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Piezoelectric catalysis could convert mechanical energy into chemical energy, which can combine with solar energy for a high-efficiency piezo-photocatalysis reaction. In this work, NiTiO 3 nanorods were synthesized via the sol-gel method and initially employed for the removal of U(VI) from radioactive-contaminated water. The NiTiO 3 nanorods will generate an internal electric field in an ultrasonic environment, which could greatly improve the performance of piezo-photocatalysis in reducing U(VI) by promoting the generation of photoexcited electrons and reactive oxygen species (ROS). After exposure to visible light and ultrasound for 3 h, the NTO-R-1 exhibited superb U(VI) degradation efficiency of 93.91%, which was 2.58, 6.15, and 6.68 times greater than those of visible light, ultrasonic irradiation, and dark, respectively. Moreover, photoexcited electrons and oxygen-active species play a decisive role in the piezo-photocatalysis process. Therefore, NiTiO 3 with excellent piezo-photocatalysis properties exhibits good potential for the development of efficient wastewater purification catalysts and also helps to probe the possible mechanism of piezo-photocatalysis removal of U(VI) in wastewater.

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.