Halogen-Ion-Mediated Dielectric Regulation in Ionic Covalent Organic Frameworks for Efficient Photocatalytic H₂O₂ Production and Sterilization

Covalent organic frameworks (COFs) have emerged as a platform for photocatalysis owing to their modular architectures and well-defined porous frameworks. However, the low dielectric constants of organic frameworks lead to strong dielectric confinement and large exciton binding energies, which severely limit charge separation efficiency and photocatalytic performance. Herein, we report a viable strategy for modulating dielectric confinement via counteranion engineering. Halogen-functionalized ionic COFs were fabricated by first synthesizing a highly conjugated EB-COF:Br scaffold via Schiff base condensation between the ionic amino monomer ethidium bromide and the aldehyde linker 2,4,6-triformylphloroglucinol, followed by ion exchange with F⁻, Cl^-, and I⁻. We found that the strategy can modulate photocatalytic H₂O₂ production and bactericidal performance, which is attributed to variations in permittivity and exciton binding energy resulting from the differential polarization of ionic moieties. Notably, EB-COF:Cl exhibits enhanced exciton dissociation efficiency and a remarkably elevated H₂O₂ production (1400 μmol·g⁻¹·h⁻¹) when using seawater as the reaction medium, which is 1.65 times that of the pure water system. This work establishes a feasible strategy for regulating the dielectric confinement effect of iCOFs to enhance H₂O₂ production, with the improved performance in seawater systems endowing the material with promising practical applicability for marine-related environmental remediation.