Design and Construction of Ultrahigh Charge Density Ionic Covalent Organic Polymer for Efficient ReO₄^- Capture

Developing designable strategies to construct ionic covalent organic polymers (iCOPs) with ultrahigh charge density is critical for enhancing efficient and selective ion separation. Herein, we report a stepwise organic salt-forming strategy to fabricate iCOP with tunable and ultrahigh charge density using a new dicationic bipyridine-based block with dual reactive sites. The resulting iCOP, TPB-MBP-4Cl, shows an exceptional ReO₄^- capture capacity of up to 1577 mg g^-1, along with an ultrahigh distribution coefficient (7.49 × 10⁷ mL g^-1) and adsorption efficiency of 99.997%, respectively, exhibiting superior adsorption performance compared to most previously reported adsorbents. More importantly, TPB-MBP-4Cl also demonstrates remarkable selectivity for ReO₄^- even in the presence of excess interfering anions, as well as excellent recyclability. Kinetic studies demonstrate an ultrafast adsorption process, achieving 99.3% removal of ReO4^- within 1 min at an initial concentration of 1000 ppb, with the residual concentration reduced to 0.02 ppb. Theoretical investigations reveal that the ultrahigh charge density plays a decisive role in adsorption capacity and selectivity. This work establishes a designable strategy for constructing high charge density iCOPs and provides a new sorbent for highly efficient capture of ReO₄^-.