Advanced photocatalysts for uranium extraction: Elaborate design and future perspectives

Nuclear energy has been regarded as one of the promising energy sources to replace traditional fossil fuels due to its advantages of high energy density and carbon-free emission. Unfortunately, the limited storage of uranium ore restricted the sustainable development of nuclear energy, together with the generation of uranium-containing wastewater resulting in the problems of environmental pollution. Therefore, extracting and recycling uranium from seawater and radioactive uranium-containing wastewater is necessary for the sustainable development of nuclear energy and environmental protection. The light-driven heterogeneous photocatalytic technology is an appealing strategy to significantly promote the kinetics, capacity, and selectivity during uranium extraction. However, the recovery of uranium from radioactive wastewater/seawater is restricted by various factors, such as abundant competing ions, low uranium concentration, coexisting organic matter, and strong acidity or alkalinity in special environmental in the process of practical application. In this review, we described the general background of uranium extraction, followed by a brief discussion of the several possible reduction paths for photocatalytic reduction of uranium. Then, the effects of experimental conditions, photocatalyst stability and environmental adaptability on the performance of photocatalytic uranium reduction were systematically discussed. After having some fundamental understanding on photocatalytic uranium reduction, we summarized the design guidelines of photocatalysts for uranium reduction, and further discussed the corresponding advantages and disadvantages in photocatalytic uranium reduction. In addition, we concluded the current available characterization techniques for identifying uranium species after reduction, which is critical to the mechanistic study. Finally, we end this review with an outlook into the remaining challenges and future perspectives of photocatalytic uranium reduction.