Chalcogenide Aerogels as Sorbents for Noble Gases (Xe, Kr)

High-surface-area molybdenum sulfide (MoSx) and antimony sulfide (SbSx) chalcogels were studied for Xe/Kr gas separation. The intrinsic soft Lewis basic character of the chalcogel framework is a unique property among the large family of porous materials and lends itself to a potential new approach toward the selective separation of Xe over Kr. Among these chalcogels, MoSx shows the highest Xe and Kr uptake, reaching 0.69 mmol g–1 (1.05 mmol cm–3) and 0.28 mmol g–1 (0.42 mmol cm–3) respectively, at 273 K and 1 bar. The corresponding isosteric heat of adsorption at zero coverage (Qst0) is 22.8 and 18.6 kJ mol–1 and both are the highest among the selected chalcogels. The IAST (10:90) Xe/Kr selectivity at 273 K for MoSx is 6.0, whereas for SbSx chalcogels, it varies in the range 2.0–2.8. The higher formal charge of molybdenum, Mo4+, in MoSx versus that of antimony, Sb3+, in SbSx coupled with its larger atomic size could induce higher polarizability in the MoSx framework and therefore higher Xe/Kr selectivity.