Reversal of Ion Selectivity Beyond Ligand Affinity in Covalent Organic Frameworks: A Pore‐Size Confinement Synergistic Chemical Trapping Strategy

Abstract Most current strategies for targeted metal ion capture rely on a single adsorption mechanism, limiting their selectivity and precision. Synergistic regulation offers an effective solution to overcome this challenge. In this work, angstrom‐level control (16.0–20.0 Å) over the pore size of 2D covalent organic frameworks (COFs) is achieved through precise molecular‐level side‐chain engineering (R = H, OH, OMe). A novel “pore sieving‐chemical recognition” dual‐dimensional synergistic regulation strategy is proposed, revealing a reversed adsorption selectivity between Th 4+ and Pb 2+ ions. This reversal arises from the combined influence of chemical coordination and pore size exclusion, fundamentally overturning conventional ion capture trends governed solely by functional group affinity. Furthermore, the powder‐form COFs are fabricated into interwoven porous nanofiber membranes via an “electrospinning‐in situ growth” strategy. A hierarchical membrane separation system is then constructed, enabling high‐throughput and high‐precision sequential separation of Th 4+ /Pb 2+ /Ba 2+ ions under dynamic conditions. This study highlights the significant advantages of “chemical‐physical” dual‐dimensional synergistic effects in achieving precise metal ion separation and provides valuable insights for the rational design and fine‐tuning of next‐generation functional separation materials at the molecular level.