PHASE-CHANGE PERFLUORINATED METAL ORGANIC FRAMEWORKS FOR CARBON DIOXIDE CAPTURE

Introduction Carbon Capture and Storage (CCS) strategies play a central role in mitigating carbon dioxide (CO2) emissions. Solid adsorbents for post-combustion carbon capture appear to be a promising solution due to their easier application into existing facilities. Of special interest are the so-called "phase-change" Metal-Organic Frameworks (MOFs) that display steep CO2 uptake when a threshold partial pressure is reached, because they can afford superior separation performance with a reduced energy penalty. Material and Methods In this work, recently discovered perfluorinated MOFs based on Ce and Al were deeply studied. An advanced multi-technique characterization approach was carried out to unveil the origin of their peculiar CO2 adsorption mechanism. In particular, we combined gas sorption analysis, in situ infrared spectroscopy, in situ powder X-ray diffraction, multinuclear solid state nuclear magnetic resonance spectroscopy and adsorption microcalorimetry with periodic density functional theory simulations. Results and discussion CO2 adsorption/desorption isotherms were collected in the 195-343 K temperature range (p = 0-5 bar) confirming the presence of "phase-change" isotherms. A basic IR characterization using specific molecular probes allowed the identification of open metal sites in the MOF containing CeIV, which become available for interaction after dehydration. Increasing amounts of CO2 were dosed on the samples and the response was followed by IR spectroscopy. Significant changes in the MOFs IR spectra were observed, suggesting a "phase-change" adsorption mechanism was occurring. Microcalorimetry was also employed to follow the peculiar adsorption behavior and to solve the CO2 adsorption mechanism. Further proof of this mechanism was provided by a wide pool of characterization techniques, including in PXRD, XAS, SSNMR and DFT simulations. This multi-technique approach allowed solving the "phase-change" behavior of these MOFs, associated with very specific interactions of the adsorbate with the surface of the sorbent that trigger a structural rearrangement.