Enhanced photocatalytic U(VI) reduction via double internal electric field in CoWO/covalent organic frameworks p-n heterojunction.

Photoreduction of highly toxic U(VI) to less toxic U(IV) is crucial for mitigating radioactive contamination. Herein, a CoWO/TpDD p-n heterojunction is synthesized, with TpDD serving as the n-type semiconductor substrate and CoWO as the p-type semiconductor grown in situ on its surface. The Fermi energy difference between TpDD and CoWO provides the electrochemical potential for charge-hole separation. Moreover, the Coulombic forces from the distinct carrier types between the two materials synergistically facilitate the transfer of electrons and holes. Hence, an internal electric field directed from TpDD to CoWO is established. Under photoexcitation conditions, charges and holes migrate efficiently along the curved band and internal electric field, further enhancing charge-hole separation. As a result, the removal capacity of CoWO/TpDD increases from 515.2 mg/g in the dark to 1754.6 mg/g under light conditions. Thus, constructing a p-n heterojunction proves to be an effective strategy for remediating uranium-contaminated environments.