Modulating intramolecular polarity and internal electric field in covalent organic frameworks via aromatic metrics for high-efficacy photocatalysis-self-Fenton micropollutant removal.

The photocatalysis-self-Fenton system based on covalent organic frameworks (COFs) holds promise as an advanced oxidation process for purifying aqueous emerging contaminants (ECs), yet its efficiency is frequently hampered by insufficient excition dissociation and sluggish charge transfer. Herein, we reported a facile and effective strategy based on aromatic metric engineering to overcome these challenges. Two donor-acceptor conjugated COF photocatalysts featuring different numbers of aromatic rings, namely diphenyl-based COF-TAPT-TFPT and tetraphenyl-based COF-TTPB-TFBPT, were designed and synthesized. Integrated experimental and theoretical analyses revealed that COF-TAPT-TFPT, with fewer aromatic ring moieties, possessed more pronounced intramolecular polarity between its donor and acceptor units. This enhanced polarity induced a stronger internal electric field, which significantly promoted exciton dissociation and charge carrier mobility. Benefiting from these enhancements, the synergistic interaction between photocatalytic and self-Fenton oxidations was strengthened over COF-TAPT-TFPT, enabling outstanding degradation performance toward several antibiotic ECs (e.g. 99.4% degradation of 20 mg L-1 oxytetracycline within 20 min) in a visible-light-driven photocatalysis-self-Fenton process. This performance substantially surpassed that of COF-TTPB-TFBPT and most previously reported systems. Furthermore, COF-TAPT-TFPT demonstrated excellent stability, adaptability across a wide pH range, tolerance to complex water matrices, and high effectiveness in scaled-up experiments under natural sunlight and continuous-flow conditions for antibiotic EC removal.