Fullerene Soot Research Articles

Using High Performance Liquid Chromatography to Determine the C60:C70 Ratio in Fullerene Soot: An Undergraduate Chemistry Lab

The discovery of a technique for fullerene production in macroscopic quantities has lead to an explosion of research, particularly in chemistry, over the past few years. As more and more interest is generated in this field, an increasing number of chambers are being constructed for classroom, laboratory, and commercial use to meet subsequent demand. The carbon soot produced in these chambers is made up primarily of C60 and C70, which are then extracted usually by dissolving and filtering. However, since this extraction is a mixture, it is of interest to determine the ratio of one fullerene-type to the other. Such a determination can be carried out by first separating the C60 and C70 on an analytical high performance liquid chromatography (HPLC) column and then measuring the relative absorptions in the ultra-violet (UV). The importance of this result cannot be exaggerated. Commercialy, specification of the ratio must be made before sale. In the laboratory this result can aid in determining what operating parameters are required to favor the production of one fullerene over the other. As for the classroom, besides the edifying value of working with new materials, the student can gain insight into production and analysis. The experiment described here demonstrates a relatively simple separation of C60 and C70 using a 1:1 acetonitrile/toluene mobile phase through a silica-bonded C18 column. The separation is detected by UV absorption analysis which allows for determining the ratio of the two fullerenes based on results also given.

Free-Radical Copolymerization of Fullerenes with Styrene

Various methods to chemically modify the fullerenes have been reported in the last few years since the production of large-scale amounts of fullerene soot that contains primarily C{sub 60}, a lesser amount of C{sub 70}, and traces of higher fullerenes. Fortunately, these components can be separated from each other by standard chromatographic methods, permitting convenient experimentation on relatively pure components. The authors have found that C{sub 60} and C{sub 70} copolymerize with styrene in a standard free-radical polymerization, either in the bulk or codissolved in an aromatic solvent. The resulting polymers are soluble in common solvents that dissolve polystyrene and possess a dark brown color. The absorption spectrum of the copolymer is strongly modified from that of the parent fullerene, and the fluorescence is blue-shifted and much stronger. The present paper describes a very simple method for direct incorporation of C{sub 60} or C{sub 70} into polystyrene by direct free-radical copolymerization under routine conditions. While a great deal remains to be done to characterize fullerenes as comonomers in free-radical polymerization, this method is so direct and simple that it may be of interest to a wide range of researchers working in the area of fullerene chemistry. The authors note amore » report by Gong et al. in which a polymerization of styrene and {alpha}-methylstyrene was carried out in the presence of C{sub 60} using benzoyl peroxide as an initiator. These authors explicitly state that the C{sub 60} retains its normal absorption spectrum and is dispersed within the resulting solid polymer matrix. No other characterization is presented to demonstrate if chemical attachment of the C{sub 60} to the polymer occurred.« less

Characterization of Fullerene Materials and Their Oxidative Stability Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Since the generation and IR spectral detection of C60 in laboratory-produced carbon soot a few years ago, the constituents of the raw fullerene soot have been intensely investigated. The soot, which is prepared by vaporization of graphite with resistive heating under an inert gas, typically contains <20% fullerene by mass. With the recent interest in the reactivity of both the raw soot and purified fullerene products, new techniques are needed which can quickly identify changes in composition of these materials. Diffuse reflectance infrared Fourier transform specsoot, evident at 2335 cm-1, has been reported in other studies.

Combustion Energy of Fullerene Soot

The standard energy of combustion of fullerene soot generated in arc discharge was determined to be [minus]36.0 [+-] 0.5 kJ g[sup [minus]1] by oxygen-bomb combustion calorimetry. The value was much closer to those of C[sub 60] and C[sub 70] than that of graphite. This result provides an energetic reason for the remarkable yield of fullerenes in arc discharge and supports the mechanism of fullerene formation, where fullerenes are the lowest energy products. Fullerene onion formation is interpreted in terms of energy relaxation of the fullerene soot. 20 refs., 1 tab.

Tandem mass spectrometry studies of oxygen interactions with fullerenes and metallofullerenes

The reaction products of oxygen with fullerenes and metallofullerenes have been characterized by thermal desorption mass spectrometry and low energy collisional activation on a triple quadrupole mass spectrometer. C 60O, which is present in fullerene soot, fragments primarily with the loss of O, although CO loss can be observed at higher collision energies. Fragmentation of C 60O − n adducts, formed by reactions with oxygen in the chemical ionization source or by reactive collisions with O 2 in the collision cell, is characterized by CO loss at relatively low energies, followed by CO 2 loss and loss of 2CO. The results indicate that O 2 must interact as the intact diatomic species in order to initiated fragmentation of the fullerene cage, consistent with other reports in the literature. O 3 induced fragmentation occurs in a similar fashion, and the results may explain the first step in the recently reported formation of higher, odd-numbered fullerenes (e.g. C 119) in ozonolysis. Studies with metallofullerenes indicate that the extractable metallofullerenes (LaC 82, La 2C 80) are less reactive toward oxygen than their less extractable counterparts (LaC 60, LaC 70). The stability of LaC 82 and La 2C 80 was demonstrated by the formation of He uptake products (e.g. He@LaC 82) in high energy collisions with He in a hybrid (BEqQ) mass spectrometer.

Oxidative Stability of Fullerenes

Mixtures of fullerenes are more susceptible to oxidation than the pure phases of fullerenes. For example, a mixture of 90 wt % C[sub 60]/10 wt % C[sub 70] reacts with air at 300[degree]C for 24 h to yield a product containing 95% of the initial mass but which manifests an atomic ratio of carbon to oxygen of 2.3; in contrast, there is [le]1 wt % loss and no detectible oxygen content in 99.5% C[sub 60] under the same conditions. Furthermore, toluene-extracted fullerene soot prepared via the Kratschmer synthesis is found to be reactive to oxygen at ambient and higher temperatures. Room temperature handling of a toluene-extracted soot prepared from graphite leads to a steady-state oxygen content of about 3.8 wt % and a C/O atomic ratio of 33. Moreover, the reaction of extracted fullerene soot with air for 24 h at 300[degree]C yields a product of 60% of the initial mass of soot which contains 16.70 wt % oxygen and which shows a strong photoacoustically detected carbonyl infrared band at 1771 cm[sup [minus]1] and a C[sub sp2]-O band at 1249 cm[sup [minus]1]. With respect to changes in structure on heating in air, there is evidence for buckminsterfullerene (C[sub 60]) enhancingmore » the growth of crystallite size measured along the (002), (100), and (110) directions of the soot relative to the case in which there is no buckminsterfullerene in the soot. 26 refs., 1 tab.« less

Purification of C60 and C70 by selective complexation with calixarenes

MOLECULAR complexation of fullerenes in host–guest complexes has the potential to afford efficient large-scale purification of fullerenes1. This method would avoid the losses inherent in the chromatographic techniques currently in use, which arise from irreversible absorption on the stationary phase2. Several host-guest interactions have been reported for C60, including the formation of complexes with 1,4-hydroquinone3,4, azacrown compounds5, certain water-soluble macrocycles such as γ-cyclodextrin6–8, and complexation between C60 and an iridium phosphine in which pendant groups attached to a phosphorus atom form a cradle for an adjacent C60 molecule9. Other relevant studies are the inclusion of C60 into a microporous aluminophosphate10 and the formation of a charge-transfer complex between C60 and a thiafulvalene11. Here we show that both C60 and C70 will form discrete complexes with calixarenes, bowl-shaped macrocycles with hydrophobic cavities. Complexation of p-Bu'-calix[8]arene with a mixture of the toluene extract of 'crude' fullerene soot, followed by a series of recrystallizations, affords >99.5% pure C6. Our approach could lead to a substantial reduction in the cost of purifying C60 and C70.

Fullerene-Based Catalysts for Methane Activation

ABSTRACTWe investigated fullerene based catalysts for the conversion of methane into higher hydrocarbons. Fullerene soot, CO2 activated soot, and extracted soot as well as a Norit-A carbon were examined as catalysts for methane activation. The soot was found to easily activate the C-H bond of methane, allowing methane conversion at lower temperatures (lower by 250°C) than found under purely thermal conditions. Furthermore, soot catalysis appears to produce a minimal amount of aromatic hydrocarbons. Extracted soot was found to have a lower selectivity for C2 hydrocarbons than the non-extracted soot, and the CO2 activation of the soot did not appear to dramatically alter the catalytic activity.

Isotope fractionation in the synthesis of fullerenes

The synthesis of fullerenes by the direct current (DC) carbon arc evaporation method produces a number of different carbon materials. This investigation has involved the structural characterisation of the materials and the study of their isotopic composition. The cathode deposit was a highly ordered graphite with the basal planes oriented in the axial direction of the graphite rod. Raman microprobe spectroscopy, X-ray powder diffraction, and temperature programmed combustion measurements also showed that the material was heterogeneous. The structural characterisation results were consistent with the deposit being formed at progressively lower heat-treatment temperatures with increasing deposition. The fullerene soot was a very heterogeneous material with a large surface area. Isotope composition studies showed that the raw fullerene soot, fullerene depleted soot (toluene extract), C 60, and C 70 were enriched in 13C relative to the graphite anode, whereas the cathode deposit was depleted in 13C. The measurements show that C 60 is richer in 13C compared with both C 70 and the toluene-extracted soot. The implications regarding the mechanisms for the formation of fullerenes are discussed.

Isotopic fractionation during fullerene, nanotube, and nanopolyhedra formation

The production of fullerenes by electrical arcing or resistively heating produces a number of other products including nanotubes and nanopolyhedra, microtubes, and pyrolytic carbon. The mechanism of formation of these different products is still speculative. We report here that the isotopic distributions in the various products named above differ, and this sheds new light on the mechanism by which they are formed. We electrically arced graphite rods of high purity (99.99% C) in a helium atmosphere according to the general procedure for preparing fullerenes. Pyrolytic carbon on the shell of the cathode deposit has an isotopic ratio close to that of the graphite. This is strong evidence that the pyrolytic carbon is formed by a mechanism different from nanotube, nanopolyhedra, or soot formation. We conclude that nanotubes and nanopolyhedra, pyrolytic carbon, microtubes, and fullerene soot in the arcing process are formed by different mechanisms. The nanotubes and nanopolyhedra are produced preferentially from ions with lowest mass-to-charge ratio and atoms. It is probable that the nanotubes and nanopolyhedra are formed by direct electrode-electrode interchange of charged monoatomic ions. Fullerene soot is formed from species with higher mass-to-charge ratios which can escape the electromagnetic field of the arc. 18 refs., 1 tab.

X-ray diffraction study of fullerene soot

The X-ray diffraction pattern of pure buckminsterfullerene (C[sub 60]) is compared to that of exhaustively toluene-extracted fullerene soot. Both show diffraction lines which may be indexed to the 1.420 [+-] 0.005 nm cubic lattice of C[sub 60]. Additionally, the extracted fullerene soot shows diffraction peaks which may be indexed as the (002), (004), (100), (110), and (112) peaks of a planar benzenoid lattice. The coefficients of thermal expansion for the (311) peak of the C[sub 60] lattice and the (002) peak of the planar benzenoid lattice are both 3 [times] 10[sup [minus]5] [degree]C[sup [minus]1], which is the value of the (002) peak of graphite. Both phases of the extracted fullerene soot change on exposure to air at 600[degree]C: the C[sub 60] phase vanishes, and the in-plane component of the benzenoid phase grows. 22 refs., 3 figs.

Large Odd-Numbered Carbon Clusters from Fullerene-Ozone Reactions

The odd-numbered carbon clusters C(119), C(129), and C(139) have been observed in the mass spectra of toluene extracts of fullerene soots and of the products of ozone-fullerene reactions. Specifically, ozone-C(60) reactions yield C(119), ozone-C(70) reactions yield C(139), and ozone-(C(60)/C(70)) reactions produce C(119), C(129), and C(139). These unexpected species correspond to dimers of C(60), C(60)/C(70), and C(70), respectively, less one carbon atom, and are stable gas-phase ions with behavior similar to that of fullerenes. The results suggest a new route to functionalization and derivatization of fullerenes through controlled ozone-catalyzed cage-opening reactions.

Improved Purification of C60 and Formation of σ‐ and π‐Homoaromatic methano‐bridged fullerenes by reaction with alkyl diazoacetates

AbstractA rapid and inexpensive method for the large‐scale purification of C60 is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C60 with ethyl and tert‐butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene‐bridged isomers 1a–3a and 1b–3b, respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b, respectively. Isomers 1a/b possess the methano bridge at the 6–6 ring junction, whereas structures 2a/b and 3a/b are bridged at the 6–5 junction. A dramatic influence of local and π‐ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a/b and over a hexagon ring in 3a/b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the 13C‐NMR chemical shifts of the bridgehead C‐atoms and the 1J(C,H) coupling constants for the methano‐bridge atoms reveals conclusively that the 6‐5‐ring‐bridged structures 2a/2b and 3a/3b are π‐homoaromatic (‘open’ transannular bond) and the 6‐6‐ring‐bridged structures 1a/b are π‐homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π‐homoconjugation in 2a/b and 3a/b represents a much smaller electronic perturbation of the original C60 chromophore than σ‐homoconjugation in 1a/b. The results of this study demonstrate an impressive linkage between the chemistry of methano‐bridged annulenes and methano‐bridged fullerenes.

Formation of giant fullerene gas‐phase ions (C, 60 ⩽ 2n ⩽ 500): Laser desorption/electron ionization Fourier‐transform Ion cyclotron resonance mass spectrometric evidence

AbstractLaser desorption (followed by electron ionization) Fourier‐transform ion cyclotron resonance (LD/EI‐FTICR) mass spectra have been obtained for thin and thick deposits of purified C60 as well as benzene extracts of fullerene‐laden arc‐welded graphite soot under identical mass spectral conditions. Thick (but not thin) deposits exhibit ‘giant fullerene’‐like carbon cluster‐ion distributions, in either positive‐ or negative‐ion mode; giant fullerene ions observed by mass spectrometry therefore do not necessarily prove that neutral giant fullerenes were present in the original sample, which is consistent with recent laser vaporization and plasma desorption mass spectrometry results. FTICR‐MS of the residual soot remaining after benzene extraction yielded much more abundant ‘giant fullerene’ ions extending above C, which are probably derived both directly from the corresponding giant neutral carbon clusters in the sample and by the nucleation process seen for thick deposits of the extracts. The results shown here firmly establish the importance of sample thickness in the mass spectrometric examination of fullerene soot.

Analysis of minor constituents in fullerene soots by LC–MS using a heated pneumatic nebulizer interface with atmospheric pressure chemical ionization

The minor constituents of toluene extracts of three fullerene-rich materials have been characterized by on-line LC–MS techniques, incorporating both positive and negative ion mass spectra obtained by atmospheric pressure chemical ionization. Two of the materials were soots, produced by resistive heating of graphite in an inert atmosphere, from different commercial suppliers. The third material was obtained as a condensate from a controlled laminar flame, and was shown previously (Anacleto etal:, Rapid Commun. Mass Spectrom. 6, 214 (1992)) to contain significant quantities of compounds that behaved under the present LC–MS conditions as isomers of the C60 and C70 fullerenes, and which reverted to the latter upon heating. This finding was confirmed here, and extended to the higher clusters C76, C84, C90, and C94. One of the graphite-derived soots contained monoxides of the carbon clusters as the principal minor components, while the other soot contained hydrogenated species including C60H2, C60H4, C70H2, and (C60•CH4). The flame-generated material contained all of these minor constituents, together with complexes of C60 with larger aliphatic molecules as well as large quantities of polycyclic aromatic hydrocarbons and related species. Photo-oxidation of a purified C60 preparation, from the graphitic soot containing mostly monoxide impurities, was shown to lead to increased levels of the mono-, di-, and tri-oxides of C60.

Density of fullerene containing soot as determined by helium pycnometry

Mass-spectrometric techniques have demonstrated the presence of carbon clusters C 2 n with n as high as 300, in carbon soot material produced using the “arc-synthesis” method. While new techniques are being explored for solvation of larger fullerene cages, beyond the more conventional solvation of the “smaller” fullerene molecules such as C 60 and C 70, the question arises: how much of the soot is fullerene cage molecules? One expects the density of fullerene soot composed of, say, C 240 and larger cages, to be significantly less than graphite, 2.2670 g cm −3, and also less than C 60, 1.65 g cm −3. The helium pycnometry determined density of a sample of commercially available raw “fullerene” soot is 1.5651 g cm −3. It is likely that this is an upper bound to the density, due to permeation by helium resulting from the large size of some fullerenes present in the soot.