Song Yuting, Huo Feng, Jiang Yi, Zhang Suojiang, Chen Shimou
Beijing Key Laboratory of Ionic Liquids Clean Process, Key Laboratory of Green Process and Engineering State Key Laboratory of Multiphase Complex Systems Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China.
Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu, 610041, China.
Chemphyschem. 2018 Oct 19;19(20):2741-2750. doi: 10.1002/cphc.201800476. Epub 2018 Aug 3.
The molecular structures of ionic liquids at interfaces play a crucial role in determining their chemical activities in applications. In situ X-ray photoelectron spectroscopy (XPS) was used to track the evolution of X-ray irradiation-induced chemical reactions in a series of ionic liquids ([C mim][AuCl ]; n=4, 6, 8, 10) on the Si (111) single-crystal surface. Analyses of microstructure and chemical bonding based on the XPS results indicated that reactions occurred at the vapor/liquid interfaces of the ionic liquids. The time-resolved XPS spectra revealed that with increasing irradiation time, the intensity of the peak corresponding to trivalent Au anion decreased for the four ionic liquids as Au was continually reduced to a lower chemical state and finally converted to gold nanoparticles. The rate and conversion of the reaction were associated with the length of the alkyl chain of the ionic liquids cation. Molecular dynamics simulations further revealed that the alkyl chain of the cation in the ionic liquids was oriented towards the vacuum environment at the vapor/liquid interface. Our results provide a real-time atomic-scale experimental evidence of organic reactions at the vapor/liquid interfaces of ionic liquids. The findings are important for understanding the roles of ionic liquids in catalysis, separation, electrochemistry, functional materials, and so on.
离子液体在界面处的分子结构在决定其应用中的化学活性方面起着关键作用。原位X射线光电子能谱（XPS）被用于追踪一系列离子液体（[C mim][AuCl ]; n = 4、6、8、10）在Si(111)单晶表面上X射线辐照诱导的化学反应的演变。基于XPS结果对微观结构和化学键的分析表明，反应发生在离子液体的气/液界面处。时间分辨XPS光谱显示，随着辐照时间的增加，对于这四种离子液体，由于Au不断被还原到较低的化学状态并最终转化为金纳米颗粒，对应三价Au阴离子的峰强度降低。反应的速率和转化率与离子液体阳离子的烷基链长度有关。分子动力学模拟进一步表明，离子液体中阳离子的烷基链在气/液界面处朝向真空环境取向。我们的结果为离子液体气/液界面处的有机反应提供了实时原子尺度的实验证据。这些发现对于理解离子液体在催化、分离、电化学、功能材料等方面的作用具有重要意义。
