Highly Selective Separation Intermediate-Size Anionic Pollutants from Smaller and Larger Analogs via...

Selective separation of organic species, particularly that of intermediate-size ones from their analogs, remains challenging because of their similar structures and properties. Here, a novel strategy is presented, cooperatively (thermodynamically and kinetically) controlled crystallization for the highly selective separation of intermediate-size anionic pollutants from their analogs in water through one-pot construction of cationic metal-organic frameworks (CMOFs) with higher stabilities and faster crystallization, which are based on the target anions as charge-balancing anions. 4,4'-azo-triazole and Cu²⁺ are chosen as suitable ligand and metal ion for CMOF construction because they can form stronger intermolecular interaction with p-toluenesulfonate anion (Ts-) compared to its analogs. For this combination, a condition is established, under which the crystallization rate of a Ts--based CMOF is remarkably high while those of analog-based CMOFs are almost zero. As a result, the faster crystallization and higher stability cooperatively endow the cationic framework with a close-to-100% selectivity for Ts- over its analogs in two-component mixtures, and this preference is retained in a practical mixture containing more than seven competing (analogs and inorganic) anions. The nature of the free Ts- anion in the cationic framework also allows the resultant CMOF to be recyclable via anion exchange.