The preparation, spectroscopic characterization and thermal stability of neutral complexes of uranyl ion, UO22+, with phosphonate ligands, such as diphenylphosphonic acid (DPhP), diphenyl phosphate (DPhPO) and phenylphosphonic acid (PhP)
are described. The complexes were prepared by a reaction of hydrated uranyl nitrate with appropriate ligands in methanolic
solution. The ligands studied and their uranyl complexes were characterized using thermogravimetric and elemental analyses,
ESI-MS, IR and UV–Vis absorption and luminescence spectroscopy as well as luminescence lifetime measurements. Compositions
of the products obtained dependent on the ligands used: DPhP and DPhPO form UO2L2 type of complexes, whereas PhP forms UO2L complex. Based on TG and DTG curves a thermal stability of the complexes was determined. The complexes UO2PhP·2H2O and UO2(DPhPO)2 undergo one-step decomposition, while UO2PhP · 2H2O is decomposed in a two-step process. The thermal stability of anhydrous uranyl complexes increases in the series: DPhPO < PhP < DPhP.
Obtained IR spectra indicate bonding of P–OH groups with uranyl ion. The main fluorescence emission bands and the lifetimes
of these complexes were determined. The complex of DPhP shows a green uranyl luminescence, while the uranyl emission of the
UO2PhP and UO2(DPhPO)2 complexes is considerably weaker.
Authors:Leigh Martin, Bruce Mincher, and Nicholas Schmitt
Recently the use of the more unusual hexavalent oxidation state of americium has been receiving increased attention for the
purpose of developing an efficient Am/Cm or Am/lanthanide separation system. We have already demonstrated the feasibility
of performing this separation with 30% TBP in dodecane, and are now looking at different extractants to increase Am(VI) distribution
ratios. Following on from this the extraction of bismuth oxidized americium from nitric acid solutions by dibutyl butyl phosphonate
has been studied. The results of this study indicate that increasing the basicity of the extractant molecule has significantly
improved the extraction efficiency.