The preparation of carbon aerogels based upon the gelation of resorcinol-furfural in isopropanol with organic base catalyst

Carbon aerogels with high BET surface area were developed by sol-gel polycondensation of resorcinol and furfural in isopropanol using hexamethylenetetramine (HMTA) as a catalyst, and then directly drying the organic gels under isopropanol supercritical conditions, followed by carbonization under a nitrogen atmosphere. The preparation conditions of carbon aerogels were explored by changing the mole ratio of resorcinol to basic catalyst HMTA (R/C), the ratio of resorcinol to isopropanol (R/I), and the mole ratio of resorcinol to furfural (R/F). The effect of these preparation conditions on the porous structure of the carbon aerogels obtained was studied by nitrogen adsorption isotherms. According to the characterizations of TEM, SEM and nitrogen adsorption, the carbon aerogels obtained have a three-dimensional network that consists of carbon nano-particles with size from 20 to 30 nm, which define numerous micropores, mesopores and macropores. HMTA reacts not only as a catalyst but also as a reagent in the gelation polymerization. XRD characterization indicates that carbon aerogels have disordered nanocrystalline structures similar to activated carbon.     

Structure and electrochemical properties of carbon aerogels polymerized in the presence of Cu

Copper-loaded organic aerogels were prepared by sol–gel polymerization of resorcinol and formaldehyde in a solution of Cu(NO₃)₂. Carbon aerogels derived from the heat-treatment of the organic precursor kept their particulate structure, according to TEM observations. The particle size in Cu-loaded carbon aerogel samples becomes larger with a higher concentration of Cu incorporated into their texture, due to the presence of Cu²⁺ rather than the pH conditions in the sol–gel process. The nitrogen adsorption measurement of Cu-loaded samples showed their characteristic pore structure, i.e., a combination of microporosity and mesoporosity both developed in their texture. Especially, their advanced microporosity, which was still found after carbonization at 1273 K, was very unique, considering that micropores in organic aerogels often decreased in size during heat-treatment around this temperature range. This microporosity could be related to their stacking structure of aromatic layers revealed by STAC–XRD analysis, indicating a looser packing of aromatic layers in their structure. Application of Cu-loaded samples to electric double-layer capacitor is also discussed from the viewpoint of the amount of Cu as well as the pore structure of the samples.     

Phonon trigonal warping effect in graphite and carbon nanotubes

The one-dimensional structure of carbon nanotubes leads to quantum confinement of the wave vectors for the electronic states, thus making the double resonance Raman process selective, not only of the magnitude, but also of the direction of the phonon wave vectors. This additional selectivity allows us to reconstruct the phonon dispersion relations of 2D graphite, by probing individual single wall carbon nanotubes of different chiralities by resonance Raman spectroscopy, and using different laser excitation energies. In particular, we are able to measure the anisotropy, or the trigonal warping effect, in the phonon dispersion relations around the hexagonal corner of the Brillouin zone of graphite.     

Infrared-active vibrational modes of single-walled carbon nanotubes

The IR-active vibrational modes of single-walled carbon nanotubes have been observed by optical transmission through thin films of bundled nanotubes. Because IR-active chemical functional groups, e.g., -COOH, -OH, might be attached to the tube walls and contribute additional spectral features, we have also studied the effects of chemical purification and long-term high-temperature vacuum annealing on the IR spectrum. Through comparison with theory, we are able to assign much of the sharp structure observed in our IR spectra.     

Polarized raman study of aligned multiwalled carbon nanotubes

Polarized Raman spectra of high purity aligned arrays of multiwalled carbon nanotubes, prepared on silica substrates from the thermal decomposition of a ferrocene-xylene mixture, show a strong dependence of the graphitelike G band and the disorder-induced D band on the polarization geometry employed in the experiments. The experimental G-band intensity exhibits a minimum at straight theta(m) = 55 degrees in the VV configuration, in good agreement with theoretical predictions of a characteristic minimum at 54.7 degrees for A(1g) modes in single wall nanotubes, where straight theta(m) denotes the angle between the polarization direction and the nanotube axis.     

Magnetic phases in transition metal chloride intercalation compounds of graphite

Magnetic susceptibility measurements on graphite-FeCl₃ (stage 2), graphite-CoCl₂ (stages 2 and 3), and graphite-NiCl₂ (stages 3 and 5) intercalation compounds are reported, showing anomalies associated with magnetic transitions. The effect of magnetic fields on the transition suggests that the magnetic phases in all these systems are similar and independent of the separation of the planes of magnetic ions. The results for all samples for stage ≥ 2 imply two magnetic phase transitions closely separated in temperature.     

Lattice dynamics of graphite intercalation compounds

We apply a k_z-axis zone folding model that accounts for the staging symmetry to calculate the phonon dispersion curves for graphite intercalation compounds of arbitrary stage. The results are applied to calculate the phonon density of states, velocity of sound, and elastic constants for intercalated graphite.     

Electrical properties of ion-implanted poly(p-phenylene sulfide)

Ion implantation of impurities into thin films of poly(p-phenylene sulfide) (PPS) is found to increase the conductivity of the material by up to 12 orders of magnitude. The increase is stable under exposure to ambient conditions, in contrast to the instability of the conductivity increases in PPS produced by chemical doping with AsF₅. PPS films 0.1–0.2 μm thick are spin cast from solution onto interdigitated electrodes patterned on an oxidized silicon substrate. The room-temperature interelectrode resistance is measured as a function of implantation fluence. An estimate of film conductivity is obtained from this resistance with a simple model for the electrode and film geometry. A first experiment yielded similar conductivity increases for implantation of either arsenic or krypton. At a fluence of 1 × 10¹⁶cm^?;2, which corresponds to an average impurity concentration of 2.5 × 10²¹cm^?3, the conductivity reaches an apparently saturated value of 1.5 × 10^?5 (Ω cm)^?1. Infrared spectra of the films before and after implantation suggest that crosslinking may be present in the implanted films, and Auger studies show stoichiometric changes throughout the implanted layer. These results suggest that the observed conductivity changes are the result of molecular rearrangements produced by the implantation rather than the result of specific chemical doping. Specific chemical doping may, however, explain the results of a second experiment in which implantation of bromine resulted in substantially larger conductivities found to increase at an approximate linear rate from a value of 1.0 × 10^?4 (Ω cm)^?1 at a fluence of 1 × 10¹⁶ cm^?2 to a value of 4.0 × 10^?4 (Ω cm)^?1 at a fluence of 3.16 × 10¹⁶ cm^?2.     

On the possible magnetic field dependence of the nickel carbonylation rate

The interaction of Ni with CO gas to produce Ni(CO)₄ at 1 atm pressure, has been studied as a function of time, temperature (25 < T < 95°C) and externally applied magnetic field (H ? 500 Oe). We find no significant magnetic field dependence of the nickel carbonylation rate, in sharp contrast with results previously reported by Krinchik et al. The activation energy for this reaction is found to be 0.21 ± 0.05 eV independent of magnetic field.