Hollow S-Doped ZnFe 2 O 4 Microcubes with Magnetic Separability for Photocatalytic Removal of Uranium(VI) under Different Light Intensity.

Under xenon lamps, ZnFe 2 O 4 (ZFO) has been shown to be effective in removing uranium through photocatalysis. However, its performance is still inadequate in low-light environments due to low photon utilization and high electron-hole complexation. Herein, S-doped hollow ZnFe 2 O 4 microcubes (S x -H-ZFO, x = 1, 3, 6, 9) were synthesized using the MOF precursor template method. The hollow morphology improves the utilization of visible light by refracting and reflecting the incident light multiple times within the confined domain. S doping narrows the band gap and shifts the conduction band position negatively, which enhances the separation, migration, and accumulation of photogenerated charges. Additionally, S doping increases the number of adsorption sites, ultimately promoting efficient surface reactions. Consequently, S x -H-ZFO is capable of removing U(VI) in low-light environments. Under cloudy and rainy weather conditions, the photocatalytic rate of S 3 -H-ZFO was 100.31 μmol/(g·h), while under LED lamps (5000 Lux) it was 72.70 μmol/(g·h). More interestingly, a systematic mechanistic investigation has revealed that S doping replaces some of the oxygen atoms to enhance electron transfers and adsorption of O 2 . This process initiates the formation of hydrogen peroxide, which reacts directly with UO 2 2+ to form solid studtite (UO 2 )O 2 ·2H 2 O. Additionally, the promising magnetic separation capability of S x -H-ZFO facilitates the recycling and reusability of the material. This work demonstrates the potential of ZnFe 2 O 4 extraction uranium from nuclear wastewater.