Constructing compressed hexagonal COFs via “Debus-Radziszewski” multicomponent reaction based on “two-in-one” monomers for Ba2+/Pb2+ separation

The “two-in-one” strategy has been widely adopted for constructing diverse covalent organic frameworks (COFs) due to its excellent solvent adaptability. However, its reliance on simple single component reactions limits access to COFs with higher complexity and functionality. Herein, we integrated multicomponent reactions (MCRs) with the “two-in-one” strategy for the first time, fabricating three dual-linkage COFs (TAPQ-COF, 2,3-DHTAPQ-COF, and 2,5-DHTAPQ-COF) featuring compressed hexagonal pore structures. The concurrent presence of imine and imidazole linkages in the COF skeletons induced distinct crystallization pathways compared to counterparts with single linkage. Crucially, hydrogen bonding was found to modulate final crystallinity by influencing crystallization pathways. When applied to Ba 2+ /Pb 2+ separation—simulating the isolation of medical radionuclide 212 Pb from 224 Ra/ 212 Pb or 228 Ra/ 212 Pb generators—the isomeric 2,3-DHTAPQ-COF significantly outperformed 2,5-DHTAPQ-COF in adsorption performance. 2,3-DHTAPQ-COF exhibited exceptional selectivity for Pb 2+ (separation coefficient β Pb/Ba up to 54.2). Experimental and theoretical evidence revealed that the enhanced selectivity originates from the enhanced coordination ability of ortho-hydroxyl groups. This work ingeniously merges MCRs with the “two-in-one” strategy, expanding the structural diversity of COFs accessible through simplified synthesis and broadening the scope of MCR applications. The superior Ba 2+ /Pb 2+ separation capability of 2,3-DHTAPQ-COF provides new insights for designing COFs targeting medical radionuclide purification.