title: Theoretical insights on the interaction of uranium with amidoxime and carboxyl groups.
abstract: Recovery of uranium from seawater is extremely challenging but important for the persistent development of nuclear energy, and thus exploring the coordination structures and bonding nature of uranyl complexes becomes essential for designing highly efficient uranium adsorbents. In this work, the interactions of uranium and a series of adsorbents with various well-known functional groups including amidoximate (AO(-)), carboxyl (Ac(-)), glutarimidedioximate (HA(-)), and bifunctional AO(-)/Ac(-), HA(-)/Ac(-) on different alkyl chains (R'═CH3, R″═C13H26) were systematically studied by quantum chemical calculations. For all the uranyl complexes, the monodentate and η(2) coordination are the main binding modes for the AO(-) groups, while Ac(-) groups act as monodentate and bidentate ligands. Amidoximes can also form cyclic imide dioximes (H2A), which coordinate to UO2(2+) as tridentate ligands. Kinetic analysis of the model displacement reaction confirms the rate-determining step in the extraction process, that is, the complexing of uranyl by amidoxime group coupled with the dissociation of the carbonate group from the uranyl tricarbonate complex [UO2(CO3)3](4-). Complexing species with AO(-) groups show higher binding energies than the analogues with Ac(-) groups. However, the obtained uranyl complexes with Ac(-) seem to be more favorable according to reactions with [UO2(CO3)3](4-) as reactant, which may be due to the higher stability of HAO compared to HAc. This is also the reason that species with mixed functional group AO(-)/Ac(-) are more stable than those with monoligand. Thus, as reported in the literature, the adsorbability of uranium can be improved by the synergistic effects of amidoxime and carboxyl groups.
authors.affiliation: Group of Nuclear Energy Chemistry, 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, China.
authors.forename: Cong-Zhi
authors.initials: CZ
authors.lastname: Wang
authors.forename: Jian-Hui
authors.initials: JH
authors.lastname: Lan
authors.forename: Qun-Yan
authors.initials: QY
authors.lastname: Wu
authors.forename: Qiong
authors.initials: Q
authors.lastname: Luo
authors.forename: Yu-Liang
authors.initials: YL
authors.lastname: Zhao
authors.forename: Xiang-Ke
authors.initials: XK
authors.lastname: Wang
authors.forename: Zhi-Fang
authors.initials: ZF
authors.lastname: Chai
authors.forename: Wei-Qun
authors.initials: WQ
authors.lastname: Shi
mesh_terms: D000327:Adsorption; D000577:Amides / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D010091:Oximes / Q000737:chemistry*; D012623:Seawater / Q000737:chemistry; D014501:Uranium / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D000577:Amides; D002264:Carboxylic Acids; D010091:Oximes; D014501:Uranium