The adsorption of hydrogen gas into single-walled carbon nanotubes (SWNTs) and idealized carbon slit pores is studied by computer simulation. Hydrogen-hydrogen interactions are modeled with the Silvera-Goldman potential. The Crowell-Brown potential is used to model the hydrogen-carbon interactions. Calculations include adsorption inside the tubes, in the interstitial regions of tube arrays, and on the outside surface of isolated tubes. Quantum effects are included through implementation of the path integral formalism. Comparison with classical simulations gives an indication of the importance of quantum effects for hydrogen adsorption. Quantum effects are important even at 298 K for adsorption in tube interstices. We compare our simulations with experimental data for SWNTs, graphitic nanofibers, and activated carbon. Adsorption isotherms from simulations are in reasonable agreement with experimental data for activated carbon, but do not confirm the large uptake reported for SWNTs and nanofibers. Although ...

Molecular simulation of hydrogen adsorption in single-walled carbon nanotubes and idealized carbon slit pores

Potentials of physical adsorption

Two-dimensional phase transitions as displayed by adsorption isotherms on graphite and other lamellar solids

Catalytically grown graphite nanofibers (GNF) are molecularly engineered structures that are produced by the interaction of carbon-containing gases with small metal particles at temperatures around 600 °C. The fibrous solids consist of minuscule graphene sheets stacked at various angles with respect to the fiber axis. This arrangement generates a material possessing unique chemical properties because unlike conventional graphite crystals, only edges are exposed. Such a conformation produces a material composed entirely of nanopores that can accommodate small-sized adsorbate molecules, such as hydrogen, in the most efficient manner. In addition, the nonrigid pore walls can expand to accommodate the gas in a multilayer conformation. GNF exhibit extraordinary behavior toward the sorption and retention of hydrogen at high pressures and abnormally high temperatures. In this paper we discuss some of the critical factors involved in the adsorption of molecular hydrogen and the influence that this process exerts ...

Further Studies of the Interaction of Hydrogen with Graphite Nanofibers

This article reviews, from a very personal point of view, the origins and the early work on transitions driven by topological defects such as vortices in the two dimensional planar rotor model and in (4)Helium films and dislocations and disclinations in 2D crystals. I cover the early papers with David Thouless and describe the important insights but also the errors and oversights since corrected by other workers. I then describe some of the experimental verifications of the theory and some numerical simulations. Finally applications to superconducting arrays of Josephson junctions and to recent cold atom experiments are described.

https://iopscience.iop.org/article/10.1088/0034-4885/79/2/026001/pdf

Kosterlitz-Thouless physics: a review of key issues

Two-dimensional phase diagram of neon adsorbed on exfoliated graphite. Heat-capacity measurements

Low density specific heat measurements of para-hydrogen adsorbed on exfoliated graphite☆

High precision adsorption isotherms of3He and4He on bare Grafoil and on Grafoil coated with a monolayer of argon have been measured in the temperature range 4–20 K, using a high resolution, pressure-sensitive capacitance gauge located at 4.2 K close to the sample chamber. This gauge obviated thermomolecular pressure effects and corrections. The isotherms yielded the following resultant data: The monolayer coverage Vm for4He on bare Grafoil was 0.42 cm3 (STP)/m2 and for3He on bare Grafoil was 0.395 cm3 (STP)/m2: the isosteric heat of adsorptionQst/R of the second layer of3He on bare Grafoil was 23.5 K andQst/R for3He on argon-coated Grafoil for the first layers was 47.5 K. Also, the data for3He and4He on bare Grafoil at and just aboveVm have been used by Novaco (see subsequent paper) for determination of the virial coefficients of the gas phase occuring in the early formation of the second layer.

Helium adsorption on exfoliated graphite

Isotherms of neon adsorbed on compressed exfoliated graphite were measured, using a standard volumetric method, in the temperature interval of 12–24 K for the four first layers. The critical temperatures for the first three layers were determined to be 16.0±1.0, 19.0±1.0 K, and 18.0±1.0 K, respectively. From the isotherms, the isosteric heats of adsorption were calculated as a function of coverage, indicating some interesting features, which may be attributed to possible phase transitions. The isosteric heat of adsorption for the fourth layer on,Q
 st/R=.275 K, is comparable to the three-dimensional latent heat of sublimation 256 K at the triple point. The binding energies for the first, second, and third layers were obtained from the isosteric heats as V → 0, yielding 302.5, 237.5, and 227.5 K, respectively. The differential molar entropies and internal molar energies were also calculated as a function of coverage. The possibility of a coexistence region with two solids having different structures in the phase diagram for the first layer is discussed. Whenever possible, the results are compared with theoretical evaluations and previous experimental data.

Multilayer isotherms of neon adsorbed on exfoliated graphite

Monolayer isotherms were measured for 15, 18, and 20 K for para-hydrogen adsorbed on exfoliated graphite foam, and for the second, third, and fourth layers in the temperature interval of 8 to 20 K, using the standard volumetric method. From the data, the isosteric heat of adsorption, molar entropies and internal energies were obtained as a function of coverage. The values for coverages above the third layer were compared to those at the p-H2 bulk triple point, showing that, within our experimental uncertainty, the results are closer to the values of bulk solid para-hydrogen. Critical temperatures for the second and third layers and the triple point temperature for the second layer, were determined, yielding values of Tc2 = (10.0±0.1) K, Tc3 = (11.0±0.5) K and Tt2 = (6.5±0.1) K respectively. “Features” occurring along the monolayer coverages are compared to transitions which occur in the para-hydrogen phase diagrams adsorbed on graphite, obtained from heat capacity measurements by other authors. From the isotherms, compressibilities were calculated as a function of coverage for several temperatures. Whenever possible the obtained results were compared to existing data in the literature.

E. Lerner

Papers

Two-dimensional phase diagram of neon adsorbed on exfoliated graphite. Heat-capacity measurements

Low density specific heat measurements of para-hydrogen adsorbed on exfoliated graphite☆

Helium adsorption on exfoliated graphite

Multilayer isotherms of neon adsorbed on exfoliated graphite

Vapor pressure measurements of para-hydrogen adsorbed on exfoliated graphite