BACKGROUND Ionic liquids have become promising media for the treatment of tail gases containing ammonia (NH3), which causes serious environmental problems and threatens human health. RESULTS In this work, four dual-functionalized protic ionic liquids (DPILs) [C(n)OHim]X (n = 1, 2; X = [NTf2](-), [BF4](-), [SCN](-)) with both weak acidity proton and hydroxyl group were designed and synthesized for enhanced NH3 separation. Among them, the maximum NH3 molar solubility of 3.11 mol NH3 mol(-1) IL was achieved in [EtOHim][NTf2] at 40 degrees C and atmospheric pressure, and the highest mass solubility of NH3 could be 0.221 g NH3 g(-1) IL in [EtOHim][SCN]; this is the highest value of any absorbent ever reported under the same conditions. Not only superior NH3 solubility, along with excellent selectivity of NH3/CO2 (65) and NH3/N-2 (104), but also outstanding recyclability was exhibited in DPILs. CONCLUSIONS The highly efficient performance of NH3 absorption by DPILs was ascribed to the synergistically physicochemical interaction between weak acidity proton, hydroxyl group and NH3, which was confirmed through both spectrum analysis and quantum chemical calculations. This work implied that DPILs have great potentials in NH3 separation and recovery of NH3-containing tail gases. (c) 2020 Society of Chemical Industry