Hydrothermal synthesis of UO2 nanoparticles and their formation mechanism

We report a simple and general method for the production of UO 2 nanoparticles by heat-treating an aqueous mixture of uranyl acetate dihydrate and ethylenediamine. The products were characterized, and the effects of heat treatment temperature and time were investigated. When heat treatment time was fixed at 24 h, UO 2 could not be obtained at temperature lower than 160 °C, both UO 2 and ianthinite were obtained at 200 and 240 °C, while pure UO 2 nanoparticles were collected at 280 °C and higher temperatures. The average size of these nanoparticles varied in the range of 250–450 nm, which could be adjusted by tuning the reaction temperature and incubation time. Longer incubation time led to slight size increase due to Ostwald ripening . The mixture precursor took shorter time to transform to UO 2 at higher temperatures. A possible synthesis mechanism was proposed, including three stages: (I) initial precursor formation and transformation, (II) mid-term formation of ianthinite and UO 2 , and (III) the final formation of UO 2 nanoparticles. This research provides a facile method for the synthesis of UO 2 nanoparticles with excellent size stability in a relatively wide range of experimental conditions. Moreover, this method provides a new way for synthesis of ianthinite, a rare and hard-to-synthesize hydrous uranyl oxide .