Effects of H2O2 Concentration on Formation of Uranyl Peroxide Species Probed by Dissolution of Uranium Nitride and Uranium Dioxide

Boosted charge transfer in a naturally formed Ca(Al2Si2O8)/Fe2O3 heterojunction for piezocatalytical formation of H2O2 and solidification of U(VI)

Energy and environmental issues make the generation of H2O2 and the separation of U(VI) from water very important topics. In this work, we disclosed a low-cost, high-efficiency method for separating U(VI) from water based on the naturally formed catalyst (red volcanic stone powders, RVSP) of Ca(Al2Si2O8)/Fe2O3 heterojunction through a piezocatalytic pathway induced by ultrasonication. The charges were found to be elevatedly separated due to the formation of the heterojunction. It is found that under ultrasonication, charges were effectively separated and then reacted with water to form H2O2 with a high yield of 196.7 μmol·g-1 in 4 h, which further solidifies U(VI) to form a solid of UO2O2. The removal rate of U(VI) in water reached 96 % (50 ppm) within 150 min. Furthermore, the results calculated by VASP show that the cyclic variation of the conduction bands under a cyclic force field facilitates the charge separation, and thus may promote piezocatalysis. Most importantly, the application study in real seawater indicates that U(VI) piezocatalysis based on natural minerals has great potential. This work presents a comprehensive investigation of U(VI) piezocatalysis by Ca(Al2Si2O8)/Fe2O3 and provides a new idea for piezocatalytic extraction of uranium.

Piezo-catalysis in BiFeO3@In2Se3 Heterojunction for High-Efficiency Uranium Removal

Piezo-catalysis emerges as an efficient, safe, and affordable strategy for removing hazardous substances from aquatic environments. Here, the BiFeO3@In2Se3 heterojunction demonstrates remarkable prowess as a piezo-catalyst, enabling the high-efficiency removal of uranium (U) from U(VI)-containing water. A total U(VI) removal efficiency of 94.6% can be achieved under ultrasonic vibration without any sacrificial agents. During the entire catalytic process, piezo-induced electrons, hydroxyl radicals, and superoxide radicals play important roles in U(VI) removal, while the generated H2O2 is responsive to the transformation of soluble U(VI) into insoluble (UO2)O2•2H2O and UO3. Furthermore, auxiliary illumination can accelerate the increase of free charges, enabling the piezo-catalyst to retain more charges. This leads to an improved U(VI) removal efficiency of 98.8% and a significantly increased reaction rate constant. This study offers a comprehensive analysis of the fabrication of high-efficiency piezo-catalysts in the removal or extraction of U(VI) from U(VI)-containing water.

Mechanochemical synthesis of crystalline U(vi) triperoxide solids

Mechanochemical reaction of UO3 with metal peroxides (M2O2) yields U(vi) triperoxide materials without producing radioactive solvent wastes.

Stability of Solid Uranyl Peroxides under Irradiation

The effects of radiation on a variety of uranyl peroxide compounds were examined using γ-rays and 5 MeV He ions, the latter to simulate α-particles. The studied materials were studtite, [(UO₂)(O₂)(H₂O)₂](H₂O)₂, the salt of the U₆₀ uranyl peroxide cage cluster, Li₄₄K₁₆[(UO₂)(O₂)(OH)]₆₀·255H₂O, the salt of U₆₀Ox₃₀ uranyl peroxide oxalate cage cluster, Li₁₂K₄₈[{(UO₂)(O₂)}₆₀(C₂O₄)₃₀]·nH₂O, and the salt of the U₂₄Pp₁₂ (Pp = pyrophosphate) uranyl peroxide pyrophosphate cage cluster, Li₂₄Na₂₄[(UO₂)₂₄(O₂)₂₄(P₂O₇)₁₂]·120H₂O. Irradiated powders were characterized using powder X-ray diffraction, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. A weakening of the uranyl bonds of U₆₀ was found while studtite, U₆₀Ox₃₀, and U₂₄Pp₁₂ were relatively stable to γ-irradiation. Studtite and U₆₀ are the most affected by α-irradiation forming an amorphous uranyl peroxide as characterized by Raman spectroscopy and powder X-ray diffraction while U₆₀Ox₃₀ and U₂₄Pp₁₂ show minor signs of the formation of an amorphous uranyl peroxide.