Speciation of technetium-99 incorporated into metal oxide matrices: A molecular level understanding of technetium-99 reduction and its complexation into polyoxometalates and Innovation and assessment of general chemistry education in a college setting

Technetium-99 (99Tc) is a long-lived (T 1/2 = 2.13 x 105 years) beta-emitting (Emax = 294 KeV) radionuclide formed during the fission of 235U and fallout from nuclear weapons testing. It exists in relatively high concentrations in nuclear waste tanks, and the pertechnetate (TcO4-) anion has been shown to leach into surrounding subsurface soils and groundwaters. Due to its long half-life and the high mobility of the pertechnetate (TcO 4-) anion, 99Tc management is an issue for both waste characterization and long-term storage. A better understanding of both its extensive redox chemistry and the parameters that affect the speciation and coordination environment of Tc will promote the development of more appropriate methods for the separation of Tc from nuclear waste tanks as well as more fitting mediums for storage.;Polyoxometalates (POMs) are early transition metal oxide clusters that are chemically robust. They have homogeneous crystalline structures and are known to be good model systems for metal oxide solid-state materials such as the glasses and ceramics used to house nuclear waste. The synthesis of pure 99Tc-POM compounds, however, is complicated by both the unwanted hydrolysis of the Tc(V) starting material and difficulties with the separation of the free POM ligand from the desired 99Tc-POM complex. We have developed methods for the clean synthesis of the 99Tc - (alpha1-P2W17O61) 10- and (alpha2-P2W17O61) 10- Wells-Dawson POM compounds (as both organic and aqueous soluble complexes) and characterized them using various spectroscopic techniques.;POMs also have unique, tunable, electron transfer abilities and can be reduced, both electrochemically and photochemically in the presence of a sacrificial electron donor, by multiple electrons while maintaining their structural integrity. To this end we have investigated a number of POMs; Keggin ions, (XW12 O40n-, X=P, n=3; Si, n=4; Al, n=5), the Wells-Dawson lacunary isomer (alpha2-P2W17O61) 10-, and a "wheel" POM, P8W48O184 40-, for their ability to reduce pertechnetate and sequester low valent 99Tc. The resulting low valent Tc species have been characterized by physical methods including multinuclear NMR and electrochemistry.