RESUMEN
Photoreduction of highly toxic U(VI) to less toxic U(IV) is crucial for mitigating radioactive contamination. Herein, a CoWO4/TpDD p-n heterojunction is synthesized, with TpDD serving as the n-type semiconductor substrate and CoWO4 as the p-type semiconductor grown in situ on its surface. The Fermi energy difference between TpDD and CoWO4 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 CoWO4 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 CoWO4/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.
RESUMEN
Plasmonic photocatalysis is an effective strategy to solve radioactive uranium hazards in wastewater. A plasmonic photocatalyst Bi/Bi2O3-x@COFs was synthesized by in-situ growth of covalent organic frameworks (COFs) on Bi/Bi2O3-x surface for the U(VI) adsorption and plasmonic photoreduction in rare earth tailings wastewater. The presence of oxygen vacancy in Bi/Bi2O3-x and Schottky potential well formed by Bi and Bi2O3-x interface increased the number of free electrons, which induced localized surface plasmon resonance (LSPR) and enhanced the light absorption performance of composites. In addition, oxygen vacancy improved the Fermi level of Bi/Bi2O3-x, leading to another potential well between Bi2O3-x and COFs interface. The electron transport direction was reversed, thus increasing the electron density of COFs layer. COFs was an N-type semiconductor with specific binding U(VI) groups and suitable band structure, which could be used as an active reaction site. Bi/Bi2O3-x@COFs had 1411.5 mg g-1 removal capacity and high separation coefficient for U(VI) due to the synergistic action of photogenerated electrons and hot electrons. Moreover, the removal rate of uranium from rare earth tailings wastewater by regenerated Bi/Bi2O3-x@COFs was over 93.9%. The scheme of introducing LSPR and Schottky potential well provides another way to improve the photocatalytic effect.
RESUMEN
Photocatalytic reduction of UVI to UIV can help remove U from the environment and thus reduce the harmful impacts of radiation emitted by uranium isotopes. Herein, we first synthesized Bi4Ti3O12 (B1) particles, then B1 was crosslinked with 6-chloro-1,3,5-triazine-diamine (DCT) to afford B2. Finally, B3 was formed using B2 and 4-formylbenzaldehyde (BA-CHO) to investigate the utility of the D-π-A array structure for photocatalytic UVI removal from rare earth tailings wastewater. B1 lacked adsorption sites and displayed a wide band gap. The grafted triazine moiety in B2 introduced active sites and narrowed the band gap. Notably, B3, a Bi4Ti3O12 (donor)-triazine unit (π-electron bridge)-aldehyde benzene (acceptor) molecule, effectively formed the D-π-A array structure, which formed multiple polarization fields and further narrowed the band gap. Therefore, UVI was more likely to capture electrons at the adsorption site of B3 and be reduced to UIV due to energy level matching effects. UVI removal capacity of B3 under simulated sunlight was 684.9 mg g-1, 2.5 times greater than B1 and 1.8 times greater than B2. B3 was still active after multiple reaction cycles, and UVI removal from tailings wastewater reached 90.8%. Overall, B3 provides an alternative design scheme for enhancing photocatalytic performance.