Tuning local charge polarization of covalent organic frameworks for enhanced photocatalytic uranium (VI) reduction

[Display omitted] •Electronegative PEO-chains modified PEO-COF had strong local charge polarization.•The DFT was used to prove PEO-COF creates a big electrostatic potential difference.•PEO-COF provided a strong drive force for the separation of electrons and holes.•PEO-COF exhibited strong hydrophilicity and rapid uranium mass transfer ability.•PEO-COF exhibited excellent photocatalytic uranium reduction capability. The introduction of local charge polarization is an effective strategy to improve the electrostatic potential difference of covalent organic frameworks (COFs) photocatalysts. Herein, BPDA-COF with donor–acceptor (D-A) structure was firstly synthesized by using triphenyl-triazine and biphenyl monomers. Subsequently, the hydroxyl and bis(2-methoxyethyl)ether (PEO)-chains with increasing local charge polarization were introduced to synthesize DHBD-COF and PEO-COF, respectively. PEO-COF with electronegative and flexible PEO-chains created a strong local charge polarization to enhance the electrostatic potential differences, thus promoting the spontaneous transfer of electrons and inhibiting the recombination of electrons and holes. Furthermore, the super-hydrophilic PEO-chains provided super-strong uranium mass transfer capacity. Benefiting from these, PEO-COF exhibited excellent photocatalytic uranium reduction capabilities (1427.9 mg g−1). This work provides a novel insight to adjust the local charge polarization at the molecular level and broadens the strategy of photocatalytic reduction of U(VI) with COFs.