Synthesis, characterization and gas transport properties of MOF-5 membranes

Continuous and crake-free MOF-5 membranes of about 14 μm in thickness were prepared by seeding size-reduced MOF-5 crystals followed by the secondary growth synthesis. The membrane quality was examined by a molecule probing method using a series of organic compounds with sizes ranging from 0.56 nm to 1.4 nm. Negligible pervaporation flux (1.39 × 10−6 mol/m2/s) of 2-dicyclohexylphosphino-2′-(N, N-dimethylamino) biphenyl through the MOF-5 membrane shows absence of the defects larger than the MOF-5 crystalline pores in the MOF-5 membranes. The gas permeance for the MOF-5 membranes, under conditions of T = 298–374 K, pf = 270 kPa and pp = 101 kPa, decreases with increasing molecular weight of the molecules in the order of H2 > He > CO ∼ N2 > CO2 > SF6, showing a diffusion-dominating permeation mechanism for the MOF-5 membranes. CO2 permeation data for the MOF-5 membranes were analyzed by a permeation model with the input of the adsorption isotherm data to obtain more reliable CO2 diffusivity data in MOF-5, which is in the order of 1 × 10−9 m2/s with activation energy for diffusion of about 14.8 kJ/mol.