【作者】 李燕；

【导师】 胡仰栋；

【作者基本信息】 中国海洋大学 ， 应用化学， 2010， 硕士

【摘要】 自从1991年Iijima发现纳米碳管以来,纳米碳管以其众多独特的性能已经得到了广泛的研究和应用。本文在前人研究的基础上,将纳米碳管以密堆积的方式构筑水和离子的膜通道,采用分子动力学方法模拟了300K、1.01×105Pa下不同尺寸的扶手椅型纳米碳管中水分子和盐离子的扩散和渗透行为。通过分子动力学模拟可以发现,在膜两侧不存在渗透压差的情况下,水分子可以通过自扩散的形式进入狭窄的(6,6)纳米碳管,并且可以在纳米碳管内快速传递,钠离子不能通过自扩散形式进入直径较小的(6,6)纳米碳管,只能通过尺寸较大的(8,8)纳米碳管且传递速度小于水分子,主要是钠离子以水合离子的形式存在,故只能通过直径较大的(8,8)碳管。此外,本文得到了水分子和钠离子在(6,6)和(8,8)碳管内的平衡构型,水分子在(6,6)碳管内以氢键相连形成一条纵列,在(8,8)管内,水分子形成四条交错的纵列,钠离子位于管内轴线位置且被包裹在水分子中间。在自扩散研究的基础上,本文进一步模拟了膜两侧存在渗透压差的情况下(6,6)、(7,7)、(8,8)、(9,9)、(10,10)、(11,11)六种不同直径的纳米碳管内水分子和盐离子的渗透行为,纳秒级的模拟让我们得到了水分子和盐离子在管内的平衡构型、水分子在管内的径向密度分布和轴向密度分布等静态性质,管内水分子数目随时间的变化、水通量变化、水分子和钠离子在管内的轴向运动等动态行为,最后,本文计算了不同直径的纳米碳管膜对盐离子的截留效率,综合各个管内水通量的变化情况,本文在六种不同直径的纳米碳管中筛选出了性能最佳的(8,8)纳米碳管,其大的水通量和高的阻盐率有望作为一种有效的渗透膜为实现海水淡化作出贡献。总之,本文作为一种基础性研究,希望通过对纳米碳管中受限水分子和盐离子微观性质和行为的研究,为纳米碳管内受限流体的研究以及海水淡化领域正渗透的研究提供理论参考和技术支持。更多还原

【Abstract】 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.更多还原