Imidazopyridinium-Linked Covalent Organic Frameworks for Efficient Gold Recovery

Covalent organic frameworks (COFs) with high surface areas and specialized binding sites garnered attention in the field of gold (Au) adsorption. The adsorption capacity mostly depends on the functional skeletons and porous structures, however, the roles of linkages have not been thoroughly explored. In this study, imidazopyridinium-linked COFs, specifically im-PYTA-PZDH-COF and im-PYTA-BPDH-COF were synthesized, to enhance gold adsorption efficacy. These engineered COFs exhibit excellent crystallinity and high surface areas, with the charged linkages demonstrating a strong binding ability for Au, which results in high Au uptake and rapid adsorption kinetics. The optimized COF, im-PYTA-PZDH-COF, offered a maximum adsorption capacity of 1558 mg g^-1, achieving 95% of this capacity within a mere 10 min. Theoretical calculations further confirm that the carbon atoms adjacent to the nitrogen in the imidazopyridinium ring, serving as adsorption sites, directly interact with AuCl₄ ^- through coulombic forces, thereby enhancing both the adsorption capacity and rate. This work provides a new strategy for designing COFs for effective Au adsorption.