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

Abstract

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_NH3/CO2 = 25.4–56.3) and N₂ (S_NH3/N2 = 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.