Positron Spectroscopy of Nanodiamonds after Hydrogen Sorption (original) (raw)

Effect of γ-ray irradiation on the sorption of hydrogen by nanoporous carbon materials

Low Temperature Physics

The effects of radiation exposure in a hydrogen atmosphere on hydrogen sorption by a synthetic porous carbon nanosorbent, SCN (spherical carbonite saturated). The exposure was created by γ-rays from cobalt-60 (photon energy 1.2 MeV, irradiation dose 4.8 × 107 rad) in a normal hydrogen atmosphere at a pressure of 1 atm and a temperature of 300 K. The processes of hydrogen sorption-desorption by SCN samples before and after irradiation were studied in a temperature interval of 15-1173 K. It was found that the irradiation of SCN in a hydrogen atmosphere significantly increased the amount hydrogen sorbed in the sample. We conducted a comparison with the results of earlier studies investigating the influence of irradiation on the sorption of hydrogen by single-walled carbon nanotubes. The amount of physically sorbed hydrogen in the synthetic SCN sorbent that was irradiated in the hydrogen atmosphere, is four times greater than the amount of hydrogen that was physically sorbed by the sing...

Calorimetric and Positron Lifetime Measurements οf Hydrogenated Carbon Nanocones

Acta Physica Polonica A, 2010

Two carbon nanostructured samples containing 5 and 20% of carbon nanocones in their volume were investigated. Using the Sieverts apparatus the hydrogen was loaded into the samples. The measurements of heat capacity in the temperature range from 100 K to 320 K and the positron lifetime measurements at the room temperature were performed for hydrogenated and non-hydrogenated carbon nanocones. The desorption of hydrogen at the temperature of 230 K is deduced from the heat capacity measurements. The detection of the positronium, the bound state of positron and electron, in the measured samples reveals the presence of open volume defects of ca. 0.198 ± 0.002 nm.

Atomic hydrogen treatment of nanodiamond powder studied with photoemission spectroscopy

Physical Review B, 2007

The effect of atomic hydrogen treatment upon the surface of partially graphitized nanodiamonds has been studied by photoemission spectroscopy. The C1s core level peak and valence band spectra of a partially graphitized nanodiamond sample were compared with those following hydrogen treatment and following subsequent annealing. We have observed a difference in the binding energy of the sp 3 component of the C1s peak and in the valence band which we believe can be assigned to either upward or downward band bending due to surface graphitization and hydrogenation of nanodiamonds, respectively. The data confirms that the graphitic layers which initially cover the nanodiamond particles can be removed through exposure to atomic hydrogen. This method could enable the preparation of hydrogen terminated and separate nanodiamond particles.

Hydrogen sorption by carbon nanomaterials

Russian Microelectronics, 2011

Hydrogen sorption by carbon nanomaterials has been investigated at a temperature of 298K and pressure of 10 MPa by single and multiwalled nanotubes, graphitic nanofibers, and split graphite. The mea surement error is calculated for the presented method. The obtained results are analyzed on the base of the physical-chemical foundation of sorption.

Hydrogen sorption by the bundles of single-wall carbon nanotubes, irradiated in various gas media

Low Temperature Physics, 2013

The effect of radioactive irradiation on H 2 sorption by bundles of single-wall carbon nanotubes (SWNTs) has been investigated in various gas media. The samples were irradiated with c-quanta (1.2 MeV) of 60 Co ((1.5-1.7) Â 10 7 rad) radiation at room temperature in deuterium, nitrogen, and oxygen atmosphere (P ¼ 1 atm), and in a vacuum. The processes of H 2 sorption and desorption in the SWNT bundles were investigated before and after irradiation in the temperature interval 12-1270 K. It is found that irradiation in a gas environment has a significant effect both on the low-temperature H 2 sorption induced by the weak physical interaction, and the chemical H 2 sorption by the SWNT bundles. A phenomenological model has been proposed to explain the defect generation in carbon nanotubes irradiated in gas media. V

Low-temperature sorption of hydrogen by porous carbon material containing palladium nanoclusters

Low Temperature Physics, 2020

The sorption of hydrogen isotopes by a composite nanostructured carbon material containing palladium clusters with an average size of 3-5 nm was studied in the temperature range of 8-290 K. The total amount of sorbed hydrogen strongly depends on the method of manufacturing the composite and is 2-4.5% of the sample mass. In the kinetics of hydrogen sorption and desorption by a composite, two processes with characteristic times differing by more than an order of magnitude are identified. The relatively fast process seems to be related to the filling of the cavities of the carbon matrix with hydrogen molecules, the longer one corresponded to the diffusion of hydrogen into the crystal lattice of palladium nanoclusters. Two temperature regions are found for the temperature dependences of the diffusion coefficients of hydrogen and deuterium in composite samples. Above 60 K, the diffusion activation energies in the sample containing palladium nanoclusters were more than twice the values obtained for the pure carbon matrix. Below 60 K, the diffusion coefficients of deuterium in the pure carbon matrix weakly depended on temperature. In the case of diffusion of hydrogen and deuterium into palladium nanoclusters, a change in the character of the temperature dependence was observed at a lower temperature (30 K). Below this temperature the activation energy decreased by approximately an order of magnitude.

Hydrogen sorption by carbon nanotubes and other carbon nanostructures

Journal of Alloys and Compounds, 2002

We have analyzed the hydrogen storage capability of a set of carbon samples including a variety of carbon nanotubes, in the gas phase and in the electrolyte as well. The nanotube samples synthesized in our laboratory by pyrolysis of acetylene are of the multi-wall type. The hydrogen sorption properties of our synthesized nanotubes were compared with the properties of commercially available nanotubes and high surface area graphite as well. The nanotube samples and the high surface area graphite as well absorb hydrogen up to 5.5 mass% at cryogenic temperatures (77 K). However, at room temperatures this value drops to¯0.6 mass%. The electrochemical experiments on the carbon samples showed a maximum discharge capacity of 2.0 mass% at room temperature (298 K). The hydrogen tends to covalently bind to carbon when the absorption takes place at elevated temperatures (.573 K). Therefore, hydrocarbons desorbed from the sample were analyzed by means of temperature programmed desorption measurements. We conclude that the adsorption of hydrogen on nanotubes is a surface phenomenon and is similar to the adsorption of hydrogen on high surface area graphite.

Comparison of hydrogen and deuterium adsorption on Pd"100

Low energy ion recoil spectroscopy is a powerful technique for the determination of adsorbate position on metal surfaces. In this study, this technique is employed to compare the adsorption sites of hydrogen and deuterium on Pd͑100͒ by detection of either H or D recoil ions produced by Ne + bombardment. Comparisons of experimental and Kalypso simulated azimuthal yield distributions show that, at room temperature, both hydrogen isotopes are adsorbed in the fourfold hollow site of Pd͑100͒, however, at different heights above the surface ͑H-0.20 Å and D-0.25 Å͒. The adsorbates remain in the hollow site at all temperatures up to 383 K even though they move up to 0.40-0.45 Å above the surface. Density functional theory calculations show a similar coverage dependent adsorption height for both H and D and confirm a real difference between the H and D adsorption heights based on zero point energies.