MECHANOCHEMICAL OXIDATION METHOD

Abstract

The invention provides a method for preparing an actinide metal peroxide from a corresponding actinide metal oxide under solid reaction conditions.

Claims

1. A method for preparing an actinide metal peroxide, comprising contacting an actinide metal oxide with a solid metal peroxide under conditions that provide the actinide metal peroxide.

2. The method of claim 1, wherein the actinide metal is uranium.

3. The method of claim 1, wherein the actinide metal oxide is an actinide VI metal oxide.

4. The method of claim 1, wherein the actinide metal oxide is an actinide IV metal oxide.

5. The method of claim 1, wherein the solid metal peroxide comprises Li, Na, Mg, Ca, Sr, or Ba.

6. The method of claim 5, wherein the solid metal peroxide comprises Li.sub.2O.sub.2 or Na.sub.2O.sub.2.

7. The method of claim 1, wherein the actinide metal oxide and the solid metal peroxide are contacted by rotary milling.

8. The method of claim 1, further comprising converting the actinide metal peroxide to a solid.

9. The method of claim 8, wherein the solid is a crystalline or amorphous solid.

10. The method of claim 1, which is carried out without solvent.

11. The method of claim 1, which comprises liquid-assisted grinding

12. An actinide metal peroxide prepared according to the method of claim 1.

Description

EXAMPLES

Example 1. Preparation Of Uranium Triperoxide from UO.SUB.3

Materials

[0021] Solid-state mechanochemical reactions were prepared using powders of uranium trioxide (International Bio-Analytical Industries Inc., 99%), lithium peroxide (Acros Organics, 95%), sodium peroxide (Acros Organics, 96%), magnesium peroxide complex (Aldrich, technical grade), calcium peroxide (Spectrum, 60%), strontium peroxide (Aldrich, 98%), barium peroxide (Acros Organics, 95%). Caution: UO.sub.3 contains radioactive .sup.238U, which is an a emitter, and like all radioactive materials must be handled with care. These experiments were conducted by trained personnel in a licensed research facility with special precautions taken toward the handling, monitoring, and disposal of radioactive materials. Recrystallization reactions were prepared using ultrapure Millipore water (18.2 MΩ). Chemicals purchased were used directly without further purification.

Mechanochemical Synthesis

[0022] Synthetic procedure for m.sub.30-UO.sub.3—Li.sub.2O.sub.2 involved combining 0.03 gr of UO.sub.3 solid (1.10.sup.−4 moles) with 0.05 gr of Li.sub.2O.sub.2 solid (1.10.sup.−3 moles) in the 5 mL stainless steel FTS “SmartSnap” grinding jars using two 5 mm stainless steel balls (304 grade) for grinding. The grinding jars were sealed using a Teflon insert and inserted into a Form-Tech Scientific (FTS) FTS1000 shaker mill operating at 1800 rpm. The samples were ground in 5-minute grinding intervals for the total of 15 minutes or 30 minutes. Reactions between UO.sub.3 and Na.sub.2O.sub.2, MgO.sub.2, CaO.sub.2, SrO.sub.2, and BaO.sub.2 were performed according to the same procedure with varying the total time of grinding to optimize the yield of the reactions, if applicable.

Vibrational Spectroscopy

[0023] Solid-state and solution-state Raman spectra were acquired on a SnRI High-Resolution Sierra 2.0 Raman spectrometer equipped with 785 nm laser energy and 2048 pixels TE-cooled CCD. Laser power was set to the maximum output value of 15 mW, giving the highest achievable spectral resolution of 2 cm.sup.−1. Each sample was irradiated for an integration time of 5-60 seconds (depending on the sample) and automatically reiterated three times in multi-acquisition mode. Three Raman spectra acquired per sample, averaged together, and normalized based on laser power and integration time. FT-IR spectra were collected on a Nicolet Nexus FT-IR Spectrometer from 500-4000 cm.sup.−1. Approximately 10-20 mg of the fine reaction powder was mixed with the anhydrous KBr salt and pressed into a transparent pellet for data collection. To accurately process the vibrational signals observed, the background was subtracted, multiple peaks were fit using the peak analysis protocol with Gaussian and Lorentz functions, and all the fitting parameters converged in the OriginPro 9.1.0 (OriginLab, Northampton, Mass.) 64-bit software.

Powder X-Ray Diffraction

[0024] Powder X-ray diffraction data was collected on a Bruker D8 Advance diffractometer with Ni-filtered Cu Kα radiation (λ=1.5418 Å), voltage 40 kV and current 40 mA, in the continuous mode with scan range of 5-60° 2θ and step size of 0.05°. Samples were ground to fine powders using a mortar and pestle and run using zero background silica sample holders. Processing of the PXRD patterns, background subtraction, smoothing, Kα2 stripping, and peak selection was done using PreDICT indexing software from ICDD. The PXRD diffractograms were matched using the ICDD PDF-4+ database.

Scanning Electron Microscopy

[0025] Secondary electron and backscattered electron images were obtained with a Hitachi 3400N Scanning Electron Microscope for each sample. Reaction powders were removed from the grinding jar and directly adhered to a SEM stub by double-sided carbon tape. The operating voltage and the emission current were 15.0 kV and 80-120 μA respectively.

Results and Discussion

[0026] The mechanochemical reaction between UO.sub.3 and Li.sub.2O.sub.2 powders resulted in a crystalline product after 30 minutes of rotary grinding at 1800 rpm (m.sub.30-UO.sub.3—Li.sub.2O.sub.2). The powder X-ray diffraction pattern of the solid product matched to the known crystalline phase [UO.sub.2(O.sub.2).sub.3].sub.12[(UO.sub.2(OH).sub.4)Li.sub.16(H.sub.2O).sub.28].sub.3.Li.sub.6[H.sub.2O].sub.26, otherwise known as ULi.sub.16 with no evidence of the U(VI) starting material (M. Nyman, et al., Inorganic Chemistry, 2010, 49, 7748-7755). ULi.sub.16 is a nanoclustered assembly of uranyl triperoxide UO.sub.2(O.sub.2).sub.3.sup.4− and uranyl tetrahydroxide UO.sub.2(OH).sub.4.sup.2− anionic monomers counterbalanced with extensive hydrated lithium frameworks. Vibrational spectra were complicated by the bands at 814 cm.sup.−1 and 864 cm.sup.−1 in the IR spectrum and 789 cm.sup.−1 in the Raman spectrum due to the presence of unreacted Li.sub.2O.sub.2 (H. H. Eysel and S. Thym, Zeitschrift für anorganische and allgemeine Chemie, 1975, 411, 97-102). Raman spectrum of ULi.sub.16 product showed two bands at 715 and 737 cm.sup.−1 that corresponded to the ν.sub.1(U═O) stretch of the UO.sub.2(O.sub.2).sub.3.sup.4− species (M. Dembowski, et al., Inorganic Chemistry, 2017, 56, 1574-1580). Low vibrational frequency of the uranyl symmetric stretch is rather common among uranyl triperoxide complexes due to significant σ-electron donation by the peroxide O.sub.2.sup.2− ligands into the equatorial plane of the UO.sub.2.sup.2+ cation (G. Lu, et al., Coordination Chemistry Reviews, 2018, 374, 314-344). Such additional σ-donation causes weakening of the uranyl (U═O.sub.y1) bond and enables the oxo group to engage in actinyl-cation interactions with surrounding Li.sup.+ cations. The band at 767 cm.sup.−1 could be assigned to residual, amorphous UO.sub.3; however, due to the large FWHM of the peak, it could also be associated with the ν.sub.1(U═O) stretch of a UO.sub.2(OH).sub.4.sup.2− phase in the final product. Finally, Raman band at 844 cm.sup.−1 is well-aligned with symmetric ν.sub.1(O—O) of the peroxide ligand bound to the uranyl cation (M. Dembowski, et al., Inorganic Chemistry, 2017, 56, 1574-1580). Weak band at 1090 cm.sup.−1 corresponded to the CO.sub.3.sup.2− stretching of Li.sub.2CO.sub.3 that is produced as a byproduct of reaction between activated Li.sub.2O.sub.2 and molecular CO.sub.2 from open air. The IR spectrum for mechanochemically synthesized m.sub.30-UO.sub.3—Li.sub.2O.sub.2 was well-matched to the vibrational bands of ULi.sub.16 synthesized in solution from previous literature reports (M. Nyman, et al., Inorganic Chemistry, 2010, 49, 7748-7755).

[0027] While the mechanochemical reaction between UO.sub.3 and Li.sub.2O.sub.2 took 30 minutes to create a highly crystalline product, a similar product was noted only after 15 minutes of rotary grinding of UO.sub.3 with Na.sub.2O.sub.2 (m.sub.15-UO.sub.3—Na.sub.2O.sub.2). The PXRD pattern of the crystalline product matched the Na.sub.4[UO.sub.2(O.sub.2).sub.3].9H.sub.2O phase (NaUT), reported by Dembowski et al. (M. Dembowski, et al., Inorganic Chemistry, 2017, 56, 1574-1580). The synthesized m.sub.15-UO.sub.3—Na.sub.2O.sub.2 phase once again contains uranyl triperoxide monomers UO.sub.2(O.sub.2).sub.3.sup.4− that are charge balanced by Na.sup.+ cations and engage in hydrogen bonding interaction with water molecules within the crystalline lattice. In case of m.sub.15-UO.sub.3—Na.sub.2O.sub.2, the analysis of vibrational spectra was more straightforward because bands associated with the Na.sub.2O.sub.2 starting material was not observed in this case. The major feature in the Raman spectrum of m.sub.15-UO.sub.3—Na.sub.2O.sub.2 was centred at 701 cm.sup.−1 and corresponded to the ν.sub.1(U═O) stretch of the uranyl cation. The vibrations at 808, 819, and 842 cm.sup.−1 corresponded to ν.sub.2, ν.sub.3, and ν.sub.1(O—O) stretches of the coordinated peroxide ligands O.sub.2.sup.2− based on previously reported computational results (M. Dembowski, et al., Inorganic Chemistry, 2017, 56, 1574-1580). A weak band at 770 cm.sup.−1 was assigned to a minor amount of unreacted UO.sub.3 and a medium intensity band at 1080 cm.sup.−1 corresponded to the carbonate CO.sub.3.sup.2− in form of sodium carbonate Na.sub.2CO.sub.3. A notable feature in the IR spectrum of m.sub.15-UO.sub.3—Na.sub.2O.sub.2 is the red-shifted asymmetric ν.sub.3(U═O) stretch at 865 cm.sup.−1, following a trend of the red-shifted symmetric ν.sub.1(U═O) stretches in the Raman spectra.

[0028] Increasing the reaction time of the UO.sub.3—Na2O.sub.2 solid mixture to 30 minutes (m.sub.30-UO.sub.3—Na.sub.2O.sub.2) resulted in the formation of a different crystalline product mixture as evidenced by the experimental PXRD pattern. The powder pattern of m.sub.30-UO.sub.3—Na.sub.2O.sub.2 exhibits preferred orientation of particles and addition peaks in the diffractogram also indicate that the resulting phase was not a monophasic compound (C. F. Holder and R. E. Schaak, ACS Nano, 2019, 13, 7359-7365). Raman spectroscopy indicated that a uranyl triperoxide species (UO.sub.2(O.sub.2).sub.3.sup.4−) was present in the solid phase based on similar spectroscopic features at 701 and 722 cm.sup.−1 associated with the symmetric ν.sub.1(U═O) stretch of the uranyl cation coordinated to three O.sub.2.sup.2− ligands. Vibrational bands associated with peroxide ligands were assigned to 790 (ν.sub.2), 808 (ν.sub.3), and 838 cm.sup.−1 (ν.sub.1), whereas the peak at 767 cm.sup.−1 can again be assigned with residual UO.sub.3. The most unusual feature within the Raman spectrum of m.sub.30-UO.sub.3—Na.sub.2O.sub.2 was a weak band at 878 cm.sup.−1 that has been previously observed for uranyl superoxide complex (D. V. Kravchuk, et al., Angewandte Chemie International Edition, 2021, 60, 15041-15048). Mechanochemically induced radical formation is particularly common for molecules containing peroxides or disulfides (G. Kaupp, CrystEngComm, 2009, 11, 388-403); thus, formation of reactive oxygen species from metal peroxide powders upon mechanical grinding is plausible. Presence of superoxide radicals within the m.sub.30-UO.sub.3—Na.sub.2O.sub.2 powder may explain the high reactivity of the mechanochemical reaction. In addition, ingrowth of carbonate in the solid-state compound was observed based on Raman bands at 1080 and 1057 cm.sup.−1 that correspond to the ν.sub.1 stretch of CO.sub.3.sup.2− associated with Na.sup.+ and UO.sub.2.sup.2+, respectively. Capture of molecular CO.sub.2 from air by the powder mixture is most likely a due to the creation of the reactive oxygen species and NaOH, which can form when Na.sub.2O.sub.2 is exposed to moisture in air.

[0029] Additionally, the mechanochemical reactions between UO.sub.3 and solid alkali-earth metal peroxides (MgO.sub.2, CaO.sub.2, SrO.sub.2, BaO.sub.2) were explored under similar synthetic conditions. PXRD patterns and Raman analysis suggests that reactivity of alkali-earth metal peroxides increases down the group with MgO.sub.2 being least reactive and BaO.sub.2 being most reactive. In case of MgO.sub.2 the resulting reaction product is still a mixture of starting materials. Moving down the group, PXRD patterns of product powders show decrease in crystallinity, as well as systematic decrease in vibrational signatures of UO.sub.3 starting material (˜6 vibrational bands in the 200-600 cm.sup.−1 region). The reaction between UO.sub.3 and BaO.sub.2 results in UO.sub.3 powder losing crystallinity and becoming completely amorphous as the diffraction peaks associated with uranium trioxide completely disappear from the diffractogram. Despite the increase in reactivity down the group, mechanochemical reactions with alkali-earth metal peroxide solids do not yield any U(VI) peroxide materials under the conditions explored herein.

[0030] The formation of the U(VI) triperoxide phase in the case of m.sub.30-UO.sub.3—Li.sub.2O.sub.2 and m.sub.15-UO.sub.3—Na.sub.2O.sub.2 has important implications to the development of starting material for use in the synthesis of larger U(VI) peroxide nanospheres or other phases. Monomeric U(VI) triperoxides have previously been shown to exhibit aqueous reactivity and self-assemble into peroxide/hydroxide bridged uranyl nanosphere polyoxometalate clusters over time (A. Arteaga, et al., Chemistry—A European Journal, 2019, 25, 6087-6091; and M. Nyman, et al., Inorganic Chemistry, 2010, 49, 7748-7755). For instance, Liao et al. dissolved lithium U(VI) triperoxide solids [Li.sub.4(UO.sub.2)(O.sub.2).sub.3.4H.sub.2O] in water and a catalyst solution to study the self-assembly of the Li—U.sub.24 nanocapsule. The triperoxide starting material in this case was produced by dissolving uranyl nitrate hexahydrate in a solution containing 3 mL 30% H.sub.2O.sub.2 and 3 mL of 4 M LiOH solution and resulted in product yields of 75% based upon U.

[0031] To evaluate the transformation of the mechanochemically produce triperoxide phases, the synthesized powders for m.sub.30-UO.sub.3—Li.sub.2O.sub.2 and m.sub.30-UO.sub.3—Na.sub.2O.sub.2 were each dissolved in 2 ml of water and the capped vial was allowed to sit undisturbed on the benchtop. Overnight both solutions changed color from light yellow to deep orange and Raman spectroscopy of the resulting solution showed a significant amount of free carbonate based on the ν.sub.1 CO.sub.3.sup.2− band at 1068 cm.sup.−1 (for m.sub.30-UO.sub.3—Li.sub.2O.sub.2 and m.sub.30-UO.sub.3—Na.sub.2O.sub.2 solutions, respectively). Ingrowth of the dissolved carbonate was somewhat surprising due to relative stability of uranyl triperoxide monomers in solutions up to 96 hours after the dissolution (Z. Liao, et al., Inorganic Chemistry, 2014, 53, 10506-10513). However, the presence of mechanochemically induced reactive oxygen species within the solid-state could cause formation of uranyl superoxide species, which in turn has been shown to capture carbon both in solid-state and in solution (D. V. Kravchuk, et al., Angewandte Chemie International Edition, 2021, 60, 15041-15048; and D. V. Kravchuk and T. Z. Forbes, ACS Materials Au, 2021, DOI: 10.1021/acsmaterialsau.1c00033).

[0032] Recrystallized powder of m.sub.30-UO.sub.3—Li.sub.2O.sub.2 appeared to be crystalline mixture of Li.sub.2CO.sub.3 and an unknown phase that could not be matched to any known compound in the in the ICDD PDF-4+ database. Raman spectrum of recrystallized m.sub.30-UO.sub.3—Li.sub.2O.sub.2 displayed vastly different vibrational features compared to the original powder. The major intensity band centred at 1091 cm.sup.−1 (vi CO.sub.3.sup.2− bound to Li.sup.+) further confirmed a significant amount of Li.sub.2CO.sub.3 present in the mixture and the peak at 1063 cm.sup.−1 corresponds to the carbonate ligand symmetric stretch of the uranyl tricarbonate species UO.sub.2(CO.sub.3).sub.3.sup.4−. This was well aligned with vibrational bands at 845 (ν.sub.2 out-of-plane bend of CO.sub.3.sup.2−), 744, and 711 cm.sup.−1 (ν.sub.4 in-plane bend of CO.sub.3.sup.2−) (J. Cĕjka, et al., Journal of Raman Spectroscopy, 2010, 41, 459-464). The position of the uranyl symmetric stretch band at 816 cm.sup.−1 in the Raman and antisymmetric stretch at 908 cm.sup.−1 in the IR further suggested the formation of a U(VI) tricarbonate species (UO.sub.2(CO.sub.3).sub.3.sup.4−). As a result, the unidentified crystalline phase in the PXRD of recrystallized m.sub.30-UO.sub.3—Li.sub.2O.sub.2 likely has a general chemical formula of Li.sub.4[UO.sub.2(CO.sub.3).sub.3].xH.sub.2O; however, a mineral or synthetic phase of lithium uranyl tricarbonate has not been reported in the literature to confirm this assignment.

[0033] Powder X-ray diffraction of recrystallized m.sub.30-UO.sub.3—Na.sub.2O.sub.2 resulted in highly crystalline material that matched a known sodium U(VI) tricarbonate phase, Na.sub.4[UO.sub.2(CO.sub.3).sub.3] (cĕjkaite). Vibrational signatures of carbonate anion were present in the Raman spectrum, including the symmetric stretching ν.sub.1 at 1073 (bound to Na.sup.+) and 1063 cm.sup.−1(bound to UO.sub.2.sup.2+), as well as doubly-degenerate in-plane bending ν.sub.4 at 702 and 734 cm.sup.−1. Uranyl ν.sub.1 symmetric stretch was centered at 806 cm.sup.−1 in the Raman spectrum with a complementary ν.sub.3 antisymmetric stretch showing up as a shoulder at 887 cm.sup.−1 in the IR, both being characteristic of uranyl tricarbonate mineral phases (G. Lu, et al., Coordination Chemistry Reviews, 2018, 374, 314-344).

[0034] In both cases, the formation of larger U(VI) peroxide nanoclusters due to the presence of additional reactive oxygen species in the system was not observed. It is likely that if the experiment was performed in a CO.sub.2 free atmosphere, then peroxide or novel materials containing reactive oxygen species may have been isolated from the solution. This methodology does lead to the formation of pure phase U(VI) tricarbonate species, which are somewhat difficult to form from aqueous solutions.

CONCLUSIONS

[0035] Mechanochemical synthesis has been successfully applied to UO.sub.3 powders mixed with solid alkali metal peroxides, Li.sub.2O.sub.2 and Na.sub.2O.sub.2, resulting in crystalline uranyl triperoxide compounds [UO.sub.2(O.sub.2).sub.3].sub.12[(UO.sub.2(OH).sub.4)Li.sub.16(H.sub.2O).sub.28].sub.3.Li.sub.6[H.sub.2O].sub.26 and Na.sub.4[UO.sub.2(O.sub.2).sub.3].9H.sub.2O, respectively. This is the first successful report using mechanochemistry to convert a U(VI) oxide phase to a crystalline peroxide product. The timeframe of the mechanochemical grinding played a significant role in driving the reaction to completion and controlling the overall product. In both cases, mechanicalochemical reactions of the solid metal peroxides likely induced the formation of reactive oxygen species, such as superoxide radical, which combined with alkalinity of reaction powders, resulting in carbon capture and formation of the carbonate anions. Both m.sub.30-UO.sub.3—Li.sub.2O.sub.2 and m.sub.30-UO.sub.3—Na.sub.2O.sub.2 reaction products were recrystallized in water yielding uranyl tricarbonate UO.sub.2(CO.sub.3).sub.3.sup.− phases charge balanced by either Li.sup.+ or Na.sup.+ cations, as confirmed by powder X-ray diffraction and vibrational spectroscopy. Such mechanochemical synthetic pathway to uranyl triperoxides may not only afford access to new crystalline compounds, but also avoid significant generation of radioactive liquid waste in the laboratory setting.

Example 2. Preparation Of Uranium Peroxide from UO.SUB.2

[0036] Mechanochemical reactions were carried out on a mixture of 0.03 g of UO.sub.2 with 0.05 g of Li.sub.2O.sub.2 (or a molar equivalent of Na.sub.2O.sub.2) for neat grinding and with addition of 100 μL of 30% H.sub.2O.sub.2 (aq) as a liquid additive for liquid-assisted grinding LAG, where parameter η≈1 μL/mg (P. Ying, J. Yu and W. Su, Advanced Synthesis & Catalysis, 2021, 363, 1246-1271). Liquid-assisted grinding (solvent-drop grinding) is an extension of solvent-free mechnanochemical methods, where a small amount of liquid is introduced to the milling reaction in order to enhance the reactivity of reagents. Parameter η refers to the ratio of the volume of liquid additive to the combined weight of the reactants η=V.sub.liquid(μL)/m.sub.reagents (mg). While η=0 μL/mg refers to neat solid on solid grinding, the typical values for liquid-assisted grinding are in the range η=0-2 μL/mg compared to η≈1 μL/mg, which is used in the experiments herein. Samples were ground for 30 minutes in the 5 ml stainless steel milling jar with four 5 mm stainless steel balls on the rotary mill at 1800 rpm.

[0037] Mechanochemical activation of UO.sub.2 powder itself was first evaluated using powder X-ray diffraction with an addition of corundum Al.sub.2O.sub.3 standard (25% by weight) to assess changes in crystallinity across the samples. The initial PXRD pattern of UO.sub.2 solid showed strong diffraction peaks associated with UO.sub.2 confirming a highly crystalline starting material with weak and broadened peaks matching to UO.sub.3 suggesting minor surface oxidation of UO.sub.2 upon exposure to air during handling. The intensity ratio between the diffraction peak associated with (111) crystallographic plane of UO.sub.2 (2θ=28.5°) and (104) plane of Al.sub.2O.sub.3 (2θ=35.1°) in the initial PXRD was calculated to be 24.6:1 (UO.sub.2:Al.sub.2O.sub.3) (Y. Hu, X. Han, F. Cheng, Q. Zhao, Z. Hu and J. Chen, Nanoscale, 2014, 6, 177-180). The powder pattern of solid uranium dioxide ground for 30 minutes (m.sub.30-UO.sub.2) revealed a significant decrease in peak intensities, as well as, peak broadening, suggesting the decrease in crystallinity and possible nanoscale domains of coherent diffraction. The peak intensity ratio against the standard in case of m.sub.30-UO.sub.2 was decreased to 4.2:1 (UO.sub.2:Al.sub.2O.sub.3), suggesting a decrease of crystallinity from the original sample by a factor of 5.8. The mechanochemical impact on solid UO.sub.2 alone demonstrated breakdown of crystallinity, decrease of particle size, which leads to increased surface area and enhanced reactivity of ground UO.sub.2 powders.

[0038] This was further confirmed after the liquid-assisted grinding reaction with Li.sub.2O.sub.2 (m.sub.30-UO.sub.2-Li.sub.2O.sub.2 LAG) resulting in a new uranium crystalline phase and complete disappearance of peaks associated with crystalline UO.sub.2 in the powder diffraction pattern. Reaction with solid Li.sub.2O.sub.2 was first performed as neat grinding to assess the oxidative capabilities of Li.sub.2O.sub.2. Powder X-ray diffraction pattern of the resulting solid m.sub.30-UO.sub.2—Li.sub.2O.sub.2 showed diffraction peaks associated with starting materials UO.sub.2 and Li.sub.2O.sub.2 indicating no formation of crystalline product. However, Raman spectroscopy on the solid product revealed partial oxidation of UO.sub.2 in form of amorphous uranium oxides. Vibrational band at 443 cm.sup.−1 was assigned to the stoichiometric UO.sub.2, while the shoulder at 458 cm.sup.−1 corresponded to non-stoichiometric UO.sub.2+x (J. M. Elorrieta, L. J. Bonales, M. Naji, D. Manara, V. G. Baonza and J. Cobos, Journal of Raman Spectroscopy, 2018, 49, 878-884). The band at 627 cm.sup.−1 matched very well with U.sub.4O.sub.9 formed during oxidation of UO.sub.2 (J. M. Elorrieta, L. J. Bonales, M. Naji, D. Manara, V. G. Baonza and J. Cobos, Journal of Raman Spectroscopy, 2018, 49, 878-884). Bands at 562 cm.sup.−1 and 593 cm.sup.−1 can possibly correspond to vibrational bands of U.sub.3O.sub.7 and U.sub.3O.sub.8 (J. B. Lü, G. Li and S. L. Guo, Guang Pu Xue Yu Guang Pu Fen Xi, 2014, 34, 405-409). Weak bands at 717 cm.sup.−1 and 730 cm.sup.−1 match well with vi symmetric stretch of uranyl U═O bound to three peroxide ligands, suggesting minimal conversion to U(VI) triperoxide phase. A strong band at 785 cm.sup.−1 is associated with the ν.sub.1(O—O) of peroxide anion in the Li.sub.2O.sub.2 starting material. Band at 1090 cm.sup.−1 corresponds to ν.sub.1 stretching mode of CO.sub.3.sup.2− bound to lithium. Mechanochemical impact on solid peroxide results in the formation of reactive oxygen species such as superoxide anions, that readily react with molecular CO.sub.2 resulting in the ingrowth of carbonate phases (G. Kaupp, CrystEngComm, 2009, 11, 388-403; D. V. Kravchuk and T. Z. Forbes, ACS Materials Au, 2021, DOI: 10.102 1/acsmaterialsau.1c00033). As a result, the neat grinding in case of m.sub.30-UO.sub.2—Li.sub.2O.sub.2 does not produce any crystalline product, however, vibrational spectroscopy suggests evidence of partially oxidized UO.sub.2.

[0039] Liquid-assisted grinding approach with Li.sub.2O.sub.2 demonstrated significant ingrowth of crystalline material in the PXRD pattern of m.sub.30-UO.sub.2—Li.sub.2O.sub.2 LAG, while the peaks associated with crystalline UO.sub.2 disappeared. The PXRD pattern of m.sub.30-UO.sub.2—Li.sub.2O.sub.2 LAG was not matched to any previously reported materials in the ICDD PDF-4+ database. However, Raman spectroscopy of the solid m.sub.30-UO.sub.2—Li.sub.2O.sub.2 LAG revealed two major vibrational bands at 716 cm.sup.−1 and 735 cm.sup.−1 aligning with ν.sub.1 symmetric stretch of U═O for uranyl triperoxide species (M. Dembowski, V. Bernales, J. Qiu, S. Hickam, G. Gaspar, L. Gagliardi and P. C. Burns, Inorganic Chemistry, 2017, 56, 1574-1580). The band at 786 cm.sup.−1 was still associated with ν.sub.1 stretching of the peroxide anion from the Li.sub.2O.sub.2 starting material, however, the band at 847 cm.sup.−1 corresponded to the symmetric O—O stretching of peroxide ligand bound to the uranyl cation, thus confirming the presence of uranyl triperoxide species. Liquid-assisted grinding was demonstrated to enhance the reactivity of UO.sub.2 with Li.sub.2O.sub.2 under the same reaction conditions resulting in the formation of U(VI)O.sub.2(O.sub.2).sub.3.sup.4− species.

[0040] Oxidation of UO.sub.2 was reasonably enhanced during neat grinding with Na.sub.2O.sub.2 as compared to the Li.sub.2O.sub.2 counterpart. The PXRD pattern of the product m.sub.30-UO.sub.2—Na.sub.2O.sub.2 still showed major diffraction peaks associated with UO.sub.2 starting material, however, additional weaker peaks suggested ingrowth of a new crystalline phase that partially matched to Na.sub.4[UO.sub.2(O.sub.2).sub.3].9H.sub.2O uranyl triperoxide phase reported previously (N. W. Alcock, Journal of the Chemical Society A: Inorganic, Physical, Theoretical, 1968, DOI: 10.1039/J19680001588, 1588-1594). Raman spectroscopy of m.sub.30-UO.sub.2—Na.sub.2O.sub.2 revealed a complex mixture of uranium oxides, similar to the one observed in m.sub.30-UO.sub.2—Li.sub.2O.sub.2. Vibrational bands at 443 cm.sup.−1 and 458 cm.sup.−1 were assigned to UO.sub.2 and UO.sub.2+x, respectively, while a band at 627 cm.sup.−1 was aligned with U.sub.4O.sub.9. A prominent band at 698 cm.sup.−1 was associated with the uranyl symmetric stretch, while weaker bands at 810 cm.sup.−1 and 838 cm.sup.−1 corresponded to ν.sub.3 and ν.sub.1 O—O stretching of peroxide ligands, indicating a presence of uranyl triperoxide species. The neatly ground m.sub.30-UO.sub.2—Na.sub.2O.sub.2 displayed vibrational bands associated with the symmetric stretch of superoxide anion O.sub.2.sup.−.Math. centered at 1136 cm.sup.−1 and 1152 cm.sup.−1(H. H. Eysel and S. Thym, Zeitschrift für anorganische and allgemeine Chemie, 1975, 411, 97-102). Presence of reactive oxygen species, such as superoxide anion, in the solid, suggests a mechanochemically induced electron transfer from the peroxide in the starting material to UO.sub.2 solid, resulting in U(V) and U(VI) phases. The remaining superoxide radical can potentially undergo another electron transfer reaction with U(IV) or U(V) and leave the solid as molecular oxygen gas. A different reaction pathway for superoxide is reactivity with CO.sub.2 from air resulting in the formation of CO.sub.3.sup.2−, presence of which is also evident in vibrational spectroscopy of m.sub.30-UO.sub.2—Na.sub.2O.sub.2 by the strong band at 1080 cm.sup.−1.

[0041] Utilizing the liquid-assisted grinding approach with Na.sub.2O.sub.2 has further improved the crystallinity of the new uranium phase seen in the PXRD pattern of m.sub.30-UO.sub.2—Na.sub.2O.sub.2 LAG. The major diffraction peaks fully matched the sodium uranyl triperoxide phase Na.sub.4[UO.sub.2(O.sub.2).sub.3].9H.sub.2O confirming that the crystalline phase is fully converted from U(IV) to U(VI). Raman spectroscopy has supported the uranyl triperoxide species based on the vibrational bands centered at 695 cm.sup.−1 (vi symmetric U═O stretch), 813 cm.sup.−1(ν.sub.3 O.sub.2.sup.2− uranyl), and 842 cm.sup.−1 (ν.sub.1 O.sub.2.sup.2− uranyl). The band at 877 cm.sup.−1 is most likely associated with free peroxide anion due to hygroscopic surface of the solid sample, however, we previously observed a band associated with uranyl superoxide stretch at 880 cm.sup.−1, so the precise assignment of the band may be ambiguous (D. V. Kravchuk, N. N. Dahlen, S. J. Kruse, C. D. Malliakas, P. M. Shand and T. Z. Forbes, Angewandte Chemie International Edition, 2021, 60, 15041-15048).

[0042] All publications, patents, and patent documents (including Kravchuk, D. and Forbes, T. Chem. Comm., 2022, 58, 4528-4531 and Kravchuk, D. and Forbes, T., CrystEngComm, 2022, 24, 775-781) are incorporated by reference herein, as though individually incorporated by reference. The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention.