International Collaboration in Chemistry: A Combined Computational and Spectroscopic Study of Structure and Charge Transfer Dynamics of Ionic Liquids in Heterogeneous Environments

卡内基梅隆大学的Hyung Kim由化学系化学结构、动力学和机制计划支持，通过国际化学合作倡议，与英国阿伯丁大学由Johannes Kiefer博士和James Anderson教授领导的实验小组合作，对多相环境中离子液体的结构和动力学进行计算和光谱研究。英国合作者的研究部分将通过EPSRC提供资金。美国研究员Kim教授将在金属有机骨架(MOF)和碳化环境(包括碳黑、碳纳米管和石墨烯)中对基于咪唑阳离子的室温离子液体(RTIL)进行分子动力学(MD)模拟，并分析RTIL的结构和动力学，特别关注环境效应。利用所得到的平衡结构，将在QM/MM(量子力学/分子力学)框架下进行量子化学计算，以确定RTIL振动光谱。将分析RTIL离子，特别是咪唑阳离子的电子密度重组，并将研究与石墨材料界面上的非均相电荷转移。我们将构建一个阳离子与石墨烯表面之间电子转移的经验价键描述，并将其纳入分子动力学模拟。将考虑几种不同的阴离子物种，如双(三氟甲基磺酰基)亚胺和双(氟磺酰基)亚胺，以了解阴离子如何调节咪唑阳离子的氧化还原化学。计算结果将与英国合作者通过傅里叶变换红外光谱(FTIR)、X射线吸收光谱(XAS)和非弹性中子散射(INS)等方法获得的实验结果进行详细比较。具有明确孔径和形状的MOF中RTIL的实验结果将被用于校准计算结果和微调力场参数。随后，RTIL体系将扩展到有机溶剂的混合物，并将研究共溶剂对RTIL结构、动力学和与碳基材料界面电荷转移的影响。室温离子液体(RTIL)具有许多独特的性质，使其成为有望用于绿色技术的溶剂：它们具有非挥发性、不可燃、化学惰性和热稳定性。由于具有较高的离子导电性和较大的电化学窗口，RTIL也有望作为能量转换和存储系统的组件。这些电化学性质也使RTIL在催化和其他工业过程中具有潜在的应用价值。Kim教授的研究结合了理论/计算和实验/光谱学，通过研究RTIL与类似于此类应用中使用的界面的相互作用，帮助提供了对RTIL结构和性质的详细微观洞察。因此，这项研究将对RTIL界面过程的基本理解及其许多潜在的应用产生长期的影响。这项研究的主要成果将被纳入化学集体，这是卡内基梅隆大学开发的大学和高中一级入门化学课程教育材料的数字图书馆，以向包括高中生、本科生和他们的教师在内的广大受众传播结果。

Hyung Kim of Carnegie Mellon University is supported by the Chemical Structure, Dynamics and Mechanisms program of the Division of Chemistry through the International Collaboration in Chemistry initiative to carry out computational and spectroscopic study of structure and dynamics of ionic liquids in heterogeneous environments in collaboration with experimental groups at University of Aberdeen, UK headed by Dr. Johannes Kiefer and Prof. James Anderson. The research component of the UK collaborators will be funded through EPSRC. The US investigator, Professor Kim, will perform molecular dynamics (MD) simulations of room-temperature ionic liquids (RTILs) based on imidazolium cations in metal organic frameworks (MOFs) and in carbonaneous environments, including carbon black, carbon nanotubes and graphenes, and analyze RTIL structures and dynamics with special attention paid to the environmental effect. Using the equilibrium structure thus obtained, quantum chemistry calculations will be performed in the QM/MM (quantum mechanics/molecular mechanics) framework to determine RTIL vibrational spectra. Reorganization of electron density of RTIL ions, in particular, imidazolium cations, will be analyzed and heterogeneous charge transfer at the interface with graphitic materials will be investigated. An empirical valence-bond description for electron transfer between cations and graphene surface will be constructed and incorporated into MD simulations. Several different anionic species, such as bis(trifluoromethylsulfonyl)imide and bis(fluorosulfonyl)imide, will be considered to understand how redox chemistry of imidazolium cations could be modulated by anions. Detailed comparison of computational results will be made with the experimental results that will be obtained via, among other methods, Fourier-transform infrared spectroscopy (FTIR), x-ray absorption spectroscopy (XAS) and inelastic neutron scattering (INS) by the UK collaborators. Experimental results for RTILs in MOFs with well-defined pore size and shape will be used to calibrate computational results and fine-tune force field parameters. Later, RTIL systems will be extended to mixtures with organic solvents and the influence of co-solvents on RTIL structure, dynamics and charge transfer at the interface with carbon-based materials will be studied.Room-temperature ionic liquids (RTILs) have many unique properties that make them promising solvents for green technology: they are non-volatile, non-flammable, chemically inert and thermally stable. RTILs are also promising as components of systems for energy conversion and storage because of their high ion conductivity and large electrochemical window. These electrochemical properties also make RTILs potentially useful in catalysis and other industrial processes. Prof. Kim's research helps to provide detailed microscopic insight into the structure and properties of RTILs by studying their interactions with interfaces similar to those used in such applications using a combination of theory/computation and experiment/spectroscopy. As such, the research will have long-range impacts on both the fundamental understanding of RTIL interfacial processes and their many potential applications. Key results of the research will be incorporated into ChemCollective, a digital library of educational materials for introductory chemistry courses at both the college and high school level, developed at Carnegie Mellon University, to disseminate the results to a broad audience, including high school students, undergraduates and their instructors.