Reversible Exfoliation-Aggregation Dynamics in Ionic COFs for Tunable Interfacial Catalysis

2D covalent organic frameworks (COFs) have emerged as promising functional materials for catalysis, adsorption, sensing, and energy storage. Their interfacial behavior and surface microenvironment play a decisive role in performance, yet these features are typically considered static or irreversible due to the lack of dynamic structure models. In this study, we report the construction of an ionic COF (iCOF), I-4, designed through precise tuning of its skeleton and counterions, which uniquely exhibits reversable dynamic exfoliation and aggregation behavior in aqueous environments. This enables bidirectional control over particle size and phase states. Photocatalytic hydrogen evolution (PHE) studies reveal a strong correlation between solution concentration, particle size, and hydrogen production efficiency. Notably, I-4 achieves a remarkable PHE rate of 190 mmol g^-1 h^-1 at 35°C. Moreover, the material can be fully precipitated and recovered from solution by simple iodide salt addition, enabling closed-loop material recycling. Mechanistic analysis based on weak-force interactions and soft-hard acid-base theory provides insight into the dynamic exfoliation process, highlighting the synergistic roles of counterion assembly and framework structure. These findings pave the way for the tailored synthesis of next-generation dynamic COF materials with reversible interfacial adaptability, offering broad application potential in catalysis, ion transport, and molecular separation.