本文關鍵詞： 雙壁碳納米管 分子動力學模擬 反滲透 海水淡化 管間距　出處：《大連理工大學》2015年碩士論文　論文類型：學位論文

【摘要】：反滲透是目前大規(guī)模海水淡化推廣中的主流技術。開發(fā)高效通水阻鹽性能與高機械強度的膜材料是目前反滲透技術中急需解決的問題之一。隨著碳納米管的高速通水性質以及對鹽離子有較高的截留性質逐漸被人們所熟知,將碳納米管摻雜在反滲透膜材料中成為解決上述問題的途徑之一。而在諸多類型的碳納米管材料中,雙壁碳納米管的性質優(yōu)于單壁碳納米管,故本文以雙壁碳納米管作為研究對象,采用分子動力學模擬方法對非常規(guī)雙壁碳納米管在反滲透過程中進行研究。通過調節(jié)內外管間距來考察管間距對管道內水分子與鹽離子運動特性的影響。首先,本文采用單層反滲透膜模型,以0.5 mol·L-1氯化鈉水溶液模擬海水,在鹽水一側施加靜水壓力模擬反滲透條件。其次,滲透膜的主體為公度雙壁碳納米管,其內外壁均為扶手椅型,且內壁手性保持為(8,8)。本文重點考察模擬過程中不同尺寸雙壁碳納米管的阻鹽效率與通水性能,計算管內水分子平均力勢,并分析水分子的氫鍵與偶極矩特性。另外,我們采取了三種不同的水分子勢能模型(TP3P、TIP4P與SPC/E)來考察水模型的選取對模擬結果的影響。研究結果表明,管間距不僅會影響傳輸通道內水分子的納觀構型(平均力勢、氫鍵與偶極矩等),還會使鹽離子與水分子在碳納米管中呈現(xiàn)滲透差異性。在通水阻鹽方面,小尺寸雙壁碳納米管可以有效實現(xiàn)鹽水分離但水通量較小,大尺寸雙壁碳納米管的通水量較高但阻鹽效率有所下降,而中尺寸雙壁碳納米管的截鹽效率可達100%,并且在凈水流量的數(shù)值上與大尺寸雙壁碳納米管相近,這說明中尺寸雙壁碳納米管(即：管間距為0.815nm)具有優(yōu)異的通水阻鹽性能。另外,水分子模型會在一定程度上影響阻鹽率、通水量及水分子的氫鍵特性,例如：TIP3P水分子在反滲透模型中的滲透性較高,氫鍵壽命較短。然而,在不同的水模型體系中,通水阻鹽性能隨管間距的變化趨勢相近。由模擬結果可知,水分子模型對通水阻鹽性能的影響小于雙壁碳納米管幾何尺寸的影響。本文采用分子動力學模擬方法,從分子層面闡述雙壁納米碳納米管的通水阻鹽機理,以期為高性能碳納米管摻雜反滲透膜的制備提供依據(jù),并為人們改進海水淡化滲透技術提供理論支持。
[Abstract]:Reverse osmosis (RO) is the mainstream technology in large-scale seawater desalination. The development of membrane materials with high water and salt resistance and high mechanical strength is one of the most urgent problems in reverse osmosis. With the development of carbon nanotubes (CNTs) at high speed. The water permeability and the high retention of salt ions are becoming more and more familiar. Doping carbon nanotubes into reverse osmosis membrane materials is one of the ways to solve the above problems. In many kinds of carbon nanotube materials, the properties of double-walled carbon nanotubes are better than that of single-walled carbon nanotubes. So this paper takes double walled carbon nanotubes as the research object. In this paper, molecular dynamics simulation was used to study the effect of tube spacing on the movement of water molecules and salt ions during reverse osmosis (RO) process of unconventional double-walled carbon nanotubes. In this paper, a single-layer reverse osmosis membrane model was used to simulate seawater with 0.5 mol 路L ~ (-1) sodium chloride solution, and the hydrostatic pressure was applied on one side of the salt water to simulate the reverse osmosis condition. Secondly, the main body of the membrane was a double-walled carbon nanotube, and the inner and outer walls of the membrane were all armchair. The chirality of the inner wall of the tube is kept at 8%. In this paper, the salt inhibition efficiency and water permeability of different size double walled carbon nanotubes are investigated, the average force potential of water molecules in the tube is calculated, and the characteristics of hydrogen bond and dipole moment of water molecule are analyzed. Three different water molecule potential energy models (TP3PnTIP4P and SPC / E3) are used to investigate the influence of water model selection on the simulation results. The results show that tube spacing not only affects the nanometries (mean force potential) of water molecules in the transport channel. Hydrogen bonds and dipole moments can also make salt ions and water molecules permeate differently in carbon nanotubes. In terms of water retention and salt resistance, small size double-walled carbon nanotubes can effectively separate brine but have less water flux. Large size double-walled carbon nanotubes have higher water flux but lower salt resistance efficiency, while medium size double-walled carbon nanotubes have a salt cutting efficiency of 100, and are similar to large size double-walled carbon nanotubes in the value of water purification flow. This indicates that the medium-size double-walled carbon nanotubes (that is, the spacing of the tubes are 0.815 nm) have excellent water-salt resistance. In addition, the water molecular model can influence the salt resistance, water flux and hydrogen bonding properties of water molecules to some extent. For example, the water molecule of TIP3P has higher permeability and shorter hydrogen bond lifetime in the reverse osmosis model. However, in different water model systems, the variation trend of water resistance and salt resistance with the tube spacing is similar. The effect of water molecular model on the salt resistance of double-walled carbon nanotubes is less than that on the geometry of double-walled carbon nanotubes. In this paper, the molecular dynamics simulation method is used to explain the mechanism of water-permeation and salt resistance of double-walled carbon nanotubes at the molecular level. In order to provide the basis for the preparation of high performance carbon nanotube doped reverse osmosis membrane and provide theoretical support for improving seawater desalination osmosis technology.
【學位授予單位】：大連理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB383.1;O613.71

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本文編號：1515978