The Influence of Ir and Pt Addition on the Synthesis of Fullerenes at Atmospheric Pressure

Abstract

The addition of metallic Ir and Pt to a fullerene‐forming, atmospheric‐pressure plasma reactor was found to influence the generation of carbonaceous products. It was observed that the added metals were efficiently dispersed into the plasma and that their presence increased the yield of fullerenes. The addition of Ir led to a noticeable shift in the fullerene distribution towards C₆₀, whereas the addition of Pt increased the proportion of C₆₀ oxides and decreased the proportion of higher fullerenes. Addition of Ir also caused a reduction of the soot particle size and the formation of a considerable quantity of carbon nanotubes.     

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.     

C60 Dimers Revisited

Several dimers: C₁₂₀, C₁₄₀, C₁₃₀ and their oxygen-containing derivatives as well as some oligomers or polymers of the well known spherical fullerenes have been synthesized so far. Some of the formulas attributed to such compounds represent the first steps in a more complex fate leading to trivalent capped tubulenes. Such a way could even be followed by functionalized fullerenes. A detailed network transformation is given for C₆₀ and its mono- and di-epoxy derivatives. Semiempirical calculations support the presented findings.     

Optical Emission Study of RF Thermal Plasma During Fullerene Synthesis

Results on studies of molecular spectra emitted in the initial stages of fullerene synthesis during processing of graphite powder in RF thermal plasma conditions are presented in this work. CN—usually present in carbon plasmas—and C₂ were found as dominant molecular species. The role of CN radicals on the fullerene formation was discussed in detail. Intensities of CN and C₂ lines were studied against the composition of gas phase and the feed rate of graphite powder. The rotational-vibrational temperatures of CN species were calculated by fitting the experimental spectra to the simulated ones. It was concluded that in the plasma region CN radicals could be formed by the reaction of C₂ with atomic nitrogen at smaller loads. This reaction lowered the yield of fullerenes. At larger loads, C₂ formation was decreased due to lower temperature of the particles compared to smaller load. The CN radicals were produced by the surface reaction of the hot carbon particles with nitrogen atoms. Results confirmed that for effective fullerene synthesis, the nitrogen content of the precursors and the plasma gases should be minimized.     

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.     

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.     

Investigation of Iron-Fullerene Mixture Plasmas in ECR Discharge

Fullerene+iron (C₆₀+Fe) mixture plasmas were produced and studied in the ECR ion source of ATOMKI. The two main components of the plasma were obtained by different filament ovens. In this series of measurements we concentrated on the maximum ratio of C₅₈ (damaged fullerene) in the plasma. C₅₈ is less stable than C₆₀ and the probability to form new materials is higher. Using this method we produced molecules of mass M=752 both in single- and double-charged states with beam intensities of 8 · 10^-10A and 2 · 10^-10A, respectively. We identified this beam as a mixture of FeC₅₈, O₂C₆₀ and CO₂C₅₉, while the experiment did not give information on the exact location of the iron and oxygen in the carbon ball.     

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.     

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.     

Some New Aspects of Chlorination of Fullerenes

The effect of the reagent ratio, reaction time and power of the reagent on the product composition in chlorination of [60]fullerene was studied. Chlorofullerenes C₆₀Cl₆, C₆₀Cl₈, C₆₀Cl₁₀, C₆₀Cl₁₂, C₆₀Cl₁₄, and C₆₀Cl₂₆ were synthesized and characterized by chemical analysis, FTIR, ¹³C NMR, and MALDI TOF mass spectrometry. The experimental data supported the coexistence of several isomers of C₆₀Cl_n (n = 8, 10, 12, 14, 26); the mixtures were not separated so far. Semiempirical calculations (AM1, PM3) were used to analyze the addition patterns and resulted in the most favorable structures of C₆₀Cl_8-26. Chlorination of C₇₀ under various conditions invariably yielded C₇₀Cl₁₀.     

Investigations of the Interaction of Nickel and Carbon Monoxide with Solid Films of C60 and C70 by UV and X-Ray Photoelectron Spectroscopy

Based on UV and X-ray photoelectron spectroscopy, it is shown that nickel metal clusters deposited on solid C₆₀ and C₇₀ films cause marked changes in the valence band spectra. In addition, the C 1s core-level of the fullerenes shift to lower binding energies while the Ni 2p_3/2 core level shifts towards higher binding energies, especially at small metal coverages. These observations signify the occurrence of charge-transfer from the nickel metal to the fullerene. We also show that CO adsorbs weakly on C₆₀ and C₇₀ surfaces.     

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.     

Penetration of Fullerene C60 Derivatives Through Biological Membranes

Penetration of fullerene C₆₀ in hydrated molecular-colloidal form (FMC) and various C₆₀ water-soluble derivatives (FDs) through membranes of human erythrocytes, platelets and symbiosomes (subcellular organelles of plant origin) were tested. The FDs bearing amino acids induced pronounced depolarization of symbiosome membranes energized with Mg-ATP. In erythrocytes and platelets incubated in K⁺-free medium in the presence of FCCP, FDs with malonic acid pendants promoted acidification of the intracellular medium thereby simulating an effect of the K⁺ ionophore valinomycin. Dissipation of ΔpH artificially induced on the plasma membrane of these cells was observed in the presence of C₆₀-γ-aminobutiric acid which, in addition, strongly stimulated Mg-ATP-dependent generation of membrane potential on symbiosome membranes. C₆₀-Arg was shown to dissipate K⁺-diffusion potential on erythrocyte membranes induced by valinomycin. Fullerene C₆₀ used in hydrated molecular-colloidal form (FMC) also entered symbiosomes and platelets as evidenced by the quenching of the fluorescence of the Ca²⁺ indicator chlorotetracycline localized in the interior of these cells. These findings provide evidence for ease of permeation of these fullerene-based compounds through biological membranes from different type cells.     

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.     

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.     

Electronic structure and electrical transport characteristics of C60, 2C60 and 4C60 fullerene molecules

The extended H?ckel method and the Green s function method were used to calculate the electronic structure and electrical transport of Au electrode-C₆₀, 2C₆₀ or 4C₆₀ fullerene-Au electrode systems. Furthermore, their electronic structure and electrical transport characteristics were compared and analyzed. The results show that (i) owing to the contact with the Au electrodes, the C₆₀, 2C₆₀ and 4C₆₀ molecules change in their electronic structures significantly, and their energy gaps between LUMO and HOMO are narrow; (ii) the bonding between C₆₀, 2C₆₀ or 4C₆₀ fullerene and Au electrodes is partially covalent and partially electrovalent; and (iii) the conductance of the three fullerenes conforms to the order of C₆₀>2C₆₀>4C₆₀.     

Preparation, Separation and Characterisation of Fullerene - C60 and C70

This paper reports a simple apparatus for the synthesis of fullerenes and an efficient method for the separation of C₆₀ and C₇₀ in large amounts. The positive and negative ion mass spectra of C₆₀ and C₇₀ were measured using electron ionization and in-beam methods. Vibrational Raman spectra showed that the C₆₀ molecule adsorbed on the substrate surface may be distorted and its symmetry may be reduced under the action of the substrate surface.     

Thermal Stability in Pure Oxygen of Soot Generated During the Production of C60 by the Contact Arc Vaporization of Graphite

The thermal stability in oxygen of residual soot, after extraction with toluene, has been found to be lower than that of C₆₀. Since the residual soot has been shown from previous studies to contain higher fullerenes, the present results suggest that the oxidative stability of higher fullerenes, rather surprisingly, is lower than that of C₆₀.     

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.     

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.