Smart Metal-Organic Frameworks (MOFs): Switching Gas Permeation through MOF Membranes by External Stimuli

The switching of gas permeation and adsorption on polymers, zeolites, and metal-organic frameworks (MOFs) by external stimuli like temperature, pressure, light, and electric fields is discussed. Especially MOFs as soft porous crystals are suitable candidates for switching gas transport. If the linker of a MOF contains a cis-trans switchable azo moiety, switching of the trans state into the cis state reduces gas transport through a MOF membrane. On the other hand, MOFs with dipolar or ionic components can be switched upon polarization with an electric field into polymorphs of the starting MOF. A ZIF-8 membrane can be switched into a polymorph with a rather stiff lattice, which sharpens the molecular sieving effect of the membrane, and, as an example, the propene/propane selectivity increases.