Flexible Material from Ionic Liquid via Synergic Coordination−Hydrogen Bonding for Reversible Ammonia Capture

This work presents the design of flexible ionic liquid-derived materials for efficient and reversible ammonia capture leveraging synergistic coordination bonding and hydrogen bonding. BpyEt-Co-TA and BpyBu-Co-TA were synthesized and exhibited distinct gate-opening adsorption behaviors at 25 °C, with threshold pressures of 4.7 kPa and 22.9 kPa and maximum capacities of 10.6 mmol/g and 8.5 mmol/g, respectively. In situ spectroscopic analyses confirm that adsorption proceeds via the accommodation among the lattices, formation of [Co(NH 3 ) 6 ] 2+ complexes, and the hydrogen bonding between NH 3 and the pyridinium α-H. While both materials follow this mechanism, their cyclic stability diverges dramatically due to ligand side-chain conformation. BpyBu-Co-TA demonstrates complete structural recovery and consistent performance over 11 adsorption−desorption cycles, whereas BpyEt-Co-TA suffers irreversible ethyl-group conformational locking, leading to capacity decay. The flexibility of the framework enables an energy-efficient desorption process, and TG-DSC reveals an exothermic structural reorganization, which supplies internal heat and lowers the external energy demand. Combined with excellent selectivity for NH 3 over N 2 /CO 2 and good moisture stability, this study establishes that engineering flexible IL derived materials through coordination−hydrogen bond synergy offers a promising strategy for developing highly reversible and energy-smart NH 3 adsorbents.