Bioinspired Buffered Microenvironment Enables Highly Crystalline 3D COF Gels With Controllable Structures for Exceptional Molecular Adsorption

Reconciling long-range crystallinity with macroscopic network formation remains a central challenge in constructing three-dimensional covalent organic framework (3D COF) gels. Inspired by biomineralization and tofu coagulation, we propose a synergistic buffered system with salt bridges for direct assembly of crystalline 3D COF gels via imine condensation. Ten metal salts were selected to regulate stable and buffered pH microenvironment. Comparing various salts revealed a correlation between pH microenvironment and the formation state and crystallinity of COFs. NaAc emerges as representative regulator for multiple roles: (i) forming AcO^-/AcOH buffer to maintain a stable weakly acidic microenvironment and promote disorder-to-order transition, (ii) regulating kinetics, defect healing, and COF topology, and (iii) Na⁺ as salt bridges stabilizing the 3D gel network. Pore topology can be switched between two crystalline phases by varying side substituents and salt addition sequence, as seen by XRD peak shift from 8.9° to 6.6°. The gels have low density (0.028-0.042 g/cm³), high compressive strength, CO₂/N₂ selectivity of 140, organic solvent uptake up to 80 times their weight, and over 90% capacity retention after 20 cycles. Overall, this work establishes a paradigm from microenvironment engineering and ion selection to topology regulation and adsorption, providing a blueprint for functional 3D COF gels.