Bi2O3/g-C3N4 hollow core–shell Z-scheme heterojunction for photocatalytic uranium extraction

Photocatalytic uranium extraction from radioactive nuclear wastewater and seawater is critical for promoting the sustainable advancement of nuclear industry, but the complexity of real-world environments, particularly the occurrence of anoxic and oxygen-enriched states, presents significant challenges to effective uranium extraction. Here, a layered hollow core–shell structure of Bi2O3/g-C3N4 Z-scheme heterojunction photocatalyst has been designed and successfully applied for photocatalytic uranium extraction in both aerobic and oxygen-free conditions, and the extraction efficiency of uranium can reach 98.4% and 99.0%, respectively. Moreover, the photocatalyst still has ultra-high extraction efficiency under the influence of pH, inorganic ions, and other factors. The exceptional capability for uranium extraction is on the one hand due to the distinctive hollow core–shell architecture, which furnishes an abundant quantity of active sites. On the other hand, benefiting from the suitable band gap structure brought by the construction of Z-scheme heterojunction, Bi2O3/g-C3N4 exhibits current densities (1.00 µA/cm2) that are 5.26 and 3.85 times greater than Bi2O3 and g-C3N4, respectively, and the directional migration mode of Z-scheme carriers significantly prolongs the lifetime of photogenerated charges (1.53 ns), which separately surpass the pure samples by factors of 5.10 and 3.19. Furthermore, the reaction mechanism and reaction process of photocatalytic uranium extraction are investigated in the presence and absence of oxygen, respectively.