Molecular-sieve type sorption on alkali graphite intercalation compounds

Abstract

The sorption of H 2 , D 2 , N 2 , CH 4 and rare gases was studied on alkali graphites C 8 M and C 24 M (M = K, Rb, Cs) at 196-63 K. The C 24 M compounds sorbed gases to various degrees, while all the C 8 M compounds were non-sorptive. The systematic study of the sorption isotherms for all the compound-gas systems revealed the dependence of the types of the isotherms and that of heats of sorption upon the size of the gas molecules and that of the intercalated alkali metals. Sorption from gas mixtures was also studied for several selected systems, to manifest the actual molecular-sieving action of C 24 K. The structural study for the system C 24 K-D 2 by means of neutron diffraction technique confirmed that the sorption is due to the occlusion of the gas molecules between the intercalated carbon layers of graphite, and also suggested that the compounds 'swell up’ by sorption. Based on these results, the relation between the structure of the compounds and the sorption characteristics was discussed.

Enrichment of tritium by hydrogen-gas sorption in potassium-carbon lamellar compounds.

“…In addition, it was reported that when mixed gas of protium (H,) and deuterium (D,) is absorbed in the compounds, the heavier isotope D, is enriched in the absorbed phase (2). It should be noted that the hydrogen absorption in KC, is characterized by the remarkably large isotope effect, as well as the large amount of absorbed gas.…”

Skyrmion-Like Solitons, Topological Quasi-Positroniums, and Soliton-Catalytic Effects in Graphite-Potassium Intercalation Compounds and Metal Surfaces

“…The behaviors of these compounds have been known to depend on the structure, sort of metals and temperature. Hydrogens are physisorptively accommodated in the molecules in the interstices among the alkali-metal ions in intercalant layers of stage-2 compounds C 24 M (M = K, Rb and Cs) at temperatures below 200 K [1]- [3]. Chemisorption of hydrogen takes place in both first and second stage compounds at higher temperatures [4] [5].…”

Hydrogen diffusion in potassium intercalated graphite studied by quasielastic neutron scattering

“…13,14 Overlapping graphite corrugation potentials from the host GIC structure are another significant feature. Hydrogen adsorption in KC 24 has an isosteric heat 9,10,15 of approximately −9 kJ mol −1 , in comparison to −4 kJ mol −1 for adsorption on graphite. 16 Although the hydrogen molecule is nonpolar, the importance of hydrogen sorption sites with strong Coulomb interactions has been reported for metal-organicframeworks 17 and ion-exchanged zeolites.…”

“…[9][10][11] Gas adsorption by KC 24 is known to exhibit molecular-sieving behavior due to size mismatch between the diameters of the sorptive gas molecules and the gap between graphite layers. 9 Extensive inelastic neutron scattering measurements on H 2 /MC 24 (M = K, Rb, Cs) all indicate strong barriers to out-of-plane H 2 rotation, as evidenced by the large splitting of the J = 0 to J = 1 rotational transition. 12 Two kinds of structures for the in-plane alkali metal lattice have been reported: (1) a √ 7 × √ 7 R19.11…”