Metal-binding polymer continues to surprise

The world’s oceans contain more than 4 billion tons of uranium, an amount that could supply fuel for nuclear power production for centuries. The trick is how to harvest the metal ions, which occur at a dilute 3.3 ppb in the vast and deep blue sea.

Chemists have long been developing polymeric materials that selectively absorb uranium, gold, and other valuable metals from seawater. For uranium, researchers have focused on sorbent mats made from poly(amidoxime)s in which the nitrogen-oxygen functional groups in the polymers selectively bind uranium ions.

In a new study, Alexander S. Ivanov of Oak Ridge National Laboratory (ORNL) and coworkers report a nuance in this chemistry: poly(amidoxime)s actually bind vanadium ions better than uranium ions. This observation could lead to developing better materials for plucking uranium out of seawater, Ivanov says, but also help in efforts to mine the oceans for metals like vanadium and lithium, which are used in batteries, rather than using environmentally destructive surface mining (Nat. Commun. 2017, DOI: 10.1038/s41467-017-01443-1).

By using a combination of titration, X-ray spectroscopy, and computer simulation, ORNL researchers in collaboration with Lawrence Berkeley National Laboratory and UC Berkeley found that the cyclic imide-dioxime units in poly(amidoxime)s preferentially bind V⁵⁺ over UO₂²⁺. They also found that linear amidoxime units in the polymers don’t bind V⁵⁺ but do bind UO₂²⁺. This knowledge should help researchers design polymers for more efficient capture of uranium, vanadium, and other metals.