物理化学学报 >> 2011, Vol. 27 >> Issue (07): 1725-1729.doi: 10.3866/PKU.WHXB20110731

催化和表面科学 上一篇    下一篇

离子液体[EMIM][PF6]负载纳米SiOx表面的熔点及结构

刘玉胜1,2, 付海英1, 唐忠锋1, 黄卫1, 吴国忠1   

  1. 1. 中国科学院上海应用物理研究所, 上海 210800;
    2. 徐州工程学院, 江苏 徐州 221000
  • 收稿日期:2011-03-14 修回日期:2011-05-03 发布日期:2011-06-28
  • 通讯作者: 吴国忠 E-mail:wuguozhong@sinap.ac.cn
  • 基金资助:

    国家自然科学基金(11079007, 20973192)资助项目

Melting Point and Structure of Ionic Liquid [EMIM][PF6] on the Surface of Nano-SiOx Particles

LIU Yu-Sheng1,2, FU Hai-Ying1, TANG Zhong-Feng1, HUANG Wei1, WU Guo-Zhong1   

  1. 1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 210800, P. R. China;
    2. Xuzhou Institute of Technology, Xuzhou 221000, Jiangsu Province, P. R. China
  • Received:2011-03-14 Revised:2011-05-03 Published:2011-06-28
  • Contact: WU Guo-Zhong E-mail:wuguozhong@sinap.ac.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (11079007, 20973192).

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摘要：

制备了离子液体(1-乙基-3-甲基咪唑六氟磷酸 [EMIM][PF6])负载量不同的多孔纳米氧化硅(SiOx), 并采用差式扫描量热分析(DSC)、X射线衍射(XRD)、激光Raman光谱、傅里叶变换红外(FTIR)光谱分析等手段研究离子液体负载纳米氧化硅后的熔点变化及相行为. 研究表明负载于纳米氧化硅表面的离子液体熔点明显下降, 且负载于不同表面羟基含量的氧化硅表面熔点下降幅度不同. 纯离子液体[EMIM][PF6]熔点为62 ℃, 在纳米氧化硅表面负载量为35%时熔点为52 ℃, 比负载前下降10 ℃; 负载于另两种不同羟基含量的纳米氧化硅表面后熔点分别下降20和17 ℃. 而同一种纳米氧化硅(比表面积为640 m2·g-1)在负载量小于50%时, 熔点下降明显; 进一步增大负载量, 熔点逐渐趋于本体. XRD和Raman光谱分析显示, 离子液体负载于氧化硅表面后其衍射峰或吸收峰相对强度发生明显改变. 分析负载前后纳米氧化硅的结构变化, 推断离子液体熔点下降的主要原因是离子液体分子与纳米氧化硅表面之间存在强烈的界面相互作用, 而表面羟基的密度及比表面积是影响负载后[EMIM][PF6]离子液体相行为的主要因素.

关键词: 纳米SiOx, 离子液体, 熔点, 相变

Abstract:

The 1-ethyl-3-methyl imidazolium hexafluorophosphate ionic liquid ([EMIM][PF6]) was absorbed onto the surfaces of several kinds of nano-SiOx particles by mechanical grinding using an agate mortar. The samples were investigated by differential scanning calorimetry (DSC), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). We found that the melting point of the [EMIM][PF6] adsorbed on the surface of nano-SiOx was significantly less than that of the bulk ionic liquid. For the pure ionic liquid [EMIM][PF6], the melting point was 62 ℃. After absorption onto SiOx nanoparticles the melting point decreased to 52 ℃ and ΔT was -10 ℃. For the other two types of nano-SiOx particles the ΔT was -20 and -17 ℃, respectively. These results indicate that the melting point depression was dependent on the surface properties of the nano-SiOx particles. Furthermore, the characteristics of the surface-adsorbed ionic liquid were also found to be quite different from that of the bulk ionic liquid by Raman and XRD analyses. The difference in the density of the surface hydroxyl groups and the specific surface area of the nano-SiOx particles may induce different interfacial interactions between [EMIM][PF6] and the nano-SiOx particles. Our results suggest that the density of the surface hydroxyl groups and specific surface area are the major factors responsible for the behavior of the adsorbed ionic liquid [EMIM][PF6].

Key words: Nano-SiOx, Ionic liquid, Melting point, Phase transition