Publications (5)0 Total impact
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Article: Fullerenes, PAH, Carbon Nanostructures, and Soot in Low Pressure Diffusion Flames
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ABSTRACT: The formation of fullerenes C60 and C7O is known to occur in premixed laminar benzene/oxygen/argon flames operated at reduced pressures. High resolution transmission electron microscopy (HRTEM) images of material collected from these flames has identified a variety of multishelled nanotubes and fullerene 'onions' as well as some trigonous structures. These fullerenes and nanostructures resemble the material that results from commercial fullerene production systems using graphite vaporization. As a result, combustion is an interesting method for fullerenes synthesis. If commercial scale operation is to be considered, the use of diffusion flames might be safer and less cumbersome than premixed flames. However, it is not known whether diffusion flames produce the types and yields of fullerenes obtained from premixed benzene/oxygen flames. Therefore, the formation of fullerenes and carbon nanostructures, as well as polycyclic aromatic hydrocarbons (PAH) and soot, in acetylene and benzene diffusion flames is being studied using high performance liquid chromatography (HPLC) and high resolution transmission electron microscopy (HRTEM).06/1997; -
Article: Generation of Higher Fullerenes in Flames
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ABSTRACT: The presence of fullerenes up to C116 was observed in condensable material from a benzene/oxygen flame. The flame material was Soxhlet-extracted with toluene for 363 h, fractionationed by means of a silica-based semipreparative HPLC column, and analyzed by HPLC coupled to a mass spectrometer via a heated nebulizer interface using a 2-(1-pyrenyl)ethylsilica stationary phase. UV−vis spectra were measured for C60, C60O, C60·CH4, C70, C70O, C76, C78, C80, C84, a C84 adduct, C86, C88, C90, C92, C94, C96, C98, C100, C102, and C108. Isomers could be discerned for C78, C90, and C94. A calibration using external standards was performed for C60, C70, C76, C78, and C84. For all other species the relative abundances were estimated based on HPLC peak integration results. Electric arc soot was extracted under similar conditions and the quantification of fullerenes compared to the data obtained with flame-generated condensable material. Except for C60 and C76, the abundances were significantly higher in the case of flame-generated condensable material. Also, striking differences between the two fullerene production methods are seen in the relative abundances of C78 isomers. Considering the present results and the ease with which the experimental setup could be scaled up, flame-generated condensable material represents an excellent starting material for the preparative isolation of higher fullerenes.02/1997; -
Article: Preparative-Scale Liquid Chromatography and Characterization of Large Fullerenes Generated in Low-Pressure Benzene Flames
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ABSTRACT: Soot generated in a premixed benzene/oxygen/argon low-pressure flame was extracted sequentially with dichloromethane, toluene, CS2 and 1,2-dichlorobenzene. Quantifications by HPLC were performed for C60, C70, C76, C78, and C84 by means of external standards using a monomeric octadecylsilica (ODS) bonded stationary phase and acetonitrile/toluene (55:45) as a mobile phase. Toluene was found to be the most suitable solvent for all the cases studied here. After the partial removal of smaller fullerenes with preparative HPLC, the presence of fullerenes up to C104 was shown by means of HPLC−APCI−MS using a heated nebulizer interface. The macroscopic isolation of C86, C90, C92, C94, and C96 was performed using a two-step HPLC separation with a 2-(1-pyrenyl)ethylsilica stationary phase and toluene as eluent preceded by the partial removal of C60 and C70 with a poly(divinylbenzene) HPLC column. UV−vis spectra were measured, and the presence of a C90 adduct could be discerned. Based on the results of this work, the estimated ratios C60:C70:C76:C78:C84 in the investigated flame-generated soot are 100:100:4:3:6 while the corresponding values for C84:C86:C90:C92:C94:C96 are 100:0.5:5:0.5:1.25:1.12/1996; -
Article: Fullerenic carbon in combustion-generated soot
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ABSTRACT: Soot samples collected as bulk solids and by thermophoretic sampling at different residence times in a fullerene-forming premixed benzene/oxygen flat flame (C/O=0.96, P=5.34 kPa, 10% argon, v=25 cm/s) were analyzed by high resolution electron microscopy. The samples contained soot particles that were composed to some extent of amorphous and fullerenic carbon (e.g., curved layers and fullerene-molecule-sized closed-shell structures). Qualitative and quantitative analyses of residence time-resolved samples showed that the length of curved layers increases and their radius of curvature decreases with increasing residence time in the flame. The number of closed-shell structures in the soot as well as the concentration of fullerene molecules in the gas phase increase with increasing residence time, consistent with fullerenes concentration increasing with residence time and with the consumption of fullerenes by reaction with soot. The data suggest that the formation of amorphous and fullerenic carbon occurs in milliseconds, with the fullerenic carbon becoming more curved as a soot particle traverses the length of the flame. Conversely, the formation of highly ordered carbon nanostructures, such as tubes and onions, appears to require much longer residence times, perhaps seconds or minutes depending on the temperature, in the flame environment.Carbon. -
Article: Fullerenes and PAH in low-pressure premixed benzene/oxygen flames
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ABSTRACT: The formation of fullerenes is though to be a molecular weight growth process similar to the formation of polycyclic aromatic hydrocarbon (PAH) and soot in flames, although little is known about the specific mechanisms involved. The goal of this study is to investigate possible fullerences formation pathways. This work measures for the First time concentration profiles of fullerences C60, C70, C76, C78, and C84, PAHs (up to 300 amu), and unidentified PAHs in the mass range between PAHs and soot in a heavily fullerene-forming premixed benzene/oxygen flame operated at the following conditions: fuel equivalence ratio, 2.4 (atomic C/O ratio, 0.96): cold gas velocity, 25 cm/s: pressure, 5.33 kPa: and fraction of argon in fuel mixture, 10 mol%. Two regions of fullerenes formation are identified in this flame. The First formation region occurs early in the flame simultaneously with PAH consumption. The rate of PAH consumption is more than large enough to account for the obsered rate of fullerenes formation, so this formation region may involve reactions of PAH. The Second region, which accounts for most of the fullerenes mass produced in the flame, occurs later in the flame and is more consistent with stepwise acetylene addtion to fullerene precursors. In both regions, fullerenes consumption that may involve reactions between fullerenes and soot is observed. In addition, measurements indicate that the different PAHs grow roughly simultaneously, reach a peak concentration, and decay together in a consumption process that occurs at the same time as a rapid rise in soot mass concentration early in the flame. This behavior is consistent with the major soot formation being from PAH and occurring along with the minor fullerenes formation in this flame.Symposium (International) on Combustion.
