Intracrystalline Diffusivities and Surface Permeabilities Deduced from Transient Concentration Profiles: Methanol in MOF Manganese Formate

Abstract

The intracrystalline concentration profiles during molecular uptake of methanol by an initially empty, single crystal of microporous manganese(II) formate (Mn(HCO2)2), representing an ionic inorganic-organic hybrid within the MOF family, are monitored by interference microscopy. Within these profiles, a crystal section could be detected where over the total of its extension ( approximately 2 microm x 50 microm x 30 microm) molecular uptake ideally followed the pattern of one-dimensional diffusion. Analysis of the evolution of intracrystalline concentration in this section directly yields the permeability of the crystal surface and the intracrystalline diffusivity as a function of the concentration of the total range of 0 <or= theta <or= 0.57 covered in the experiments. Within this range, the surface permeability is found to increase by 1 order of magnitude, while, within the limits of accuracy (+/-30%), the transport diffusivity remains constant, thus reflecting the properties of the lattice gas model.