Highly efficient photocatalytic uranium extraction from seawater via oxidation pathway: Performance and mechanism

Photocatalytic uranium extraction from seawater traditionally focuses on photogenerated electron reduction, overlooking the potential of oxidation pathways mediated by photogenerated holes and reactive oxygen species. In this study, we demonstrate that oxidative interfaces achieve 1.96‑fold higher uranium extraction rates than reducing interfaces. Oxidative surfaces generate hydroxyl radicals and predominantly form the stable uranyl peroxo hydrate, (UO₂)O₂·4 H₂O, while also exhibiting superior anti-fouling properties through microbial growth inhibition and rejection of competing ion. In contrast, reducing interfaces produce a mixture of (UO₂)O₂·4 H₂O and unstable UO₂, the latter prone to reoxidation and release into seawater. Band structure analyses reveal that heterojunctions between TiO₂ and (UO₂)O₂·4 H₂O on oxidative interfaces promote sustainable hydroxyl radical generation, yielding a 78 % increase in pre‑saturation (unsaturated) uranium uptake capacity. Overall, oxidation-driven uranium extraction offers advantages in extraction efficiency, product stability, process sustainability, and anti-fouling performance, thereby guiding the design of advanced photocatalysts for uranium extraction.