STRUCTURAL AND DYNAMIC CHARACTERIZATION OF MIXED MATRIX MEMBRANES BASED ON FLUORINATED METAL-ORGANIC FRAMEWORKS BY SOLID STATE NUCLEAR MAGNETIC RESONANCE

Mixed matrix membranes (MMMs) are emerging as a promising technology for gas separation. These materials are composites made from a polymer blended with a porous filler with exceptional adsorption properties, such as a covalent organic framework or a metal-organic framework (MOF). Thanks to their composition, they are considered next-generation membranes, since they combine the benefits derived from the processability of the polymer with the enhanced separation properties of the filler.[1] The physico-chemical properties of both the filler and the polymer as well as their interactions in the composite play a key role in obtaining MMMs with enhanced separation performances. It is thus important to unravel these properties at the molecular level to understand the structure-property relationship and to guide the design of optimized materials. Solid State Nuclear Magnetic Resonance (SSNMR) has established itself as one of the most powerful techniques for the characterization of structural and dynamic properties of MOFs and composite materials at the atomic scale, as well as to gain insight into the interaction with adsorbents.[2,3] In fact, high-resolution SSNMR spectra provide information on local structure and spatial proximity between nuclei. Moreover, other nuclear observables (e.g. nuclear relaxation times and anisotropic line shapes) give unique possibilities for the study of molecular dynamics. In this work, multinuclear SSNMR is applied to investigate structural and dynamic properties of perfluorinated MOFs with high affinity towards CO2,[4,5] gas separation membranes obtained from commercial polymers and the corresponding MMMs. In particular, 13C, 19F and 1H high-resolution SSNMR experiments based on magic angle spinning (MAS) are carried out to study the structural properties of each material, while 1H and 19F spin lattice relaxation times (T1) are exploited to gain information on the dynamics of polymer and MOF moieties. MAS and static 13C SSNMR experiments are also applied to unravel the interaction of CO2 with MOFs and membranes on selected samples. Acknowledgements: The authors thank the Italian Ministry of University and Research through the Project PRIN 2020 doMino (ref. 2020P9KBKZ) References [1] J. Dechnik, J. Gascon, et al. Angew. Chem. Int Ed. 2017, 56, 9292-9310. [2] B. E. G. Lucier, S. Chen, Y. Huang Acc. Chem. Res. 2018, 51, 319-330. [3] B. Reif, S. E. Ashbrook, et al. Nat. Rev. Methods Primers 2021, 1, 2. [4] R. D'Amato, A. Donnadio, et al. ACS Sustainable Chem. Eng. 2019, 7, 394-402. [5] M. Cavallo, C. Atzori, et al. J. Mater. Chem. A. 2023, 11, 5568-5583.