Synthesis of fullerenes and fullerenic nanostructures in a low-pressure benzene/oxygen diffusion flame

Abstract

Samples of condensable material from laminar low-pressure benzene/argon/oxygen diffusion flames were collected and analyzed by high-performance liquid chromatography to determine the yields of fullerenes and by high-resolution transmission electron microscopy (HRTEM) to characterize the fullerenic material (i.e., curved-layer nanostructures) on and within the soot particles. The highest concentration of fullerenes was always detected just above the visible stoichiometric surface of a flame. The percentage of fullerenes in the condensable material increases with decreasing pressure. The overall highest amount of fullerenes was found for a surprisingly high dilution of fuel with argon. A comparison of the flames with the same cold gas velocity of fuel and oxygen showed a strong dependence of fullerene content on flame length. A shorter flame, resulting from higher dilution or lower pressure, favors the formation of fullerenes rather than soot, and the amount of soot and precursors of both soot and fullerenes is less at lower pressure and higher dilution. This behavior indicates a stronger correlation of fullerene consumption to the total amount of soot than of fullerene formation to precursor concentration. The maximum flame temperature seems to be of minor importance in fullerene formation. The HRTEM analysis of the soot showed an increase of the curvature of the carbon layers, and hence increased fullerenic character, with increasing distance from the burner up to the point of maximum fullerene concentration. After this maximum, where soot and fullerenes are consumed by oxidation, the curvature decreases. In addition to the soot, the samples included fullerenic nanostructures such as tubes and spheroids including highly ordered multilayered or onionlike structures. The soot itself shows highly ordered regions that appear to have been cells of ongoing fullerenic nanostructure formation.

Combustion synthesis of fullerenes and fullerenic nanostructures

“…These two parameters are both correlated to chamber pressure, argon dilution, and cold gas fuel velocity. Typical fullerene yields of 0.5% (by mass) of total carbon fed were observed but can possibly be higher [90,91].…”

“…The premixed study also found that nanostructures require a much longer residence time to form than do fullerenes [37]. The diffusion flame analysis showed that nanostructures are formed higher than the point of maximum fullerene production where soot and fullerenes are being consumed by oxidation and the flame is the hottest [90,91]. Additionally, structures similar to those observed in fullerene-forming flames have also been found in commercially-produced carbon black [100,101].…”

“…The formation of fullerenic nanostructures in combustion was first identified in 1994 [38] and has since been studied in both premixed and diffusion laminar benzene/oxygen/argon flames [36,37,90,91]. These studies all used high resolution transmission electron microscopy (HRTEM) images to perform a qualitative analysis of the evolution of nanostructures in flames while Grieco [37,99] also performed a quantitative analysis.…”

“…It was observed that nanostructures are formed in fullerene-forming flames and that the amount of closed-shell structures and fullerenic material increases with residence time, or distance from the burner. These HRTEM images show that soot becomes more ordered farther from the burner [37,90,91,99]. The premixed study also found that nanostructures require a much longer residence time to form than do fullerenes [37].…”

Synthesis of New Carbon Compounds: N-doped Fullerene (C50N10)O3H10 and “Pyridine” Nanocarbon

“…27.1 ) and technological. Note that direct synthesis of fullerenes from benzene is carried out in fl ame jet at benzene combustion at defi cit of oxygen and at low pressure [ 7,8 ] .…”