ as exchange ions, with levels of success varying from no detectable exchange to almost complete replacement of the potassium by a combination of the desired exchange ion and free protons. The final exchange products were characterized primarily using powder X-ray diffraction, complemented by energy dispersive spectroscopy, thermogravimetric analysis, and Fourier-transform infrared spectroscopy. Unit cell parameters, site occupancies, and structures were then refined using the Rietveld method.