Ultrafast vibrational spectroscopy (2D-IR) of CO2 in ionic liquids: Carbon capture from carbon dioxide's point of view
Ultrafast vibrational spectroscopy (2D-IR) of CO2 in ionic liquids: Carbon capture from carbon dioxide's point of view
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DOI：
10.1063/1.4917467
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发表时间：
2015-06-07
影响因子：
4.4
通讯作者：
Garrett-Roe, Sean
中科院分区：
文献类型：
--
作者：
Brinzer, Thomas;Berquist, Eric J.;Garrett-Roe, Sean
建立了CO2 nu(3)不对称拉伸模式作为离子液体局部结构和动力学的超快二维红外（2D-IR）光谱研究的振动发色团，这对碳捕获应用有重要意义。CO2溶解在一系列1-丁基-3-甲基咪唑离子液体中([C(4)C(1)im][X]，其中[X]（-）是六氟磷酸盐（PF6-）、四氟硼酸盐（BF4-）、双（三氟甲基）磺酰亚胺（Tf2N-）、三氟酸盐（TfO-）、三氟乙酸盐（TFA(-)）、二氰酰胺（DCA（-)）和硫氰酸盐（SCN-））系列的阴离子。在所研究的离子液体中，nu(3)中心频率对局部溶剂化环境敏感，并报告了局部结构弛豫的时间尺度。密度泛函理论计算预测电荷从阴离子转移到CO2和从CO2转移到阳离子。电荷转移驱动CO2的几何畸变，从而改变nu(3)的频率。观察到的结构弛豫时间尺度在离子液体之间的变化可达一个数量级。2D-IR光谱中的肩部是由CO2的nu(2)和nu(3)正态模的非谐波耦合引起的。nu(2)种群的热波动随机调节nu(3)频率并产生动态交叉峰。这些时间尺度归因于离子笼的破裂，离子笼为二氧化碳创造了一个明确的局部环境。结果表明，CO2的皮秒动力学是由阴离子和阳离子的局部扩散控制的。(C) 2015 AIP出版有限责任公司
The CO2 nu(3) asymmetric stretching mode is established as a vibrational chromophore for ultrafast two-dimensional infrared (2D-IR) spectroscopic studies of local structure and dynamics in ionic liquids, which are of interest for carbon capture applications. CO2 is dissolved in a series of 1-butyl-3-methylimidazolium-based ionic liquids ([C(4)C(1)im][X], where [X](-) is the anion from the series hexafluorophosphate (PF6-), tetrafluoroborate (BF4-), bis-(trifluoromethyl) sulfonylimide (Tf2N-), triflate (TfO-), trifluoroacetate (TFA(-)), dicyanamide (DCA(-)), and thiocyanate (SCN-)). In the ionic liquids studied, the nu(3) center frequency is sensitive to the local solvation environment and reports on the timescales for local structural relaxation. Density functional theory calculations predict charge transfer from the anion to the CO2 and from CO2 to the cation. The charge transfer drives geometrical distortion of CO2, which in turn changes the nu(3) frequency. The observed structural relaxation timescales vary by up to an order of magnitude between ionic liquids. Shoulders in the 2D-IR spectra arise from anharmonic coupling of the nu(2) and nu(3) normal modes of CO2. Thermal fluctuations in the nu(2) population stochastically modulate the nu(3) frequency and generate dynamic cross-peaks. These timescales are attributed to the breakup of ion cages that create a well-defined local environment for CO2. The results suggest that the picosecond dynamics of CO2 are gated by local diffusion of anions and cations. (C) 2015 AIP Publishing LLC.