IISc Scientists Design a Membrane That Filters Uranium Out of Seawater

Scientists at the Indian Institute of Science (IISc) in Bengaluru have developed a new method to extract uranium from seawater that could also be used to remove uranium contamination from groundwater. The institute says the technique could help meet nuclear fuel needs over the long term while addressing uranium in groundwater, which poses an environmental and health risk. Uranium reserves on land are being depleted rapidly: there are an estimated 7.5 million tonnes of uranium on land, compared with about 4.5 billion tonnes dissolved in seawater.

Earlier methods for capturing uranium used porous organic polymers and functional nanomaterials that chemically bind to uranium ions, but seawater also contains many other ions, making it difficult to extract uranium selectively. Researchers in IISc's Department of Physics tackled this by designing 'slipped' covalent organic framework (COF) membranes, layered materials that completely block uranyl ions while letting seawater's common ions pass through freely.

The team, led by Yogendra Kumar and Binu Varghese under the guidance of Prabal K. Maiti, in collaboration with Accenture Labs in Bengaluru, studied the hydration structure of the ions along with the membrane's free-energy barrier and friction, finding that the specific structure of the COF layers controls the movement of individual ions. Where older methods relied on chemical functional groups to bind uranium, the new method controls ion transport primarily through the nanoscale structure of the COF layers, achieved by slightly slipping the layers relative to each other.

The researchers say the work demonstrates that the path and energy levels of ions can be controlled by precisely designing the structure of layered COF membranes, opening a route to new technologies for selectively separating substances in the environmental and energy sectors.