铀酰与羧酸和肟基类配体相互作用的理论研究

Theoretical Studies on the Interaction of Uranyl with Carboxylic Acids and Oxime Ligands

深入了解各种功能基团与铀酰离子的络合行为有助于设计和开发高效海水提铀吸附剂.本工作通过密度泛函理论(DFT)方法系统地研究了两种典型铀酰络合配体吡啶-2,6-二羧酸(H_(2)DPA)和戊二酰偕亚胺二肟(H_(2)A)与铀酰离子及碳酸根离子形成的配合物的结构、成键性质以及热力学稳定性.研究结果表明,所有配合物中,配体与铀酰离子之间具有不同强度的共价相互作用.由于H_(2)A配位时发生了质子重排,而且配体的解离能较高,使其更难与[UO_(2)(CO_(3))_(3)]^(4−)发生取代反应,因此H_(2)DPA配体是海水提铀中一种潜在的有效配体.本工作的相关研究结果为海水提铀中高效吸附基团的设计和开发提供了理论线索.

Uranium is the main raw material for nuclear reactor fuel.However,uranium resources on land are limited.According to the statistic,the total amount of proven about uranium ore in the world is about 7.64×10^(6)t.The uranium reserves in seawater are about 4.5×10^(9)t,which is abundant in seawater.It is expected to alleviate the shortage of uranium resources on land by extraction of uranium from seawater.An in-depth understanding of the complexation behavior of various functional groups with uranyl ions is helpful for the design and development of high-efficient seawater uranium adsorbents.Pyridine-2,6-dicarboxylic acid group(H_(2)DPA)and glutarimidedioxime group(H_(2)A)are two typical uranyl extractants with the same coordination pattern.In the present work,we have systematically studied the uranyl extraction complexes with these two ligands and carbonate ions by quasi-relativistic density functional theory(DFT)methods.The structures,bonding properties and thermodynamic stability of the 1∶1(metal/ligand molar ratio)and 1∶2 type extraction complexes were investigated at the B3LYP/6-311G(d,p)/SDD level of theory.The results show that the covalent interaction strength between uranyl cations and these two ligands are different in the 1∶1 and 1∶2 type complexes.H_(2)DPA has a stronger coordination ability with uranyl in the 1∶1 type of complexes,while in the 1∶2 type complexes H_(2)A has a stronger coordination ability.For each complex,the covalent interaction between oxygen atom and uranyl ions is stronger than that of nitrogen atom.Due to the high proton rearrangement energy and dissociation energy of the H_(2)A ligand,the H_(2)DPA ligand is more likely to react with[UO_(2)(CO_(3))_(3)]^(4−).Therefore,the H_(2)DPA ligand is a potential effective ligand for uranium extraction from seawater.In addition,the presence of Ca^(2+)in seawater inhibits the complexation of uranyl cations and these ligands.The results of this work provide the theoretical clue for the design and development of highly effective adsorption groups in uranium extraction from seawater.