磁场辅助电弧放电法制备单壁碳纳米管

发布时间：2018-02-01 17:08

本文关键词： 磁场辅助电弧放电法单壁碳纳米管拉曼光谱　出处：《新疆大学》2015年硕士论文　论文类型：学位论文

【摘要】：根据手性和直径的不同,单壁碳纳米管可以是金属性的或者是半导体性的,而且半导体性单壁碳纳米管的带隙与其直径成反比关系,同时单壁碳纳米管优异的光学、电学及机械特性与其直径或手性密切相关。但目前所制备的单壁碳纳米管样品中绝大多数是由不同直径和手性的单壁碳纳米管组成的,并且难以分离,不适于用来制作高性能微纳米器件。因此获得特定直径和手性的单壁碳纳米管已经成为单壁碳纳米管制备方面急需解决的科学问题。本文以煤和石墨粉为碳源,研究了催化剂组成、外加磁场及强度、缓冲气体压强及组成对直流电弧放电法制备碳纳米材料结构和组成的影响,具体研究内容如下:以新疆库车煤炭为碳源,首先研究了不同催化剂(Ni、Ni-La2O3、Ni-Y2O3)的催化效率,确定了当以氦气为缓冲气体时,Ni-Y2O3作催化剂,产物中单壁碳纳米管的纯度最高。进一步研究了以Ni-Y2O3为催化剂,磁场辅助电弧放电制备单壁碳纳米管实验中磁场和缓冲气体氦气的压强对单壁碳纳米管直径的协同影响,通过拉曼表征发现,在相对较低的氦气压强下(35 kPa),施加外加磁场后可以明显降低单壁碳纳米管的直径(不加磁场时最小直径为1.36 nm,施加磁场后最小直径可达1.20 nm),同时可以获得单一的半导体性单壁碳纳米管。在直流电弧放电实验中,通过引入反应性气体(氢气)对单壁碳纳米管成核与生长过程进行主动干预来调控单壁碳纳米管直径的分布。拉曼测试结果表明,增加氢气在缓冲气体中的含量能够抑制小直径单壁碳纳米管的形成,而使单壁碳纳米管直径分布向更大直径的方向移动。同时,引入少量(在缓冲气体中所占体积分数不大于3%)氢气在一定程度上可以提高产物中单壁碳纳米管的纯度。以石墨粉为碳源,研究了Ni-Y2O3催化剂、缓冲气体组成及外加磁场对电弧放电产物结构的影响。通过拉曼光谱和场发射扫描电子显微镜表征发现,氦氢缓冲气体中氢气的含量对磁场辅助电弧放电法制备的碳材料形貌结构影响较大,氢气的存在会抑制石墨片层卷曲成单壁碳纳米管,随着氢气含量的增加,单壁碳纳米管的含量逐渐减少,而石墨烯片层的含量逐渐增加,但当氢气的含量超过最佳值时,产物主要由比较大的石墨化多面体组成。高分辨透射电子显微镜及拉曼表征结果表明在氢气含量占3%(体积分数)时所制备的石墨烯具有较少的层数,且缺陷较少。并进一步研究了磁场强度对石墨烯产率的影响,研究发现当磁场强度在42-51G之间时可以制备出较高含量的石墨烯。
[Abstract]:Depending on the chirality and diameter, single walled carbon nanotubes can be gold or semiconductive, and the band gap of semiconductor single walled carbon nanotubes is inversely proportional to their diameter. At the same time, single-walled carbon nanotubes have excellent optics. Electrical and mechanical properties are closely related to their diameters or chiral properties. However, most of the single walled carbon nanotubes (SWNTs) made up of different diameters and chiral properties are difficult to separate. It is not suitable to be used to fabricate high performance micro-nanodevices. Therefore, obtaining single-walled carbon nanotubes with specific diameter and chirality has become a scientific problem in the preparation of single-walled carbon nanotubes. In this paper, coal and graphitic powder are used as carbon sources. The effects of catalyst composition, applied magnetic field and intensity, buffer gas pressure and composition on the structure and composition of carbon nanocomposites prepared by DC arc discharge were studied. The main contents are as follows: Kuqa coal was used as carbon source in Xinjiang. Firstly, the catalytic efficiency of different catalysts Ni Ni La 2O 3 O 3 Ni Y 2O 3 was studied, and Ni-Y 2O 3 was used as catalyst when helium was used as buffer gas. The purity of single-walled carbon nanotubes was the highest among the products. Ni-Y2O3 was used as catalyst. The cooperative effect of magnetic field and helium pressure on the diameter of single-walled carbon nanotubes (SWNTs) prepared by magnetic-assisted arc discharge was investigated by Raman spectroscopy. At a relatively low helium pressure of 35 KPA, the diameter of single-walled carbon nanotubes can be significantly reduced by applying an applied magnetic field (the minimum diameter is 1.36 nm without magnetic field added). The minimum diameter can reach 1.20 nm after the application of magnetic field, and a single semiconductor single-walled carbon nanotube can be obtained at the same time. The diameter distribution of single-walled carbon nanotubes was regulated by introducing reactive gas (hydrogen) into the nucleation and growth process of single-walled carbon nanotubes. Increasing the hydrogen content in the buffer gas can inhibit the formation of small diameter single-walled carbon nanotubes and make the diameter distribution of single-walled carbon nanotubes move towards the direction of larger diameter. The purity of single-walled carbon nanotubes in the product can be improved to a certain extent by introducing a small amount of hydrogen (the volume fraction in buffer gas is no more than 3). The Ni-Y2O3 catalyst was studied using graphite powder as carbon source. Effects of buffer gas composition and applied magnetic field on the structure of arc discharge products were investigated by Raman spectroscopy and field emission scanning electron microscopy. The content of hydrogen in helium hydrogen buffer gas has a great influence on the morphology and structure of carbon materials prepared by magnetic field assisted arc discharge method. The existence of hydrogen will inhibit the graphite lamellar curling into single-walled carbon nanotubes, with the increase of hydrogen content. The content of single-walled carbon nanotubes decreases gradually, while the content of graphene layer increases gradually, but when the hydrogen content exceeds the optimal value. The products were mainly composed of larger graphitized polyhedrons. The results of high resolution transmission electron microscopy (TEM) and Raman spectroscopy showed that the graphene prepared at the hydrogen content of 3 / 3 (volume fraction) had a small number of layers. The effect of magnetic field intensity on the yield of graphene was further studied. It was found that a higher content of graphene could be prepared when the magnetic field intensity was between 42 and 51G.
【学位授予单位】：新疆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ127.11;TB383.1

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