title: Template-free synthesis and mechanistic study of porous three-dimensional hierarchical uranium-containing and uranium oxide microspheres.
abstract: A novel type of uranium-containing microspheres with an urchin-like hierarchical nano/microstructure has been successfully synthesized by a facile template-free hydrothermal method with uranyl nitrate hexahydrate, urea, and glycerol as the uranium source, precipitating agent, and shape-controlling agent, respectively. The as-synthesized microspheres were usually a few micrometers in size and porous inside, and their shells were composed of nanoscale rod-shaped crystals. The growth mechanism of the hydrothermal reaction was studied, revealing that temperature, ratios of reactants, solution pH, and reaction time were all critical for the growth. The mechanism study also revealed that an intermediate compound of 3 UO3 ⋅NH3 ⋅5 H2 O was first formed and then gradually converted into the final hydrothermal product. These uranium-containing microspheres were excellent precursors to synthesize porous uranium oxide microspheres. With a suitable calcination temperature, very uniform microspheres of uranium oxides (UO2+x , U3 O8 , and UO3 ) were successfully synthesized.
authors.affiliation: Key Laboratory of Nuclear Radiation and Nuclear Energy Technology and Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (P.R. China), Fax: (+86) 10-88235294.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.forename: Ran
authors.initials: R
authors.lastname: Zhao
authors.forename: Cong-Zhi
authors.initials: CZ
authors.lastname: Wang
authors.forename: Li-Yong
authors.initials: LY
authors.lastname: Yuan
authors.forename: Zhan-Jun
authors.initials: ZJ
authors.lastname: Gu
authors.forename: Cheng-Liang
authors.initials: CL
authors.lastname: Xiao
authors.forename: Shu-Ao
authors.initials: SA
authors.lastname: Wang
authors.forename: Xin-Wei
authors.initials: XW
authors.lastname: Wang
authors.forename: Yu-Liang
authors.initials: YL
authors.lastname: Zhao
authors.forename: Zhi-Fang
authors.initials: ZF
authors.lastname: Chai
authors.forename: Wei-Qun
authors.initials: WQ
authors.lastname: Shi
keywords: actinides; oxides; phase transitions; porous structures; uranium