Defect-Engineering of Anionic Porous Aromatic Frameworks for Ammonia Capture

Defects in many types of porous materials have been demonstrated for controlling the pore size distribution and specific surface area as well as manipulating chemical functionality, which strongly affects their mass-transport pathways and gas adsorption behaviors. Here, unraveled structural evidence for the presence of defects in porous ionic polymers (PIPs) with weakly coordinating anions is presented. We present the concise synthesis of a tetraphenylborate-based anionic porous framework, which allows for the construction of PIPs with tricoordinated boron vacancies via a defect-engineering strategy. The resultant PIP-X possesses a high surface area of 935 m² g^–1 and displays excellent chemical stability in water and organic solvents. Importantly, the controllable vacancies and porosity of polymers were investigated using the solid-state nuclear magnetic technique. The prepared polymer (Cu@PIP-X) has multiple active sites that contain charged skeletons, Lewis acid defects, and metal ions and thus exhibits improved ammonia (NH₃) adsorption performance compared with a neutral polymer (PAF-1) and a defect-free polymer (PIP-H). Notably, the strong interactions between the gas molecules and the PIP-X are reversible with simple heating to 100 °C and display outstanding recyclable ability without structure collapse. This work thereby provides a perspective to develop defective anionic polymers as a versatile type of ion-exchange material for gas uptake.