In-situ oxidized tungsten disulfide nanosheets achieve ultrafast photocatalytic extraction of uranium through hydroxyl-mediated binding and reduction

Photoreduction of hexavalent uranium (U(VI)) by semiconductor provides a novel and effective avenue for uranium extraction. Unfortunately, the traditional metal oxide and sulfide semiconductors suffer from the lack of confinement sites to U(VI), which resulted in the long period (~ 1 h) to achieve a high U(VI) extraction efficiency of > 90%. Herein, we successfully constructed WS₂ nanosheets and created in-situ oxidized domains on the surfaces (O-WS₂) to promote the uranium extraction and the corresponding removal kinetics. In this system, the O_7.7-WS₂ nanosheets exhibited a considerable U(VI) extraction efficiency of > 90% within 20 min in 8 mg·L^–1 U(VI)-containing solution, which represented the highly efficient U(VI) removal performance. In 200 mg·L^–1 U(VI)-containing solution, the O_7.7-WS₂ nanosheets exhibited an extraction capacity of 652.4 mg·g^–1. The mechanism study revealed that the oxidized surface tended to trap hydrogen atom and in-situ form hydroxyl groups in defect sites. Evidenced by a series of experiment, such as kinetic isotope effect, ¹H nuclear magnetic resonance (NMR) spectra, and X-ray absorption near-edge structure (XANES) spectra, the in-situ formed hydroxyl groups participated in the uranium reduction, which dramatically enhanced uranium extraction kinetics and efficiency.