Probe Molecule-Dependent Particle Density and its Effect on the Supercritical Gas Adsorption Isotherm of Nanoporous Cu Complex Crystals

Accurate particle densities of the Cu-based metal organic framework [Cu(4,4'-bipyridine)₂(BF₄)₂] for He, N₂ and CH₄ molecules using the high-pressure buoyancy method have been determined. A smaller probe molecule gave a larger particle density (1.70 g/ml from He, 1.66 g/ml from N₂, 1.60 g/ml from CH₄). The effect of particle density on the evaluation of the surface excess mass for supercritical gas adsorption was examined; the above particle density difference gave rise to a 2–4% difference in the surface excess mass.