Isomer-tailored vinylene-based COFs for photo-enhanced uranium extraction from seawater: Mechanistic insights into carrier dynamics and structural superiority

Addressing the challenges of uranium extraction from seawater (UES) requires innovative strategies to overcome ultralow concentration (3.3 ppb) and thermodynamic limits. Herein, we propose a regioisomeric engineering strategy to design vinylene-linked covalent organic frameworks (COFs) for synergistic adsorption-photocatalytic UES. Two isomeric COFs, β-PTTN-AO and α-PNNB-AO, were synthesized by tuning the substitution positions of amidoxime (AO) groups on olefin bonds. The β-PTTN-AO isomer achieves a remarkable UES capacity of 12.74 ± 0.21 mg·g⁻¹ in nature seawater, surpassing its α-positioned counterpart (8.9 ± 0.18 mg·g⁻¹) and outperforming most reported photocatalysts. Combined experiments and density functional theory (DFT) theoretical studies correlate regioisomeric configurations with electronic structure modulation and photocatalytic activity. Specifically, β-PTTN-AO enhance π-electron delocalization and strengthen built-in electric fields, promoting exciton dissociation, charge separation, and uranium reduction. This work establishes a molecular design paradigm for COF photocatalysts, advancing sustainable nuclear energy through structural isomerism.