Researchers have a new material that selectively binds dissolved uranium with a low-cost polymer adsorbent. This could lower the cost and increase the efficiency of extracting uranium from oceans for sustainable energy production.
There is about 4 billion tons of uranium in the oceans with a concentration of 3 milligrams per ton.
Popovs took inspiration from the chemistry of iron-hungry microorganisms. Microbes such as bacteria and fungi secret natural compounds known as “siderophores” to siphon essential nutrients like iron from their hosts. “We essentially created an artificial siderophore to improve the way materials select and bind uranium,” he said.
The team used computational and experimental methods to develop a novel functional group known as “H2BHT”—2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine—that preferentially selects uranyl ions, or water-soluble uranium, over competing metal ions from other elements in seawater, such as vanadium.
The fundamental discovery is backed by the promising performance of a proof-of-principle H2BHT polymer adsorbent. Uranyl ions are readily “adsorbed,” or bonded to the surface of the material’s fibers because of the unique chemistry of H2BHT. The prototype stands out among other synthetic materials for increasing the storage space for uranium, yielding a highly selective and recyclable material that recovers uranium more efficiently than previous methods.
In addition to the successful synthesis and testing of the adsorbent, complete agreement between computational and experimental results from small-molecule studies have been validated by a proof-of-principle synthesis of the adsorbent material that exhibits the same features as small-molecule ligand. This study ushers in a practical approach towards the polymer design and synthesis of adsorbent materials decorated with the tailor-made ligands.
Over millennia, nature has evolved an ability to selectively recognize and sequester specific metal ions by employing a wide variety of supramolecular chelators. Iron-specific molecular carriers—siderophores—are noteworthy for their structural elegance, while exhibiting some of the strongest and most selective binding towards a specific metal ion. Development of simple uranyl (UO22+) recognition motifs possessing siderophore-like selectivity, however, presents a challenge. Herein we report a comprehensive theoretical, crystallographic and spectroscopic studies on the UO22+ binding with a non-toxic siderophore-inspired chelator, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H2BHT). The optimal pKa values and structural preorganization endow H2BHT with one of the highest uranyl binding affinity and selectivity among molecular chelators. The results of small-molecule standards are validated by a proof-of-principle development of the H2BHT-functionalized polymeric adsorbent material that affords high uranium uptake capacity even in the presence of competing vanadium (V) ions in aqueous medium.
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