Highly Selective Separation Intermediate‐Size Anionic Pollutants from Smaller and Larger Analogs via Thermodynamically and Kinetically Cooperative‐Controlled Crystallization

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 Cu(2+) are chosen as suitable ligand and metal ion for CMOF construction because they can form stronger intermolecular interaction with p‐toluenesulfonate anion (Tsˉ) compared to its analogs. For this combination, a condition is established, under which the crystallization rate of a Tsˉ‐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 Tsˉ 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 Tsˉ anion in the cationic framework also allows the resultant CMOF to be recyclable via anion exchange.