Uranium remains a key fuel for nuclear power, but conventional mining raises environmental and economic concerns, prompting interest in extracting uranium from wastewater, seawater, and contaminated industrial effluents. Electrochemical extraction offers controllable operation, fast response, and selectivity, yet progress has been limited by electrode passivation, interference from competing ions, and the cost and complexity of fabricating efficient electrodes.
In this work, the research team reports a self-supporting covalent organic framework electrode on carbon cloth that performs sorption and electrochemical functions at the same time. The electrode uses a polyarylether backbone to drive the two-electron oxygen reduction reaction that generates hydrogen peroxide, while amidoxime groups selectively coordinate uranyl ions to create a coupled chemical and electrochemical pathway for uranium capture.
The authors systematically examined how operating conditions affect uranium extraction and identified solution pH as a critical parameter. Under acidic conditions, protonation of amidoxime groups weakens their interaction with uranyl ions, reducing extraction efficiency. At neutral to alkaline pH, amidoxime sites bind uranium more strongly and favor formation of studtite, a crystalline uranium peroxide phase that forms on the electrode during operation, enabling extraction efficiencies above 90 percent when pH is kept in a favorable range.
Applied voltage is another central control factor because it regulates the rate of hydrogen peroxide generation via the oxygen reduction reaction. Higher potentials increase the local hydrogen peroxide concentration at the electrode surface, which accelerates studtite growth and raises uranium recovery, especially at higher uranium concentrations in solution.
Performance tests in electrolytes containing sodium ions and organic additives typical of industrial wastewater show that the electrode maintains uranium extraction efficiencies above 85 percent. These results indicate that amidoxime functional groups retain strong selectivity for uranyl ions even in high ionic strength or organic-rich environments that would normally interfere with extraction processes.
Long-duration trials in organic-rich radioactive wastewater highlight the system's durability and capacity. Over 450 hours of continuous operation, the self-standing electrode accumulates more than nine thousand milligrams of uranium per gram of electrode material, placing its performance among the highest reported for electrochemical uranium recovery technologies.
The extraction mechanism combines two linked steps: amidoxime groups first chelate uranyl ions and act as nucleation centers, and electrochemically generated hydrogen peroxide then sustains studtite crystal growth on the electrode surface. This coupled process stabilizes uranium capture under chemically challenging conditions and supports extended operation without rapid loss of activity.
The researchers note that several issues still need to be addressed for wider deployment, including improving scalable electrode fabrication, reducing sensitivity to pH fluctuations, and limiting blockage of active sites during long-term cycling. They point to future work that could use data-driven material design, improved potential control protocols, in situ or operando characterization, and modular flow system engineering to adapt the approach for large-scale uranium recovery and broader environmental remediation.
Research Report:Synergistic parameter optimization in electrochemical upcycling of uranyl: mechanisms and perspectives of self-standing COF electrodes
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