离子液体因其特有的低挥发性、较好的化学/热稳定性、良好的气体溶解性和结构可设计性等优势，已成为气体分离领域备受关注的一类新型吸收剂。目前离子液体在SO2、CO2和NH3等气体分离方面已开展了较为系统的研究，并积累了大量数据和理论基础，展现出良好的应用前景，但要真正实现工业化应用，仍存在气体吸收能力较低、粘度和成本较高等问题。因此如何设计高性能、低粘度和低成本的离子液体实现高效可逆捕集分离气体成为目前研究的难点和热点。本论文针对SO2、CO2和NH3三种典型气体，开展了离子液体构效关系、新型功能化离子液体设计合成及吸收解吸性能、吸收过程中离子液体物性动态变化规律，以及吸收机理的系统研究，为形成具有工业应用价值的新一代气体分离技术提供了科学依据。本论文的主要研究内容及成果如下： （1）吡啶类离子液体的合成及其吸收SO2的构效关系研究。设计合成了一系列稳定性好、成本较低及生物降解性较好的吡啶类离子液体捕集SO2，系统研究了阴阳离子结构和吸收条件如温度、压力和水含量对SO2吸收性能和气体选择性的影响规律，并结合实验表征、量化计算和分子动力学模拟对吸收机理进行深入分析。研究表明，与阳离子相比，阴离子结构对SO2吸收性能的影响更为明显，其中阴离子与SO2间静电作用较强的[C4Py][SCN]不仅表现出较高的质量吸收量0.841 gSO2·gIL-1，还具有良好的气体选择性和再生循环性，是一种极具应用潜力的新型吸收剂。 （2）新型功能化吡啶类离子液体的设计合成及其高效分离SO2研究。为了进一步提高对SO2的吸收性能，设计合成了叔胺基、腈基和醚基三种新型阳离子功能化吡啶类离子液体[NEt2C2Py][SCN], [C4CNPy][SCN]和[C4OPy][SCN]，系统研究了功能化基团对离子液体物性、SO2吸收性能、SO2/CO2选择性和再生循环性的影响。发现叔胺基、腈基和醚基的引入能有效提高对SO2的吸收能力和SO2/CO2选择性，功能化离子液体同样具有良好的循环性，其中[NEt2C2Py][SCN]和[C4CNPy][SCN]分别具有最高的SO2吸收量（1.06 gSO2·gIL-1）和SO2/CO2选择性（79）。红外、核磁谱图和量化计算结果表明，[C4CNPy][SCN]和[C4OPy][SCN]与SO2间主要是物理作用，而[NEt2C2Py][SCN]与SO2间同时存在物理和化学作用，叔胺基与SO2间的化学作用是导致其较高吸收量的主要原因。 （3）吸收SO2过程中离子液体的物性动态变化及其机理分析。系统研究了吸收过程中常规离子液体[C4Py][BF4]和[C4Py][SCN]与功能化离子液体[NEt2C2Py][SCN]的密度和粘度随SO2吸收量和吸收时间的变化规律，结合原位红外、分子动力学模拟和量化计算对离子液体物性动态变化的原因进行了分析。结果表明，随SO2吸收量的增加，[C4Py][BF4]、[C4Py][SCN]与[NEt2C2Py][SCN]的密度逐渐增加，但粘度却出现不同的变化趋势。对于[NEt2C2Py][SCN]，其粘度先增加随后剧烈下降，但[C4Py][BF4]和[C4Py][SCN]粘度仅呈单一下降趋势。其主要原因是在吸收过程初期，[NEt2C2Py][SCN]阳离子上的叔胺基与SO2形成电荷转移络合物导致粘度增加，而后期功能化离子液体和常规离子液体粘度的下降主要是因为阴离子与SO2间的作用造成阴阳离子间静电作用明显减弱所导致。 （4）醚基功能化吡啶类离子液体的设计合成及其选择性分离CO2研究。为了实现天然气中高效脱碳，将不同个数的醚基引入吡啶阳离子上成功合成了三种醚基功能化离子液体[EnPy][NTf2]，研究了醚基对离子液体物性、CO2和CH4溶解度与CO2/CH4选择性的影响规律，计算得到CO2和CH4在离子液体中的吉布斯自由能、溶解焓和熵等热力学性质，进一步分析了CO2和CH4的溶解机理。研究表明，与常规离子液体[CmPy][NTf2]相比，醚基的引入不仅可降低离子液体粘度，且随着醚基数目的增加，降粘效果更加显著，降幅最高达42.5%。同时醚基的加入虽然轻微降低CO2的溶解度，却大幅度降低了CH4的溶解度，导致[EnPy][NTf2]具有较高的CO2/CH4选择性。但两种气体溶解度的降幅与的溶解机理有关，对于CH4溶解来说，CH4与离子液体间的相互作用起主要作用，但CO2溶解主要由CO2与离子液体间的相互作用和离子液体的自由体积共同决定。 （5）金属配合物离子液体的结构设计合成及其吸收NH3性能研究。金属离子能与NH3发生化学络合形成氨配合物达到较好的NH3吸收效果，但往往络合作用较强会增加解吸难度，因此筛选合适的金属离子调节与NH3间的作用是设计离子液体的关键。基于此成功合成了三种新型含钴金属配合物离子液体[Cnmim]2[Co(NCS)4]实现对NH3的高效可逆吸收。系统研究了[Cnmim]2[Co(NCS)4]的物性、吸收温度、压力和离子液体水含量对NH3吸收性能、NH3/CO2选择性和离子液体的再生循环性能的影响规律。研究表明，与常规离子液体[Cnmim][SCN]相比，[Cnmim]2[Co(NCS)4]不仅具有较高的热稳定性（高于280℃）、非常高的NH3吸收能力（0.198 gNH3·gIL-1）和NH3/CO2选择性（53），还具有很好的再生循环性。其主要原因是[Cnmim]2[Co(NCS)4]中每摩尔二价钴离子与6摩尔NH3形成稳定常数适宜的[Co(NH3)6]2+络合离子，同时实现了对NH3的高效吸收和解吸。

Ionic liquids (ILs) have been developed as one of the most promising alternatives for gas separation owing to their unique characteristics, such as extremely low vapour pressure, high chemical/thermal stability, optimistic gas solubility and tuneable properties. Although a large number of researches have focused on SO2, CO2 and NH3 absorption and separation by ILs in the literatures, there are still some inherent drawbacks such as lower gas absorption capability, higher viscosities and costs than traditional solvents, which causes great barriers for industrial applications of ILs. Therefore, it is crucial to design low viscous and cheap ILs with excellent absorption performances for efficient and reversible absorption of gas. In this work, the relationship between the structures of ILs and the properties, the design and synthesis of novel functionalized ILs and gas absorption/desorption performances, the dynamic changes in physical properties of IL-gas systems during gas absorption as well as the interaction mechanisms between ILs and gas have been systematically studied for SO2, CO2 and NH3 absorption and separation. The main innovative work and results of the dissertation are as follows: (1) Study on the synthesis of pyridinium-based ILs and the relationship between the structures of ILs and SO2 absorption performances. A series of thermally stable pyridinium-based ILs with lower cost and higher biodegradability were synthesized for SO2 capture. The effect of cations and anions on physicochemical properties and SO2 absorption performances were investigated, and SO2 capacity under different temperatures, pressures and water contents, gas selectivity and the recyclability of ILs were also studied. The pyridinium-based IL [C4Py][SCN] not only exhibits higher SO2 capacity of 0.841 gSO2·gIL-1 than most of reported imidazolium-based ILs, but also shows higher selectivity for SO2 to other gases and excellent reversibility. Moreover, the mechanisms were explained by spectroscopic investigation and simulation calculations. Comparing with cation of IL, the anion plays a dominant role in SO2 absorption, and the higher capacity of [C4Py][SCN] is mostly due to the stronger electrostatic interaction between anion and SO2. (2) The design and synthesis of novel functionalized pyridinium-based ILs for highly efficient and reversible separation of SO2. Based on the previous work, three kinds of novel cation-functionalized ILs [NEt2C2Py][SCN], [C4OPy][SCN] and [C4CNPy][SCN] were developed by introducing a tertiary amino group, ether group and nitrile group on the pyridinium ring to improve SO2 capture. The effect of functionalized groups on physicochemical properties, SO2 absorption performances, SO2/CO2 selectivity and the recyclability of ILs were investigated in detail. Comparing with [C4Py][SCN], the cation-functionalized ILs exhibit much higher SO2 capacity and SO2/CO2 selectivity, and excellent reversibility. [NEt2C2Py][SCN] and [C4CNPy][SCN] showed the highest capacity of 1.06 gSO2·gIL-1 and SO2/CO2 selectivity of 79, respectively. Spectroscopic characterizations and simulation calculation results indicated that only physical absorption occurs in [C4CNPy][SCN] and [C4OPy][SCN], but both chemical and physical interaction coexists between [NEt2C2Py][SCN] and SO2. The great enhancement in SO2 capacity by [NEt2C2Py][SCN] mainly originates from the chemical interaction between the tertiary amino group and SO2. (3) Study on the dynamic changes in physical properties of ILs during SO2 absorption and the mechanisms. The effect of SO2 on densities and viscosities of pyridinium-based ILs during SO2 absorption, such as the conventional ILs [C4Py][BF4] and [C4Py][SCN], the functionalized IL [NEt2C2Py][SCN], were investigated. The mechanisms of the variations in physical properties were explained through experimental methods and simulation calculations. With the increasing amounts of SO2, the densities of the conventional ILs and the functionalized IL increased, but the viscosities of two kinds of ILs showed different variations. For [NEt2C2Py][SCN], the viscosity increased sharply at first due to the formation of a charge transfer complex between cation and SO2, and then decreased drastically because of physical interaction between anion and SO2. However, there was a monotonous decline in viscosity of the conventional ILs, which is similar to that of [NEt2C2Py][SCN] in physical absorption stage. The viscosity reduction may be mainly attributed to the decrease in the electrostatic interaction between cation and anion of ILs caused by the anion-SO2 interaction. (4) The design and synthesis of ether-functionalized pyridinium ILs for highly selective capture of CO2. Three kinds of ether-functionalized pyridinium-based ILs [EnPy][NTf2] were designed for highly selective separation of CO2 from natural gas, the effect of ether groups on physicochemical properties, CO2 and CH4 solubilty as well as CO2/CH4 selectivity under different temperatures was investigated. The thermodynamic properties including the Gibbs free energy, enthalpy and entropy of CO2 and CH4 in these ILs were also calculated, and CO2 and CH4 dissolution mechanisms were further analyzed. Compared with the nonfunctionalized analogues [CmPy][NTf2], the viscosities of [EnPy][NTf2] are lower and obviously decrease with the increasing number of ether oxygen atoms. The presence of ether groups has weak impacts on CO2 solubility in ILs, but it contributes to a much lower CH4 solubility, which leads to the great increase in CO2/CH4 selectivity using [EnPy][NTf2]. However, the reduction degree of CO2 and CH4 solubilities is related to the mechanisms of gas dissolution. The gas-IL interaction plays a dominate role in CH4 solubility, but CO2 dissolution in ILs is determined by both IL-gas interaction and free volume of ILs. (5) The design and synthesis of metal-containing ILs for efficient absorption of NH3. By screening the suitable metal ion to adjust the interaction between metal ion and NH3, three kinds of the cobalt-containing ILs [Cnmim]2[Co(NCS)4] were successfully designed and synthesized for efficient and reversible absorption of NH3 through chemical complexation. The physicochemical properties, NH3 absorption performances under different temperature, pressure and water contents, NH3/CO2 selectivity and the recyclability of ILs were investigated. Comparing with the conventional ILs [Cnmim][SCN], [Cnmim]2[Co(NCS)4] not only exhibits more excellent thermal stability (above 280℃), but also shows much higher NH3 capacity (0.198 gNH3·gIL-1) due to the formation of [Co(NH3)6]2+ complex and NH3/CO2 selectivity (53), which is over 10 times and 8 times than those in [Cnmim][SCN], respectively. Meanwhile, [Cnmim]2[Co(NCS)4] can keep the stable absorption performances after five cycles of absorption and desorption, implying that the process is completely reversible.