Carboxylate‐Driven Metal Pre‑Fixation COF@MOF Synthesis: Enabling Tailored Structural, Dimensional, and Defect Engineering

ABSTRACT Hierarchical composites composed of covalent‐organic frameworks (COFs) and metal‐organic frameworks (MOFs) (COF@MOF), exhibiting superior tunability in terms of pore structure and electronic distribution, have gained increasing attention in various fields. However, the development of a universal strategy for controllable assembly of COF@MOF composites, enabling precise tuning of composition and structure, remains a significant challenge. Here, a flexible and adjustable COF@MOF synthesis strategy (metal pre‑fixation, MPF) is proposed, which facilitates the extensive growth of MOFs with varying morphologies and particle sizes on the surface of PY‐COF‐COOH. By employing a hypothesis‐deduction approach alongside experimental and density functional theory (DFT) calculations, systematically elucidated that the MPF strategy enables controllable modulation of morphology, size, and coordination structure through ion distribution‐guided synthesis (IDGS), a proposed working hypothesis of crystal‐facet shielding (CFS), and aperture synergistic regulation (ASR) effects. Furthermore, the MPF‐derived PY‐COF‐COOH@MOFs exhibit significantly enhanced CH ₄ /C ₂ H ₆ /C ₃ H ₈ separation performance and sustained H ₂ O ₂ activation efficiency. These results demonstrate significant potential in designing high‐performance COF@MOF composites and offer a comprehensive application guide for MPF‐based design.