Ultrafine 5 nm ceria isotropic nanoparticles were prepared using the rapid chemical precipitation approach from cerium(III) nitrate and ammonium hydroxide aqueous solutions. The as-prepared nanoparticles were shown to contain predominantly Ce(IV) species. The solubility of nanocrystalline CeO 2 at several pH values was determined using ICP-MS and radioactive tracer methods. Phase composition of the ceria samples remained unchanged upon partial dissolution, while the shape of the particles changed dramatically, yielding nanorods under neutral pH conditions. According to X-ray absorption spectroscopy investigation of the supernatant, Ce(III) was the main cerium species in solution at pH < 4. Based on the results obtained, a reductive dissolution model was used for data interpretation. According to this model, the solubility product for ceria nanoparticles was determined to be logK sp =-59.3 ± 0.3 in 0.01M NaClO 4. Taken together, our results show that the pH-dependence of ceria anti-and pro-oxidant activity can be related to the dissolution of CeO 2 in aqueous media.
Porous aromatic frameworks
(PAFs) incorporating a high concentration
of acid functional groups possess characteristics that are promising
for use in separating lanthanide and actinide metal ions, as required
in the treatment of radioactive waste. These materials have been shown
to be indefinitely stable to concentrated acids and bases, potentially
allowing for multiple adsorption/stripping cycles. Additionally, the
PAFs combine exceptional features from MOFs and inorganic/activated
carbons giving rise to tunable pore surfaces and maximum chemical
stability. Herein, we present a study of the adsorption of selected
metal ions, Sr2+, Fe3+, Nd3+, and
Am3+, from aqueous solutions employing a carbon-based porous
aromatic framework, BPP-7 (Berkeley Porous Polymer-7). This material
displays high metal loading capacities together with excellent adsorption
selectivity for neodymium over strontium based on Langmuir adsorption
isotherms and ideal adsorbed solution theory (IAST) calculations.
Based in part upon X-ray absorption spectroscopy studies, the stronger
adsorption of neodymium is attributed to multiple metal ion and binding
site interactions resulting from the densely functionalized and highly
interpenetrated structure of BPP-7. Recyclability and combustibility
experiments demonstrate that multiple adsorption/stripping cycles
can be completed with minimal degradation of the polymer adsorption
capacity.
We report a full characterization of PuO2 nanoparticles at the atomic level and probe their local and electronic structure by a variety of methods available at the synchrotron and theoretical approaches.
The facile chemical precipitation method and subsequent thermal treatment were shown to be suitable for preparation of crystalline ThO2 nanoparticles (NPs) in a wide range of particle sizes (from 2.5 to 34.3 nm). The obtained NPs were investigated with X-ray diffraction, high-resolution transmission electron microscopy and X-ray absorption techniques to find out the possible size effects associated with nanocrystalline thoria. For 2.5 nm NPs, the lattice parameter of ThO2 was found to increase by up to 1.1 %, in comparison with the bulk material. The decrease in the particle size was also accompanied by a significant decrease in the Th-Th coordination number.
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