Electro-adsorption and reduction of Uranium(VI) by Fe3O4@COFs electrode with enhanced removal performance

Electro-adsorption is a promising technology for the removal of radionuclides, the development of electrodes is the key to achieve efficient separation. Herein, Fe3O4@COFs composites were obtained via one-step preparation strategy, and then loaded onto carbon felts to achieve efficient uranium(VI) electro-adsorption and reduction. The morphological and chemical structures of the prepared Fe3O4@COFs composites were confirmed by multiple analysis techniques. The results of adsorption experiments indicated that the adsorption equilibrium can be reached in half an hour at the potential of 1.2 V and 298.15 K. And the adsorption data for uranium(VI) is well consistent with pseudo-second-order kinetics model and Langmuir isotherm model with the maximum uptake capacity of 492.6 mg/g. Meanwhile, the functionalized electrode revealed good selectivity for uranium against other competing ions according to the calculated distribution coefficient Kd (3.24 × 104 mL/g). The simulated uranium-containing wastewater experiment results indicated the vast potential of Fe3O4@COFs electrodes for uranium(VI) removal from wastewaters. XPS studies confirmed that part of the hexavalent uranium(VI) is reduced to tetravalent uranium(IV) by Fe2+ in Fe3O4@COFs composites besides being bound by carboxyl ligands. This work can be extended to efficiently remove other charged pollutants by rational ligands design.