Synthesis And Purification Of Single-walled Carbon Nanotubes By Arc Discharge Method

Since the first discovery of single-walled carbon nanotubes (SWNTs) in 1993, an upsurge of research on carbon materials science throughout the world has being inspired for the novel physical and chemical properties as well as excellent electronic and mechanical performances of SWNTs due to their special structure. SWNTs have wide potential application in fields such as nano-electronic devices, hydrogen storage, field-emission and complex materials etc. To achieve all these application rely on the commercial and cheap synthesis of SWNTs. Among all methods, the arc discharge method is giving more attention because of its low investment, easy operation and high crystallity of SWNTs product. Transition metals are often used as catalysts and the cost of SWNTs is high, which block the wide application of SWNTs. So the one effective way to lower the cost of SWNTs is to find cheap, available and performance-well catalyst. Therefore, the ferric oxides as catalysts to produce high quality SWNTs by arc discharge are investigated for the purpose of reducing the cost. The morphology, structure and purity of SWNTs were characterized by SEM, HRTEM, EDX and Raman spectrum.All the results revealed that the ferric oxides could be used as catalysts to synthesize high quality SWNTs by arc discharge. The macroscopical morphology of products were cloth-like and web-like, and typical SEM images and HRTEM images showed that there were many SWNTs with very low impurities entangled together in cloth-like fraction, while strip-like products containing even high purity SWNTs congregated closely in the web-like. EDX analysis and Raman spectra further confirmed the high purity of the SWNTs synthesized by arc discharge using ferric oxides as catalysts.The activity of Fe₂O₃,Fe₃O₄ and the mixture of Fe₂O₃ and Fe₃O₄ with varies ratios were studied, and the parameters would be affected in synthesis were also analyzed and optimized. The optimal conditions for synthesis of high quality SWNTs catalyzed by ferric oxides were that, 12 wt.% Fe₃O₄ as catalyst, 3 wt.% FeS as growth accelerate, mixture of Ar and H₂ (Ar 60%, H₂ 40% by mol) as buffer gas, pressure was 200 Torr, flux was 4.8 L/h, current was 90 A.In this thesis, we tried to purify the SWNTs using physical method and chemical method together. Firstly, oxidated the sample at 450℃under oxygen atmosphere for 3h, then dispersed in alcohol by ultrasonic (above 400 W) for 3h, then washed by dense hydrochloric acid under stirring for 12h, and lastly filtered by micro-hole membrane (2μm). The purity of SWNTs after purification increased highly, most of the amorphous carbon impurities and the catalyst particles were removed.