The Research On Preparation And Organic Functionalization Of Carbon Nanomaterials

Since their discovery in 1991, carbon nanotubes (CNTs) have attracted much attention in various disciplines such as physics, chemistry, biology, and material science due to their unique structural, mechanical, electronic and thermal properties. So far, plenty of progress on CNTs related studies has been achieved. However, many challenges for large-scale applications of CNTs still exist. On the basis of the present research advancement, the high-yield and controllable production of high-quality CNTs at low cost is still an important developing aim. In addition, it is also a very intractable problem to achieve the industrial production of aligned CNTs. In this dissertation, we firstly develop a new kind of catalyst with great efficiency for the mass production of CNTs by CVD. The synthetic route of the aligned CNTs has been systemically investigated by spray pyrolysis method. Moreover, the organic functionalization of CNTs is developed to improve the dispersibility of CNTs and to enhance the chemical compatibility between CNTs and matrix material. The research is fundamental and pioneering, and is of great significance on the theory and application potential.Firstly, the Ni/Mo/Mg catalysts with high activity and efficiency were synthesized by sol-gel method. CNTs with high quality were obtained on the catalyst at 750℃by decomposition of acetylene. After reaction of 30min, the yield of synthesized CNTs is closed to 10 times of the pristine catalyst. The results of SEM and TEM show that the CNTs with hollow and multi-walled structure possess a relatively uniform diameter of about 30～35nm, and their length is about 50μm.Secondly, single-walled carbon nanotubes(SWNTs) were prepared by decomposition of CH4 at 900℃on Fe/Mg/Mo catalyst in a CVD reaction furnace. Moreover, carbon nanobelts made of graphite layers were successfully synthesized by adjusting the experimental parameters. The SEM and TEM results reveal that the nanobelts have the thickness of approximate 10nm, the width of several hundreds nanometer, and the length of several hundreds micron.Thirdly, the aligned CNTs with high quality were synthesized by spray pyrolysis of ferrocene/xylene solutions and their growth mechanism was also discussed based on the experimental phenomena and results. Furthermore, ultralong aligned CNT bundles (8.2mm), wave-like CNT arrays, carbon spheres and chains were also obtained in the spray pyrolysis method.Fourthly, by selecting some homologous series, including three aromatic hydrocarbons, four straight-chained alkanes, and a cyclane, as carbon sources, we systemically and comparatively investigated the relationship between properties of precursory carbon source and quality of aligned CNTs in a similar growth condition. It is found that the thermodynamic properties of precursory carbon sources such as Gibbs free energy and formation enthalpy play decisive roles in the morphology and structure of the nanotube samples in four straight-chained alkanes, while for three aromatic hydrocarbons, the decomposition mechanism rather than the thermodynamic property strongly influences the quality of the products. The results of SEM, HRTEM and Raman reveal that the aligned CNTs obtained from them have different nanotube parameters such as diameter and degree of graphitization. We find also that xylene, n-heptane and cyclohexane are favored for the growth of aligned CNTs with high quality and yield. These will be very helpful for the controllable preparation of aligned CNTs at relatively low cost in the spray pyrolysis method.Fifthly, by using eletrophilicity of formaldehyde, multi -walled carbon nanotubes (MWNTs) were methylolated and then grafted by maleic anhydride. The IR spectra showed that there were many hydroxyl and methylene groups on the surface of the methylolated MWCNTs(MWNTs-OH). Some ester and methylene groups appeared on the MWNTs grafted by maleic anhydride(MWNTs-MAH). The dispersion of MWNTs-OH in water was improved significantly and the dispersion of the MWNTs-MAH in xylene was enhanced remarkably. Moreover, the graft functionalization with poly (acrylic acid) (PAA) was also carried out for the MWCNTs-OH and MWNTs-PAA composites have been formed. The IR and TEM results show presence of covalent band and so-called"core-shell"structures for MWNTs-PAA. The MWNTs-PAA exhibits excellent solubility in water, which is significant to explore the potential application of carbon nanotube in biological and medical systems.Finally, MWNTs were functionalized with polyimide (PI) via an in-situ polymerization. The TEM and SEM images show that the functionalized MWNTs were wrapped by PI. The TGA and DSC results indicate that the thermal stability of the functionalized MWNTs with PI was improved. In addition, using polyethylene glycol-200 as processing aids, we successfully prepared CNTs-reinforced polyimide composite with well-dispersed and high-loading of CNTs. The content of CNTs in composite can arrive at 43 wt %. The preparation process will give birth to a promising strategy for the production of CNTs/polymer composite materials.