Characterization of gas permeation in the pores of Zn(II)-based metal organic framework (MOF)/polymer composite membranes

The separation of greenhouse gases from industrial processes is an ongoing focus for research aimed at mitigating environmental impacts. As a result, it is important to develop experimental techniques for the characterization of the transport of gases through porous crystalline materials with potential applications in gas separations. We report on the fabrication and characterization of gas transport in supported Zn(II)-based MOF membranes. The MOF membranes were used to develop an approach to study membrane quality and determine the transport mechanism through the pores of the crystalline membrane. Membranes were synthesized via a solvothermal method with structural defects sealed by a low-permeability polymer coating, allowing for the measurement of permeation in materials that do not form uniform, defect-free films. Membrane permeation was proportional to the inverse square root of the molecular weight of the permeant gases, indicating that diffusion occurs via Knudsen diffusion. Membrane quality was studied via selectivity measurements as a function of temperature. A study of the gas permeation through a polymer coated sparse MOF membrane, was used to confirm that gas transport occurs through the pores of the MOF, rather than through pinholes or defects in the structure.