Synthesis Characterization And Purification Of Single-wall Carbon Nanotubes By CVD

Since the discovery of carbon nanotubes in 1991, the investigation on carbon nanotubes has become a hot topic in the world. Due to the ultimate form of single-wall carbon nanotubes (SWNTs) in the carbon family with special structure, SWNTs have excellent properties and wide potential application. However, the limitation of large-scale production and the high cost have restrained the development of the research on their application. Comparing to arc discharge and laser ablation, chemical vapor deposition (CVD) is the most possible method with large-scale, low-cost and high-yield advantage to fabricate SWNTs. However, it is difficult to control the uniform structure of SWNTs by CVD. Therefore, it is very important for controllable, low-cost and large-quantity fabrication of SWNTs by CVD, which is achieved by optimization of its growth condition.The synthesis process of SWNTs by catalytic chemical vapor deposition (CCVD) was investigated and the product was characterized by transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA) and Raman scattering spectra and so on in this thesis. To attain the largest quantity and the best quality of SWNTs, the preparing process of the catalysts and their parameters' optimizing are investigated. And the parameters of the synthesis process were also optimized. Furthermore, some efforts on purifying the SWNTs grown on Fe/Al2O3 catalyst were also carried out.It was indicated that the yield and quality of SWNTs were affected obviously by the catalyst involved. After a lot of contrastive experiments, we found that binary catalyst is more active than unitary catalyst on the synthesis of SWNTs. The content of the elements have great effects on the final product, and the best catalyst in our experiments is Fe/Co/Mo/Al2O3 with the mixture ratio of 0.9/01/0.25/10 (mole ratio). Moreover, the additives that introduced during the catalyst preparation also have great effects on the yield and quality of the SWNTs. And PEG (200) can furthest improve the yield of SWNTs using citric acid, PEG (2000), and PEG (200) as dispersant, respectively. In all the methods of catalysts preparation, sol-gel process drying by high temperature decrepitation could achieve the best catalyst. Above-mentionedconditions are all beneficial to improve the dispersion of catalyst, consequently enhance specific surface area of catalyst, and also increase the binding force between the active sites and support materials resulting in keeping the small size of sites. The best parameters of synthesis process are also achieved by optimization of SWNTs growth condition. As the results show, the main diameter of the SWNTs is about 1.5nm and most of them are in big bundles beside some individual SWNTs with diameter even above 4 nm. The largest yield of the SWNTs is about 33%. Finally, some efforts were employed to eliminate the support Al2O3, which is very difficult to remove after the crystallization of Al2O3 during the synthesis process. It is proved that hydrothermal process is an effective method to remove Al2O3.