Enhanced seawater uranium extraction via flow capacitive deionization by amidoxime-functionalized MXene/CoZn-MOF...

Uranium is an essential resource for the development of sustainable nuclear industry. Flow electrode capacitive deionization (FCDI) is a promising technology for uranium extraction from natural seawater to meet the uranium shortage, due to its superior ion capture ability and continuous operation capability. Here, amidoxime-functionalized MXene/CoZn-MOF heterojunction electrodes (MMA) are designed for FCDI uranium extraction. The MMA features a hierarchical porous structure and large internal active surface area, which provide extensive mass transport pathways. Meanwhile, the amidoxime groups ensure high uranyl selectivity. Accordingly, MMA electrodes achieve a superior uranium adsorption capacity of 2322.4 mg g^-1 and remove 95.6 % uranium from 500 mg L^-1 solution using an applied voltage of 1.2 V within 2 h. In a non-circulating mode, the MMA exhibits a uranium adsorption rate of 1.43 mg g^-1 day^-1 from seawater desalination concentrate (SDC). Additionally, the MMA retain a 90.5 % removal efficiency even after 20 reuse cycles. The density functional theory and molecular dynamics simulation results indicate that the efficient charge-transfer channels of the heterojunction and strong chelation of amidoxime groups contribute to improving the uranium adsorption capacity and selectivity. Our findings unravel underlying mechanisms of FCDI and provide valuable insights for designing electric field assisted uranium extraction.