Constructing donor-acceptor covalent organic frameworks with bex topology for efficient photocatalytic reduction of uranium

Abstract

Effective elimination of uranium from wastewater is crucial for sustainable development in the nuclear industry. Extracting U(VI) by photocatalytic reduction using covalent organic frameworks (COFs) is regarded as an effective and environmentally friendly method. However, COFs with unconventional bex topology for photocatalytic uranium reduction remain largely unexplored. Herein, we synthesized three COFs that have distinct bex topology, and their performances in the photocatalytic reduction of U(VI) were investigated. Among these COFs, Py-TAPT-COF, in which triazine unit acts as an electron acceptor and the pyrene unit functions as an electron donor, showed excellent photocatalytic reduction capability and reached 92.1% for U(VI). Additionally, from a mixture containing 13 competing metal ions, Py-TAPT-COF demonstrated remarkable uranium extraction selectivity, and maintained its original photocatalytic efficiency, reaching 78.8% after four consecutive cycles. Density Functional Theory (DFT) calculations revealed that the triazine and pyrene units are potent active photocatalytic reaction sites, which significantly promote the separation of photoelectrons from vacancies.