Fullerene Mixture Research Articles

Growth and Characterization of C60Crystals from Pure C60and Fullerite

ABSTRACT Good quality C60 crystals have been grown from high purity C60 powder and fullerene mixture (C60/C70) by vacuum sublimation method. The grown crystals were characterized with Optical micro...

Separation of C60/C70 mixture on activated carbon and activated carbon fibres

The possibilities for preparative separation of fullerene (C60/C70) mixture by flash chromatography on activated carbon or activated carbon fibres as a stationary phase are shown. The effect of the nature of the activated carbon and of its specific surface area on the elution time, Chromatographic peak width, amount, and purity of the recovered product (C60 or C70) was studied. Different possibilities for diminution of the quantities of the stationary phase and the eluent and of the duration of separation are described.

Fullerene doped glasses

Optical glasses doped with a fullerene mixture of C60/C70 were made in our lab. Three peaks, corresponding to C60, C70, and a modified fullerene (possibly its oxide), respectively, were found in the chromatogram of high performance liquid chromatography (HPLC) analysis of the 0.1-wt % fullerene doped phosphate glass. Depending on the doping procedure and impurity, weak to strong interacting between C60 and its environment was found by the nuclear magnetic resonance study. For both phosphate and fluorophosphate glasses with 0.01-wt % fullerene mixture doping, the eigen UV absorption edge showed a significant blueshift, indicating that the bonding between the nonbridging oxygen in these glasses was subjected to a strong change due to the fullerene doping.

Convenient separation of high-purity C60 from crude fullerene extract by selective complexation with AlCl3.

A purification procedure for C60 from the fullerene extract has been developed using the differential complexation of C60 and C70 with AlCl3 (or its conjugate acid) in CS2 solution. In addition to pure C60 (>99.8%), the procedure also provides C70-enriched fullerene mixture.

Preparation and characterization of Langmuir-Blodgett films containing fullerene

Langmuir-Blodgett films containing a mixture of fullerene (C 60) and arachidic acid (C 20H 40O 2) were deposited on three different substrates (glass, quartz and silicon). The details of the dipping procedure are explained for three different values of the monolayer pressure. Optical studies in air at room temperature on films of various thicknesses deposited on quartz substrates were performed. From transmittivity and reflectivity measurements the refractive index n and extinction coefficient k have been evaluated in the UV-visible spectral range. Finally, a preliminary structural analysis carried out by means of scanning electron microscopy has shown that the films are homogeneous with some isolated cracks.

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

3He NMR: A Powerful New Tool for Following Fullerene Chemistry

The fullerenes react readily with a variety of reagents. Following their reactions with NMR spectroscopy has not been easy. If several products are formed or, as is common, bis-adducts are produced, assigning the carbon peaks is difficult or impossible. Continuing our studies of endohedral fullerene compounds of noble gases, we have recently used high pressure and heating to introduce [sup 3]He into C[sub 60] and C[sub 70], increasing incorporation levels to around 0.15%. We have used this material to obtain the first [sup 3]He NMR spectra of helium compounds. Each helium-labeled fullerene gives a single sharp peak. The large chemical shifts (C[sub 60], [minus]6.3 ppm; C[sub 70], [minus]28.8 ppm from dissolved [sup 3]He as reference) show that there are substantial aromatic ring currents modifying the magnetic field experienced by the helium nucleus in the center of the fullerenes. We expected that altering the [pi]-bonding structure of the fullerene through reaction would produce substantial shifts in the [sup 3]He peak. We have now verified this expectation. We have subjected a [sup 3]He-labeled fullerene mixture (about 70% C[sub 60], 30% C[sub 70]) to the reaction conditions recently reported by Maggini, Scorrano, and Prato for the azomethine ylide addition to fullerenes to formmore » N-methylpyrrolidines. It is striking that addition to just one of the 30 double bonds of [sup 3]He C[sub 60]produced a 3 ppm shift of the helium upfield. At this point, even qualitative rationalization of the direction of these shifts would be speculative. It is interesting that the adducts of C[sub 70] shift downfield. 6 refs., 2 figs.« less

Nonaqueous packed capillary electrokinetic chromatographic separations of large polycyclic aromatic hydrocarbons and fullerenes.

Polycyclic aromatic hydrocarbons (PAH) and a fullerene mixture (C60/C70) were separated with capillary columns (50 microns ID) packed with a reversed-phase packing (octadecylsilica, 3 microns diameter) using electrokinetic pumping. Nonaqueous (acetonitrile modified with methylene chloride or tetrahydrofuran, THF) mobile phases were used for these experiments. The effects of mobile phase composition on such factors as electroosmotic flow, plate height, and capacity factor (k') are reported. The less polar solvents methylene chloride and THF produced predictable reductions in k' when used to modify an acetonitrile mobile phase. Large amounts of the less polar modifiers (50% v/v) also resulted in a fourfold decrease in flow rate. This meant that even with a decrease in k', the retention time increased. Nonaqueous capillary electrokinetic chromatographic (CEC) separations gave efficiencies as high as 160,000 plates/m. Use of nonaqueous mobile phases provided small currents which in turn diminished the role of heating effects on efficiency. The nonaqueous system also provided greater solubility for the hydrophobic solutes. A Van Deemter plot for an acetonitrile mobile phase was obtained that exhibited expected trends in plate height with flow rate and k'. Solvent rinses with water and THF are shown to have only small effects on retention and flow rate.

Analysis of fullerenes by reversed-phase high-performance liquid chromatography

Chromatographic separation of fullerenes was achieved with a conventional reversed-phase analytical system. A tetrahydrofuran—acetonitrile mobile phase (60:40) (1.0 ml/min) used with a 25 cm ODS column separates C 60 and C 70 with a resolution of 6.4 and an analysis time of 11.4 min. This method is convenient and offers sufficient resolving power to be applied to the analysis of a variety of fullerenes and fullerene reaction product mixtures. The mobile phase allows use of the sensitive ultraviolet absorbance bands of fullerenes in detection. The method is compared with other reversed-phase methods for analysis of fullerene mixtures.

Fullerenes as Photocatalysts: Studies on Decomposition of Water and Oxalic Acid

Abstract The paper presents data on the photocatalytic decomposition of water and destruction of oxalic acid using the fullerene mixture as a photocatalyst. Based on the data obtained, mechanisms are proposed for the destruction of oxalic acid and splitting of water.

Preparative separation of higher fullerenes by high-performance liquid chromatography on a tetrachlorophthalimidopropyl-modified silica column

The preparative chromatographic separation of buckminsterfullerene (C 60) and the larger, related carbon spheres C 70, C 76, C 2 v - and D 3-C 78 and C 84 on a tetrachlorophthalimidopropyl-modified silica stationary phase was achieved and quantified. A 1-mg amount of a mixture of the higher fullerenes per injection can be separated on a 250 mm × 20 mm I.D. column using dichloromethane- hexane (33:67, v/v) as the mobile phase and 1,2-dichlorobenzene as the sample solvent.

High-performance liquid chromatographic separation of fullerene mixtures using a novel stationary phase

High-performance liquid chromatographic separation of fullerene mixtures in the range C60 to C100 can be achieved using a novel stationary phase which rivals the performance of the more expensive ‘Pirkle-type’ columns currently employed.

Formation and collision‐induced dissociation behaviour of doubly charged gas‐phase fullerene anions C, C and higher homologues. Collision‐induced electron‐stripping process

AbstractDoubly charged molecular anions M2− of fullerenes are formed in the gas phase under chemical ionization conditions with isobutane as the reagent gas. The efficiency of double electron attachment increases with increasing size of the fullerenes: the C ion is the most abundant doubly charged anion in the negative‐ion CI mass spectrum, although the concentration of C70 was about 12% in the fullerene mixture examined. Under low‐energy collision‐induced dissociation conditions an electron is ejected from the doubly charged C ion resulting in the singly charged molecular anion C˙. This process appears to be the first report of the ejection of an electron (electron stripping) from a doubly charged anion in the gas phase: .

Determination of C60/C70 ratios in fullerene mixtures and film characterization by scanning tunneling microscopy

Fullerene powder mixtures with different C60/C70 ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C60/C70 ratios show that C70 molecules display a larger apparent diameter (0.8 nm) and corrugation than C60 molecules (0.7 nm). The C60/C70 ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C60/C70 ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C70 molecules and vacancies). In films prepared to have a C60 coverage of less than one monolayer, stable structural units of the C60(111) surface consisting of three or seven C60 molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed.

Structure and dynamics of buckyballs

Abstract C60 (buckminsterfullerene) is the most well-known, the most stable, the most readily available, and in many respects, the most interesting member of a recently discovered class of pure carbon molecules known as the fullerenes (1). A method of making macroscopic quantities of fullerene mixtures was described in late 1990 (2), and since that time many scientists have been investigating the properties of C60 the higher fullerenes, and their various compounds and derivatives. To date most of the neutron scattering research on these materials has been carried out either at the 20 MW research reactor of the National Institute of Standards and Technology (NET) (3), or at the ISIS spallation source, Rutherford-Appleton Laboratory (RAL) (4). In this article we shall describe the research that has interested and occupied us the most, namely diffraction and low energy inelastic scattering studies of solid C60,. Much of the work that we omit is discussed in two recently published reviews (5,6).

Some applications of thermal analysis to fullerenes

Thermal analysis is a convenient means of characterizing the soot used as a source of the carbon clusters, the extracted mixture of fullerenes, and the individual clusters themselves. TG in an inert atmosphere will rapidly assay the volatile fractions, presumably the lower molecular weight clusters. TG in oxygen indicates — a slight weight gain for the soots and clusters prior to their combustion. DSC in oxygen is used to determine the heat of combustion for the separated C60 and C70 materials. The combustion occurs around 300°C for the clusters. There is a small exothermic peak before this which is attributed to the oxidation associated with the slight weight gain. The heats of combustion measured are −18.7 and −21.0 kJ·mol−1 for the C60 and C70 respectively. MS-EGA indicates the loss of small amounts of water and argon at temperatures around 250°C in vacuum and of solvent at about 350°C prior to sublimation.

Thermal analysis of fullerenes

The ready synthesis of significant quantities of carbon clusters from soot has thrust this class of materials into the scientific limelight. Thermal analysis is a convenient means of characterizing the soot used as a source of the clusters, the extracted mixture of fullerenes, and the individual clusters themselves. The relative amounts and reactivities of the clusters are currently under intensive scientific investigation.