HiPco method

SWNTs were prepared by high-pressure CO decomposition over the Fe catalyst (HiPco method [13]) at Carbon Nanotechnologies Inc. Houston, Texas, USA. The raw sample was purified by controlled thermal oxidation in air followed by sonication in HC1. The purity estimated by elemental analysis, TGA, XRD and TEM gave in result 99% content of SWNT in the samples studied [4],... 

SWCNT bundles containing nanotubes with different diameters are easy to obtain experimentally, but such samples may lead to overlapping RBM modes and complex Raman spectra that are difficult to interpret. In contrast, SWCNTs synthesized via the HiPCO method are favored for spectroelectrochemical studies due to their small diameters, which lead to well-separated RBM peaks, thereby simplifying nanotube chirality assignments significantly [58, 72]. 

The typical voltammetric curve for a solution of SWNTs in organic solvents displays a continuum of diffusion-controlled current, with onset, in both the negative and the positive potential region, that depends on the nanotube average diameter and ultimately on the NT preparation technique. In fact, SWNTs prepared according to the arc-discharge method display an anticipated onset with respect to HiPco ones... 

Derivatized products such as alkyl-, aryl-, alkoxyl- and amino-nanotubes and cross-linked nanotubes are obtained (Scheme 1.2). F-SWCNTs prepared by the HiPCO process exhibited a higher degree of alkylation using alkyllithium reagents than fluorinated SWCNTs from the laser-oven method. Dealkylation occurred at 500 °C. 1-Butene and n-butane were formed during the thermolysis... 

Basic studies on diazonium-CNT chemistry led to two very efficient techniques for SWCNT derivatization solvent-free functionalization [176] and functionalization of individual (unbundled) nanotubes [175], With the solvent-free functionalization (Scheme 1.26), heavily functionalized and soluble material is obtained and the nanotubes disperse in polymer more efficiently than pristine SWCNTs [176], With the second method, aryldiazonium salts react efficiently with the individual (unbundled) HiPCO produced and sodium dodecyl sulfate (SDS)-coated SWCNTs in water. The resulting functionalized tubes (one addend in nine tube carbons) remained unbundled throughout their entire lengths and were incapable of reroping. [175],... 

The polyaniline was prepared by emulsion polymerization following the procedure outlined in US patent 5,863,465 with DNNSAused as a dopant [22]. Carbon Nanotubes (CNI) manufactured the nanotubes used in the work either by a high-pressure fabrication method (Hipco SWNT) or via laser ablation (Laser SWNT). We found that excellent dispersions of the nanotubes in PANI could be produced by two different procedures. The nanotubes could either be directly sonicated into the PANI solution or first sonicated into xylene and that dispersion afterwards sonicated into the DNNSA-PANI solution. 

It would be in order to compare the present work with the other procedures reported in the literature. All of the methods make use of acid washing to remove the metal particles where present. In the procedures involving air oxidation, SWNTs are subjected to heat treatment in the 350—500 C range depending on the method of synthesis. The present method however employs hydrogen treatment around 1000 °C for all SWNTs and MWNTs, except for HiPCO SWNTs which require a lower temperature. Whereas in air oxidation the amorphous carbon is converted into CO2, it is converted lo CH4 on hydrogen treatment. 

Figure 6.60. Illustration of two methods used for the commercial production of SWNTs. Shown are (a) the CoMoCat fluidized bed method using CO as the precursor and a Co/Mo bimetallic catalyst,[84] and (b) the HiPco floating catalyst process using the thermal decomposition of iron pentacarbonyl at pressures of 1-10 atm.[85]...

The preparation of single-walled nanotubes succeeds more easily by the so-called HiPCo-process that was published for the first time in 1998. The name is deduced from high-pressure carbon monoxide and signifies a crucial aspect of the method Here the carbon source is not a hydrocarbon, but carbon monoxide that does not suffer pyrolysis at the relevant temperatures. The formation of carbon material is based on the Boudouard equilibrium (3.9) ... 

The feasibility of continuous operation counts among the major advantages of the HiPCo-process over most alternative methods. The catalytic decomposition of carbon monoxide can thus be considered as a potential way of scaling up SWNT-production from a few grams to kilograms or even tons. 

The thermal decomposition of organic compounds can also be employed to generate small carbon clusters or atoms. The borderline with chemical vapor deposition (CVD) as presented in the next section is not really fix. In both cases, the method is based on the thermal decomposition of organic precursors. Processes both with and without catalyst have been reported. Contrary to the chemical vapor deposition, however, the catalyst (if applied) is not coated onto a substrate, but the substance or a precursor is added directly to the starting material ( floating catalyst ). The resulting mixture is then introduced into the reactor either in solid or in liquid state by a gas stream. From this point of view the HiPCo-process could also be considered a pyrolytic preparation of SWNT, but due to its importance it is usually regarded as autonomous method. 

A well-known floating catalyst method developed at Rice Uruversity is the so-called HiPCO (high-pressure CO) method. In this case, the growth of SWNTs is realized by disproportionation of CO catalyzed by Fe clusters generated in situ by decomposition of Fe(CO)s in continuously flowing CO at high pressure and elevated temperature (79). A mixture of the Fe precursor and CO is injected into the reactor... 

Other than the ultracentrifugation, the ssDNA-dispersed HiPCO SWNTs have been separated by ion exchange chromatography. However, the method was reported to be ineffective in the separation of metallic SWNTs. In another method that exploited the dispersion of SWNTs by DNA or conceptually similar surfactant species, agarose gels (originally developed for DNA separation) were used to separate metallic and semiconducting SWNTs. 

PEDOT with and without the dopant PSS has been the most commonly used conductive polymer for SWNT composites. De et al prepared composite films by vacuum filtration from aqueous dispersions with PEDOT PSS as the matrix and both arc and HiPCO SWNTs as the filler. The optimal performance was observed for a 80 nm thick film containing 60 wt /o arc SWNTs, with a sheet resistance of 80 Q sq at 75 /o transmittance. Electromechanical testing showed these films to be stable under flexing and cycling. Later, a modified PEDOT copolymer with enhanced solubility, perchlorate-doped poly(3,4-ethylenedioxythiophene)-Z /ock-poly(ethyleneox-ide) (P-PEDOT-b-PEO) was used to disperse SWNTs and then to fabricate conductive nanocomposites via vacuum filtration method.The sheet resistance of the composite film was approximately 600 Q sq with 80 /o transmittance. 

High-pressure CO conversion (HiPCO) is a new method for the bulk production of SWCNTs under high-pressure, high-temperature flowing CO on catalytic clusters of Fe. Fe catalyst is formed in situ by thermal decomposition of iron pentacarbonyl (i.e., Fe(CO)j) which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the FefCO) decomposes into atoms that condense into larger clusters. SWCNTs nucleate and grow on these particles in the gas phase via CO disproportionation CO-i-CO (catalyzed) CO -i-C(SWCNT) [14,15],... 

The approaches are principally based on the subtle difference between various properties such as density, chemical reactivity, dielectric constant, etc., of M- and S-CNTs. Moreover, the growth parameters also affect the fractional amounts of M- and S-CNTs in a mixture. Li et al. have observed that CNTs synthesized by PECVD at 600°C are preferably S-CNTs (90%), while those produced by HiPco and Laser ablation consist of 61 and 70% M-CNTs, respectively [187]. The first successful approach for M/S CNT separation is alternating current dielectrophoresis [188]. It uses the different dielectric constants of M- and S-CNTs. In an electric field gradient, metallic CNTs are attracted towards the electrode, while the semiconducting CNTs remain in the solution. Song et al. have reported a separation method based on the observation that metallic CNTs are burned faster compared to... 

SWNT were produced by laser ablation and subsequently purified via acid treatment. Single-wall nanotubes were manufactured by laser vaporization of carbon rods doped with Co, Ni and FeS in an atmosphere of Ar H2. Standard SWNT products made by HiPCO and other methods contain significant amount of sooth, graphite flakes, and remnants of the catalyst, which need to be removed prior to the assembly. The quality of the dispersion directly affects the mechanical performance of the resulting composite. 

Five methods of synthesis of CNTs are (1) arc discharge, (2) laser ablation, (3) CVD, (4) the HIPCO process, and (5) surface-mediated growth of vertically aligned tubes. CNTs can have different morphologies such as SWNT, DWNT, MWNT, nanoribbon, nanosheet, nanopeapods, linear and branched CNTs, conically overlapping bamboo-like Y-shaped tubules, nanopores, nanovoids, nanowire, and nanofiber. 

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