A study of uranium speciation in acetate solutions at temperatures from 25 to 250 degrees C

We report U L3-edge XAS analysis results from a study of the speciation of U(VI) in acetate solutions between 25 and 250 degrees C, at pH's between 1.82 and 2.57 and [acetate]:[U] ratios of 0.5 to 50. At 25 degrees C in excess acetate there are at least two acetate ligands in the equatorial plane with a U-O bond distance of 2.44 A. At elevated temperatures with excess acetate, acetate is still coordinated but the speciation mixture appears more complicated. Less evidence exists for acetate coordination when [acetate]:[U] ratio is unity or below. pH within this limited range appears to have little effect on the uranyl speciation.

Effect of Si(IV) substitution on the stability of microporous ZnAPSO-44 solid acid catalysts: a combined XAS/XRD study

The combined XAS/XRD technique has been used to investigate the stability of the microporous structure during calcination process for a series of ZnAPSO-44 materials. Incorporation of large amounts of Zn is found to produce materials that are unstable upon removal of the structure directing organic template molecule. However, simultaneous incorporation of Si is found to increase the thermal stability of the materials, yielding catalysts that are well suited for acid catalysed reactions.

Hydrothermal synthesis of (C6N2H14)2(UVI2UIVO4F12), a mixed-valent one-dimensional uranium oxyfluoride

A new hybrid organic-inorganic mixed-valent uranium oxyfluoride, (C6N2H14)2(U3O4F12), UFO-17, has been synthesized under hydrothermal conditions using uranium dioxide as the uranium source, hydrofluoric acid as mineralizer, and 1,4-diazabicyclo[2.2.2]octane as template. The single-crystal X-ray structure was determined. Crystals of UFO-17 belonged to the orthorhombic space group Cmcm (no. 63), with a = 14.2660(15) A, b = 24.5130(10) A, c = 7.201(2) A, and Z = 4. The structure reveals parallel uranium-containing chains of two types: one type is composed of edge-sharing UO2F5 units; the other has a backbone of edge-sharing UF8 units, each sharing an edge with a pendant UO2F5 unit. Bond-valence calculations suggest the UF8 groups contain UIV, while the UO2F5 groups contain UVI. EXAFS data give results consistent with the single-crystal X-ray structure determination, while comparison of the uranium LIII-edge XANES of UFO-17 with that of related UIV and UVI compounds supports the oxidation-state assignment. Variable-temperature magnetic susceptibility measurements on UFO-17 and a range of related hybrid organic-inorganic uranium(IV) and uranium(VI) fluorides and oxyfluorides further support the formulation of UFO-17 as a mixed-valent UIV/UVI compound.