Porous acid-base hybrid polymers for enhanced NH₃ uptake with assistance from cooperative hydrogen bonds

Carboxylic acid-modified materials are a common means of achieving efficient NH₃ adsorption. In this study, we report that improved NH₃ adsorption capacity and easier desorption can be achieved through the introduction of substances containing Lewis basic groups into carboxylic acid-modified materials. Easily synthesized mesoporous acid-base hybrid polymers were constructed with polymers rich in carboxylic acid and Lewis base moieties through cooperative hydrogen bonding interactions (CHBs). The hybrid polymer PAA-P4VP presented higher NH₃ capacity (18.2 mmol g^-1 at 298 K and 1 bar NH₃ pressure) than PAA (6.0 mmol g^-1) through the acid-base reaction and the assistance from CHBs with NH₃, while the NH₃ desorption from PAA-P4VP was easier for the reformation of CHBs. Based on the introduction of CHBs, a series of mesoporous acid-base hybrid polymers was synthesized with NH₃ adsorption capacity of 15.8-19.3 mmol g^-1 and high selectivity of NH₃ over CO₂ (S_NH = 25.4-56.3) and N₂ (S_NH = 254-1068), and the possible co-existing gases, such as SO₂, had a lower effect on NH₃ uptake by hybrid polymers. Overall, the hybrid polymers present efficient NH₃ adsorption owing to the abundant acidic moieties and CHBs, while the concomitant Lewis bases promote NH₃ desorption.