In-situ encapsulation of NiS into Ni-MOF as a photoelectrochemical cathode for HER-driven uranium extraction from aqueous solution

Extracting uranium from uranium-containing wastewater can effectively address the issues of environmental pollution and uranium shortage. Reducing soluble U(VI) to insoluble U(IV) represents an effective strategy for uranium extraction from solution. However, the two axially coordinated oxygen atoms in the uranyl ion (UO₂ 2+ ) create a high energy barrier for electron migration, which impedes the reduction of UO₂ 2+ . Herein, an innovative photochemical system for the efficient uranium extraction from aqueous solutions through the hydrogen evolution reaction (HER) process is designed. In this process, NiS nanoclusters were in-situ encapsulated within Ni-MOF to form a cathode (NiS@Ni-MOF) with high HER activity. The photoanode consists of FTO-supported TiO₂ nanorod arrays coupled with a back-contact silicon solar cell (Si SC). Due to the high HER activity of the NiS@Ni-MOF cathode and the incorporation of the Si SC in the photoanode, the uranium extraction efficiency can reach 99.5 % within 15 min of illumination. This enhancement is attributed to the formation of NiS nanoclusters and the synergistic interaction between NiS and Ni-MOF, which alters the electronic structure. This work opens a new perspective for the extraction of uranium from the aqueous solution.