纳米气泡对污染物的吸附及其影响因素探究

发布时间：2018-07-31 17:49

【摘要】：纳米气泡是人们在研究水中的两个疏水表面间的疏水长程作用机制时提出的。特别是2000年纳米气泡原子力图像的发表以及随后大量的实验验证,固液界面上存在纳米气泡的观点逐渐被越来越多的人所接受。近年来,界面问题越来越受到人们的广泛关注,纳米气泡的产生及应用等有关问题也成为人们研究的热点。经典热力学表明纳米气泡在水中存在时间仅为几微秒,然而大量实验表明界面纳米气泡在溶液中可以存在几天,原子力显微镜也直接观察到了纳米气泡。研究表明,纳米气泡在界面上的稳定存在对纳米科技、界面科学、流体力学、生物学和其他领域都有广泛的影响。此外,纳米气泡会引起流体在界面的滑移,减少流动阻力,并与表面粘附、胶体分散、矿石浮选、废渣处理等方面密切相关。因此,界面纳米气泡具有十分重要的研究应用价值。目前原子力显微镜(AFM)是直接探测固液界面纳米气泡的最有力手段。在用AFM对纳米气泡成像时,通常选用表面较为平整的基底。主要有高序热解石墨(HOPG),云母,金,聚苯乙烯薄膜,以及修饰过的硅。产生纳米气泡的方法有很多,如直接浸渍法,两种溶剂替换以及快速加热,电化学法等。其中,醇水替换被广泛应用并被证明是能高度重复的在不同基底上获得大量纳米气泡的有效方法。同样,也能使用其它有机溶剂与水替换来产生纳米气泡。然而,有机溶剂与水的替换存在着一些局限性,例如不能用于生物膜上,溶剂中易引入有机污染物等。为了探究在原子级平整的电极表面能否生成纳米气泡,我们采用了循环伏安法法,用电化学工作站监测电极表面双电层电容的变化。实验中我们采用溶液替换法利用双电层电容与相对介电常数的关系来推测电极表面的纳米气泡生成与否。实验结果表明,该方法同样可以在电极表面生成纳米气泡。我们分别用深度脱气后的醇水、盐水在电极表面替换,我们发现这时候的双电层电容和裸电极相比几乎没有什么变化,也就是说双电层的介质几乎没有什么改变,这时在电极表面几乎没有纳米气泡生成。我们还探究了盐溶液的浓度和种类对纳米气泡生成的影响。盐溶液的浓度越大,盐溶液与水的浓度差就越大,产生的纳米气泡就越多。这是由于高浓度的盐溶液所含自由离子较多,成核驱动力比较大,形成晶胚就会多,可以在电极表面形成更多的成核位点。由于纳米气泡的特殊性质,在生活生产中的应用前景也十分广阔。我们通过模拟重金属污染和有机物污染两大类,用交流阻抗法研究了超声法在电极表面产生的纳米气泡对水中污染物的吸附作用。通过电化学工作站检测出电极表面超声后的阻抗比裸电极在污水中的阻抗大,这说明了超声法产生的纳米气泡能够增强污染物的吸附。而且随着超声时间的增长,纳米气泡会越来越多,但是增长率会有所下降,最后几乎趋于稳定,阻抗值也越来越大,也就是说纳米气泡的多少会影响水中污染物的吸附。
[Abstract]:Nano bubbles are proposed by people to study the mechanism of hydrophobic long-range interaction between two hydrophobic surfaces in water. In particular, the publication of the atomic force images in 2000 and a large number of experiments have proved that the existence of nano bubbles on the solid-liquid interface has gradually been accepted by more and more people. In recent years, the interface problem has become more and more popular. To people's widespread concern, the production and application of nano bubbles have become a hot spot of research. Classical thermodynamics shows that the existence of nanoscale in water is only a few microseconds. However, a large number of experiments show that the nano bubbles can exist in the solution for several days, and the original sub force microscope also directly observed the nano bubbles. It is shown that the stability of nanoscale on the interface has a wide influence on nanotechnology, interface science, fluid mechanics, biology and other fields. In addition, the nano bubbles will cause the fluid to slip at the interface, reduce the flow resistance, and closely related to surface adhesion, colloid dispersion, ore flotation, waste residue treatment and so on. Surface nanoscale has very important research and application value. At present, atomic force microscopy (AFM) is the most powerful means for direct detection of nanoscale in solid-liquid interface. When using AFM to imaging nanoscale, the surface of the surface is usually used. There are mainly high order pyrolytic graphite (HOPG), mica, gold, polystyrene film, and modified There are many ways of producing nanoscale, such as direct impregnation, two solvent replacement, rapid heating, electrochemical method, etc. in which alcohol water replacement is widely used and proved to be an effective method for obtaining a large number of nanoscale bubbles on different substrates. However, there are some limitations in the substitution of organic solvents and water, such as the inability to use the organic pollutants in the biofilm. In order to explore the formation of nano bubbles on the surface of the atom level flat electrode, we used the cyclic voltammetry to monitor the double layer capacitance on the electrode surface. In the experiment, we use the solution substitution method to make use of the relationship between the double layer capacitance and the relative dielectric constant to speculate on the formation of nano bubbles on the electrode surface. Experimental results show that the method can also produce nano bubbles on the surface of the electrode. At this time, there is little change in the double layer capacitance compared with the bare electrode, that is to say, there is little change in the medium of the double layer. At this time, there are almost no nanoscale bubbles on the surface of the electrode. We also explore the effect of the concentration and type of salt solution on the formation of nanoscale. The greater the concentration of salt solution, the concentration of salt solution and the concentration of water. The greater the degree difference is, the more nano bubbles are produced, which is due to the more free ions in the high concentration of salt solution, the larger the driving force of the nucleation, the formation of more crystal embryos and the formation of more nucleation sites on the surface of the electrode. Two kinds of heavy metal pollution and organic matter pollution are proposed. The adsorption of nano bubbles produced by ultrasonic method on the surface of the electrode is studied by the method of AC impedance. The impedance of the electrode surface after ultrasonic is detected by the electrochemical workstation. The impedance of the bare electrode in the sewage is larger than that of the bare electrode. This shows the nano bubble energy produced by the ultrasonic method. With the increase of the ultrasonic time, there are more and more nanoscale bubbles, but the growth rate will decrease. Finally, it tends to stabilize, and the impedance value is increasing. That is, the number of nano bubbles will affect the adsorption of pollutants in the water.
【学位授予单位】：上海师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X703;O647.3

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