Studies On Purification Of Carbon Nanotubes And Their Use As The Carriers Of Highly Dispersed Metal Catalyst

With their chemical inactivity, extremely mechanical strength and unusual electronic properties, carbon nanotubes (CNTs) are a one-dimension nanostructural material. For many unique performance and potential application of the new carbonaceous materials, they have generated great interest since their discovery in 1991, producing a main focus of fullerene field. Carbon nanotubes can now be obtained in quantity by the electric arc method, laser ablation method, and most recently the chemical vapor deposition method. However, all the CNTs products from these methods include impurities, such as amorphous carbon, graphitic carbon, and carbon nanoparticles, Ceo and other fullerenes. These impurities, mostly carbonaceous species, are a serious impediment to detailed characterization of the properties and applications of the aanotubes. Purification of CNTs is a very important step in their use as industrial materials and considered a bottleneck of the CNTs industrialization.Various methods for purifying carbon nanotubes were reviewed, and their purification effects were also compared. Though there were many suggested methods to purify CNTs, the widely used procedure was still chemical oxidation with cone. HNO3-H2SO4. However, this method may cause intercalation and partial exfoliation of the nanotubes, and mass reduction in the following washing steps. In this work, a new technique for purifying carbon nanotubes (CNTs) ultilizing anodic oxidation in a solid polymer electrolyte (SPE) cell had been proposed at first time. The possible purification mechanism was studied by the cyclic voltammetry on Pt/SPE in raw and purified CNT slurry. The samples were characterized by TEMobservations, TG-DTA graphs and Raman analyses, and the results showed that most of amorphous carbon, graphitic carbon, carbon nanoparticles and fullerenes were removed from the roots without remarkable damage of the bundles. After purification, only transition-metal catalyst particles adhered on inner wall of tubes still existed. Compared with the widely used cone. HNO3-H2SO4 method, SPE electrolysis can be carried out in pure water, so it demands minimal steps of following wash and separation. This is helpful for developing a simplified process and reducing the product loss.In second part of this work, an effective method had been developed for the preparation of highly dispersed Ag/CNT catalyst. We had introduced the functional ion preadsorption method and studied the optimum conditions of the catalyst preparation. On the basis of adsorption curves, TEM observations and catalytic activity analyses, it was found that the functional ion preadsorption was helpful for the formation and dispersion of small metal particles'. The catalysts that were prepared under ultrasonic or ultrasonic-mechanic agitation and high reaction temperature conditions had excellent activities.