Synthesis and structural investigation of new graphite intercalation compounds containing the perfluoroalkylsulfonate anions C10F21SO3, C2F5OC2F4SO3, and C2F5(C6F10)SO3

The preparation of graphite intercalation compounds (GIC’s) of three perfluorinated alkylsulfonate anions, C₁₀F₂₁SO₃⁻, C₂F₅OC₂F₄SO₃⁻ and C₂F₅(C₆F₁₀)SO₃⁻ is described for the first time. Pure stage 2 GIC’s are obtained by chemical oxidation of graphite with K₂MnF₆ in a solution containing hydrofluoric and nitric acids for 72 h. One-dimensional electron density maps derived from powder diffraction data are fit to obtain models for the intercalate interlayer regions (galleries) structures: the structure models provide details on anion concentrations, orientations, and conformations. In all cases, anion bilayers are observed with anion sulfonate headgroups oriented towards graphene sheets. Compared with structures calculated for the isolated anions, the intercalated anion conformations show changes in dihedral angles, involving rotations about C-C or C-O bonds. For the GIC containing C₂F₅(C₆F₁₀)SO₃⁻, the anion conformation change is related to the more efficient packing of anions in the intercalate gallery.     

Stability of hexagonal modification of fullerite C60

Stability of the hcp modification of fullerite C₆₀ under heating, compression, and mechanical grinding was studied. It was established that uniaxial load and mechanical grinding caused transition of the hcp modification into more stable fcc modification, while no transition was observed upon heating or hydrostatic pressure. The results were discussed in terms of the theory of the deformation of solids.     

New solid solvates of C60 and C70 fullerenes: The relationship between structures and lattice energies

The goal of this study was to establish the relationship between the X-ray and the thermodynamic data on fullerene’s solvated crystals. X-ray diffraction study of 12 solid solvates of C₆₀ and C₇₀ with different aromatic solvents have been performed. It has been demonstrated that the solid solvates under consideration were typical van-der-Waals complexes with the negative excess volumes, packing coefficients from 0.72 to 0.78, stable due to the formation of the fullerene to solvent bonds, reasonably described by six to 12 Lennard-Jones potentials. The atom-atom potential method has been used to describe both the crystal structures and the thermodynamics of the solid solvates. The minimization of the lattice energy with respect to the cell and rigid body parameters (T=0 K) has led to the crystal structures very close to the experimental ones. The minimum energies found have reasonably reproduced the calorimetric lattice energies of the solvates. The theory has also demonstrated its ability to account for the trends in thermodynamic stability of solid solvates, e.g., has predicted correctly the low stability of the hypothetical monoclinic solvate C₆₀·2C₆H₁₄.     

Synthesis of a hexagonal modification of C60 using cryoextraction

Samples of the hexagonal close-packed phase (h.c.p.) of fullerite C₆₀ with a low (less then 7%) content of more stable face-centered cubic (f.c.c.) phase were synthesized using cryoextraction with n-hexane. X-Ray diffraction analysis and thermogravimetry were applied for characterization of the samples. The role of n-hexane in the formation of the h.c.p. structure is discussed.     

C60 encapsulation inside single-walled carbon nanotubes using alkali-fullerene plasma method

It is reported that alkali-fullerene plasmas consisting of positive alkali-metal ions, negative fullerene ions, and residual electrons are effective in encapsulating fullerenes inside single-walled carbon nanotubes (SWNTs). When positive or negative bias-voltages are applied to SWNTs in plasmas, accelerated negative fullerene or positive alkali-metal ions are irradiated to the SWNTs through the plasma sheath, respectively. Field emission gun transmission electron microscopy (FEG-TEM) clearly shows that drastic structural modifications such as severe bending of SWNT bundles, tube dislocation, and tube tip termination take place after the ion irradiation. Energy dispersive X-ray spectrometry (EDS) confirms the existence of the alkali-metal elements in the sample after the alkali-metal irradiation. In addition to this, the SWNTs encapsulating fullerene molecules are directly observed after only 1 h fullerene-ion irradiation. These results suggest that our experimental system could permit us to intercalate not only fullerenes but also other elements inside the SWNTs by the applied-bias control. Raman scattering spectroscopy is also adopted for the purpose of evaluating pure SWNTs and fullerene encapsulated SWNTs.     

Polymeric fullerene oxide (fullerene ozopolymers) produced by prolonged ozonation of C60 and C70 fullerenes

The prolonged ozonation of C₆₀ and C₇₀ fullerene produces light brown to brown amorphous solids which are insoluble in chlorinated and hydrocarbon solvents but which are readily soluble in water, acetone and ethanol where they give dark-brown solutions. The polymeric and polyelectrolytic nature of these solids has been shown by viscosimetric and cryoscopic measurements. Due to the polymeric nature the solids have been called ‘ozopolymers’. The reactivity and the ozone uptake have been measured quantitatively during the ozonation of C₆₀ and C₇₀ fullerene in CCl₄. Three different C₆₀ ozopolymer samples have been produced at different degrees of ozonation: at O₃/C₆₀ molar ratio of 8, 14 and 26. The C₇₀ ozopolymer has been produced at an O₃/C₇₀ molar ratio of 30. All the samples have been studied by FT-IR spectroscopy and the C₆₀ ozopolymers have been easily reduced by the action of Zn dust and acetic acid or by the action of H₂S and studied by FT-IR. The action of oxidizing agents has been studied as well. C₆₀ ozopolymer is a polyelectrolyte rich in carboxyl groups and for this reason it possesses a high metal binding capacity similar to that of humic acids. The thermal stability of C₆₀ ozopolymer and its reduced derivatives as well as the thermal stability of C₇₀ ozopolymer has been checked by thermogravimetric analysis in nitrogen and air flow. Finally, the electrical conductivity of C₆₀ ozopolymer was found to be σ=2.8×10⁻⁸ S/cm which is three orders of magnitude lower than that of pure C₆₀.     

C60-polymer nanocomposites: evidence for interface interaction

Polyaniline-fullerene (PA-C₆₀) composites have been studied by Surface Enhanced Raman scattering (SERS) spectroscopy and X-ray diffraction. They were obtained by mixing solutions of polyaniline-emeraldine base (PA-EB) and C₆₀, as well as by chemical synthesis from aniline, sulfuric acid and potassium dichromate, with addition of C₆₀. The Raman bands peaking at 1330-1370 cm⁻¹, associated with a protonated structure were used as indicative for changes of the PA-EB phonon spectrum resulting from C₆₀ doping. The two types of compounds show different SERS spectra, also dependent on the metallic support used (Au or Ag). Variation of the SERS spectra with the type of metallic support is related to a chemical interface interaction between composite and metal. In mixture samples, a doped polymeric chain (with ionically attached C₆₀⁻) was evidenced by an increased fraction of quinoid rings. The SERS spectra of the chemically synthesized PA-C₆₀ reveals the existence of two polymeric structures: a doped PA (doped with C₆₀⁻ ions) and an undoped one, the latter with a structure of ‘pendant chain’ type. Structural (XRD) data reveal the presence of C₆₀ nano-zones, with a lattice parameter increase of 0.3-0.6%, attributed to slight oxidation. Detailed analysis of the fcc(111) line asymmetry suggests, in mixture samples, a boundary zone with an ‘expanded’ lattice, induced by ionic interface effects.     

Surface-enhanced Raman scattering studies on C60 fullerene self-assemblies

Surface-enhanced Raman scattering (SERS) was used to investigate C₆₀ self-assembling in solvents like pyrrolidine (Py) and N-methyl-2-pyrrolidinone (NMP) as well as in binary mixtures of o-dichlorobenzene (DCB)/acetonitrile (ACN) and DCB/NMP. For a correct evaluation of the modifications of Raman spectra induced by the C₆₀ aggregation, we have also presented the variations due to the measuring method, i.e., the signal dependence of the metallic support type and the surface roughness. The interaction between C₆₀ and the Au substrate, appearing as a chemical component in SERS generation, is mainly evidenced by a band at ∼342 cm⁻¹. In the aggregated phase, the intermolecular interactions lead to a reduction in the parent I_h C₆₀ symmetry as observed by a modified phonon spectrum. As a general feature, the spectral range below 800 cm⁻¹ is the most diagnostic for the aggregate assignment, the main indicative being the disappearance of the Raman bands associated to the radial vibration modes. SERS measurements have revealed two stages in the self-assembling of C₆₀ in NMP. In the beginning, charge-transfer molecular complexes that associate slowly in stable aggregates are formed by the binding of an NMP molecule to the C₆₀ cage. These complexes are noticed in the SERS spectrum by the replacement of the original H_g(1) band at ∼269 cm⁻¹ with two others at ∼255 and ∼246 cm⁻¹. In the aggregated phase, when using NMP and P as a solvent, the Raman spectrum reveals new bands that appear around 94 and 110-118 cm⁻¹, which are associated with the interball interactions. In a DCB/ACN solvent mixture, the self-assembling process is driven by weak van der Waals type forces and resembles a precipitation, yielding C₆₀ clusters of different size.     

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.     

Influence of the pressure-temperature treatment on the polymerization of C60 single crystals at 2 GPa-700 K

X-ray diffraction and Raman spectroscopy have been used to characterize the structures obtained when C₆₀ single crystals are treated at 2 GPa-700 K. Two different experimental procedures have been applied: the temperature is raised before the pressure is applied, or the opposite. The “heating-then-pressing” path leads to the tetragonal polymer structure (P4₂/mmc) together with a minor fraction of rhombohedral structure, which confirms previous results. In contrast, the “pressing-then-heating” path leads to a different state presenting similarities with both the rhombohedral and the disordered dimer structures. The results are discussed in light of the orientational and dynamical aspects of the C₆₀ polymerization.     

Impact of moisture on the thermal behavior of K2CO3-impregnated respirator carbons

The effect of moisture on the kinetics of the reaction of K₂CO₃-impregnated carbons with air at elevated temperature has been studied. Differential scanning calorimetry (DSC) measurements, isothermal DSC measurements and oven exposure tests all show that the reaction of the impregnated carbons with air is accelerated by the presence of moisture adsorbed by the impregnated carbon. Reaction kinetics extracted from isothermal DSC measurements show that this acceleration is caused by an increase in the frequency factor (γ₂) while the activation energy (E_a2) remains unchanged. For example, for an impregnated carbon containing 22.4% by weight moisture, the frequency factor was found to increase by about 65% compared to that of the dry precursor. X-ray diffraction experiments show that the increase in frequency factor is caused by a decrease in the particle size of the impregnant through a series of steps initiated by the adsorbed water. First, the deliquescent K₂CO₃ impregnant dissolves in sufficient adsorbed water; then this solution dries during heating to initially form KHCO₃, which subsequently decomposes to form small nano-particles of K₂CO₃ that apparently have a larger specific surface area and hence more catalytic activity. We suspect that the adsorbed moisture will cause such impregnant redistribution, and hence accelerated reaction kinetics with air, whenever deliquescent impregnants on hydrophilic surfaces are used.     

Rheological examination of C60 in low density solutions

Fullerene (C₆₀) in solutions of decahydronaphthalene (decalin) and a petroleum solvent viscous standard (PSVS) were studied to understand the rheological properties of fullerene-laden solutions. Although fullerene solubility limits have been published for a variety of solvents, little has been reported on the effect that fullerenes have on flow properties of fluids. In this study, the solvents were studied up to the point of saturation, whereby measurements of solubility, density, viscosity and elasticity were conducted varying the concentration level of C₆₀. Rheological measurements based on molecular interactions and on distortion of the flow were studied. No significant elastic contribution from the fullerenes resulted for the solutions below saturation. A pseudoplastic behavior with a lubrication effect imparted by the C₆₀ molecules was observed in the decalin solutions at concentrations below the saturation level. The PSVS solutions remain Newtonian for all C₆₀ concentrations while leading to an increase in viscosity.     

Ethylene physisorption on C60 fullerene

Monte Carlo computer simulation results on the adsorption of ethylene on C₆₀ fullerene are employed to locate the adsorption sites observed for the adsorption of other simple gases. The distributions of molecules according to the gas-solid interaction energy obtained from the simulations are in agreement with experimental results reported in the literature. We focused our attention on the isotherm obtained at 150 K. At this temperature, the molecules with a certain gas-solid energy have been identified and their location employed to find out the adsorption sites. This sort of distribution has been averaged over all the equilibrated configurations generated during the simulation. The results obtained confirm the assignment of adsorption sites previously reported for the adsorption of N₂, Ar, and CO₂. The distribution of molecules over the gas-gas interaction energy is also analyzed and the obtained results suggest that the adsorbed molecules prefer a T-shaped stacking. This conclusion is obtained through the analysis of the distributions with the aid of the gas-gas interaction potential. This observation agrees with recently published results by other authors. The information obtained from the microdensity profiles has also been employed to locate the adsorption sites.     

Electric current induced light emission from C60

We report the luminescence of C₆₀ crystals and films due to the passage of an electrical current. The current-voltage behavior is highly non-linear with light-emission beyond a threshold voltage. The emission spectrum is featureless and resembles black-body radiation with an effective temperature on the order of 1700 K. We report experiments aimed at distinguishing between electro- and thermoluminescence.     

XRD and TEM study of high pressure treated single-walled carbon nanotubes and C60-peapods

In situ synchrotron X-ray diffraction measurements of single-walled carbon nanotube and C₆₀-peapod samples under high pressures up to 13 GPa and at high temperature were carried out. Anisotropical shrinkages of their bundle two-dimensional lattices by compression at room temperature were observed. It was found that the lattices recover original forms reversibly upon pressure release. It was also found that irreversible phase transformations occur by raising temperature at the highest pressure. The high pressure and high temperature treated samples were examined by X-ray diffraction, transmission electron microscope, and Raman measurements. It was indicated by transmission electron microscope observation that hexagonal diamond is able to be synthesized by high pressure and high temperature treatment of C₆₀-peapods.     

Observation of intrinsic magnetic domains in C60 polymer

A C₆₀ polymer has been characterized for the first time with respect to impurity content and ferromagnetic properties by laterally resolved particle induced X-ray emission (PIXE), superconducting quantum interference device (SQUID) and magnetic force microscopy (MFM) in order to detect intrinsic ferromagnetic domains. In parts of the pure regions (concentration of magnetic impurities <1 μg/g), we found stripe-domain magnetic images with different orientations of domain magnetization. The size of the regions where magnetic domains were observed is ∼30% of the pure region. All these results reveal that the polymerized C₆₀ sample is a mixture of magnetic and non-magnetic parts and only a fraction of the sample contributes to the ferromagnetism.     

High energy-storage properties of [(Bi1/2Na1/2)0.94 Ba0.06] La(1−x) ZrxTiO3 lead-free anti-ferroelectric ceramics

Energy-storage properties of [(Bi_1/2Na_1/2)_0.94Ba_0.06]La_(1−x)Zr_xTiO₃ (BNT-BLZT, x=0, 0.02, 0.04, and 0.06) lead-free anti-ferroelectric ceramics fabricated via the conventional sintering technique were first investigated. Calculation from the X-ray diffraction results reveals that BNT-BLZT ceramic possesses a single perovskite structure phase. In addition, the P–E hysteresis loops measured at room temperature show that the BNT-BLZT (x=0.02) ceramics obtain the maximum P value of 37.5 μC/cm² and the largest energy-storage density W_max is 1.58 J/cm³. The temperature dependence of dielectric permittivity ε_r and dielectric loss tanδ illustrate that the addition of Zr can improve the piezoelectric properties of BT-BLZT ceramics. These properties indicate that BNT-BLZT ceramics might be a promising lead-free anti-ferroelectric material for energy storage application.