Novel Synthesis Methods of Carbon-Nanotube-Based Composite Materials.

This thesis reports novel methods for carbon nanotube synthesis, purification and decoration, which have been designed to be facile processes, with high potential for scale-up manufacture. The synthesis routes outlined compares with methodologies highlighted in the recent literature, with respect to the quality of materials produced, and ease of sample preparation with reduced processing steps. Decoration of carbon nanotubes with magnetic iron nanoparticles has been achieved using a novel synthesis route with cyclopentadienyl iron dicarbonyl dimer as a precursor to the nanoparticle formation. The thermal decomposition protocol for the material is key to the beneficial properties of the final carbon nanotube hybrid material being realised. Decomposition forms iron nanoparticles that have shown catalytic activity and absorb carbon (also provided by the compound) which is subsequently exuded as a protective graphitic shell. A wide range of synthesis temperatures have been studied, 250°C to 1200°C, and led to varying degrees of graphitization, analysis of the protective abilities of the shell to the "core" nanoparticles has been studied. Resistance to acid dissolution has been shown and a potential application for removal of organic materials (rhodamine dye) from water has also been demonstrated. The synthesis of single and few-walled carbon nanotubes of very high quality has also been shown, using the organometallic compound used to decorate CNTs, the first time this has been demonstrated for this compound. Synthesis has been carried out on silicon and quartz substrates in a photo-thermal chemical vapour deposition (PT-CVD) chamber, with minimal sample preparation required. The quality of the CNTs produced has been assessed by Raman Spectroscopy (ID/IG ratio), showing extremely high CNT quality, some of the highest reported using a CVD based technique. The defect concentration has been shown to be lower than some commercially available products. Simplification of the sample preparation required for carbon nanotube synthesis has been achieved; the compound and method used in this study has the potential for scale-up manufacture and to be a competitive high quality carbon nanotube product. The purification of carbon nanotubes and carbon nanotube loaded composite materials has been investigated using a customised steam treatment process. Reduction in defect concentration and amorphous carbon content has generated super-resilient CNTs, a fraction of which are resistant to oxidation in air at temperatures of up to 900°C, compared to 550°C before steam treatment. Diameter selective oxidation of CNTs is also discussed. This process has the potential to further purify commercial CNT materials, obtaining a higher quality product, and has been applied to CNT loaded fibres to remove polymeric and surfactant materials to obtain highly aligned carbon nanotube sheets. This thesis outlines straightforward synthesis routes that can reduce sample preparation and processing times whilst maintaining, and in some cases improving, the quality of comparable materials that are commercially available. Quality of carbon nanotube materials has been assessed using Raman spectroscopy and thermogravimetric analysis; corresponding to the defect concentration, amorphous carbon content and oxidation temperature. The facile processes have been carried out on small scales to prove the underlying principles; the processes have great potential for up-scaling to industrial scales. Future work should be directed at incorporating these high quality carbon nanostructures into composites, such as carbon paper for lightweight electronic screening and composites requiring low weight and increased tensile strength