As the world moves away from fossil fuels, nuclear power is expected to become a key source of energy. Uranium mined from geological reserves is finite and may fuel nuclear energy production for only a hundred years. Meanwhile, the ocean has accumulated enough uranium — several billion tonnes, carried from eroded rocks by waterways over millions of years — to potentially sustain nuclear power far into the future. The challenge is designing a material that can capture this uranium from seawater, where it is present at very dilute, parts-per-billion concentrations along with a medley of other metals and ions that vie for binding sites. To meet commercial needs and compete with land-based mining, a material must extract 30 mg g–1 uranium from seawater in a single use — a value so far unmet.Key to the nanowires’ photocatalytic performance is their morphology. Semiconducting COFs have drawn interest as photocatalysts in recent years, but in their typical irregular bulk forms, their performance for uranium recovery has fallen short. “Conventional semiconductor catalysts have low fluorescence photocurrent intensities, which cannot effectively perform electron transmission, leading to poor performance of uranium extraction from seawater,” says Zhu. The team reasoned that a low-dimensional version of a semiconducting COF might dramatically improve the performance over the bulk, owing to increased surface area-to-volume ratios (and more active sites) and the effect of confined dimensions on charge transport.
