Highly efficient and reversible absorption of NH3 by dual functionalised ionic liquids with protic and Lewis acidic sites

Ammonia (NH 3 ) pollution poses a serious environmental threat. Ionic liquids (ILs) are regarded as potential solvents to treat NH 3 -containing gases because of their unique properties, including tunable structures and high affinity for NH 3 molecules. In order to achieve an efficient and reversible absorption of NH 3 , a series of protic ionic liquids (PILs) with multiple active sites were designed by introducing acidic protons, as well as the Li + ion into ILs, resulting in PILs with two acidic protons on cations ([2-Mim][NTf 2 ] and [Im][NTf 2 ]), as well as dual functionalised PILs with a Lewis acidic Li + -based anion and acidic protons on cations, namely, [2-Mim][Li(NTf 2 ) 2 ] and [Eim][Li(NTf 2 ) 2 ]. The NH 3 absorption capacity of [Im][NTf 2 ] was found to be 3.46 mol NH 3 /mol IL, which is the highest among the NH 3 absorption capacities of all known nonmetallic ILs, and is ascribed to the hydrogen bonding interactions between the NH 3 and PIL molecules. Furthermore, [2-Mim][Li(NTf 2 ) 2 ] exhibited the highest NH 3 absorption capacity, with a value of 7.01 mol NH 3 /mol IL, which is about 30 times higher than that of conventional ILs. The superior NH 3 absorption performance of the dual functionalised PILs is attributed to the combination of hydrogen bonding interactions between the protons and the NH 3 molecules, and the formation of coordination complexes between the Li + -based anion and the NH 3 molecules. Moreover, the ILs studied here exhibited excellent recyclability, indicating a great potential for their use in applications involving efficient and reversible NH 3 absorption from NH 3 -containing industrial gases.