Facet-dependent electrochemical uranium extraction in seawater over Fe3O4 catalysts

Electrochemical uranium extraction from seawater represents an efficient strategy for the sustainable supplement of nuclear fuel, whereas the rational design of highly active electrocatalysts remains challenging due to the lack of study on structure–activity relationship. In this work, we demonstrated that the facet-dependent electrochemical uranium extraction from seawater by comparing Fe3O4 nanooctahedra with exposed {2 2 2} facet and Fe3O4 nanocubes with exposed {2 0 0} facet. In uranium-spiked electrolyte, the Fe3O4 nanooctahedra possessed extraction efficiency of 93.7 % in 8 h, which was 1.45-time larger than Fe3O4 nanocubes. In 10 L of real seawater, the Fe3O4 nanooctahedra extracted 17.49 μg of uranium within 8 h, corresponding to 3.49 mg/g of extraction capacity. The theoretical model revealed that {2 2 2} facet of Fe3O4 possessed a proper atomic distance to form a pocket of four O atoms and two Fe atoms. Such pocket enabled the binding of UO22+ with four O atoms, together with the low valent Fe atoms binding with the original two O atoms of UO22+. This binding model accounted for the more negative adsorption energy for UO22+ on {2 2 2} facet than that on {2 0 0} facet and the enhanced uranium extraction of Fe3O4 nanooctahedra.