Confined dual functionalized ionic liquids in metal-organic frameworks for selective NH3 adsorption

The capture and separation of ammonia (NH3), a typical hydrogen-rich, carbon-free, but highly corrosive and pungent odorous gas, is significantly important for resource utilization, sustainable development and environment protection. The combination of functionalized ionic liquids (ILs) and porous supports to develop novel porous composites for NH3 adsorption is an efficient way to achieve the above goals. In this work, dual functionalized IL (DFIL) simultaneously containing Lewis acidic sites and hydrogen bond sites supported porous Zr-MOF (Zr-bptc) with high stability and reversibility are developed for NH3 adsorption. The DFIL confined in the nanopores not only provides high NH3 affinity, but also reduces the pore size to form selective NH3 diffusion pathways. Thus, the highest NH3 adsorption capacity of 10.26 mmol/g at 1 bar and 25 °C was achieved by DFIL@Zr-bptc-50 wt%. Especially, the optimal composites showed high NH3/N2 IAST of 3146.21 for NH3/N2 (0.5/99.5, v/v) and 593.97 for NH3/N2 (5/95, v/v), which is 269 % and 346 % higher than that of pristine Zr-bptc, respectively, indicating the composites have great potential for low-concentration NH3 separation. Moreover, the mixed gas breakthrough experiments demonstrated that optimal DFIL@Zr-bptc also exhibits outstanding NH3/N2 separation performance under simulative conditions including ammonia synthesis process and air purification. In addition, the DFIL@Zr-bptc composites show great structural stability and recyclability. This work provides a feasible way to design novel porous IL composites for NH3 efficient removal and recovery.