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Bifunctional amidoxime fibers are synthesized from commercially available polyacrylonitrile as sorbents for the recovery of U­(VI) from seawater. The purpose of introducing a second ligand is to enhance the affinity of the amidoxime (AO) ligand via two possible mechanisms: by acting directly upon the AO to increase its ability to ion exchange or providing additional coordination sites to the uranyl ion. Amines are chosen as the second ligand since they have a high affinity for U­(VI) at ppm levels from synthetic seawater. Diethylenetriamine (DETA) is utilized as the amine because it is sufficiently flexible to interact with AO and able to bind metal ions. Along with AO and AO-DETA fibers, the primary NH2 moieties were modified with phosphonic acid ligands (AO-phon-DETA). All fibers have high affinities (>99% sorption) for the uranyl ion when initially present at 0.90 ppm in synthetic seawater. When contacted with actual seawater at the Pacific Northwest National Laboratory for 20.8 days, the loadings for the fibers are 124 μg/g (AO), 535 μg/g (AO-DETA), and 789 μg/g (AO-phon-DETA). For comparison, a polyethylene fiber on which was grafted polyacrylonitrile and then converted to AO at the Oak Ridge National Laboratory gave a uranyl loading of 2610 μg/g at the same contact time, perhaps due to its optimized support structure and/or the presence of diamidoxime groups. FTIR spectra indicate that the effect of DETA is through a hydrogen bonding interaction with the AO to facilitate dissociation of the acidic N–O–H. Continuing research on optimizing the loading onto the bifunctional fibers emphasizes the effect of phosphorus capacity, amine ligand, and synthesis conditions.

International audiencet/Vulcan XC 72 powders were prepared via a colloidal method. TEM and XRD studies were carried out from 273 to 573 K under oxidizing, inert, and reducing atmospheres. Under air flow, a small aggregation of platinum particles is observed, but neither fusion of particles nor increase of the Sherrer's length L-v This is explained by the presence of oxygen species on the platinum surface. Under reducing atmosphere (3%H-2/He), aggregation of platinum particles and increase of the crystallinity and/or apparent mean crystallite size are observed. L-v increases from ca. 3 nm for the fresh Pt(40 wt %)/C catalyst to ca. 7 nm after thermal treatment at 573 K. Under inert atmosphere, TEM and XRD measurements did not show any reconstruction process or L-v increase for temperatures lower than 473 K. But from 523 K, some platinum entity reconstruction was evidenced, Under reducing atmosphere, two kinetics of grain growth process seem to exist. The "induction time" tau before the second growth process is dependent on the temperature, but independent of the platinum loading. For T < 523 K, the formation of a surface Pt-H quasiliquid phase leading to crystalline reconstruction and an agglomeration process are proposed to occur. This step is then followed by grain boundary formation and grain boundary diffusion leading further to the increase of L-v (controlled by the second growth kinetics). For T >= 523 K, reconstruction by size effect is invoked for the first growth process

The primary amine −CH2NH2 ligand bound to cross-linked polystyrene has a high affinity for the uranyl ion from a matrix of artificial seawater. The uranyl capacity is 14.8 mg U/gpolymer, compared to 2.34 mg U/gpolymer for a diamidoxime ligand on a polystyrene support. Secondary and tertiary amines have much lower affinities, indicating that steric effects are important to the complexation. The results with polystyrene-bound −CH2NH2 thus suggest at least a 3-fold increase in uranyl capacity (calculated on a per mole ligand basis (not per gram of polymer, in order to make the results independent of the weight of the polymer support)) and a 4-fold increase when ligands with two primary amines per ligand are utilized. An additional advantage of the primary amine over amidoxime is that it is a simpler ligand to prepare.

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