Photo-switching and tuning of gas transport through metal-organic framework membranes
A method for switching and tuning gas transport and gas separation through metal-organic framework membranes by applying light of certain wavelengths is claimed. The metal-organic framework (MOF) membrane contains linker molecules with photo-switchable units in the side group of the backbone of the linker molecules. These photoactive units in the side groups can be switched reversibly into two conformations if enlightened with light of a specific wavelength.
The proposed optical switching of the photoactive unit in the backbone of the linker molecules of the MOF as claimed in WO 2014015383 A1 and EP 13823026 is not practical since the whole crystal structure expands and shrinks upon optical switching like an accordion or like bellows.
This repeated shrinking and expansion cycles damage the membrane mechanically.
It is the object of the present invention to provide a technique for the optical switching of a membrane without mechanical damage, and for the continuously tuneable switching in defined amounts between the two conformations with a defined gas selectivity. This goal is achieved by using the photoinduced trans-cis photoisomerization of a photoactive unit in the side group of the stable and rigid linker molecule of the MOF.
- In the novel process, gas transport through a supported MOF membrane, a self-supporting MOF membrane and a Mixed Matrix Membrane containing MOF crystals as filler can be controlled. Control means that the amount and the composition of gas passing the MOF membrane can be tuned by enlightening the photoswitchable MOF membrane with external light.
- The amount of gas streaming from the feed side through the membrane is characterized by the permeances. The change in the composition of the mixture is defined by the separation factor. When the feed gas composition is changing, the switchability enables a stable separation factor, thus a constant permeate composition.
Chemical Synthesis and Purification, Industrial Membrane Separation Processes
License for commercial exploitation; Research & Development cooperation
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