Graphite and carbon black samples were laser ablated in an FT-ICR (Fourier transform-ion cyclotron resonance spectrometer) by Nd-YAG laser under high vacuum in conditions recalling those existing in the interstellar medium. It is shown that graphite gives a regular sequence of polyyne and cyclopolyyne chains from C-10 to C-27 and additionally produces 2% of C-60 fullerene. When carbon black is used in place of graphite under the same conditions, no C-60 fullerene was produced and also the sequence of polyyne species generated was very irregular. If really carbon black structure and elemental composition approaches more closely than pure graphite the structure of the carbon dust, we can predict that C-60 fullerene should not be produced from the thermal decomposition of this dust in high vacuum.
Molecular dynamics simulations of the high temperature phase of C-60 have been performed for different intermolecular potentials proposed previously for the intermolecular interactions in solid C-60, i.e. the van der Waals (vdW) potential and two different bond charge models. In contrast to what has been previously inferred from a mean-field theory, bond charges do lead to a much better reproduction of the experimental results, including the preferred orientations of the C60 molecule, than the vdW potential.
The solubility of [60]fullerene in various solvents has been correlated to the molar volume ratio of [60]fullerene and the respective solvent. The solubility varies linearly with the molar volume for the alcohol series and the heteroatom containing solvents, though specific interactions of the charge transfer type seem to dominate in the case of aromatic hydrocarbons and the halogenated solvents. The symmetric nature of the [60]fullerene and its clustering behavior could be the reason for the solubility variations observed in the solvents where specific interactions are present. The aggregation behavior of [60]fullerene molecule studied by laser light scattering technique in the solvent mixture of toluene and N,N-dimethyl formamide confirms the cluster formation and its dependence on the volume ratio in the binary solvent mixture.
Graphite and carbon black N234 radiation damaged with gamma radiation or with neutron bombardment have been studied with Raman spectroscopy. The radiation damaging results completely evident in the case of graphite with the development of the I-D band, but it is less evident in the case of an already disordered material like carbon black. The radiation damage caused by gamma radiation appears comparable to that caused by neutrons, at least for the radiation dose used. Moreover, in both cases there are evidences that the radiation-induced defects appear in carbon material under the form of fullerene-like sites (onion-like carbon and carbon nanotubes) as well as under the form of hexagonal diamond and hence sp(3) hybridized carbon.Neutron damaged carbon black once treated with laser light at 782 nm shows a featureless Raman spectrum with a maximum at 2287 cm(-1) suggesting that neutron bombardment followed by laser light annealing causes the formation of carbyne (polyyne) domains.The radiation treatment of graphite, carbon black and even amorphous precipitated silica enhances in a spectacular way their natural rubber adsorption power. This has been measured through the "bound rubber phenomenon" which is the irreversible rubber grafting, reaction on filler surface. This enhancement has been attributed to the increased concentration of "defective" sites on filler surface induced by radiation treatment which improves the rubber-filler interaction. Another macroscopic consequence of this increased interaction can be manifested in SBR-based or in natural rubber based vulcanizates filled with radiation pre-treated carbon blacks. In both cases a dramatic improvement in the reinforcing effect as measured by stress-strain curve can be observed.
C-60 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 C-60 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 C-60 acts as an antioxidant for cis-1,4- polyisoprene, provided that the heating rate of the samples is slow (5 degrees /min). At higher heating rates (20 degreesC/min) C-60 does not show any antioxidant effect.
Carbon nanotubes were produced by plasma discharging of graphite electrodes in air at 1 atm. The combined yield of CNTs and carbon nanoparticles is similar to 20 wt % relative to the mass of cathode deposits or 14 wt% of graphite electrode consumed. The yields of CNTs and carbon nanoparticles under different inert gas atmospheres, such as He, Ar, N-2, and air were compared.
Carbonaceous matter containing carbyne has been synthesized by thermal decomposition of diiodoacetylene in boiling xylene or in o-dichlorobenzene. FT-IR and Raman spectroscopy together with powder x-ray diffraction were used to study the structure of the decomposition products and to identify the presence of carbyne domains. Together with carbyne domains, amorphous carbon was produced having residual iodine in its structure as shown by TGA-DTA. Additionally a crystalline charge-transfer complex between diiodoacetylene and o-dichlorobenzene has been identified. Thermodynamic calculations were performed in order to better understand the possible decomposition pattern from diiodoacetylene.
It is shown by AM1 and MM+ calculations that the heat of formation of chlorinated derivatives of C60 reaches a minimum for adducts having 20–26 chlorine atoms. Another minimum (at higher energy than the previous) is observed for the adduct having 36 chlorine atoms. The theoretical results obtained are compared with the previous experimental results. Some of the experimental results can now be more easily understood. The electronic spectra of chlorinated derivatives and the thermodynamic spontaneity of the nucleophilic substitution reaction of chlorofullerene are also elucidated by means of theoretical calculations.
Fullerene derivatives which have carboxylic acid moiety effectively inhibited glutathione reductase activity. Preincubation of the reductase and fullerene derivative at 37 degreesC enhanced the inhibition activity.
The quasiclassical approach has been used to calculate a fullerene and an endofullerene molecular interaction with electric fields. A physical model for an endofullerene molecular polarizability in electric fields has been developed and equations describing the interaction have been deduced.
The free radical scavenging property of fullerenes and their derivatives is demonstrated by a facile color reaction of C60 with the 1,1-diphenyl-2-picryl hydrazyl radical. A rapid test by simply monitoring the reaction using ultraviolet-visible spectroscopy is suggested.
Two star-like C60-polymethylmethacrylate (C60PMMA) copolymers, which are soluble in a wide range of organic solvents, have been synthesized by free-radical polymerization. The polymers can be described by the formula 1%C60PMMA and 10%C60PMMA. They consist of a C60 core with a maximum of 6 polymethylmethacrylate (PMMA) chains. The difference between these derivatives is the weight distribution of C60. Nanosecond pulse radiolysis and laser flash photolysis studies, UV/VIS spectroscopic and fluorescence measurements have been performed to investigate the photophysical properties of 1%C60PMNIA and 10%C60PMMA. The absorption spectra of the C60PMMA co-polymers exhibit a band at 210 to 220nm for PMMA and at 330nm for C60 independent of the solvent polarity showing that they have a small dipole moment in the electronic ground state. The triplet-triplet (T-T) absorption spectra of 10%C60PMMA in toluene and chloroform peak at the same wavelength and are broader than those of C60, indicating that they are addition spectra of 10%C60PMMA and neat C60. Physical addition of PMMA increases the solubility of C60 in chloroform, but does not change the T-T absorption spectrum, unless PMMA is chemically bound to C60. Gaussian band analysis of the T-T absorption spectra of 10%C60PMMA results in an additional and for pure 10%C60PMMA at (626.8 +/- 15.7)nm in toluene and (652.4 +/-1.9)nm in chloroform. The triplet state lifetime of 10%C60PMMA is smaller than that of C60 at 79 mus. The quantum yields of singlet oxygen production (DA) decrease with the C60 content in the co-polymer. The values for 1%C60PMMA and 10%C60PMMA in polar chloroform are 4% and 26% respectively. The intersystem crossing from S(1) to T(1) as well as the triplet state lifetime decrease with increasing number and length of PMMA chains connected to C60. 1%C60PMMA also shows no T-T absorption suggesting a relative high photochemical stability for 1%C60PMMA.
The thermal stability of the C-60 photopolymer, the C-60 ozopolymer, and photochlorinated C-60 was studied by thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and TGA-differential thermal analysis techniques up to 950 degreesC in comparison to graphite and pure C-60 The ozopolymer was found to be the least stable material followed by C60Clx. The resulting residual carbonaceous matter formed by the decomposition of the photopolymer and the ozopolymer has been studied by Fourier transform-infrared (FTIR) spectroscopy and has been found to be completely comparable to carbon black. The thermal decomposition of the C-60 photopolymer prepared in solution yields negligible amounts of C-60 The main product is carbon black.
Since endohedral fullerenes exhibit unique features there is growing demand for their production and purification in high quality and quantity. This work shows how the chromatographic enrichment process can be optimized, for the separation of N@C60 and N@C70 from their respective empty parent compounds.
In this work, we report the production of NbSe2 (niobium diselenide) nanotubes formed by irradiating NbSe2 with high doses of electron irradiation. The apparatus used for the irradiation was a 2 MeV Van de Graaff accelerator at the following conditions: voltage 1.3 MeV, current 5 muA, dose rate 25 kGy/min, and total dosage 1000 kGy. These conditions were maintained fixed while irradiation dosage was changed between 100, 250 and 500 Mrad. We observed enormous and very well defined nanotubes with a length of several nm and width of a few nm, which are hollow and capped at one end. As the level of irradiation is increased to 500 Mrad, onion-like structures were observed.
Diels-Alder reactions of quinuclidines with fullerenes C-60 and C-70 and mono- and bisadducts from the fullerenes C-60 and C-70 are reported.
C-60 was incorporated onto poly(ethyl methacrylate), poly(methyl acrylate) and poly(ethyl acrylate). The miscibility of poly(vinylidene fluoride) (PVDF) with the C-60-containing polymers was examined. PVDF is miscible with all the Six C-60-containing polymer samples as shown by the optical clarity of the melt and the existence of a single glass transition temperature in each blend. The polymer-polymer interaction parameters of various blend systems were evaluated by the melting point depression method.
Although there exists no general agreement on mechanistic pathways for fullerene formation, there are some reasonable schemes in the literature explaining most of the features. However, as far as the existing production processes and the final yields are concerned, not the formation but rather chemical stabilization of the relatively hot products was more influence on the final production yield. A continuous helium jet was blown into the reactive zone by a quartz microprobe located 20 mm away from the are to enhance rapid removal of the products from the high temperature zone. Decreased residence times appear to improve production efficiency.
We have investigated the photopolymerization and thermal decomposition of photochemical products with high density excitation (11–480 mW/mm2) by means of time-gated Raman scattering experiments in C60 single crystal. The temperature of laser-illuminated area was measured by Stokes and anti-Stokes Raman scattering of C60 Hg(1) mode, which shows the local temperature rise with increase of laser power density. The Raman intensity of Ag(2) mode rapidly decreases with irradiation time for I<170 mW/mm2 indicating the rapid decrease in C60 monomer density due to photopolymerization. For higher power densities, however, the Raman intensity increases after showing a minimum, which suggests a dissociation of photopolymers. The results are well explained by the rate equation model taking into account photochemical generation and thermal decomposition of photo-produced dimers. These results indicate the strong laser illumination simultaneously induces the photopolymerization and thermal decomposition.
We report the formation of carbon nanotubes (CNTs) in, high density when mischmetal Mm (a natural mixture of several rare earth elements) is used as catalyst. Mm has been found to work as a better catalyst than either lanthanum (La) or cerium (Ce). The formation of composite nanorods when the catalyst La is used in very high concentration (∼90wt.%) has also been described and discussed.
