多壁碳纳米管的团聚与沉降规律及在微模型中的迁移

发布时间：2019-05-29 04:14

【摘要】：碳纳米管具有十分独特的物理化学性质,在材料学、电子学、医药学等多个领域得到了广泛的应用,这增加了其被释放到环境中的机会。大量文献证明碳纳米管对微生物、动物、植物等的毒性效应,表明碳纳米管会对生态环境造成负面影响。因此,了解碳纳米管在自然界中的环境过程,尤其是其团聚与沉降等行为,对其安全使用具有重要的意义。本文以多壁碳纳米管作为研究对象,将牛血清白蛋白吸附于碳纳米管表面,研究吸附有蛋白质的多壁碳纳米管的团聚、沉降行为及在孔隙介质中的迁移情况,并探讨电解质对多壁碳纳米管的环境过程所造成的影响。碳纳米管的团聚和沉降分别使用动态光散射和石英晶体微天平进行研究,而孔隙介质中的迁移使用微模型的手段研究。与传统的填充柱实验相比,微模型实验能够直接观察碳纳米管在孔隙介质中的迁移随时间和空间的分布情况。研究表明,吸附有蛋白质的多壁碳纳米管的团聚行为符合胶体经典的DLVO理论,团聚行为分为反应控制阶段和扩散控制阶段,在NaCl和CaCl2溶液中,碳纳米管的临界团聚浓度分别为175 mM和2.7 mM。碳纳米管的团聚行为影响其重力沉降行为,碳纳米管达到最快团聚后才能够达到最快重力沉降,使碳纳米管达到最快重力沉降所需NaCl和CaCl2浓度分别为400 mM和4 mM。碳纳米管在二氧化硅表面的界面沉降同样符合DLVO理论,沉降行为分为不利沉降阶段和有利沉降阶段,在NaCl和CaCl2溶液中,碳纳米管的临界沉降浓度分别为100 mM和0.9 mM。碳纳米管在氧化铝表面的沉降始终处于有利沉降阶段。电解质的存在能够加速碳纳米管的团聚与沉降,表明静电作用为碳纳米管的团聚与沉降的主要控制机制。碳纳米管在微模型中的迁移实验表明,电解质浓度的增大能够加剧碳纳米管在微模型中的沉积,减弱其迁移能力。在无电解质的情况下也出现了沉积,说明流体运动的相向传输方式影响了碳纳米管在微模型中的迁移。碳纳米管的团聚和沉降行为影响其孔隙沉积行为,除了静电作用以外,不同位置流速的差异以及碳纳米管的独特结构也造成了碳纳米管在微模型中团聚体的形成。碳纳米管在微模型中的沉积分布较为均匀,且沉积多发生在孔隙较窄处,表明物理阻塞作用是导致碳纳米管在孔隙介质中沉积的主要原因。二价的Ca~(2+)对碳纳米管的团聚、沉降以及孔隙沉积行为的影响均大于一价的Na+,除了 Ca~(2+)本身带有更多电荷之外,其与碳纳米管、牛血清白蛋白以及二氧化硅表面的基团产生的特异性作用也是重要的原因之一。也是由于这种特异作用,在高浓度的Ca~(2+)溶液中,碳纳米管界面沉降的沉降层的刚性迅速增大。本研究证明了电解质能够影响碳纳米管的环境过程,为预测碳纳米管的环境行为、评估其风险提供重要依据。
[Abstract]:Carbon nanotube (CNT) has been widely used in materials, electronics, medicine and other fields because of its unique physical and chemical properties, which increases the opportunity for CNT to be released into the environment. A large number of literatures have proved the toxic effects of carbon nanotubes on microorganisms, animals, plants and so on, indicating that carbon nanotubes will have a negative impact on the ecological environment. Therefore, it is of great significance to understand the environmental process of carbon nanotubes in nature, especially its agglomeration and deposition, for its safe use. In this paper, bovine serum albumin was adsorbed on the surface of multi-wall carbon nanotubes, and the agglomeration, sedimentation behavior and migration in porous media of multi-wall carbon nanotubes adsorbed with proteins were studied. The effect of electrolytes on the environmental process of multi-wall carbon nanotubes was also discussed. The agglomeration and settlement of carbon nanotubes were studied by dynamic light scattering and quartz crystal microbalance, respectively, while the migration in porous media was studied by means of micromodel. Compared with the traditional packed column experiment, the micromodel experiment can directly observe the distribution of carbon nanotube migration with time and space in porous media. The results show that the agglomeration behavior of multi-wall carbon nanotubes adsorbed with protein accords with the classical colloidal DLVO theory. The agglomeration behavior is divided into reaction control stage and diffusion control stage. In NaCl and CaCl2 solutions, the agglomeration behavior is divided into reaction control stage and diffusion control stage. The critical agglomeration concentrations of carbon nanotubes are 175 mM and 2.7 mM., respectively. The agglomeration behavior of carbon nanotubes affects the gravity deposition behavior. The NaCl and CaCl2 concentrations required for carbon nanotubes to reach the fastest gravity deposition are 400 mM and 4 mM., respectively. The interfacial settlement of carbon nanotubes on silicon dioxide surface is also in accordance with DLVO theory. The settlement behavior is divided into unfavorable settlement stage and favorable settlement stage. In NaCl and CaCl2 solutions, the critical deposition concentrations of carbon nanotubes are 100 mM and 0.9 mM., respectively. The deposition of carbon nanotubes on alumina surface is always in a favorable settlement stage. The existence of electrolytes can accelerate the agglomeration and deposition of carbon nanotubes, indicating that electrostatic interaction is the main control mechanism of agglomeration and deposition of carbon nanotubes. The migration experiment of carbon nanotube in micromodel shows that the increase of electrolyte concentration can aggravate the deposition of carbon nanotube in micromodel and weaken its migration ability. Deposition also occurs in the absence of electrolytes, which indicates that the phase transport mode of fluid movement affects the migration of carbon nanotubes in the micromodel. The agglomeration and sedimentation behavior of carbon nanotubes affect the pore deposition behavior. In addition to electrostatic action, the difference of velocity at different positions and the unique structure of carbon nanotubes also lead to the formation of aggregates of carbon nanotubes in the micromodel. The deposition distribution of carbon nanotubes in the micromodel is more uniform, and most of the deposition occurs in narrow pores, which indicates that physical blocking is the main reason for the deposition of carbon nanotubes in porous media. The effect of divalent Ca~ (2) on the agglomeration, sedimentation and pore deposition behavior of carbon nanotubes is greater than that of univalent Na, and it is more charged with carbon nanotubes than Ca~ (2) itself. The specific effect of bovine serum albumin and groups on silica surface is also one of the important reasons. It is also due to this specific effect that the rigidity of the settling layer deposited at the interface of carbon nanotubes increases rapidly in high concentration Ca~ (2) solution. This study proves that electrolytes can affect the environmental process of carbon nanotubes, and provides an important basis for predicting the environmental behavior of carbon nanotubes and evaluating their risks.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X131

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