Continuous and crake-free MOF-5 membranes of about 14 mu m 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 x 10(-6) mol/m(2)/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, p(f) = 270 kPa and p(p) = 101 kPa, decreases with increasing molecular weight of the molecules in the order of H(2) > He > CO similar to N(2) > CO(2) > SF(6), showing a diffusion-dominating permeation mechanism for the MOF-5 membranes. CO(2) 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 CO(2) diffusivity data in MOF-5, which is in the order of 1 x 10(-9) m(2)/s with activation energy for diffusion of about 14.8 kJ/mol. (C) 2011 Elsevier B.V. All rights reserved.