Molecular-sieve type sorption on alkali graphite intercalation compounds

The sorption of H2, D2, N2, CH4 and rare gases was studied on alkali graphites C8M and C24M (M = K, Rb, Cs) at 196-63 K. The C24M compounds sorbed gases to various degrees, while all the C8M 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 C24K. The structural study for the system C24K-D2 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.