Efficient photoreduction of hexavalent uranium over defective ZnO nanoparticles by oxygen defect engineering

Photoreduction of soluble hexavalent uranium to insoluble tetravalent uranium U(iv) is a promising strategy to achieve effective uranium extraction from radioactive wastewater. Herein, ZnO nanoparticles (ZnO NPs) with an abundance of oxygen vacancies (O-v) were prepared to achieve U(vi) photoreduction under simulated sunlight irradiation. The analysis of the band structure revealed that the introduction of O-v into ZnO NPs both effectively broadened the response range to visible light and narrowed the band gap. ZnO-400 displayed the maximum removal rate which reached 98.5% with an apparent rate value of 0.019 h(-1) in 200 mg L-1 of U(vi) solution. Accordingly, the introduction of O-v into ZnO NPs tailored the energy level structure and enhanced the spatial separation efficiency of electron-hole pairs, thereby further realizing the improvement of U(vi) extraction efficiency for ZnO-400. This work provided a promising strategy for designing advanced photocatalysts by the vacancy engineering of metal oxides for selective U(vi) extraction.