Uranyl
peroxide compounds are important to the nuclear fuel cycle
and are typically formed from the direct addition of hydrogen peroxide
or through photochemical pathways that utilize a sacrificial solvent.
In this study, we explore the use of THF as a peroxide forming solvent
that could be used to promote the crystallization of uranyl peroxide
materials. Compound 1 (Li(H2O)2(UO2)(C7H3NO4)(C4H5NO4)·2H2O) was originally
crystallized after aging for 10 days at room temperature and was characterized
by X-ray diffraction, elemental analysis, Raman spectroscopy, and
UV/vis spectroscopy. Exposure to ambient light for one month led to
the complete transformation of 1 to compound 2 ((C5NH6)2[(UO2)2(μ-O2)(H2O)2(C7NO4H3)2]·4H2O). Oxidation of the THF molecule was proposed as the major mechanism
for the formation of the secondary uranyl peroxide compound, which
was accelerated in the presence of the UO2
2+ cation and light. Presence of THF hydrogen peroxide was confirmed
by spectral (NMR and Raman) analysis of the mother liquor. Compound 3 ((C4N2H12)[(UO2)2(μ-O2)(H2O)2(C7NO4H3)2]·2.75H2O) formed in the presence of transition metal cations and additional
experiments indicated that photoexcitation was not necessary to create
free peroxide in this system. Autoxidation of the THF molecule is
the most likely mechanism for peroxide formation and indicates that
judicial choice of solvent can lead to the formation of new uranyl
peroxide materials.
Water adsorption experiments combined with vibrational and radiochemical analyses reveal significant differences in uptake of H2O over D2O, HDO, and HTO within metal organic nanotubes.
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