Confining Ti-oxo clusters in covalent organic framework micropores for photocatalytic reduction of the dominant uranium species in seawater

Photocatalytic reduction is a promising strategy for uranium extraction from seawater. However, due to the lack of accessible active sites, current photocatalysts work poorly under visible-light irradiation in reducing UO2(CO3)34−, the dominant uranium species in seawater. Here, a one-pot precursor preorganized encapsulation strategy was applied to confine Ti-oxo clusters (TiOCs) within the micropores of a photosensitive covalent organic framework (TiOCs∈COF-TZ), leading to the first utilization of confined photocatalysis in uranium extraction. This strategy endows the material with photocatalytic reduction capability toward UO2(CO3)34− in natural seawater, where ∼89.9% of UO2(CO3)34− was extracted by TiOCs∈COF-TZ under visible-light irradiation. In comparison with the unloaded COF-TZ and surface-loaded TiOCs@COF-TZ, the TiOCs∈COF-TZ exhibits a clear superiority both in catalytic activity and efficiency. Density functional theory (DFT) calculations infer that the photoinduced electrons are derived from the COF-TZ, whereas the TiOCs act as indispensable mediums during the electron transfer process.