Fine-tuning and pore environment control of covalently connected metal–organic framework (MOF) and mixed-matrix membrane (MMM) composite materials were achieved. Core–shell-type, dual-functionalized, zirconium-based MOFs were prepared through a postsynthetic ligand exchange (PSE) process, and active vinyl functionalities on the surface of MOF nanoparticles were utilized for polymerization by forming interfacial-covalent connections between MOF nanoparticles and polymeric membranes via thiol–ene click photopolymerization. The target functionality of the MOF pore originated from the parent MOFs, allowing pore engineering of the MOF–MMM composite materials. A series of defect-free, interface-controlled, and core-functionalized MOF–MMMs were prepared through the present methodology, and the NO2-functionalized/covalently connected MOF–MMM showed the highest CO2 permeability and solubility without loss of selectivity. This facile and versatile approach will be useful for the fabrication of functional MOF nanoparticle-based membranes for various applications, such as catalysis and separation.

We developed a facile methodology for fabricating a free-standing mixed-matrix membrane (MMM) containing covalently incorporated metal–organic framework (MOF) particles up to 60 wt% by utilizing thiol–ene photopolymerization with the MOF consisting of vinyl functionality. Vinyl-functionalized UiO-66 (UiO-66-CH[double bond, length as m-dash]CH2) was synthesized from 2-vinyl-1,4-dicarboxylic acid with ZrCl4, and a free-standing MMM was readily produced by irradiation of a polymerization mixture containing UiO-66-CH[double bond, length as m-dash]CH2, poly(ethylene glycol) divinyl ether (PEO-250), pentaerythritol tetra(3-mercaptopropionate) (PETM), 2,2′-(ethylenedioxy)diethanethiol (EDDT), and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoradical initiator. Assorted analyses combining FTIR, thermogravimetric analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction strongly supported the fact that the desired MMM containing well-dispersed UiO-66-CH[double bond, length as m-dash]CH2 particles was successfully produced by C–S bond formation, which provided strong union of the MOF with the polymer matrix without interfacial voids. The produced MMM was highly flexible and showed improved mechanical properties as compared to the pristine polymeric membrane, indicating that the covalently immobilized UiO-66-CH[double bond, length as m-dash]CH2 particles were homogeneously distributed in the polymer matrix. Gas permeability across the MMM was significantly enhanced compared with the pristine polymeric membrane as diffusion of the gas molecules was facilitated in the porous space in the MOF.

Global production for NF3 is continuously increasing, especially due to its heavy consumption in the semiconductor industry. Even though the amount of its emission is relatively small compared to other greenhouse gases, particularly CO2, the relatively long atmospheric lifetime of NF3 makes its emission cumulative, possibly contributing to the global climate change. Membrane-based separation techniques are very promising for the energy-efficient NF3 recovery. It is, therefore, critically important to evaluate the N2/NF3 separation performance by using commercial polymeric membranes. Here, for the first time, the empirical N2/NF3 upper bound relationship is established by using a wide variety of commercial polymeric membranes including both glassy and rubbery polymers based on their single gas (i.e. N2 and NF3) permeation characterization. Among those tested, 6FDA–DAM:DABA (3:2), Teflon® AF 2400 and PTMSP exhibited relatively high N2/NF3 separation performance. The theoretical N2/NF3 upper bound curve was also defined and found comparable with our empirical upper bound limit. In an effort to improve the N2/NF3 separation performance, mixed matrix membranes were prepared by incorporating zeolitic imidazolate framework molecular sieves into Matrimid® 5218. The effects of solvents, particle sizes, and ligands on the transport properties in mixed matrix membranes were investigated.