Tunable molecular separation by nanoporous membranes

Abstract

Metal-organic frameworks offer tremendous potential for efficient separation of molecular mixtures. Different pore sizes and suitable functionalizations of the framework allow for an adjustment of the static selectivity. Here we report membranes which offer dynamic control of the selectivity by remote signals, thus enabling a continuous adjustment of the permeate flux. This is realized by assembling linkers containing photoresponsive azobenzene-side-groups into monolithic, crystalline membranes of metal-organic frameworks. The azobenzene moieties can be switched from the trans to the cis configuration and vice versa by irradiation with ultraviolet or visible light, resulting in a substantial modification of the membrane permeability and separation factor. The precise control of the cis:trans azobenzene ratio, for example, by controlled irradiation times or by simultaneous irradiation with ultraviolet and visible light, enables the continuous tuning of the separation. For hydrogen:carbon-dioxide, the separation factor of this smart membrane can be steplessly adjusted between 3 and 8.

Surface‐Mounted Metal–Organic Frameworks: Crystalline and Porous Molecular Assemblies for Fundamental Insights and Advanced Applications

“…[47] The length of these linkers used in fabricating the MOF has to be adjusted so that the transition from the trans to the cis conformation is not hindered. [50,53] Copyright 2014 and 2016, American Chemical Society and Nature Publishing Group. Alternatively to the controlled incorporation of the photoswitches as dangling side groups to the MOF structure, the light-responsive mole cules may also be embedded in the pores, resulting in straightforward preparation of photoswitchable nanoporous materials.…”

“…[53] In these membranes, the separation selectivities could be varied over a wide range by illumination with light (Figure 6c). Due to their large variety and the ability to adjust their functionalization and pore size by modification of the building units, MOFs are promising materials for efficient membrane separation.…”

The Virtuous CO2 Circle or the Three Cs: Capture, Cache, and Convert

“…E.g. Wang et al [31] recently showed that continuous tuning of the separation ratio was possible by embedding a nanostructured metalorganic framework (MOF), assembled from a photoresponsive organic molecule, in a nanoporous membrane. 2 .…”

Thermal cis-to-trans Isomerization of Azobenzene Side Groups in Metal-Organic Frameworks investigated by Localized Surface Plasmon Resonance Spectroscopy

“…It was demonstrated that SURMOFs with azobenzene side groups can be used for various Brought to you by | MIT Libraries Authenticated Download Date | 5/11/18 10:18 PM purposes: as membranes which allow the remote-controlled switching of the separation performance [24], for the remote-controlled release of guest molecules from multi-layered nanoporous films [25] as well as for switching the adsorption capacity [26]. Using fluorinated azobenzene side groups enables the switching of the MOF material properties with visible light only, avoiding UV light [27].…”