Purity and Solubility of Nanotubes in Arc Discharge Carbon Powder
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Purity and Solubility of Nanotubes in Arc Discharge Carbon Powder Jonathan N. Coleman, Alan B. Dalton, Brendan McCarthy, Robert C. Barklie and Werner J. Blau Materials Ireland Polymer Research Centre, Department of Physics, Trinity College Dublin, Dublin 2, Ireland.
ABSTRACT We have described a novel experimental technique to separate nanotubes from other unwanted carbon species in arc generated carbon soot. A conjugated polymer was used to bind to nanotubes in solution. The resultant hybrid was soluble while extraneous carbon material formed a sediment at the bottom of the sample bottle. This process was monitored using electron paramagnetic resonance (EPR) which showed that 63% of nanotubes were kept in solution while 98.1% of impurities were rejected. This allowed the calculation of the nanotube content in the carbon soot using EPR and thermo-gravitational analysis (TGA) yielding a purity value of 34% for the soot used in this study. This is compatible with estimates made using electron microscopy. INTRODUCTION Carbon nanotubes[1] have generated interest in all areas of science due to their novel structural, mechanical and electronic properties[2]. In the physical sciences nano-devices have already been demonstrated including transistors[3] and rectifying hetero-junctions[4]. In microbiology they have been used as probes to study the structure of biomolecules[5,6] and as templates for the self assembly of proteins[7]. In medicine the oxidation of dopamine has also been studied using nanotubes as charge injectors[8]. However, at present, as-produced carbon soot remains low in nanotube content[9]. Furthermore, neither quantitative techniques to analyse soot content nor methods to measure nanotube content exist. This is an important issue in both biology and nanotechnology and limits the long term potential of nanotubes to research and application. This work presents the first measurement of nanotube content in impure carbon soot. Using a conjugated polymer as a nanotube “filter”, carbon nanotubes are separated from all other soot components. An absolute value for the nanotube content can then be calculated for the first time using electron paramagnetic resonance and thermo-gravimetric measurements. This is a vital step towards making nanotubes a practical material for novel scientific developments. EXPERIMENTAL PROCEDURE In order to produce the polymer nanotube composites used in this work 80 mg of poly(mphenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) [10] were mixed with 25.5 mg of multiwall nanotube (MWNT) containing Krätschmer-generated [11] carbon soot in 4 ml of toluene. The mixture was then sonicated for 4 hours in a sonic bath. The solution was then allowed to stand undisturbed for 48 hours after which the sediment was removed by decantation. This sediment was then dried and weighed. Various mass fractions could be produced by blending the initial composite solution with polymer solution in the desired ratios.
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The natures of the sediment and remaining solute were studied using ele
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