Efficient and reversible absorption of ammonia by cobalt ionic liquids through Lewis acid–base and cooperative hydrogen bond interactions

Abstract

Ammonia (NH₃) emissions have caused a wide range of environmental problems and serious harm to human health. However, efficiently separating NH₃ and simultaneously recovering high purity NH₃ easily remains a great challenge. A new strategy to design transition metal ionic liquids (MILs) by combining specific metal centers and ligands with ILs was proposed for efficient and reversible absorption of NH₃. Not only exceptional NH₃ absorption capacity and high NH₃/CO₂ selectivity, but also excellent recyclability were achieved by cobalt ILs [C_nmim]₂[Co(NCS)₄]. The maximal capacity of NH₃ is up to 6.09 mol NH₃ mol IL⁻¹ at 30 °C and 0.10 MPa, which is much higher than all reported ILs to date, and is over 30 times higher than the conventional ILs [C_nmim][SCN]. The superior NH₃ capacity and desorption performance originate from the moderate Lewis acid–base and cooperative hydrogen bond interactions between the metal center-ligands and NH₃.