Gu Zhen-Nan

Separation of C60 and C70 fullerenes in gram quantities by fractional crystallization

Abstract A simple and inexpensive method for the purification of gram quantities of >99.5% pure C60 and > 98% pure C70 by a fractional crystallization process in carbon disulfide or o-xylene is described. This process is based on the finding that C60 was enriched in the solid deposit, whereas C70 was enriched in the mother liquor during crystallization of fullerenes due to differential solubilities of these two fullerenes, C60 and C70, in these solvents.

Superconductivity in Sn-doped C60

Abstract The superconductivity has been detected in the Sn-doped C60 samples by AC susceptibility measurements. The Sn-doped C60 sample is insensitive to air. EDS and XRD examinations show that the Sn-atoms have intercalated into the interstitial positions of the C60 lattice during a very slow diffusion reaction process.

Superconductivity and structure of alkali-doped fullerenes : K3C60 and Rb3C60

The linearly polarized Cu L3-edge x-ray-absorption near-edge structure (XANES) of Bi2Sr2CaCu2O8 + delta has been measured and the spectra are interpreted by the full multiple-scattering approach in real space. The polarized spectra over a range of 20 eV can be predicted in terms of the one-electron dipole (DELTA-l = +1) transition Cu 2p --> epsilon-d, probing the unoccupied d-like (l = 2) density of states projected on the Cu site with orbital angular momentum m(l) = 0, 1 in the E parallel-to z spectra, and the m(l) = 2, 1, and 0 in the E perpendicular-to c spectra. The oscillator strength for the dipole allowed transitions (DELTA-l = -1) Cu 2p --> epsilon-s is shown to be a factor of 100 weaker than the 2p --> 3d transitions. The Coulomb interaction in the final state between the Cu 2p core hole and the excited Cu 3d electron is found to be 5.5 eV forming a bound state below the continuum threshold, the well-known Cu L3 white line. On the contrary, the core hole induces a nearly rigid redshift about 1 eV of the high-energy conduction bands.

Single wall carbon nanotubes and their electrical properties

Single-wall carbon nanotubes (SWCNTs) were synthesized and purified. A water colloid of SWCNTs was prepared and used to assemble SWCNTs onto a gold film surface. Scanning tunneling microscopy (STM) images showed that short SWCNTs stood on gold film surfaces. Using STM tips made of SWCNTs, a crystal grain image of a gold thin film and an atomic resolution image of highly oriented pyrolytic graphite were successfully obtained. The electrical properties of short SWCNTs, which stood on the surface of gold film, were measured using STM. That SWCNTs stand on gold thin films is a promising technique for studying structures and properties of carbon nanotubes, as well as assembling and fabricating high-intensity coherent electron sources, field emission flat panel display, tips for scanning probe microscopes, new nanoelectronic devices, etc.

Field-ion microscopy observation of single-walled carbon nanotubes

Field-ion microscopy (FIM), a tool for surface analysis with atomic resolution, has been employed to observe the end structure of single-walled carbon nanotubes (SWCNTs). FIM images revealed the existence of open SWCNT ends. Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them. Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles. Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.

Preparation and Catalytic Properties of SWNTs-Supported Pd Catalyst

A Pd catalyst supported by single-walled carbon nanotubes (SWNTs) was prepared by a redox reaction between SWNTs and PdCl2 solution. The supported catalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermo-gravimetric (TG) techniques. Results showed that large quantities of Pd particles with diameters of ca 2 nm distributed evenly on the surface of SWNTs and the content of Pd was 14.13% (w, mass fraction) when using SWNTs and 12 mmol·L-1 PdCl2 as reactants. The supported catalyst, after reduction by H2, exhibited high catalytic activity in Suzuki reaction. The yield of biphenyl was 98.10% after 30 min reaction at 90 ℃.