Deposition of amorphous carbon films from C60 fullerene sublimated in electron beam excited plasma

C₆₀ fullerene clusters are used as a carbon source for amorphous carbon films deposition in an electron beam excited plasma. C₆₀ clusters are sublimated by heating a ceramic crucible containing the C₆₀ powders up to 850 °C, which is located in a highly vacuumed process chamber. The sublimated fullerene powders are injected to the electron beam excited argon plasma and dissociated to be active species that are propelled toward the substrates. Consequently, the carbon species condense as a thin film onto the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 μm/h and the average surface roughness of 0.2 nm over an area of 400 μm² are achieved. Decomposition of the C₆₀ fullerene after injecting into the plasma is confirmed by optical emission spectroscopy that shows existence of small carbon species such as C₂ in the plasma. X-ray diffraction pattern reveals that the microstructure of the film is amorphous, while fullerene films deposited without the plasma show crystalline structure. Raman spectroscopic analysis shows that the films deposited in the plasma are one of the types of diamond-like carbon films. Different negative bias voltages have been applied to the substrate holder to examine the effect of the bias voltage to the properties of the films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 28 GPa. In addition, the films are droplet-free and show superior lubricity.     

Formation of fullerenes by pyrolysis of perchlorofulvalene and its derivatives

In a retro-synthetic approach, [60]fullerene might be accessible by condensing six fulvalene fragments. In order to explore the potential of such a route for direct synthesis of [60]fullerene we have investigated the pyrolysis of perchlorofulvalene (PCF). Low temperature pyrolysis of PCF at 250 °C resulted mainly in the formation of dimers, trimers, tetramers and products of subsequent intramolecular condensation of these oligomers. Increasing the temperature to 300-350 °C leads to the formation of perchlorinated polynuclear aromatic hydrocarbons. Pyrolysis at 400-450 °C gives a cross-linked polymer structure which is the result of intermolecular condensation of the polynuclear aromatic intermediates. Pyrolysis at higher temperatures (>500 °C) mainly leads to graphite. It was found that the two-step pyrolysis of PCF (heating first at 450 °C, after that at 750 °C) yielded a fullerene containing soot via an intermediate polynuclear aromatic net. High temperature rearrangement of the latter gave fullerenes C₆₀ and C₇₀. The best results were obtained when a PCF oligomer obtained by Ullmann condensation was used as a precursor. By two-step pyrolysis and further high vacuum sublimation of the soot the fullerenes C₆₀ and C₇₀ were obtained in extractable amounts.     

High-pressure solubility of fullerene C60 in toluene

The solubility of fullerene C₆₀ in toluene was measured at temperatures between 278.2 and 308.2 K and pressures up to 340 MPa, and also at temperatures between 258.2 and 298.2 K under atmospheric pressure. The solubility increased with increasing pressure, and then decreased with a sharp maximum, suggesting a transition between solid phases. A thermodynamic analysis of the solubility supported the proposal of Korobov, et al. that the two solids correspond to C₆₀ (fcc) and C₆₀ · 2 (toluene) solvate. The solubility enhancement of C₆₀ by pressure in a low-pressure region is an unusual phenomenon when compared with the decrease in solubility of nonpolar molecular solids generally observed with rises in pressure.     

In situ EPR spectroelectrochemistry of single-walled carbon nanotubes and C60 fullerene peapods

The first in situ electron paramagnetic resonance (EPR) spectroelectrochemical study of C₆₀ fullerene peapods (C₆₀@SWCNT) as well as that of single-walled carbon nanotubes (SWCNTs) in different electrolyte solutions describes the formation of spin states by charge transfer reactions. Electrochemical reduction of peapods at high negative potentials causes the production of spins at the SWCNT site, while the intratubular fullerene is unchanged.Slightly anisotropic EPR signals were detected during electrochemical reduction of single-walled carbon nanotubes and fullerene peapods in the potential region from −1.75 to −2.15 V vs. decamethylferrocene/decamethylferrocinium couple. They are centered at g = 2.0038 and exhibit a hyperfine structure indicating the presence of functional groups containing N, O, H atoms in neighborhood. They differ from the EPR signals of chemically (potassium) doped SWCNT and C₆₀@SWCNT. As the EPR signal is influenced by the electrolyte counter ions a reaction with electrolysis products of tetraalkylammonium cations is taken into consideration. No EPR lines of fullerene anions were found in electrochemically treated peapods, but these anions are detectable, if a free C₆₀ in solution is cathodically reduced on a SWCNT electrode.     

Fabrication and characterization of fullerene-Nafion composite membranes

Fullerene-Nafion composite membranes have been fabricated through a new solution casting for the first time. The fullerenes used for the composites included C₆₀ and polyhydroxy fullerene (PHF), C₆₀(OH)_n (n ∼ 12). The dispersion of the fullerene in the composite membrane was much more refined with smaller agglomeration particles, relative to the previously prepared fullerene-Nafion composites in which the fullerene was introduced through doping. The miscibility of the hydrophobic fullerene, C₆₀, in the Nafion matrix was further improved by a new fullerene dispersant, poly[tri(ethylene oxide)benzyl]fullerene, C₆₀[CH₂C₆H₄(OCH₂CH₂O)₃OCH₃]_n (n ∼ 5), synthesized in this work. The solution-cast fullerene composites also demonstrated a significant improvement in the physical stability relative to the fullerene-doped Nafion composites through a better integration of the fullerene into the Nafion matrix. Furthermore, increased loadings of the fullerene in Nafion were made possible through the new solution-casting method, compared to the previous doping method. The water characteristics in the fullerene composites have been examined by TGA and ¹H pulse NMR measurements. The interactions between the fullerene and the Nafion have been studied through ATR FT-IR and molecular dynamics simulations which suggested PHF resides primarily in the hydrophobic domain of Nafion when the loading was low. The voltammetric measurements also have shown that the fullerene composites have the reduced limiting current density, compared to Nafion membranes without fullerenes.     

Reaction of silica-supported fullerene C60 with nonylamine vapor

The reaction of silica-supported [60]fullerene with vaporous nonylamine at 150 °C produces a mixture of addition products. Quantum chemical calculations, at the B3LYP/STO-3G level of theory, support that the addition reaction most likely takes place across the 6,6 bonds of C₆₀ pyracyclene units (and not across the 5,6 bonds). Numerous peaks were found in high-performance liquid chromatograms, apparently due to a large number of possible isomers. According to elemental analysis data (C:N ratio), the number of nonylamine molecules attached to C₆₀ is 3 on average. Thermogravimetric analysis of the nonylamine adduct showed two weight losses, one between 360 and 590 °C due to thermal decomposition of nonylamine moieties, and one between 725 and 840 °C due to decomposition of the remaining fullerene-derived carbonized material. Field-desorption mass spectrometric study revealed a number of molecular and fragment ions corresponding to the adducts with up to six nonylamine moieties attached to [60]fullerene; some of them were observed as multiply-charged ions. The temperature behavior of these peaks is similar to that for TGA, with maxima shifted to lower temperatures due to the cooperative effect of the strong electric field. C₆₀ can be partially regenerated by pyrolysis of the nonylamine adduct, although at very low yields (below 1%, after heating at 350 °C under air for 2 h).     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Hydrogen adsorption on partially truncated and open cage C60 fullerene

C₆₀ buckyball molecules were partially truncated by a controlled oxidation at 400 °C and 2 bar oxygen pressure to create unique pore textures suitable for hydrogen adsorption. Pore textural analysis and density measurement confirmed the success of cage-opening and the creation of pore structures accessible to gas molecules. The specific surface area of the C₆₀ sample were increased from below detection to a measurable value (BET: 85 m²/g). Raman spectral study showed that the three main bands of C₆₀, H_g(1), A_g(1) and A_g(2) remained and significant defects were created after the C₆₀ fullerenes were partially oxidized. XRD and SEM measurements suggested that the C₆₀ fullerenes lost their crystallinity and the crystal surfaces were etched after the oxidation step. Hydrogen adsorption on the C₆₀ fullerenes were measured at three temperatures (77, 143 and 228 K) and hydrogen pressures up to 150 bar. Hydrogen adsorption capacity on C₆₀ fullerenes at 77 K at 120 bar was more than tripled (from 3.9 to 13 wt.%) after the C₆₀ fullerenes were partially oxidized. The average heat of adsorption of hydrogen on the partially oxidized C₆₀ fullerene molecules (2.38 kJ/mol) is within the range of the reported values of heat of adsorption on other porous adsorbents.     

Theoretical calculations of the structure and UV-vis absorption spectra of hydrated C60 fullerene

A combined Monte Carlo simulation with semiempirical quantum mechanics calculations has been performed to investigate the structure of hydrated fullerene (C₆₀HyFn) and the influence of hydration on its UV-vis spectra. The statistical information of the C₆₀ fullerene aqueous solution (C₆₀FAS) is obtained from NPT ensemble including one C₆₀ fullerene immerses in 898 water molecules. To obtain an efficient ensemble average, the auto-correlation function of the energy has been calculated. The analyzed center-of-mass pair-wise radial distribution function indicates that, on average, there are 65 and 151 water molecules around the first and second hydration shells, respectively, of a single C₆₀ molecule. To calculate the average UV-vis transition energies of C₆₀HyFn, only the statistically uncorrelated configurations are used in the quantum mechanical calculations (INDO/CIS). These involve hundreds of supramolecular structures containing one C₆₀ fullerene surrounded by the first hydration shell. The calculated average transitions at 268 and 350 nm are in very good agreement with the experimental prediction.     

Fluorination of pressure-polymerized C60 phases

The reactivity of O-, T- and R-phases of the high pressure-high temperature (HPHT) polymerized C₆₀ towards gaseous fluorine in the temperature range of 50-250 °C was investigated. The reaction products were characterized by FTIR, powder X-ray diffraction, SEM, EDX, and VTP-EIMS to determine the bulk stoichiometries, bonding patterns, phase compositions, crystalline structures and thermal decomposition behavior of the fluorinated polymers. At 1 h isothermal treatment duration, fluorinated products with various bulk stoichiometries were obtained from different polymer phases with the R-phase showing the highest fluorine uptake. At 250 °C, all C₆₀ polymers showed partial decomposition to unfluorinated C₆₀ monomer under fluorine atmosphere. At 200 °C, the fluorination of R-phase yielded a pure fluoropolymer most likely having a {C₆₀F_x}_n (x = 36-44) composition. The same fluoropolymer was presumably obtained from O- and T-phases in lower yields. The linear chain structure was suggested for this new fluorocarbon polymer in agreement with the molecular mechanics modeling calculations.     

Synthesis and self-assembly in bulk of six-arm star-block copolymers with a C60 core

This study focuses on the synthesis and the structural characterization of various branched star-block copolymers (polyisoprene-block-polystyrene)₆C₆₀ with a fullerene C₆₀ as a core. Well defined 6-arm stars (PI-b-PS)₆C₆₀ with a low polydispersity and a precise control of the number of branches were prepared by grafting PI-b-PS diblock copolymers through the polystyrene block onto the C₆₀ core. The self-assembled structures formed in bulk were studied by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS) for both symmetric and asymmetric polystyrene-block-polyisoprene (PS-b-PI) diblock arms in the strong-segregation regime (65 ≤ χN ≤ 115). Various microstructures including lamellae, hexagonal packings of PS and PI cylinders as well as a gyroid phase were obtained by varying the volume fraction of polystyrene (f_PS) of the branches, leading to the formation of ordered, periodic and localized nanoscale dispersions of the C₆₀ in a polymer matrix including planes, threads and a 3D bicontinuous network of C₆₀.     

Nanosized cordierite–sapphirine–spinel glass-ceramics from natural raw materials

Inexpensive nanosized sintered cordierite glass-ceramic was prepared from quartz sand, kaolin, and magnesite. The addition of nucleation catalysts, such as TiO_2, Cr₂O_3, and admixed TiO₂–Cr₂O₃, was tested in the cordierite base glass. Cordierite, sapphirine, spinel, magnesium aluminium silicate, and cristobalite were developed using the crystallisation process. These glass-ceramics have ultra-fine grain sizes with nanorounded crystals measuring less than 200 nm, particularly in the Cr₂O₃-containing samples. Due to its different crystalline phases, the new glass-ceramics varied in hardness from 6374 to 8139 MPa and had coefficients of thermal expansion (CTE) from 0.83 to 6.89×10⁻⁶ °C⁻¹. In glass-ceramic samples, the spinel and sapphirine imparted high CTE (from 6.89 to 5.31×10⁻⁶ °C⁻¹) and hardness values (from 8139 to 7894 MPa), whereas cordierite provided lower CTE (from 0.83 to 2.66×10⁻⁶ °C⁻¹) and hardness values (from 7453 to 6374 MPa).     

Poly(l-lactide)/nano-structured carbon composites: Conductivity, thermal properties, crystallization, and biodegradation

The effects of nano-structured carbon fillers [fullerene C₆₀, single wall carbon nanotube (SWCNT), carbon nanohorn (CNH), carbon nanoballoon (CNB), and ketjenblack (KB)] and conventional carbon fillers [conductive grade and graphitized carbon black (CB)] on conductivity (resistance), thermal properties, crystallization, and proteinase K-catalyzed enzymatic degradation of poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)] films were investigated. Even at low filler concentrations such as 1 wt%, the addition of SWCNT effectively decreased the resistivity of PLLA film compared with that of conventional CB, and PLLA-SWCNT film with filler concentration of 10 wt% attained the resistivity lower than 100 Ω cm. The crystallization of PLLA further decreased the resistivity of films. The addition of carbon fillers, except for C₆₀ and CNB at 5 wt%, lowered the glass transition temperature, whereas the addition of carbon fillers, excluding C₆₀, elevated softening temperatures, if an appropriate filler concentration was selected. On heating from room temperature, cold crystallization temperature was determined mainly by the molecular weight of PLLA, whereas on cooling from the melt, the carbon fillers, excluding KB, elevated the cold crystallization temperature, reflecting the effectiveness of most of the carbon fillers as nucleating agents. Despite the nucleating effects, the addition of carbon fillers decreased the enthalpy of cold crystallization of PLLA on both heating and cooling. The addition of CNH, CNB, and CB elevated the starting temperature of thermal degradation of PLLA, whereas the addition of SWCNT reduced the thermal stability. Furthermore, the addition of C₆₀ and SWCNT enhanced the enzymatic degradation of PLLA, whereas the addition of KB and CNB disturbed the enzymatic degradation of PLLA. The reasons for the effects of carbon fillers on the physical properties, crystallization, and enzymatic degradation of PLLA films are discussed.     

Nanocrystalline diamond synthesized from C60

A bulk sample of nanocrystalline cubic diamond with crystallite sizes of 5–12 nm was synthesised from fullerene C₆₀ at 20(1) GPa and 2000 °C using a multi-anvil apparatus. The new material is at least as hard as single crystal diamond. It was found that nanocrystalline diamond at high temperature and ambient pressure kinetically is more stable with respect to graphitisation than usual diamonds.     

Raman study of the temperature-induced decomposition of the two-dimensional rhombohedral polymer of C60 and the intermediate states formed

Raman spectra of single crystalline two-dimensional rhombohedral (2D-R) polymer of C₆₀ were measured at ambient conditions after its high temperature treatment (HTT) in order to study the polymer decomposition process. The data obtained indicate that the 2D-R polymer remains stable after 0.5 h treatment up to ∼503 K, while at higher temperatures a material transformation takes place. New Raman lines appear in the Raman spectrum after HTT in the range of 513-553 K, related to the A_g(2) pentagon pinch (PP) mode of 2D tetragonal-like (2D-T-like) and 1D orthorhombic-like (1D-O-like) oligomers as well as to C₆₀ dimers and monomers, typical for an intermediate state of partially decomposed 2D-R polymer. Above 553 K, the material changes completely and its new composition is dominated by C₆₀ monomers with some possible inclusion of C₆₀ dimers. The activation energy of the 2D-R polymer decomposition, obtained from the dependence of the decomposition time on the treatment temperature, is E_A = 1.76 ± 0.07 eV/molecule.     

A simple carbon growth mechanism using atomic carbon addition by ring opening

Linear-carbon-chain molecules have been shown to form by the atomic carbon addition-ring opening reaction (ACAROR) mechanism. In this study, the synthesis of fullerene by ACAROR was attempted in order to determine the universality of this mechanism. The photochemical reaction of fullerene C₆₀ with C₃O₂ at 1100 °C produced fullerene C₇₀ with negligible side-products. The fact that the only chemically active species in the reaction system were :C and carbonyl carbene, :CCO, and that there were no by-products produced by the cleavage of the overall structure, together with the reported results on the gas phase reaction of fullerene C₆₀ with carbon atoms, leads to the conclusion that the likely formation mechanism is ACAROR. Carbon growth by ACAROR is simple and efficient and hence, becomes overwhelmingly dominant in unfavorable conditions, such as ultra low temperatures and incomplete combustion conditions.     

Ecotoxicology of carbon-based engineered nanoparticles: Effects of fullerene (C60) on aquatic organisms

To more fully assess the toxicity of water-soluble fullerene (nC₆₀), acute toxicity assays were performed on several environmentally relevant species. Included were the freshwater crustaceans Daphnia magna and Hyalella azteca, and a marine harpacticoid copepod, and two fish species, fathead minnow Pimephales promelas and Japanese medaka Oryzias latipes. The latter two species were used to assess sublethal effects of fullerene exposure by also assessing mRNA and protein expression in liver. Because prior studies found that both sonication and using tetrahydrofuran to solubilize fullerene increased the toxicity of nC₆₀, the nC₆₀ used in this study was prepared by stirring. For the invertebrate studies, nC₆₀ could not be prepared at high enough concentration levels to cause 50% mortality (LC₅₀) at 48 or 96 h. The maximum concentrations tested were 35 ppm for freshwater and 22.5 ppm for full-strength (35 ppt) seawater, since at higher concentrations the nC₆₀ precipitated out of solution. Daphnia 21-day exposures resulted in a significant delay in molting and significantly reduced offspring production at 2.5 and 5 ppm nC₆₀, which could possibly produce impacts at the population-level. For the fish, we found that neither the mRNA nor protein-expression levels of cytochrome P450 isozymes CYP1A, CYP2K1 and CYP2M1 were changed. The peroxisomal lipid transport protein PMP70 was significantly reduced in fathead minnow, but not medaka, indicating potential changes in acyl-CoA pathways.     

Low extraction recovery of fullerene from carbonaceous geological materials spiked with C60

Soxhlet extraction, sonication, and ultracritical extraction were tested with respect to their capacity to extract fullerenes from natural carbonaceous materials. Toluene solutions with various contents of synthetic C₆₀ were added to powdered graphite, shungite, bituminous coal, and quartz, with final C₆₀ concentration 0.1-100 ppm. The C₆₀-doped materials were leached in three kinds of extraction apparatus. High-performance liquid chromatography (HPLC) was used to analyse the fullerene content in the obtained toluene extracts. Surprisingly low yields of the C₆₀ extraction (most of them well below 5%) were determined for all the carbonaceous matrices and all the extraction techniques employed in the fullerene isolation. This finding has serious consequences for better understanding of the reported fullerene occurrence in the geological environment, because a greatly limited extraction yield can be responsible for some negative results of fullerene analyses in various geological samples. Both fullerene stability in solvents and fullerene interaction with the surfaces of geological carbonaceous matrices are discussed to explain the obtained results.     

Solid state studies of the C60. 2(CH3)CCl3 solvate

At room temperature, the hexagonal C₆₀. 2(CH₃)CCl₃ solvate (a = 10.13(1) Å, c = 10.84(1) Å), made of alternating layers of C₆₀ and solvent molecules, forms with a negative excess volume, and its desolvation enthalpy is virtually the same as the sublimation enthalpy of the pure solvent. Crystallographic and calorimetric studies vs temperature indicate that hexagonal C₆₀. 2(CH₃)CCl₃ changes at 211.7 K (1.3 kJ mol⁻¹ of solvate) into an intermediate triclinic phase which transforms at 189.7 K (4.1 kJ mol⁻¹ of solvate) into another triclinic phase.A crystallographic analysis in the series of hexagonal C₆₀. 2 YCCl₃ solvates (Y = H, Cl, Br, CH₃) reveals that: (i) the change in the unit-cell volume values is due to a change in axis c whose value depends on the size of Y, (ii) the molar volume of the solvates depends linearly on the molar volume of the solvents.Ageing studies at room temperature show that C₆₀. 2(CH₃)CCl₃ loses its solvent molecules within a few days or a few months, depending on storage conditions.