The annual global emission of carbon dioxide, the most abundant greenhouse gas, has reached more than 35 billion tonnes in 2021 and new estimates suggest a further increase of 1.0% in 2022.1 Metal-Organic Frameworks (MOFs) are nowadays emerging as promising porous materials for CO2 capture and separation. Compared to other porous sorbents such as zeolites or activated carbons, the strength point of MOFs deals with the possibility of finely tuning their properties exploring a large variety of synthesis and post-synthesis procedures. For example, the synthesis of frameworks exposing specific functional groups on the surface can bring multiple benefits in terms of selectivity towards a specific adsorbate, leading to more efficient and energy-saving capture processes with a smaller environmental footprint.2 Furthermore, some MOFs present peculiar intrinsic features that can enhance their performances; MOFs exhibiting framework flexibility are extremely interesting examples. Such feature can be induced by host-guest interactions, but also be triggered by external stimuli.3 Regarding this topic, we present a new per-fluorinated MIL53(Al) MOF (F4-MIL53) obtained by simply mixing the solid precursors (F4-H2BDC and Al(NO3)3o9H2O) in a solvent-free synthesis route.4 Nevertheless, such extremely simple and environmental friendly procedure is just one of the interesting aspects regarding this fluorinated MOF. Basic characterization techniques, such as PXRD and thermogravimetric analysis (TGA), have been coupled with more advanced experimental tools, including spectroscopies (mainly ATR, DRIFT, in situ and operando IR, and SSNMR), volumetry and microcalorimetry, to finely study the features of F4-MIL53 focusing on the role of fluorine atoms and, most of all, on the flexible behavior of this framework, a major peculiarity of the MIL53 family. Unexpectedly, the breathing capability of F4-MIL53, induced by both specific host-guest interactions and temperature, was detected by using different experimental techniques. Even if a similar behavior is already known for non-fluorinated MIL53, some interesting differences came out. The CO2-MOF interaction is an attractive example. The adsorption of CO2 has been studied with both volumetric and gravimetric adsorption-desorption measurements. Such host-guest interaction is peculiar and causes a phase transition of the MOF resulting in an enlargement of the pores. Such structural modification is expressed as a defined step on the isotherm occurring in the pressure range 0-5 bar (T range 195-313K). The fast kinetics of transition together with the total reversibility of such phenomenon are clues that lead us to consider F4-MIL53 a promising CO2 adsorbent. Furthermore, the presence of fluorine atoms on the 20th International Conference on Carbon Dioxide Utilization - ICCDU XX aromatic ring increases the framework hydrophobicity, affecting its stability towards moisture and pollutants, perhaps favoring the adsorption of CO2 also in humid conditions. 1. Ritchie, H., Roser, M. & Rosado, P. CO2 and Greenhouse Gas Emissions. Our World in data (2020). 2. Li, J.-R., Kuppler, R. J. & Zhou, H.-C. Selective gas adsorption and separation in metal-organic frameworks. Chem Soc Rev 38, 1477-1504 (2009). 3. Schneemann, A. et al. Flexible metal-organic frameworks. Chem Soc Rev 43, 6062-6096 (2014). 4. Venturi, D. M. et al. Solvent-Free Synthesis of a new Perfluorinated MIL-53(Al) with a Genuine Temperature- Induced Breathing Effect.
Disclosing the CO2 adsorption-induced phase change behavior of a new Per-fluorinated MIL53(Al) metal organic framework
Lucia Calucci;
2023
Abstract
The annual global emission of carbon dioxide, the most abundant greenhouse gas, has reached more than 35 billion tonnes in 2021 and new estimates suggest a further increase of 1.0% in 2022.1 Metal-Organic Frameworks (MOFs) are nowadays emerging as promising porous materials for CO2 capture and separation. Compared to other porous sorbents such as zeolites or activated carbons, the strength point of MOFs deals with the possibility of finely tuning their properties exploring a large variety of synthesis and post-synthesis procedures. For example, the synthesis of frameworks exposing specific functional groups on the surface can bring multiple benefits in terms of selectivity towards a specific adsorbate, leading to more efficient and energy-saving capture processes with a smaller environmental footprint.2 Furthermore, some MOFs present peculiar intrinsic features that can enhance their performances; MOFs exhibiting framework flexibility are extremely interesting examples. Such feature can be induced by host-guest interactions, but also be triggered by external stimuli.3 Regarding this topic, we present a new per-fluorinated MIL53(Al) MOF (F4-MIL53) obtained by simply mixing the solid precursors (F4-H2BDC and Al(NO3)3o9H2O) in a solvent-free synthesis route.4 Nevertheless, such extremely simple and environmental friendly procedure is just one of the interesting aspects regarding this fluorinated MOF. Basic characterization techniques, such as PXRD and thermogravimetric analysis (TGA), have been coupled with more advanced experimental tools, including spectroscopies (mainly ATR, DRIFT, in situ and operando IR, and SSNMR), volumetry and microcalorimetry, to finely study the features of F4-MIL53 focusing on the role of fluorine atoms and, most of all, on the flexible behavior of this framework, a major peculiarity of the MIL53 family. Unexpectedly, the breathing capability of F4-MIL53, induced by both specific host-guest interactions and temperature, was detected by using different experimental techniques. Even if a similar behavior is already known for non-fluorinated MIL53, some interesting differences came out. The CO2-MOF interaction is an attractive example. The adsorption of CO2 has been studied with both volumetric and gravimetric adsorption-desorption measurements. Such host-guest interaction is peculiar and causes a phase transition of the MOF resulting in an enlargement of the pores. Such structural modification is expressed as a defined step on the isotherm occurring in the pressure range 0-5 bar (T range 195-313K). The fast kinetics of transition together with the total reversibility of such phenomenon are clues that lead us to consider F4-MIL53 a promising CO2 adsorbent. Furthermore, the presence of fluorine atoms on the 20th International Conference on Carbon Dioxide Utilization - ICCDU XX aromatic ring increases the framework hydrophobicity, affecting its stability towards moisture and pollutants, perhaps favoring the adsorption of CO2 also in humid conditions. 1. Ritchie, H., Roser, M. & Rosado, P. CO2 and Greenhouse Gas Emissions. Our World in data (2020). 2. Li, J.-R., Kuppler, R. J. & Zhou, H.-C. Selective gas adsorption and separation in metal-organic frameworks. Chem Soc Rev 38, 1477-1504 (2009). 3. Schneemann, A. et al. Flexible metal-organic frameworks. Chem Soc Rev 43, 6062-6096 (2014). 4. Venturi, D. M. et al. Solvent-Free Synthesis of a new Perfluorinated MIL-53(Al) with a Genuine Temperature- Induced Breathing Effect.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
