The Growth Of Multi-walled Carbon Nanotubes, Doping And Related Application Research

As one of the hot research areas in nano materials, carbon nanotubes (CNTs) have aroused a great deal of attention, which is not only in the controllable fabrication of CNT arrays, but also involved the applications of the doped CNTs. Up to nowadays, lots of researches focus on the morphology of the catalyst particles for the synthesis of CNT arrays with high quality and the application of nitrogen-doped CNTs as high performance catalyst for oxygen reduction reactions.An iron catalyst film for the growth of carbon nanotube (CNT) arrays has been prepared by sol-gel method. In this thesis, it is initially addressed that the hydrolytic extent of the catalyst precursor strongly affects the morphology of the iron particles on the surface of the film. Through the AFM and SEM tests, it is shown that the hydrolytic time has strong impacts on the size and density of iron catalyst particles. Detailedly, iron catalysts form big clusters (110nm) at the early stage of the hydrolysis, which do not benefit the growth of CNTs. However, at the later period of the hydrolysis, the particle size decreases dramatically to20-30nm with high density and well distribution, which apparently results in vertical long CNT arrays. This is because of the reaction between the hydrolytic product of the precursor and the iron oxide particles which effectively influence the morphology of catalysts during the process of annealing precursor films and reducing the iron oxide particles into iron catalysts. It is believed that the hydrolytic product limits the mobility of the catalyst particles, preventing them from aggregating into big clusters during the annealing and reduction process. Therefore, by controlling the extent of hydrolysis, it is possible to find the optimal conditions for the size and density of iron catalysts, and thus obtain well ordered and high quality of CNT arrays.On the other hand, concerned the unfitness of the sol-gel method for the synthesis of the nitrogen-doped carbon nanotubes(NCNTs), in the second section of the thesis, we present that the vertical aligned NCNTs have been synthesized by the pyrolysis of acetonitrile in the presence of ferrocene catalyst (2wt.%) with floating catalyst-chemical vapor deposition. With water assisted growth, the structure and the nitrogen content of NCNTs can be tailored. Additionally, the NCNT arrays can be successfully synthesized even though the water introduced was as much as33.3wt.%. The resultant data from SEM and TEM characterization indicate that a small water amount (1.2wt.%) assisted which can etch the amorphous carbon and lead to NCNTs with decreased diameter and wall-thickness. While with more H2O mixed into the liquid precursor, it is suggested that the11.1wt.%H2O introduced can increase the diameter, the thickness of walls and bamboo-like compartments of the NCNTs which due to the larger catalyst particles caused by the decreased dissolvability of ferrocene in the solvent.The further electrochemical analysis of the as-grown NCNTs indicates that the NCNTs have more superior electrocatalytic performance than pristine CNTs in oxygen reduction reactions. In addition, the electrocatalytic activities can be modulated with different amount of water introduced.