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To expose carboxyl groups on metal-organic frameworks (MOFs) while avoiding their coordination, the core strategy involves steric hindrance shielding + ligand design + synthesis control. The specific approach is as follows:
Ligand molecule design: Select ligands containing multiple carboxyl groups, introduce large-volume groups (such as tert-butyl, phenyl) to shield some of the carboxyl groups, utilize steric hindrance to prevent their coordination with metal ions, and retain the active carboxyl groups.
Synthesis condition control: Control the molar ratio of metal ions to ligands (ligand excess), use low-temperature short-time reactions (e.g., room temperature / 40°C, 6–12 hours), reduce the probability of carboxyl groups coordinating with metals; choose weakly coordinating solvents (such as ethanol), reduce solvent competition for coordination interference.
Post-treatment activation: After synthesis, use a good solvent (such as DMF, methanol) to extract uncoordinated ligands by Soxhlet extraction, then vacuum heat activate to remove residual solvents and expose the uncoordinated carboxyl groups on the surface.
