Theoretical Implications of Bifunctional Ligands to Improve Uranium Extraction Performance

Extraction of uranium from seawater is considered to be an effective way to solve the shortage of uranium resources, and the development of efficient adsorption functional groups is the key to uranium extraction. In this work, the complexation of uranyl cations with a series of diamidoxime and bifunctional (amidoximate-carboxylate, amidoximate-phosphate) ligands has been probed by quantum chemical calculations. For most of the uranyl complexes, the amidoxime groups adopt eta 2 mode to uranyl cations. Based on bonding analyses, we found that the uranyl complexes with methyl-substituted ligands (H2L ') possess stronger covalent interactions than those with phenyl-substituted ligands (H2L). Consequently, the uranyl complexes with H2L' are more stable in the extraction process according to thermodynamic analysis. The amidoximate-phosphate bifunctional ligand (H2L3 ') has stronger extraction capacity to uranyl cations than other ligands, which is related to the relatively lower decomposition energy, and it shows selectivity in seawater for uranyl cations over vanadium ions, which may be a potential ligand for uranium extraction. Therefore, the introduction of synergistic functional groups, i. e. the bifunctional ligands, enhance the extraction properties of uranyl cations. This work improves understanding of synergistic ligands, and may contribute to design and development of efficient ligands for recovery of uranium from seawater.