Conduction Study Through Carbon Nanotubes As Channels Of Salt And Water

Since the discovery of carbon nanotube in 1991 by Iijima, extensive studies and applications have been carried out due to its some unique characteristics. Based on the studies reported by some researchers, the diffusion and osmotic behaviors of water molecules and ions through membranes formed from armchair carbon nanotubes with different diameters are investigated by dynamic simulations at 300K,1.01×105Pa in this thesis.Simulation results show that water molecules can enter the narrow (6,6) carbon nanotubes by self-diffusion when there is no osmotic pressure, while Na+ can only come into the wide (8,8) carbon nanotubes by diffusion. This may be because Na+ is coordinated with water molecules, (8,8) carbon nanotube is roomy enough to allow the Na+ to enter with its hydration shell intact. Moreover, the equilibrated configurations of water and ions in (6,6) and (8,8) carbon nanotubes are also obtained in this work. That is, water molecules form one single-file which is linked by hydrogen bond in (6,6) carbon nanotubes, whereas in (8,8) carbon nanotubes, water molecules form four interlaced single-files. And, Na+ is encapsulated in water molecules located in axial position.In addition, the transport behaviors of water molecules and ions through the (6, 6), (7,7), (8,8), (9,9), (10,10), (11,11) armchair carbon nanotubes under osmotic pressure are also performed in this work. According to the simulations in the scale of nanosecond, we get equilibrated configurations of water and ions, radial and axial density profile of water inside different carbon nanotube membranes. Furthermore, the relevant information, such as the number of water molecules inside carbon nanotubes, water flux, axial movement of water and ions are also acquired. Finally, we calculate the efficiency of salt rejection possessed by the carbon nanotube membranes. Simulation results show that the membrane composed of (8,8) carbon nanotube can achieve not only the optimum salt rejection property but also the largest water flux. In a word, as a kind of fundamental study, we hope this work aiming at microscopic property and conduction study of confined water molecules and ions in carbon nanotubes can provide theoretic reference and technical support for the potential applications of carbon nanotubes in the field of seawater desalination.