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No description available.

Many of the wastes associated with the nuclear fuel cycle are toxic to the biosphere; advancing the use of high resolution spectroscopy applied to these materials will provide the chemical speciation of the interaction between nuclear waste and geological material, improving confidence in a permanent disposal method and informing clean-up operations. Luminescence spectroscopy of uranyl(VI) is a well-established technique for the molecular speciation of uranium-mineral interactions. This work explores the use of both micro- and macroscopic luminescence spectroscopy to expose uranyl(VI) speciative heterogeneity in a range of minerals which have been exposed to uranyl(VI) salt solutions. A comprehensive review of the available literature on the interaction of uranyl(VI) with a range of geological media is assessed and compared. The review finds considerable ambiguity in the speciation of uranyl(VI) at the mineral water interface. A database reporting the multi parametric luminescence properties of uranyl(VI) with silica gel, quartz, bayerite, boehmite, muscovite, kaolinite and montmorillonite (SWy-2 and STx-1b) is presented and discussed. Although some of the results are consistent with previously reported values, many newly identified species are reported and their identification speculated. Parallel factor analysis is used to deconvolute the excitationemission matrix of uranyl(VI) sorbed to silica gel between pH 3 and pH 10. The results are used to identify the spectroscopic properties of complexes >(SiO)2UO2 and >(SiO)2UO2OH and thus new complexation coefficients (log(K)) for their formation with the silica gel surface are determined, log(K1) = 9.22 ± 0.02 and log(K2) = 3.45 ± 0.01, respectively. The investigation also provides insight into the fundamental properties of uranyl(VI) excitation pathways, which are not yet fully understood. Confocal microscopy and phosphorescent lifetime image mapping (PLIM) is used to expose the sub-micron heterogeneity of uranyl(VI) sorption complexation across mineral surfaces of silica gel, bayerite and montmorillonite (STx-1b). The results suggest that changes in the uranyl(VI) lifetime can be used to observe and understand submicron changes in uranyl(VI) complexation at hitherto unknown temporal resolution.

No description available.

Uranyl hybrid materials attract interest owing to promise of synthesizing functional materials, but typically experience limitations in extending dimensionality. This is due to the tendency of the uranyl cation to oligomerize along its equatorial plane, leading to the formation of flat secondary building units. One way to overcome these limitations is to utilize weak interactions to hold a structure together. This can be achieved through using ligands to build secondary building units through strong coordinative bonds that simultaneously provide supramolecular interactions as a means to extend dimensionality in the structure. We examined amino acids as a ligand choice because of its dual features of having a carboxyl group for coordination to the uranyl cation and an amino group that can be protonated to provide charge-assisted hydrogen bonding between to secondary building units in the structure. Aqueous benchtop chemistry in ambient conditions were used to synthesize and crystallize thirteen uranyl-glycine coordination compounds whose structures were elucidated with single crystal X-ray diffraction. Under these conditions, 1D coordination polymers form. The structural features in these compounds were varied to investigate their effects on the hydrogen bonding, including the presence/absence of metal center hydrolysis, the presence of other H-bond accepting carboxylate ligands, the use of dicarboxylic acid ligands to connect uranyl centers, and the addition of a secondary metal. The compounds provide insight into how the charge-assisted hydrogen bonding provided by zwitterionic amino acids is a viable means to extending the dimensionality of uranyl hybrid materials in a variety of chemical systems.

Density functional (DFT) methods are first used to study 22 of the most stable solution-phase UN4O12 isomers containing uranyl nitrate, UO2(NO3)2. Based on relative free energy calculations, 4 solution (a6, a5, a8, and a1) and 5 gas-phase isomers (a1, a2, a3, b1, and b2) are identified as the strongest candidates to exist and possibly predominate within their respective environments. DFT is then applied to a new form of binucleating Schiff–base polypyrrolic macrocycles containing actinyl ions [AnO2]n+ (An = U, Np, Pu; n = 1, 2) and 3d transition metals (TM): Mn, Fe, Co, and Zn. Formal bond order evidence is provided for 24 TM to actinyl–endo–oxygen partial bond formations. Special structural cases are discussed. Redox potentials for AnVIO21/AnVO21– couples closely follow the Np > Pu > U trend seen for AnO2(H2O)52+/1+. Predictions of –1.10, 0.25, and 0.01 eV are made for U, Np, and Pu redox potentials.

Density functional (DFT) methods are first used to study 22 of the most stable solution-phase UN4O12 isomers containing uranyl nitrate, UO2(NO3)2. Based on relative free energy calculations, 4 solution (a6, a5, a8, and a1) and 5 gas-phase isomers (a1, a2, a3, b1, and b2) are identified as the strongest candidates to exist and possibly predominate within their respective environments. DFT is then applied to a new form of binucleating Schiff–base polypyrrolic macrocycles containing actinyl ions [AnO2]n+ (An = U, Np, Pu; n = 1, 2) and 3d transition metals (TM): Mn, Fe, Co, and Zn. Formal bond order evidence is provided for 24 TM to actinyl–endo–oxygen partial bond formations. Special structural cases are discussed. Redox potentials for AnVIO21/AnVO21– couples closely follow the Np > Pu > U trend seen for AnO2(H2O)52+/1+. Predictions of –1.10, 0.25, and 0.01 eV are made for U, Np, and Pu redox potentials.

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.