Enhanced photocatalytic U(VI) reduction via double internal electric field in CoWO4/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 4 /TpDD p-n heterojunction is synthesized, with TpDD serving as the n-type semiconductor substrate and CoWO 4 as the p-type semiconductor grown in situ on its surface. The Fermi energy difference between TpDD and CoWO 4 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 4 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 4 /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. [Display omitted] • CoWO 4 /TpDD heterojunction was formed by CoWO 4 in situ grown on the TpDD surface. • The differences in energy levels and carrier types facilitate carrier separation. • The electric field and energy band facilitate the photogenerated carrier separation. • Photogenerated electrons moving to TpDD contribute to the photoreduction of U(VI). • DFT and in-situ XPS confirm the mechanism of carrier transfer in heterojunction. [ABSTRACT FROM AUTHOR]