Carbon HiPCO process

Single-wall carbon nanotubes (SWNTs) can be prepared by laser-vaporization of a graphite source. A newer process uses carbon monoxide as the source of the carbon and is called the HiPco process. The catalyst is generated in situ from iron carbonyl. The SWNTs from the HiPco process are characterized by a smaller diameter and exhibit greater reactivity with organic reagents. 

Ceo = Fullerene SWNTs = Single-walled carbon nanotubes MWNTs = Multiwalled carbon nanotubes DWNTs = Double-walled carbon nanotubes CNTs = carbon nanotubes TEM = Transmission electron microscopy HRTEM = High-resolution transmission electron microscopy SEM = Scanning electron microscopy AFM = Atomic force microscopy Ch = Chiral vector CVD = Chemical vapor deposition HiPco process = High-pressure disproportionation of CO RBM = Radical breathing vibration modes DOS = Electronic density of states. 

The SWNTs produced from the HiPco process exhibit a smaller average diameter and, hence, a mild wet-air oxidation is done to avoid damages to the tubes. The oxidation of SWNTs in the presence of wet-air is found to selectively oxidize the nontubular carbon impurities without affecting the small diameter tubes. In this procedure, the oxidation is done in the presence of air saturated with water vapor at 225 °C for 24 h. This is followed by sonication for 15 min or... 

Carbon nanotubes and nested fullerenes were also prepared by reductive carbonization of CO2 with magnesium metal. Motiei et al. [104] reported on the production of nanotubes in ca. 0% yield and nested fullerenes in ca. 12% yield at 1000°C by the reaction of dry ice and magnesium. The reductive carbonization of CO2 is reminiscent of the HiPco process [105, 106], based on disproportionation of carbon monoxide (the Boudouard reaction) ... 

Bronikowski, M.J. Willis, P.A. Colbert, D.T. Smith, K.A. Smalley, R.E. Gas-phase production of carbon single walled nanotubes from carbon monooxide via the HIPCO process a parametric study. J. Vac. Sci. Technol. A 2001, 19, 1800-1805. 

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. 

Nikolaev P. Gas-phase production of single-walled carbon nanotubes from carbon monoxide a review of the HiPco process. J Nanosci Nanotechnol 2004 4 307-16. 

CNTs can be made by means of arc-discharge, laser ablation, high pressure carbon monoxide decomposition (HiPCO), and chemical vapor decomposition (CVD) processes. The HiPCO process delivers high quality SWCNTs but the upscaling is difficult. Arc-discharge, laser ablation and CVD systems are currently used to produce SWCNTs as well as MWCNTs in laboratory scales. However, until now only CVD processes have been upscaled successfully to produce MWCNTs in commercially relevant amounts. For this purpose the synthesis is usually performed in fluidized beds [10-12]. Currently (2011), industrial grades of MWCNTs can be purchased for less than 130 USD/kg. 

While both SWNT and MWNT existed in small quantities from the first wood fires at the dawn of Earth s history, their discovery and methods of preparation are only recent, as described above. Briefly, some synthetic methods include nickel catalyzed pyrolysis of methane at bOO C (64) for MWNT, and the so-called HiPCO (high pressure carbon monoxide) process for SWNT.This latter involves thermal decomposition of iron pentacarbonyl in a flow of CO at 800-1200°C (65). 

Chiang, I.W. Brinson, B.E. Hnang, A.Y. Willis, PA. Bronikowski, M.J. Margrave, J.L. Smalley, R.E. Hauge, R.H. Pnrification and characterization of single-wall carbon nanotubes (SWNTs) obtained from the gas-phase decomposition of CO (HiPco process). J. Phys. Chem. B 2001, 105, 8297-8301. 

Dateo CE, Gokcen T, Meyyappan M (2002) Modeling of the HiPco process for carbon nanotube production. 1. Chemical kinetics. J Nanosci Nanotechnol 2 523-34... 

A number of methods have been developed to produce single- and multiple-wall carbon nanotubes. The most prominent are laser ablation, arc discharge, and catalytic growth (vapor deposition (CVD) and high pressure carbon monoxide (HipCO) process). 

Among the processes developed for mass production of carbon nanotubes (SWNTs), we need to emphasize the HiPCO process, optimized for relatively high yield and production rate by scientists at Rice University [16]. The quantity of the product is still behind the amount predicted [17] and its price has not dropped as was expected. Nowadays, this is the most widely available and used S WNT product on the market produced by the CVD technique. 

Hipco processed single wall CNTs are obtained from Carbon Nanotechnologies Inc, with a diameter of -l-2nm and a length of -1 pm. CNFs (PR-19) are obtained from Applied Science Inc their diameter is in the range of 100-200 nm and they are 30-100 pm long. CNTs and CNFs are... 

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