SOLID STATE NMR INVESTIGATION OF MATERIALS FOR GAS SEPARATION

Over the last years, metal organic frameworks (MOFs), porous membranes, and MOF-based mixed matrix membranes (MMMs) have gained a lot of interest in the research community as promising materials for gas separation [1,2]. MOFs are organic/inorganic materials constituted of metal oxide clusters linked by organic ligands. Their gas separation properties can be finely tuned by combining different metals and linkers, as well as adopting post-synthetic modification procedures. MMMs, comprised of polymeric matrices and MOF fillers, are considered next-generation membranes for gas separation because they combine the benefits of the polymer processability with the enhanced separation properties of the filler. The physico-chemical properties of both the MOF 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 relationships and to guide the design of optimized materials for gas separation. Solid-state Nuclear Magnetic Resonance (SSNMR) spectroscopy has established itself as one of the most powerful techniques to characterize structural and dynamic properties of MOFs, polymeric membranes, and MMMs at the atomic scale, as well as to gain insight into the interaction with gases [3-7]. 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, SSNMR is applied to investigate structural and dynamic properties of perfluorinated MOFs with high affinity towards CO2 [8], membranes, and MMMs. Multinuclear high-resolution SSNMR experiments are carried out to study the structural properties of each material and their changes upon gas adsorption. MAS and static 13C SSNMR experiments are also applied to investigate the interaction of CO2 with MOFs and membranes. Acknowledgements: MUR is acknowledged through the Project PRIN 2020 doMino (ref. 2020P9KBKZ).