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We report a novel system for sorting single wall carbon nanotubes (SWCNTs) by length via cross-flow filtration with three membrane filters of different pore sizes, 1.0, 0.45, and 0.2 μm. SWCNTs dispersed in water with the help of polymer type detergents, such as sodium carboxymethylcellulose (CMC) and polyoxyethylene stearyl ether (Brij 700), were successfully fractionated into four samples, and the atomic force microscopy (AFM) observation of those samples confirmed that their length distribution peaks are within the expected ranges from pore sizes of used filters. However, the result of the similar filtration process using a non-polymer detergent, sodium dodecylbenzenesulfonate (SDBS), showed no pronounced correlation between the length distribution of SWCNTs and the pore size. The observed difference in the sorting phenomena caused by the detergent type suggests that the permeation property depends on the complex structure resulting from the dispersed SWCNTs and detergent molecules.
A thermal treatment was applied with CO2 and air for the development of a porous structure. Adsorption isotherms of nitrogen were measured on well-characterized Ni-C nanoparticles. The thermal treatment with CO2 increased the total surface area and micropore volume. In addition, the thermal treatment with CO2 increased the hydrogen adsorption.
Double-wall carbon nanotubes (DWCNTs) and single-wall carbon nanotubes (SWCNTs) have been synthesized by the DC abnormal glow discharge plasma CVD method using methane and hydrogen gas on a Si substrate coated with catalyst. Fe(NO3)2 and Mo(CH3COCHCOCH3)2O2 with Al2O3 support were used as catalysts. The growth temperatures were 1000 − 1400°C and the gas pressures were 9kPa - 13kPa. DC plasma was generated between an array of four W cathodes and a Cu disk anode, and the applied power was 4000–10000W (2.5–4.0A per cathode, 400–800V). Samples were characterized by high-resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy using 514.5 nm Ar ion laser excitation. The HRTEM images showed that many carbon nanotubes had a concentric cylindrical graphene layer structure (DWCNTs). We measured the diameters of the carbon nanotubes (CNTs) from HRTEM images. The outer diameter of the DWNT was 1.52–1.64nm and the inner diameter of the DWNT was 0.73–0.81nm.
Aligned multi-wall carbon nanotubes (MWNTs) were successfully grown on a Si substrate based on a thermal chemical vapor deposition (CVD) method. We employed Co metal nanoparticles as the catalyst for nanotube growth, which were prepared by a reverse micelle method. The reverse micelle method provides nanoparticles covered with surfactants so that they are dispersed in organic solvent and, thus highly processible. The present MWNT arrays are promising for application in field emission displays, because of much lower nanotube density compared with the previously reported arrays.
Aligned carbon nanofibers and hollow carbon nanofibers were grown by MW ECR-CVD method using methane and argon mixture gas at the temperature of 550••. Carbon nanofibers and hollow carbon nanofibers were deposited perpendicularly on Si substrate and on Si substrate coated with Ni catalyst, respectively. Raman spectra of aligned carbon nanofibers and hollow carbon nanofibers showed new bands of 1340 and 1612 cm-1 of the first-order Raman scattering and 2660, 2940 and 3220 cm-1 of the second-order Raman scattering. The second-order Raman scattering bands were assigned to two overtone and one combination bands on the basis of a similar assignment of micro crystal graphite. Combination bands are intense unusually. Field emitter characteristics of the well-aligned carbon nanofibers and hollow carbon nanofiberswere investigated and the current densities were 7.25 mA/cm2 and 0.69 mA/cm2at 12.5 V/μm, respectively.
Fine molecular straw, carbon nanotube (NT) is aligned to form a bundle. The purified NTs are mixed with a plastic polymer (polypropylene: PP) and extruded from a small die with a diameter of 2 mm kept at 200°C. The threads of NT/PP blend are characterized by small angle X-ray diffractometry and transmission electron microscope to confirm the existence of nanobundle of NTs, which orient along the spinning direction.
Purification process to obtain nanotubes out of the cathode product mostly including fragments of graphitic sheet and/or amorphous carbon has been established. Structures and electronic properties of carbon nanotubes were studied. By the Raman scattering measurement, only one peak at 1581 cm−1 akin to that of graphite was found out. It was confirmed by STM observation of purified nanotubes. Purified nanotubes was semiconductor or semimetal.
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