No abstract

Lithium- or potassium-doped carbon nanotubes can absorb approximately 20 or approximately 14 weight percent of hydrogen at moderate (200 degrees to 400 degrees C) or room temperatures, respectively, under ambient pressure. These values are greater than those of metal hydride and cryoadsorption systems. The hydrogen stored in the lithium- or potassium-doped carbon nanotubes can be released at higher temperatures, and the sorption-desorption cycle can be repeated with little decrease in the sorption capacity. The high hydrogen-uptake capacity of these systems may be derived from the special open-edged, layered structure of the carbon nanotubes made from methane, as well as the catalytic effect of alkali metals.

Silver nanoparticles have been prepared by photoreduction of silver nitrate with 254 nm UV light in the presence of poly(N-vinylpyrrolidone). The effects of PVP concentration on the particle size, the UV−vis absorption peak, and the rate of the photoreduction process were studied. The average particle size ranged from 15.2 to 22.4 nm, with the corresponding UV−vis absorption peak position at 404−418 nm in 1−0.25 wt % PVP. The rate of the photoreduction process was observed to increase with the PVP concentration. X-ray photoelectron spectroscopic studies further revealed that the polymer interacts with silver particles through the oxygen atom in the >CO group. A negative shift of binding energy in the Ag 3d5/2 for silver nanoparticles was observed.

Carbon nanotubes prepared by catalytic (CO) disproportionation were studied using TEM, XRD, UPS, XPS, and optical spectroscopies. In comparison with graphite, the carbon nanotubes show greater interplanar distance, smaller work function, steeper Fermi edge, negative core-level shift, and stronger plasma excitation. Their valence band is basically the same as that of graphite, with lower intensity in the binding energy region of 2-7 eV. The carbon nanotubes exhibit a strong optical limiting effect, superior to both carbon black and C 60. [S0031-9007(99)08764-5]

Carbon nanotubes can be functionalized by oxidation of HNO 3 or H 2 SO 4 -HNO 3 . The latter shows a higher capability in producing a high density of surface functional groups. These groups can act as specific nucleation sites for a well-dispersed deposition of Pt clusters on the surface of carbon nanotubes. These modified carbon nanotube materials were investigated by TEM, XPS, and DRIFT. A deposition mechanism is tentatively proposed and discussed.