Construction of stable IL@MOF composite with multiple adsorption sites for efficient ammonia capture from dry and humid conditions

For ammonia (NH3), a kind of vital pollutant and raw chemical material, it is of great importance to develop materials with high stability and efficient capture performance from dry and humid atmosphere. Herein, a new IL@MOF composite was designed to enhance the NH3 adsorption capacity using the ionic liquids (ILs) and stable metal-organic frameworks (MOFs). The obtained [BOHmim][Zn2Cl5]@MIL-101(Cr) exhibits a record NH3 uptake of 24.12 mmol/g among the reported porous materials at 298 K and 1 bar, more than twice that of MIL-101(Cr) (8.92 mmol/g). More importantly, the composite is stable under the humid NH3 conditions and the excellent NH3 adsorption capacity can be well maintained (23.55 mmol/g) in a 20% NH3 solution (approaching the saturated ammonia solution) steam atmosphere with good regenerability. The mechanism reveals that the metal center and hydroxyl-functionalized alkyl chain of IL confined in the framework of MOF provide multiple adsorption sites and large free volume for NH3 capture. Moreover, the adsorbed water molecules can act as the additional adsorption sites, contributing to the excellent adsorption capacity in humid conditions. This work provides a general way to develop adsorbents for the capture of corrosive gases in combination of the advantages of IL and MOFs.