We investigated the influences of the changes in the electronic structure and size of the anion of an imidazolium ionic liquid (IL) on gas adsorption and separation performance of the IL/ZIF-8 (zeolitic imidazolate framework) composites. We studied four different imidazolium ILs having the same cation, 1-n-butyl-3-methylimidazolium, [BMIM]⁺, with anions having structures allowing a systematic comparison of the changes in the electronic structure and size. To examine the influence of changes in the electronic structure, we considered anions representing the fluorination on the anion, methanesulfonate, [MeSO₃]⁻, and trifluoromethanesulfonate, [CF₃SO₃]⁻. To investigate the change in the anion size, methyl sulfate, [MeSO₄]⁻, and octyl sulfate, [OcSO₄]⁻, were studied. Characterization of IL/ZIF-8 composites demonstrated successful incorporation of each IL in ZIF-8 without causing any detectable changes in the crystal structure and morphology of ZIF-8. Thermogravimetric analysis and infrared (IR) spectroscopy indicated the presence of direct interactions between ILs and ZIF-8, which directly control gas separation performance of the composite. Gas adsorption measurements illustrated that incorporation of ILs significantly improves the gas separation performance of the pristine ZIF-8. [BMIM][MeSO₄]/ZIF-8 composite had 3.3- and 1.8-times higher CO₂/N₂ and CH₄/N₂ selectivities compared to ZIF-8, respectively, at 1 bar. When the IL has a fluorinated anion, CO₂/CH₄ selectivity improved 3-times compared to its non-fluorinated counterpart. Upon the incorporation of IL with a small anion, IL/ZIF-8 composite showed higher CO₂/N₂ and CH₄/N₂ selectivities compared to the composite having an IL with a bulky anion. These results will contribute in guiding rational design of IL/MOF composites for different gas separations.

我们研究了咪唑离子液体（IL）的电子结构和阴离子大小变化对IL / ZIF-8（沸石咪唑酸盐骨架）复合材料的气体吸附和分离性能的影响。我们研究了具有相同阳离子的四个不同的咪唑ILs，即1 - n-丁基-3-甲基咪唑鎓[BMIM] ⁺，其阴离子的结构允许系统比较电子结构和尺寸的变化。为了检查电子结构变化的影响，我们考虑了代表氟化的阴离子对阴离子，甲磺酸根，[MeSO ₃ ] ^-和三氟甲磺酸根，[CF ₃ SO ₃ ] ^-。为了研究阴离子大小的变化，研究了硫酸甲酯[MeSO ₄ ] ^-和辛基硫酸酯[OcSO ₄ ] ^-。IL / ZIF-8复合材料的表征证明每个IL成功地掺入ZIF-8中，而不会引起ZIF-8晶体结构和形态的任何可检测变化。热重分析和红外（IR）光谱表明IL与ZIF-8之间存在直接相互作用，这直接控制了复合材料的气体分离性能。气体吸附测量结果表明，掺入IL可以显着改善原始ZIF-8的气体分离性能。[BMIM] [MeSO ₄ ] / ZIF-8复合材料的CO _2分别高3.3和1.8倍在1 bar下与ZIF-8相比，分别具有/ N ₂和CH ₄ / N ₂选择性。当IL具有氟阴离子时，与非氟对应物相比，CO ₂ / CH ₄选择性提高了3倍。与具有大阴离子的IL的复合物相比，在IL与小的阴离子的结合中，IL / ZIF-8复合物显示出更高的CO ₂ / N ₂和CH ₄ / N ₂选择性。这些结果将有助于指导针对不同气体分离的IL / MOF复合材料的合理设计。