Amidoximes as ligand functionalities for braided polymeric materials for the recovery of uranium from seawater. (18th April 2016)

• Record Type: Journal Article
• Authors: Lashley, Mark A.; Mehio, Nada; Nugent, Joseph W.; Holguin, Erick; Do-Thanh, Chi-Linh; Bryantsev, Vyacheslav S.; Dai, Sheng; Hancock, Robert D.
• Is Part Of: Polyhedron. Volume 109(2016)
• Page Start: 81
• Page End: 91
• Publication Date: 2016-04-18
• Subjects: Uranium -- Extraction from ocean -- Formation constants -- Fluorescence -- Density functional theory; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2016.01.026
• Languages: English
• ISSNs: 0277-5387

Abstract

Abstract : Graphical abstract: The formation constants of the amidoximate ligands bzam (benzamidoxime) and acetam (acetamidoxime) with the uranyl ion were measured by absorbance and fluorescence spectroscopy, which yield at 25 °C and ionic strength = 0, for bzam: log K 1 = 12.4, log β 2 = 22.3, for acetam: log K 1 = 13.6, log β 2 = 23.7. These log K values are related to the possible use of amidoximate groups as the functional groups attached to polymeric materials as the basis for recovering uranium from the oceans. Abstract: The formation constants of the UO2 2+ cation with the amidoximate ligands bzam (benzamidoxime) and acetam (acetamidoxime) are reported. These are of interest in light of their proposed use as the functional groups of extractants for uranium in seawater. The formation constants of bzam with UO2 2+ were measured by monitoring the absorbance of the π → π ∗ transitions in the UV spectrum of the bzam ligand in the presence of 1:1 UO2 2+ as a function of pH. This yielded log K 1 = 12.4 for UO2 2+ with bzam, and log K = 6.9 for the equilibrium UO2 (bzam) + + OH − = UO2 (bzam)OH at 25 °C and ionic strength zero. The bzam complexes were also studied monitoring the fluorescence of the UO2 2+ system. Analysis of the intense fluorescence that occurs in 5 × 10 −6 M UO2 2+ solutions between pH 5 and 9 suggested that this was due to the [(UO2 )3 O(OH)3 ] + trimer. Monomeric species such as UO2 2+ and [UO2 (OH)4 ] 2−, and dimers such as [(UO2 )(OH)2 ] 2+, fluoresce only weakly. Titration of such solutions with bzam supported the above log K values measured by absorbance, and with higher bzam concentrations yielded log β 2 = 22.3. The acetam ligand does not have any absorbance, so that complex-formation was monitored by fluorescence only. Formation constants measured by fluorescence may differ from those measured by other techniques such as absorbance. The agreement obtained between log K values measured by absorbance and fluorescence for the bzam complex of UO2 2+ supported the log K values measured for the acetam complexes by florescence alone were reliable: log K 1 = 13.6, log β 2 = 23.7, and log K UO2 (acetam) + + OH − = UO2 (acetam)OH = 6.8. The high log K values found for the bzam and acetam complexes of UO2 2+ were analyzed using DFT calculations. These log K values are related to the ability of polymer-based extractants bearing bzam or acetam type functional groups to extract UO2 2+ at a concentration of 1.3 × 10 −8 M and in the competing 0.0025 M CO3 2− present in the oceans.