Radiation-Induced Trichloromethylation of C60 Fullerene in Carbon Tetrachloride

The radiolysis of C₆₀ in CCl₄ has been studied in detail from the organic chemistry point of view. Solutions of C₆₀ in CCl₄ have been treated with γ radiation at 25, 50, 150, and 600 kGy, and the resulting products have been studied by electronic absorption spectroscopy, FT-IR spectroscopy, solid state ¹³C-MAS-NMR and by thermogravimetric analysis. The products have also been separated by liquid chromatographic analysis (HPLC). C₆₀ undergoes a multiple trichloromethylation reaction and on average about 6 trichloromethyl radicals add to the fullerene cage. The trichloromethylation reaction is accompanied by the dimerization and trimerization of C₆₀ fullerene. Also the oligomers appear to be trichloromethyl-substituted.

For reference the C₆₀ solutions in CCl₄ have also been photolyzed with UV light. Similar product as those observed in the radiolysis experiment have been detected. The main difference is that the photolysis products appear both chlorinated and trichloromethylated while the radiolysis product appear almost exclusively trichloromethylated.     

A STUDY ON THE THERMAL STABILITY TO 1000°C OF VARIOUS CARBON ALLOTROPES AND CARBONACEOUS MATTER BOTH UNDER NITROGEN AND IN AIR

The thermal behavior of graphite, C₆₀ fullerene, fullerene black (carbon soot containing fullerenes), extracted fullerene black and diamond has been analyzed to 1000°C by TGA-DTA (thermogravimetric analysis and differential thermal analysis) under a nitrogen flow at a heating rate of 20°C/min. Very small weight losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization has been observed. The sublimation of pure C₆₀ and the fullerene fraction of fullerene black (both pristine and extracted) has been observed and discussed.

The combustion reaction in air flow of graphite, C₆₀ and C₇₀ fullerenes, fullerene black (both unextracted and extracted), carbon nanotubes and diamond has been studied by TGA-DTA at a heating rate of 20°C/min. C₇₀ fullerene and fullerene black have been found to be the most reactive carbon materials with O₂. The role played by C₇₀ in the degradation of fullerites has been discussed. Among the carbon materials examined, the best resistance to O₂ attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C₆₀ fullerene appears closer to that of graphite although it appears to be more reactive with O₂. Samples of graphite and carbon blacks N375 and N234 have been studied by TGA-DTA in air flow before and after a radiation treatment with neutrons or γ radiation. The effect of the radiation damage in the combustion reaction of these carbon materials has been discussed.     

He ION BOMBARDMENT OF C60 FULLERENE: AN FT-IR AND RAMAN STUDY

C₆₀ fullerene films have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₆₀ have been followed by both FT-IR and Raman spectroscopy. Raman spectroscopy was the most useful tool for this scope. It has been clearly discovered that at low radiation dose C₆₀ forms oligomers but at higher radiation doses it is converted into an amorphous carbonaceous matter. The implications of these results on the possible survival of C₆₀ fullerene in the interstellar space have been discussed briefly in connection with the previous results on the effects of various types of electromagnetic radiation over C₆₀.     

Fullerane, the Hydrogenated C60 Fullerene: Properties and Astrochemical Considerations

Hydrogenated C₆₀ fullerene, C₆₀H₃₆ was prepared in different solvents using Zn/HCl as reducing agents. The structure of C₆₀H₃₆ was confirmed both by electronic and FT-IR spectroscopy and the purity of the reaction product was checked by HPLC analysis. It has been confirmed that C₆₀H₃₆ is not stable in air, especially in presence of light which enhances the oxidation. The oxidation of C₆₀H₃₆ was studied by FT-IR spectroscopy and by differential scanning calorimetry (DSC) in air; the formation of hydroxyl groups on the fullerene cage and ketonic groups (involving cage breakdown) have been detected. Furthermore, the action of O₃ on C₆₀H₃₆ was investigated and it has been found that O₃ exerts practically the same effect of air but causing an enhanced cage breakdown. The thermal stability of C₆₀H₃₆ was checked by a thermogravimetric analysis (TGA) coupled with a differential thermal analysis (DTA) under N₂ flow. The vaporization of C₆₀H₃₆ occurs at very high temperature: the DTA trace has shown an endothermic peak at 540°C (at a heating rate of 20°C/min). C₆₀H₃₆ shows an electronic absorption spectrum with a maximum at about 217 nm and it is able to match both in position and in half width the peak at 217.5 nm observed in the spectrum of the interstellar extinction of light which was attributed to hydrogenated, radiation processed and thermally annealed carbon dust. Similarly, the absorption spectrum of C₆₀H₃₆ is able to match several infrared emission bands (called UIBs) detected from certain astrophysical objects like the protoplanetary nebulae (PPNe). It is proposed that hydrogenated fullerenes can be used as model compounds in the laboratory simulation studies of interstellar carbon dust.     

ON THE REACTIVITY OF C60 FULLERENE WITH DIENE RUBBER MACRORADICALS. I. THE CASE OF NATURAL AND SYNTHETIC CIS-1,4-POLYISOPRENE UNDER ANAEROBIC AND THERMOOXIDATIVE DEGRADATION CONDITIONS

C₆₀ fullerene has been studied as thermal stabilizer and as antioxidant of both natural rubber (cis-1,4-polyisoprene) and synthetic cis-1,4-polyisoprene. The study has been conducted respectively under nitrogen flow and under air flow by simultaneous thermogravimetric analysis and differential thermal analysis (TGA-DTA) on rubber samples containing known quantities of fullerene in comparison to a “blank” of pure rubber. The results show that C₆₀ fullerene (in absence of oxygen) is a thermal stabilizer of cis-1,4-polyisoprene because it reacts with the polyisoprene macroradicals formed by the thermally-induced chain scission reaction slowing down the degradation reaction. Conversely, under thermo-oxidative degradation conditions (in air flow) fullerene C₆₀ acts as an antioxidant for cis-1,4-polyisoprene, provided that the heating rate of the samples is slow (5°/min). At higher heating rates (20°C/min) C₆₀ does not show any antioxidant effect.     

Solubility of Fullerene C60 and C70 in Toluene, o-Xylene and Carbon Disulfide at Various Temperatures

The solubilities of fullerene C₆₀ and C₇₀ in toluene, o-xylene and carbon disulfide between the melting point and boiling point of the solvents, respectively, have been measured. The temperature dependent solubility of C₆₀ displays anomalous behaviors. A solubility maximum of C₆₀ around 0 °C for toluene and carbon sulfide and around 30 °C for o-xylene was observed. The temperature-dependent solubility of C₇₀ behaves normally for all the three solvents studied.     

FORMATION OF FULLERENES AND CARBON CLUSTERS BY LASER IRRADIATION OF POLYMERIC FULLERENE OXIDE (FULLERENE OZOPOLYMER)

Polymeric fullerene oxide (PFO) prepared by prolonged ozonation of C₆₀ fullerene has been laser irradiated and the resulting products formed have been studied by ion cyclotron resonance mass spectrometry. It has been found that PFO produces a complete set of carbon clusters from C₆₀ up to C₁₆₄. The mechanism of formation of this set of fullerenic clusters implies necessarily a laser-induced carbonization step of the PFO substrate. Once the PFO target has been changed into the opportune carbon nanostructure by the laser radiation, the sequence of fullerene carbon clusters has been produced.     

He Ion Bombardment of C70 Fullerene: An FT-IR and Raman Study

C₇₀ fullerene films deposited on a silicon substrate have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₇₀ have been followed by both FT-IR and Raman spectroscopy. The results have been compared to the behavior of C₆₀ fullerene and discussed in an astrochemical context. The main conclusion is that C₇₀, contrary to C₆₀, does not form oligomers at low radiation dose but it is directly and gradually degraded to amorphous carbon (carbon black).     

Adsorption of Krypton and Cyclopentane on C60: An Experimental Study

The adsorption of krypton and cyclopentane on C₆₀ has been compared with that on reference carbon adsorbents. From krypton adsorption isotherms it follows that the fresh surface of C₆₀ has similar adsorption properties as electrochemical carbon. Cyclopentane molecules penetrate into the bulk of C₆₀ crystals and are localized in the octahedral interstices between fullerene molecules.     

A Model Compound Study About Carbon Black and Diene Rubber Interaction: The Reactivity of C60 Fullerene with Squalene

The reaction between squalene and C₆₀ fullerene was studied by electronic and FT-IR spectroscopy as well as by thermal analysis (TGA and DTA). This study was conducted to simulate in vitro, with model compounds, the interaction occuring during mixing between dienic rubber and carbon black. Squalene was used as model compound for dienic rubber and C₆₀ fullerene as model compound for carbon black since fullerene-like sites have been recently identified on carbon black surface.

The experimental results show that 2,5 molecules of C₆₀ become chemically bound to each squalene molecule under thermo-oxidative conditions simulating part of the mixing cycle between rubber and carbon black.

The implications of this result involve the explanation of the phenomenon known as “bound rubber”, which is the amount of chemisorbed polymer on filler surface after mixing, as well as the reinforcement effects observed by filling rubber with carbon black and the mechanical hysteresis of a rubber compound.     

On the Action of γ Radiation on Solid C60 and C70 Fullerenes: A Comparison with Graphite Irradiation

C₆₀ and C₇₀ fullerene have been treated in sealed flasks under Ar with γ radiation using radiation dosages ranging from 10 to 1000 kGy. The treated samples studied by electronic and FT-IR spectroscopy have not shown any evidence about fullerenes decomposition or radiopolymerization. However, through Raman spectroscopy it was possible to observe that γ radiation induces C₆₀ dimerization and trimerization. It has additionally been discovered that γ-treated C₆₀ (oligomerized) can be easily photopolymerized in the solid state by post-irradiation with laser light at 514 nm while this phenomenon has not been observed by using laser light at 782 nm and considerably higher laser power. Previously to this study, C₆₀ photopolymerization was known to occur only by using ultraviolet light.

For comparison also graphite was irradiated with 1000 kGy of γ radiation. Irradiated graphite shows considerably changes in its Raman spectrum, showing the formation of glassy carbon domains, perhaps carbon onions. The l_d bandshift to 1310 cm^-1 could be interpreted in terms of formation of hexagonal diamond.     

HPLC Diode-Array Analysis of C60 and C70 Polymeric Fullerene Oxides (Fullerene Polymeric Ozonides)

It is shown by HPLC diode-array analysis that the C₆₀ and C₇₀ polymeric fullerene oxides ([C₆₀]-PFOs and [C₇₀]-PFOs) which are polymeric ozonides, are composed by nine different components. The ozonide derivatives of C₆₀ and C₇₀ have been proved to be practically analogous in chemical structure and composition. The most important component of both [C₆₀]-PFOs and [C₇₀]-PFOs accounts for about 3/4 of each sample. The overozonation of [C₆₀]-PFOs in methanol has been studied and shown to not produce any significant changes.     

CO-DEPOSITION OF FULLERENES AND SULFUR FROM DILUTED SOLUTION

A new method to synthesize fullerene and sulfur compounds has been developed. Using this method, C₆₀S₁₆ and C₇₀S₁₆ compounds were grown from dilute fullerene and sulfur toluene solution. Their atomic structures were analyzed by x-ray diffraction with the single crystal. The C₆₀S₁₆ crystal is C-centered monoclinic structure of a=2.0874 nm, b=2.1139 nm, c=1.05690 nm and β=111.93°, and the C₇₀S₁₆ has a primitive monoclinic, P2₁/c, with lattice parameters of a=1.5271 nm, b=1.49971 nm, c=2.18024 nm and β=109.791°. In this compound, the structure of fullerenes is maintained and sulfur atoms form S₈ rings placed around the fullerenes.     

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.     

C60H18, C60H36 and C70H36 Fullerene Hydrides: Study by Methods of IR, NMR, XPS, EELS and Magnetochemistry

Fullerene hydrides of C₆₀H₁₈, C₆₀H₃₆ and C₇₀H₃₆ are studied by using IR, ¹H and ¹³C NMR, X-ray photoelectron and electron energy loss spectroscopies, and magnetochemistry. The comparison of IR and solid state ¹H and ¹³C NMR data for C₆₀H₃₆ with the theoretical ones allows the suggestion that fullerene hydride has a T symmetric structure and contains 4 isolated benzenoid rings located at tetrahedral positions on the surface of a closed skeleton of the molecule. The EELS revealed that the transition from fullerene to the hydride is accompanied by the decrease of the density of valence electrons. Magnetization measurements showed C₆₀H₃₆ to be a ferromagnet. The hydrogenated fullerenes were prepared by transfer hydrogenation procedures involving 9,10-dihydroanthracene. The compositions of the hydrides are determined by field desorption mass-spectral analysis.     

Near-Infrared Laser-Induced Decomposition of C60 Dissolved in Toluene

In this paper we describe the efficient and substantial decomposition of C₆₀ in toluene solution, induced by moderate intensity (I = 20 - 55 MW cm^-2) near infrared (γ = 1064 nm) laser radiation. This behavior is surprising since both uncharged fullerene and toluene do not have any absorption bands at this wavelength. The decomposition efficiency and products are investigated with UV-Vis absorption spectrophotometry and high-performance liquid-chromatography (HPLC). Possible mechanisms of the fullerene decomposition are discussed.     

GENERATION OF HIGHER FULLERENES FROM LASER ABLATION OF CARBYNE AND C60 PHOTOPOLYMER ASTROCHEMICAL IMPLICATIONS

Laser ablation of targets of carbonaceous matter containing carbyne nanodomains (the sp hybridised carbon chains) or targets of C₆₀ photopolymer produced carbon clusters which have been detected by FT-ICR (Fourier-Transform Ion Cyclotron Resonance) mass spectrometer. When the carbonaceous matter containing carbyne has been employed as laser target, no C₆₀ has been generated but only fullerene cages from C₇₄ up to C₁₂₄. Larger cages were also obtained but with odd number. Starting from C₆₀ photopolymer, laser ablation regenerates free C₆₀ and creates a sequence of C₆₀ superior homologues all possessing even number and each member of the series is separated from the preceding and the following member by the loss or by the addition respectively of a C₂ unit. Fullerenes up to C₁₆₂ have been recorded. The implications about the presence of free C₆₀ fullerene in the interstellar and circumstellar space, its formation from carbyne chains and its stability towards its photopolymerization tendency and its regeneration from the photopolymer together with its superior homologues have been discussed thoroughly in the present paper.     

Preparation and characterization of C60S16 and C70S48 thin films

In this study, we have investigated different methods for preparation of thin films of C₆₀ and C₇₀-sulfur compounds. Films of good quality were obtained by reaction of amorphous C₆₀ and C₇₀ films with a saturated sulfur solution in toluene at 40°C or with saturated sulfur vapour at a temperature of 140°C for several hours. The quality of the fullerene-sulfur films were strongly dependent on the microstructure of the initially deposited fullerene film and the synthesis temperature. X-ray diffraction analyses showed that both methods lead to the formation of films consisting of C₆₀S₁₆ and C₇₀S₄₈ (space groups C 2/c and Amm2, respectively). C₆₀S₁₆ films synthesised on Al₂O₃(012) and Si(100) substrates were texture-free while C₇₀S₄₈ films typically exhibited a preferential (100) orientation. The films were also characterised by Raman and IR- spectroscopy, which confirmed that the interactions between the fullerene molecules and the S₈ rings are weak. The fullerene-sulfur compounds were found to be unstable at high vacuum conditions. Both materials C₆₀S₁₆ and C₇₀S₄₈ are non-conductive at room temperature with conductivities less then 10⁻⁵ (Ω/cm).     

The Solubility of C60 Fullerene in Long Chain Fatty Acids Esters

A series of fatty acid esters of glycerol as linseed, sunflower, soybean and olive oils have been tested as C₆₀ fullerene solvents together with a mixture of methyl ester fatty acids derived from brassica oilseeds and used as a biofuel known as “biodiesel.” All the oils evaluated are effective solvents of C₆₀. The solubility of C₆₀ in the selected vegetable oils has been determined spectrophotometrically. The C₆₀ solubility in vegetable oils may pave the way for easier application of C₆₀ fullerene in medicinal chemistry and in additive chemistry for varnishes and fuels. It has been found that C₆₀ is not only soluble in the fatty acid esters but is also reactive with them under mild conditions, giving addition products easily recognized by a characteristic absorption band at 435 nm. The addition reaction mechanism has been discussed.     

Pyrolytic Trifluoromethylation of [76]-, [78]-, [84]-, and Aza[60]Fullerenes with Silver Trifluoroacetate; Evidence for Coordination of Fullerenes to Silver

Pyrolytic trifluoromethylation of [76], [78], [84], and aza[60]fullerenes with silver trifluoroacetate at 300°C results in extensive polyaddition of up to 18, 18, 20 and 20 CF₃ groups, respectively. In contrast to trifluoromethylation of [60]- and [70]fullerenes that give a full range of derivatives ranging upwards from C_n(CF₃)₂, [76]-, [78]-, and [84]-fullerenes only give C_n(CF₃)_6-18 derivatives, largely in the 10-12 CF₃ range; reaction with [76]fullerene is accompanied by formation of C₆₀(CF₃)₆ attributed to cage fragmentation. For aza[60]fullerene the hexa-addition level dominates, in contrast to its other reactions which give predominantly penta-addition products. All the compounds showed peaks at 1256±2 and 1180-1190 cm^-1, due to the CF₃ group, and peaks in this region are shown also by the soluble extract obtained on trifluoromethylation of nanotubes. As in trifluoromethylation of [60]- and [70]-fullerenes, the products obtained initially are involatile, attributed to formation os silver complexes; these are decomposed on subsequent solution in toluene. Mixed isomeric trifluoromethylated C₆₀F₈ derivatives viz. C₆₀F₇CF₃, C₆₀F₆(FG₃)₂, C₆₀F₅(CF₃)₃ and C₆₀F₄(CF₃)₄, and C₆₀F₄CF₃CF₂CF₃ (a C₆₀F₆ derivative) have been isolated from fluorination of [60]fullerene with MnF₃/K₂NilF₆ at 510°C.