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.

Photocatalytic reduction of U(VI) represents a novel and effective manner for the removal of U(VI) pollutant from radioactive wastewater. Herein, we successfully incorporated hydrogen into VO₂ nanosheets, which strengthened the interaction between VO₂ and U(VI), thereby achieving a highly active and stable photocatalyst for U(VI) reduction. With the increase of H content in hydric VO₂ (H_x-VO₂) nanosheets, the bandgap shrank from 2.29 to 1.66 eV, whereas the position of conduction bands remained more negative than the reduction potential of U(VI)/U(IV) (0.41 V vs. NHE). When irradiated by simulated sunlight, the U(VI) removal efficiency over H_0.613-VO₂ nanosheets reached up to 95.4% within 90 min, which largely outperformed 28.3% of pristine VO₂ nanosheets. The mechanistic study demonstrated that the hydroxylated surface gave rise to the balanced O confinement sites in VO₂ (011), leading to the stabilized adsorption configuration and increased binding strength of UO₂²⁺ on H_x-VO₂ nanosheets.

Photocatalytic aerobic oxidation by using oxygen molecules (O₂) as green and low-cost oxidants is of great attraction, where the introduction of irradiation has been proved as an efficient strategy to lower reaction temperature as well as promote catalytic performance. Moreover, the oxygen vacancies (OVs) of catalyst are highly active sites to adsorb and activate O₂ during photocatalytic aerobic oxidation. However, OVs are easily blocked by oxygen atoms from active oxygen species during the catalytic process, leading to the deactivation of catalysis. Herein, a promising catalyst toward photocatalytic aerobic oxidation was successfully developed by recovering the OVs through doping Au atoms into Ti₃C₂T_x MXene (Au/Ti₃C₂T_x). Impressively, Au/Ti₃C₂T_x exhibited remarkable activity under full-spectrum irradiation towards photooxidation of methyl phenyl sulfide (MPS) and methylene blue (MB), attaining a conversion of >90% at room temperature. Moreover, Au/Ti ₃C₂T_x also manifested remarkable stability by maintaining >95% initial activity after 10 successive reaction rounds. Further mechanistic studies indicated that the OVs of Au/Ti ₃C₂T_x served as the active centers to efficiently adsorb and activate O₂. More importantly, the doped Au atoms of Au/Ti₃C₂T_x were conducive to the recovery of OVs during photocatalytic process from the results of theoretical and experimental aspects. The recovered OVs of Au/Ti₃C₂T_x continuously and efficiently activated O₂, directly contributing to the remarkable catalytic activity and stability.