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.     

Atmospheric pressure photoionization mass spectrometry of fullerenes

Atmospheric pressure photoionization (APPI) was evaluated for the analysis of fullerenes. An important response improvement was found when using toluene mediated APPI in negative mode if compared with other atmospheric pressure ionization (API) sources (electrospray and atmospheric pressure chemical ionization). Fullerene APPI negative mass spectra were dominated by the isotopic cluster of the molecular ion, although isotopic patterns for M+1, M+2, and M+3 ions showed higher than expected relative abundances. These discrepancies are explained by the presence of two isobaric ions, one due to (13)C and the other due to the addition of hydrogen to a double bond of the fullerene structure. Triple quadrupole tandem mass spectrometry, ultrahigh resolution mass spectrometry, and accurate mass measurements were used to confirm these assignments. Additionally, cluster ions M+16 and M+32 were characterized following the same strategy. Ions due to the addition of oxygen and alkyl additions were attributed to the presence of methanol in the mobile phase. For the fast chromatographic separation of fullerenes (less than 3.5 min), a sub-2 μm C18 column and isocratic elution (toluene/methanol, 45:55 v/v) was used. Highly selective-selected ion monitoring (H-SIM) mode (mass resolving power, >12,500 fwhm) was proposed monitoring the two most intense isotope ions in the [M](-?) cluster. Method limits of quantitation down to 10 pg L(-1) for C(60) and C(70) fullerenes and between 0.75 and 5.0 ng L(-1) for larger fullerenes were obtained. Finally, the ultrahigh performance liquid chromatography (UHPLC)-APPI-MS method was used to analyze fullerenes in river and pond water samples.     

Extracting of fullerene-like nanoparticles from environmental soots

It is well known that burning graphite electrodes in electric arc is an efficient method for obtaining of fullerenes. However, fullerenes form in any sooting flames. Therefore, detection fullerene in natural burning fuel is of a great interest for understanding of mechanism of soot formation. This research extracted samples of environmental soots in toluene. Soots and products of extraction were characterized by UV-vis spectroscopy, sedimentation analysis, atomic force microscopy. Analysis of extracts found fullerene-like clusters. The concentration of particles decreased in the following sequence: charcoal – carbon black – gas soot.     

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.     

An Invariant of Carbon Arc Synthesis of Fullerenes

Abstract

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.     

Catalytic Hydrogenation of Fullerenes in the Presence of Metal Catalysts in Toluene Solution

The catalytic hydrogenation of fullerenes was studied in the presence of various metal catalysts in toluene solution under several conditions. Fullerenes were found to be catalytically hydrogenated in toluene solution in the presence of the Ru/carbon, Pdharbon, NiDiatomaceous Earth or Ptharbon as the catalysts. The reactivity of catalytic hydrogenation of the Ru/C was the highest for the among the used metal catalysts.     

Fullerenes in Chinese Ink Sticks (“Sumi”)

Small amounts (up to 0.1%) of C₆₀ and C₇₀ have been detected by high-pressure liquid chromatographic (HPLC) analysis of toluene extracts from soots used to manufacture Chinese ink sticks, or Sumi. These soots have been prepared by slow burning of pine wood, and later various seed oils. Turpentine oil, the major constituent of pine wood oil, have been found to produce twice as much fullerenes as does toluene when used as the combustion material. The yields of fullerene from unsaturated combustion materials decrease with the iodine number, reaching zero in the saturated compounds. Possible role of fullerenes as the effective gloss enhancer for black color is suggested in reference to the known technique of adding a natural red pigment to Sumi practiced in Japan.     

High-Temperature, High-Pressure Extraction of Metallofullerenes Gd@C2n

A high-temperature, high-pressure extraction technique with toluene and pyridine were employed for the extraction of metallofullerenes Gd@C_2n. A series of Gd@C_2n for 2n from 70 to 96 were effectively extracted by toluene. Gd@C₇₄ was shown to be a new stable soluble metallofullerene species. Pyridine was found to be more useful for the extraction of Gd@C₈₂ and Gd₂@C₈₀ from empty fullerenes and other metallofullerene species.     

Modifications of Fullerenes Extractions and Chromatographies with Different Solvents

In the Bucky System II, based on electrical arc method, carbon soot was produced. Fullerenes C₆₀ and C₇₀ were Soxhlet extracted from the collected soot samples with toluene, chlorobenzene and with both of them successively, modifying the original methods. The yields of the both obtained toluene extracts were 5.4%. Chlorobenzene extract yield was 5.8%. After extraction of toluene insoluble soot with chlorobenzene, the entire extract yield was increased from 5.4% to 5.8%, due to modification of the existing methods. The difference of fullerenes solubilities in these solvents has been concluded. In the second part of our work toluene and chlorobenzene fullerenes extracts were separated by column chromatographies on active Al₂O₃, modifying the existing methods, by elution with hexane and mixtures of benzene, toluene, or xylene with hexane in determined ratios and orders. Identifications of buckminsterfullerene C₆₀ in the first chromatographically purified fractions were achieved by electron impact ionization (EI) mass, IR, and UV/VIS spectroscopy. The second and the third purified fullerene fractions, toluene and chlorobenzene soot extracts were characterized by IR and UV/VIS methods.     

Endohedral Formation from Neutron Activation of Interstitial Rare Cas C60 Fullerides

Rare gas interstitial fullerenes, produced by hot isostatic pressing solid C₆₀ in the presence of Ar, Kr or Xe, have been neutron irradiated and their behaviour investigated. The activity of the generated radionuclides was found to be in agreement with calculations and this combined with X-ray powder diffraction showed that both the activated radionuclides and the unactivated rare gas remained trapped in the solid after they have been subjected to the harsh conditions encountered in a nuclear reactor. Gamma spectroscopy of the irradiated solids and solutions of them in toluene provided strong evidence for endohedral compound formation. We estimate 1-2% of the activated rare gas atoms, which recoil as a result of prompt gamma emission, end up in the centre of what is most likely too be the C₆₀ molecule or some other fullerene derivative. On this basis, we postulate the formation of RN@C_6o where the radionuclide (RN)is ^125gXe, ^133gXe, ^I35gXe, ⁴¹Ar or^85mKr.     

Ab Initio and DFT‐Based Assignment of the Vibrational Spectra of Polymerized Fullerenes

Abstract

Several high‐level quantum chemical methods are used to calculate the vibrational properties of fullerenes, and the PBE/tz2p approach is shown to be the optimal one. The model to simulate the vibrational spectra of fullerenes polymers from the quantum chemical calculations of their finite fragments was analyzed. The complete interpretation of the spectra of 1D and 2D polymerized fullerenes is fulfilled.     

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.     

Synthesis evaluation of nitrogen atom encapsulated fullerenes by optical emission spectra in nitrogen plasmas

The nitrogen atom encapsulated fullerene (N@C₆₀) with relatively high yield has been synthesized by a plasma irradiation method. We have examined the relationship between optical emission spectra of a radio frequency (RF) discharge nitrogen plasma and the synthesis yield of N@C₆₀. As a consequence, the increasing amount of nitrogen molecule ions (N₂⁺) impinging on the sublimated fullerenes are found to enhance the synthesis of N@C₆₀. Furthermore, it is clarified that there is an optimum condition of the nitrogen plasma for the high-yield synthesis of N@C₆₀, which is generated under lower gas pressure and is irradiated to the larger amount of fullerenes.     

Photophysical and Photochemical Properties of the Fullerenes

This article primarily reviews the recent work of this laboratory on the photophysical and photochemical properties of the fullerenes, C₆₀ and C₇₀, in solution. Properties of the excited singlet and triplet states of them have been characterised by static and transient fluorescence spectroscopy. Charge and/or proton transfer dynamics in ground and excited singlet state of the fullerenes with the amines have been investigated in detail. Strong evidence has been obtained for weak interaction between the fullerenes and the aromatic solvents, like benzene, toluene etc. A novel method has been described to solubilise C₆₀ in aqueous solution via formation of inclusion complex with γ-cylodextrin.     

Application of two-dimensional correlation spectroscopy to chemometrics: self-modeling curve resolution analysis of spectral data sets

This paper demonstrates the use of two-dimensional (2D) correlation spectroscopy in conjunction with alternating least squares (ALS) based self-modeling curve resolution (SMCR) analysis of spectral data sets. This iterative regression technique utilizes the non-negativity constraints for spectral intensity and concentration. ALS-based SMCR analysis assisted with 2D correlation was applied to Fourier transform infrared (FT-IR) spectra of a polystyrene/methyl ethyl ketone/deuterated toluene (PS/MEK/d-toluene) solution mixture during the solvent evaporation process to obtain the pure component spectra and then the time-dependent concentration profiles of these three components during the evaporation process. We focus the use of asynchronous 2D correlation peaks for the identification of pure variables needed for the initial estimates of the ALS process. Choosing the most distinct bands via the positions of asynchronous 2D peaks is a viable starting point for ALS iteration. Once the pure variables are selected, ALS regression can be used to obtain the concentration profiles and pure component spectra. The obtained pure component spectra of MEK, d-toluene, and PS matched well with known spectra. The concentration profiles for components looked reasonable.     

High Pressuee Synthesis of Alkali Metal Doped C60 Polymers

Alkali metal doped fullerenes, AC₆₀ (A = Li, Na) were polymerized under a pressure of 5 GPa at 573 K. the X-ray diffraction patterns of the products were very similar to that of the rhombohedral two-dimensional C₆₀ polymer, the basal spacings being slightly increased by the intercalation of the alkali atoms between the two-dimensional polymer layers. the alkali metal doped C60 polymers were insoluble in toluene and found to be semiconductors over a temperature range of 200 - 300     

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.     

Modifications of Fullerenes Extractions and Chromatographies with Different Solvents

Abstract

In the Bucky System II, based on electrical arc method, carbon soot was produced. Fullerenes C₆₀ and C₇₀ were Soxhlet extracted from the collected soot samples with toluene, chlorobenzene and with both of them successively, modifying the original methods. The yields of the both obtained toluene extracts were 5.4%. Chlorobenzene extract yield was 5.8%. After extraction of toluene insoluble soot with chlorobenzene, the entire extract yield was increased from 5.4% to 5.8%, due to modification of the existing methods. The difference of fullerenes solubilities in these solvents has been concluded. In the second part of our work toluene and chlorobenzene fullerenes extracts were separated by column chromatographies on active Al₂O₃, modifying the existing methods, by elution with hexane and mixtures of benzene, toluene, or xylene with hexane in determined ratios and orders. Identifications of buckminsterfullerene C₆₀ in the first chromatographically purified fractions were achieved by electron impact ionization (EI) mass, IR, and UV/VIS spectroscopy. The second and the third purified fullerene fractions, toluene and chlorobenzene soot extracts were characterized by IR and UV/VIS methods.     

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.     

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.