Acta Chimica Sinica ›› 2014, Vol. 72 ›› Issue (4): 487-494.DOI: 10.6023/A13121223 Previous Articles     Next Articles



王新华a, 冯莉a, 曹泽星b   

  1. a 中国矿业大学化工学院 徐州 221116;
    b 厦门大学化学化工学院 厦门 361005
  • 投稿日期:2013-12-08 发布日期:2014-02-11
  • 通讯作者: 冯莉; Tel.:13852488050
  • 基金资助:


Structure, Energetics and Vibrational Frequency Shifts of Water Molecules Confined Inside Single-walled Carbon Nanotubes:A DFT Study

Wang Xinhuaa, Feng Lia, Cao Zexingb   

  1. a School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116;
    b College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
  • Received:2013-12-08 Published:2014-02-11
  • Supported by:

    Project supported by the National Basic Research Program of China (No. 2012CB214901) and the National Natural Science Foundation of China (No. 51274197).

The study of confined water molecules has attracted much attention because of their fascinating properties. In the present work, small water clusters (H2O)n=3~6 encapsulated in different diameter of single-walled carbon nanotubes (SWCNT) were investigated using density functional theory (DFT). The DFT-based M06-2X method along with mixed basis sets (6-311+G(d, p)//6-31+G(d)) was employed in all calculations for structure, interaction energy, charge transfer and vibrational frequency. The results indicate that as compared to water molecules in vacuum, the geometries of confined water molecules changed significantly due to the confinement effect of carbon nanotubes, for example, the (H2O)6 cluster can form chain-like configuration via hydrogen bond. The tube-water interaction energy decreased with the increase of the nanotubes diameter, while the hydrogen bond energy between water molecules changes slightly. Vibrational analysis reveals the red shift of the majority of the O—H stretching modes inside SWCNT compared to vacuum vibrational frequencies due to the tube-water interaction. The Bader's theory of atoms in molecule (AIM theory) has been used to characterize the tube-water interactions. Electron density ρ that reflects the strength of a bond has been used to explain the phenomenon of the red shift. The AIM analysis suggests that the red shift of O—H vibrational frequencies for confined water molecules should be attributed to the decrease of the electron density ρ. This fact demonstrates that the tube-water interaction is not a simple effect of geometry confinement, but weak electronic interaction between the molecular orbital of the confined water molecules and the delocalized π electrons from carbon nanotube. It mainly includes the H…π hydrogen bond interaction and O…π orbital interaction, resulting in a slight charge transfer from water molecules to SWCNT. Therefore, when constructing carbon nanotube devices, one should not ignore the existence of water molecules. We hope that our results can provide a guidance to the understanding of the behavior of water molecules encapsulated inside nanoscale environment.

Key words: density functional theory, single-walled carbon nanotubes, water clusters, red-shifted hydrogen bond, AIM theory