Triazine-based cationic organic networks with anion-exchange dominance for high-capacity chromate remediation

The rational design of advanced functional materials for targeted water decontamination, especially the removal of toxic heavy metal oxyanions, represents a critical challenge in environmental materials science. Ionic organic networks (IONs), featuring strong covalent linkage, abundant ionic sites and exchangeable counterions within the network, have emerged as a new generation of ionic porous materials for specific environmental remediation. Herein, we present two novel triazine-based cationic organic network materials (CON-LDU100 and CON-LDU101) synthesized through a facile quaternization reaction of 2,4,6-tris[4-(bromomethyl)phenyl]-1,3,5-triazine (TBT) with 4,4′-bipyridinium (BiPy) and 1,4-bis(4-pyridinyl)benzene (BiPyB). The optimized CON-LDU100 material, featuring densely distributed ionic sites and dynamically exchangeable counterions within its covalent framework, demonstrated exceptional chromate (CrO₄²⁻) removal performance with a maximum capacity of 222 mg g⁻¹ and remarkable cycling stability. Mechanistic studies revealed that anion-exchange played a predominant role in the adsorption process. These findings establish ionic organic networks as a promising platform for targeted remediation of ionic water pollutants through rational structural design.