Metallo‑hydrogen bonded organic frameworks (MHOFs) for efficient capture and selective separation of ammonia

A novel copper-based metallo‑hydrogen bonded organic framework MHOF- 1 ([H 4 ETTA] 4+ ·[CuCl 5 ] 3− ·Cl − ·4H 2 O, ETTA = 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetraaniline) was designed and synthesized via the second-sphere coordination (SSC) strategy for efficient ammonia (NH 3 ) capture and selective separation of NH 3 from CO 2 -containing gas streams. At 298 K and 1 bar, MHOF- 1 exhibits a high NH 3 uptake capacity of 8.76 mmol/g together with an NH 3 /CO 2 selectivity of 447, which is competitive with most reported adsorbents. Kinetic analysis based on Fick's diffusion model indicates rapid mass transfer of NH 3 in the pore channels. XPS, FT-IR, PXRD, DFT calculations, and electrostatic potential (ESP) simulations reveal that the excellent NH 3 adsorption and separation performance is mainly attributed to the synergistic effect of coordination interactions and hydrogen-bonding forces, which endow the material with highly specific recognition and efficient capture toward NH 3 molecules. MHOF- 1 also exhibits good structural stability, favorable thermal stability, and excellent cyclic regenerability with negligible capacity loss after seven adsorption–desorption cycles. This work provides a promising MHOF adsorbent for high-efficiency NH 3 /CO 2 separation and offers new insights into the rational design of advanced porous materials for ammonia separation and industrial flue gas purification.