Photo-switchable smart metal-organic framework membranes with tunable and enhanced molecular sieving performance

Developing a novel MOF membrane material with switchable separation performance is an exciting and challenging research project. In the present work, we report preparation of a new kind of light induced smart MOF membrane, i.e., Cu(AzDC)(4,4′-BPE) _0.5 membrane, which shows (i) enhanced molecular sieving performance, and (ii) is able to respond quickly to external light stimuli. Two photo-switchable moieties are addressed in the Cu(AzDC)(4,4′-BPE) _0.5 membrane: azobenzene and bis(4-pyridyl)ethylene. When the Cu(AzDC)(4,4′-BPE) _0.5 membrane is in situ irradiated with Vis and UV light, the separation factor of a H ₂ /CO ₂ mixture can be switched reversibly between 21.3 and 43.7. This switching effect is mainly caused by reduced CO ₂ adsorption in the UV-cis state as proven by independent adsorption studies. For a steric reason, adsorption of CO ₂ is limited for the UV-cis state. In full agreement with this model, the adsorption of other gases H ₂ , CH ₄ and N ₂ as well as their permeation behaviour is not observably influenced by the trans-cis switching.