Metal ionic liquid-based hybrid membranes for ammonia separation through moderate interaction sites and cooperative transport channels

Abstract

The combination ionic liquids (ILs) with membranes is a potential method for direct NH₃ separation. In particular, ILs can modulate the interactions with NH₃ and construct pathways in membranes for preferential NH₃ transport, which is expected to overcome the trade-off effect and achieve a desirable separation performance. In this work, four metal ILs (MILs) with different metal centres and hydrogen bond donating ability, including [2-Mim][Li(NTf₂)₂], [Eim][Li(NTf₂)₂], [Bmim]₂[Co(NCS)₄], and [Bim]₂[Co(NCS)₄], were incorporated into sulfonated block copolymers to prepare MIL-based hybrid membranes for NH₃ separation. The investigation of structure–performance relationships suggested that the interaction sites and transport channels could be tuned by the MIL type, which greatly affects the NH₃ separation performance of the membranes. The Nexar/2-Mim-Li-10 membrane exhibits NH₃ permeability of 735.6 Barrer with NH₃/N₂ selectivity of 844.5 and NH₃/H₂ selectivity of 154.7, which is higher than other MIL-based hybrid membranes owing to self-assembled transport channels and moderate complexation. Increasing the MIL content and feed pressure significantly improved NH₃ separation performance.