Improving the synthesis of single-walled carbon nanotubes by pulsed arc discharge in air by preheating the catalysts

Single-walled carbon nanotubes (SWCNTs) were synthesized in reduced pressure air using pulsed arc discharge after preheating the catalyst. Our experimental results revealed that preheating the catalysts can assist the synthesis of SWCNTs in air under a pressure of 5-10 kPa. The SWCNTs have a diameter of 1.5-2 nm and length can reach several micrometers. The consumption rate of the anode and the production rate of CNTs and SWCNTs in air are lower than in helium atmosphere at the same pressure, respectively. Further experiment demonstrates that 600 °C is optimum temperature for preheating the catalysts to synthesize SWCNTs in air.     

Diameter-control of single-walled carbon nanotubes produced by magnetic field-assisted arc discharge

We have demonstrated a scalable approach to synthesize single-walled carbon nanotubes (SWCNTs) with selected diameter distributions by applying a magnetic field perpendicular to the electric field in the arc plasma. It is found that the purity and orientation of SWCNTs can be controlled by the magnetic field. SWCNTs with different diameter distributions can be separated into two different regions by the applied magnetic field, and the diameter-selection efficiency is improved by modifying the direction of the magnetic field. Our findings suggest that the motion of the catalyst particles with different sizes, positive carbon ions and electrons are significantly influenced by Lorentz forces, resulting in the difference in the growth processes of the SWCNTs due to the collective interactions between the arc plasma and the magnetic field.     

Single-chirality separation of ultra-thin semiconducting arc discharge single-walled carbon nanotubes

Ultra-thin single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution are prepared with a Fe catalyst under an optimized H₂/He atmosphere by arc discharge first time. These SWCNTs were enriched with a pH–temperature controlled gel chromatography single-chirality separation process. The separation process uses the electrostatic interaction between the gel and the functional groups on the sidewalls of nanotubes, which is defined by the curvature of the C–C bond and the chiral vector (n, m). Tuning the interaction through varying the pH and temperature enables the separation of five species from the sodium dodecyl sulfate (SDS) wrapped SWCNTs in aqueous solution, namely (7, 5), (9, 4), (7, 6), (8, 6), and (8, 7), as evidenced by several optical spectroscopy techniques.     

Direct and large scale electric arc discharge synthesis of boron and nitrogen doped single-walled carbon nanotubes and their electronic properties

Boron and nitrogen co-doped single-walled carbon nanotubes (BN-SWCNTs) were directly synthesized at large scale using an electric arc discharge method. X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and UV-vis-NIR spectroscopy were performed to investigate structure and properties of BN-SWCNTs. These results show that the band gaps of SWCNTs have been tuned greatly with B and N doping.     

Synthesis of multiwall carbon nanotubes by electric arc discharge in liquid environments

This work reports the experimental results from the production of multiwall carbon nanotubes (MWCN) synthesized by an electric arc discharge performed in liquid environments between pure graphite electrodes. Both liquid nitrogen and deionised water were suitable for a successful synthesis of this form of carbon aggregation. We report a successful synthesis of MWCN by arc discharge submerged in deionised water. Electron microscopy observations of both the reaction products and the surface of the as-synthesized raw material showed the presence of structural degradation of the MWCN, which probably operates after their growth at the cathode. The degradation is tentatively ascribed to a combination of overheating and high current density experienced by the as-synthesized MWNT, which can be caused by the loose structure of the as-deposited material. The damage appeared to be less severe in water environments, probably owing to the better cooling capacity of water relative to liquid nitrogen.     

Influence of carbon structure of the anode on the synthesis of single-walled carbon nanotubes in a carbon arc plasma

Arc plasma evaporation of carbon electrodes doped with various catalysts is one of the most effective methods of single-walled carbon nanotube fabrication. It was found that the reaction yield is strongly influenced not only by the appropriate choice of the catalyst(s), but also by the type of carbon material used for electrode fabrication. Several different carbon powders i.e. graphite powders, glassy carbon and coke, have been tested in order to establish which parameters (primary particle size, granulation, density or conductivity of the electrode) affected the outcome of the reaction the most. The highest yield of single-walled nanotubes was found for anodes fabricated from graphite powders, whilst the electrodes made from glassy carbon or coke yielded significantly smaller amounts of nanotubes. The reaction zone where carbon radicals nucleate (close to the arc gap) was probed by optical absorption spectroscopy. The estimated temperature distributions and contents of C₂ radicals did not depend on the anode characteristics.     

Magnetic-field-induced diameter-selective synthesis of single-walled carbon nanotubes

We report a facile and scalable approach to synthesize single-walled carbon nanotubes (SWNTs) with selected diameter distribution by applying a magnetic field perpendicular to the electric field in the arc plasma region. It is found that this magnetic field-induced diameter-selectivity strategy enables the control of the SWNTs with different diameter distributions in different regions, and the diameter-selective efficiency could be enhanced by modifying the direction of magnetic field. Our results indicate that the motions of the catalysts with different particle sizes, positive carbon ions and electrons are significantly influenced by the magnetic field and electromagnetic force, resulting in the different nucleation and growth processes of SWNTs due to the collective interactions between the magnetic field and arc plasma. This approach would enable a viable route towards the synthesis of SWNTs with desired diameter through the tuning of arc parameters in the arc discharge process.     

High-efficient synthesis of double-walled carbon nanotubes by arc discharge method using chloride as a promoter

With trace halide as a promoter in an iron sulfide catalyst, relatively perfect structural integrity double-walled carbon nanotubes (DWNTs) have been synthesized in large quantity and high yield by arc discharge method. Scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used for structural characterization and yield determination. The results revealed that halide was a crucial factor for selectively synthesizing high yield DWNTs. The detailed experimental parameters were systematically investigated. The possible role of halide in growth of DWNTs was discussed as well.     

Direct synthesis of self-aligned single-walled carbon nanotubes on paper

A technique of micro chemical vapor deposition (μCVD) is reported for the direct synthesis of self-aligned SWCNTs on various substrates including plastics and paper. With the guidance of micro flow channels, self-aligned SWCNTs up to hundreds of microns in length have been collected. Both Raman spectral and transmission electron microscopy have validated the high quality of these SWCNTs. In conclusion, μCVD could be a versatile method to synthesize pristine SWCNTs for various applications.     

Trial for diameter-selective synthesis of single-walled carbon nanotubes

The diameter-controlled synthesis of single-walled carbon nanotubes (SWNTs) has been examined experimentally. The catalysis of the Rh and Pd atoms has been confirmed by blending with Co atoms at 950 °C in a furnace, although the Rh/Pd catalyst has not been recorded to act efficiently at this temperature before. Raman spectra indicate that the Rh/Co and Pd/Co catalysts can synthesize narrow-diameter SWNTs more selectively than the Fe/Co and Ni/Co catalysts, which can only synthesize SWNTs with slightly larger diameters. These results suggest that by changing the combination of catalysts, the persistent problem of controlling the diameter of SWNTs can be solved without any expensive setup or complicated techniques.     

Lattice-directed growth of single-walled carbon nanotubes with controlled geometries on surface

How to control the orientations of single-walled carbon nanotubes (SWCNTs) on surface is the key point to controlling their geometries. In this work, we chose quartz (0 0 1), MgO (0 0 1) and layered mica with 3-, 4- and 6-fold symmetry, respectively as substrates to grow SWCNTs using gas-flow and lattice-directed modes. The produced SWCNTs were aligned along the symmetrical directions and displayed the homologous angles of 120°, 90° and 60° during growth on quartz (0 0 1), MgO (0 0 1) and mica surfaces, respectively. The obtained SWCNTs with controlled geometries would have wide applications in nanoelectronic devices in the future.     

Aligning carbon nanotubes,synthesized using the arc discharge technique,during and after synthesis

Alignment of multi-walled carbon nanotubes (MWCNTs) is demonstrated using physical forces both during synthesis, as well as post-synthesis through the arc discharge technique. The arc discharge process results in relatively straight and defect free MWCNTs compared to other techniques such as chemical vapor deposition. A scraper enables alignment of these straight MWCNTs during synthesis. Additional tailoring of the direction of alignment is seen to be possible even at room temperature, using physical forces in the form of scratch marks on the soot. Using a hand operated roller, on the surface of the soot, also results in the alignment of MWCNTs along the rolling direction. Alignment of MWCNTs is confirmed using scanning electron microscopy and it results in distinct changes in X-ray diffraction and energy dispersive spectroscopy data. These results are significant from the perspective of obtaining aligned MWCNTs, in large quantities, in a relatively inexpensive manner.