Preparation Of Carbon Nanofibers By Chemical Vapor Deposition Using Water-Soluble Catalysts

Carbon nanofiber has excellent physical and chemical properties, such as greater specific surface area, high mechanical strength and conductive properties, long fiber structure, better chemical stability. At present, the growth of carbon nanofibers usually uses Fe, Co, Ni and theirs alloy as catalysts. So, all of the catalysts require strong acids to remove them from the deposited carbon materials, and these reagents may destroy the structures of the carbon nanofibers. In addition, strong acids are less desirable for large-scale production due to environmental concerns. This research work focuses on resolving this problem.Firstly, we used the catalysts prepared by different precursors and the C₂H₂ a carbon source to synthesize carbon nanofibers through chemical vapor deposition. The influences of the catalyst which was prepared by different catalyst precursors and temperature on the morphology of carbon nanofibers were studied. The catalyst precursors and catalysts were characterized using TG and XRD, the morphologies and structures were characterized using SEM, TEM and HRTEM. The results indicate that the main ingredient of the catalyst is K₂CO₃. There are helical, tubular and straight carbon nanofibers in the products. The diameter of carbon nanofibers increases with increasing deposition temperature. The optimum reaction temperature is 600oC. For all catalyst systems, the catalyst which is prepared by C₆H₅O₇K₃ has the best activity, and the productivity is the highest.Secondly, we directly used the alkali salts catalysts and the C₂H₂ a carbon source to synthesize carbon nanofibers through chemical vapor deposition. The results indicate that the diameter of carbon nanofibers usually increases with increasing deposition temperature for the same catalyst. The carbon nanotubes can be more easily prepared when the size of catalyst particles is from 30nm to 50nm. The helical carbon nanofibers can be more easily prepared when the size of catalyst particles is from 50nm to 100nm. The linear carbon nanofibers can be more easily prepared when the size of catalyst particles is above 100nm. For all catalysts, the NaF and CsCl have the worst activity.