Synthesis Of Single Walled Carbon Nanotubes By Magnetic Field Assisted Arc Discharge Method

Single walled carbon nanotubes(SWNTs) might be metallic or semiconducting depending upon their chirality(helicity) and diameter, and the band gap of semiconducting SWNTs is inversely proportional to their diameter, the superior optical, electronic and mechanical properties of SWNTs strongly depend on their diameter and chiral angle. However, the as-synthesized SWNTs always come as a mixture of nanotubes with different chirality and diameter, resulting in the heterogeneous performance of SWNT-based devices. This presents a major obstacle to many advanced applications of SWNTs. In this paper, we use coal and graphite as carbon source, investigated the effect of catalyst, magnetic field, the pressure and composition of buffer gas on the structure of carbon nano-materials.Firstly, we used coal as the carbon source, investigated the effect of different catalyst on the production of SWNTs. When He was used as the buffer gas, Ni-Y2O3 is the best catalyst. We further investigated the coordinated effect of helium pressure and magnetic field on diameter distribution of SWNTs produced by arc discharge. And Raman results show that the application of magnetic field can effectively decrease the diameter of SWNTs at a relatively low helium pressure of 35 kPa, SWNTs with the smallest diameter of 1.2 nm can be got, and the synthesized SWNTs were mainly of semiconducting with the application of magnetic field.Secondly, the active intervention to the nucleation and growth process of SWNTs was proposed by adding low-pressure reactive gases, which is supposed to control the diameter distribution of SWNTs. Low-pressure reactive gases(H2) with different contents were mixed with buffer gas during arc discharge process, and the increasing of the reactive gas results in the enrichment of SWNTs with big diameters. Meanwhile, the purity of SWNTs can be improved to some extent when a little H2(3vol%) was added.Lastly, few-layer graphene sheets were synthesized by magnetic field assisted arc discharge method using He-H2 mixture as buffer gas. The Ni-Y2O3 powder was used as catalyst. The effect of hydrogen pressure, magnetic field, and Ni-Y2O3 catalyst were studied with respect to the morphology and structure of the synthesized carbon materials. The samples were characterized by SEM, TEM, TGA and Raman spectroscopy. The SEM images and Raman spectroscopy results revealed that the hydrogen pressure and magnetic field played a key role in the catalytic growth of graphene. High resolution-TEM analysis showed that the graphene sheets are mainly of 1-5 layers. To further quantify the effect of magnetic field on the grephene growth, a series of experiments were carried out under other different magnetic field strength distribution. When the magnetic field strength in the discharge gap is between 42G-51 G, the higher percentage of graphene in the final products can be obtained. The magnetic field induced arc discharge method provided a low cost and ecofriendly route for the preparation of high-quality and few-layer graphene sheets.