Synthesis of fullerenes from carbon powder by using high power induction thermal plasma

Radio frequency (rf) inductively coupled thermal plasma (ICTP) was used to fabricate fullerenes (C₆₀,C₇₀, etc.) by direct evaporation of carbon powder injected into the plasma. Spectroscopic observation of the plasma was made for molecular band spectra of C₂ and atomic lines of C. The formation of fullerenes C₆₀ and C₇₀ as well as higher fullerenes were checked and recognized by high performance liquid chromatography (HPLC) and time-of-flight mass spectrometer (TFMS). The suitable conditions for the synthesis of fullerenes within the experimental conditions adopted were 10-kPa plasma pressure, with a considerably higher flow rate of approximately 150 l/min for mixed-gas condition of Ar, He and CO₂, with carbon powder of average diameter 20 μm. The results showed that the productivity of fullerenes has a relation to the intensity of C₂ molecular and C atomic spectra from the induction plasma. Mixing of Si with C particles has a kind of role in enhancing the synthesis rate of fullerenes C₆₀, as well as the higher order fullerenes.     

Synthesis of C60-NBN and C70-NBN(N=L, 2) by DC arc Burning Method

Macroscopic quantities of boron-doped fullerenes, such as C_60-nB_n and C_70-nB_n(n = 1, 2), were successfully synthesized by DC arc burning method, extracted by CS₂, and characterized by field desorption mass spectra. Among them C₅₈B₂ and C₆₈B₂ were extracted for the first time. The boron-doped fullerenes were found to be less stable than their pristine fullerene analogs. When the electric current becomes too high, no boron doped fullerene, but more higher fullerenes, were formed.     

C60 and Giant Fullerenes in Soot Condensed in Vapors with Variable C/H2 Ratio

A transmission electron microscope (TEM) study of individual soot grains forming fluffy carbon particles produced using the arc-discharge technique revealed close-packed arrangements of single-wall ring structures with average diameters of 0.7, 1.1, 3.0, 5.5, and 8.2 nm. These structures were hypothesized to be C₆₀ and giant, C₅₄₀, C₉₆₀, and C₁₅₀₀, fullerenes that could form by coalescence during condensation and soot agglomeration, although in situ solid-state growth cannot be excluded. Mass spectroscopy and high performance liquid chromatography (HPLC) chromatography of the samples confirmed the presence of C₆₀ fullerene in all samples giving confidence to the giant fullerene growth scenario. Our results suggest that fullerenes could be common in soot grains produced by this technique as well as being an important carbon phase in C-rich accretion disks around young stellar objects and among the dust in the interstellar medium.     

Fullerene Research in Poland

Main results of the investigations of fullerene and its derivatives are briefly reviewed. Such topics as plasma spectroscopy, fullerenes and nanotubes formation, C₆₀ carbyne knots, fullerene reduction and doping, charge transfer states and electroabsorption of C₆₀, electrical conductivity, superconductivity, ESR properties, fullerene clathrates, C₆₀/C₇₀ complexes with organic donors, fullerene adducts, hydrogenated fullerenes, metallofullerenes and carbon nanotubes are discussed.     

Preparation of Fullerene Derivatives by Resistive Heating With Graphite Crucible

We report here the preparation of both endohedral fullerenes (La°C₈₂, La₂°C₈₀) and exohedral fullerenes (C₆₀ (C_mO_n)) by the resistive heating with graphite crucible filled with lanthanum oxide.     

SIMULTANEOUS DETERMINATION OF C60 AND C70 FULLERENES BY A SPECTROPHOTOMETRIC METHOD

In all fullerene-producing systems, reaction products were black soot extracts reported to contain a 5-25% fullerene mixture. Toluene extraction of the soot results in a solution of C₆₀, C₇₀, and higherc fullerenes. Without separation, absolute determination of the contents is not possible, leaving the researcher to comment only on the C₆₀/C₇₀ ratio of the solution. High-performance liquid chromatography, nuclear magnetic resonance, and scanning tunneling microscopy imaging techniques were reported in the literature for determining the C₆₀/C₇₀ ratio of the mixtures. These methods require tedious experiments and produce slightly differing results as well. In this communication, a new and relatively quick method is proposed for the simultaneous determination of the yields of C₆₀ and C₇₀ (not the ratio) in fullerene-containing solutions by ultraviolet-visible spectrophotometric analysis.     

Raman Spectra of Chlorinated C60 and C70 Fullerenes

Raman spectra of chlorinated C₆₀ and C₇₀ fullerenes prepared by photochlorination have been reported and discussed. The Raman lines suggest structural analogies with already fully characterized brominated fullerenes. Intense laser light irradiation cause a decomposition of fullerene chloro-derivatives leading to the formation of C₆₀ polymer.     

Modifying the buckyball

Structural and electronic properties of carbon clusters, in particular the C₆₀ “buckyball” molecule as well as structurally and chemically modified fullerenes, are calculated using a combination of predictive ab initio techniques and parametrized total energy schemes. These calculations indicate that single- and multi-shell fullerenes are the most stable C_n isomers at T = 0 for n < 20. More open structures are favored by entropy at higher temperatures. Upon interaction with donor elements, C₆₀ molecules form stable M@C₆₀ endohedral complexes; analogous acceptor-based complexes are unstable. Solid C₆₀ reacts with alkali metals and forms a stable intercalation compound which shows superconducting behavior. The relatively high value of the critical temperature for superconductivity can be explained quantitatively within the Bardeen-Cooper-Schrieffer formalism.     

Which Fullerene Is Appropriate to Host C20? A Molecular Modeling Study

Molecular mechanics (MM) and molecular dynamics (MD) study of fullerene complexes of the short-lived “smallest fullerene” C₂₀ with icosahedral C₆₀, C₈₀, C₁₄₀, C₁₈₀, and C₂₄₀ of I_h, I_h, I, I_h, I_h symmetry, respectively, using CVFF and ESFF forcefields revealed that the most stable complexes can be formed only if the intershell distance between fullerenes is similar to that in graphite or in experimentally observed buckyonions. The fullerenes C₁₄₀ and C₁₈₀ are the smallest suitable candidates to form such complexes with C₂₀. Similarly to the stabilization of short-lived cyclobutadiene or benzyne in hemicarcerands, C₂₀ is expected to be stabilized inside the C₁₄₀ and C₁₈₀ cages which would enable a deeper understanding of the highly nonplanar system of conjugated bonds of this exotic molecule.     

Structures, Stabilities and Strain in C60 and C70 Derivatives

The stabilities of a number of small adducts as well as larger hydrides of C₆₀ and C₇₀ are reported using semiempirical MO methods. The data are shown to be consistent with the nature of bond alternation in the parent fullerenes and strain effects in the cage systems.     

An Invariant of Carbon Arc Synthesis of Fullerenes

The yields of fullerenes C₆₀ and C₇₀ were determined in a wide range of controlled parameters. The total yield of fullerenes varied from 3 to 24%. The molar relative contents C₆₀/C₇₀ appeared to be constant for all samples of toluene extracts of the soot and equal to 5.06 ± 0.1. The accuracy of this constancy (± 2%) was determined by application of a special mathematical processing to the spectra of toluene extracts.     

Structural transformations, reactions, and electronic properties of fullerenes, onions, and buckytubes

We describe the results of extensive quantum molecular dynamics calculations of the properties of fullerenes and microtubules. The topics to be discussed include: (i) stability of C₆₀ isomers and barriers to isomerization; (ii) reactivity of C₆₀ and C₅₈ with C₂ and C₃, and its implications on the formation and growth of fullerenes; and (iii) atomic and electronic structure and doping of semiconducting microtubules. We also discuss the structures, stabilities and atomic transformations of large multishell fullerenes and offer an explanation for the formation of spheroidal “onions” under high fluence electron irradiation conditions. The last results, which involved calculations for up to 15 000 atoms, were obtained using classical three-body potentials.     

Instrumental Neutron Activation Analysis of Trace Element Impurities in Graphite Soot, Gold Grade C60 and C70 and in Super Gold Grade C60

Actually the purity of fullerenes is in general characterized as the percentage of the main component (e.g. C₆₀) versus the higher fullerenes (e.g. C₇₀, etc.) and/or in a few cases of some other polycyclic organic components.

We are reporting here for the first time detailed data on trace element impurities in fullerene precursors and in the main fullerenes. For studying the element impurities instrumental neutron activation analysis (INAA) was used. Our measurements have shown that all these materials contain trace elements at ppb (ng/g) ami ppm (μg/g) levels. From the results it comes (Hit that in the future investigations of the elemental purity of the C₆₀ and C₇₀, and even of the higher fullerenes would have to be also considered when their electrical, magnetic, etc. properties are studied.     

Determination of C60 and/or C70 Concentrations

Two methods of quantitative analyses of the fullerenes C₆₀ and C₇₀ are described. Quantitative Infrared Spectroscopy permits the determination of the concentrations of pure and mixed compositions of C₆₀ and C₇₀ in carbondisulfide solutions. Alternatively, the ratio of C₆₀/C₇₀ is analyzed by evaluating the lattice parameters of a solid solution of the fullerene species and cyclohexane according to Vegard's Law. Both methods show high accuracy and are suited for calibration of mass spectrometric analyses of fullerene samples.     

Ozone Reaction with C70 and C60 Fullerenes: The Effect of Temperature on the Reaction Kinetics

It has been confirmed that the effect of temperature on the rate constants (k) of ozone reaction with C₇₀ and C₆₀ fullerenes follows the Arrhenius law. The experimental values of activation energy (E_a) and pre-exponential factor (A), like as those of other simple alkenes, are in the order of 2.4-2.6 kcal mol^-1 and (1.2-1.8) × 10⁷ L mol^-1 sec^-1, respectively. They are practically equal for the both fullerenes. It has also been found that the value of the rate constant k of C₇₀ fullerene ozonolysis is higher in comparison to the respective k-value of C₆₀.     

Natural Fullerenes-Will they Offer a Hint to the Selective Synthesis of Fullerenes?

In addition to the known laboratory methods of preparing fullerenes, which generally start from carbon vapor, studies of naturally occurring C₆₀/C₇₀ suggest a catalytic process of fullerene formation that proceeds in solid phase under mild condition. Recent observation of C₆₀/C₇₀ in Yunnan coal and Kalerian C-rich rock is reviewed in the light of the above perspective.     

Laser Pyrolysis of Hydrocarbons in Synthesis of Soot Containing Fullerenes

Using a high power CW CO₂ laser, the pyrolysis in a flow reactor of different hydrocarbons/oxidizer mixtures with/without sensitizer lead to soots containing weightable quantities of fullerenes which were identified by FTIR spectroscopy, high performance liquid chromatography (HPLC) and time-of-flight mass spectrometry. The C₆₀ and C₇₀ quantification was done by HPLC. The FTIR spectroscopy of toluene extracts from the soots and of exhaust gases allowed to discuss some aspects concerning the influence of sensitizer (SF₆) addition as well as of the oxidiser (O₂/N₂O) on the fullerene production in laser pyrolysis of benzene-based mixtures.     

Characterization of Fullerenes Obtained from Boron Nitrite Containing Graphite Electrodes: Electronic Structure of C60-X-YBXNY and Deformed C60

The electronic structure of C₆₀ molecules with carbon substituted by other elements such as boron or nitrogen has been calculated for molecules in the singlet state with even number of electrons. Therefore, in the case of boron and nitrogen substituents, calculations have been performed for ionized molecules. The results obtained from our density functional calculations prove than in the C_60-x-yB_xN_y molecules both HOMO and LUMO levels are split due to the lower symmetry of the molecule Influence of deformation of C₆₀ molecules on electronic states, which is interesting because fullerenes may undergo deformation in solvate crystals, is also shown These C₅₉B and C₅₉N, as well as C₅₈BN molecules are of special interest because samples containing such species can be prepared The Electron Spin Resonance (ESR) in those samples differs from the results obtained in pure C₆₀ samples, it consists of several lines which are very sensitive to the temperature.     

The Effects of Fullernes on the Initiation and Promotion Stages of Balb/3t3 Cell Transformation

Fullerene C₆₀ and a mixture of fullerenes C₆₀ and C₇₀ were solubilized in a culture medium with poly(vinylpyrrolidone) and examined for the effects on two-stage cell transformation in vitro, a model of carcinogenesis. They showed neither initiating nor promoting activity in the assays.